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Geochronology of Torrejonian sediments,Nacimiento Formation, San Juan Basin, New Mexico

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Authors Taylor, Louis Henry, 1944-

Publisher The University of Arizona.

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GEOCHRONOLOGY OF TORREJONIAN SEDIMENTS,

NACIMIENTO FORMATION, SAN JUAN BASIN, NEW MEXICO

by

Louis Henry Tay lor

A Thesis Submitted to the Faculty o f the

DEPARTMENT OF GEOSCIENCES

In P a rt ia l F u lf il lm e n t o f the Requirements For the Degree o f

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 7

STATEMENT BY AUTHOR

This th es is has been submitted in p a r t ia l f u l f i l lm e n t o f re quirements fo r an advanced degree a t The U n iv e rs ity o f Arizona and is deposited in the U n iv e rs ity L ib ra ry to be made a v a ila b le to borrowers under ru les o f the L ib ra ry .

B r ie f quotations from th is th es is are a llow ab le w ithout special perm ission, provided th a t accurate acknowledgment o f source is made. Requests fo r permission fo r extended quotation from or reproduction o f th is m anuscript in whole or in p a rt may be granted by the head o f the major department or the Dean o f the Graduate College when in his judgment the proposed use o f the m ateria l is in the in te re s ts o f sch o larsh ip . In a l l o th er instances , however, permission must be obtained from the au thor.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This th es is has been approved on the date shown below:

77Associate Professor

o f Geosciences

Date

ACKNOWLEDGMENTS

I thank Drs. E. H. Lindsay, R. F. B u tle r , and G. G. Simpson

fo r th e ir guidance and co n stru c tive c r it ic is m during the course o f

th is p ro je c t . I also thank Dr. B u tle r , S. L. B re s s le r, Y. Tomida, and

R. A. Haskin fo r th e ir assistance in measuring paleomagnetic specimens.

Assistance in the c o lle c tio n o f both paleomagnetic samples and

fo s s ils was provided by Drs. Lindsay, B u tle r , and L. L. Jacobs, I I I .

Also in d isp en s ib le in the f ie ld were J . G. Honey, L. J . F lynn, B. R.

Standhardt, and Y. Tomida. For th e ir help I thank them.

I would also l ik e to thank my w ife Mary fo r her encouragement

and fin a n c ia l support.

i i i

TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS ...................................................................................... v i

LIST OF T A B L E S ...................... v l l l

ABSTRACT................................................................................................................. ix

1. INTRODUCTION .......................................................................................................... 1

2 . THE SAN JUAN B A S IN ........................................................................................... 5

Geography ........................................................................................................ 5Geology ............................................................................................................. 7Previous Geological In v e s tig a tio n .................................................. 8

3. THE NACIMIENTO FORMATION............................................................................. 11

S tra tig ra p h ic Nomenclature . . . .................................................. 11S tra tig ra p h y ............................................................................................... 13

4 . METHODS OF CHRONOLOGICAL CORRELATION .................................................. 18

B io s tra t i g r a p h i c ...................................................................................... 18The Torre jon ian Land Mammal A g e .............................................. 19

M agnetostrati g r a p h i c ............................................................................. 21G eom agnetic-Polarity Time Scale .............................................. 22M eth o d s .................................................................................................... 23

5 . STRATIGRAPHY . . . . . .................................................................... . . . 37

The Study A r e a s ........................................................................................... 37L ith o s tra tig ra p h y ....................................................................................... 43B io s t r a t ig r a p h y ................................................................................ ...... . 45M a g n e tic -P o la rity S tra tig ra p h y ....................................................... 52

6. GE0CHR0N0L0GIC CORRELATION ......................................................................... 60

The Ojo End no and Big Pocket A r e a s .............................................. 60The B arrel Spring Arroyo Section .................................................. 65

7 . SUMMARY...................................................................................................................... 69

i v

V

TABLE OF CONTENTS-Continued

Page

APPENDIX A: PALEOMAGNETIC DATA........................................................... . 72

L o c a lity 10, Ojo Encino A r e a ......................................... .... 72L o c a lity 11 , Ojo Encino A r e a .................................................. 76Composite S ectio n , Big Pocket Area .............................................. 78Radio Tower S ec tio n , Big Pocket Area ......................................... 87

REFERENCES CITED ............................................................................................... 88

LIST OF ILLUSTRATIONS

Figure Page

1. Regional Map o f the San Juan B a s i n .................. ........................................ 3

2. Geologic Map o f Nacim iento, Animas, and San JoseForm ations, San Juan B a s i n .............................................. 12

3. AF Demagnetization Curves and NRM Vector M otions,S ite SJ342 ...................................................................................................... 29

4. NRM Vector M otions, S ite SJ480 30

5 . NRM Vector M otions, S ite SJ585 31

6 . AF Demagnetization Curves and NRM Vector M otions,S ite SJ356 .............................. ........................................................................ 32

7. NRM Vector M otions, S ite SJ309 34

8 . NRM Vector M otions, S ite SJ482 35

9. AF Demagnetization Curves and NRM Vector M otions,S ite SJ044 36

10. Map o f the Ojo Encino A r e a ...................................................................................38

11. Map o f L o c a lity 10 , Ojo Encino A r e a .................................................................39

12. Map o f L o c a lity 11 , Ojo Encino Area . ............................................................. 40

13. Map o f the Big Pocket Area .................................................................................. 42

14. L ith o lo g ic C o rre la tio n o f L o c a lit ie s 10 and 11 ,Ojo Encino A r e a .....................................................................................................44

15. Magnetic C o rre la tio n o f L o c a lit ie s 10 and 11,Ojo Encino A r e a .....................................................................................................54

16. M a g n e tic -P o la rity S tra tig ra p h y o f the Ojo Encino Area .................... 55

17. M a g n e tic -P o la rity S tra tig ra p h y o f the Big Pocket Area .................... 58

v i

v l i

LIST OF ILLUSTRATIONS-Continued

Figure Page

18. Geochronological C o rre la tio n o f the Ojo Encino andBig Pocket A r e a s ................................................................................................ 61

19. C o rre la tio n o f Revised Cenozoic P o la r ity TimeScale and B arre l Spring Arroyo Section .......................................... 66

LIST OF TABLES

Table Page

1. H ierarchy o f Paleomagnetic S ites ................................................................ 27

2 . Faunal L is t fo r the Ojo Encino and Big PocketStudy A r e a s .................................................................................................... . 46

viii

ABSTRACT

This study compares two areas o f the San Juan Basin w ith

respect to b io s tra tig ra p h y , l ith o s tra t ig ra p h y , and m a g n e tic -p o la rity

s tra tig ra p h y . The Ojo Encino A rea, near Cuba, New Mexico and the Big

Pocket Area o f Kutz Canyon, near B loom fie ld , New Mexico were c o lle c te d

fo r v e rte b ra te fo s s ils and magnetic samples.

Both study areas contained fo s s ils o f Torre jon ian Land Mammal

Age. W ith in th is age two c o lle c t in g le v e ls are recognized. The upper.

Panto!ambda, le v e l is ch a ra c te rized by the presence o f Panto!ambda,

Claenodon, and possib ly Mixodectes pungens and T o rre jo n ia w lls o n i . The

low er, D e lta th eriu m , le v e l is ch aracterized by the presence o f

D e lta th eriu m , T riis o d o n , Haploconus, Mixodectes m a la r is , and possib ly

Palaechthon n a c im ie n tl. These c o lle c t in g le v e ls are also defined by

th e ir m a g n e tic -p o la rity s tra tig ra p h y . C o rre la tio n o f the two study

areas demonstrates th a t the Panto!ambda le v e l is from w ith in a normal

magnetozone and th a t the D eltatherium le v e l is from w ith in the under

ly in g reversed magnetozone.

Comparison o f the m a g n e tic -p o la rity s tra tig ra p h y from the two

study areas w ith the p o la r i ty tim e scale demonstrates th a t the normal

magnetozone conta in ing the Panto!ambda le v e l is e ith e r anomaly 26 or

anomaly 27.

i x

CHAPTER 1

INTRODUCTION

The San Juan Basin has been Im portant to v e rte b ra te p a leon to lo

g is ts fo r over a cen tury . This reg io n , located in northwestern New

Mexico and southwestern Colorado, is p a le o n to lo g ic a lly s ig n if ic a n t be

cause i t contained the c h a ra c te riz in g assemblages th a t served as the

basis fo r the Puercan (E a r ly Pal eocene), Torre jon ian (M iddle Pal eocene),

and T iffa n ia n (Late Pal eocene) North American P ro v in c ia l Ages o f Wood

e t a l . (1 9 4 1 ), p resen tly re fe rre d to as North American Land Mammal Ages

(Evernden e t a l . 1964).

This study was undertaken to defin e the m a g n e tic -p o la rity se

quence in a section from Arroyo Torreon and to c o rre la te th a t section

w ith a section in Kutz Canyon th a t has also y ie ld e d fo s s ils o f T o rre -

jon ian Land Mammal Age. These sec tio n s , consis ting p r im a r ily o f

sedim entary rocks, were from two areas w ith in the San Juan Basin . The

faunas from both areas have been known fo r some tim e but th e ir precise

geochronological re la tio n s h ip has n o t.

T im e -c o rre la tio n o f the two areas was attem pted through the use

o f m a g n e tic -p o la rity s tra tig ra p h y and b io s tra tig ra p h y . Each area was

c o lle c te d e x te n s iv e ly fo r magnetic samples th a t were used to construct

m a g n e tic -p o la rity columns. Comparison o f th e ir r e la t iv e m agnetic-

p o la r ity columns then perm itted c o rre la t io n o f s im ila r magnetozones,

1

which gives a more precise chronological framework than does e ith e r

l ith o s tra t ig ra p h y or b io s tra tig ra p h y .

Areas chosen fo r th is study w ere, f i r s t , the head o f Arroyo

Torreon (F igure 1) re fe rre d to as the Ojo Encino Area; and second, an

area on the west side o f Kutz Canyon (F igure 1) c a lle d the Big Pocket

Area. The Ojo Encino Area includes fo s s il lo c a l i t ie s 10 and 11 o f

S in c la ir and Granger (1914) which contained the o r ig in a l Torrejon

le v e ls discovered by Wortman in 1896 (Matthew 1 89 7 ), named by Matthew

(1 8 9 7 ), and used to defin e the Torre jon ian P rov inc ia l Age by Wood e t

a l . (1 9 4 1 ). The Ojo Encino Area is approxim ately 40 k ilom eters (25

m iles ) west o f Cuba, New Mexico.

The Big Pocket Area is approxim ately 16 k ilom eters (10 m iles )

south o f B loom fie ld , New Mexico. The Big Pocket Area includes the

U n iv e rs ity o f Kansas fo s s il lo c a l i t y 13 (KUPV 13 in Wilson 1956b and

NM 13 in Wilson and Szalay 1972) discovered by Wilson in 1948 and de

scribed by him (Wilson 1951) as the Angels Peak fau n u le . M o d ifica tio n s

and add itions to W ilson's (1951) o r ig in a l d escrip tio n o f the area were

made in Wilson (1 9 5 6 a ), Russell (1 9 6 7 ), and Wilson and Szalay (1 9 7 2 ).

Wilson (1 9 5 1 ), in his p re lim in a ry survey, assigned the

Angels Peak fauna to Torre jon ian Land Mammal Age and suggested th a t i t

may not be contemporaneous w ith o th er Torre jon ian faunas from the San

Juan Basin. He, a t th a t tim e , d id not fe e l ju s t i f ie d in determ ining

the temporal d iffe re n c e between his Angel Peak fauna and those from

other San Juan Basin Torre jon ian lo c a l i t ie s . In 1972, Wilson and

Szalay (1972) pointed out th a t the Kutz Canyon lo ca l fauna (= Angels

Peak faunule o f Wilson 1951) is o f T o rre jon ian age but o ld e r than the

2

3

So 0 ^ 2 ^ (

UTAH

ARIZONA

x COLORADO

y XNEW MEXICOX V V *Farmington •VeBloomfield

Canyon Xb De Chelly Nat. Mon.

N

Durango e Ragosa?ADO any ^ ( S p r i n g s

BarrelSpringArroyo

KimbetohArroyo

\K utzCanyon

•z •Tsosie

30 Mi.i l l t i

Ojo". ( /eCuba Encmo ) / *

/A rro y o j L // Torreon>-.j)Rio

VPuercoV

\Albuquerquel

Km.Z Boundary of the ' San Juan Basinl\ Continental Divide

Figure 1. Regional Map o f the San Juan Basin

4

upper c o lle c t in g le v e l ( Panto!ambda zone) from the Ojo Endno Area.

N evertheless, the chronological d if fe re n c e , or lack th e re o f, between

s im ila r faunal le v e ls in the San Juan Basin has not been determ ined,

nor has the technique o f m a g n e tic -p o la rity s tra tig ra p h y been a v a ila b le

w ith which to do so. This was the main purpose o f th is study; to apply

the technique o f m a g n e tic -p o la rity s tra tig ra p h y to sediments th a t con

ta in fo s s ils o f Torre jon ian age. T im e -c o rre la tio n o f v e rte b ra te

faunal remains is im portant to the understanding o f both evo lu tio n and

biogeography. Simpson (1933 , p. 79) emphasized the importance o f

chronostra tigraphy when he w ro te , "The f i t t i n g o f a l l these faunas

in to th e ir r e la t iv e pos itions in a tim e scale and the establishm ent o f

app ro pria te conventional d iv is io n s o f th is time scale c o n s titu te one

o f the most im portant aims o f mammalian pa leon to logy." This statem ent

is as tru e w ith respect to the faunal horizons w ith in each Land Mammal

Age as i t was fo r the Land Mammal Ages them selves. R ecen tly , Woodburne

(1977) re ite ra te d the need fo r in creas in g the p rec is io n and refinem ent

o f the North American Land Mammal Ages.

CHAPTER 2

THE SAN JUAN BASIN

Figure 1 shows the boundaries o f the San Juan Basin. I t in

cludes the areas o f in te re s t to th is study as w ell as the geographical

features b r ie f ly discussed below.

Geography

Located in the Four Corners Region, the San Juan Basin occupies

p art o f M cKinley, Rio A rr ib a , and Sandoval Counties and a l l o f San Juan

County in New Mexico; p a rt o f A rch u le ta , La P la ta , and Montezuma

Counties in Colorado; and a small fra c tio n o f Apache County, A rizona.

N early 52,000 square k ilom eters (20 ,000 square m iles ) in a re a , i t is

bounded roughly by C o rtez, Durango, and Pagosa Springs in Colorado and

by Cuba, G rants, and Gallup in New Mexico.

A major portio n o f the San Juan Basin is drained by the SaiT

Juan R iver System, a t r ib u ta r y to the Colorado R iv e r . East o f the

Continental D iv ide the Rio Chama System to the north and the Rio Puerco

System to the south flow so u th easterly out o f the basin and in to the

Rio Grande R iv e r.

There is a tremendous d iffe re n c e in topographic r e l i e f between

the rim areas and the basin in te r io r o f the San Juan Basin . The e leva

t io n d iffe re n c e between the h ighest bordering peak and the San Juan

R iver where i t leaves the basin is about 2835 meters (9300 fe e t )

5

6

(K e lle y 1950a). The basin in t e r io r is less spectacu lar in r e l i e f ; less

than 500 meters (1609 fe e t ) separate i t s h ighest and low est e le v a tio n s .

Cuba Mesa, Arroyo Torreon, and Kutz Canyon show some o f the most spec

ta c u la r r e l i e f in the basin in te r io r w ith topographic r e l i e f o f 290

meters (950 f e e t ) , 152 meters (500 f e e t ) , and 473 meters (1550 f e e t ) ,

re s p e c tiv e ly .

The in te r io r o f the San Juan Basin is most im portant to th is

study. Extensive badlands in th is region have y ie ld e d numerous remains

o f v e rte b ra te s . The w ell studied portio n o f the San Juan Basin con

ta in s geographical fea tu res th a t are c a rto g ra p h ic a lly p ro b le m a tic a l.

The geographical lo c a t io n , s p e ll in g , or even the name o f some o f these

fea tu res remains in d isp u te . For example, Simpson (1959) f e l t i t nec

essary to discuss the h is to ry o f names and sp e llin g s app lied to Tsosie ,

Kimbetoh, and Torreon Arroyos as w e ll as to provide a b r ie f account o f

the change in name and lo c a tio n o f the present town o f Cuba, New Mexico.

His suggested names, s p e llin g s , and locatio ns are used in th is study.

M acIntyre (1966) also discussed some geographical features from th is

reg io n . In a t le a s t one instance (Angel Peak) he is in e r r o r . Near

the Big Pocket Area o f Kutz Canyon is an erosional remnant v a rio u s ly re

fe rre d to as Angel or Angels Peak1 (F ig u re 13, p. 4 2 ) . M acIntyre (1966)

1. S in c la ir and Granger (1 9 1 4 ), Wilson (1 9 5 1 ), and various maps r e fe r to th is fe a tu re as Angels Peak. Granger (1 9 1 7 ), however, c a lle d i t Angel Peak. At the suggestion o f G. G. Simpson th is erosional remnant w i l l be re fe rre d to as Angel Peak. He pointed out th a t i t was named by pioneers who saw, in i t s o u t l in e , an an g e l. The peak was n e ith e r thought to have been in the possession o f angels nor was an in d iv id u a l w ith the surname Angel i t s eponym.

72

concluded th a t th is peak is located in the NW o f Section 5 , T .2 7 N .,

R.9W. Angel Peak is found in the NW o f Section 23 , T .2 7 N ., R.10W. on

the U. S. Geological Survey B loom fie ld 15 Minute Quadrangle Map.

Geology

G e o lo g ic a lly , the San Juan Basin is the southernmost o f several

la rg e interm ontane s tru c tu ra l basins among or p a r t ia l ly bounded by the

Rocky Mountains. I t occupies approxim ately the eastern o n e -h a lf o f the

Navajo Physiographic Section o f the Colorado Plateau Physiographic

Province. The several s tru c tu ra l elements th a t define the San Juan

Basin are discussed in K e lley (1950b) and B a ltz (1 9 6 7 ).

The geo logical boundaries o f the San Juan Basin have not been

agreed upon (K e lle y 1950b). Bauer (1916) and Reeside (1924) lim ite d

the San Juan Basin to th a t region conta in ing concentric inw ard ly d ip

ping s t r a ta . This corresponds to the northern h a lf o f the basin

in te r io r mentioned above. This Central Basin (B a ltz 1 9 6 7 ), asymmetrical

w ith a northwest trend ing a x is , is th a t p a rt o f the basin noted fo r i t s

v e rte b ra te faunas; i t contains both the Ojo Encino and Big Pocket Areas.

2 . M acIntyre (1966) wrongly id e n t if ie d an unnamed peak a t approxim ately 36e36 l N. L a t . , 107*48* W. Long, as Angel Peak. S in c la ir and Granger's (1914) map places the peak a t about 36 *3 41 N. L a t . , 107* 53* W. Long, and W ilson's (1951) re ference was to a peak a t approxim ately 36*32 ' N. L a t . , 107*58' W. Long. The coordinates o f Angel Peak on the U. S. Geological Survey B loom field 15 Minute Quadrangle Map are 36*341 N. L a t . , 107*52' W. Long. A lso , W ilson's (1951) map showed Angel Peak to be near the head o f Armenta Canyon and eas t southeast from his fo s s il lo c a l i t y 13 . The peak th a t M acIntyre (1966) id e n t if ie d as Angel Peak is east northeast o f fo s s il lo c a l i t y 13 . F u rth e r,Granger (1917) c le a r ly associated Angel Peak w ith Kutz Canyon.

8

The s tra tig ra p h ic column o f the Central Basin is a succession

o f m arine, brackish w a te r, and fresh w ater s tra ta (Bauer 191 6 ). These

s t r a ta , th ic k e s t in the cen ter o f the bas in , are estim ated to represent

from 3050 to 4570 meters (10 ,000 to 15,000 fe e t ) o f sediment (K e lle y

1950b). Although predom inantly o f Cretaceous age, these s tra ta rep re

sent a broken sequence from Late Paleozoic to the Eocene (Simpson 1948,

B a ltz 1967). This study is concerned w ith the Pal eocene Nacimiento

Formation. For fu r th e r in q u iry in to the geology o f the San Juan Basin

see Reeside (1 9 2 4 ), Beaumont and Read (1 9 5 0 ), K e lley (1950 b ), and B a ltz

(1 9 6 7 ).

Previous Geological In v e s tig a tio n

The San Juan Basin has been in v e s tig a ted by many workers since

J. S. Newberry f i r s t traversed the region w ith the Macomb Expedition in

1859 (Simpson 1948, 1950). The h is to ry o f in v e s tig a tio n has been ade

quate ly developed by Simpson (1948) and B a ltz (1967) and only those

in v e s tig a tio n s p e rt in e n t to the present study are included h ere .

The f i r s t recognized Pal eocene mammals from the San Juan Basin

were c o lle c te d by David Baldwin w h ile in the employ o f E. D. Cope,

sometime between 1880 and 1888. These fo s s ils are now p a rt o f the

Pal eocene c o lle c t io n o f the American Museum o f Natural H is to ry (Matthew

1937). That in s t i tu t io n began a successful associa tion w ith the fo s s il

r ic h badlands o f the San Juan Basin by de lega ting J . L. Wortman to lead

an exp ed ition there in 1892. Wortman led a second exp ed ition to the

San Juan Basin during which he c o lle c te d over 1500 Pal eocene specimens

and discovered the T o rre jon ian faunal le v e l o f the Ojo Endno Area

(Matthew 1897, 1937). The Wortman c o lle c tio n was described by Osborn

and E arle (1895) and by Matthew (1 9 3 7 ).

W alter Granger b r ie f ly examined the Paleocene s tra ta o f the San

Juan Basin fo r the American Museum in 1912. The fo llo w in g year he re

turned w ith W. J . S in c la ir o f Princeton U n iv e rs ity to study the

s tra tig ra p h y and v e rte b ra te faunas o f the area (S in c la ir and Granger

1914). They recognized what they considered to be two c o lle c t in g

le v e ls in the Torre jon ian o f Arroyo Torreon. Granger (1917) la t e r c o l

lec ted Torre jon ian fo s s ils from the northern portion o f the Central

Basin; he found fo s s ils in several arroyos near A ztec , New Mexico and

in Kutz Canyon, south o f B lo o m fie ld , New Mexico. Further d e ta ils o f

the two c o lle c t in g le v e ls o f the San Juan Basin w i l l be discussed below.

A fte r the Second World War in te re s t in the paleontology o f the

San Juan Basin Pal eocene was revived and personnel from a number o f in

s t itu t io n s were in the area a t th a t tim e . Of In te re s t to the present

study are in v e s tig a tio n s o f the Torre jon ian s tra ta and faunas. Conse

quently no mention is made o f in v e s tig a tio n s o f s tra ta and faunas o f

Puercan or T if fa n ia n age. As mentioned above, Wilson led a U n iv e rs ity

o f Kansas group in to the San Juan Basin in 1948 and returned to the

area in 1956 and 1962 (Wilson 1950, 1951, 1956a, 1956b, Wilson and

Szalay 1 97 2 ). C. L. Gazin c o lle c te d fo s s ils fo r the U. S. N ational

Museum from Middle Pal eocene s tra ta in 1949 (Gazin 1968). P art o f

W ilson's (1951 , 1956a) c o lle c t io n came from Kutz Canyon w h ile p a rt o f

G azin 's (1968) c o lle c t io n was found near Arroyo Torreon. A lso , G. G.

Simpson, o f the American Museum, c o lle c te d Torre jon ian fo s s ils from

near Cuba in 1949 (Simpson 1959).

9

10

The most recent in v e s tig a tio n o f fo s s ils and s tra tig ra p h y o f

the San Juan Basin has been by the U n iv e rs ity o f Arizona p a rty under

the leadersh ip o f E. H. Lindsay and R. F. B u tle r . This group is a t

tempting to resolve the chronology o f Late Cretaceous to Eocene s tra ta

in the San Juan Basin by applying modern methods o f both v e rte b ra te

paleontology and paleomagnetism. The present study is a p a rt o f the

most recent s c ie n t i f ic e f f o r t in the San Juan Basin.

CHAPTER 3

THE NACIMIENTO FORMATION

Rocks deposited during the Torre jon ian age In the San Juan

Basin are found w ith in the Nacimiento Formation. The Nacimiento is one

o f the several l i th o s tr a t ig r a p h ic un its concentric about the basin in

t e r io r . I t crops out p r im a r ily in the southern h a l f o f the cen tra l

portion o f the San Juan Basin. Badlands and c l i f f s in the Nacimiento

Formation are exposed from the Colorado-New Mexico boundary southeast

ward to Cuba Mesa, and along the Rio Puerco east and north o f Cuba

(Simpson 1950, Fassett and Hinds 197 1 ). The Nacimiento Formation is

thought to grade la t e r a l ly in to the Animas Formation (Reeside 1924,

S ilv e r 1950) which crops out in the northwestern area o f the San Juan

Basin (F ig ure 2 ) .

Torre jon ian fo s s ils are found throughout the ex ten t o f the

Nacimiento but e s p e c ia lly : 1) near the head o f Arroyo Torreon (S in c la ir

and Granger 1914, Gazin 1968 ); 2 ) near the head o f Kimbetoh Arroyo

(S in c la ir and Granger 1914, Wilson 1951 , 1956c); 3) in Kutz Canyon

(Granger 1917, Wilson 1951, 1956c, Wilson and Szalay 1972); and 4 ) in

the Animas R iver V a lle y near Aztec (Granger 1917 ).

S tra tig ra p h ic Nomenclature

The Nacimiento has had a long h is to ry o f nomenclature! change.

I t has been recognized as a u n it since f i r s t designated the "Puerco

11

12

Durango PagosaSprings

COLORADO NEW MEXICO

•Aztec

Bloomfield*

Jose

10 20 30 Mi. Cuba

50 Km.

Figure 2 . Geologic Map o f Nacim iento, Animas, and San Jose Formations San Juan Basin. — (Adapted from S ilv e r 1950; Fassett and Hinds 1971)

13

Marls" by Cope in 1874 (Simpson 1948 ). This th ree quarters o f a cen

tu ry o f Nacimiento h is to ry , as presented by Simpson (1948 , 195 9 ),

includes the problem re s u lt in g from the e rro r o f confusing b io s t r a t i -

graphic and l ith o s tr a t ig r a p h ic u n its . The Nacimiento has long been

divided in to separate l i th o lo g ic and associated faunal u n its , the

Puerco and the T o rre jo n . Usage o f the terms Puerco, T o rre jo n , and

Nacimiento was not con s is ten t u n t i l 1948 when Simpson (1948) a p t ly

pointed out th a t the Puerco and Torrejon are l i t h o lo g ic a l ly inseparab le

and, consequently, cannot be considered fo rm ations, which are l i t h o

s t r a t i graphic u n its . He considered Puerco and Torrejon as faunal zones

w ith in the rocks o f the Nacimiento Formation; the term "Nacimiento fo r

mation" had been used by Dane (1946) but had not been proposed as a

formal l i th o s tr a t ig r a p h ic u n it . Simpson (1959) demonstrated the occur

rence o f T o rre jon ian fo s s ils from the type Puerco, emphasizing the need

to d is tin g u ish faunal concepts from s tra tig ra p h ic concepts. The

Torre jon ian Land Mammal Age is o f importance to the present study and

is discussed in more d e ta il below.

S tra tig ra p h y

The Nacimiento Formation consists o f v a rio u s ly colored beds o f

c la y , s h a le , and s i lts to n e w ith interbedded sandstones. The f in e

grained s tra ta vary in co lo r from the common gray or green-gray to red

or b lack . The sandstones, u s u a lly lo c a l and le n t ic u la r , vary in co lo r

from b u ff or ye llow to gray or w h ite . The sandstones also vary in

th e ir res is tan ce to w eathering; some are f r ia b le w h ile others are in

durated. A few re s tr ic te d black carbonaceous claystone and s ilts to n e

14

lenses occur w ith in the Nacimiento Formation. Also p resen t, but ra re ,

are th in beds o f c o a l.

The upper and lower boundaries o f the Nacimiento Formation are

not e a s ily recognized throughout the San Juan Basin and g e n e ra lly have

been placed a t unconform ities w ith the underlying Ojo Alamo Sandstone

and the o ve rly in g San Jose Form ation. The lower unconformity was noted

by S in c la ir and Granger (1 9 1 4 ), but B a ltz , Ash, and Anderson (1966)

were unable to confirm i t s presence. In s tead , they found evidence th a t

the Nacimiento intertongues w ith the underlying Ojo Alamo a t th ree lo

cations in B arrel Spring Arroyo. More recent work on the s tra tig ra p h y

o f th is area by B u tle r e t a l . (1977) sub stan tia tes th is in te rto n g u in g

re la t io n s h ip .

The upper boundary o f the Nacimiento is not simple e i th e r . In

the southern p a rt o f the San Juan Basin an unconformity appears to sep

a ra te the Nacimiento Formation from the o ve rly in g San Jose sediments

(Reeside 1924, Simpson 194 8 ). However, to the north the Nacimiento

apparently grades in to the San Jose w ith no apparent break in sedimen

ta t io n . The T iffa n y beds o f Granger (1 9 1 7 ), here considered a p a rt o f

the San Jose Formation (Simpson, in Simons 1 9 6 0 ), are thought to con

formably o v e r lie the Nacimiento in the northern p a rt o f the bas in .

More f ie ld work is needed to determine the accurate s tra tig ra p h ic

re la tio n s h ip s o f the Nacim iento, San Jose, and T if fa n y .

The re la tio n s h ip o f the Nacimiento to the Animas Formation is

not f u l l y understood. North and west o f the Nacim iento, the Animas was

thought by B a ltz (1967) to be contemporaneous w ith the form er. The

15

Animas Formation is d is t in c t iv e in co lo r (tan or green) and contains

much a n d e s itic d e b ris . Red s t r a t a , comon in the M acim iento, are

ra re ly seen in the Animas (Reeside 1 92 4 ). The d iffe re n c e in lith o lo g y

d istingu ish es the Animas from the Nacim iento, but whether th e ir s t r a t i

graphic re la tio n s h ip is la te r a l or p a r t ly superpositional has not been

determined (F asse tt and Hinds 1971).

B a ltz 's (1967) measurements show the Nacimiento to be only h a l f

as th ic k in the southern p a rt o f the San Juan B asin , near Cuba, New

Mexico, as in the more n o rth e r ly p a rt o f the bas in . This th in n in g ,

according to B a ltz (1967) is p a r t ly in tra fo rm a tio n a l. I t is also p a rt

ly due to erosion o f the upper Nacimiento p r io r to San Jose d ep o s itio n .

Simpson (1959) suggests th a t the probable lack o f Puercan fo s s ils in

the type Nacimiento area a t Cuba Mesa in d ic a tes th in n in g o f the Naci

miento due to progressive overlap o f younger rocks to the south. T h is ,

o f course, could also account fo r p a r t o f the sou th eas te rly th in n in g

tre n d .

I t is agreed g en era lly (B a ltz 1967) th a t the Nacimiento sed i

ments were deposited in a f lu v ia l environm ent. The many lo ca l

le n t ic u la r sandstones th a t represent channels and the in te rg ra d in g

lenses o f clays and s i l t s mentioned by Simpson (1948) support th is

in te rp re ta t io n . M acIntyre (1966) suggests th a t streams and bodies o f

w ater la rg e enough to support la rg e aquatic r e p t ile s were present but

th a t enough s o lid ground was present to support a f a i r l y la rg e pop

u la tio n o f t e r r e s t r ia l mammals. R e s tric te d p a r t ia l ly paludal

environments were suggested by both M acIntyre (1966) and B a ltz (1 9 6 7 ).

16

Such an environment is evidenced by a t le a s t two areas encountered dur

ing the present study, both o f which are w ith in S in c la ir and Granger's

(1914) fo s s il lo c a l i t y 10 in the Ojo Encino Area. One a re a , in the NW%

o f Section 26 , T .2 1 N ., R .5W ., contains a 2 meter (6 .6 fo o t) th ic k black

carbonaceous c lay la y e r exposed over a r e la t iv e ly f l a t area o f approxi

m ately 740 square meters (8000 square f e e t ) . T u r t le remains and p la n t

m ateria l were found in the stratum . A second, s im ila r , exposure was

located approxim ately 0 .8 k ilo m e te r (1 .5 m ile ) southeast o f the f i r s t .

S tra ta o f black carbonaceous c lay w ith numerous f is h , aqu atic r e p t i l e ,

and p la n t fo s s ils were also seen in B arrel Spring Arroyo and Kutz Can

yon. A fu r th e r in d ic a tio n o f paludal environment was a th in coal seam

present near the base o f the lo c a l i t y 10 section in the Ojo Encino Area.

B a ltz (1967) demonstrated the tendency toward a g re a te r pro

portion o f sandstone in the northern p a rt o f the San Juan Basin. This

trend was noted during the present study w h ile c o lle c t in g paleomagnetic

samples in the Ojo Encino and Big Pocket study areas . The presence o f

a g rea te r amount o f sandstone in the Nacimiento to the north could be

in d ic a t iv e o f a n o rth e r ly source area fo r the sediments o f th a t forma

t io n . However, the d e ta ile d s tra tig ra p h ic ana lys is o f the Nacim iento,

necessary to demonstrate th is concept, has not been undertaken.

The Nacimiento is considered lower and middle Pal eocene in age.

In the past i t has been considered basal Eocene o r post-Cretaceous

(Gardner 191 0 ). The discovery o f the la te Pal eocene T if fa n y beds,

s t r a t i g ra p h ic a lly h igher than the Nacim iento, reduced the upper age

l im i t o f the Nacimiento from e a r ly Eocene or la te Pal eocene to middle

Pal eocene (Simpson 1933). P resently the Puerco, T o rre jo n , and T iffa n y

le ve ls are considered low er, m idd le , and upper Paleocene, re s p e c tiv e ly ,

as suggested by Simpson (1933) and Matthew (1937 ).

17

CHAPTER 4

METHODS OF CHRONOLOGICAL CORRELATION

Two methods o f t im e -c o rre la t io n are useful in the Nacimiento

Formation o f the San Juan Basin. The v e rte b ra te fo s s ils fo r which the

basin has long been noted can be used b io s t r a t i g ra p h ic a lly fo r

chronological c o r re la t io n . A lso , the fin e -g ra in e d sediments o f th is

form ation have been found to be recorders o f reve rsa ls in the e a rth 's

magnetic f ie ld ; they are useful in the m a g n e tic -p o la rity s tra tig ra p h ic

method o f t im e -c o rre la t io n .

B io s tra tig ra p h ic

The Nacimiento Formation has long been recognized as two

d is t in c t b io lo g ic a l u n its , the Puerco and Torrejon faunas mentioned

above. The Puerco fauna is the o ld es t o f a series o f Cenozoic faunas

in North America which served to d efin e the North American P ro v in c ia l

Ages o f Wood e t a l . (1 9 4 1 ). Now re fe rre d to as North American Land

Mammal Ages (Evernden e t a l . 1 9 6 4 ), these un its are used by v e rte b ra te

paleo n to lo g is ts to c o rre la te the Cenozoic o f North America. T h e ir de

velopment by m o d ifica tio n s to concepts f i r s t proposed in the la te 1800s

was w ell d e ta ile d by Tedford (1 9 7 0 ). He also discussed, as did Savage

(1955) and Wilson (1 9 6 7 ), the use o f fo s s il mammals in c o rre la t io n and

concluded th a t the p rese n tly developed Land Mammal Ages have proven .

useful in c o r re la t io n .

18

19

Wood e t a l . (1941) defined the Land Mammal Ages on the basis o f

the faunal assemblages w ith in them. The faunas were separated in to

four aspects: 1) genera known only from the age being defined (index

fo s s i ls ) ; 2) genera found in North America fo r the f i r s t tim e ( f i r s t

appearance); 3) genera found in North America fo r the la s t tim e ( la s t

appearance); and 4) genera corranon in the age being defined (ch arac te r

i s t i c f o s s i ls ) .

The Torre jon ian Land Mammal Age

This study is concerned w ith one o f the p resen tly recognized

North American Land Mammal Ages, the middle Pal eocene T o rre jo n ia n .

The T o rre jon ian was defined by Wood e t a l . (1941, p. 9) as "-new pro

v in c ia l term , based upon the T o rre jon ian form ation o f the San Juan

Basin, New Mexico, type lo c a l i t y , the heads o f Arroyo T o r r e jo n ; . . . "

The fo llo w in g genera were used by them to define the T o rre jon ian Land

Mammal (P ro v in c ia l) Age:

F ir s t appearance: C hriacus, P s itta co th eriu m , D id y m ic tis ,Pantolambda, Claenodon, Tetraclaenodon

Last appearance: E llip so d o n , Eucosmodon, Haploconus

Index fo s s ils : Conoryctes, D e lta th e n urn, M loclaenus, Trlisodon

C h a ra c te r is tic fo s s ils : Anisonchus, P erip tychu s, P tilodus

Since the d iscovery o f the o r ig in a l Torrejon fauna, the d e fin

ing genera o f the Torre jon ian have been found outside the San Juan

Basin. Wood e t a l . (1941) included some Torre jon ian c o rre la t iv e s in

th e ir re p o rt and, more re c e n tly . Van Valen and Sloan (1966) constructed

a ch a rt l is t in g a l l known Pal eocene mammal lo c a l i t ie s and faunas.

Since Van Valen and S loan ’ s (1966) p u b lica tio n some lo c a l i t ie s have

been discovered or found to be o f Torre jon ian age. A l i s t o f these

lo c a l i t ie s is included below:

Tongue R ive r: Fort Union Formation; B il lin g s County, NorthDakota; Simons ( I9 6 0 ) and Brown (1962)

(? )A lb e rta O il W e ll: Paskapoo Formation; Research Council o fA lb e rta Core Hole 6 6 -1 ; B a lzac , A lb e r ta , Canada; Fox (1968)

L i t t l e Muddy Creek: Evanston Formation; southwestern Wyoming;Gazin (1969)

Black Peaks: Black Peaks Form ation; Big Bend N ational Park,Texas; Schiebout (1974)

The Torre jon ian o f the San Juan Basin includes two horizons

described by S in c la ir and Granger (1914) and named the Panto!ambda and

D eltatherium l i f e zones by Osborn and Matthew (1909) and Osborn (1 9 2 9 ).

These faunal le v e ls , each o f which was defined by and named fo r the

genus re s tr ic te d to i t , have been problem atical since th e ir d iscovery .

S in c la ir and Granger (1914) reported the D eltatherium zone 30.5 meters

(100 fe e t ) below the Panto!ambda zone and Osborn (1929) considered the

le v e ls d is t in c t l i f e zones. Matthew (1 9 3 7 ), however, be lieved them to

be e ith e r fac ies d iffe ren c es or accidents o f c o lle c t in g because many

o f the same species were found in both le v e ls and no s ig n if ic a n t faunal

changes could be recognized. Wilson (1951 , p. 10) a lso s ta ted th a t the

d iffe re n c e between the Panto!ambda and D eltatherium zones is " . . . l a r g e

l y , i f not e n t i r e ly , fa c ia l in c h a ra c te r ." Wilson (1956a) also

expanded the d e f in it io n o f the zones. He pointed out th a t , in a d d itio n

to D e lta th e riu m , Triisodon and Haploconus are re s tr ic te d to the

20

21

D eltatherium zone and th a t Claenodon as w e ll as Panto!ambda is re

s t r ic te d to the Pantolambda zone.

More re c e n tly , Szalay (1969) discussed the Torre jon ian le v e ls

w ith respect to the genus M ixodectes. He found fi. m alar!s to occur

only in the D eltatherium zone and thought i t l i k e ly th a t M. pungens

occurs only in the Pantolambda zone. He noted th a t the provenance o f

the M. pungens specimens.was, however, suspect.

Gazin (1968) obtained the prim ate T o rre jo n ia w ilso n i from the

Pantolambda zone and Wilson and Szalay (1972) discovered Palaechthon

nacim ienti w ith in the D eltatherium zone. These primates are not re

presented by enough m ateria l to be considered d iagnostic o f e ith e r

horizon but a t the present tim e are re s tr ic te d to on ly one c o lle c t in g

le v e l .

The d e f in it io n o f the D eltatherium zone w ith D e lta th e riu m ,

T riis o d o n , Haploconus, and Mixodectes m alaris re s tr ic te d to i t and the

d e f in it io n o f the Pantolambda zone w ith Pantolambda and Claenodon re

s t r ic te d to i t are con sis ten t w ith b io s t r a t i graphic ranges determined

in the Ojo Encino and Big Pocket areas during the present study.

M agnetostratig raph ic

S c ie n t i f ic in te re s t in paleomagnetism began in the m id-

nineteenth century but a p p lic a tio n o f th is f ie ld was la rg e ly ignored

u n t il the re v iv a l in p o p u la rity o f the theory o f co n tin en ta l d r i f t in

the 1950s (McElhinny 197 3 ). The volume o f l i t e r a t u r e in th is f ie ld

increased from about 200 to about 1500 independent studies from 1959

22

to 1973 (Cox and Doell I9 6 0 , McElhinny 1973) and continues to increase

a t a rap id r a te .

G eom agnetic-Polarity Time Scale

One re s u lt o f the renewed in te re s t in paleomagnetism has been

the m a g n e tic -p o la rity tim e s c a le ; i t was la rg e ly the re s u lt o f attempts

to demonstrate Matuyama's (1929) hypothesis th a t a time synchronous

magnetic reversa l had occurred in the e a r ly P le istocene (Watkins 1972,

Cox 1973). C a lib ra tio n o f the m a g n e tic -p o la rity tim e scale is possib le

through rad io m etric age determ inations made on rocks o f known p o la r i ty .

The developmental h is to ry o f the m a g n e tic -p o la rity tim e scale has been

chron icled by Watkins (1972) and Cox (1 9 7 3 ).

P resen tly the m a g n e tic -p o la rity tim e scale is r e l ia b ly c a l i

brated fo r only the past four m il l io n years but attempts have been and

are being made to extend th is s c a le . Opdyke (1972) and McDougall e t

a l . (1977) extended the tim e sca le in to the Miocene. E a r l ie r ,

H e ir tz le r e t a l . (1968) had extended the m a g n e tic -p o la rity tim e sca le

in to the Cretaceous. However, because the dates used were ex trap o la ted

from an In te rv a l o f known age, e ith e r ra d io m e tr ic a lly or pa leo n to lo

g ic a l ly determ ined, ages e a r l ie r than la te Cenozoic are not as y e t w ell

determ ined. They should be used w ith cau tio n . The H e ir t z le r e t a l .

(1968) tim e scale used the p rese n tly accepted Hays and Opdyke (1967)

convention fo r la b e lin g magnetozones; magnetic epochs are lab e led w ith

Arabic numerals and magnetic events w ith in an epoch are lab e led w ith

l e t t e r s , both beginning w ith the most rece n t.

23

The H e ir t z le r e t a l . (1968) m a g n e tic -p o la rity time sca le has

been m odified by Larson and Pitman (1 9 7 2 ), Berggren and VanCouvering

(1 9 7 4 ), and T a r lin g and M itc h e ll (1 9 7 6 ). The T a r lin g and M itc h e ll

(1976) p o la r ity time scale is used in th is study.

A recent advance in the f ie ld o f m agnetostratigraphy has been

the c o rre la t io n o f t e r r e s t r ia l sediments known fo r th e ir v e rte b ra te

faunas. E arly in 1975, Johnson, Opdyke, and Lindsay (1975) showed

th a t such c o rre la t io n was possib le in the San Pedro V a lle y o f southern

A rizona. L indsay, Johnson, and Opdyke (1975) and Opdyke e t a l . (1977)

have demonstrated the c o rre la t io n o f o th er t e r r e s t r ia l sediments w ith

the m a g n e tic -p o la rity tim e s c a le . The p ro je c t undertaken by workers

from The U n iv e rs ity o f Arizona in the San Juan Basin is designed to

c o rre la te the v e r te b ra te -fo s s il-b e a r in g t e r r e s t r ia l sedim entary se

quences o f th a t region through the use o f m a g n e tic -p o la rity

s tra tig ra p h y .

Methods/

Since Johnson e t a l . (1975) f i r s t pointed out th a t some t e r r

e s t r ia l sediments have acquired s ta b le remanent m agnetization in the

form o f dep ositiona l remanence (DRM), the techniques o f f ie ld c o lle c

t io n , la b o ra to ry p re p a ra tio n , and la b o ra to ry ana lys is have been re fin e d

through fu r th e r a p p lic a t io n .

For the purposes o f th is study 265 paleomagnetic s ite s were

c o lle c te d and analyzed . The o rien ted -b lo c k technique was used in the

badlands o f the San Juan Basin. D e ta ils o f th is sampling technique

24

are described in Lindsay e t a l . ( in p ress ). At le a s t th ree o rien ted

samples were c o lle c te d from each s i t e . A s tra tig ra p h ic separation o f

approxim ately th ree meters (te n fe e t ) was m aintained between successive

s ite s whenever p o ss ib le . Samples were c o lle c te d from the f in e s t

grained c la y l ith o lo g ie s a v a ila b le in the a rea ; some s ilts to n e s were

c o lle c te d out o f n ec ess ity . I t is suggested, however, th a t the choos

ing o f an acceptable l ith o lo g y takes p r io r i t y over the maintenance o f

an exact s tra tig ra p h ic in te r v a l . Unacceptable l ith o lo g ie s o ften pro

vide ambiguous p o la r ity determ inations and are not u s e fu l, regardless

o f th e ir s tra tig ra p h ic e le v a t io n . In the la b o ra to ry each sample was

cut and trimmed in to a block specimen th a t f i t in to a p la s t ic box w ith

an in s id e volume o f approxim ately 4 cubic centim eters (1 .0 2 cubic

in ch es ). Johnson e t a l . (1975) estim ate th a t these techniques o f c o l

le c tio n and specimen prepara tion cause an approximate e rro r o f ±5° in

the re s u lt in g magnetic d e c lin a tio n and in c lin a t io n measurements.t

One problem encountered during specimen prepara tion was th a t o f

d es icc a tio n . Many samples were found to be dry and cracked s u f f i

c ie n t ly to d is in te g ra te in p re p a ra tio n . For th is reason some s ite s are

represented by only two specimens. Some o f the d is in te g ra tio n d i f f i

c u lt ie s were avoided by c o lle c t in g more than th ree o rien ted samples

from s ite s o f f i s s i l e l i th o lo g y . In the la b o ra to ry some o f the d is in

te g ra tio n problems were solved through the use o f Elm er's G lu e -A ll .

Sample d is in te g ra tio n might be avoided by trimming and p lac ing poorly

preserved samples in p la s t ic boxes w h ile a t the outcrop.

25

Once prepared, the specimens were measured fo r na tu ra l remanent

magnetism (NRM) w ith a Superconducting Technology C-102 cryogenic mag

netom eter. This ins tru m ent, w ith the capacity o f measuring magnetic

moments w ith in te n s it ie s as low as 10" gauss-cubic c en tim e te rs , can

e a s ily measure the weak magnetic moments o f t e r r e s t r ia l sedim ents.

Many o f the rocks have acquired a secondary component, u s u a lly in the

d ire c tio n o f the e a rth 's present magnetic f i e l d , which must be removed

to determine the p o la r ity o f the a lte rn a tin g f ie ld (AF) demagnetized

NRM which approximates the prim ary DRM. A lte rn a tin g f ie ld demagneti

za tio n w ith a Schondstedt GSD-1 demagnetizer was used to remove the

secondary, viscous remanent m agnetization .

Data from these measurements (Appendix A) were in te rp re te d to

in d ic a te the magnetic beh avio r, as w e ll as the magnetic p o la r i ty , o f

the sedim ents. P o s itive in c lin a t io n s and n o rth e r ly d e c lin a tio n s are

in d ic a t iv e o f normal magnetic p o la r ity whereas negative in c lin a t io n s

and so u th erly d ec lin a tio n s in d ic a te the presence o f a re v e rs e ly mag

n etized in t e r v a l . C a lcu lated v ir tu a l geomagnetic pole (VGP) la t itu d e s

are also used to construct m a g n e tic -p o la rity columns. A norm ally mag

n etized s i te e x h ib its a p o s itiv e VGP la t i tu d e and a m ag n e tica lly

reversed s i te e x h ib its a negative VGP la t i tu d e ; p o s itiv e VGP la t itu d e s

are north o f the equator and negative VGP la t itu d e s are south o f i t .

As suggested by Lindsay e t a l . ( in p re s s ), in in te rp re t in g the data a

reversed d ire c tio n is considered prim ary and any c o n f l ic t in g normal

d ire c tio n is suspect because an unremoved secondary component may have

been acquired during the Brunhes Normal Epoch.

26

Opdyke e t a l . (1977) re c e n tly provided a p r io r i t y l i s t fo r the

r e l i a b i l i t y o f magnetic data from in d iv id u a l s ite s (Table 1 ) . T h e ir

hierarchy includes f iv e c lasses: I ) s ite s in which the data in d ic a te

a l l specimens are o f the same p o la r ity and the re s u lts are s t a t i s t i

c a l ly s ig n if ic a n t ; I I ) s ite s from which only two specimens are known

but th e ir d ire c tio n s are concordant; I I I ) s ite s th a t show s t a t is t i c a l ly

random d ire c tio n s o f m agnetization but two o f the th ree specimens are

concordant and the th ir d is w id e ly d ivergen t in an in te rm ed ia te d ire c

t io n ; IV ) s ite s th a t demonstrate a strung d is tr ib u t io n but the

d ire c tio n s change w ith AF dem agnetization in a system atic way so th a t

p o la r ity is determ ined; and V) fo r which no d e f in it io n was g iven .

Lindsay e t a l . (in press) redefined the above h ierarch y (Table 1) such

th a t i t consists o f Opdyke e t a l . ' s (1977) Class I , Classes I I and I I I

combined,Class IV , and a new class fo r s ite s w ith random d ire c t io n s .

I t seems th a t f iv e classes are r e a l ly necessary because the Class I I

and I I I s ite s o f Opdyke e t a l . (1977) are not the same; Class I I s ite s

are d is t in c t because there is not a th ir d sample to be d iv e rg e n t. I f

presen t, the th ir d sample could change the Class I I in to e ith e r a Class

I or a Class I I I s i t e , depending upon i t s magnetic d ire c t io n s . The

f iv e class h ie ra rc h y , as summarized in ta b le 1 , consists o f the fo u r

classes o f Opdyke e t a l . (1977) and the a d d itio n a l class o f Lindsay e t

a l . ( in p re s s ). The s ig n ific a n c e o f the la s t (Class V) category is

th a t i t is the on ly le v e l in the h ierarch y which provides no useful

data (Lindsay e t a l . in p re s s ).

Table 1 . H ierarchy o f Paleomagnetic S ites

Class Opdyke e t a l . (1977) Lindsay e t a l . ( In press) This Paper

I A ll specimens o f the same p o la r ity w ith s t a t is t i c a l ly s ig n if ic a n t re s u lts

A ll specimens o f one p o la r i ty and s t a t is t i c a l ly s ig n if ic a n t

Same as Opdyke e t a l . (1977) and Lindsay e t a l . ( In press)

I I Only two samples known but th e ir d ire c tio n s are concordant

Two samples are concordant and th ir d forms an angle to the o th er two - P o la r ity u su a lly c le a r

Same as Opdyke e t a l . (1977)

I I I S t a t is t ic a l ly random d ire c tio n s o f magnetiza tio n but two o f the th ree specimens are concordant but the th ird is w id e ly d ivergen t in an in te rm ed ia te d ire c tio n

Sample d ire c tio n s strung between a reversed d ire c tio n o f f ie ld and the present d ire c tio n o f f ie ld


IV Strung d is tr ib u t io n but d ire c tio n s change w ith AF dem agnetization in a system atic way so th a t p o la r i ty is determined

D irec tio n s o f m agnetization randomly d ire c te d and w ith o u t useful re s u lts


V Mentioned but not defined D irectio ns o f m agnetization randomly d ire c te d and w ithout useful re s u lts - Class IV o f Lindsay e t a l . ( In press)

Selected s ite s from the Ojo Encino and Big Pocket study areas

provide examples o f the classes l is te d in ta b le 1 . S ite SJ342 (F igure

3) from lo c a l i t y 10 in the Ojo Encino Area had a r e la t iv e ly weak, un

s tab le secondary component o v e rp rin tin g the NRM. The mean NRM

in c lin a t io n and d e c lin a tio n ( I = 71.6® , D = 3 5 8 .1 ° ) in d ic a ted th a t the

s ite was norm ally m agnetized. Removal o f the secondary component by

AF dem agnetization a t a peak f ie ld o f 200 oersteds perm itted the AF

demagnetized NRM in c lin a t io n and d e c lin a tio n to be reve a le d . These

angles ( I = 5 4 .3 ° , D = 3 4 5 .2 °) in d ic a te d th a t the AF demagnetized NRM

p o la r ity was also in a normal d ire c t io n , but w ith less s c a tte r than

p r io r to dem agnetization. A s i te such as SJ342 provides unambiguous

p o la r ity determ ination and is considered a Class I s i t e .

S ite SJ480 (F igure 4 ) , from the Big Pocket A rea, also re p re

sents a Class I s i t e . I t c le a r ly shows the p o la r ity change re s u lt in g

from the removal o f the norm ally magnetized secondary component by AF

dem agnetization.

S ite SJ585 (F igure 5 ) , from lo c a l i t y 10 in the Ojo Encino

Area, is an example o f a Class I I s i t e . I t contains no th ir d sample.

The two samples present do have concordant d ire c t io n s .

The magnetic vectors o f s i te SJ356 (F igure 6) from lo c a l i t y 11

in the Ojo Encino Area demonstrate the removal o f a s tro n g e r, more

s tab le secondary magnetic component than th a t removed from s i te SJ342.

SJ356 had w ide ly sca tte red NRM d ire c t io n s ; specimens A and C showed

possib le reversed p o la r ity and specimen B showed normal p o la r i ty . The

mean NRM d ire c tio n ( I = 6 7 .9 ° , D = 2 3 8 .6 °) was tenuously in d ic a t iv e o f

28

Rem

anen

t M

agne

tizat

ion

(Gau

ss)

29

Peak Demagnetizing Field (Oersteads)

N

Figure 3. AF Dem agnetization Curves and NRM V ecto r M otions, S ite SJ342

30

N

SJ480

NRM

Figure 4. NRM V ecto r M otions, S ite SJ480

31

Figure 5. NRM V ecto r M o tions, S ite SJ585

Rem

anen

t M

agne

tizat

ion

(Gau

ss)

32

3X10 r


Figure 6 . AF Demagnetization Curves and NRM V ecto r M o tions, S ite SJ356

33

reversed p o la r i ty . The vec to r motions during AF dem agnetization showed

the NRM d ire c tio n s to be masked by a norm ally magnetized secondary com

ponent. Although th is norm ally magnetized secondary component was

incom pletely removed from specimen B, the mean AF demagnetized NRM d i r

ection ( I = 2 6 .7 ° , D = 1 6 1 .5 ° ) in d ic a ted a re v e rs e ly magnetized s i t e .

The magnetic vec to r motion o f specimen B in d ic a ted th a t a negative in

c lin a t io n was not reached but the p o s it iv e in c lin a t io n became lower in

angle and the d e c lin a tio n became c le a r ly a sou therly d ire c t io n . This

trend showed th a t , even though the norm ally magnetized secondary com

ponent o f specimen B was s t i l l in flu e n c in g the magnetic d ire c t io n s , the

vector was trend ing toward the reversed p o la r ity demonstrated by speci

mens A and C. This Class I I I s i te shows the value o f in te rp re t in g the

trend o f magnetic vector m otions.

S ites SJ309 (F igure 7) and SJ482 (F igure 8 ) , both from the Big

Pocket Area, e x h ib ited a magnetic vec to r trend toward reversed p o la r i

t y . These s ite s are also examples o f Class I I I s i te s .

S ite SJ044 (Figure 9 ) , from the Ojo Encino lo c a l i t y 10 , is an

example o f a s i te w ith a strung d is t r ib u t io n . The 200 oersted demag

n etized NRM d e c lin a tio n was c le a r ly In d ic a t iv e o f reversed p o la r ity

and the trend in both in c lin a t io n and d e c lin a tio n was toward th a t o f a

reversed s i t e . This trend perm itted s i te SJ044 to be in te rp re te d as

re v e rs e ly magnetized w ith a norm ally magnetized secondary o v e rp rin t

p a r t ia l ly removed by AF dem agnetization. This s i te was considered a

Class IV s i t e .

34

N

SJ309

Figure 7. NRM V ecto r M o tions, S ite SJ309

35

N

SJ482

NRM:200

Figure 8 . NRM V ecto r M otions, S ite SJ482

36

. 0 .2 -


300NRM

S

Figure 9. AF Dem agnetization Curves and NRM Vector M o tions, S ite SJ044

CHAPTER 5

STRATIGRAPHY

The b io s tra tig ra p h y , 11th o s tra tig ra p h y , and m a g n e tic -p o la rity

s tra tig ra p h y o f two study areas were determined so th a t the two areas

could be c o rre la te d unambiguously.

The Study Areas

The Ojo Encino Area is the s i te o f the o r ig in a l Torre jon ian

fauna (Matthew 1897). The area was studied and c o lle c te d by S in c la ir

and Granger (1914) and lab e led by them as two la rg e American Museum

ve rte b ra te fo s s il lo c a l i t ie s . T h e ir lo c a l i t ie s 10 and 11 are on op

pos ite sides o f Arroyo Torreon , near i t s head, and approxim ately f iv e

kilom eters (th re e m ile s ) a p a rt (F igure 1 0 ) .

L o c a lity 10 includes the badlands near the heads o f Toledo

Arroyo and Encino Wash (F igure 11) and contains fo r ty th ree U n iv e rs ity

o f Arizona (UALP) v e rte b ra te fo s s il lo c a l i t ie s . I t includes a l l or

p art o f Sections 21 , 2 6 -2 8 , and 34 in T .2 1 N ., R.5W. on the U. S. Geo

lo g ic a l Survey Deer Mesa 7 .5 Minute Quadrangle Map.

L o c a lity 11 , s itu a te d near the heads o f Lopez Arroyo and an un

id e n t if ie d wash (F igure 1 2 ) , is the sm alle r o f the two S in c la ir and

Granger (1914) lo c a l i t ie s and contains about o n e - f i f th as many UALP

v e rte b ra te fo s s il lo c a l i t ie s as does lo c a l i t y 10. I t is found on the

U. S. Geological Survey Ojo Encino Mesa 7 .5 Minute Quadrangle Map and

includes Sections 4 and 5 , T .2 0 N ., R.4W.

37

/?ti

X:!3 1 \

v

,Wi/

y

Y.:,,c|"r

— ,

Km.

/ vC |V

% . fOjo Encinof y -

N

l i1 Mi.

1

F igu re 10. Map o f the Ojo End no Area W00

UALP uFossil Locality

y Magnetic

F igure 11. Map o f L o c a l i ty 10, Ojo E nd no Area

^ . A r

•UALP Fossil Locality /M agnetic Section

1 Mi.

F igure 12. Map o f L o c a l i ty 11, Ojo End no Area 4*O

The name fo r th is study area was derived from Ojo Encino, a

spring located south o f the fo s s il lo c a l i t ie s . This spring has been

used to name several geographical and p o l i t ic a l fea tu res in the reg ion ;

a wash, a school, several dams, and the mesa upon which the spring is

located are a l l named Ojo Encino.

The Big Pocket Area (F igure 1 3 ) , approxim ately 80 k ilom eters

(50 m ile s ) north and west o f the Ojo Encino Area includes R. W.

W ilson's (1951) U n iv e rs ity o f Kansas v e rte b ra te fo s s il lo c a l i t y 13 ,

the "Big Pocket" lo c a l i t y . L o c a lity 13 is on the western edge o f Kutz

Canyon, approxim ately 16 k ilom eters (10 m iles ) south o f B lo o m fie ld , New

Mexico. I t is in the SVPs o f Section 14, T .2 7 N ., R.11W. The study area

is much la rg e r than lo c a l i t y 13 and includes most o f the west side o f

Kutz Canyon. I t extends from the SW% o f Section 33 , T .2 9 N ., R.11W.

southward along the edge o f Kutz Canyon to the NW% o f Section 5 , T .2 6 N .,

R.10W ., a d istance o f approxim ately 20 k ilom eters (12 m ile s ) .

The study area includes fo s s il lo c a l i t ie s o th er than th a t o f

Wilson (1 9 5 1 ). Granger (1917) discovered a t le a s t two T o rre jo n ian lo

c a l i t ie s in the c l i f f s along the west s ide o f Kutz Canyon. A lso , he

located a fo s s il s i te about 1 .5 or 3 .2 k ilom eters (1 or 2 m ile s ) west

o f Angel Peak (F igure 1 2 ) . Recent in v e s tig a tio n s in Kutz Canyon have

resu lted in the d iscovery o f over twenty UALP v e rte b ra te fo s s il lo c a l

i t i e s . These new lo c a l i t ie s w i l l provide data fo r fu tu re research in to

the b io s tra tig ra p h y o f the San Juan Basin .

41

BigPocket

Angel Peak

UALPFossil Locality Magnetic Section

G ) Granger (1917) Fossil Locality

1 2 Mi.

3 Km.

F igure 13. Map o f the B ig Pocket Area

43

L ith o s tra tig ra p h y

Figure 14 shows two measured sections taken in the Ojo Encino

Area. The l i th o lo g ic section consists o f various colored c la y s , s i l t -

stones , and sandstones common to the Nacimiento Form ation; the f in e r

sediments were predominant w ith the sandstones represented as loca l

channel deposits ra th e r than as continuous h o rizo n ta l s t r a ta .

The n early 185 m eter (607 fo o t) th ic k section from lo c a l i t y 10

contains th ree d is t in c t iv e black carbonaceous c lay beds (Marked L , M,

and U on fig u res 14 and 15) w ith two probable vo lcan ic ashes, one s tra t-

ig ra p h ic a lly above and the o th er s t r a t ig r a p h ic a lly below the lowest

black la y e r . The section from lo c a l i t y 11 is s l ig h t ly over 60 meters

(180 fe e t ) in th ickness . I t contains two d is t in c t black s t r a ta w ith a

probable vo lcan ic ash s t r a t i g ra p h ic a lly below the lower black la y e r .

There appears to be no evidence o f s tru c tu ra l displacem ent in

the d istance separating the lo c a l i t ie s and the l i th o lo g ic c o rre la t io n

shown in f ig u re 14 was made by using the black la y e rs , the probable

ashes, and a capping sandstone.

The l i th o lo g ic s im i la r i t y between the Big Pocket and Ojo Encino

areas can be seen in the presence o f gray or green-gray and red s i l t -

stones and clays w ith interbedded w hite or l ig h t gray sandstone channel

deposits . The Big Pocket A rea, however, contains a h igher number o f

p e rs is te n t tan sandstones than does the Ojo Encino Area. In g e n e ra l,

the Big Pocket s tra tig ra p h ic column contains a h igher r a t io o f sand

stone to shale than found to the south. Because o f the lack o f

44

STRAY.ELEV.M. FT.

r600

150-"500

-400

100-

-300

-200

50-

-100

o-t-o

Figure 14.

LOCALITY 10 LOCALITY 11

ZONEPANTOLAMBDA

DELTATHER1UM ZONE

— Rock Correlation 8=a Fossil Level

C lay:U PPER ;M ID D LE;

Siltstone L0WER Sandstone ?Volcanic Ash Coal l

L ith o lo g ic C o rre la tio n o f L o c a lit ie s 10 and 11 , Ojo Encino Area

l a t e r a l ly continuous exposures, s tra tig ra p h ic c o rre la t io n o f the two

areas is made by m a g n e tic -p o la r ity s tra tig ra p h y and b io s t r a t i graphic

methods.

45

B io s tra tig rap h y

The above l i th o lo g ic c o rre la t io n from the Ojo Endno Area

(F igure 14) in d ic a tes th a t the uppermost faunal le v e l a t lo c a l i t y 10

is c o r re la t iv e w ith the faunal le v e l a t lo c a l i t y 11. Fossils recovered

from lo c a l i t y 10 in d ic a te th a t the upper le v e l is the Panto!ambda zone

o f Osborn and Matthew (1909 ). The lower fo s s il horizon from lo c a l i t y

10, the D eltatherium zone o f Osborn (1 9 2 9 ), appears to have no cor

r e la t iv e in lo c a l i t y 11 . Discussion o f the faunal zones and t h e ir

probable s ig n ific a n c e w i l l be included below.

Granger (1917) noted th a t Kutz Canyon did not appear to contain

the c la s s ic faunal le v e ls o f the San Juan Basin T o rre jo n ia n . Wilson

(1951) suggested th a t , although h is U n iv e rs ity o f Kansas lo c a l i t y 13

(the "Big Pocket" lo c a l i t y ) c lo s e ly resembled the D eltatherium zone,

the Torre jon ian o f the San Juan Basin could be found to consis t o f more

than two c h a ra c te r is t ic le v e ls . O r, as he (Wilson 1951, p. 11) put i t ,

" . . . a se ries o f faunules o f s l ig h t ly d if fe r e n t a g e s .. ." Paleomagnetic

data and new UALP fo s s il lo c a l i t ie s in Kutz Canyon lend support to

W ilson's (1951) id eas .

Table 2 in d ic a tes the known taxa from the Ojo End no and Big

Pocket study areas . I t was compiled from Matthew (1 9 3 7 ), Wilson (1951 ,

1956a, 1956b), M acIntyre (1 9 6 6 ), Russell (1 9 6 7 ), Van Valen (1 9 6 7 ),

Gazin (1 9 6 8 ), and Wilson and Szalay (1 9 7 2 ). This ta b le shows th a t a

Table 2 . Faunal L is t fo r the Ojo End no and Big Pocket Study Areas

46

Taxon Ojo End no Big Pocket

Class Mammalia Linneaus 1758 X xa

Subclass A llo th e r ia Marsh 1880 X xa

Order M u ltitu b e rc u la ta Cope 1884 X xa

Suborder Taen io lab ido idea (Granger and Simpson 1929) X

Family Taen io lab id idae (Granger and Simpson 1929) X

Catopsalis Cope 1882 XC. fo lia tu s Cope 1882 XC. fiss id e n s Cope 1884 X

Family Eucosmodontidae (Jepsen 1940) X

Stigimys Sloan and Van Valen 1965 XS. te i lh a r d i (Granger and Simpson 1929) X

Eucosmodon Matthew and Granger 1921 XE. molestus (Cope 1885) X

Suborder P tilodo n to idea (Simpson 1927) X xa

Family P tilo d o n tid ae Gregory and Simpson 1926 X

Ptilodus Cope 1881 XP. mediaevus Cope 1881 X

Family Neoplagiaulacidae Armeghino 1890 X xa

Ectypodus Matthew and Granger 1921 xbbE.1 sp. Wilson 1956a xb

Mimetodon Jepsen 1940 x : xeM. tro vessartianus (Cope 1882) xeM. near M. tro vessartianus (Cope 1882) xe

Subclass Theria Parker and Haswell 1897 X xa

In fra c la s s M eta theria Huxley 1880 x i

47

Table 2. C ontinued, Faunal L is t

Taxon Ojo Encino Big Pocket

Order M arsup ia lia I l l i g e r 1811 Xj

Family D idelphidae Gray 1821

In fra c la s s Eutheria G i l l 1872 X Xa

Order In s e c tiv o ra Bowditch 1821 X x a

Family L e p tic tid a e G il l 1872 X x a

Prodiacodon Matthew 1929 X x aP. puercensis (Matthew 1918) X£ . n. sp.? Wilson 1956a x a

Family Panto !estidae Cope 1884 X

Pantominia Van Valen 1967 X9P. ambigua Van Valen 1967 X9

Family Pentacodontidae (Simpson 1937) X x b

Pentacodon S cott 1892 X x bP. Inversus (Cope 1888) XP. occultus Matthew 1937 X£ . n. sp. Wilson 1956a x b

Coriphagus Douglass 1908 X x bC. encinensis (Matthew and Granger 1921) X x b

Family M ixodectidae Cope 1883 X x a

Mixodectes Cope 1883 X x aM. pungens Cope 1883 XM. m alaris (Cope 1883) X x b

Order Primates Linneaus 1758 X X1

Family Paromomyidae Simpson X X1

T o rre jo n ia Gazin 1968 <T. w ilso n i Gazin 1968 x h

Palaechthon G idley 1923 P. nac im ienti Wilson and Szalay 1972 $

48



n. gen. and n. sp. Wilson 1956a Xb

Order D e lta th e r id ia Van Valen 1965 X x a

Family Palaeoryctidae (Winge 1917) X x a

Acmeodon Matthew and Granger 1921 X xbA. c f . A. secans Matthew and Granger 1921 x bA . secans Matthew and Granger 1921 X

Palaeoryctes Matthew 1913 XP. puercensis Matthew 1913 XP. c f . P. puercensis Matthew 1913 x a

Order Taeniodonta (Cope 1896) X x a

Family S ty lin o d o n tid ae Marsh 1875 X x a

Conoryctes Cope 1881 XC. comma Cope 1881 X

Psittaco therium Cope 1882 X xbP. m ultifragum Cope 1882 X x bP. aspasiae Cope 1882 X

Order Condylarthra Cope 1881 X x a

Family Arctocyonidae Giebel 1855 X x a

Tricentes Cope 1884 X x aT. truncatus (Cope 1884) X x a

M im otricentes Simpson 1937 X x aM. subtrigonius (Cope 1881) X x a

Chriacus Cope 1883 XC. pelvidens (Cope 1881) XC. baldw ini (Cope 1882) . X

D eltatherium Cope 1881 X . x aD. fundaminis Cope 1881 X x a

Claenodon (S co tt 1892) XC. ferox (Cope 1888) XC. procyonoides (Matthew 1937) X

49



Goniacodon Cope 1888 X x !G. levisanus (Cope 1888) X x a

Triisodon Cope 1881 X x aY . q u iv ire n s is Cope 1881 XT. antiquus (Cope 1882) XT. sp. Wilson 1956a x b

Family Hyopsodontidae Nicholson andLydekker 1889 X x °

Mioclaenus Cope 1881 X x aM. turg idus Cope 1881 X x aM. lydekkerianus Cope 1888 X

Ellipsodon S cott 1892 X x aE. inaequidens (Cope 1884) x XE. granger! Wilson 1956b x c

Promioclaenus Trouessart 1904 X x aP. acolytus (Cope 1882) X xP. lemuroides (Matthew 1897) X ? x c

Protoselene Matthew 1897 X x aP. opisthacus (Cope 1882) X x a

Family Phenacodontidae Cope 1881 X x a

Tetradaenodon S co tt 1892 X x aY . puercensis (Cope 1881) X x a

n. gen. and n . sp. Wilson 1956a x b

Family Perip tych idae Cope 1882 X x a

Anisonchus Cope 1881 X x aA. sec to rius (Cope 1881) X x a

Haploconus Cope 1882 XH. angustus (Cope 1882) XH. co rn icu la tus Cope 1888 X

Periptychus Cope 1881 X x aP. carin idens Cope 1881 X x a

50



Order Carnivora Vicq d 'A zyr 1792 X Xa

Family M iacidae Cope 1880 X Xa

P ro t ic t is Matthew 1937 X , XfP. haydenianus (Cope 1882) P. vanvaleni M acIntyre 1966 j * fF . n. sp. a Wilson 1956a X fP_. n. sp. b Wilson 1956a XT

Order Pantodonta Cope 1883 X

Family Panto!ambdidae Cope 1883 X

Panto!ambda Cope XP. bathmodon Cope 1882 XP. c a v ir ic tu s Cope 1883 X

a .b.c .d.e .f .g.h.i .j .

Wilson 1951Wilson 1956aWilson 1956bM acIntyre 1966Van Valen and Sloan 1966Russell 1967Van Valen 1967Gazin 1968Wilson and Szalay 1972 This paper

A ll o th er id e n t if ic a t io n s from Matthew 1937

51

to ta l o f 18 fa m il ie s , 36 genera, and 18 species are common to both

areas. 6 fa m ilie s , 11 genera, and 28 species are re s tr ic te d to the Ojo

Encino Area whereas on ly 5 genera and 8 species are r e s tr ic te d to the

Big Pocket Area.

The apparent g re a te r d iv e r s ity o f the fauna from the Ojo Encino

lo c a l i t ie s is a t le a s t p a r t ly due to more extensive c o lle c t in g from th a t

study a rea . The Ojo Encino Area has been accessib le to v e rte b ra te

paleon to log is ts since i t s 1896 discovery whereas the Big Pocket lo c a l i t y

has been known only since 1948. At present the Big Pocket c o lle c t io n

has not received more than a p re lim in a ry d e s c r ip tio n . Recent v e rte b ra te

fo s s ils c o lle c te d from Kutz Canyon by workers from the U n iv e rs ity o f

Arizona in d ic a te th a t a g re a te r d iv e r s ity than now recognized is pres

ent in th a t a rea .

N everthe less , i t is ev id en t th a t some mammals are re s tr ic te d

to the Ojo Encino Area. The c h a ra c te r is t ic Panto!ambda zone genera

Claenodon and Panto!ambda are not known from the Big Pocket Area. Only

one c h a ra c te r is t ic D eltatherium zone genus, Haploconus, is unknown from

the Big Pocket Area although recen t U n iv e rs ity o f Arizona c o lle c t in g

in d ica tes th a t Haploconus is present in Kutz Canyon. D e lta th e riu m ,

T riis o d o n , and Mixodectes m a la r is , o th er c h a ra c te r is t ic D eltatherium

zone ta x a , are known from both study areas .

Table 2 in d ic a tes th a t the Ojo Encino study area contains both

p resen tly recognized T o rre jon ian c o lle c t in g le v e ls w h ile the Big Pocket

study area contains no taxa c h a ra c te r is t ic o f the Panto!ambda c o lle c t in g

zone. The Big Pocket Area does, however, conta in taxa d iag n o stic o f the

52

lower, Deltathenuro, c o lle c tin g zone o f Torrejonian age. Wilson (1951)

concluded th a t the Big Pocket fo s s il lo c a l i ty bears more resemblance to

the Deltatherium zone than the higher Panto!ambda zone.

M agnetic -P o larity S tratigraphy

Paleomagnetic samples were co llec ted from 73 s ite s in the Ojo

Encino Area; 52 from lo c a l i ty 10 and 21 from lo c a l i ty 11. The lo c a l i ty

10 paleomagnetic s ite s represent a s tra tig ra p h ic in te rv a l o f 171.5

meters (562.5 fe e t) th a t includes seven ind iv idu al sections (Figure 1 1 ).

The three paleomagnetic sections from lo c a l i ty 11 (Figure 12) represent

a 61.6 meter (202 fo o t) th ic k composite section . S ites from lo c a l i ty

10 had a geometric mean in te n s ity o f 4 .0 X 10”6 gauss fo r the NRM. The

range o f in te n s itie s was 4 .6 X 10” to 1 .0 X 10~* gauss. The NRM in

te n s itie s from lo c a l i ty 11 s ite s ranged from 4 .2 X 10“® to 1 .0 X 10"^

gauss, w ith a geometric mean In te n s ity o f 6 .2 X 10~® gauss.

190 s ite s were co llected from the Big Pocket Area. The geo

m etric mean value fo r the NRM in te n s itie s o f these s ite s was 3.24 X 10“®

gauss w ith in a range from 3.38 X 10“ to 1.14 X 10""* gauss. The Big

Pocket Area s ite s f a l l w ith in ind iv idu a l sections (Figure 13) th a t

cover a s tra tig ra p h ic in te rv a l over 300 meters (98*- fe e t) th ic k .

Paleomagnetic data from the Ojo Encino and Big Pocket study areas is

included in Appendix A.

AF demagnetization a t peak f ie ld s o f 100 to 300 oersteds was

s u ff ic ie n t to remove secondary m agnetization a t most s ite s . Six s ites

from the Ojo Encino Area contained a secondary component s tab le enough

to require a peak f ie ld o f 400 oersteds to remove i t . Unambiguous

53determ ination o f AF demagnetized p o la r ity was possib le fo r n e a rly a l l

s ite s from the Ojo Encino Area. However, in the Big Pocket A rea , on ly

those s ite s above a s tra t ig ra p h ic e le v a tio n o f 61 meters (200 fe e t )

provided unambiguous p o la r i ty determ in ations . For some s ite s from both

study areas i t was necessary to in te rp re t data concerning both the NRM

vector motions during AF dem agnetization and the re s u lt in g c lu s te r o f

d ire c tio n s fo r the samples a t those s ite s . S ites used as examples o f

s ite classes in chapter 4 in d ic a te th a t the paleomagnetic p o la r ity from

the Ojo Encino and Big Pocket study a re a s , as in te rp re te d from the ob

ta ined in c lin a t io n and d e c lin a tio n d ire c tio n s and magnetic vec to r

tre n d s , are r e l ia b le and could be used in th is study w ith o u t susp ic ion .

The data from the Ojo Encino Area (Appendix A) were in te rp re te d

to determine the magnetic p o la r i ty o f the p rev io u s ly constructed l i t h o

lo g ic column from lo c a l i t ie s 10 and 11 (F igure 1 4 ) . In f ig u re 15 each

c ir c le represents one paleomagnetic s i t e ; closed c irc le s represent nor

mal p o la r ity w h ile open c irc le s in d ic a te reversed p o la r i ty . The

magnetic p o la r ity determ inations fo r lo c a l i t ie s 10 and 11 , based upon

VGP la t i tu d e s , are shown in f ig u re 16 . With the exception o f two s ite s

from lo c a l i t y 10 , the data provide unambiguous p o la r i ty de term in ations .

However, the NRM vectors from these s i t e s , SJ334 and SJ335, e x h ib it a

d e f in ite trend towards reversed d ire c t io n s . The re s u lt in g m agnetic-

p o la r ity s tra tig ra p h y strengthens the tenuous l ith o lo g ic c o rre la t io n

o f f ig u re 14 by in d ic a tin g a norm ally magnetized in te rv a l extending

from the middle black stratum upward in to the o ve rly in g s ilts to n e s a t

both lo c a l i t ie s . The minimum length o f th is normal in te rv a l in lo c a l i t y

54

STRAY.ELEV.M. FT.

r600

150-L500

-400

100-

-300

-200

50-

-100

0 - K )

LOCALITY 10

r.'77_L-.;

■

LOCALITY 11

E -.E -C rT IpANTOLAMBDA ZONE

a V A V A .

— 8 DELTATHER1 UM ZONE

Normal Polarity Reversed Polarity Time Correlation Rock Correlation Fossil LevelClay:UPPER;MIDDLE;

E S Siltstone L1°WER EE1 Sandstone IH3 ? Volcanic Ash E 3 Coal

Figure 15. Magnetic C o rre la tio n o f L o c a lit ie s 10 and 11 , Ojo Encino Area

0o

oo

o

ogO

;eee

e ee

e*e

joo

°

STRAT.M.

1 5 0 -

100-

5 0 -

0

ELEV. LOCALITY 10 LOCALITY 11FT. VGP LATITUDE POLARITY VGP LATITUDE POLARITY

1 o rev.

Figure 16. M a g n e tic -P o la r ity S tra tig ra p h y o f the Ojo Enclno Area

56

10 is 27 .4 meters (90 fe e t ) w h ile in lo c a l i t y 11 i t is represented by

24.1 meters (79 fe e t ) o f sedim ent. The upper, Panto!ambda, zone o f the

Torre jon ian is included w ith in the upper magnetozone w h ile the lower

fo s s il le v e l , the D eltatherlum zone, is w ith in the upper o n e -h a lf o f

the underlying reversed magnetozone.

The longer m a g n e tic -p o la r ity column from lo c a l i t y 10 in d ic a te s

the presence o f a second, s t r a t i g ra p h ic a lly lo w e r, norm ally magnetized

in te r v a l . The length o f th is in te rv a l and i t s s tra t ig ra p h ic re la t io n

to the l ith o lo g y and faunal le v e ls preclude i t s c o rre la t io n w ith the

norm ally magnetized in te rv a l from lo c a l i t y 11. Figure 15 c le a r ly dem

onstrates th a t any attem pt to c o rre la te from lo c a l i t y 1 0 .to lo c a l i t y 11

must account fo r l ith o lo g y , pa leon to logy, and paleomagnetism. Only the

c o rre la tio n shown in f ig u re 15 is co n s is ten t w ith known data from the

Ojo Encino Area.

The boundary between a norm ally magnetized and a re v e rs e ly mag

netized in te rv a l represents a geologic tim e l in e (Cox, D o e ll , and

Dalrymple 1963, 1964). T h e re fo re , the c o rre la t io n o f magnetic in te rv a l

boundaries from lo c a l i t ie s 10 and 11 represents a geochronological cor

r e la t io n . C o rre la tio n o f synchronous boundaries in d ic a te s th a t during

the upper magnetozone the ra te o f sediment accumulation was s l ig h t ly

more rap id a t lo c a l i t y 10 than a t lo c a l i t y 11 . Although the paleomag-

n e tic data do not provide absolute d a tes , the data show co n c lu s ive ly

th a t 3 .3 more meters (11 more fe e t ) o f sediment were deposited a t

lo c a l i t y 10 than were deposited a t lo c a l i t y 11 in the same amount o f

tim e.

57

A lso , the synchronous lower boundary o f the c o r re la t iv e norm ally

magnetized in te rv a l in d ic a tes th a t deposition o f the middle black la y e r

commenced s l ig h t ly la t e r a t lo c a l i t y 10 than a t lo c a l i t y 11 . A g rea te r

proportion o f the middle black la y e r is found below the tim e l in e a t

lo c a l i t y 11 than a t lo c a l i t y 10 . This demonstrates th a t the c o r re la t iv e

black s tra ta were not p re c is e ly contemporaneous but the tim e d iffe re n c e

is probably not s ig n if ic a n t . The synchronous upper boundary o f th is

normal in te rv a l demonstrates th a t the opposite is tru e fo r the c o r re l

a tiv e upper black s t r a ta . The upper black la y e r was deposited e a r l ie r

a t lo c a l i t y 10 than a t lo c a l i t y 11. The amount o f time represented be

tween the deposition o f s im ila r sediments in the two areas is s l ig h t

but demonstrably nonsynchronous.

The fo s s il evidence from lo c a l i t ie s 10 and 11 suggests th a t the

faunal le v e l from lo c a l i t y 11 was contemporaneous w ith the upper fo s s il

horizon from lo c a l i t y 10 . The geochronological c o rre la t io n in f ig u re

15 in d ic a tes th a t th is was not e n t i r e ly so; the faunal le v e ls are shown

to be only p a r t ia l ly contemporaneous. Deposition o f the fo s s ils a t

local i t y 11 was s l ig h t ly la t e r than a t lo c a l i t y 10 . Perhaps close ex

am ination and comparison o f the e a r l ie s t lo c a l i t y 10 f o s s i ls , from th is

le v e l and the la te s t lo c a l i t y 11 fo s s ils would demonstrate th is tim e

d iffe re n c e . T h is , o f course, depends upon the amount o f tim e rep resen t

ed by the s tra tig ra p h ic d iffe re n c e .

Figure 17 shows the composite l i th o lo g y , s tra t ig ra p h ic p o s it io n ,

VGP la t i tu d e s , and magnetic p o la r i ty fo r each o f the 190 s ite s c o l le c t

ed from the Big Pocket Area. The m agnetostratigraphy o f the Big Pocket

Area revea ls th a t the upper 15 meters (50 fe e t ) o f the composite section

58STRAT. ELEV. M. FT

1 0 0 -

-1 0 0 0

2 0 0 -

- 5 0 0

1 0 0 -

VGP LATITUDE POLARITYLITHOLOGY

*ee #

KL-~

m

i i jioo

■NOR.□REV.

za=

Lithology Symbols Same as Figures 6&10

c rLU

$Oi -

o

Q<cr

Figure 17. M a g n e tic -P o la rity S tra tig ra p h y o f the Big Pocket Area

are o f normal p o la r i ty . Although the length o f th is norm ally magnetized

in te rv a l is unknown, the s t r a t i g ra p h ic a lly h igher Radio Tower section

contains the reversed in te rv a l above i t . U n fo rtu n a te ly , the Radio Tower

section is c o rre la te d to the composite section w ith on ly enough accuracy

to determine th a t the normal in te rv a l from the Radio Tower sec tion is

c o rre la t iv e to the uppermost magnetozone o f the composite s e c tio n . How

much sediment and tim e was represented by the area between the two sec

t io n s , i f any, is unknown. I t is hoped th a t fu tu re in v e s tig a tio n can

lengthen the Radio Tower section and th a t the base o f the normal mag

netozone can be located and used to geo chronolog ically c o rre la te th is

section to the longer composite s e c tio n .

A second norm ally magnetized in te rv a l is shown in the composite

sec tio n . This in te rv a l extends fo r some 55 meters (180 fe e t ) above

the lowest le v e l o f r e l ia b le d a ta . Approxim ately 146 meters (480 fe e t )

o f sediment w ith reversed p o la r i ty separate the two norm ally magnetized

in te rv a ls . From base to top the Big Pocket m a g n e tic -p o la r ity column

contains 55 meters (180 fe e t ) o f normal m ag n e tiza tio n , 146 meters (480

fe e t ) o f reversed m ag n e tiza tio n , and 15 meters (50 fe e t ) o f norm ally

magnetized sediments. The Big Pocket fo s s il lo c a l i t y (U n iv e rs ity o f

Kansas lo c a l i t y 1 3 ) , w ith in the D eltatherium c o lle c t in g zone (Wilson

195 1 ), is in the bottom o n e -th ird o f the reversed in te r v a l .

59

CHAPTER 6

GEOCHRONOLOGIC CORRELATION

The Ojo End no and B1g Pocket Areas can be geochronolog lcally

co rre la te d by b io s tr a t i graphic and m agnetostrati graphic methods. They

can also be compared w ith a th ir d paleomagnetic section (constructed

e a r l ie r ) from the San Juan Basin and w ith the Cenozoic geomagnetic

p o la r ity tim e sca le o f T a r lin g and M itc h e ll (1976 ).

The Ojo End no and Big Pocket Areas

Figures 16 and 17 show th a t the Ojo Endno and Big Pocket Areas

both have a m a g n e tic -p o la r ity column ch arac te rized by two norm ally

magnetized in te rv a ls separated by a re v e rs a l. The reversa l is consid

erab ly th ic k e r than the normal in te rv a l o ve rly in g i t in the Ojo Endno

A rea. This p a tte rn is ap p aren tly repeated in the Big Pocket Area since

the h o rizo n ta l d istance between the composite and Radio Tower sections

was walked out and does not appear to a llow fo r the 120 meters (400

fe e t ) o f sediment necessary to make the reversa l and the o ve rly in g

normal in te rv a l equal in th ickn ess . A temporal c o rre la t io n o f the two

areas is shown in f ig u re 18. This c o rre la t io n is co n s is ten t w ith the

m agnetostratigraphy, b io s tra tig ra p h y , and lith o s tra t ig ra p h y o f both

areas.

The lower norm ally magnetized in te rv a l from lo c a l i t y 10 is

apparently u n fo s s ilife ro u s , as is th a t from the Big Pocket A rea. The

60

61

STRAT. ELEV.

M. FT.

200

-5 0 0

100-

O -L -0

Figure 18.

OJO BIGENCINO POCKET

• UALP Fossil Level P Pantolambda Zone D Deltatherium Zone

Magnetic Anomaly ■Nor. oRev.

Geochronological C o rre la tio n o f the Ojo Encino and Big Pocket Areas

62reversed in te rv a l from lo c a l i t y 10 , p a rt o f which is present in lo c a l i t y

11, contains the S in c la ir and Granger (1914) lower c o lle c t in g le v e l , the

Deltatheriurn zone. The D eltatherium horizon is s itu a te d in the middle

o f the approxim ately 64 meter (200 fo o t) th ic k reversed in te r v a l . In

the Big Pocket Area the D eltatherium zone, represented by W ilson 's

(1951) lo c a l i t y 13 , is located a t the s tra tig ra p h ic le v e l o f about 100

meters (335 f e e t ) , about o n e -th ird o f the way up section from the base

o f the approxim ately 146 meter (480 fo o t) th ic k reversed in te r v a l . The

presence o f the D eltatherium zone w ith in a reversed magnetozone in the

Ojo Encino Area and the Big Pocket fauna in a s im ila r reversed in te rv a l

suggests th a t they are contemporaneous and w ith in the same magnetozone.

However, because the zones are not found in the same r e la t iv e s t r a t i

graphic pos ition s w ith in the magnetozone, i t is possib le th a t the faunas

from the D eltatherium zone in the Ojo Encino Area could have been de

posited la t e r than in the Big Pocket Area. How much la t e r cannot be

determined as no absolute dates are known. I f they are w ith in the same

magnetozone, as they appear to be, the tim e d iffe re n c e is probably

s l ig h t . A lso , the ra te o f sediment accumulation in each area would

have to be d if fe r e n t fo r the temporal d iffe re n c e to be e x a c tly th a t

shown in f ig u re 18. The c o rre la t io n in fig u re 18 is co n s is ten t w ith

the general thickness trend o f the Nacimiento Fom ation as in d ic a te d

by w ell log data and measured sections (B a ltz 196 7 ).

The upper norm ally magnetized in te rv a l from lo c a l i t ie s 10 and

11 o f the Ojo Encino Area contains the Panto!ambda zone o f Osborn and

Matthew (1 9 0 9 ); the upper c o lle c t in g le v e l o f S in c la ir and Granger

63(1914 ). T h is , o f course, does not demonstrate th a t the upper normal

magnetozones from the two study areas are the same magnetozone. I t does

n o t, however, c o n tra d ic t such a c o r re la t io n . I t I s , th e re fo re , consis

te n t w ith the above c o rre la t io n o f the reversed in te rv a l based upon the

presence o f D e lta th e riu m , T r iis o d o n , and Mixodectes m a la r is , ch a ra c te r

is t ic taxa o f the D eltatherium zone (Wilson 1956a, Szalay 1 9 6 9 ).

The D eltatherium and Panto!ambda zones o f the San Juan Basin

can be defined by the presence o f d is t in c t iv e genera (See pages 19 and

20 above). They can also now be defined by th e ir m a g n e tic -p o la r ity

s tra tig ra p h y ; the D eltatherium zone is w ith in a reversed magnetozone

and the Panto!ambda zone is w ith in the o ve rly in g normal magnetozone.

The m a g n e tic -p o la rity s tra t ig ra p h ic d e f in it io n shows the zones to have

been deposited a t d i f fe r e n t times and not the accidents o f c o lle c t in g

or la te r a l fac ies as thought by Matthew (1 9 3 7 ). Faunal d iffe re n c e s

among th ree U n iv e rs ity o f Kansas v e rte b ra te lo c a l i t ie s (KU 9 , 13 , and

15) w ith in the San Juan B asin , two from the D eltatherium le v e l (9 and

13) and one from the Panto!ambda le v e l (1 5 ) , prompted Wilson (1956a)

to conclude th a t the zones represent d if fe r e n t environments ( f a c ie s ) ,

s l ig h t ly tem porally separated. Wilson (P ers . Comm.) m aintains th a t

environmental fa c to rs con tro l the zones and are more im portant than the

temporal d iffe ren c es presen t. I t is d i f f i c u l t to d is tin g u is h faunal

d iffe ren ces re s u lt in g from environm ental d iv e r s ity and e v o lu tio n ary

change and n e ith e r has been shown to contro l the zones o f the San Juan

Basin T o rre jo n ia n . I t seems th a t W ilson (1956a) too e a s ily assumed

Panto!ambda's absence a t h is two D eltatherium lo c a l i t ie s was c o n tro lle d

64

by fac ies or geographical r e s t r ic t io n . The absence o f Panto!ambda

could mean th a t i t d id not e x is t a t th a t tim e , anywhere in the San

Juan Basin. A lso , the l ith o lo g y o f the study areas does not d isp lay

any outstanding d iffe re n c e th a t could have re s u lte d from an environment

al change s ig n if ic a n t enough to change the faunal assemblage encased

w ith in i t . The absence o f such d iffe re n c e s is p a r t ic u la r ly n o ticeab le

in the Ojo Encino Area where the two zones can be seen in the same ex

posure a t lo c a l i t y 10.

The f in a l re s u lt could be th a t the Deltatheriurn and Panto!ambda

zones may be only two o f several faunal le v e ls in the T o rre jo n ian o f

the San Juan Basin , or th a t these zones may not be l im ite d to on ly one

c o lle c tin g le v e l . As mentioned above, the UALP lo c a l i t ie s in the Big

Pocket Area in d ic a te th a t o th er c o lle c t in g le v e ls are p resen t. I t

should be noted th a t there is no a p r io r i reason why the T o rre jon ian o f

the San Juan Basin should be l im ite d to only two d is c re te c o lle c t in g

zones. At p resen t, however, only the D eltatherium and Panto!ambda

zones can be separated.

Perhaps the most r e l ia b le use o f San Juan Basin To rre jo n ian

b io s tra tig ra p h y would be to ignore the somewhat im precise " c o lle c tin g

zone" concept and u t i l i z e the more precise "range zone" concept. The

known m a g n e tic -p o la rity s tra tig ra p h y o f the San Juan Basin perm its the

use o f the l a t t e r concept. To do t h is , however, is beyond the scope

o f th is th e s is .

65

The B arre l Spring Arroyo Section

The m a g n e tic -p o la rity columns o f the Ojo Encino and Big Pocket

Areas can be compared w ith th a t o f the B arrel Spring Arroyo section o f

B u tle r e t a l . (1977) which has been c o rre la te d w ith the T a r lin g and

M itc h e ll (1976) rev ised Cenozoic p o la r i ty tim e s c a le . B arre l Spring

Arroyo is located geograph ica lly between the two study areas; i t is

approxim ately 20 k ilom eters (1 2 .5 m ile s ) south and west o f the Big

Pocket Area and approxim ately 60 k ilom eters (37 m ile s ) north and west

o f the Ojo Encino Area (F igure 1 ) . C o rre la tio n o f the B arre l Spring

Arroyo section and the Cenozoic p o la r i ty tim e scale is shown in f ig u re

19. The m a g n e tic -p o la rity column from B arre l Spring Arroyo is char

ac te rize d by a basal reversed magnetozone o v e r la in , in sequence, by a

normal, a reversed , a norm al, a reversed , and a topmost normal in t e r v a l .

The B u tle r e t a l . (1977) c o rre la t io n shows the normal in te rv a ls to be

anomalies 27, 28 , and 29 o f the T a r lin g and M itc h e ll (1976) tim e scale

w ith anomaly 29 the lowest normal in te r v a l . Anomaly 28 is shown to

contain the Ectoconus and T aen io lab is Puercan c o lle c t in g le v e ls o f

Osborn (1929) and is above the C re tac eo u s -T ertia ry boundary found near

the base o f anomaly 29.

M a g n e tic -p o la rity s tra tig ra p h y o f the Ojo Encino and Big Pocket

Areas compare w ith the B arrel Spring Arroyo section to show two pos

s ib le geochronologic c o r re la t io n s , both o f which are co n s is ten t w ith

the known b io s tra tig ra p h y and m a g n e tic -p o la r ity s tra tig ra p h y o f the San

Juan Basin. The lowermost normal in te rv a l from the Ojo Encino and Big

Pocket Areas is c o r re la t iv e w ith e i th e r anomaly 27 or 28 o f the T a r lin g

66

POLARITY HIVE SCALE BARREL SPRING ARROYO

5 1

5 0 -

5 5 -

6 0 -

6 5 -

7 0 -

75—1

c z i2 . 3^ fD

aCL

//

ofD“ 5

c"DUa>“ j

5rmOnmzm

o

mH>OmOccn

T ) □ m2 . % i z

r+

IQn<-+■*

f s

2 3 !

4 0 0 -

300”

-1200

■1000

-8 0 0

-no“ 3

3Qr+

O3

z>o

mz

« T

T-Taeniolabis Zone E-Ectoconus Zone C’•Cretaceous Level

Figure 19. C o rre la tio n o f Revised Cenozoic P o la r ity Time Scale and B arrel Spring Arroyo S ection . — (Adapted from T a rlin g and M itc h e ll 1976; B u tle r e f a l . 1977)

and M itc h e ll (1976) geomagnetic tim e s c a le . I t is not c o r re la t iv e w ith

anomaly 29 because the Torre jon ian D eltatherium zone is younger than

the Ectoconus and Taen io lab is zones o f Puercan age and must be s t r a t i -

g ra p h ic a lly h ig h er. Anomaly 26 appears to be too young to be c o r r e l

a tiv e w ith th is magnetozone. This lowest magnetozone from the Ojo

Encino Area is u n fo s s ilife ro u s . Therefore i t could represent the tim e

during which Puercan fo s s ils were being deposited in the B arre l Spring

Arroyo section (anomaly 2 8 ) . This would mean th a t , fo r some reason,

Puercan fo s s ils are not present in e ith e r the Ojo Encino or Big Pocket

Area and th a t the D eltatherium zone is absent in B arrel Spring Arroyo.

Aside from the above l im i t to c o r re la t io n , there is evidence

which suggests th a t the uppermost normal magnetozone from the Ojo

Encino and Big Pocket Areas is e i th e r anomaly 26 or 27 o f the T a r lin g

and M itc h e ll (1976) geomagnetic p o la r i ty tim e s c a le . S in c la ir and

Granger (1914) reported a T o rre jo n ian faunal le v e l 75 meters (245 .5

fe e t ) above the base o f the Macimiento Formation in B arre l Spring

Arroyo. This lo c a l i t y is included w ith in anomaly 27 o f B u tle r e t a l . ' s

(1977) B arre l Spring Arroyo s e c tio n . U n fo rtu n a te ly th is a lle g ed

Torre jon ian lo c a l i t y , based upon th ree specimens o f Periptychus

c a rin id e n s , has not been found during the recent in v e s t ig a t io n . I f

present, however, i t could show the uppermost normal in te rv a l from the

study areas to be anomaly 27 as th is lo c a l i t y and the Panto!ambda zone

are both w ith in norm ally magnetized rocks. Periptychus carin idens is

not a d e fin in g mammal o f the Panto!ambda zone, however, and i t is

67

conceivable th a t S in c la ir and G ranger's (1914) le v e l in the B arre l

68Spring Arroyo area has not y e t been discovered in o ther areas o f the San .

Juan Basin (e .g . the Ojo Encino and the Big Pocket Areas) and is o ld e r

than the D eltatherium zone. A c o rre la t io n between th is upper normal

In te rv a l and anomaly 26 is suggested by the thickness o f the reversed

magnetozone s t r a t i g ra p h ic a lly beneath i t . T a r lin g and M itc h e ll (1976)

show anomalies 26 and 27 separated by a th ic k reversed In t e r v a l , over

four times as th ic k as e ith e r o f the ad jacent normal magnetozones. The

reversed in te rv a l separating the two normal magnetozones in the study

areas is considerably th ic k e r than the anomaly o verly in g i t and is q u ite

un like the reversed in te rv a l sep arating anomalies 27 and 28 in the

Barrel Spring Arroyo s e c tio n ; i t is th in n e r than e ith e r o f the ad jacent

normal magnetozones. I t should be noted th a t th is comparison w ith the

T a rlin g and M itc h e ll (1976) anomaly thicknesses is v a lid only i f a

constant ra te o f sedim entation was present in the study a re a s . This

has not been demonstrated. N everthe less , th is p o s s ib il i ty should be

kept in mind.

At p resen t, th en , i t is not possib le to show c le a r ly which ~

anomalies are found in the m a g n e tic -p o la r ity column from the Ojo Encino

and Big Pocket A reas. B io s tra tig ra p h y h in ts th a t they may be anomalies

27 and 28 w h ile r e la t iv e thickness o f magnetozones h in ts th a t they may

be anomalies 26 and 27. I t is hoped th a t fu r th e r in v e s tig a t io n in the

San Juan Basin s tra ta may supply a s o lu tio n to th is dilemma.

CHAPTER 7

SUMMARY

This study compared two areas o f the San Juan Basin o f n o rth

western New Mexico w ith respect to b io s tra tig ra p h y , 11th o s tra tlg ra p h y ,

and m a g n e tic -p o la rity s tra tig ra p h y . The areas chosen fo r in v e s tig a tio n

were: 1) the Ojo Encino A rea , in c lu d in g S in c la ir and Granger's (1914)

American Museum o f Natural H is to ry v e rte b ra te fo s s il lo c a l i t ie s 10 and

11, from which the d e fin in g fauna o f the T o rre jo n ian Land Mammal Age

was c o lle c te d (Wood e t a l . 1941 ); and 2) the Big Pocket Area o f Kutz

Canyon, inc lu d in g W ilson's (1951) U n iv e rs ity o f Kansas v e rte b ra te

fo s s il lo c a l i t y 13 , from which T o rre jo n ian fo s s ils were c o lle c te d .

L o c a lity 13 fo s s ils included those c h a ra c te r is t ic o f the T o rre jo n ian

Deltatherium zone, f i r s t recognized by Osborn (1929) and la t e r defined

by Wilson (1956a). As shown in f ig u re 1 , the study areas are approx

im ate ly 80 k ilom eters (50 m ile s ) a p a r t , w ith the Ojo Encino to the

south and east o f the Big Pocket A rea.

Paleomagnetic samples were c o lle c te d from both areas to con

s tru c t m a g n e tic -p o la rity columns. C o rre la tio n o f the S in c la ir and

Granger (1914) lo c a l i t ie s in the Ojo Encino Area by the m ag n e to s tra ti

graphy demonstrates th a t the upper. Panto!ambda, zone o f the T o rre -

jon ian Land Mammal Age is from w ith in the upper normal magnetozone and

th a t the lo w er, D e lta theriu rn , zone o f the T o rre jo n ian is from w ith in

the medial reversed magnetozone o f the a rea . The lower normal

69

70

magnetozone is u n fo s s ilife ro u s in the Ojo End no A rea. This shows th a t

the two c la s s ic a l c o lle c t in g le v e ls o f the San Juan Basin T o rre jo n ian

are s t r a t i g ra p h ic a lly separated and perm its m a g n e tic -p o la r ity d e f in it io n

o f them. The D eltatherium le v e l is from w ith in a reversed magnetozone

and the Panto!ambda le v e l is from w ith in the o ve rly in g normal magneto

zone. •

The D eltatherium zone from the Big Pocket Area is a lso found

w ith in the reversed medial magnetozone o f th a t a rea . I t is c o r re la t iv e

w ith the D eltatherium zone from the Ojo End no Area and perm its the

above d e f in it io n . The c o rre la t io n is shown in f ig u re 18 and is con

s is te n t w ith the known b io s tra tig ra p h y and thickness trends o f the

Macimiento Formation.

C h a ra c te r is tic taxa o f the Deltatheriurn zone include

D e lta th eriu m , T r iis o d o n , Haploconus, Hixodectes m a la r is , and possib ly

Palaechthon n a c im ie n ti. The Panto!ambda zone is recognized by the

presence o f Panto!ambda, Claenodon, and possib ly Mixodectes pungens

and T o rre jo n ia w ils o n i.

The m a g n e tic -p o la rity s tra tig ra p h y o f the two study areas was

compared to th a t from B arre l Spring A rroyo , located geo graph ica lly

between them. The b io s tra tig ra p h y o f the Barrel Spring Arroyo section

o f B u tle r e t a l . (1977) perm its the upper norm ally m agnetized,

magnetozone from th a t section to be c o r re la t iv e w ith e i th e r normal

magnetozone from the study areas . C o rre la tio n o f the B arrel Spring

Arroyo section w ith the rev ised Cenozoic p o la r i ty tim e sca le (T a r lin g

and M itc h e ll 1976) by B u tle r e t a l . (1977) demonstrates th a t the

71

normal magnetozones from the Ojo Enclno and Big Pocket areas are e ith e r

anomalies 26 and 27 or anomalies 27 and 28. E ith e r c o rre la t io n is

consis ten t w ith the known b io s tra tig ra p h y but the r e la t iv e thicknesses

o f the magnetozones suggest the former c o r re la t io n . However, fu r th e r

study is necessary to show c le a r ly which anomalies are present in the

m a g n e tic -p o la rity columns o f the study a rea s .

v

APPENDIX A

PALEOMAGNETIC DATA

L o c a lity 10 , Ojo End no Area

S ite S tr a t .No. ( F t . )

559 0

560 14

561 31

562 48

563 64

578 67

564 76

579 76

580 86

581 96

583 ‘ 99

le v . AF (Oe)(M .)

0.0 000100

4 .3 000100

9 .5 000100

14.6 000100

19.5 000100

20.4 000100

23.2 000 100

23.2 000 100

26.2 000 100

29.2 000 100

30.2

D ( ° ) I ( ° )

31 .026 .8

77.360 .6

353.0350.7

48 .842 .0

2 6 .8351.2

55 .359.6

21 .931 .6

32.014 .5

17 .418 .8

56 .054.9

350.1344.1

52 .248 .2

306.1346 .5

37.025 .9

320.2319 .8

62 .960 .0

317.4333 .7

57 .048 .8

358 .4359 .0

38 .032 .8

279 .687 .6

82 .474.1

0 VGP L a t. (Gauss) ( ° )

5.9X10“ !2.8X10“ ' 68 .5

4.8X10“®3.1X10"® 75 .8

1.0X10'®7.9X10“® 81 .8

2.7X10"®1.8X10"® 49 .4

7.6X10"®5.5X10“® 74 .8

1.7X10“ ®1.3X10“® 64 .6

1.7X10“*2.1X10“ ® 75 .0

3.4X10“®1.8X10"® 58 .4

3.6X10"®1.6X10"® 67.1

2.0X10"®1.6X10"® 71 .8

2.3X10"®9.4X 10"° 73 .4

000100

72

S iteNo.

582

584

585

586

587

589

588

590

327

328

037

038

329

330

331

73

S tr a t . E lev . AF (Oe) D ( ° ) ( F t . ) ( M . ) __________

106 32.3 000 332.9100 340.3

109 33.2 000 327.4100 329.0

124 37.8 000 311.4100 325.0

131 39.9 000 11.3100 359.1

146 44.5 000 144.3100 155.4

148 45.1 000 134.9100 136.4

159 48.5 000 181.7100 212.1

162 49.4 000 177.0100 178.2

176 53.6 000 159.5300 60.1

184 56.1 ooo 175.0300 199.1

191 58.2 000 195.4300 194.1

231 70.4 000 190.1200 200.3

241 73.5 000 165.2200 178.0

251 76.5 000 223.3300 204.3

258 78.7 000 160.9400 143.9

I ( ° ) VGP L a t.__________ (Gauss) ( ° )

55.652.3

7.5X10"G4 .7X10-6 31.8

62.248.1

2.3X10-61.7X10-6 63.1

70.276.2

I.OXIO'61.8X10-6 55.1

65.261.6

4.9X10-63.7X10-6 83.2

-20.9-49.1

1.7X10-62.5X10-* -68.6

-36.1-41.0

1.3X10-61.3X10-6 -50.5

54.0-55.8

8 .eXlO'g 1.1X10-6 -64.2

-58.8-69.0

4.0X10*65.3X10-6 -73.4

-25.6-76.8

3.9X10"!4.1X10-6 -21.2

55.9-15.2

4.6X10*62.2X10*6 -56.8

-43.8-47.4

2.6X10*62.4X10*6 -76.0

43.5-31.1

1.3X10*61.1X10*6 -63.7

35.2-26.0

4.1X10*63.4X10*6 -67.6

65.9-56.3

1.3X10*69.0X10*' -70.5

24.2-57.2

2.2X10*61.6X10*6 -61.3

S iteNo.

332

333

334

039

335

336

040

337

338

041

339

340

042

341

342

74

S tr a t . E lev . AF (Oe) D ( ° ) I ( ° ) J VGP L a t.( F t . ) (M .)______________________'______ ’_________ (Gauss) ( ° )

9 .8 2.6X10"®-6 3 .2 3 .4X 10"* -6 9 .2

268 81.7 000 105.7300 155.0

279 85.0 000 155.5300 162.7

288 87 .8 000 346.9400 63 .4

299 91.1 000 87 .8400 169.4

308 93.9 000 44.6300 83 .3

314 95.7 000 208 .3300 161.9

339 103.3 000 265 .8300 119.4

349 106.4 000 334.2200 318.5

355 108.2 000 336.1300 353.0

365 111.3 000 342.5300 326.9

380 115.8 000 357.0200 359.3

390 118.9 000 359.2200 359.2

000 7 .0200 5 .0

400 121.9 • 000 358.1200 351.3

409 124.7 000 358.1200 345.2

- 2 .5 -2 2 .0

1.0X10"®8.4X10’ * -6 0 .9

73.2-1 6 .6

8.5X10"®3.3X10"* 15 .8

70 .7-1 1 .7

5.1X10’ ®1.3X10’ ® -5 8 .4

70 .065 .4

1.3X10"®1.9X10’ * 29 .8

56.7 —38.5

1.6X10"®1.6X10’ ® -6 2 .7

68 .9-4 5 .3

2.5X10"®9.2X 10"° -3 8 .3

70.260 .8

5.2X10"?8.2X 10"° 57 .5

42 .021 .7

1.2X10’ ®6 .0X 1 0" ' 64 .5

68 .666 .8

1.7X10"®8 .6X 1 0" ' 62 .5

62 .456 .9

4.6X10"®3.5X10"* 88 .4

48 .745 .4

l.O X IO ’ J6.4X10"® 80 .9

57 .458 .4

1.3X10"®8.4X10"* 84 .9

47 .643 .8

5.3X10"®3.5X 10"* 77 .2

71 .657 .3

2.7X10"®1.6X10’ * 77 .9

S iteNo.

343

043

344

345

044

346

347

348

349

350

351

352

75

S tr a t . E lev . AF (Oe) D ( ° ) ( F t . ) (M .)

419 127.7 000 11 .5200 5 .2

428 130.5 000 358.1200 ’ 4 .3

429 130 .8 000 353.1200 355.7

439 133.8 000 5 .7200 351.8

453 138.1 000 231.1300 187.9

463 141.1 000 134.1400 114 .0

473 144.2 000 112.5300 118.2

483 147.2 000 128.4200 138 .3

493 150.3 000 121.1200 127 .3

508 154 .8 000 114.6400 174.7

542 165.2 000 248.2300 138.1

549 167.3 000 340.0300 74 .4

i . C ) J(Gauss)

VGP Lat ( ° )

63 .666 .4

2.1X10’ ®1.1X10’ * 76 .6

68 .764 .5

2.0X10’ %1.2X10’ * 79 .2

22 .969 .2

1.9X10'®8.6X 10"* 73 .0

63.160 .3

2.4X10’ ®7 .0 X 1 0 '* 81 .7

64 .426.1

4.2X10’ ®8.1X10’ ° -3 9 .7

38.1-1 1 .4

2.0X10’ ®6 .4X 10"' -2 2 .7

-6 0 .2-6 3 .3

6.6X10’ ®6.2X 10"* -4 3 .3

-5 4 .4-6 3 .2

6.5X1O’ Z 7 .4X 1 0" ' -5 7 .4

-4 8 .0-5 5 .6

8.6X10'®9.1X10’ * -1 2 .0

70.9-1 6 .9

1.7X10’ S2 .2X 1 0" ' -6 2 .2

36.1-4 9 .3

1 .2X 10"!4 .8X 10" ' -5 4 .6

36 .0-7 1 .2

1 .7X 10"!2 .3 X 1 0 " ' -2 1 .3

S iteNo,

353

354

355

356

357

358

359

360

361

362

363

364

365

366

76

L o c a lity 11 , Ojo Encino Area

S tr a t . E lev . AF (Oe) D ( ° ) I ( ° ) J VGP L a t.( F t . ) (M .)_____________________ ________________ (Gauss) ( ° )

0 0.0 000300

10 3.1 000400

20 6.1 000200

30 9.1 000300

40 12 .2 000200

60 18 .3 000200

70 21 .3 000200

70 21 .3 000200

81 24 .7 000300

91 27 .7 000200

101 30 .8 000200

111 33 .8 000200

121 36.9 000200

39.9 000200

100.3147 .0

-1 7 .5-4 6 .7

46 .9178.5

68.2-1 8 .9

147.1174.1

-6 1 .9-73 .1

238.6161.5

67 .9-2 6 .7

137.8155.3

-1 6 .9-3 2 .4

184 .0192 .5

-1 4 .6-3 2 .2

228 .4192 .7

38.1-6 3 .7

94 .3158.4

29 .0-5 7 .3

54 .7147.6

74.1-58 .1

15 .325 .2

55 .551 .8

19 .7349.7

72 .973 .6

26 .315 .3

78 .674.1

4 .9355.2

63 .475.9

357.7357 .8

88 .488 .2

4.0X10"®2.6X10"b -6 1 .0

1.6X10'®8.1X10"b -6 3 .7

2.7X10"®1.7X10"® -6 7 .0

1.4X10"®8 .3X 10"' -6 2 .6

6.4X10"® 6.6X10 "b -6 1 .4

3.3X10"®3.4X10"6 -6 8 .4

4.6X10"?4 .9X 1 0" ' -7 6 .6

1.2X10"®1.6X10"® -7 2 .7

5.8X10"?1 .0X 1 0" ' -6 4 .2

3.5X10"®2.0X10"® 68 .9

4.9X10"®2.2X10"® 65 .6

4.7X10"®3.1X10"® 63 .8

6.6X10"®4.1X10"® 62 .5

4 .0X 10"!3.3X10"® 39.6

131

77

S iteNo.

S t r a t .( F t . )

m3:

m•

< AF (Oe) D ( ° ) I ( ° ) J(Gauss)

VGP Lat ( ° )

367 141 43 .0 000 22 .0 67 .9 1.7X10"®200 2 .2 59 .2 5.8X10"b 85.7

368 151 46 .0 000 340.8 58 .6 6 .7 X 1 0 " |200 335.0 55 .9 4.1X10"® 69.9

369 160 48 .8 000 354.8 49 .2 1 .0X 10"*200 349 .8 44 .5 5 .4X 10"* 76 .9

370 170 51.8 000 354.8 59 .7 3.7X10"®200 351.3 57 .6 1.5X10"® 82.7

371 182 55.5 000 342.8 67.1 1 .3X 10"!400 137 .8 -1 7 .7 2.1X10"® -4 3 .2

372 192 58.5 000 80 .2 80 .5 2 .0X 10"!300 168.7 -4 1 .3 2 .7X 1 0" ' -7 4 .3

373 202 61 .6 000 181.2 -2 3 .5 7 .8X 10"!200 184.7 -3 5 .4 9.1X10’ ® -73 .1

S iteNo.

251

252

253

254

255

256

257

258

259

260

261

262

263

264

78

Composite S ec tio n , Big Pocket Area

S t r a t . E lev . AF (Oe) D ( ° ) I ( ° ) 0 VGP L a t.( F t . ) (M .)_____________________ ________________ (Gauss) ( * )

198 60 .4 000200

226 68 .8 000200

226 68 .8 000200

256 78.0 000200

262 79.9 000200

260 79 .3 000200

270 82 .3 000200

282 86 .0 000200

292 89 .0 000200

302 92.1 000200

313 95 .4 000200

327 99 .7 000200

330 100.6 000200

102.4 000200

300.9285 .8

57.216 .8

2 .69 .6

69 .337 .8

9 .67 .4

57 .849 .5

310 .7334.1

53.233.9

332 .0334.2

35 .030.2

325 .7350.6

56.943 .3

335.9331.9

48 .544 .3

346 .0349 .2

30 .325 .8

355 .6355 .0

63 .962 .3

13.123 .5

63 .365 .0

337.1334 .5

60 .563 .8

21 .40 .2

31.720 .4

317 .4325 .3

36 .826 .9

333 .0326.1

23 .542 .4

1.8X10"®8.7X10"6 17 .8

1.7X10"®1.4X10"® 73.0

4.3X10"®3.7X10"® 81 .7

1.4X10"S7 .2X 1 0" ' 61 .3

6.8X10“®4 .8 X 1 0 'b 59 .7

3.8X10"®1.2X10"® 76.6

1.0X10"®6.6X10"® 64 .0

4.7X10"®3.5X10"® 65 .6

8.9X10'®7.6X10"® 81 .5

3.4X10"®2.6X10"® 69 .4

2.6X10"®1.2X10"® 68 .6

2.3X10"®8 .9X 1 0" ' 64 .5

3.1X10"®1.2X10'® 52.1

8 .1X 1 0"!3 .0X 1 0" ' 58 .8

336

S iteNo.

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

79

S tr a t . E lev . AF (Oe) D ( ° ) ( F t . ) ( M . ) ________________

235 71.6 000 22 .8200 20 .6

245 75.7 000 339.4200 348.3

255 77.7 000 165.1200 288.1

266 81.1 000 354.2200 355.1

276 84.1 000 325.6200 334.2

286 87.2 000 300.1200

296 90.2 000 28 .7200 3 .7

266 81.1 000 323.2200 303.5

276 84.1 000 278 .9200 327.0

286 87.2 000 24 .9200 343.8

296 90.2 000 0 .6200 337.0

306 93 .3 000 357.3200 335.4

316 96 .3 000 28 .7200 353,8

326 99.4 000 0 .4200 349.3

336 102.4 000 60.2 .200 338.0

I ( ° ) J VGP L a t.__________ (Gauss) ( ° )

52.149 .9

3 .3X 10"! 2 . 1X10"6 72 .0

55.950 .4

7 .8X 10"!6 .6X 10"* 79.1

87 .356 .9

2 .3X 10"!1.2X10"6 33 .9

44 .041 .5

1 .7X 10"! 1.3X10"* 77.1

59 .451.1

3.5X 10"!2.0X10"* 68 .3

45.9 4.5X10"6

73 .879 .8

3.5X 10"!1 .8X 10*6 55 .7

71 .061.1

5 .1X 10"!3.4X10“ * 46 .5

54.152 .8

3.7X1 O '6 1.6X10"* 62 .9

50 .336 .0

6 .9X 10"!3.2X10"* 68 .6

60 .849 .7

1.1X10"67 .4 X 1 0 '6 70.1

55 .761 .7

2 .4X 10"!7 .9X 1 0" ' 69 .9

65.162 .2

5.4X10"6 3.2X10"* 81 .2

60.258 .2

5 .7X 10"!2 .7X 10"* 81 .0

86 .575 .6

6 .2X 10"!2.3X10“ * 60 .0

S iteNo.

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

80

S tr a t . E lev . AF (Oe) D ( ° ) I ( ° ) J VGP L a t.( F t . ) (M .)_____________________ ________________ (Gauss) (°1

345 105.2

356 108.5

366 111.6

376 114.6

356 108.5

370 112 .8

382 116.4

412 125.6

350 106.7

360 109 .7

370 112 .8

380 115 .8

390 118.9

400 121 .9

125.0

000200

59 .314 .0

77.561 .5

3.7X10"®2.3X10"6 77 .3

000200

328.9333.5

69 .660.9

3 .6X 10"!2 .6X 10"* 68 .6

000200

308.5344.7

80 .460 .3

3 .6X 10"!2 .2X 10"* 77 .0

000200

31 .734 .0

65 .470.1

4 .5X 10"!3 .2 X 1 0 '* 60 .4

000200

343.93 .0

68 .964 .3

6 .3X 10"!3 .9X 10"* .79 .6

000200

13 .318 .5

51.2 - 9 .8

4 .9X 10"!2 .3X 10"* 45 .6

000200

38.914.1

75.757.9

4 .4X 1 0"!2 .6 X 1 0 '* 78 .5

000200

112.9135 .6

44 .7 - 4 .6

2 .4X 10"!1 .1 X 1 0 '* -3 6 .9

000200

15 .2351.1

65 .354.1

5 .3X 10"!3.1X10"* 82 .6

000200

353.80.1

66 .858 .2

1 .1X 10"!7.8X10"* 87.1

000200

24.91 .5

80 .572 .9

3 .4X 10"!1 .9X 10"* 67 .6

000200

70 .854 .8

52 .542 .7

3 .8X 10"!1 .6X 10"* 42.1

000200

186.5174 .8

5 .4-3 5 .9

3 .2X 10"!3.6X10"* -7 3 .3

000200

111.1214 .6

33.1-5 4 .2

2 .5X 10"!1 .6X 10"* -6 1 .9

000100

135.7192 .8

76.1-5 5 .5

1 .3X 1 0"!1.0X10"6 -7 9 .7

410

S iteNo.

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

81

S tr a t .( F t . )

E lev .(M .)

AF (Oe) D ( ° ) I ( ° ) J(Gauss)

VGP L a t. ( ° )

394

404

414

425

435

445

455

465

455

462

472

482

492

502

120.1

123.1

126.2

129 .5

132 .6

135 .6

138 .7

141 .7

138 .7

140 .8

143.9

146.9

150.0

153 .0

156.1

000100

000200

000200

000200

000200

000200

000200

000200

000200

000200

000200

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151.4155 .7

184.1179 .2

159.5161.7

158 .5161 .9

184 .8167 .8

132.1127.1

163.6154 .3

134 .0140 .0

194.6142 .8

305.9219 .2

190 .3166 .5

178.5179 .4

163.1179 .7

167 .3169.1

353 .7231 .0

44 .2 -4 7 .7

- 0 .9 -3 3 .3

-2 2 .9 -3 6 .8

-3 3 .5-4 5 .7

-1 4 .9-4 4 .4

- 22.0-5 4 .5

0.1-4 0 .7

-3 3 .3-5 3 .6

61 .6-3 4 .6

67.2 -81 .1

59 .5-3 7 .4

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11 .7- 21.8

-2 3 .2-3 8 .5

77 .731.1

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3.6X103.5X10

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-6-6

6.3X106.0X10

3.6X104.0X10"

2.4X104.1X10"

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1.4X102.3X10

2.7X103.2X10"

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-4 8 .4

-7 0 .9

-70 .1

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-7 2 .8

-1 8 .5512

S iteNo.

310

311

312

313

314

B004

321

322

323

324

421

422

423

424

425

82


502 153 .0 000200

512 156.1 000100

522 159.1 000400

546 166.4 000200

557 169 .8 000200

535 163.1 000

197 60.1 000300

220 67.1 000200

226 68 .9 000200

241 73 .5 000200

535 163.1 000200

548 167 .0 000200

558 170.1 000200

568 173.1 000200

179.2 000200

100.8181 .4

77.118 .6

159 .6167.6

-1 4 .6-5 0 .5

140.4152 .3

35 .617.5

90 .4136.7

42 .2-67 .1

198 .0180 .2

-1 8 .8-44 .1

192 .7 -4 6 .3

272 .5267.1

42 .818 .7

301 .4317.0

78.961 .8

0 .5357.2

46 .041 .8

18 .915 .3

38.756 .3

158 .3159.1

-40 .1-4 3 .8

235 .2202 .0

61 .9-3 9 .8

177.5180 .4

-2 4 .3-3 3 .8

150.1147 .9

- 2 .7 -2 9 .6

193 .4199 .9

8 .0 - 7 .3

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1.7X10"®2.5X10"® -7 8 .6

8.0X10*58 .5X 1 0" ' -3 8 .0

3.0X10"®3.0X10"* -5 6 .0

2.2X10"®3.5X10"® -7 9 .9

7.1X10"® -5 6 .0

2.7X10"®1.9X10"® 3 .3

2.2X10"®7 .4 X 1 0 " ' 56 .5

1.3X10"®1.0X 10"* 77 .8

3.5X10"®3.7X 10"* 77 .7

3.8X10"®4.0X 10"* -6 9 .4

1.1X10"®7 .9 X 1 0 " '

1.2X10"®3.3X 10"* -7 2 .5

1.4X10"®1.6X10"® -5 5 .0

3.7X10"®3.8X10"* -5 2 .8

588

S iteNo.

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

83


615 187.5 000 274 .8200 181.1

624 190.2 000 164.5200 161.7

664 202.4 000 156.0200 156.3

677 206.4 000 149.2200 150.5

355 108.4 000 1 .8200 15 .3

365 111 .3 000 332.3200 325 .3

376 114.6 000 85 .5200 93.1

383 116.7 000 12 .3200 308.1

391 119.2 000 179.5200 180.4

404 123.1 000 179 .5200 202.1

414 126.2 000 34 .5200 250 .8

428 130.5 000 327.8200 206.5

440 134.1 000 108.7200 138.8

450 137.2 000 111.3200 128.1

460 140.2 000 82 .8200 111.2

14 .9-6 0 .5

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-3 4 .3-4 7 .5

5 .0X 10"! 5.1 X I0 "6 -7 2 .9

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6 .4X 10"!6 .2X 10"* -6 5 .6

32.0-2 9 .4

1 .7X 10"! 1.7X 10"* -5 6 .9

46 .558 .7

2 .7X 10"!2 .0X 10"* 77.5

51 .450.5

2 .2X 10"!1 .8X 10"* 60 .9

-3 7 .5-3 8 .8

2 .9X 10"! 2.4X 10"* -15 .1

-3 7 .5-8 0 .5

2 .9X 10"!1 .7X 10"* -2 3 .5

-2 1 .5-2 4 .8

4 .0X 10"! 4.3X 10"* -6 7 .0

-2 1 .5-6 6 .6

4 .0X 10"!1 .7X 10"* -6 9 .3

24 .0-45 .1

1.1X10"?7 .8X 1 0" ' -30 .1

-1 7 .2-5 3 .0

7 .6X 10"!6 .9 X 1 0 " ' -6 8 .2

-2 7 .2-6 2 .7

2 .6X 10"!2.1X10"6 -5 7 .8

-6 2 .8-6 5 .5

5 .9X 10"!5.8X10"* -5 0 .8

-4 9 .6-5 2 .5

1 .4X 10"! 1.4X 10"* -3 4 .5

S iteNo,

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

84

S tr a t . E lev . AF (Oe) D ( ° ) I ( ° ) . J VGP L a t. ( F t . ) (M ,)_____________________ ________________ (Gauss) ( ° )

470

480

351

452

464

466

484

452

462

472

495

143.3

146 .3

106 .8

137 .8

141.4

142.0

147.5

137 .8

140.8

143 .9

150.9

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000200000200

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000200

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000200

000200

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231.9185 .3

140 .4159 .0

333 .8314.1

109.1123 .7

159.5154 .5

167 .5167.1

235 .7200.8

114.2120.8

155.6162 .8

192 .6189 .4

199.1195 .0

- 66.2-5 6 .7

-1 9 .4-3 6 .3

43 .238 .3

-5 5 .7-5 8 .6

-5 2 .4-5 1 .4

-5 1 .0-4 8 .5

-3 7 .9-3 9 .2

-4 5 .6-5 7 .6

-5 3 .6-5 4 .5

-6 4 .2-5 7 .0

-2 6 .0-3 6 .2

2.9X102.9X10

9.5X101.2X10

3.4X102.4X10

3.3X102.8X10

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- 68.6

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495 150.9

510 155 .4

541 164.9

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193.9192.1

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180 .4185 .8

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4 .3 X 1 0 '* 4.2X1 O '6 -7 2 .0

519

S iteNo.

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

85

S tr a t .( F t . )

E lev .(M .)

AF (Oe) D ( * ) i o J(Gauss)

VGP Lat ( ' )

528 160.9 " 000 69 .4 -69 .1 1 .4X 10"!200 151.2 -5 5 .2 . 1 .8X10"6 -6 6 .8

538 164.0 000 117 .8 -6 9 .6 9.8X10"!200 157.6 -66 .1 9 .1 X 1 0 " ' -6 9 .4

544 165 .8 000 150 .8 -5 4 .9 2 .5X 10"!200 151.0 -6 1 .4 2 .2X 10"* -6 8 .7

554 168.9 000 158.3 -5 9 .5 1 .7X 10"!200 166.3 -5 6 .6 2 .2X 10"* -7 8 .9

565 172.2 b o o 137.9 -5 8 .6 2 .2X 10"!200 141 .8 -5 4 .8 2.2X10"* -5 9 .2

581 177.1 000 145 .0 -4 2 .3 3 .1X 10"!200 152.3 -4 1 .5 3.4X10"* -6 3 .3

591 180.1 000 80 .0 -7 3 .6 1 .3X 10"!200 288.5 -6 9 .0 7 .8X 1 0" ' -1 8 .0

601 183.0 000 156.6 -3 4 .4 1 .7 X 1 0 '*200 156.9 -3 4 .8 1 .5X 10"* -6 3 .6

601 183.0 000 172.6 -5 2 .8 6 .8X 10"*200 174.3 -5 2 .9 7 .2 X 1 0 '* -8 4 .7

618 188.2 000 120.2 -6 4 .7 1 .4 X 1 0 '*200 143.9 -5 9 .2 1 .5X 10"* -4 5 .0

625 190.4 000 157.1 -5 1 .0 3.2X 10"*200 155 .4 -5 0 .8 3.3X 10"* -6 9 .1

636 193.7 000 164 .3 -3 3 .3 3 .4 X 1 0 '*200 167.2 -3 6 .5 3 .6X 10"* -7 0 .7

646 196.8 000 172.7 -4 4 .8 2 .0 X 1 0 '*200 172.1 -4 7 .7 2 .0X 10"* -8 0 .1

662 201.6 000 145.6 -5 0 .0 2 .9X 10"*200 156 .3 -4 7 .9 3 .2 X 1 0 '* -6 8 .9

676 206 .0 000 160.3 - 7 .5 4 .9X 10"!200 165.2 -1 1 .0 4 .7X 10"* -5 6 .6

S iteNo.

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

86

S tr a t .( F t . )

E lev .(M .)

AF (Oe) D ( ° ) I ( • ) J(Gauss)

VGP LatC )

687 209.4 000 178.5 -3 6 .3 5.2X10-7200 164.3 -4 6 .0 6 .1X 1Q -' -7 5 .5

705 214.9 000 314.8 -8 0 .4 1.9X10"®200 179.5 -6 9 .0 1.7X1 O '6 -7 3 .6

722 219.9 000 206.0 10.1 5.3X10” !200 192.6 -4 5 .3 7.4X10” ' -7 5 .9

733 242.1 000 147.1 -39 .1 1.8X10”®200 163 .4 -4 6 .3 2.1X10”* -7 3 .6

748 228.1 000 66 .5 -5 9 .7 2.6X10”®200 151.5 -71 .1 2.5X10” ® -6 2 .5

763 232.4 000 157.0 -5 5 .6 7.6X10"®200 158.0 -5 5 .9 7.9X10” ® -7 2 .2

776 236.5 000 176 .4 -5 3 .0 2.1X10” ®200 180.7 -50 .1 2.4X10’ ® -8 4 .9

788 240.2 000 147.2 -6 0 .4 2.5X10”®200 164.5 -6 5 .9 3.4X10’ ® -7 3 .3

795 242.3 000 248.2 -7 3 .7 4.0X10”!200 190.4 -4 6 .9 6.2X10” ' -7 8 .2

835 254.5 000 80 .6 13.1 3.9X10”®200 160.3 -3 9 .4 1.6X10” ® -68 .1

847 258.2 000 132.3 -6 9 .0 2.9X10’ ®200 144.3 -6 4 .9 3.6X10”® -6 1 .4

859 261.8 000 246 .0 22 .0 5.0X10”!200 235 .8 7 .6 4 .2X 1 0" ' -4 0 .8

882 268.8 000 337.5 37 .0 1.8X10”®200 340.8 44 .6 1.5X10’ ® 70.9

907 276.5 000 8 .0 53 .3 3.2X10” ®200 13 .0 53 .5 2.4X10”® 79 .2

926 291.4 000 356.9 36 .5 4.7X10” ®200 358.5 29 .4 3.8X10’ ® 69 .7

S iteNo.

486

487

488

489

490

491

492

493

494

495

496

497

87

Radio Tower S e c tio n , Big Pocket Area

S t r a t . E lev . AF (Oe) D ( ° ) I ( ° ) J VGP L a t.( F t . ) (M .)_____________________ '______ _________ (Gauss) ( ° )

0

29

43

93

104

121

0.0

8 .3

13.1

28 .4

31 .7

36.9

000200

000200

000200

000200

000200

000

16 .43 .5

16 .8120.1

347.1346.8

157.5140 .2

244 .9199 .9

314.1

61 .665 .0

68 .784.1

44 .750.1

-1 1 .3-2 3 .5

83 .2 -3 0 .9

2.2X101.5X10

1.1X105.3X10

1.2X105.1X10

4.7X105.2X10

-6-6

-6-7

-6-7

-6-6

4.6X106.0X10

-7-7

78 .7

- 3 .9

77.9

-47 .1

-6 3 .8

16 .3 5.7X10 -7

130 39.2

141 42.9

150 45 .9

161 49.1

189 57.6

60.1

000200

193.6196.5

-2 1 .6-2 9 .8

6.4X10"®5.2X10"6 -6 5 .2

000200

98.6125.2

-4 5 .9-4 5 .5

5.9X10"?7 .0X 10" ' -64 .1

000200

147 .4164 .9

-5 8 .4-5 4 .4

1.1X10"®1.8X10"® -7 7 .7

000200

343.4192 .6

37 .4-2 5 .5

2.8X10"?1.1X10“ ' -6 4 .7

000200

155.3174 .5

8 .6-2 6 .0

1.4X10"®1.6X10"®

000200

186.9189 .2

-4 3 .9-5 3 .2

3.5X10"®3.4X10"® -8 2 .2

197

REFERENCES CITED

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89Dane, C. H. 1946. S tra tig ra p h ic re la tio n s o f Eocene, Paleocene, and

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Osborn, H. F. and C. E a r le . 1895. Fossil mammals o f the Puerco beds. C o lle c tio n o f 1892. B u ll . Amer. Mus. N at. H is t . , 8 ( l ) : l - 7 0 .

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