Cenozoic Sedimentation in the Eastern Tropical Pacific

Geological Society of America Bulletin

doi: 10.1130/0016-7606(1973)84<1941:CSITET>2.0.CO;2 1973;84, no. 6;1941-1954Geological Society of America Bulletin

WOLFGANG H. BERGER Cenozoic Sedimentation in the Eastern Tropical Pacific

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WOLFGANG H. BERGER Scripps Institution of Oceanography, La Jolla, California 92037

Cenozoic Sedimentation in the Eastern Tropical Pacific

ABSTRACT

The method of paleodepth backtracking consists of assigning depths of deposition to dated sediments for which the age of under-lying basement is known. Paleobathymetric facies distributions in the equatorial Pacific suggest minor fluctuations of the calcite com-pensation depth (CCD) in post-Eocene time, but a relatively shallow CCD during the Eocene period. Fluctuations in the Atlantic show an entirely different pattern. It is specu-lated that CCD fluctuations in different ocean basins may be in part parallel and in part op-posed in response to such factors as varying global carbonate supply, amount of carbonate deposited in shelf seas, latitudinal productivity variation, and deep-sea circulation patterns.

INTRODUCTION

Calcite Compensation Depth

The facies boundary between calcareous and noncalcareous sediments, the calcite compensa-tion depth (CCD), tends to follow bathymétrie contours in any one area of the ocean, although it cuts across contours when larger regions are considered. The CCD may be thought of as the intersection of a compensation depth sur-face with the local topography. This surface tends to resemble a somewhat warped pan, with the brims rising to the continents and with a furrowlike depression along the highly productive equatorial area (Lisitzin, 1971, p. 208-209).

The CCD is a product of various processes and reflects conditions both in upper waters and in the deep sea (Bramlette, 1961; Berger, 1970, 1971). Each ocean basin has its own CCD surface, and in each basin the surface changes through time in response to changing climatic, oceanographic, and geologic conditions. In order to extract the paleoceanographic infor-mation contained in the motions of the CCD,

the configurations of the corresponding sur-faces during past times have to be recon-structed. The concepts and operations ap-propriate to facies-boundary reconstruction are subsumed in the term "plate stratigraphy."

Plate Stratigraphy The present distribution of facies bounda-

ries, including the CCD, is in part a result of sea-floor subsidence and of horizontal plate motions (Fischer and others, 1970; Hay, 1971; Ramsay, 1972). The effects of sea-floor sub-sidence can be accounted for by using the hypothesis of age-depth constancy (Berger, 1972). According to the theory of sea-floor spreading, the ocean floor becomes older away from ridges and parallel to fracture zones; and as the oceanic crust ages, it cools and subsides in a predictable manner (Sclater and Franche-teau, 1970). Empirical data support this con-clusion (Menard, 1969) to the extent that sinking rates for all major parts of the ocean resemble each other closely, regardless of spreading rate (Sclater and others, 1971). This consistency is the basis of the hypothesis of age-depth constancy which maintains that at any point in geological time, the age of the sea floor determined how far it moved down-ward from the original ridge crest. This hy-pothesis has proved useful in paleodepth recon-structions (Berger, 1972; Berger and von Rad, 1972) and in the explanation of the distribu-tion of sediment thickness in the equatorial Pacific (Winterer, 1973).

In this paper, I attempt to reconstruct the paleo-distributions of deep-sea sediments in the equatorial Pacific, using age-depth con-stancy to interpret drilling results from JOIDES Leg 5 (McManus and others, 1970), Leg 7 (Winterer and others, 1971b), Leg 8 (Tracey and others, 1971), Leg 9 (Hays and others, 1972), Leg 16 (van Andel and others, 1971), and Leg 17 (Winterer and others, 1971a; see Fig. 1). The reconstructions are used to

Geological Society of America Bulletin, v. 84, p. 1941-1954, 12 figs., June 1973

1941

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Figure 1. Drill site locations.



CENOZOIC SEDIMENTATION, EASTERN TROPICAL PACIFIC 1943

trace the variations of the calcite compensation depth in the central equatorial Pacific through the last 50 m.y.

METHODS

Backtracking Procedure The age-depth curve used here (Fig. 2) is

based on the tabulation of Sclater and others (1971) and extrapolated on the basis of drilling results (Berger, 1972). According to this curve, the actively spreading basement subsided 1,000 m during the first 10 m.y. of its existence, a further 1,000 m during the following 26 m.y., and yet another 1,000 m within the subse-quent 50 m.y. Thus, both the total amount of subsidence and the rate of subsidence of a piece of basement formed at the ridge crest depends on its age (see nomogram, Fig. 2). According to the nomogram, basement of a certain age has a certain depth at the present time (x-axis = 0). Newly forming basement at the present ridge crest, for example, is near 2,700 m. Basement that is 10 m.y. old (see curve starting at age = 10 m.y.) presumably was at 2,700 m 10 m.y. ago, but intersects the present (x-axis = 0) at 3,700 m. Basement 45 m.y. old intersects the present at about 5,000 m, after subsiding from an (assumed) initial elevation of 2,700 m. These curves can be used for reconstructing the subsidence path of a slab of basement that is loaded with sedi-ment, while noting at which depth the various facies were accumulated. For example, if a piece of basement is 80 m.y. old, overlying sediment of age 30 m.y. would plot at the intersection of the 80-m.y. curve with the ordinate value 30 m.y., at about 5,100-m depth (age-only depth, or A-depth).

While this idealized relation holds on the average, actual sites do not necessarily conform exactly to the absolute age-depth scale. Base-ment of a given age may be either somewhat deeper or shallower than prescribed by the nomogram due to local topography and sedi-ment accumulation. Assuming that local relief on the basement-surface is inherited from the ridge topography, it is possible to correct for this difference in water depth, which is done by adding or subtracting it to the A-depth. This means that the shape of the subsidence curve is kept constant, even though its position varies vertically. In the above example, if the basement is 80 m.y. old, but the sea floor is only 5,000 m deep (with part of the difference to the "expected" 5,600 m being due to the

AGE (106/)

to both basement and sediment ages. "Dep th" is paleodepth except at age = 0 where new basement at ridge crest is near 2,700 m. Plotted from data given in Sclater and others (1971). All curves shown are seg-ments of the age-depth curve in Berger and von Rad (1972).

sediment burden), the intersection of water depth with 30 m.y. is 4,500 m. If the 30-m.y.-old sediment was reached after 200 m of drill-ing, one adds 100 m to this depth of 4,500 m— so that in this instance, the final paleodepth is 4,600 m (backtracking depth, or B-depth). One adds one-half the depth-in-hole rather than the total to allow for isostatic adjustment of the basement to the sediment load (upper mantle sima: p = 3.3; sediment: p = 2.4; excess of sediment over water: pdiff = 1.4; hence replacement of 10 m of water by sedi-ment increases the pressure by an amount equivalent to 4.2 m of sima. The corresponding sinking of the crust increases the water pressure providing an additional load. Hence, 10 m of sediment should depress the basement by about 5 m). In the following, "paleodepth" refers to B-depths found by this "backtracking" pro-cedure.

Reduction of Drill-Site Data The drill sites shown in Figure 1 were back-

tracked in the described manner to find the paleodepths for the sediments cored (Fig. 3). The generalized sediment profile (Fig. 3A), converted from a thickness scale to Berggren's (1972) time scale (Fig. 3B), is plotted along the B-track (Fig. 3C). This track, as outlined above, depends upon the age of basement that is assumed. Cenozoic basement ages derived from dating sediment overlying basalt tend to be less reliable than magnetic ages, owing to nondeposition or redistribution of sediment in ridge crest areas and the likely presence of



1944 W. H. BERGER

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200

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O a. 2 < -i IU o

ÜJ 2 ÜJ <• a -J o ÜJ M . E O .

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Chalk

ooze

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0

10

20

' 3 0 »

4 0

5 0

Illl Hiatus

Illl P L I O . Illl

Hiatus

Illl LT. M10 Illl

Hiatus

Illl M.MI0

Illl Hiatus

Illl E . M I O

Illl Hiatus

Illl E . M I O Chalk

a s l l i c . ooze

LT. OLI

Chalk a s l l i c .

ooze LT. OLI Chalk

ooze

E . O L I

Chalk ooze

E . O L I

Chalk LT. EO

Chalk LT. EO

Sil ic. ooze

M . E O Sil ic. ooze

M . E O ?

Basal t ? E . E O ?

Basal t ?

? Basal t ?

5 0 A g e ( M y )

__ chalk a sine. 31 h io tus |sll ic.ooz|cholk ooz»| chalk |ooze |baso l t

10 ~r 20 3 0 4 0 5 0 ( M y )

Pilo. Lt.M.M.Mio. e.MIo I I I I

U.OII. I E.OII. I U Eo. M.EO. I I 3r

r r

Tdcr

LEGEND + basalt w si l ica

H limestone t V I'fne ooze O hiatus

S i t e I E q u .

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H Lt. Eo.

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A Lt. Oli.

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„. 8 Figure 3. Conversion of drill-site results (site 161)

to paleobathymetric facies distributions (see text for description of method). Present water depth: 4,939 m. Three different basement age assignments are shown

basalt sills, among other factors (Fig. 2 in Berger, 1972). Throughout this paper, there-fore, basement ages are interpolated and extrapolated from magnetic anomaly patterns (Hayes and Pitman, 1970; Herron, 1972; Lar-son and Chase, 1972), supplemented by basal sediment ages.

The facies sequence is plotted along the most probable B-track (Fig. 3D) and the se-quence is then turned through 90 degrees (Fig. 3E). In this fashion, each of the drill sites appears as a vertical subsidence track in a latitude versus depth plane (Fig. 4). The tracks constitute a base map for plotting paleo-distri-butions.

Error Sources One source of error has already been men-

tioned—the uncertainty associated with the basement age (see van Andel, 1973). In places where basement age and sediment age are

J 5 in Figure 3C to illustrate the resulting spread in paleodepths. (Magnetic age assignments are older than those derived from biostratigraphy of basal sedi-ments) .

widely different, errors are quite modest. In the example given (Fig. 3), different basement age assignments (50, 60, and 70 m.y.) lead to a discrepancy of no more than 200 m for sedi-ment 30 m.y. old or younger. In most cases, errors from this source appear to be less than this (Fig. 5). Another error arises from various possible ways of drawing the age-depth curve through the points available (Fig. 1 in Berger, 1972). This error is estimated to be less than 100 m.

The main assumption in paleodepth back-tracking, that local relief on the basement sur-face is inherited from the ridge topography, is the simplest one to work w:.th in the face of ignorance about the actual sea-floor motions. With sufficient coverage, the distribution of carbonate dissolution facies through time may yield enough paleodepth refinement to check [his assumption.

Minor errors (for the present Cenozoic re-



NORTH 2 0 ° 10°

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SOUTH 20°

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41 (67)

+ T

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162 « (60)(5D

68 (100)

160 (42)

167 (Cr/J)

78 (34)

161 (60)

71 ^ (60)

81 (16)

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75 (39)

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LEGEND

present site location

former locat ions (10 My i n t e r v a l s )

te rminat ion of dr i l l ing in b a s a l t in cher t in l imestone in p r e - T e r t i a r y site number

( 8 5 ) assumed basement age 65 (Cr /J )

Figure 4. Paleodepth tracks of drill sites in a north- apparent paleodepths of the basalts encountered, as- than shown and hence to have originated at south profile. "Former locations": 10-m.y. intervals suming that the overlying sediment dates the basalts, depths, counted backward, starting with the present. Note the In reality, most basalts may be presumed to be older



1 9 4 6 W. H. B E R G E R

Estimate of Basement A g e ( * 5 M y )

3 0 4 0 5 0 6 0 7 0 1 0 0

10

2 0 -

3 0

4 0

5 0

Figure 5. Errors in dep th estimate f rom uncertain-ties ( ± 5 m.y.) in assigning basement ages. T h e n u m -bers labeling the vertical lines are drill site numbers .

constructions) are introduced by the uncer-tainties in the absolute age of sediments and by the somewhat crude isostatic correction applied. In all, it appears reasonable to assume that paleodepth assignments for sediments more than 10 m.y. younger than basement are correct to within 200 to 300 m.

RESULTS AND DISCUSSION

Paleobathymetry of Facies Patterns Quaternary facies distributions in the equa-

torial Pacific (Fig. 6) show the familiar patterns produced by the equatorial high production zone, in combination with dissolution at depth and nondeposition or erosion (or both) to the north and south of the zone (Arrhenius, 1952, 1963; Bramlette, 1961; Riedel, 1963, 1971; Riedel and Funnell, 1964; Ewing and others, 1968; Heath, 1969; Hays and others, 1969; Berger, 1971).

The patterns shown in Figure 6, based solely on drilling data, may be thought of as a view from a position in the western equatorial region to the east, toward the ridge crest. Mountains above the CCD show lime-covered peaks, lower elevations being covered with siliceous ooze, clay, or pre-Quaternary sediments. Since the sea floor deepens from east to west, Figure 6

Note that errors are small for sediments younger t h a n basement by 10 m.y . or more.

also may be viewed as a map, with north and south as shown, east up and west down, after bathymétrie offsets alonç; the (approximately east-west trending) fracture zones are elimi-nated by appropriate shafting of the inter-fracture sections.

South of the equator, the CCD is close to the lysocline (the facies boundary zone be-tween well-preserved an:l poorly preserved calcareous fossils; see Parker and Berger, 1971) with very little deposition below 4 km depth. Near the equator, because the rate of supply of carbonate is greatly increased, the CCD is lowered into depths of greater dissolution until supply and dissolution rates again balance. Siliceous ooze accumulates below this depth as residue after complete dissolution of the carbonate. The zone of advanced partial dissolution between lysocline (well above 4,000 m) and CCD (4,500 to 5,000 m) is thick in this fertile area and is characterized by silica-rich calcareous oozes, typically in cyclic facies. To the north, outcrops of older sediments are widespread, indicating little or no deposition, except for a silica band near 12° N.

The depths in the plot of Quaternary pat-terns are, of course, the present ones. For the reconstruction of the older patterns, paleo-depths have been substituted (Figs. 7 and 8).




QUATERNARY

I I I -Figure 6. Quaternary bathymetric facies distribu-

tions in the equatorial Pacific in a north-south versus depth of water projection. The projection forms a matrix which indicates the type of surface sediment found on the sea floor at a given depth and latitude. Black dots indicate control points. Narrowly spaced rad ooze symbols indicate area of rapid deposition. Clay areas which are regions with outcrops of pre-Quat-ernary sediment (hiati) are shown as trellis pattern. (The Holocene CCD appears somewhat lower than the average one for the Quaternary period shown here.)

Except for a noticeable general northward shift of facies patterns with age as well as some vertical fluctuation of the CCD, distributions remain strikingly constant back through the early Oligocene. The constancy of the patterns for the last 35 m.y. provides an independent argument in favor of the sea-floor subsidence curve adopted.

Northward Shift For the last 35 m.y., the width of the car-

bonate belt at 4.5 km paleodepth varied to some extent (Fig. 9). Quaternary and late Oligocene apparently have the widest belts, late Miocene and early Oligocene the narrowest ones. There is a general shift of the carbonate belt northward with age. The belt may be truncated at the northern end, for the last 10 m.y. (Fig. 9, late Miocene to Quaternary), although control on this effect is rather poor. The CCD in this region is essentially a bound-ary between carbonate facies and nondeposi-tion (Figs. 6, 7). Thus, erosion by bottom currents along the Clipperton Fracture Zone may push the CCD toward shallower depths, from its "normal" position. Johnson (1972) has suggested that the Clipperton Fracture Zone, with its several-hundred-meter-high north-facing escarpment (Heath and Moore, 1965) may control the direction of transport of bottom water in the eastern equatorial Pacific. Current velocities and hence compe-

LATE MIOCENE

MIODLE MIOCENE

h I. i W t f

EARLY MIOCENE

Figure 7. Paleobathymetric facies distributions for Pliocene (A), and Miocene (B, C, D) times. Compare with Figure 6.



1944 W. H. BERGER

LATE OLIGOCENE Width of Corbonate Be l t a t 4.5 Km (B-depth )

Y ì y r y ì i i ^ i M m IXC

EARLY OLIGOCENE

.1.I.T I I LX

LATE EOCENE

MIDDLE EOCENE

N 10" 1

10° s

h —I no calcareous sediment

no calcareous sediment

Quaternary

P l iocene

Lt. Miocene

M. Miocene

E. Miocene

Lt .Ol igocene

E. Oligocene

Lt. Eocene

M.Eocene

Figure 9. Width of (sublysocline) carbonate belt at 4.5-km B-depth from the Eocene to the present.

tence for mechanical ar.d chemical dissolution are possibly increased considerably along this zone. The possible existence of such a "fracture zone effect" makes a quantitative study of the northward shift problematical (Fig. 10). Maxi-mum sedimentation rate (compared between equal paleo-depths), congruency (maximum overlap of facies patterns), and greatest paleo-depth of the CCD arc used as possible indi-cators of the paleoequator. Winterer (1973) discusses the geophysical and radiometric evi-dence bearing on the northward shift. His proposed rate of northward movement of 0.23°/iri.y. based on sediment thickness pat-terns fits the present data well, as does the average rate for the last 40 m.y. in the similar diagram, by van Andel and Heath (1973). Their diagram proposes a change in rate at 30 m.y.

N - s h i f t ( d e g r e e s l a t i t u d e ) 5 10

Q u a t e r n a r y

P l i o c e n e

:;o* s 11

Lt . O l i g o c e n e

E . O l i g o c e n e

Figure 8. Paleobathymetric facies distributions for Oligocene (A, B) and Eocene (C, D) times. Compare Figure 10. Latitudinal position of equatorial facies with Figure 6. aspects through time.




However, since the relation of sediment thick-ness and facies patterns to the paleoequator may conceivably vary somewhat through time, I suggest that the straight-line "f i t" best represents our current understanding of the data available. Any longitudinal differences in the general northward shift are eliminated by the projection on a latitude-depth plane.

Facies Constancy in the Equatorial Pacific For the last 50 m.y., only the transition from

the Eocene to the Oligocene shows a change in major facies patterns (Fig. 8) sufficiently striking to necessitate postulating an environ-ment fundamentally different from the present one: during the Eocene, the CCD stood much shallower than it is today, and the silica belt was much wider.

After correcting for northward shift—that is, substituting paleo-latitudes in the latitude versus paleo-depth frame, post-Eocene sedi-ments are easily accommodated in a generalized model of Pacific equatorial facies domains (Fig. 11). In fact, there is virtually no overlap be-

tween carbonate and noncarbonate facies, so that the CCD zone is rather narrow for this time interval. The various facies domains (ridge lime, equatorial lime, lime-silica cycle, radiolarian, and clay facies) are quite well defined and can be matched to the diachronous formations named on Leg 8 (Marquesas For-mation and Clipperton Formation with vari-colored, cyclic, and siliceous units; Tracey and others, 1971). The over-all facies constancy in the equatorial Pacific does not exclude changes in more subtle sediment properties than are recorded in the highly generalized diagram of Figure 11. These properties (differ-ential preservation of calcareous and siliceous fossils, cyclicity of sedimentation, evidence of reworking, diastems, and so on) will have to be closely scrutinized within a paleobathy-metric frame, to decipher the paleo-oceano-graphic trends in this area.

On the whole, the sedimentation rates in Figure 11 compare well with those in the model of Winterer (1973). The rates given are aver-ages, however, and are subject to some fluctua-

P A L E O L A T I T U D E S

2 0 ° 1 0 ° 10° L_

2 0 ° I

I . I . I . I . I ~ T

I l ' i ' i ' i ' i ' i ' i ' r ^ T I I I I I - w - I I I I

i I i I xn

a

Q . Ld O I

CO

Figure 11. Model of post-Eocene facies domains in a paleo-depth versus paleo-latitude frame, highly generalized. Numbers are rates of sedimentation in

Equa t . c y c l e s

Rod . ooze

3 Z Z ! P e l a g i c c l a y

I I I I E r o s i o n a n d I I M n o n - d e p o s i t i o n

m/m.y. Equatorial lime/silica cycles appear to be well developed in Miocene time and later.



1944 W. H. BERGER

tion. Notably, the rates for silica deposi'ior. in the Oligocene appear considerably lower than average. Before rate patterns for Hib-division of epochs can be established, the absolute time scale for biostratigraphic de.ring must become much more reliable than it has been so far (Moore, 1972).

Prediction of Sediment Profiles Facies constancy for post-Eocene sediments

allows reasonably accurate prediction of post-Eocene sediment profiles anywhere in the pelagic areas of the equatorial Pacific. The necessary information for any one site for which a prediction is to be made consists of present latitude, present depth, and basement age. Latitude and depth define the starting point in Figure 11, while basement age defines a track moving upward and to the right, being in essence the appropriate age-depth curve (Fig. 2) with 2.3° corresponding to 10 m.y. on the ordinate. The track will indicate the suc-cession of facies and the rate at which they were deposited, from which the desired profile can be reconstructed. Greater accuracy can be expected if the appropriate facies diagram for each geologic time interval is used, rather than the generalized one of Figure 11. It is necessary to use the Eocene pattern for reconstruction of the Eocene profile because facies distribu-tions of this epoch differ so markedly from later ones. The kind of profile reconstruction here proposed—by backtracking of drill sites and forward tracking of arbitrarily selected sites for which sediment profiles are desired—is simply a method of interpolation and Extra-polation of drill site results based on the hypothesis of age-depth constancy.

CCD Fluctuations Facies constancy for post-Eocene equatorial

sediments in the Pacific implies that CCD fluctuations were of minor importance during the last 35 m.y. However, the silica-lime cycles near the CCD indicate that dissolution regimes varied to some degree. The cycles (Tracey and others, 1971, p. 319) occur on a time scale of about 20,000 to 100,000 yrs and nay be caused by short term climatic fluctuations (Arrhenius, 1952) at least in post-Oligocene sediments. When the record is smoothed over a larger scale, these short-term fluctuations disappear and the CCD shows but minor devia-tions from an average position between 4,500 m and 5,000 m for post-Eocene time (Fig. 12).

A G E o f S E D I M E N T ( 1 0 e y ) 0 1 0 2 0 3 0 4 0 5 0

Figure 12. Fluctuations of the CCD in the equa-torial Pacific during the last 50 m.y. The curve con-nects the deepest points o f the CCD profiles in Figures 6 to S.

The Eocene CCD apparently stood about 1,000 m shallower than this depth.

It is of interest to compare the CCD record in the Pacific with that of the Atlantic. At first glance, there is little resemblance of the Pacific CCD curve with the deposition rate isoline of 2.5 m/m.y. , which approximates the South Atlantic CCD (Fig. 4 in Berger, 1972). The outstanding feature of the Atlantic curve is the great shallowness of the CCD in Miocene time and the considerable deepening (by at least i. ,000 m) since that time to the present. In the Oligocene period, the CCD was about halfway between these extremes, shallowing toward the Eocene.

The shallowness of both Atlantic and Pacific CCDs in Eocene time, if true, suggests a dearth of carbonate in the deep ocean compared with the present. Before the major alpine orogenies, carbonate supply from the continents may have been low. In addition, widespread trans-gression of shelf areas apparently coincided with an extensive tropical belt and prolific shallow-water carbonate production, including the famous Numwulites limestones (Brink-mann, 1959, p. 269 and 278). Thus, the shelves may have acted as carbonate traps while the silica was carried out to the deep sea by deep saline outflow (basin-shelf fractionation; Ber-ger, 1970). Entrapment of silica at the con-tinental margins through biological uptake and sedimentation would have been less effec-




tive than it is today, because of reduced upwell-ing along the flooded continents under condi-tions of but moderate climatic gradients. Also, the present Antarctic silica sink presumably was weak or nonexistent since the circumpolar passages south of Australia (McKenzie and Sclater, 1971, Fig. 44) and south of Patagonia (J. G. Sclater, 1971, personal commun.) were closed.

A common response to a global factor also seems indicated by the lowering of the average CCD in both oceans with the approach of the glacial ages. Apparently carbonate deposition is more restricted to low latitudes during times of intense cooling of higher latitudes, as implied by Arrhenius' (1952) explanation of equatorial carbonate cycles and as proposed in the oceanic productivity model of Mclntyre and others (1972).

The notion of global factors controlling carbonate deposition in a similar fashion in distinct ocean basins leads one to look for in-phase CCD fluctuations, or indeed any other parallel fluctuations in facies patterns. Some evidence for counter-phase fluctuations may also exist. The Miocene CCD seems slightly lowered in the Pacific at the time that it stood shallow in the Atlantic. Furthermore, Oligocene silica deposition rates appear high in the tropical Atlantic and low in the tropical Pacific. These antipathic distributions suggest basin-basin fractionation by the oceanic water exchange patterns at the time (Berger, 1970).

SUMMARY AND CONCLUSIONS Paleodepth backtracking along a sea-floor

subsidence curve based on present age-depth data (Sclater and others, 1971) leads to a more or less steady-state facies distribution for the equatorial Pacific for post-Eocene time. This facies constancy supports the hypothesis that the age-depth relation has remained the same for the last 40 m.y. The method outlined can be used to compare results between drill sites in a paleo-bathymetric frame and to interpolate and extrapolate sediment distributions in the pelagic equatorial Pacific. It appears possible to make reasonable predictions of sedimentary profiles for arbitrarily chosen sites. The facies pattern of the Eocene is the only one that is radically different from present distributions. The reason for this difference is not clear, but neither is that for the post-Eocene facies con-stancy. CCD fluctuations of the Atlantic and of the Pacific do not look alike but may never-

theless be related through global controlling factors and through basin-basin fractionation.

ACKNOWLEDGMENTS The present report was prepared for the

symposium "Contribution of the Deep-Sea Drilling Project to Geology," convened by B. C. Heezen and M.N.A. Peterson, and pre-sented at the 24th International Geological Congress, Montreal, Canada, August 1972.

I am indebted to ]. G. Sclater and E. L. Winterer for informative discussions. John Edmond, G. R. Heath, T. C. Moore, F. B. Phleger, J. G. Sclater, Tj . H. van Andel, and E. L. Winterer read the manuscript and made valuable suggestions for improvement. This research was supported by the Oceanography Section, National Science Foundation Grant GB-21259.

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M A N U S C R I P T R E C E I V E D BY T H E S O C I E T Y N O V E M B E R

7, 1972



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Cenozoic Sedimentation in the Eastern Tropical Pacific