Biogeographic patterns in terminal Cretaceous ... - Science Direct

MarineMicropaleontology, 18 ( 1991 ) 73-99

73

Elsevier Science Publishers B.V., Amsterdam

Biogeographic patterns in terminal Cretaceous planktonic foraminifera from Tethyan and warm Transitional waters Bj6rn A. Malmgren Department of Marine Geology, University of Grteborg, Box 7064, S-402 32 Giiteborg, Sweden (Received June 23, 1989; revised and accepted March 17, 1991 )

ABSTRACT Malmgren, B.A., 1991. Biogeographic patterns in terminal Cretaceous planktonic foraminifera from Tethyan and warm Transitional waters. Mar. Micropaleontol., 18: 73-99. Biogeographic patterns in terminal Cretaceous planktonic foraminifera have been analyzed from their faunal compositions at a time-slice spanning the upper parts of the calcareous nannofossil Micula prinsii Zone (approximately the latest 20-60 k.y. of the Cretaceous) at DSDP sites from low ( 16 ° ) through middle (37 ° ) paleolatitudes in either the Northern or the Southern Hemisphere. The study is based on relative abundance data of 26 species at Sites 356, 516F, 525A and 527 from the South Atlantic Ocean, Sites 384 and 548A from the North Atlantic and Sites 465A and 577A from the North Pacific. Cretaceous-Tertiary ( K - T ) boundary sections at Site 516F and 577A are poorly preserved, which prevented quantitative faunal analysis. Two major faunal assemblages, one Tethyan Assemblage and one Transitional Assemblage, are distinguished from the quantitative distribution patterns. The Tethyan Assemblage, dominating at Sites 465A, 356 and 384, is composed of Heterohelix striata, Globotruncana aegyptiaca, Pseudoguembelina kempensis, P. costulata, an undescribed form of Heterohefix with relict apertural flanges along medium suture, Rugoglobigerina hexacamerata and Trinitella scotti. Among these species P. kempensis, P. costulata and H. sp. exhibit enhanced abundances at Site 465A and constitute a Warm Tethyan Subassemblage, whereas R. hexacamerata and T. scotti, which are most abundant at Sites 356 and 384, represent a Cool Tethyan Subassemblage. Seven species show greater relative abundances at Sites 525A and 527 and are referred to a Warm Transitional Subassemblage: Abathomphalus mayaroensis, Gublerina cuvillieri, Pseudotextularia elegans, Rugoglobigerina rugosa, Racemiguembelina fructicosa, Globotruncana arca and Planoglobulina acervulinoides. In addition, an assemblage, marked by the Heterohelix glabrans-H, carinata complex, H. globulosa, GlobigerineUoides multispina and Rosita contusa, may represent a "shallower-water" subassemblage within warm Transitional waters (Site 548A ).

Introduction Temperature may be the main factor controlling distributions of marine organisms, but marine climatic zones are primarily based on distributions of organisms rather than on ocean temperatures (Hazel, 1970). One of the most important aspects of the study of paleobiogeographic history of fossil organisms is the mapping of geographic distributions of species assemblages at different times in the geologic past and the employment of fluctuations in such distributional patterns for inferences about

time-related dynamic changes in the climatic/ oceanographic system. Many studies have been carried out on the biogeographic evolution of various groups of planktonic microfossils in the Tertiary ocean. These studies were either based on analyses of continuous sections from different deep-sea sites (Haq et al., 1977 ), or a suite of selected time-slices, usually comprising sediments deposited during ½-1 m.y. ( 106 years), from some geographical transect (Haq, 1980; Hodell and Kennett, 1985; Kennett et al., 1985). Few quantitatively founded studies have dealt with biogeography of Cretaceous

0377-8398/9 !/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.

74

planktonic microfossils. Roth and Bowdler (1981), Roth and Krumbach (1986) and Thierstein ( 1981 ) analyzed calcareous nannofossil distributions at time-slices of a duration from some million years up to about 10 m.y. In the planktonic foraminifera, biogeographic provincialization probably existed since mid-Cretaceous time when the stock of globotruncanids, rotaliporids, hedbergellids and related forms underwent rapid diversification (Douglas, 1972; Berggren and Hollister, 1974). Scheibnerov~i ( 1971 ) established a series of Cretaceous foraminifer bioprovinces: a Tethyan (Tropical-Subtropical) Realm (Province in the terminology of Scheibnerov~i, 1971 ), a Boreal (cool Temperate) Realm in the Northern Hemisphere, an Austral Realm in the Southern Hemisphere (equivalent to the Boreal Realm) and a Transitional (warm Temperate) Realm, situated between the Tethyan and Boreal/Austral biogeoprovinces. Davids (1966) distinguished three planktonic foraminifer provinces in the North Atlantic, a Tethyan, a Temperate and a Boreal Realm, from fluctuations in relative abundances. Sli-

B.A. M A L M G R E N

ter (1972) identified a Tethyan, a Central, an Intermediate and a Boreal Realm from mapping of latitudinal distributional ranges of Campanian-Maastrichtian species in the North Pacific Ocean. An analogous provincial scheme was established by Sliter ( 1976 ) for the South Atlantic Ocean, but with a Transitional Realm replacing the Central and Intermediate Realms. Nyong (1984) and Olsson and Wise ( 1987 ) recognized a Transitional Realm in the Campanian-Maastrichtian of the North Atlantic. Masters (1977) provided general distribution charts tbr Cretaceous planktonic foraminifera. Sliter ( 1972, 1976) identified various assemblages that define the three major bioprovinces in the Late Cretaceous. The Tethyan Realm, extending between about 30°N and 30 ° S, is represented by the major single- and double-keeled globotruncanids and different genera of Heterohelicidae, including Pseudo-

textularia, Racemiguembelina, Planoglobulina, Guembelitria, Heterohelix and Gublerina (Sliter, 1972, 1976). Diminution of the relative abundance of two species, Trinitella scotti and Globotruncana aegyptiaca, may be useful

Fig. 1. Paleolocations in the early Paleocene ocean (about 60 Ma) of DSDP sites used in analyses of biogeographic patterns in terminal Cretaceous planktonic foraminifera (map is modified after Zachos and Arthur, 1986). White regions indicate submerged portions of the earth.

J-Anomaly Ridge 40 °N 52°W 3909 29°N (1) 3000 (4) 13-3,33 (5) 167.93 - 1 . 1 (4) - 0 . 8 (3) 0.4

S~o Paulo Plateau 28 °S 41 °W 3175 23°S (1) 1000 (2) 29-3,33 (2) 411.83

-7.5(1) - 6 . 2 (3)

2.5

Site 384

0.9-1.2

- 2 . 3 (3)

Southern Hess Rise 34 °N 179°E 2161 16°N (6,1) 1500 (7) 3-3,144 (6) 62.44

Site 465A

2.5

-7.6(9) - 6 . 0 (3)

30 °S 35°W 1313 30°S (1) 89-5,30 (8) 963.90

Rio Grande Rise

Site 516F

1.7

-5.0(12,13) - 4 . 1 (3)

29 °S 3°E 2467 36°S (1) 1000 (10) 40-2,11 (11) 451.71

Walvis Ridge

Site 525A

2.2

-6.6(12,13) - 5 . 9 (3)

28 °S 2°E 4428 36°S (1) 2700 (10) 32-4,50 (14) 280.00

Walvis Ridge

Site 527

1.5

-4.6(16) -

49 °N 12°W 1251 37°N (1) 200-500 (15) 28-7,40 (15) 471.40

Goban Spur

Site 548A

1.2

-3.5(18) - 2 . 4 (19)

32 °N 158°E 2675 17°N (1) 12-4,72 (17) 109.62

Shatsky Rise

Site 577A

*Distance below boundary. References: ( 1 ) Zachos and Arthur ( 1986); (2) Perch-Nielsen et al. ( 1977); (3) A. Henriksson (pers. commun., 1991 ); (4) Thierstein and Okada ( 1979); ( 5 ) Tucholke et al. ( 1979); (6) Vallier et al. ( 1981 ); (7) Boersma ( 1981 ); (8) Barker et al. ( 1983); (9) Hamilton and Suzyumov ( 1983); (10) Moore et al. (1984c); (11) Moore et al. (1984a); (12) Chave (1984); (13) Shackleton et al. (1984); (14) Moore et al. (1984b); (15) de Graciansky et al. ( 1985); (16) Townsend ( 1985); (17) Heath et al. ( 1985); (18) Bleil ( 1985); (19) Monechi (1985).

Latitude Longitude Waterdepth (m) Paleolatitude Paleodepth (m) K-T boundary Depth (m) Base Subchron C29R(m)* BaseM. prinsii* Sedimentation rate (cm/k.y.)

Location

Site 356

Data for DSDP sites used in biogeographic study: present-day locations and water depths, paleolatitudes at about 60 Ma and paleodepths at the K - T boundary (where available ), locations in site of K - T boundary, thicknesses of the Cretaceous portion of the paleomagnetic Subchron C29R and the calcareous nannofossil Micula prinsii Zone (paleomagnetic data were not available for Site 465A ). Estimates of sedimentation rates for all sites except Site 465A assumes that the base of Subchron C29R occurred 0.3 m.y. below the K - T boundary (Berggren et al., 1985; Shackleton et al., 1984) and the rate for site 465A that the base of the M. prinsii Zone was 0.2-0.25 m.y. below the K - T boundary (A. Henriksson, pers. commun., 1991 )

TABLEI

z

-t

N

>.

o

m

o

76

for delimiting the outer boundaries of the Tethyan Realm (Davids, 1966; Sliter, 1972, 1976). In the Transitional Realm, globotruncanids and heterohelicids continue to dominate but their importance decreases, whereas the rugoglobigerinids increase in abundance (Sliter, 1972, 1976 ). Austral and Boreal faunas are essentially composed of rugoglobigerinids, hedbergellids and heterohelicids. Species of Globotruncana and Globotruncanella are relatively rare in these provinces. Olsson and Wise (1987) employed multivariate analyses to quantitatively identify Tethyan and Transitional assemblages in the North Atlantic, Gulf of Mexico and the Caribbean. Two species, Globotruncana arca and Rosita contusa, were found to be associated with the Transitional water mass, whereas, for example, G. aegyptiaca and Globotruncanita stuartiformis, are members of the Tethyan assemblage. Quantitative variations in planktonic foraminifer assemblages and their paleobiogeographic significance were analyzed in samples from a time-slice from the Cretaceous-Tertiary ( K - T ) boundary in Tethyan through warmer parts of Transitional areas of the North and South Atlantic Oceans and the North Pacific Ocean. The study was based on eight Deep Sea Drilling Project (DSDP) sites (Fig. 1; Table I): Site 356 from the Silo Paulo Plateau (South Atlantic), Site 384 from the J-Anomaly Ridge (North Atlantic), Site 465A from the Hess Rise (North Pacific), Site 516F from the Rio Grande Rise (South Atlantic), Sites 525A and 527 from the Walvis Ridge (South Atlantic), Site 548A from the Goban Spur (North Atlantic) and Site 577A from the Shatsky Rise (North Pacific). Compositions of planktonic foraminifer faunas were analyzed at each site for a time-slice spanning the upper parts of the calcareous nannofossil Micula prinsii Zone (final 20-60 k.y. of the Maastrichtian). Such a time-slice was used to characterize the planktonic foraminifer assemblage at each site because a single sample from the boundary layers may not be representative of the fauna at that

B.A. M A L M G R E N

site in the terminal Cretaceous and because a sequence of samples provides a means of assessing the temporal stability of assemblage structures through this crucial interval of the Cretaceous. Material and methods

Present-day locations and water depths, paleolatitudes (at about 60 Ma ) and paleodepths at the paleontologic K - T boundary (about 66.4 Ma ) and the recognition of the K - T boundary for the eight sites analyzed here are shown in Table I. The table also lists the thickness of the Cretaceous portion of the magnetostratigraphic Subchron C29R for sites where paleomagnetic data are available (all sites except Site 465A). The thickness ranges between 1. l m (Site 384) and 7.6 m (Site 516F). The thickness of the calcareous nannofossil Micula prinsii Zone was used to establish an age model for Site 465A. The base of this zone lies 2.3 m below the K - T boundary at this site (A. Henriksson, pers. commun., 1991 ). Estimates of sedimentation rates are based on the assumption of a duration of about 0.3 m.y. for the Cretaceous part of Subchron C29R (Berggren et al., 1985; Shackleton et al., 1984 ) and a duration of 0.2-0.25 m.y. for the MI prinsii Zone (A. Henriksson, pers. commun., 1991 ). Sedimentation rates are highly variable during the latest Maastrichtian at these sites, ranging from 0.4 cm/k.y. ( l03 years) at Site 384 to a sixfold higher rate (2.5 cm/k.y.) at the western South Atlantic Sites 356 and 516F (Table I ). The sequences analyzed comprise between 12 and 20% of the total thickness of the Cretaceous part of the Subchron C29R and between l0 and 24% of the thickness of the M. prinsii Zone and should span an interval in the range 0-20 and 0-60 k.y. of the terminal Cretaceous (Table II ). Most sites were sampled at regular intervals of about 10 cm, except for Site 465A which was sampled at closer intervals, and Site 356 in which sampling intervals are longer

77

BIOGEOGRAPHIC PATTERNS

TABLE 11 Samples included in the biogeographic study, their depths in the various sites, and the sample sizes (N) upon which compositional data of planktonic foraminifera (PF), relative abundances of fragments of planktonic foraminifera (F), and relative abundances of benthic foraminifera (BF) were based. Most of the samples from Site 516F could not be included because of poor preservation Depth in site (m)

N for PF

N for F

N for BF

Site 356 29-3, 54-55 29-3, 80-82 29-3, 100-102 29-4, 4-5

412.04 412.30 412.50 413.04

308 336 360 351

346 418 505 393

315 342 365 351

Site 384 13-3, 34-36 13-3, 50-52

167.95 168.11

300 346

345 379

302 350

Depth in site

N for PF

N for F

N for BF

(m) Site 548A 29-1, 4-5 29-1, 14-15 29-1, 34-35 29-1, 54-55 29-1, 64-65 29-1, 84-85

471.54 471.64 471.84 472.04 472.14 472.34

381 338 457 357 305 354

476 432 554 451 416 434

393 345 479 370 313 362

Site 577A 12-4, 79-80 12-4, 89-90 12-4, 99-100 12-4, 109-110 12-4, 119-120 12-4, 129-130

109.69 109.79 109.89 109.99 110.09 110.19

345 264 359 (33) 246 432

642 505 838 (117) 626 1563

410 373 405 (76) 478 537

TABLE III Site 465A 3-3, 148-149 3-4, 4-5 3-4, 12-13 3-4, 20-22

62.48 62.54 62.62 62.70

408 352 345 360

608 539 582 510

421 368 351 375

Site 516F 89-5, 32-33 89-5, 42-43 89-5, 52-53 89-5, 62-63 89-5, 72-73 89-5, 84-85 89-5, 92-93 89-5, 102-103 89-5, 112-113 89-5, 122-123

963.92 964.02 964.12 964.22 964.32 964.44 964.52 964.62 964.72 964.82

377 -

647 -

510 -

Species included in biogeographic study (see also taxonomic notes in Appendix I)

1. Heterohelix glabrans ( C u s h m a n ) H. carinata (Cushman) complex 2. 11. globulosa (Ehrenberg) [ including H. reussi (Cushman) ] 3. H. striata (Ehrenberg) 4. H. sp.

5. 6. 7. 8. 9. 10.

11. 12. 13.

Site 525A 40-2, 42-43 40-2, 47-48 40-2 59-60 40-2, 69-70 40-2, 78-79 40-2, 92-93 40-2, 100-102

452.02 452.07 452.19 452.29 452.38 452.52 452.60

324 327 381 326 359 329 331

537 530 471 436 437 391 479

364 351 408 354 374 337 349

Site 527 32-4, 32-4, 32-4, 32-4, 32-4, 32-5,

280.07 280.18 280.37 280.57 280.83 281.07

390 423 327 345 367 324

422 489 386 405 430 376

401 426 333 348 375 328

14. 15. 16. 17. 18. 19. 20.

57-59 68-69 87-89 107-108 133-134 7-8

21. 22.

23. 24. 25. 26.

Pseudoguernbelina costulata (Cushman) P. kempensis Esker P. palpebra Br6nnimann and Brown Pseudotextularia nuttalli (Woorwijk) P. elegans (Rzehak) Racemtguernbelinafructicosa (Egger) Planoglobulina acervulinoides (Egger) P. carseyae (Plummer) Gublerina cuvillieri Kikoi'ne Globigerinelloides escheri ( Kaufmann ) G. multispina (Lalicker) G. subcarinata ( Br6nnimann ) Globotruncanella havanensis (Voorwijk ) [ including G. petaloidea (Gandolfi) ] Globotruncana aegyptiaca Nakkady G. arca (Cushman) (including G. mariei Banner and Blow ) G. ventricosa White Globotruncanita stuartiforrnis ( Dalbiez ) Rositacontusa (Cushman) Abathomphalus mayaroensis (Bolli ) Rugoglobigerina hexacamerata Br6nnimann R. rugosa (Plummer) (including R. rotundata Br6nnimann ) Trinitella scotti Br~Snnimann

78

B.A. MALMGREN

(between 20 and 54 cm). Planktonic foraminifera are poorly preserved in most of the samples from Site 516F, which prevents quantitative faunal analysis (Table II). Each sample (about 5 cm 3) was gently mechanically disaggregated on a rotating table and washed over a 63/tm sieve. The > 63/tm fraction was sieved over a 125 #m screen and the larger fraction was used for quantitative foraminiferal analyses. This fraction was split into a representative aliquot using a microsplitter. In case this split did not contain at least 300 specimens of planktonic foraminifera, splitting was repeated until the m i n i m u m required sample size had been obtained. Sample sizes ranged between 300 and 457 specimens, except in two of the most heavily dissolved samples from Site 577A, where only 33 and 246 specimens (samples 577A-12-4, 109-110 cm and 119-120 cm, respectively) were obtained despite analyses of the whole sample available (Table II). Sample 577A-12-4, 109-110 cm was not included in the biogeographic analysis. The proportion of the total sample analyzed was recorded during the census counts and was used for estimates of the number of planktonic foraminiferal tests per gram sediment. Since rate of sedimentation is not constant among the sites and thickness of the sed-

iment samples differs (Table II), amounts of planktonic foraminifera per gram sediment should not represent a reasonable estimate of absolute abundance. Instead, absolute abundance is here estimated as the number of specimens per gram sediment per k.y. (number of specimens/g sediment-sedimentation rate in cm per k.y./thickness of sediment sample in cm ), which should permit comparisons among samples. The number of fragments of planktonic foraminifera and the number of benthic foraminifera were kept track of during the counts of planktonic foraminiferal tests. A specimen was counted as a fragment if it was estimated that less than half of the test was preserved. The relative abundance of fragments (degree of fragmentation) was computed in relation to the amount of whole and fragmented tests of planktonic foraminifera. Degree of fragmentation was based on sample sizes ranging between 345 and 1536 (Table II). Relative abundance of benthic foraminifera was determined in relation to total foraminiferal content. Sample sizes for this variable ranged between 302 and 537 (Table II). A total of 43 species of planktonic foraminifera were identified. Those species or species complexes distinguished here that were pres-

TABLEIV Presences ( × ) at the various sites o f species that were too rare to be included in quantitative analysis 356

Heterohelix pseudotessera Cushman H. washitensis T a p p a n - H . moremani

384

465A

X

X

516F

525A

527

548A

577A

X X

( C u s h m a n ) complex

Pseudoguembelina costillifera Masters P. punctulata ( C u s h m a n ) P. excolata ( C u s h m a n ) Gublerina ren(formis ( Marie ) Ventilabrella eggeri Cushman 1~ glabrata Cushman Hedbergella monmouthensis ( Olsson ) Guembelitria cretacea Cushman Globotruncanita stuarti (de Lapparent ) Rosita fornicata ( P l u m m e r ) Abathomphalus intermedia ( Bolli )

X

X

X

X

X X x

X

X

X

X

X

X

X

X

X

X

X

X

X X

X

X

X

X

X

X

BIOGEOGRAPHIC PATTERNS

ent in more than half of the samples in at least one of the sites and with at least one relative abundance per site exceeding 1% were included in the study. Furthermore, it was necessary that a species possessed sufficiently stable morphologic characteristics to be consistently identified. Twenty-six taxa met these criteria and these were subsequently used in the biogeographic study (Table III). They include 21 taxa that are here considered to represent well-defined species and five taxa which are each composed of two similar morphotypes that have been described as separate species. Taxonomical notes on selected species are presented in Appendix I and SEM micrographs of all species incorporated into the biogeographic study are shown in Plates I-III. Distributions at the various sites of those species that were identified but not included into the quantitative analyses are listed in Table IV. Results

Dissolution effects After death and settling onto the sea floor, planktonic foraminiferal tests may be subject to partial or complete chemical dissolution. Dissolution operates differentially upon different species, and planktonic foraminifer compositions in deep-sea sediment samples may be modified to varying degrees compared to those of the standing stocks in the surface waters. Rankings of the order of dissolution susceptibility have been proposed for Cretaceous species (Douglas, 1969; Malmgren, 1987). Before faunal compositions at the various sites may be used to infer biogeographic provinciality, it is necessary to analyze dissolution effects and to exclude samples that show intense dissolution. The degree of fragmentation of planktonic foraminiferal tests has been employed as an index of calcite dissolution (for example, Arrhenius, 1952; Berger, 1970; Thiede, 1971 ). Deep-sea benthic foraminifera

79

are subject to dissolution once they are no longer protected by the protoplasm, but they are generally more resistant to dissolution than planktonic foraminifera (Arrhenius, 1952; Berger, 1973; Corliss and Honjo, 1981). Although a generally high correlation may be expected between degree of fragmentation of planktonic foraminifera and relative abundance of benthic foraminifera at individual sites, the benthic foraminifer abundance may not be solely applied for comparisons of dissolution at different sites, since it is also controlled, for example, by water depth and bottom-water conditions. Great abundance of benthic foraminifera, favored by ecologic factors, may thus be falsely interpreted as indicative of enhanced dissolution. For interpretations of dissolution effects, a combination of degree of fragmentation and benthic foraminifer abundance is used here (Fig. 2A). Samples with low abundance of planktonic foraminifer fragments are generally also rare in benthic foraminifera, whereas benthic foraminifera are more abundant in samples containing a greater proportion of fragments, strengthening the utility of these variables as dissolution indices. Dissolution was moderate (percentage of fragments < 40% and percentage of benthic foraminifera < 10%) at Sites 356, 384, 465A, 527 and 548A, and in most samples from Site 525A (Fig. 2A). One sample from Site 525A (the uppermost sample) shows a higher percentage of benthic foraminifera ( > 10% ), but this sample was still included in the analysis because its planktonic foraminifer composition does not deviate from the other samples from this site. Dissolution is generally greater at the shallower Walvis Ridge Site 525A than at the deeper Site 527. All samples from Sites 577A and 516F samples were apparently subject to intense dissolution (degree of fragmentation is 43-74% and benthic foraminifer abundance is 12-50%) and these sites were therefore excluded from further analysis. Percentages of the coarse fraction ( > 63 a m ) are

B.A. M A L M G R E N

80

50-

. 40-

m

ol

A

-J- 356 i 384 i A 465A 5~6F 525A 527 548A • 577

14.5

B

z~

+

x

-~ 30-

20~

0

+~

O z-

O

X x ~ ~ +{

xx

x ×

Ax AA

V~r

•

•

• 10

T--20

30=

T 50

4'0

Fragments,

' 60

, 70

10

0

20

30

40

50

Fragments,

%

6'0

70

%

Fig. 2. Relationships between (A) relative abundance of fragments of planktonic foraminifera (percentage of fragmented tests in relation to whole and fragmented tests of planktonic foraminifera) and relative abundance of benthic foraminifera (percentage of benthic foraminifera in relation to total foraminiferal content) and (B) relative abundance of fragments and percentage coarse fraction (fraction > 63#m) at the various DSDP sites. Site 384

Site 356

E d

4120

.~c°

4125

/

0

101 102 103 104 105 ~ ~ ~ T ...... KTb

0 1679

7/

.I

i°

{.-

1681

•

I

~-l

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

0

K-T b

K:T b

4s221

£3

452 6 i

"\

!

B.

__

0

./,~

_

I

--

I

J

~

L

Site 577 A I

J

T i t T

280 8281 2 __

472 2

I

I

i

_

o, lO' ,`0~1`03 1`0' 12L

101 102 103 104 105

r-4714 ~r4---- K - T b

471 8 !

r',,

_±

,

t

°[J'° [

i 9650

P,

Site 548 A

)~"

i

I

i I

*I

__

280.4 U3 E-AZ

,

•1

L

i

! I

o

9645 t

1

627 1 __

10~ 102 103 104 105 !

~ -E 45~ 8

i',

101 102 103 104 10b

.4--- K T b

964O

.I

Site 527

Site 525 A 101 102 103 104 105

0

2_

i

626L

I

C3

K Tb

1

/°

0

101 102 103 104 10! . . . . . lz J

°'1

1

,6,0

,\

0 624~

K-Tb

I i

Site 516 F

Site 465 A

101 102 103 104 105

F1096 -~--- K - T b. lo98 t 1

*~

,oo1

./

110 2.~

I i i

Fig. 3. Fluctuations in absolute abundance of planktonic foraminifera (number of specimens per gram sediment per k.y.: see p. 78) through the terminal Cretaceous at the various DSDP sites. Vertical dashed lines show the overall mean absolute abundance at these sites (4.5.103 specimens/g/k.y. ). c o n s i s t e n t l y b e l o w 2% at these sites as c o m pared to 3 - 1 5 % at the r e m a i n i n g sites (Fig. 2 B ) , reflecting the loss o f p l a n k t o n i c f o r a m i nifera to d i s s o l u t i o n . P l a n k t o n i c f o r a m i n i f e r c o m p o s i t i o n s at Sites

5 7 7 A a n d 5 1 6 F s a m p l e s i n d i c a t e their alterat i o n by d i s s o l u t i o n . F o r e x a m p l e , Site 5 7 7 A s h o w s an overall greater relative a b u n d a n c e (7-72%) of G. havanensis (a d i s s o l u t i o n - r e sistant species; M a l m g r e n , 1 9 8 7 ) than the

81

B I O G E O G R A P H I C PATTERNS

other sites ( < 2% at Site 465A from a similar latitude and < 7% at the other sites). Similarly, Site 516F is depleted in those species found by Malmgren (1987 ) to be susceptible to dissolution ( H. globulosa, P. costulata, G. rnultispina and R. rugosa), but enriched in those species that were recognized as m o r e resistant (G. cuvillieri, P. elegans and P.

Site Latitude North / South

k.y.). Biogeographic provinciality Figure 4 shows a plot o f quantitative distributions at the various sites o f some o f the taxa recognized by Davids (1966), Sliter (1972, 1976 ) and Olsson and Wise ( 1987 ) as biogeographical indicators (T. scotti, G. aegyptiaca, Pseudoguembelina, Globotruncana arca and Racemiguembelina ). On the basis o f these distribution patterns, Sites 465, 356 and 384 are interpreted to have been under the influence o f the Tethyan water mass in the terminal Cretaceous. The largely Tethyan species T. scotti and G. aegyptiaca disappear or decrease in abundance from the Tethyan to the Transitional Realm, whereas the cooler-water Transitional taxa G. arca and Racemiguembelina become more abundant. Site 465A is referred to the Warm Tethyan Province (Fig. 4) because it was situated in nearly equatorial waters at the K - T boundary ( 12-16 ° N; Vallier et al., 1981 ). Sites 356 and 384 are considered to represent a Cool Tethyan Province (Fig. 4). Nyong (1984) placed the T e t h y a n / T r a n s i t i o n a l boundary a few degrees o f latitude to the north

356 i 23 ° ! Sip

t___2

T. scotti G. a e g y p t i a c a Pseudoguembelna

I

04

i

44

I

2

~-...... I

G. arca Racemiguembelina

3 q

07 8

I

I I

36 ° S

5

I i

36 ° S

Ii

i

I

5

6

5

__j___~

10

15

18

7

2

4

--?=--4

i I

I

C~E I 2-5%

I I I

~R Province

Province

I

I I i

I

I

5-10%

37 ° N ,

~..-..-°.-% -. I

i ................ / ......................

WTE ~

525 A i 527 L 54= A I

1

9

Province

> 10%

i

384 29 ° N

i 07 ~ 0s ~ 1

I

acervulinoides ). Dissolution effects m a y be partially evident from absolute abundances o f planktonic foraminifera ( n u m b e r o f tests/g s e d i m e n t / k . y . ) (Fig. 3 ). Absolute abundance is above or about the average for the sites studied here (4.5- 103 specimens/g/k.y.) at Sites 356, 384, 465A, 525A, 527 and 548A (1- 1 0 3 - 5 5 . 103 specim e n s / g / k . y . ), but clearly below the average at Sites 516F and 577A ( < 1 - 1 0 3 s p e c i m e n s / g /

1465 A I 16 ° I N I

E.....

t 1-2%

~............ ~ 0.1-1%

Fig. 4. Quantitative distributions at the DSDP sites of some planktonic foraminiferal taxa shown previously to be useful indices of Tethyan and Transitional waters in Late Cretaceous times (Davids, 1966; Sliter, 1972, 1976; Olsson and Wise, 1987 ). N indicates location to the north of the equator and S location to the south of the equator. Figures show average relative abundances (percentages) per site. Referability of the various sites to provincial scheme adopted here (WTE Province=Warm Tethyan Province; CTE Province=Cool Tethyan Province; and WTR Province=WarmTransitional Province) is based on these distributions. of the North Atlantic Site 384 in the Campanian-lower Maastrichtian. The Walvis Ridge Sites 525A and 527 were most likely located within the Transitional water mass in the terminal Cretaceous. This is consistent with the interpretation of Todd (1970) that an assemblage from the southern parts of the Walvis Ridge is Transitional in character. According to K.rasheninnikov and Basov (1986), the northern limit by the Austral Realm in the eastern South Atlantic lay considerably to the south of the Walvis Ridge and possibly even to the south o f the African continent in the Late Cretaceous. The Walvis Ridge sites should, therefore, have been within the w a r m e r parts of the Transitional Realm (here denoted the Warm Transitional Province; Fig. 4). Relative abundances o f these taxa at Site 548 generally resemble those at Sites 525A and 527 (Fig. 4), which suggests that this site was situated within the W a r m Transitional Province.

82

B.A. M A L M G R E l X

+0.5

x 0

0 tO "0 E 0

0.0'

//

0 -0.5 -

[3~

tO O9

-1.0

i

f

-0.5

0.0

i

l

+0.5

+1.0

i

i

+15

+20

First correspondence axis Fig. 5. Distribution of sample points for the various DSDP sites on first two axes derived from correspondence analysis (Q-mode part ). This plane accounts for 73% of the variability in the 26-dimensional species space (R-mode) and the 29dimensional sample space (Q-mode) upon which the biogeographic study is based. The first axis distinguishes the warm Tethyan Site 465A from the other sites and the second axis separates the Walvis Ridge Sites 525A and 527 from the North Atlantic Site 548A. Dashed lines are drawn from the average values of the species loadings (compare Fig. 7 ).

x 0

+0.5

t'-

"O tO (/) 0 0

0.0 ¸

t'I--

i

-0.5

i

0.0

i

+0.5

r

+1.0

+1,5

1

+2.0

First correspondence axis Fig. 6. Distribution of sample points for the various DSDP sites on first and third correspondence axes (Q-mode part). The first axis accounts for 49% and the third axis for 9% of the variability. The third axis distinguishes the cool Tethyan Sites 356 and 384 from the remaining sites.

B1OGEOGRAPHICPATTERNS

83

A mayaroensis (t) G. cuvillieri

/ +0.5-

0 0 "0 tO

\

\

I ~) R. rugos~

I t G. a~ca(~1 a. fructic~sa

t

.(.o x ot(1) "10 tO ¢/)

/

~ P. a~Nulinoides/ \ /

• P. palpebra

k

• P. carseyae

\\ x

. . . . .

P. costulata ~.-[] \ I -.( -j /

0.0P. nuttall,

~3/2

:---

--'~. H. stdata [] [ ] G. aegyptiaca R. hexacamerata T. sc0tti

• H.g l o ~ l o s a -0.5 -

R. coW'usa \~,/

I

0 O0

'-.~1 ~ 4 " ]

I-1 Tethyan Assemblage [] Warm Tethyan Subassemblage

\

G. ~ultispina I

\

C) (~ (~) (~

/

-1.0 -

P. kempensis [] [] Heter0helix sp.

G. subcarinala G. eschen G. havanensis G. sluartiformis

[]

Cool

•

Warm Transitional Subessemblsge

•

Tethyan Subassemblage

Shallow Warm Trlmsltlonal $ubeasernbiage • Species without biogeogrq)hic significance

® H. gla~ans + H. carinata

i

-0.5

i

0.0

i

+0.5

i

i

+1.0

First correspondence

+1.5

i

+2.0

axis

Fig. 7. Configuration of species points (R-mode) on first two correspondence axes (the same axes as those upon which sample points are plotted in Fig 5 ). Scatter ellipses indicate the regions on this plane occupied by sample points for the various sites (derived from Fig. 5 ). Species or species groups associated with a specific cluster of sample points on planes formed by correspondence axes are characteristic of these samples. For example, Site 465A stands out from the other sites by greater abundances ofP. kempensis, Heterohelix sp. and P. costulata. Dashed lines are drawn from the average values of the species loadings. Correspondence analysis was employed to determine whether major differences in planktonic foraminifer assemblages are tied to timerelated changes through the interval studied at individual sites or whether they relate to variability along paleolatitudinal gradients that may be used to assess paleobiogeographic patterns. Correspondence analysis permits simultaneous plots o f sample points and species points on the same coordinate axes, facilitating interpretations o f the species associations responsible for clusters of samples (Benz6cri,

1973; D a v i d et al., 1974; Malmgren et al., 1978 ). The first three correspondence axes account for 82% o f the variability in the 26-dimensional species space and 29-dimensional sample space (49% is represented in the first axis, 24% in the second axis and 9% in the third axis). Figures 5 and 6 show plots of samples along the first and second and first and third axes, respectively. Samples from the same site or sites from similar paleolatitudes cluster closely together. Differences in faunal composition among sites thus dominate over time-

84

B.A. MALMGREN

+1 5 [] Tethyan Assemblage

R he×acamerata []

U) X

o c "o c o ~L

[] Cool Tethyan Subassemblage

[] T SCOtli / / /

+1.0

Warm Tronsittonol Subossemblage @ Shollow Warm Transitionol Subassemblage

G eschen • f~./ ,r" I / ~ / I // / I'J~°J H slriata I /I /o / [] ~ / / G subcari~ata [] / G aegyptiaca G. stuarli-/ / • P nuttalli formisl / P carseyae / /G. venlri- G. •havaM J // / cosa nensis, / ~1 \ /

+0.5

o f..

0.0

[] Worm Tethyan Subasaembloge

,oI . t ~ 7

~9

-0.5 -

I

-05

/~\ [ ~ ,,

,_.a_ .... ~2

~

I

0.0

\

X

,.

P. pa~pebra

/ 1525 A I

\

• Species without biogeographic significance

. . . . . .

0

H. glabrans+carinata ( ~

(~) (~) (~) (~)

P. elegans R. fructicosa P. acervulinoides G. cuvillieri I

+0.5

..__k\

\

[]

G. multispina

\

\ )

[] Heterohelixsp.

P. kempensis

(~) R. conlusa (~) A mayaroensis (~) R rugosa

I

+1.0

I

+1 5

I

+2.0

First correspondence axis Fig. 8. Distribution of species points ( R - m o d e ) o n first and third correspondence axes (compare Fig. 6). For details, see caption of Fig. 7.

dependent fluctuations at individual sites as the major controlling force behind the configuration of sample points. These clusters suggest the existence of specific assemblages characterizing different paleolatitudes in the terminal Cretaceous ocean. The first correspondence axis distinguishes the warm Tethyan Site 465A from the other sites (Figs. 5, 6 ), the third axis isolates the cool Tethyan Sites 356 and 384 (Fig. 6) and the second axis separates the warm Transitional Sites 525A and 527 (Walvis Ridge) from Site 548A (North Atlantic) (Fig. 5 ). What characterize the planktonic foraminifer assem-

blages responsible for this pattern? Figures 7 and 8 illustrate the configuration of species points upon the same correspondence axes as in Figs. 5 and 6, respectively. An assemblage of seven species is associated with the Tethyan Realm: H. striata, G. aegyptiaca, P. kempensis, H. sp. (un undescribed heterohelicid with relict apertural flanges along the medium suture; see Appendix I), P. costulata, R. hexacamerata and T. scotti (Figs. 7, 8 ). Two species, H. striata and G. aegyptiaca, are equally abundant at all three Tethyan sites (465A, 356 and 384) and constitute a general Tethyan assemblage. The relative abundance of H. striata is

BIOGEOGRAPHIC PATTERNS

85

H. striata t~ ~o O r--

to

to

G. aegyptiaca ,~*

to

t~3

to

to

to

108-

3

"O 6-

2

.D 4-

.> •~

2~

Q) fie

0-

1

0

Fig. 9. Relative abundances at the various DSDP sites of H. striata and G. aegyptiaca, which are generally associated with Sites 465A, 356 and 384 from the Tethyan Realm.

between 2 and 7% in the Tethyan Realm as compared to less than 2% in the Warm Transitional Province (Fig. 9; Table V). Globotruncana aegyptiaca is present in most samples from the Tethyan Realm (0-1.5% ) but was not found in any of the samples from the warm Transitional sites (Fig. 9; Table V). A Warm Tethyan Subassemblage, composed of P. kempensis, H. sp., and P. costulata, may be distinguished at Site 465A (Figs. 7, 8 ). Figure 10 compares relative abundances of these species between Site 465A and the remaining sites (compare Table V). Relative abundance of P. kempensis is 11-16% at Site 465A and less than 2% at Sites 356 and 384. It is absent in the Warm Transitional Province. Similarly, relative abundance of Heterohelix sp. is between 13 and 17% at 465A and less than 5% at Site 356. This species was not encountered at Sites 384, 525A, 527 and 548A. Pseudoguembelina costulata is present at all sites, but it is more abundant at Site 465A (21-28% ) than at the higher-latitudinal sites ( < 6%). Two species, R. hexacamerata and T. scotti, are particularly associated with the cool Tethyan Sites 356 and 384 (Fig. 8) and they constitute a Cool Tethyan Subassemblage. The descendant species in the lineage leading from R. hexacamerata to T. scotti (Masters, 1976, 1977) thus apparently became optimally

adapted to the same general water mass as the ancestral species (but possibly not to the same niche in the water column). These species occur in relative abundances of 0-6% in the Cool Tethyan Province, as compared to 0-3% in the Warm Tethyan Province and 0-1.5% in the Warm Transitional Province (Fig. 11; Table V). Seven species constitute the Warm Transitional Subassemblage in grouping with the Walvis Ridge Sites 525A and 527: A. mayaroensis, G. cuvillieri, P. elegans, R. rugosa, R. fructicosa, G. arca and P. acervulinoides (Fig. 7 ). Among these, G. arca and R. rugosa are the most common species (7-30% and 11-20%, respectively) (Fig. 12; Table V). Gublerina cuvillieri, P. elegans and P. acervulinoides are intermediately abundant (2-13%, 1-12% and 1-10%, respectively), whereas two species, R. fructicosa and the important uppermost Maastrichtian zone fossil A. mayaroensis are less abundant ( 1-8% and 0-1%, respectively). Globotruncana arca and R. rugosa may be relatively abundant in the Cool Tethyan Province (1-15% and 3-10%, respectively), whereas the other species of this assemblage never account for more than 4% there. All species, except A. mayaroensis, were identified in the warm Tethyan Site 465A but in low proportions ( < 3%). Site 548A, derived from a similar paleolatitude as the Walvis Ridge sites, is marked by a specific assemblage composed of the H. glabrans-H, carinata complex, G. multispina, R. contusa and H. globulosa (Fig. 7 ). Heterohelix globulosa particularly dominates the planktonic foraminifer faunas at this site (33-50% as compared to 10-32% at the other sites) (Fig. 13; Table V). Globigerinelloides multispina and the H. glabrans-H, carinata complex are also present in considerable proportions at this site (12-23% and 6-8%, respectively), and they are generally much more common there than at the other sites ( < 12% and < 5%, respectively). Likewise, R. contusa shows the highest

86

B.A. MALMGREN

TABLE V Means (~) and ranges of relative abundances of the various species re Tethyan (WTE) Subassemblage, Cool Tethyan (CTE) Subassemblage, Warm T Subassemblage, and "shallow" Warm Transitional (SWTR) Subassemblage, that were not referable to any of these assemblages

Tethyan Assemblage General H. striata Tethyan G. aegyptiaca

WTE Province

CTE Province

WTR Province

Site 465A Range

Site 356, 384 x Range

Site 525A, 527 x Range

Site 548A ~ Range

3,7 0.4

1.7-6.7 0.0-0.9

3.8 0.8

1.7-5.8 0.0-1.4

0.2 0.0

0.0-1.8 -

0.6 0.0

0.0-1.8 -

13.8 15.1 23,9

11.4-16.2 13.2-17.3 21.1-28.4

0.8 1.8 3.8

0,3-1.7 0.0-4.5 2.0-6.4

0.0 0.0 1.3

0.0-4.6

0.0 0.0 0.5

0.0-1.4

R. hexacamerata 12 scotti

1.3 1.5

0.4-2.9 1.0-1.7

3.3 3.2

1.9-5.5 0.3-6.3

0.1 0.0

0.0-0.6 -

0.4 0.9

0.0-1.1 0.0-1.4

Transitional Assemblage WTR ,4. mayaroensis Subassemblage G. cuvillieri P. elegans R. rugosa R. fructicosa G. area P. acervulinoides

0.0 0.4 1.1 1.1 0.7 1.6 0.7

0.2-0.6 0.9-1.5 0.2-3.1 0.2-1.2 0.9-3.3 0.3-0.9

0.1 0.8 1.5 7.3 0.8 9.2 1.8

0.0-0.3 0.3-1.5 0.3-4.0 2.6-9.5 0.0-1.7 0.6-14.7 0.0-3.5

0.5 7.8 6.8 15.7 3.0 16.4 5.5

0.0-1.2 2.4-13.1 0.6-12.2 10.9-20.4 0.6-7.6 7.1-30.0 t.3-10.6

0.0 0.2 0.7 2.5 1.5 6.7 3.3

0.0-0.7 0.0-1.7 0.8-4.3 0.6-2.6 3.0-15.4 2.1-4.5

0.2 1.2 0.1 12.4

0.0-0.3 0.3-1.7 0.0-0.3 9.7-15.0

2.1 8.0 0.2 18.5

0,6-4.9 4.0-11.9 0.0-0.3 14.0-25.1

0.4 4.5 0.4 18.6

0.0-1.8 2.1-11.3 0.0-1.2 11.6-32.2

6,8 17.9 1.1 41.3

6.1-8.2 11.8-22.6 0.3-2.0 33.1-49.0

6.2 0.3 7.6 0.3 1.4 2.0 O, I 1.0

5.4-8.2 0,0-0.6 5.6-12.2 0.0-0.7 0.8-2.6 1.7-2.3 0.0-0.3 0.7-1.4

2.1 3.1 7.7 2.2 3.2 5.3 0.7 2.4

0.3-5.7 1.1-4.0 4,9-13.1 1.4-4.2 1.3-5.0 3.4-7,4 0.0-1.1 0.3-4.0

4.2 2.0 5.6 0.5 1.2 2.4 0.3 1.2

0.9-10.4 0.3-4.3 1.0-10.6 0.0-1.2 0.0-4.2 1.2-4.0 0.0-0.9 0.3-2.4

0.9 2,1 1,5 0.4 1.0 3.6 0.7 1.9

0.0-1.3 0.6-3.1 0.3-2.2 0.0-1.2 0.6-2.1 2.4-5.0 0.0-2.3 1.3-2,6

WTE Subassemblage

CTE Subassemblage

SWTR Subassemblage

P. kempensis H. sp. P. costulata

H. glabrans1t, carinata complex G. multispina R. contusa H. globulosa

Species without biogeographic preference P. palpebra P, nuttalli P. carseyae G. escheri G. subcarinata G. havanensis G. ventricosa G, stuartiforrnis

maximum (2%) and average (1%) percentages there. What feature of the environmental conditions at this site during the terminal Cretaceous could have promoted the dominance of such an assemblage? The relatively shallow water depth at which the sediment of this site was deposited (200-500 m; de Graciansky et

al., 1985 ) could have been a controlling factor. Modern species of planktonic foraminifera occupy distinct depth intervals within the upper few hundred meters of the water column (B6 and Hamlin, 1967; Berger, 1969; Tolderlund and B6, 1971 ) and depth stratification has existed at least since the Late Cretaceous (Sliter, 1972; Douglas and Savin, 1973, 1978; Saito

BIOGEOGRAPH

87

IC PATTERNS

P. kempensis

Heterohelix sp.

P. costulata

co ,

20O t-

20 -

tO

~0

1515-

~0~

¢"~

CO

1010-

.->

5-

5-

~

0

0-

I

Fig. 10. Relative abundances at the various DSDP sites ofP. kempensis, Heterohelix sp. and P. costulata, which constitute the Warm Tethyan Subassemblage. T. scotti

R. hexacamerata 2n.-

o

G. ventrioosa

G. havanensis 03

t~

tt3

~_

G. stua~iformis

i] 5

ItlL

2t,11,1ll,a 1 l,l, I1ttl! 1111

Fig. 14. Relative abundances at the various DSDP sites of those eight species that are not clearly associated with any of the biogeographic provinces (compare Figs. 7, 8): P. palpebra, P. nuttalli, P. carseyae, G. escheri, G. subcarinata, G. havanensis, G. ventricosa and G. stuart(formis.

distributional patterns found here and also provides a compilation of total ranges of the various species gleaned from previous studies. The Boreal and Austral Realms distinguished in the Northern and Southern Hemisphere, respectively, by Sliter ( 1972 and 1976 ) are summarized under one heading. Most of the species analyzed here had longer distributional ranges than the latitudinal interval considered in this analysis. This study may have covered the total distributional ranges of P. kempensis and Heterohelix sp. (Tethyan Realm) and most of the ranges of T. scotti and G. aegyptiaca in the terminal Cretaceous (Tethyan Realm and warmer parts of the Transitional Realm; Fig. 15 ). Among these, P. kempensis and Heterohelix sp. appear to be typical warm Tethyan species, whereas T. scotti is here included as an element of the Cool Tethyan Subassemblage. Globotruncana aegyptiaca was distributed in equal relative

abundances in warm and cool Tethyan waters (Fig. 15). Among the species essentially confined to Tethyan and Transitional waters, H. striata was equally abundant in the Warm and Cool Tethyan Provinces, P. costulata was apparently best adapted to the Warm Tethyan Province and R. hexacamerata to the Cool Tethyan Province. Pseudoguembelina palpebra, P. nuttalli, G. subcarinata, G. ventricosa, and G. stuartiformis do not exhibit preference for any specific biogeographic unit. Gublerina cuvillieri and R. fructicosa became more abundant toward cooler waters and are characteristic of the Warm Transitional Province (Fig. 15 ). None of the species with a cosmopolitan distribution (Tethyan through Boreal/Austral Realms) is referable to the Tethyan Assemblage as distinguished here (Fig. 15). The warm Transitional species A. mayaroensis, P. elegans, R. rugosa, G. arca and P. acervuli-

90

B.A. M A L M G R E N

Trans.

Tethyan

~¢ ~ ~ ~

Species

c 356 384

if?

4

H striata G. aegyptiaca

~>, ..c:

E ~

Heterohelix

I--

~

P. costulata

"~ o 0

14

P. kempensis

~ :~

I

4

1

3

R. hexacamerata T. scotti A. mayaroensis

2

--

H. glabrans-H, G. multispina

CO

R. contusa H. gtobulosa

p. palpebra P. nuttalli

~..

G escheri

~

G. subcarinata G. havanensis

¢,~ ~:~

G. ventricosa

35

I

3

I

1

' Austral/ Boreal

+

1

I

)

I --~ I

F

~ 7

1

7

I

I

11~

3

.i.__ _ ~ . _ + 3

2

2,9

7

i

p

I

I

I

tI

I

F--- . . . . . . . . I

carinata

2

7 I - - - ~

1 12 "F-{'9- -I- -19- + 41 I 6 2 4 I I I

I

t q I

8

P. carseyae

"~ ~ O ~

Trans -

I----4-----

R. fructicosa

o~ E

I

4". . . . 1 2

P. elegans R. rugosa

c

I ....

Tethyan

4----4

~4

G. arca P. acervulinoides

I'~

527

General distribution

sp

G. cuvillieri E

I

4

sw 548A

I t

1 2 1

G. stuartiformis

I I

8 2 3 5

I

6

I

1

I

2

I

I I

4 " - - - - I - . . . . -+ 2 1 I

---

2

I

I

I

I

t ----+

t

P

1 4 2

< 1%

I

5-10%

1-5%

I

>10%

Fig. 15. Summary chart of relative abundances (percentages) of the various planktonic foraminiferal species in the Warm (W) and Cool (C) Tethyan Provinces of the Tethyan Realm and the Warm Transitional Province ( Wand SW) distinguished here, and general distribution patterns of the same species in the Late Cretaceous world ocean as gleaned from work by Sliter ( 1972, 1976), Masters ( 1977 ), Troelsen ( 1955 ), Berggren (1962), Webb and Neall (1972), Huber et al. (1983), and Nederbragt (1989).

noides all tend to increase gradually in relative abundance from warm Tethyan through warm Transitional waters (Fig. 15 ). Abathomphalus mayaroensis, which, according to Sliter ( 1972, 1976) may be found throughout the Tethyan water mass, was not encountered in the census counts of samples from Site 465A (Fig. 12), but this does not preclude its presence in low relative abundances there. Huber (in press) has demonstrated a time-transgressive migration of this species toward the low latitudes. Its first appearance in the south polar regions was about 1.5 m.y. earlier than in the Mediterra-

nean region (Huber, in press). Therefore, A. rnayaroensis may not have been well adapted to equatorial waters in the terminal Cretaceous, which might explain its absence in the census counts at Site 465A. All of the species that exhibit enhanced abundances at the exceptional Site 548A are cosmopolitan in distribution (the H. glabrans-H, carinala complex, G. multispina, R. contusa and H. globulosa) (Fig. 15). If only their abundances in the remaining sites are considered, the H. glabrans-H, carinata complex and G. multispina show the greatest abun-

BIOGEOGRAPHIC PATTERNS

dances in the Cool Tethyan Province (Fig. 15 ). Heterohelix globulosa is generally the most abundant species at the sites studied here ( 1032%), whereas the proportion of R. contusa rarely exceeds 1% (Fig. 15 ).

Summary Biogeographic distribution patterns and the possible existence of quantitatively defined bioprovinces of planktonic foraminifera in the terminal Cretaceous oceans, have been determined from studies of assemblage structures of this group in deep-sea sediments from warm Tethyan through warm Transitional waters at a time-slice encompassing the upper parts of the calcareous nannofossil Micula prinsii Zone (sections span approximately the terminal 2060 k.y. of the Cretaceous). Material from eight Deep Sea Drilling Project (DSDP) sites were analyzed; four were drilled in the South Atlantic Ocean, Sites 356 (S~o Paulo Plateau), Site 516F (Rio Grande Rise) and Sites 525A and 527 (Walvis Ridge ), two in the North Atlantic Ocean, Site 384 (J-Anomaly Ridge) and Site 548A (Goban Spur) and two in the North Pacific Ocean, Site 465A (Hess Rise) and Site 577A (Shatsky Rise) (Fig. 1 ). These sites were situated at paleolatitudes ranging from 16 ° to 37 ° in either the Southern or the Northern Hemisphere at the end of the Cretaceous (Table I). Two to ten samples were analyzed per site (Table II ); the use of a time-slice served to assess the temporal stability and degree of representativeness of faunal data through the terminal Cretaceous. These sites have been shown to contain relatively complete Maastrichtian boundary sections. Sedimentation rates range between 0.4 and 2.5 cm/k.y. (Table I). Twenty-six species or species complexes were analyzed quantitatively (Table III). ( 1 ) Degree of fragmentation of planktonic foraminiferal tests and relative abundance of benthic foraminifera indicated that terminal Cretaceous samples from Sites 516F and 577A are severely affected by dissolution (Fig. 2).

91

Samples are impoverished in dissolution-susceptible species and, therefore, not representative of faunas at those latitudes. (2) Correspondence analysis indicated differences in faunal composition between sites from warm Tethyan waters (Site 465A), cool Tethyan waters (Sites 356 and 384) and warm Transitional waters (Sites 525A, 527, and 548A) (Figs. 5, 6). ( 3 ) The Tethyan Realm is characterized by an assemblage of seven species: Heterohelix striata, Globotruncana aegyptiaca, Pseudoguembelina kempensis, P. costulata, Heterohelix sp. (an undescribed species with relict apertural flanges along medium suture; Plate I, 5, 6), Rugoglobigerina hexacamerata and Trinitella scotti (Figs. 7, 8, 15). Among these species, P. kernpensis, P. costulata and H. sp. appear to be best adapted to the warmer Tethyan waters in showing the greatest relative abundances at the Warm Tethyan Province Site 465A, whereas R. hexacamerata and T. scotti are associated with cooler Tethyan waters (the Cool Tethyan Province Sites 356 and 384). (4) Seven species, constituting the Warm Transitional Subassemblage, are associated with the Warm Transitional Province Sites 525A and 527: Abathomphalus mayaroensis, Gublerina cuvillieri, Pseudotextularia elegans, Rugoglobigerina rugosa (including R. rotundata), Racemiguembelina fructicosa, Globotruncana arca (including G. mariei ) and Planoglobulina acervulinoides (Figs. 7, 15 ). (5) Site 548A is enriched in species of the Heterohelix glabrans-H, carinata complex, Globigerinelloides multispina, Rosita contusa and Heterohelix globulosa (including H. reussi) (Figs. 7, 15 ). This site was situated in outer shelf-upper slope waters (200-500 m) during the terminal Cretaceous and this association may be interpreted as a "shallow-water" sub-assemblage within the Warm Transitional Province. (6) Other species do not show preferences for any particular water mass: Pseudoguembelina palpebra, Pseudotextularia nuttalli, Plan-

92

oglobulina carseyae, GIobigerinelloides escheri, G. subcarinata, Globotruncanella havanensis, Globotruncana ventricosa and Globotruncanita stuartiformis (Figs. 7, 8, 15 ). Acknowledgments I thank Bruce Masters, Amoco Production Company, Hans Thierstein, ETH-Zentrum, Ziirich and two anonymous reviewers for comments on earlier versions of the manuscript of this article. The help of Dr. Masters in clarifying some taxonomic problems concerning the heterohelicids is much appreciated. Gunnar Ekman, University of Grteborg, kindly assisted with the SEM micrographs. Marietta Eliason, University of Grteborg, provided drafting and photographic assistance. The deep-sea material was generously supplied through the assistance of the Ocean Drilling Program (ODP). This work was supported by grants from the Swedish Natural Science Research Council (G-GU 4076-120, G-GU 4076122 and G-GU 4076-300). Appendix I n Taxonomic notes on selected taxa The tteterohelix glabrans ( Cushman )-H. carinata ( Cushman ) complex (Plate 1, 1 ) Both these species have a laterally compressed test, acute chambers and a smooth test surface, but H. carinata differs from H. glabrans in possessing a peripheral keel. Since it is often difficult to evaluate in a light microscope whether a keel is present and to avoid introducing bias into the data set due to arbitrary assignments of intergradational forms and drift in taxonomic concept with time, specimens referable to this complex were not counted as separate species. tt. striata (Ehrenberg) (Plate I, 3-4 ) Malmgren (1987) included H. striata in the synonymy of tt. globulosa, but 1 now consider H. striata to be a well-defined species, which can be normally easily distinguished from H. globulosa. tteterohelix sp. (Plate 1, 5, 6 ) This previously undescribed form is characterized by moderate costation and relict apertural flanges along medium suture. Nederbragt (1989) recognized and figured this form in DSDP material from the North Atlantic Ocean (DSDP Site 605 ). This species may have evolved in the uppermost Maastrichtian (below the base of the ,4. mayaroensis Zone) (B.

B.A. MALMGREN Masters, Amoco Production Company, pers. commun., 1984). Data presented by Nederbragt ( 1989 ) do not contradict this inference. Pseudotextularia nuttalli ( Woorwijk ) ( Plate 1, 10 ) This form was denoted P. browni Masters in Malmgren ( 1987 ). However, to obtain a more consistent taxonomy of Late Cretaceous planktonic foraminifera, I follow Nederbragt (1989) in referring this form to P. nuttalli, which has priority (Nederbragt, 1989 ). Planoglobulina acervulinoides ( Egger ) ( Plate I, 12 ) Nederbragt (1989) considered P. brazoensis Martin to be a junior synonym ofP. acervulinoides. This form, which was named P. brazoensis in Malmgren (1987), is here included in P. acervulinoides for the sake of priority and consistency of terminology. Globotruncanella havanensis (Woorwijk) (Plate II, 6 ) Several workers have noted the close similarity between G. havanensis and G. petaloidea (Gandolfi) (Olsson, 1964: Bandy, 1967: Masters, 1977 ). Although end members of this complex may be referred to either species without much problem, these species seem to be completely intergradational. In counts of large samples, consistent differentiation of these forms is difficult, and G. petaloidea is here, following Masters ( 1977 ), regarded as conspecific with G. havanensis. Globotruncana arca (Cushman) (Plate It, 8-10) Globotruncana mariei Banner and B10w is similar to G. area but differs in being smaller, in lacking strong dorsoconvexity and in having somewhat more closely spaced keels (Olsson, 1964 ). Forms similar to G. marwi have been recognized (see Plate II, 8), but in a quantitative analysis the majority of specimens must be referred to one taxonomic category. Consistent separation of G. arca and G. mariei is not possible (compare Masters, 1977), and specimens of this complex were, therefore, counted as G. arca. These forms obviously represent natural morphovariants within a single morphospecies. Rugogloblgerina rugosa (Plummer) (Plate III, 7, 8) Rugoglobigerina rotundata ( B r r n n i m a n n ) may be differentiated from R. rugosa by its large, axially elongated chambers in the last whorl, occasionally almost subglobular test and deep and small umbilicus (Brrnnimann, 1952 ). In addition, the final two chambers may be displaced ventrally ( Masters, 1977). Rugoglobigerina rotundata is most likely an offshoot from R. rugosa (Brrnnimann, 1952: Masters, 1977). Although adult specimens of R. rotundata can be readily identified (see Plate III, 8), juvenile forms were found to intergrade with R. rugosa, making separation difficult. Therefore, specimens referable to R. rotundata are included in R. rugosa. In most samples, the typical R. rotundata morphotype is much less abundant than the R. rugosa morphotype. Trinitella scotti B r r n n i m a n n ( Plate Ill, 9 ) Masters (1976, 1977) suggested that this species evolved from R. hexacamerata ( B r r n n i m a n n ) in the upper Maas-

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93

PLATE I (see p. 94) SEM micrograPhs of species of Heterohelicidae included in this study. 1. Heterohelixglabrans (Cushman)-H. carinata (Cushman) complex, edge view, DSDP 80-548-29-1, 54-55 cm, X251]'~This specimen is referable to H. glabrans. 2. Heterohelixglobulosa (Ehrenberg), side view, DSDP 43-384-13-3, 50-52 cm, X310. 3, 4. Heterohelix striata (Ehrenberg): 3, side view, DSDP 39-356-29-4, 4-5 cm, X260; 4, edge view, DSDP 43-384-133, 34-36 cm, X270. 5, 6. Heterohelix sp.: 5, side view, DSDP 62-465A-3-4, 20-22 cm, X230; 6, side view, 62-465A-3-4, 4-5 cm, X230. 7. Pseudoguembelina costulata (Cushman), side view, DSDP 62-465A-3-4, 4-5 cm, X240. 8. Pseudoguembelina kempensis Esker, side view, DSDP 62-465A-3-4, 4-5 cm, X230. 9. Pseudoguembelina palpebra Brrnnimann and Brown, side view, DSDP 74-527-32-4, 133-134 cm, X 170. 10. Pseudotextularia nuttalli (Woorwijk), edge view, DSDP 62-465A-3-4, 20-22 cm, X180. 11. Pseudotextularia elegans (Rzehak), edge view, DSDP 43-384-13-3, 50-52 cm, X200. 12. Planoglobulina acervulinoides (Egger), side view, DSDP 43-384-13-3, 50-52 cm, X150. 13. Racemiguembelinafructicosa (Egger), side view, DSDP 43-384-13-3, 50-52 cm, X170. 14, 15. Planoglobulina carseyae (Plummer): side view, DSDP 43-13-3, 50-52 em; 14, X230; 15, X210. Specimen 14 is an example of the multiserial variety, and specimen 15 is an example of the biserial variety. The biserial form is equipped with a supplementary aperture on the back of the final chamber. Formation of such an aperture appears to usually signify the initiation of the multiserial stage. 16. Gublerina cuvillieri (Kiko'/ne), side view, DSDP 74-527-32-4, 107-108 em, X220.

PLATE II (see p. 95) SEM micrographs of species of Planomalinidae and Globotruncanidae included in this study. I. Globigerinelloides escheri (Kaufmann), umbilical view, DSDP 43-384-13-3, 50-52 cm, X330. 2, 3. Globigerinelloides multispina (Lalicker), DSDP 43-384-13-3, 50-52 cm; 2, umbilical view, X32ff, 3, edge view, X320. 4, 5. Globigerinelloides subcarinata (Brrnnimann), DSDP 43-384-13-3, 50-52 cm; 4, edge view, X240; 5, umbilical view, X270. 6. Globotruncanella havanensis (Voorwijk), umbilical view, DSDP 43-384-13-3, 50-52 cm, X230. 7. Globotruncana aegyptiaca Nakkady, umbilical view, DSDP 43-384-13-3, 50-52 cm, X 170. 8-10. Globotruncana arca (Cushman): 8, umbilical view, DSDP 43-384-13-3, 50-52 cm, X170; 9, 10, DSDP 74-52732-4, 107-108 cm; 9, umbilical view, X 150; 10, edge view, X 160. Specimen 8 shows a resemblance to G. mariei Banner and Blow in lacking strong dorsoconvexity and in having relatively closely spaced keels (compare Appendix I; p. 92).

PLATE III (see p. 96) SEM micrographs of species of Globotruncanidae included in this study. 1, 2. Globotruncana ventricosa White: 1, umbilical view, DSDP 74-527-32-4, 87-89 cm, X170; 2, edge view, DSDP 74527-32-4, 107-108 cm, XI40. 3, 4. Globotruncanita stuartiformis (Dalbiez), DSDP 43-384-13-3, 50-52 cm; 3, umbilical view, X130; 4, edge view, XI20. 5. Rosita contusa (Cushman), edge view, DSDP 80-548A-29-1, 54-55 cm, X130. 6. Rugoglobigerina hexacamerata Brrnnimann, umbilical view, DSDP 43-384-13-3, 50-52 cm, X330. 7. Rugoglobigerina rugosa (Plummer), umbilical view, DSDP 74-527-32-4, 133-134 cm, X350. 8. Rugoglobigerina rotundata Brrnnimann, umbilical view, DSDP 62-465A-3-4, 4-5 era, X 180. 9. Trinitella scotti Brrnnimann, umbilical view, DSDP 62-465A-3-4, 4-5 era, X200.

94

B.A. MALMGREN

PLATEI

L ..........................................................

(for description

see p. 93 )

,,

,,.....

BIOGEOGRAPHIC PATTERNS

PLATE II

(for description see p. 93 )

95

96 PLATE 111

(for d e s c r i p t i o n see p. 93 )

B.A. MALMGREN

BIOGEOGRAPHIC PATTERNS

trichtian by the dorsal flattening of chambers in later ontogenetic stages and development of a keel or imperforate peripheral band on these chambers. This author agrees with this interpretation. These species are occasionally difficult to distinguish because a keel may not be present on all specimens in a sample of T. scotti, but specimens referable to this lineage were identified with T. scotti if at least the latest few chambers were compressed.

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