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UNITED STATES

DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

. S. Geo Jog ic;> ' Survey _

Reports- Open file se_~ I L-1J 1 • I

\

BIOSTRATIGRAPHIC RESULTS OF DART-CORING IN THE

0

WESTERN GULF OF ALASKA, AND THEIR

TECTONIC IMPLI CATIONS

BY

C' 'I

Patri c k H. McClellan, Robert E. Arnal, John A. Barron,

Roland von Huene, Michael A. Fisher and George W. Moore

302181

U. S. Geological Survey

OPEN FILE REPORT

80- 63

This report is p r e l i minary and has not been edited or reviewed for conformity with Geological Survey standards and nomenclature.

BIOSTRATIGRAPHIC RESULTS OF DART-CORING IN THE WESTERN GULF OF ALASKA, AND

THEIR TECTONIC IMPLICATIONS

by

Patrick H. McClellan, Robert E. Arnal, John A. Barron, Roland von Huene, Michael A. Fisher and George w. Moore

ABSTRACT

Age determinations are reported for microfossils from 56 dart-cores

collected in 1978 from the Kodiak shelf. The ages suggest that rocks cropping

out along Albatross Bank, at the shelf edge, are as old as middle or late

Miocene, and that the anticline forming Albatross Bank, previously defined

with multi- and single-channel seismic records, plunges northeastward in the

sampled area. Foraminiferal paleobathymetry further suggests that m.ajor

tectonic activity has occurred on the Kodiak shelf since the early or middle

Pliocene, including two episodes of vertical movement--first subsidence on the

order of 2000 m, then uplift of at least 3000 m. Microfossil ages and

paleobathymetric determinations indicate an average uplift rate of 1000-

3000 m/m.y. for the seaward edge of the Kodiak shelf during the Quaternary.

INTRODUCTION

This report summarizes the results of biostratigraphic analyses of dart-

cores collected near Kodiak Island, in the western Gulf of Alaska. These

results include ages of diatoms (J. A. Barron), foraminifers (R. E. Arnal ),

radiolarians (S. A. Kling) and coccoliths (D. Bukry), and are summarized in

Table 1. The cores were collected on the Kodiak shelf during a sampling

cruise of the R/V SEA SOUNDER in 1978. The purpose of the sampl i ng was to

determine the age and lithology of rocks that crop out near the seaward edge

of the shelf along a bathymetric high named Albatross Bank (fig.l). This bank

forms the shelf-break locally, and is at the axis of an anticline trending

approximately parallel to the Aleutian trench. Analysis of a multichan~el

seismic line (509), which crosses the shelf-break, indicates that the

anticline has risen at least 3 km perhaps since the late Miocene (Fisher and

von Huene, in press). Ages determined from cores collected along line 509,

and along two adjacent seismic lines that also cross the shel f-break (sparker

lines 509B and 509C, fig. 1), should help to establish a lower limit on the

time of uplift of the shelf-break anticline.

The Aleutian trench has been postulated (Atwater, 1970) to be a zone of

convergence between the North American and Pacific plates. The deformed

sedimentary sequence under the Kodiak shelf, therefore, may contain a record

of tectonic events related to subduction. If so, the biostratigraphic results

presented in this report may provide evidence of the timing of these events.

Most of the dart-cores obtained during the cruise were collected on the

continental shelf in an area 40 to 75 km east of Sitkinak Island and 55 to 90

km south· of Kodiak Island. Along Albatross Bank, near the crest of the shelf­

break anticline, hogbacks of bedrock provided the most suitable dart-coring

targets. Water depths over most of the coring sites ranged from 26 to 152

m. Two dart cores (samples 09001 and 09002) were collected in water 875 and

925 m deep, respectively, on the upper continental slope, in the southeastern

corner of the sampled area (station 2; Figure 2). Frequent conditions of

rough seas and impenetrable bottom sediments limited coring success to 56

sample recoveries out of 107 attempts at 38 stations along sparker lines 509,

509B and 509C (figs. 2 and 3A-C).

Presented below are (1) the methods of data collection, (2) the results

of the biostratigraphic analyses, (3) a consolidation and interpretation of

the results, and (4) a discussion of the results.

2

We thank Stanley A. Kling and David Bukry for their paleontologic and

biostratigraphic determinations. We also thank them and Paula Quinterno for

their helpful critical reviews of this paper. Sparker records reproduced in

this report were photoprocessed by Jeffrey Young (USGS, Menlo Park) using the

CONTRAPTION at the Branch of Pacific-Arctic Marine Geology.

METHODS

Dart-cores were collected using a free-fall sampling device consisting of

a detachable steel sample barrel (60.5 em long, 4.8 em inside diameter an d 6.3

mm wall thickness), bolted to a 907 kg lead weight. A 3.5 kHz bathymetry

system was used to locate target outcrops, and NAVSAT and Loran C navigation

systems were used to determine the positions of coring stations. The number

of coring attempts made at each station varied from 1 to 8 . After each core

was extruded from the sample barrel, the core was split longitudinally;

described preliminarily in terms of lithology, structure and color; and

subsampl~d for paleontologic analysis. Sample barrels that contained cores

were not reused during the cruise to minimize the chance of microfossil

contamination. Because of a faulty onboard extruder, 20 cores (specified in

Table 1) could not be removed from the sample barrels. These unextruded cores

were subsampled from the bottom of the core. After being subsampled , each

core-half (or unextruded whole core) was wrapped in plastic and

refrigerated. The cores are presently in the marine-sample refrigerator of

the USGS Branch of Pacific-Arctic Marine Geology, at the Deer Creek facility

in Palo Alto, California . The subsamples were analyzed for microfossils after

the cruise.

3

RESULTS

Results of biostratigraphic analyses of siliceous and calcareous

microfossils in the 56 cores are listed in Table 1, together with water depth

and position of each sample site, and shipboard description of core

lithology. Among the 56 samples, microfossils are present in all but seven

(09003, 09008, 09019, 09021, 09B14, 09B15 and 09B24). In 21 of the samples

only one microfossil group (either diatoms or foraminifers) provided the

age. In the remaining 28 samples, two or more of the four analyzed

microfossil groups are present and yielded ages.

The diatom and foraminiferal determinations independently indicate a

possible late Miocene or early Pliocene age for rocks near the axis of the

shelf-break anticline. Diatom ages indicate that rocks along the axis of the

anticline may be as old as middle Miocene (i.e., at stations 25 and 27).

Sample ages tend to decrease away from the axis landward along lines 509B and

509C, and landward and seaward along line 509.

Of the microfossil groups analyzed for age, foraminifers (mostly

benthics) are the best represented, being present in 70% of the total of 56

samples. Diatoms were found in 55% of the samples, and coccoliths in only

7%. Thirty-eight samples, those collected near the axis of the shelf-break

anticline, were analyzed for radiolarians. Of these 38 samples, 45% were

found to contain radiolarians.

Except for the foraminifers, microfossils in the samples tend to be

sparse and poorly preserved, and the gr0ups present tend to be taxonomically

nondiverse. Siliceous microfossils, except diatoms in the Quaternary

assemblages, are commonly broken and in many cases were probably reworked from

older Tertiary source terranes. The radiolarian species present are not

diagnostic of an age more precise than Neogene. Although two radiolarian

4

species occur at frequencies greater than "rare", these species range in age

from at least early Miocene to the present (Kling, 1979, written comm.) •.

Calcareous microfossils are either well preserved and abundant (foraminifers)

or moderately well preserved and extremely rare (coccoliths). Only two

coccolith assemblages (in 09002 and 09B01) contain indigenous populations, and

specimens in these assemblages are of Quaternary age and are sparse and

slightly etched (Bukry, 1979, written comm.). The remaining nannofloras (in

09B03 and 09C38) each contain a single species of Cenozoic coccoliths,

specimens of which are either reworked or contaminants. Listed beside each

station in Figure 4 are the ages of the samples determined on the bases of

diatoms and foraminifers, which are the most age-diagnost ic fossil groups

present.

Seven samples (09001, 09002, 09011, 090 24 , 09C29, 09C34, and 09C41) from

the 1978 cruise were analyzed (R. E. Arnal) for paleobathymetry, based on the

paleocologies of the foraminiferal assemblages. These samples are the oldest

from the -Kodiak shelf, based on the foraminifers, and were selected for this

analysis to determine the depth of deposition of the sediments in the cores .

All of the above samples, except 09C34, contain foraminiferal assemblages

typical of the outer continental shelf and upper continental slope (between

about 200 and 500 m). Sample 09C34 (s~ation 24; early Pliocene?) contains

cold- and deep-water types of foraminifers that lived at depths from outer

neritic (about 200 m) to 2000 m.

5

CONSOLIDATION AND INTERPRETATION OF RESULTS

Microfossil ages listed for many samples in Table 1 are inconsistent,.

This is most notable between diatom and foraminiferal ages. In some cases,

ages of these fossil groups in a given sample differ by as much as two epochs

(e.g., Miocene diatoms ages vs. Pleistocene foraminiferal ages). Possible

reasons for the discordant determinations are:

(1) Quaternary fossils may have been displaced by the core barrel into

older sediment during penetration (although only the inner part of each core

was subsampled to minimize the possibility of such contamination);

(2) bioturbation (observed in 7 samples, noted in Table 1) may have

mixed modern and older assemblages;

(3) reworking of sediment may have suspended and redeposited older

microfossils with younger assemblages;

(4) sample contamination (recognized and corrected for one sample,

09C25) may have occurred during sample preparation.

(5) "precise correlation between the ordinal biostratigraphic scales of

the cold-water planktic and benthic microfossil groups has not been completely

established.

In many cases these inconsistencies have been resolved according to the

following rationales:

(I) Overlapping age ranges: If, for a given sample, a general age

determination (i.e. an age range) based on one fossil group includes all or

part of the range of another group, the restricted age defined by the interval

of range-overlap becomes the basis of a refined estimate of sample age.

(II) Constraint of superposition: In most parts of the sampled area,

the structure and relative ages of strata beneath the Kodiak shelf may be

inferred from the sparker records (figs. 3A-C). The inferred superposition

6

provides a check on the biostratigraphic determinations for the coring

stations along the sample lines.

Age estimates refined according to the above rationales are listed beside

each station in Figures 3A-C along the sparker records of lines 509, 509B and

509C. Where discrepancies between ages determined for a given sample, or

between sample ages determined for a given station, cannot be resolved, each

discordant determination is noted in Figures 3A-C.

Several of the discordant age-sets may be resolved. In one instance

(station 18; figs. 3C and 4), the discordance between the middle Pliocene

diatom and Quaternary foraminifer determinations for sample 09C10 is resolved

by the constraint of superposition as observed in the seismic stratigraphy.

Rocks cored at station 18 are part of a basinal sequence shown, in part, by

the landward portions of the sparker profiles in Figures 3A-C. The

stratigraphic position of station 18 is above strata elsewhere in the basin

that are established as Quaternary by concordant microfossil ages.

absence oT evidence of major faulting in the sampled part of the basin, the

superpositional evidence indicates a Quaternary age for rocks at station 18.

The Pliocene diatoms from this station are attributed to reworking from older

terranes, and the Quaternary age is accepted.

At station 23, the consistent dis~ordance between the late Miocene or

Pliocene diatom ages and the Quaternary foraminiferal ages is due in part to

very low taxonomic and numerical representation of microfossils in assemblages

from this station. However, the consistent absence of diatoms younger than

Pliocene from this station, in combination with diatom and forami niferal

evidence of late Miocene or Pliocene rocks at stations 22 and 24, indicates a

late Miocene or Pliocene age for station 23. The conflicting ages assigned to

station 24 are resolved to late Miocene or early Pliocene. This age is based

7

on the concordant ages of diatoms {in sample 09C36) and foraminifers {in

sample 09C34) from this station.

Station 26 is located seaward and on top of the hanging-wall block of a

normal fault. The discordant ages assigned to this station may have resulted

from reworking of the early to middle Pliocene diatoms into younger sediment

that has accumulated on the surface of the hanging-wall block.

The numerous Quaternary ages assigned to stations 27 to 30 suggest that

bedrock was not penetrated. These stations are near the core of the shelf­

break anticline. Bedrock at these stations therefore should be older, as

inferred from superposition in the sparker record, than lower to middle

Pliocene rocks at station 31. If penetration did occur, the middle and late

Miocene determination at station 27 {sample 09B03, of questionable age due to

poor diatom preservation) may represent rocks in situ that are roughly

equivalent in age to upper Miocene rocks sampled near the anticlinal axi s

along adjacent line 509C.

DISCUSSION

Despite the several inconsistent biostratigraphic determinations noted

above, the following general observations may be made. First, along lines

509B and 509C, the oldest samples tend to occur near the seaward ends of the

lines. On line 509B the oldest dated foraminiferal and diatom assemblages

were found at station 27. On line 509C the oldest foraminiferal assemblage

occurred at station 24, and the oldest diatom flora at station 25. These

oldest assemblages are most probably middle to late Miocene in a ge . Those

from stations landward of approximately station 30 {on line 509B) and station

23 {on line 509C) are probably Pliocene and Quaternary in age.

8

Second, along line 509 the oldest diatom flora (early to middle Pliocene)

was found at station 9. Except for sample 09001 (station 2), microfossils

collected landward and seaward of station 9 are all probably late Pliocene and

Quaternary in age. The late Miocene or early Plioc ene(?) foraminifers in

sample 09001 suggest that rocks of this age crop out on the continental

slope. These rocks may represent a deep portion of the sequence sampled on

the shelf that has been truncated and exposed on the slope by fault i ng or

submarine erosion (see fig. 3A, below station 2).

The position of station 9 is approximately coincident wi th the

geophysically determined axis of the shelf-break anticl i ne . The westward

continuation of this axis passes some distance seaward of the sout h ends o f

lines 509B and 509C. Multichannel seismic da t a (Fisher and von Huene, in

press) establish that this anticline is a major feature in the regiona l

structure beneath the Kodiak shelf. These seismic data and the f o rego i n g

biostratigraphic results indicate that this anticline plunges northeastwa rd

(fig. 5) ~n the sampled area.

Results of the paleobathymetric analyses of the selected foram i n ifera l

assemblages indicate that major vertical tectonic activity has occurred in the

vicinity of Albatross Bank since at least as long ago as the early or middle

Pliocene. This activity included an early episode of subsidence of abo ut 200 0

m followed by a later episode of uplift of over 3000 m. These estimated

amounts of vertical movement are based on the followi ng observations. The

oldest sample along line 509 (09016, station 9) is early or middle Pliocene in

age, based on diatoms. However this sample yielded no foraminifers for

paleobathymetr i c analysis. Analyses of foraminifers from stations 6 and 14

indicate that rocks from these stations were deposited no deeper than on the

upper continental slope (< 500 m). Rocks at station 9 were probably also

9

deposited near this paleodepth. Assuming this initial depth in the early or

middle Pliocene (3 to 5 m.y. ago), rocks at station 9 subsequently subsided

and were buried by about 2000 m of sediment (fig. 6) until the late Pliocene

or Quaternary (probably l to 3 m.y. ago). The average rate of subsidence was,

therefore, 2000 mover probably not more than 4 nor less than 1 m.y., or 500-

2000 rn/m.y. During the late Pliocene or Quaternary (probably 1 to 3 m.y.

ago), rocks on Albatross Bank, 4 krn seaward of station 9 at the core of the

shelf-break anticline, were uplifted over 3000 m (Fisher and von Huene, in

press). The average rate of uplift of the anticline is, therefore, 1000-3000

rn/m.y.

Because the depth distribution of living foraminifers in the Gulf of

Alaska is poorly known, the preceding paleobathymetric results are based on

analogy of the fossil foraminiferal assemblages from the Kodiak shelf to

living assemblages off the California coast, where a depth zonation has been

established (Bandy, 1953; Bandy and Arnal, 1957, 1960; Ingle, 1967; Arnal and

Vedder, 1976). The application of the depth zonation of living foraminifers

off California to our high-latitude, Neogene fossil assemblages, therefore,

requires two assumptions: (1) that there has been little or no physiological

evolution, with respect to bathymetric tolerances, in the histories of the

analogous fossil and Holocene foraminifer species--an assumption basic to al l

uniforrnistic approaches to paleoecology, and (2) that the development and

fluctuation in the late Tertiary trans-latitudinal, oceanographic temperature

gradients did not affect the depth distribution of high-latitude f oraminifers

independently of foraminifer distribution off the California coast. The

validity of the second assumption is presently being investigated at the u. s.

Geological Survey through a study of modern foraminifer ecology in a series of

Soutar-van Veen grab-samples recently collected in the Gulf of Alaska.

10

CONCLUSION

The results of micropaleontologic and biostratigraphic analyses of dart­

cores collected in 1978 indicate that the shelf-break structure beneath

Albatross Bank on the Kodiak shelf is a northeast-plunging anticline with

middle to upper Miocene rocks exposed at its axis on the sea floor .

Paleobathymetric analyses of foraminifers suggest that most (2000 m) of the 3

km of uplift recognized along Albatross Bank by Fisher and von Huene (in

press) has occurred since the middle Pliocene, at an average rate probably of

1000-300 0 m/ m.y.

, 1

Table 1. Biostratigraphic and lithologic data for dart-core samples from the Kodiak shelf, western Gulf of Alaska. (Samples listed in order of station number.)

Abbreviations: "B" = sample barren of fossils.

"N/A" sample not analyzed for radiolarians.

* = core lodged in dart-barrel.

Epoch subdivisions:

L late M middle E early

Comp lete sample-number sequence is 09001-09030, 09C0l-09C42, 09B0l -09B35. Unlisted sample numbers were non-recoveries.

Table 1. Biostratigraphic and lithologic data for dart-core samples from the Kodiak shelf, western Gulf of Alaska.

Station

2

2

3 3

4 5 5 6

6

7

7

B

B

9

10 ll

12 13 14

14

Sample

09001

09002

09003 09004

09005 09006 09008 09010

09011

09012

09013 09014

09015

09016

09018 09019

09021 09022 09024

09025

LINE 509 SAMPLES

LAtitude (N)

56° 15.96'

56° 15.96'

56° 21.31' 56° 21.27'

56° 21.79' 56° 22.36' 56° 22.28' 56° 22.38'

56° 22.30'

56° 22.51'

56° 22.51' 56° 22.68'

56° 22.74'

56° 22.99'

56° 23.02' 56° 23.12'

56° 23.04' 56° 23.92' 56° 25.42'

56° 25.22'

Longitude (W)

152° 43.69'

152° 43.69'

152° 50.77' 152° 50.96'

152° 51.35' 152° 52.61' 152° 52.45' 152° 52.65'

152° 52.81'

152° 53.14'

152° 53.18' 152° 53.57'

152° 53.69'

152° 54.54'

152° 55.02' 152° 55.30'

152° 55.63' 152° 54.54' 152° 56.76'

152° 56.90'

Water Depth (in m)

875

925

94 92

73 58 54 47

53

50

55 47

45

46

58 46

46 49 53

52

Lithology

silty claystone

greenish mud w/er ratic pebbles claystone claystone

silty claystone clay claystone silty claystone w/erratic pebbles silty clay

claystone w/erratic pebbles claystone claystone bioturbated claystone

clayey limes tone

silty claystone silty clay bioturbated clay, bioturbated claystone claystone w/erratic pebbles claystone*

Diatoms (Barron)

L. Pliocene or E· Quaternary, prob. E. Quat. L. Quaternary

B

Miocene to Quaternary B B

B

Miocene to Quaternary B

B

B

B

B

E. or M.

Pliocene B

B

B

B

Prob. L. Quaternary Cenozoic

FOSSIL-AGE DETERMINATIONS

Foraminifers (Arnal)

L. Miocene or E. ?

Pliocene undiff.

L. Pliocene to Holocene B

B

Quaternary Prob. Quaternary B

Prob. Quaternary

L. Pliocene to Holocene Prob. Quaternary

Prob. Quaternary Quaternary

Quaternary

B

Quaternary B

B

Prob. Quaternary Prob. L. Pliocene to Holocene Prob. Quaternary

Radiolarians (Kling)

E. Mioc ene to Quaternary

E. Miocene to Quaternary B

B

B

B

B

B

B

B

B

B

E. Miocene to Quaternary E. Miocene to Quaternary N/A N/A

N/A N/A N/A

N/A

Coccoliths (Bukry)

B

Quaternary

B

B

B

B

B

B

B

B

B

B

B

B

B B

B B

B

B

Tab l e l (cont . )

LINE 5098 SAMPLES

Station

27

27

29 30

30

31

31

32 32 33

33

34 34

35 36

37

38

39

Sample Latitude (N)

09801 56° 19.73 1

09803 56° 19.60 1

09806 56° 20 . 33 1

09808 56° 20.67 1

09809

09810

09Bl2

09814 09815 09817

09818

09820 0921

09824 09825

09826

09829

09833

56° 20.54 1

56° 2 1. 09 I

56° 20.94 1

56° 22.14 1

56° 22 . 11 1

56° 22 . 73 1

56° 22 . 69 1

56° 23 . 38 1

56° 23 . 31 1

56° 23.87 1

56° 24 . 43 1

56° 25 . 07 1

56° 25.27 1

56° 25 . 66 I

Water Longitude (W) Depth

(in m)

153° 08.18 1 126

153° 07 . 76 1 130

153° 07.82 1 71 153° 08 . 40 1 53

153° 08.38 1

153° 08 . 69 1

153° 08 . 76 1

153° 08.77 I

153° o8 . n 1

l53o 09.01 1

153° 09 . 01 1

153° 09 . 51 1

153° 09 . 68 1

153° 09.68 1

153° 09.55 1

153° 09.67 1

153° 09 . 83 1

153° 09.56 1

56

46

44

35 35 26

26

29 29

29 29

28

28

26

Lithology

sand

silty claystone*

silty claystone silty , fine-grained sandstone silty, very fine­grained sand silty clay

silty clay bioturbated silty claystone silty claystone clayey siltstone w/ erratic granules* silty claystone w/erratic pebbles

sandy claystone* silty, very fine­grained sand pebbly claystone silty claystone w/ erratic pebbles* silty claystone w/erratic pebbles

silty c laystone w/ erratic pebbles* sandy claystone w/erratic granules*

FOSSIL-AGE OETRMINATIONS

Diatoms (Barron)

L. Quaternary

M. Miocene? or E. L. Miocene? B B

Foraminifers (Arnal)

L. Plio. to Holocene Poss. L. Pliocene or E. Pleistocene Prob . Holocene

Prob . Holocene Prob. Holcene

B Prob. Holocene

L . L. Miocene or B Pliocene E. or M. Pliocene B

B B B B E. Quaternary Quaternary

L. Plioce ne or Quat . prob. Holocene Quat . Pre-latest Quaternary B Quat . prob. Holocene Cenozoic B

B B B Quaternary

Radiolarians (Kling)

N/ A

E. Miocene to Quaternary B

B

B

B

E. Miocene to Qua ternary B

B

N/ A

N/A

N/ A N/ A

N/ A N/A

Latest Miocene to Quaternary N/A Quate rneary, pre-latest Quaternary L. Pl iocene or Quaternary N/A Quaternary L· Miocene to Quat . , prob. Holocene N/ A Quaternary

Coccoliths (Bukry)

Quaternary

Tertiary or Quaternary B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

Table 1 (cont.)

LINE 509C SAMPLES FOSSIL-AGE DETERMINATIONS

Water Station Sample Latitude (N) Longitude (W) Depth Lithology Diatoms Foraminifers Radiolarians Coccoliths

(in m) (Barron) (Arnall (Kling) ( 8ukry)

18 09Cl0 56° 23.75' 153° 18.91' 39 silty claystone, M. Pliocene Quaternary N/A 8 bioturbated

19 09Cl3 56° 22.75' 153° 16.91' 37 clay w/erratic 8 Quat., prob. Holocene N/ A 8

56° 20.45' pebbles

21 09C25 153~ 15.23' 43 silty claystone 8 Quaternary 8 8 21 09C26 56° 20.27' 153 15.28' 43 claystone* 8 Quat . , prob . Holocene 8 8 22 09C27 56° 19.90' 153° 14.91' 54 silty claystone* L.L. Miocene or 8 E. Mioc ene to 8

Pliocene Quaternary 22 09C28 56° 19.92. 153° 14.84. 54 claystone, L.L. Miocene or 8 E. Miocene to 8

bioturbated Pliocene Quaternary 23 09C29 56° 19.55' 153° 14.38' 55 silty claystone* L.L. Miocene or L . Pliocene to E. Miocene to 8

Pliocene Holocene Quaternary 23 09C30 56° 19.61 ' 153° 14.30 56 silty claystone* L.L. Miocene or Quaternary E. Miocene to 8

pliocene w/re- Quaternary worked M. Miocene

23 09C31 56° 19.65' 153° 14.14' 57 silty claystone* L.L. Miocene or 8 E. Miocene to 8 Pliocene Quaternary

23 09C32 56° 19.65' 153° 14.11' 58 silty claystone L.L. Miocene or Quaternary E. Miocene to 8 w/ erratic granules, Pliocene Quaternary bioturbated

23 09C33 56° 19.64' 153° 14.25' 56 silty claystone* 8 Quaternary 8 8 24 09C34 56° 19.29' 153° 1).87' 63 silty claystone* Post-Eocene L . Miocene or E.? E. Miocene to 8

Pliocene, undiff. Quaternary 24 09C35 56° 19.31' 153° 13 . 90. 65 silty claystone* 8 Quaternary 8 8 24 09C36 56° 19.30' 153° 1), 72. 67 claystone L.L. Miocene or Quaternary E. Miocene to 8

Pliocene Quaternary 25 09C37 56° 18.80' 153° 13.47' 86 silty claystone* Miocene to Quat. 8 8 8 25 09C38 56° 18.78' 153° 13.33' 91 claystone* L.M. Miocene? or 8 E. Miocene to Tertiary or

E.L. Miocene? Quaternary Quaternary 26 09C40 56° 18.50' 153° 12.96' 140 claystone E. or M. Pliocene Prob. Quaternary E. Miocene to 8

26 09C41 56° 18 . 53' 153° 12.81' 152 clayey sand Quaternary

Latest Pliocene L. Pliocene to Halo- E. Miocene to 8 or Quat., pro b . cene, moat likely L. Quaternary Lt. Quaternary Plio. or E. Pleiat.

* * * * * * * *

FIGURES

* * * * * * * *

56"

1 54 '

57" 58. 1 5 ••

• u~oo

TUGIDAK Is.

~ -~~ a SIT KI NAK I s~

~~

"' v

I \

<\7

OJ(¢ ,o

(.) 01

0

"' ~ ....

..J

a. 0 II}

LU ;z ...

--1

~

KODIAK S H E L F

'1 l ........_ ..._ ~- ---ALBATROSS BANK

-----.......... <o olof

'so& ~ .,.Jy

56" 1s z·

,. 57"

Figure 1 . Location of sparker lines 509 , 5098 and 509C on the Kodiak shelf , weste rn Gulf of Alaska .

152"

58"

+

+ 153" 30 '

(.. ~ 'i, ~

-z."'

~\0

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IS Km

Figure 2 . Sparker lines 509, 509B and 509C showing positions of dart- coring stations relative to time - marks on corresponding sparker profiles in Figures 3A , 3B and 3C .

+ 56" 30 '

+ 56 " 15'

tsz· 30'

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3 MIOCENE t o QUAT.

4 QUATERNARY

5 Prob . QUATERNARY

6 L. PLIOCENE or QUAT ., prob . QUAT. 7 Prob . QUATERNAR Y

8 QUATERNARY 9 E.-M . PLIOCENE

10 QUATERNAR Y 11 None 12 None

13 Prob . QUATERNARY

14 L. PLIOCENE or QUAT. , prob . QUAT.

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29 QUATERNARY 30 QUATERNARY 31 E. or M. PLIOCENE

32 None

33 QUATERNARY

QUATERNARY

35 None

36 QUATERNARY 37 QUATERNARY 38 QUATERNARY

39 QUATERNARY

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Figure 4. Areal distribution of diatom and foraminifer ages determined for dart- cores collected along sparker lines 509, 5098 and 509C .

+ 56 ' 3:)'

+ 56 ' 15'

152 ' 3:)'

+

+ !5 3' 30 '

s "'

<"...,+ %-

+ 56'30''

<:.. 1t- ~

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MIOCENE

INFERRED CHRONOSTRAT ­IGRAPHIC BOUNDARY

NORMAL FAULT

/ • '\ . \ \

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IS l<m

+ 56'15'

152' JJ'

Figure 5 . Geology of sampled portion of the Kodiak shelf, as inferred from microfossil biostratigraphy and seismic stratigraphy .

-

Youngest Hor izon Antedat ing Uplift (L. Pli ocene or Quaterna r y)

Str / r <~t. h;Cfr

19ra

2o(;blf'ssD:fc

'"~ ,, /,~· 14

- .......... ~ ..........

.... ..........

- ...._ .......... "" - - ...._ -

..... ...._

........... ...._ ........... - -"'- ..........

--......... .......... - ........ _ ..........

.......... -- ......... _

.......... - -- -

0 J 6KM

SCALE

-......... -.......... -..... _ -.........

......... -......... ...._ -

~ '2 V\ 41 a. "' .. c a. ·~

...J "' ·~

... -'= 41 ...

""' ... ' ... a.trl

"' . ...J 0> 0 ·~

CD~

....,

--- -

2

3

4 - 5

6

7

Figure 6 . A 1:1 migrated depth-section of multichannel seismic line 509 (after Fisher and ·von Huene , fig. 5 , in press) showing thickness of stratigraphic section between station 9 and the youngest depositional horizon (near station 14) antedating the uplift of the anticline beneath Albatross Bank . The cross - section indicates that rocks at station 9 (early or middle Pliocene in age) were buried to a depth of about 2 . 0 km before they were uplifted at least 3 km (estimated by Fisher and von Huene , in press) during the develop ment of the anticline .

DEPTH (in km)