Late Miocene biogeography and paleoclimatology of the central North Atlantic

Marine Micropaleontology, 6 (1981): 599--616

599

Elsevier Scientific Publishing Company, Amsterdam - - P r i n t ed in The Netherlands

LATE MIOCENE B I O G E O G R A P H Y A N D P A L E O C L I M A T O L O G Y OF THE C E N T R A L N O R T H ATLANTIC

RICHARD Z. POORE

U.S. Geological Survey, 345 Middlefield Road, Menlo Park, Calif. 94025 (U.S.A.) (Revised version received July 6, 1981; approved July 14, 1981)

Abstract Poore, R.Z., 1981. Late Miocene biogeography and paleoclimatology of the central North Atlantic. Mar. Micropaleontol., 6: 599--616. Quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project (DSDP) Holes 334 and 410 demonstrate that subpolar and subtropical faunal provinces existed in the North Atlantic during the late Miocene. Climatic oscillations are clearly recorded in Hole 410 by variations in abundance of the Neogloboquadrina subpolar assemblage. These climatic oscillations have a period of about 1 m.y. Higher frequency oscillations with a periodicity of one to several hundred thousand years are evident from about 6.5 to 7.5 m.y. and are probably present throughout the entire late Miocene. A revised age of 7.0 m.y. is proposed for the first occurrence of the calcareous nannofossil Amaurolithus primus (the Amaurolithus datum).

Introduction Planktonic foraminifers are widely used to derive paleoclimatic and paleoceanographic information from deep4ea sediments. Quantitative studies of entire planktonic foraminifer assemblages have been particularly useful in deciphering the Quaternary record (e.g., Imbrie and Kipp, 1971; Kennett and Huddleston, 1972; Briskin and Berggren, 1975; CLIMAP, 1976) and are beginning to be used in the Tertiary (e.g., Thunell, 1979). Most studies of pre4~uaternary planktonic foraminifers aimed at paleoclimatology, however, are semiquantitative (e.g., Poore and Berggren, 1974} or focus on selected elements of the fauna, such as coiling ratios of a particular taxon or the variation in abundance of a particular taxon, to generate paleoclimatic trends (e.g., Ingle, 1973; Kennett and Vella, 1975; Keller, 1978). Increasing numbers of

pre-Quaternary marine sections in different areas of the world's oceans are becoming available due to efforts of the Deep Sea Drilling Project (DSDP). Availability of these sections provides opportunity for detailed investigations of pre-Quaternary climates within and between ocean basins. Use of quantitative data for such studies is desirable to aid comparison of studies done in different areas or by different workers. In this study quantitative data on late Miocene planktonic foraminifers in North Atlantic DSDP cores are used to delineate climatic trends in the North Atlantic Basin. Holes 410 and 334 (Fig. 1) were selected for time-series study because they recovered relatively complete late Miocene sequences that are not complicated by marked dissolution or redeposited sediments. Late Quaternary studies (CLIMAP, 1976) indicate that Site 410 is located in an area that shows

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significant changes between glacial and interglacial periods. Site 410 is thus well located to monitor climatic changes occurring during the late Miocene. In addition, the floras and faunas of Holes 410 and 334 contain enough low-latitude biostratigraphic markers to allow relatively confident dating. In the following sections samples are often referred to by the standard DSDP notation. For example, a sample notation of "158-35-2, 30--32 c m " means Hole 158, Core 35, section 2, 30--32 cm below the top of the section. Hole designation is often obvious from cont e x t and therefore it is usually omitted. Samples from Holes 410 and 334 are also referred to in terms of depth below sea bottom (in meters) and sample number of this study in figures and tables. Sample number, DSDP designation and depth below sea bot-

The work of Kipp (1976) provides a wealth of data on modern distribution patterns of planktonic foraminifers in the North Atlantic. Kipp's distributional data are based on analysis of numerous core-top samples throughout the North Atlantic basin. Unlike plankton tow data, which record conditions during a brief interval of time, data from core-top samples reflect conditions averaged over tens or hundreds of years and thus provide a much better modern analog for data from Miocene core samples. Fig. 2 shows relative abundance of comm o n species and species groups along a north--south transect of selected North Atlantic core-top samples from Kipp (1976). The transect was chosen to pass near the DSDP sites considered in this study (Fig. 1), and samples were chosen to provide reasonable sample density while avoiding highly dissolved assemblages. Core-top samples adjacent to those samples chosen for the transect were checked to ensure that the patterns and trends shown on Fig. 2 are representative of the central North Atlantic. High variability found in the area of 30°N was smoothed by averaging values for cores 2, 91, and 108. In tabulating the data for the transect from Kipp (1976, appendix I) several species and forms were grouped. Left- and right-coiling Globigerina pachyderm°, "P--D intergrade" and Globoquadrina dutertrei were tabulated under Neogloboquadrina; left- and rightcoiling Globorotalia truncatulinoides were combined; G. menardii and G. tumida were combined; and all representatives of Globigerinoides except G. sacculifer were tabulated under Globigerinoides spp.

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Fig. 2. C o m p o s i t i o n of p l a n k t o n i c f o r a m i n i f e r assemblages ( > 1 4 9 u m ) in m o d e r n c o r e - t o p samples in a n o r t h - - s o u t h t r a n s e c t o f the N o r t h A t l a n t i c Ocean. L o c a t i o n s of c o r e - t o p samples are o n Fig. 1~ Data are f r o m Kipp ( 1 9 7 6 ) .

Most of the assemblages delineated by Kipp's more extensive data set are recognizable in the transect. Samples 197 and 221, which consist of Neogloboquadrina and, in sample 221, a substantial a m o u n t of Turborotalita quinqueloba, represent the polar assemblage. Samples 218 through 208, which consist primarily of Neogloboquadrina, Globigerina bulloides, Globigerinita glutinata and Globorotalia inflata, represent the subpolar

assemblage. Samples 1 through 26 containing significant amounts of Globigerina bulloides, G. falconensis, Globorotalia inflata and G. truncatulinoides are referable to the subtropical assemblage whereas the remaining samples, which are dominated by Globigerinoides spp. (here G. ruber) and G. sacculifer, are referable to the tropical assemblage. The transect data do not allow discrimination of the gyre margin assemblage or the transitional assemblage of Kipp (1976). Grouping of species and plotting data in a transect obscures some of the detail in Kipp's study. Nonetheless, the trends shown on Fig. 2 provide a good model for interpreting late Miocene planktonic foraminifer assemblages of the central North Atlantic. Application of the model assumes that Miocene and Quaternary species included in the same categories have similar ecologic preferences. Especially striking features of Fig. 2 are the progressive dominance of the genus Neogloboquadrina at higher latitudes and the significant increase of the genus Globigerinoides south of about 30°N. These features should be evident in late Miocene faunas of the North Atlantic. Another feature shown on Fig. 2 is the cosmopolitan distribution of Globigerinita glutinata. Note that high- and low-latitude assemblages are dominated by a few taxa or counting groups. When diversity is tabulated from these quantitative data, faunas from mid-latitudes are more diverse than faunas from low latitudes. For example, Fig. 2 indicates that a sample from 40°N would have a diversity of 12 whereas a sample from 5°N would have a diversity of 9. In contrast, tabulations of total diversity indicate the tropics have the highest diversity (Stehli et al., 1969). Late Miocene chronology Sediment accumulation rate plots (Figs. 3 and 4) were used to assign ages to samples from Hole 410 and Hole 334. The time scale of Ryan et al. (1975) was used to construct these plots. Magnetic data indicate that Hole 410 is located on the old side of Anomaly 5 (Epoch

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Fig. 3. S e d i m e n t a t i o n rate diagram used t o date s a m p l e s f r o m Hole 410. Events or c o n t r o l p o i n t s used t o c o n s t r u c t the diagram are: E v e n t or c o n t r o l p o i n t

Highest u n e q u i v o c a l M i o c e n e F i r s t Amaurolithus primus = Amaurolithus d a t u m First Discoaster quinqueramus Base o f s e d i m e n t a r y s e c t i o n = base o f E p o c h 9

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9) (Luyendyk, Cann et al., 1978). D i s c o a s t e r Zone (CN 8 = NN 1 0 ) n a n n o fossils occur in Cores 30 through 32, whereas nannofossils from Cores 34 and 35 are less diagnostic and could represent the D i s c o a s t e r n e o h a m a t u s Zone or the D. hamatus Zone (CN 7 = NN 9) (Bukry, 1978; this study). neohamatus

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(m) Last Discoaster quinqueramus First Amaurolithus primus = Amaurolithus d a t u m Last Thalassiosira burckliana First Discoaster quinqueramus Last Coscinodiscus plicatus First Thalassiosira burckliana

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T i m e scale 1 (ts-1) was c o n s t r u c t e d using a date o f 6.2 m . y . B . P , for the Amaurolithus d a t u m . Time scale 2 (ts-2) was c o n s t r u c t e d using a d a t e o f 7.0 m . y . B . P , for the Amaurolithus d a t u m . T i m e scale 2 is p r e f e r r e d . See t e x t for discussion.

Ryan et al. (1975) show that the base of CN 8 (NN 10) is in mid Epoch 10. Nannofossil data from Hole 410 sediments are thus compatible with the magnetic data. The base of the sedimentary section in Core 35 of Hole 410 is considered to be at the base of Epoch 9 and is assigned an age of 10.3 m.y. The Miocene]Pliocene boundary in Hole 410 is within the upper part of Core 19 or

603 between Core 18 and Core 19. The highest unequivocal late Miocene sample (19-3, 92--93 cm; 173 m s u b b o t t o m ) i s assigned an age of 5.25 m.y. Other points used to construct Fig. 3 are the first appearances of Discoaster quinqueramus (top of core 28; 254.5 m subbottom) and Amaurolithus primus (within core 24; 222.5 m subbottom). Age estimates of 8.0 m.y. and 6.2 m.y. for these respective first appearances are from Haq et al. (1980). Several lines of evidence, however, suggest an age of about 7.0 m.y. for the first appearance of Amaurolithus primus, or the Amaurolithus datum. In DSDP Hole 158, the first appearance of Amaurolithus primus is in sample 17-5, 70--71 cm (Bukry, 1973), just above the first appearance of the diatom Nitzschia miocenica and the last appearance of the diatom N. porteri in sample 7-6, 30--32 cm (J.A. Barron, pers. comm., 1981). These diatom events have been paleomagnetically dated at 7.1 and 7.0 m.y. respectively (Burckle, 1978; i.e., mid Epoch 7). Similarly, the first occurrence of Amaurolithus primus in 13-6, in DSDP Hole 77B (Hays et al., 1972, p.87) closely coincides with the first appearance of Nitzschia miocenica and the last appearance of N. porteri in sample 13-6, 30--32 cm (J.A. Barron, pers. comm., 1981). Ryan et al. (1975) record the first appearance of Arnaurolithus (as Ceratolithus tricorniculatus) at the top of Epoch 7 in Core RC$2-65. This occurrence indicates an age greater than 6.5 m.y. for the first Amaurolithus. Further, Gartner {1973) and Ryan et al. (1975) record Amaurolithus primus (as C. tricorniculatus) within the top of Epoch 7 at the base of Core RC12-66. The data from RC12-66 indicate a minimum age of 6.6 m.y. for the Amaurolithus datum. The above evidence indicates that the age of the Amaurolithus datum may be 7.0, not 6.25 m.y. Both age estimates are used, however, to provide alternative time scales for the youngest part of the Miocene section in Holes 334 and 410. Calcareous nannofossil data from Bukry {1977) and diatom data from Schrader (1977) and J.A. Barron (pers. comm., 1980)

were used to date Hole 334 (Fig. 4). Nannofossil events used are the last appearance of Discoaster quinqueramus between 2-1 and 2-3 (130 m subbottom), the first appearance of Amaurolithus between 3-2 and 4-1 (135 m subbottom) and the first appearance of Discoaster quinqueramus between 7-1 and 7-5 (181 m subbottom). Age estimates for the first and last appearance of Discoaster quinqueramus are from Haq et al. (1980}. The two age assignments for the Amaurolithus datum are discussed above. Diatom events are the last appearance of Thalassiosira burckliana in sample 5-4, 70-72 cm (162 m subbottom), the last appearance of Coscinodiscus plicatus in sample 7-6, 70--72 cm (185 m subbottom), and the first appearance of T. burckliana in sample 12-3, 60--62 cm (228 m subbottom). Dates of 7.6, 8.3, and 8.7 m . y . B . P , for these events are from Burckle (1978). Note that depending upon the age estimate used for the Amaurolithus datum, a hiatus or significant change in accumulation rate occurs in Hole 334 between 140 and 160 m subbottom. The hiatus or accumulation rate change probably coincides with the top of siliceous sediments between Cores 3 and 4. Late Miocene faunal data

A microsplitter was used to obtain counting splits of about 300 planktonic foraminifers ~> 149 pm from Hole 410 and Hole 334 samples. Individuals in each counting split were separated into counting categories, and the counts were converted to relative abundances (Appendices III and IV}. In many cases morphologically similar "species" and species thought to be closely related and thus having similar ecologic preferences were included in one counting category. This grouping was done to avoid disjunct trends in species distribution caused by evolutionary changes during the late Miocene and between late Miocene and Quaternary. The grouping also helps avoid operator error in consistently identifying specimens in a highly variable plexus such as Neogloboquadrina. Counting categories are outlined in Table I, and distri-

604 TABLE I Counting categories for late Miocene planktonic foraminifer assemblages in samples from Holes 410 and 334 Counting category

Abbreviation

Included taxa

Orbulina spp. Globigerina bulloides

Ospp Gbul

Globigerina falconensis Globigerina woodi

Gfal Gwoo

Neogloboquadrina spp.

Neog

Glo boro talia scitula

Gsci

Globorotalia menardii Globorotalia conomiozea Globorotalia margaritae Globoquadrina altispira Globoquadrina dehiscens Globogerinita glutinata Globigerinoides sacculifer Globigerinoides spp.

Gmen Gcon Gmar Gait Gdeh Gglu Gsac Gspp

Sphaeroidinellopsis spp. Turborotalita spp.

Sspp Tspp

all species of Orbulina Globigerina bulloides (d'Orbigny), G. praebulloides Blow, G. pseudobesa (Salvatorini) Globigerina falconensis Blow Globigerina woodi Jenkins, G. apertura Cushman, G. decoraperta Takayanagi and Saito, G. nepenthes Todd, G. druryi Akers Neogloboquadrina acostaensis (Blow), N. atlantica (Berggren), N. pachyderma (Ehrenberg) (s.1.), N. hurnerosa (Takayanagi and Saito), Globorotalia continuousa Blow Globorotalia scitula (Brady), G. suterae Catalano and Sprovieri, G. subscitula Conato, G. lenguaensis Bolli, G. cibaoensis Bermudez, G. ventriosa Ogniben all G. menardii-like keeled globorotaliids Globorotalia conomiozea Kennett, G. conoidea Walters Globorotalia margaritae Bolli and Bermudez, G. praehirsuta Blow Globoquadrina altispira (Cushman and Jarvis) Globoquadrina dehiscens (Chapman, Parr, and Collins) Globigerinita glutlnata (Egger) (s.1.), G. uvula (Ehrenberg) Globigerinoides sacculifer (Brady) (s.l.) Globigerinoides obliquus Bolli (s.1.), G. tuber (d'Orbigny), G. bulloideus Crescenti, G. bollii Blow, G. kennetti Keller and Poore Sphaeroidinellopsis subdehiscens (Blow), S. serninulina (Schwager) Turborotalita quinqueloba (Natland), Globigerina angustiumbilicata

Catapsydrax parvulus Other

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Catapsydrax parvulus Bolli, Loeblich, and Tappan other taxa and unidentified specimens

b u t i o n o f selected c a t e g o r i e s are p l o t t e d in Figs. 5 a n d 6. In t h e f o l l o w i n g discussions c o u n t i n g c a t e g o r y labels are used t o r e f e r t o all species a n d species g r o u p s i n c l u d e d in t h a t c a t e g o r y . T h u s Globorotalia m e n a r d i i in discussion o f H o l e 3 3 4 or H o l e 4 1 0 assemblages refers to all k e e l e d G. menardii-like Globorotalia. In a d d i t i o n to q u a n t i t a t i v e d a t a o n p l a n k t o n i c f o r a m i n i f e r s , e s t i m a t e s o f t h e relative a b u n d a n c e o f the c a l c a r e o u s n a n n o f o s s i l C o c c o l i t h u s pelagicus was d e t e r m i n e d f o r samples from Hole 410. Haq (1980)found t h a t t h e a b u n d a n c e o f C o c c o l i t h u s pelagicus in M i o c e n e n a n n o f o s s i l a s s e m b l a g e s is a reliable climatic i n d e x ; high a b u n d a n c e s represent cool conditions. The abundance of C o c c o l i t h u s pelagicus was d e t e r m i n e d in s m e a r slides f r o m H o l e 4 1 0 b y c o u n t i n g t w o 1 0 0 - s p e c i m e n traverses. Results p l o t t e d o n Fig. 5 r e p r e s e n t an average f o r the t w o traverses.

Fig. 5 and A p p e n d i x I I I s h o w t h a t late M i o c e n e p l a n k t o n i c f o r a m i n i f e r assemblages f r o m H o l e 4 1 0 c o n t a i n significant n u m b e r s o f N e o g l o b o q u a d r i n a , Globigerina bulloides, G. w o o d i , Globorotalia scitula a n d G. rnenardii. N e o g l o b o q u a d r i n a is usually the m o s t abundant taxon and shows four broad abund a n c e p e a k s c e n t e r e d a r o u n d 180, 235, 265 a n d 310 m s u b b o t t o m . Globigerina w o o d i a n d Globorotalia m e n a r d i i t e n d t o v a r y inversely w i t h N e o g l o b o q u a d r i n a , w h e r e a s variat i o n s in Globigerina bulloides and Globorotalia scitula are n o t o b v i o u s l y r e l a t e d to changes in o t h e r t a x a . Fig. 6 and A p p e n d i x IV s h o w t h a t late M i o c e n e p l a n k t o n i c f o r a m i n i f e r assemblages f r o m H o l e 3 3 4 c o n t a i n significant n u m b e r s o f N e o g l o b o q u a d r i n a , Globigerina bulloides, G. w o o d i and Globorotalia rnenardii. Globigerinoides spp. is also a c o n s i s t e n t c o m p o n e n t o f H o l e 3 3 4 assemblages. T h e inverse v a r i a t i o n o f N e o g l o b o q u a d r i n a w i t h

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Fig. 5. Relative a b u n d a n c e o f selected p l a n k t o n i c foraminifers, b e n t h i c f o r a m i n i f e r s and f r a g m e n t a t i o n i n d e x in c o u n t i n g splits f r o m DSDP Hole 410 samples. F r a g m e n t a t i o n i n d e x was calculated as n u m b e r o f f r a g m e n t s / total n u m b e r of foraminifers. Relative a b u n d a n c e o f b e n t h i c f o r a m i n i f e r s was calculated as n u m b e r o f b e n t h i c f o r a m i n i f e r s / t o t a l foraminifers. Relative a b u n d a n c e o f Neogloboquadrina pachyderma s.1. is p l o t t e d in Neogloboquadrina field. C o m p o s i t i o n o f o t h e r c o u n t i n g groups is e x p l a i n e d in Table I. Relative a b u n d a n c e of the c o c c o l i t h Coccolithus pelagicus o f total n a n n o f o s s i l assemblage was d e t e r m i n e d f r o m smear slides. A = Arnaurolithus d a t u m ; B = first o c c u r r e n c e of Discoaster quinqueramus. Scale bar is the same for all plots.

Globorotalia menardii in Hole 4 1 0 also occurs in Hole 334. Globigerina falconensis also t e n d s to vary inversely w i t h Neogloboquadrina in these assemblages. V a r i a t i o n s in Globigerina bulloides, G. woodi, Globorotalia scitula, Globigerinoides spp. and G. sacculifer

do n o t a p p e a r related to changes in o t h e r taxa. G r o s s c o m p a r i s o n o f assemblages s h o w n on Figs. 5 a n d 6 reveals t h a t H o l e 334 assemblages are d e p l e t e d in Neogloboquadrina a n d Globorotalia scitula with r e s p e c t to Hole 4 1 0

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Fig. 6. Relative a b u n d a n c e of s e l e c t e d p l a n k t o n i c f o r a m i n i f e r s , b e n t h i c f o r a m i n i f e r s a n d f r a g m e n t a t i o n i n d e x in c o u n t i n g splits f r o m D S D P Hole 334 samples. F r a g m e n t a t i o n i n d e x was c a l c u l a t e d as n u m b e r of f r a g m e n t s / t o t a l n u m b e r o f f o r a m i n i f e r s . Relative a b u n d a n c e of b e n t h i c f o r a m i n i f e r s was c a l c u l a t e d as n u m b e r o f b e n t h i c foramin i f e r s / t o t a l f o r a m i n i f e r s . C o m p o s i t i o n of o t h e r c o u n t i n g g r o u p s is e x p l a i n e d in T a b l e I. A = A m a u r o l i t h u s d a t u m ; B = first o c c u r r e n c e of D i s c o a s t e r q u i n q u e r a m u s . Scale bar is t h e same for all plots.

assemblages. Moreover, Hole 334 assemblages are enriched in Globigerinoides spp., G. sacculifer and, in the lower part of the section, Globorotalia menardii. These observations are consistent with the north--south

trends shown by m o d e m data in Fig. 2. Hole 334 late Miocene assemblages closely resemble m o d e m subtropical assemblages and Hole 410 late Miocene assemblages resemble m o d e m subpolar assemblages. A

607

notable anomaly, however, is the common occurrence of Globorotalia menardii in both Holes 334 and 410. Globorotalia menardii is not recorded poleward of about 30°N latitude in modern sediments of the central North Atlantic. But at Holes 334 and 410, which are at 37°N and 45°N, respectively, the relative abundance of Globorotalia menardii often approaches and sometimes exceeds 20% of the late Miocene planktonic foraminifer assemblages. Keeled Globorotalia are resistant to dissolution (Berger, 1968), and concentration caused by dissolution might explain some of the abundance and variation of Globorotalia menardii in Holes 334 and 410. The fragmentation index and relative abundance of benthic foraminifers, which are indicators of dissolution intensity, do not correlate with the variations of Globorotalia menardii (Figs. 5 and 6). Dissolution, therefore, does not explain the abundant occurrence and variation of Globorotalia menardii in Holes 334 and 410. Although Globorotalia menardii is not recorded north of about 30°N latitude in modern sediments of the central and eastern North Atlantic, it does occur in low abundances at higher latitudes in the western North Atlantic. In addition, areal distribution m a r s of Kipp (1976) show tongue-like extensions of moderately high abundances (<10%) of Globorotalia menardii and Globigerinoides sacculifer out into the North Atlantic from the east coast of North America at about 40°N latitude. These tongue-like extensions, which help characterize a gyre margin assemblage (Kipp, 1976, fig. 27), are associated with Gulf Stream flow but do not reach as far east as Sites 334 and 410. But, occurrence of abundant Globorotalia menardii in the late Miocene of Holes 334 and 410 cannot be explained by simple increased extension of the Gulf Stream out into the North Atlantic during the late Miocene because Globigerinoides sacculifer, which is a warm-water surface dweller, is essentially absent from Hole 410 and is usually sparse in Hole 334. Greatly increased

advection of warm surface waters into the region of Sites 334 and 410 by the Gulf Stream or its Miocene analog would also have transported significant numbers of Globigerinoides sacculifer into the area. Globorotalia menardii is a d e e p - r a t h e r than a shallow-dwelling planktonic foraminifer (B~, 1977) and the extension of moderately abundant G. menardii out into the modern North Atlantic reflects changes caused by the Gulf Stream in conditions at some depth in the water column, not variations in surface water conditions. Poore et al. (1980) indicate that the distribution of some deep-dwelling Globorotalia is at least partially controlled by water density. During the late Miocene the Isthmus of Panama was still open (Berggren and Hollister, 1974), and the salinity of the North Atlantic should have been lower than modern values. Lower salinity would result in lower density (at equivalent temperature) and, therefore, presumably allow deep-dwelling Globorotalia to survive at higher (cooler) latitudes with respect to modern conditions. A less saline late Miocene North Atlantic then might account for the occurrence of abundant Globorotalia menardii in Holes 334 and 410. This explanation would also account for the generally wide late Miocene distribution of Globorotalia menardii throughout the Atlantic basin noted by Cifelli and Glacon (1979). The Globorotalia menardii counting category used for the late Miocene in this study includes several species such as G. merotumida, G. pleisiotumida and G. limbata whereas the modern G. menardii category plotted on Fig. 2 only includes two species, G. rnenardii and G. tumida. Moreover, intergradation of representatives of the Globorotalia conomiozea plexus and G. menardiilike keeled globorotaliids in samples above 149 m subbottom (Cores 2--4) in Hole 334 and above 215 m subbottom (Cores 19--23) in Hole 410 makes consistent allocation of individuals to one counting category or the other difficult; reexamination of sorted slides invariably results in shifting some specimens

608 f r o m o n e c a t e g o r y t o t h e o t h e r . T h e relatively a b u n d a n t o c c u r r e n c e o f Globorotalia menardii in Holes 3 3 4 and 4 1 0 m a y be a f u n c t i o n o f t h e greater t a x o n o m i c c o m p l e x i t y a n d t h u s wider e n v i r o n m e n t a l tolerances o f G. menardii-like f o r m s in the late Miocene as c o m p a r e d t o the H o l o c e n e . F o r e x a m p l e , did late Miocene Globorotalia menardii-like f o r m s o c c u p y niches p r e s e n t l y o c c u p i e d b y G. truncatulinoides and G.

hirsuta? In s u m m a r y , f l u c t u a t i o n s in t h e o c c u r r e n c e o f Globorotalia menardii at Holes 4 1 0 a n d 3 3 4 are p r o b a b l y partially due to changes in i n t e n s i t y o f the late M i o c e n e G u l f Stream. T h e a b u n d a n c e o f Globorotalia menardii, h o w e v e r , indicates o t h e r f a c t o r s such as variations in salinity a n d greater t a x o n o m i c c o m p l e x i t y o f the G. menardii g r o u p were i m p o r t a n t for c o n t r o l l i n g its d i s t r i b u t i o n . Principal c o m p o n e n t s analysis Q - m o d e principal c o m p o n e n t s analysis was used to f u r t h e r investigate the s t r u c t u r e o f variation in faunal d a t a f r o m Holes 4 1 0 and 334. P e r c e n t a g e d a t a given in A p p e n d i c e s I I I a n d IV were a n a l y z e d with the C A B F A C p r o g r a m o f K l o v a n and I m b r i e ( 1 9 7 1 ) . Analysis o f Hole 4 1 0 d a t a d e t e c t e d three principal c o m p o n e n t s with eigenvalues greater t h a n one. C o n t r i b u t i o n o f species to the first three principal c o m p o n e n t s (Principal C o m p o n e n t s Scores) for Hole 4 1 0 are given in Table II. The first principal c o m p o n e n t describes deviation o f samples f r o m an average sample ( L o h m a n n , 1 9 7 8 ) a n d it is n o t c o n s i d e r e d f u r t h e r . The s e c o n d principal c o m p o n e n t c o n t r a s t s samples with a b u n d a n t Neogloboquadrina with samples c o n t a i n i n g a b u n d a n t Globorotalia menardii, a n d t o a lesser e x t e n t , Globigerina woodi. This relation is s h o w n b y t h e large negative c o n t r i b u t i o n o f Neogloboquadrina, the large positive c o n t r i b u t i o n o f Globorotalia menardii and the m o d e r a t e positive c o n t r i b u t i o n o f Globigerina woodi to PC 2 in Table II. T h e s e c o n d principal c o m p o n e n t t h e n describes the t r e n d n o t e d in Hole 4 1 0 d a t a b y i n s p e c t i o n o f Fig. 5. T h e t h i r d principal c o m p o n e n t c o n t r a s t s samples with a b u n d a n t

TABLE II Principal Components Scores of first three principal components for Hole 410 (large positive or negative values for a counting category means that group is an important contributor to the principal component) PC-1 Ospp Gbul Gfal Gwoo Neog Gsci Green Gcon Gmar Gait Gglu Gsac Gspp Sspp Tspp Cpar othr

0.02 0.43 0.11 0.40 0.70 0.26 0.25 0.03 0.02 0.00 0.12 0.01 0.02 0.00 0.01 0.01 0.06

Eigenvalue 34 Variance (%) 83

PC-2

PC-3

0.00 0.11 0.13 0.29 -0.54 0.01 0.76 0.11 0.05 0.01 0.04 --0.02 0.01 0.00 --0.01 --0.01 0.01

0.00 --0.01 0.10 0.70 --0.35 0.30 --0.53 -0.08 0.01 --0.01 0.08 0.01 0.01 0.00 -0.01 0.01 0.03

3.4 8

1.7 4

TABLE III Principal Components Scores of first two principal components for Hole 334 (large positive or negative values for a counting category means that group is an important contributor to the principal component); note that the eigenvalue of PC 2 is less than one PC-1 PC-2 Ospp Gbul Gfal Gwoo Neog Gsci Gmen Gcon Gmar Gdeh Galt Gglu Gsac Gspp Sspp Tspp Cpar othr

0.06 0.44 0.20 0.61 0.44 0.19 0.24 0.02 0.02 0.00 0.01 0.17 0.08 0.21 0.02 0.01 0.00 0.14

Eigenvalue 18.3 Variance (%) 87

0.00 0.13 0.24 --0.07 -0.52 -0.02 0.74 0.06 0.00 0.00 0.00 0.17 0.01 --0.26 0.00 0.02 -0.01 0.08 0.9 4.2

609

Globigerina woodi with samples containing Globorotalia menardii and/or Neogloboquadrina. Analysis of Hole 334 data delineated one principal component with an eigenvalue greater than one and one principal component with an eigenvalue of 0.9. Contributions of species to the first two principal components for Hole 334 are given in Table III. The first principal component is not considered further for the reasons given above. The second principal component of Hole 334, which contrasts samples containing Neogloboquadrina with those containing Globorotalia menardii, resembles the second principal component of Hole 410. Inspection of both percent species plots and principal components analysis show that the antithetic variation of Neogloboquadrina and Globorotalia rnenardii is the pervasive signal in data from Holes 410 and 334.

gross comparison of Figs. 5 and 6, I infer that the increases in abundance of Neogloboquadrina represent equatorward migration of subpolar surface waters and thus cool events. Similarly, the decreases in abundance of Neogloboquadrina coupled with the increases in abundance of Globorotalia rnenardii represent poleward migration of subpolar surface waters and thus warm events. ']?he second principal c o m p o n e n t of Holes 410 and 334 contrasts samples that are more subpolar with samples that are less subpolar, or more influenced by the distal end or fringe of the Gulf Stream. The assemblage identified by PC 3 of Hole 410 as being characterized by the abundance of Globigerina woodi, and to a lesser extent Globorotalia scitula and absence of Neogloboquadrina and Globorotalia menardii, is interpreted as temperate or cool subtropical assemblage. This interpretation is based on the tendency for Globigerina woodi to positively covary with Globorotalia menardii in PC 2 of Hole 410 and on the overall increase in abundance and stability of G. woodi in Hole 334 assemblages with respect to Hole 410 assemblages. Furthermore, the species Globigerina woodi is by far

Paleoclimatic interpretation By analogy with m o d e m data shown on Fig. 2 and n o r t h ~ o u t h trends evident by

HOLE 4t0 ts-2

tS- ]

F

-40 -20 0 ~7 ~ --

+ 2 0 + 4 0 +60 I

¢

--40 --20 I I

0 +20 +40 N! r

--40 - 2 0 I

0

+20 +40 +60

I

Pc 2

I

N .....

40 --20

]

T

6~

__

..£ "-~

E

%

~

~

~=:~L~--

EsL

~ -~,

9r

]

PC 3

7~

<

~

'

6 ~-

a: i 8~

+20 +40

PC 2 "~-

7"

0

1

,\eogloboquadrma s

~l-(;Iobc~rota/~,7men,zrdll

p

p

.

,

\

~,~

~

10F

--

i

~ ~. •

°

(;h;borolaha menardu --,~rogloboquadrina spp

,'

•

~-

L l

i

l ....

I

I

1

1 |

i

I

OI _ _ l

'

- - ( , oborohdul metrard~t \~<,~loboquadrm.spp

~

"

"~' ~

•

+(;z,,b,e~,,.,,, ze,.,d, l 1 •

i

'

"~

Fig. 7. S t r a t i g r a p h i c d i s t r i b u t i o n o f s e c o n d (PC-2) a n d t h i r d (PC-3) p r i n c i p a l c o m p o n e n t s o f H o l e 4 1 0 p l o t t e d a g a i n s t t h e t w o t i m e scales s h o w n o n Fig. 3. V a l u e s p l o t t e d are p r i n c i p a l c o m p o n e n t s l o a d i n g s t i m e s 100. T i m e scale 2 (ts-2) w h i c h uses a d a t e o f 7.0 m . y . B . P , f o r t h e A m a u r o l i t h u s d a t u m is p r e f e r r e d .

610

noted in Fig. 5 are evident in the plot of PC-2 on Fig. 7. Large negative values of PC-2 indicate abundant Neogloboquadrina, or the subpolar assemblage. Excursions to the left for PC-2 on Fig. 7 reflect cool events, or equatorward migration of subpolar waters, whereas excursions to the right reflect warm events. The plot of 410 PC-2 suggests the presence of a million-year cycle. Cold events occur at a b o u t 9.5, 8.5, 7.5, and 5.5 m.y. B.P. A subdued cold event may be present near 6.5 m . y . B . P . In contrast well~lefined warm intervals occur around 9, 8, 7, and 6 m . y . B . P . The point at 10 m . y . B . P , also

the dominant form in the counting category and regional studies in the southern ocean (Kennett, 1973; Kennett and Vella, 1975) have shown that the species Globigerina woodi is a temperate or cool-subtropical indicator. Principal components loadings for Hole 410 and 334 samples are plotted against time in Figs. 7 and 8. As explained previously, time scale 2 (ts-2), which adopts an age of 7.0 m.y. for the Amaurolithus datum, is preferred. The following discussion pertains only to plots for ts-2. The four broad Neogloboquadrina peaks

HOLE 0,34

m-2

ts-]

-40 5

I

-20

+23

0

--I

-~-

-

-40

+40

I

5

-20

0

+20

I

I

I

+40

pc-2

pc-2

m

cd

~. 7

7-+Globorotalia menardii

v

I

8

I

[

[

I

I

I

I

I

I

Fig. 8. S t r a t i g r a p h i c d i s t r i b u t i o n of s e c o n d p r i n c i p a l c o m p o n e n t (PC-2) o f Hole 334 p l o t t e d against t h e t w o t i m e scales s h o w n o n Fig. 4. Values p l o t t e d are p r i n c i p a l c o m p o n e n t s loadings t i m e s 100. T i m e scale 2 (ts-2) w h i c h uses a date of 7.0 m . y . B . P , for t h e A r n a u r o l i t h u s d a t u m is p r e f e r r e d .

611 appears to represent a warm interval. Evidence of higher frequency cycles superimposed on this million-year cycle occur in the interval of high sample density between 6.5 and 7.5 m . y . B . P . Occurrence of high frequency cycles in this interval indicates that cycles with wavelengths of one to several hundred thousand years may exist throughout the entire record. Climatic cycles of about 100,000 years that correlate with variations in the eccentricity of the earth's orbit are well documented in the late Quaternary (e.g., Hays et al., 1976). Thus, the identification of high-frequency climatic cycles with a periodicity of a b o u t 100,000 years in Hole 410 suggests that variations in the earth's orbital parameters influenced global climate cycles back into the late Miocene. In fact, Dean et al. (1981) report carbonate dissolution cycles that are similar to frequencies of other parameters of the earth's orbit back into the Eocene. No cause for the 1-m.y. cycle is apparent at this time. There is, however, evidence for climatic cycles with a periodicity of about I m.y. in late Miocene records from the North Pacific (see below) which suggests that the 1-m.y. cycle is a global feature. The plot of PC-3 on Fig. 7 shows the distribution of the temperate assemblage in Hole 410. Near-zero or negative values occur during maximum negative values for the subpolar assemblage and reflect exclusion of the temperate assemblage during southward migration of subpolar waters or cool intervals. Samples representing warm intervals at Hole 410 contain a mixture of the temperate and Globorotalia menardii assemblage. Note that below 7 m.y. the Globorotalia menardii and Globigerina woodi assemblages show positive correlation whereas between 6 and 7 m.y. they show negative correlation. The interval between 6 and 7 m.y. is where problems were encountered in separating the Globorotalia menardii plexus from the G. conomiozea plexus. Thus, the change seen at 7.0 m.y. may reflect taxonomic problems in the Globorotalia rnenardii counting category.

The plot of PC-2 of Hole 334 (Fig. 8) is very noisy, and no clear indications of a million-year cycle axe evident. The cool event shown at the end of the Miocene seems to match the record of Hole 410, but correlation of the rest of the Hole 334 record with that of Hole 410 is equivocal. The eigenvalue for PC-2 of Hole 334 is small (0.9) and thus the variability measured by PC-2 is small. The relatively low variability of Hole 334 late Miocene assemblages shown on Fig. 6 suggests that Site 334 was located within a stable gyre throughout this time. The gyre was expanded with respect, to the modern North Atlantic gyre. Cool events affecting Hole 410 did not significantly affect Hole 334.

Coccolithus pelagicus abundance The relative abundance of Coccolithus pelagicus is plotted adjacent to the relative abundance of Neogloboquadrina for Hole 410 samples in Fig. 5. Following the interpretations discussed above, the Coccolithus pelagicus abundance curve is expected to parallel the Neogloboquadrina curve if C. pelagicus is an indicator of cool conditions. The plot on Fig. 5 shows that the two curves match between about 170 and 290 m subbottom although the Coccolithus pelagicus curve is subdued from 170 to 210 m. The curves do not show good correspondence in the b o t t o m part of the section. The abundance peak at about 310 m subbottom in Neogloboquadrina does not show up at all in the Coccolithus pelagicus curve. Explanation for the change in behavior of the Coccolithus pelagicus curve is not clear. One possibility is that changes in intensity of dissolution affects the character of the Coccolithus pelagicus plot. The fragmentation and percent benthic foraminifer indices (Fig. 5) do not, however, support such a conclusion. Another possible explanation is that the abundance of Coccolithus pelagicus is governed by a threshold effect. Perhaps the abundance of C. pelagicus increases slowly until a critical value is reached and then increases greatly upon further cooling.

612 Regardless of the explanation, the results of this study indicate a simple model equating the abundance of Coccolithus pelagicus to temperature should be used with caution for mid-latitude regions of the North Atlantic. North Atlantic and North Pacific comparisons Evidence for a million-year cycle, noted in this North Atlantic study, is also present in studies of nannofossil assemblages in the Pacific Basin. The pattern is most clearly illustrated in the record of DSDP Site 77B ( L o h m a n n and Carlson, 1980). At equatorial Pacific Site 77B, nannofossil assemblages show warm events at about 10, 9, 8, 7, and 6 m . y . B . P . In contrast to the pattern from Hole 410, another warm peak occurs in Hole 77B at 5.5 m . y . B . P . Equatorial Pacific Sites 158, 208, and 71 show similar oscillations, but the timing of warm peaks in different sites is variable ( L o h m a n n and Carlson, 1980). Differences in timing of warm peaks between equatorial Pacific sites and North Atlantic Site 410 may be due to different sampling density and use of different assumptions in constructing time scales. The important feature of the records from Sites 77B, 71, 158 and 208 is that they show six or seven warm events within the late Miocene which is the number of events one would expect to find if a one million-year cycle existed. Study of late Miocene planktonic foraminifers from North Pacific mid-latitude DSDP Site 310 (Keller, 1980) shows at least four major cool events occurred during the late Miocene. The youngest two cool events seen at DSDP Site 310 correlate with the broad cool event seen in the youngest Miocene of Holes 410 and 334. Detailed comparison between North Atlantic and North Pacific records require generation of additional long records from the Atlantic as well as additional work on correlations between the two basins. Preliminary comparisons drawn above, however, indicate climatic trends in the two basins do have some c o m m o n features and may have been synchronous during at least parts of the late Miocene.

Summary and conclusions Quantitative analysis of planktonic foraminifer assemblages from Holes 410 and 334 demonstrate that subpolar and subtropical faunal provinces existed in the North Atlantic during the late Miocene. Planktic foraminifer assemblages from these late Miocene provinces show great similarity with modern subpolar and subtropical assemblages. Thus, modern mid- to high-latitude faunal provinces of the North Atlantic were established by the late Miocene. The general qualitative distribution of keeled Globorotalia as well as the relative abundance of keeled Globorotalia in Holes 410 and 334 suggests that the late Miocene North Atlantic was less saline than the modern North Atlantic. Climatic oscillations having a wavelength of about 1 m.y. occur during the late Miocene. These oscillations are most clearly recorded in Hole 410 by variations in abundance of the Neogloboquadrina subpolar assemblage. Higher frequency climatic oscillations having a periodicity of one to several hundred thousand years are probably present t h r o u g h o u t this time. These high-frequency climatic cycles are probably caused by cyclic variations in the earth's orbital geometry. Evidence for climatic oscillations with a million-year wavelength is present in the equatorial North Pacific and several warm and cool events in the mid-latitude North Pacific seem to correlate with similar events detected in the North Atlantic. The North Pacific and North Atlantic climatic records are synchronous for at least part of the late Miocene.

Acknowledgements I thank Gerta Keller and G.P. L o h m a n n for constructive criticism of this manuscript. I also thank John Barron for discussions of diatom biostratigraphy and for unpublished diatom data from Holes 158 and 77B. Samples for this study were provided by the Deep Sea Drilling Project.

613

Appendix I

Appendix II

S a m p l e n u m b e r o f this s t u d y , s t a n d a r d D S D P design a t i o n a n d d e p t h b e l o w sea b o t t o m in m e t e r s o f s a m p l e s f r o m Hole 4 1 0

S a m p l e n u m b e r of t h i s s t u d y , s t a n d a r d D S D P designat i o n a n d d e p t h b e l o w sea b o t t o m in m e t e r s o f s a m ples f r o m Hole 3 3 4

Sample

Sample

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3] 32 33 34 35 36 37 38 39 40 41

DSDP designation

19-3 19-6 20.2 21-3 21-6 22-2. 22-6 23-4 23-5 23 -6 23-6. 24-1 24-2 24-3 24 - 4 24-5 24-5, 24-6, 24-7 25-1 25-2 25-3 25-4 25-5 25-5 25-6 26-2 27-1 27-3 28-1 28-3 29-2 29-5 30-2 30-4 30-6 31-2 32-2 32-3. 34-2, 35-3,

91--93 cm 110--112cm 110--112cm 105--107cm 89-91 cm 29--31 cm 83--85 cm 118--120cm 103--105cm 48--50 cm 63-65 cm 10--12 cm 66-68 cm 98--100cm 103--105cm 60-62 cm 105--107cm 47-49 cm 27--29 cm 52--54 cm 101--103cm 84--86 cm 97-99 cm 72--73 cm 100--102cm 66-68 cm 57--59 cm 125--127cm 100--102cm 94--96 cm 93-95 cm 100--102em 10--12 cm 100--102cm 86--88 cm 100--102cm 54--56 cm 78--80 cm 140--142cm 70--72 cm 140--142cm

Depth below sea b o t t o m (m) 173.0 177.5 181.0 192.0 196.5 199.0 206.0 212.8 214.1 215.0 215.1 216.6 218.7 220.5 222.0 223.0 223.5 224.5 225.8 226.5 228.5 229.8 231.5 232.7 233.0 234.2 237.5 246.2 249.0 255.5 258.5 266.5 270.0 276.0 279.0 282.0 285.0 294.8 297.0 313.6 325.5

DSDP designation

Depth below sea b o t t o m

(m)

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

2-1 52--54 2-2 1 0 3 - - 1 0 6 2-4 10--12 2-6 1 0 3 - - 1 0 6 3-1 1 2 0 - - 1 2 2 3-2 1 3 8 - - 1 4 1 4-1 53--55 5-3 89--92 5-4 50--52 6-2, 4 6 - 4 8 7-2, 2 1 - - 2 3 7-5, 6 0 - - 6 3 8-2, 1 1 2 - - 1 1 4 9-3, 1 0 - - 1 2 9-4,119--122 10-4, 5 3 - - 5 4 11-1, 1 0 5 - - 1 0 7 11-3, 1 2 0 - - 1 2 3 12-3, 5 2 - - 5 4 13-5, 1 0 2 - - 1 0 5 14-1,108--110

cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm

130.0 132.0 134.1 138.0 140.2 142.0 149.0 162.0 163.0 169.5 178.5 183.5 189.0 199.0 202.0 210.5 216.0 219.0 228.0 241.0 244.5

614

Appendix

III

Planktonic foraminifer census data (percentage) from ~>149 # m counting splits of Hole 410 samples (total pf = total number of planktonic foraminifers in counting split; taxa codes are explained in Table I) Sample Total OSpp G b u l Gfal

Gwoo Neog G s c i Gmen Gcon Gmar Galt

Gglu

Gsac Gspp Sspp Tspp C p a r othr

pf

i ---

328

I

16

5

8

47

i0

4

2

!

0

5

0

0

0

0

0

I

2 ---

338

I

25

6

4

15

18

19

3

i

0

3

0

i

0

0

0

2

3 ---

324

i

22

6

6

44

6

8

2

2

0

I

0

I

0

0

0

i

4 ---

363

1

20

!

9

24

21

16

I

i

0

5

0

I

0

0

0

0

5 ---

351

2

Ii

i

7

32

6

26

4

i

0

7

0

0

0

i

0

i

6 ---

358

2

15

8

12

19

6

26

3

4

0

3

0

0

0

0

0

1

7 ---

344

I

17

7

18

16

i0

18

5

2

0

5

0

i

i

0

0

I

8 ---

327

0

15

8

23

17

13

8

3

4

0

4

0

2

0

I

0

2

9 ---

331

i

Ii

9

27

12

15

10

i

2

0

6

0

I

0

0

0

3

i0 ---

383

0

10

4

i0

13

5

44

7

0

i

2

0

i

0

0

0

2

ii

---

361

I

9

3

16

13

3

41

8

0

i

2

0

i

0

0

0

2

12 - - -

349

i

24

7

20

18

5

15

0

i

0

5

0

I

0

0

0

2

13 - - -

319

0

29

6

12

21

19

6

0

2

0

3

0

0

0

0

0

2

14 - - -

318

0

19

8

28

14

i

22

0

0

i

3

i

2

0

0

0

2

15 - - -

284

I

8

6

22

22

17

17

0

2

0

2

0

0

0

0

0

2

16 - - -

347

0

18

8

17

14

9

19

0

4

0

5

0

i

0

0

0

3

17 - - -

330

2

19

6

15

32

11

9

0

0

0

3

0

I

0

0

0

2

18 - - -

320

I

20

8

18

25

11

8

0

0

0

4

0

i

0

0

0

3

19 - - -

322

I

14

4

ii

44

20

i

0

0

0

2

0

i

I

0

0

I

20 - - -

326

0

21

2

25

35

10

0

0

0

0

4

0

i

0

0

0

2

21 - - -

315

i

22

6

16

35

9

]

0

0

0

5

0

0

i

2

0

3

22 - - -

316

I

22

i

18

36

16

0

0

0

0

2

0

2

0

0

0

2

23 - - -

317

i

12

i

24

34

21

1

0

0

0

3

0

2

0

0

0

2

24 - - -

323

1

13

5

17

40

16

0

0

0

0

4

0

1

0

i

0

1

25 - - -

366

I

12

3

16

39

19

0

0

0

0

5

0

I

0

I

0

3

26 - - -

313

0

15

I

10

30

19

16

0

0

0

3

0

2

0

0

0

4

27 - - -

306

i

29

i

6

50

3

0

0

0

0

4

0

2

0

I

0

3

28 - - -

316

3

21

3

15

32

3

9

0

0

0

11

0

1

0

i

0

2

29 - - -

344

i

22

5

16

22

6

12

0

0

0

8

0

i

i

3

0

4

30 - - -

321

1

13

5

24

22

3

16

4

0

0

9

0

1

0

0

0

2

31 - - -

313

0

28

2

12

37

3

11

0

0

0

2

i

1

0

i

0

3

32 - - -

344

i

5

3

12

52

6

7

0

0

0

2

i

0

0

7

0

4

33 - - -

308

2

24

2

4

40

10

6

0

0

0

5

3

i

0

i

0

3

34 - - -

297

i

11

2

17

39

12

3

0

0

0

4

3

2

0

i

I

3

35 - - -

306

4

18

i

21

19

17

3

i

0

0

I0

0

i

0

i

2

3

36 - - -

330

0

25

5

19

22

13

8

0

0

0

5

0

0

0

0

0

4

37 - - -

287

0

11

3

37

21

10

4

I

0

0

6

2

0

0

i

0

2

38 - - -

314

0

9

7

26

31

15

i

0

0

0

4

i

0

0

0

i

2

39 - - -

349

0

18

2

10

45

4

5

0

0

0

8

0

i

0

0

5

3

40 - - -

366

0

11

3

i0

60

4

I

0

0

0

4

2

I

0

0

0

3

41 ° - -

341

0

21

6

20

26

8

i

0

0

0

9

3

0

0

0

2

4

615

Appendix IV Planktonic foraminifer census data (percentage) from >149 ~m counting splits of Hole 334 samples (total pf = total number of planktonic foraminifers in counting split; taxa codes are explained in Table I) Sample

Total

OSpp

Gbul

Gfal

Gwoo

Neo9

Gsci

Gmen Gcon

Gmar

Gdeh

Ga!t

Gglu

Gsac

Gspp

Sspp

Tspp

Cpar

othr

pf

I ---

338

4

11

4

25

21

5

0

0

4

0

0

I

1

18

0

0

0

4

2 ---

414

i

23

7

21

22

7

1

0

4

0

0

3

0

7

0

0

0

3

3 ---

336

3

24

4 ---

297

4

22

5 ---

311

2

b

---

296

3

7 ---

332

2

8 ---

288

2

9 ---

296

3

i0

14

ii

i

0

0

0

0

5

0

8

0

0

0

5

5

28

14

18 4

~

0

1

0

]

i

I

16

1

0

0

2

13

8

21

7

3

17

9

4

0

l

5

1

3

0

0

0

5

18

12

23

8

i

13

0

3

0

0

5

4

6

0

0

0

3

16

5

16

20

8

8

4

0

0

2

~

1

13

0

0

1

2

9

6

37

25

6

0

4

0

0

0

1

0

5

1

0

0

4

16

13

16

16

8

13

0

0

0

0

4

0

4

2

0

0

5

10 - - -

288

4

17

2

25

15

4

8

0

0

0

0

I

8

4

1

i

5

Ii

---

283

2

18

6

16

14

2

i0

0

0

0

C

ii

1

7

0

1

0

i0

12 - - -

301

i

16

19

ii

8

i

0

0

0

l

12

i

13

0

i

0

5

13 - - -

324

2

18

6

20

14

5

16

0

0

0

[

5

0

5

0

0

0

7

14 - - -

312

2

I0

4

18

20

5

7

0

0

0

1

8

9

6

I

0

0

9

ii

II

6

15 - - -

301

1

13

8

18

6

17

0

0

0

C

8

3

8

0

i

0

4

16 - - -

318

3

13

5

25

7

5

15

0

0

0

i

7

i0

2

0

i

0

5

17 - - -

303

2

13

3

19

28

6

3

0

0

0

i

4

i0

6

i

0

0

4

18 - - -

284

I

12

i0

20

14

8

15

0

0

0

1

4

4

6

0

i

0

3

19 - - -

340

i

11

4

28

23

2

4

0

0

i

0

7

6

5

0

I

2

6

20 - - -

298

3

i0

6

21

12

20

7

0

0

i

0

6

4

4

1

0

0

4

21 . . . .

337

i

18

9

22

i0

7

8

0

0

i

i

9

4

3

0

0

0

8

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