Differential dissolution of upper Cretaceous deep-sea benthonic foraminifers from the Angola Basin, South Atlantic Ocean

Marine Micropaleontology, 13 (1988) 47-78

47

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

DIFFERENTIAL DISSOLUTION OF UPPER CRETACEOUS DEEPSEA BENTHONIC FORAMINIFERS FROM THE ANGOLA BASIN, SOUTH ATLANTIC OCEAN JOEN G.V. WIDMARK and BJ(~RN A. MALMGREN Department o/Paleontology, University o/Uppsala, Box 558, S-751 22 Uppsala (Sweden) (Revised and accepted September 15, 1987)

Abstract Widmark, J.G.V. and Malmgren, B.A., 1988. Differential dissolution of Upper Cretaceous deep-sea benthonic foraminifers from the Angola Basin, South Atlantic Ocean. Mar. Micropaleontol., 13: 47-78. Material from the Deep Sea Drilling Project (DSDP) Site 527 from the Angola Basin, South Atlantic Ocean, has been analyzed to determine whether Upper Cretaceous benthonic foraminiferal taxa are differentially sensitive to calcite dissolution, and, if so, to rank their order of susceptibility. Two regimes of dissolution, established on the basis of the degree of planktonic foraminiferal fragmentation, representing stronger and less prominent dissolution within the section studied, were used as a framework for reference. A total of 60 calcareous and eight agglutinated benthonic foraminiferal taxa were identified at the species or genus level; of these, twenty-three calcareous and five agglutinated taxa were selected for the dissolution study. Relative abundance of each of the various taxa was tested statistically, using t-test, between dissolution regimes to assess the significance of the change induced by increased dissolution. Nuttallides truempyi and Neoeponides sp. intermediate form are interpreted as resistant to dissolution. Pullenia spp., Alabamina sp. a, Anomalina sp. a, Praebulimina sp. fusiform, and NuttaUinella sp. a are susceptible to dissolution. The majority of the taxa (16 in number) are unaffected by dissolution because they show no change between dissolution regimes. Among the agglutinated taxa Gaudryina pyramidata is resistant to dissolution, whereas the remaining four taxa are unaffected by dissolution. At the level of superfamilies, one calcareous superfamily (Discorbacea) is resistant, two (Orbitoidacea and Cassidulinacea) are unaffected, and two (Nodosariacea and Buliminacea) are susceptible to dissolution.

Introduction Fossil benthonic foraminifers are one of the most important indicators of paleoecological changes in the marine environment. It is well known that planktonic foraminiferal species are differentially sensitive to calcite dissolution (for example, Murray, 1897; Schott, 1935; Berger, 1970; Malmgren, 1987). Benthonic foraminifers are known to be more tolerant to dissolution than planktonic foraminifers as long as they are alive and protected by the protoplasm. 0377-8398/88/$03.50

However, benthonic foraminifers also show postmortal dissolution to some extent. Berger (1973) estimated that benthonic foraminifers are on the average approximately three times less susceptible to calcite dissolution than planktonic foraminifers. Two major factors controlling the rate of differential calcite dissolution in benthonic foraminifers are: (1) the morphology of the test (Douglas, 1973) and (2) the intensity of borings through the test wall by different predators (Sliter, 1971 ). A third possible factor control-

© 1988 Elsevier Science Publishers B.V.

48 Morphology ~1

Microhabitat

orin

Differential

calcite dissolution

Fig. 1. Suggested interaction between major factors controlling the calcite dissolution of fossil benthonic foraminiferal assemblages. The microhabitat of the living animal controls morphological features such as thickness of the test wall, the outline of the test in side view, and the distribution and size of the pores (Corliss, 1985 ). Calcite dissolution may be higher in species living epifaunally because of the exposure of the test.The test morphology (such as wall thickness and porosity) controlscalcitedissolution,whereas large pores and thin test wall increase the susceptibility (Sliter, 1971). The tendency for the test to be bored by predators is dependent on the morphology of the test (some thin-walled species with large pores are probable more easily penetrated) and indirectly dependent on the microhabitat of the living foraminifer.

ling the rate of calcite dissolution is the specific microhabitat of the living animal. A suggested interaction between these factors is shown in Fig. 1. Several workers have demonstrated the influence of differential calcite dissolution on benthonic foraminiferal assemblages. Nyong (1985) suggested that species compositions in Upper Cretaceous deep-sea sediments from the western North Atlantic are largely dependent on selective dissolution of less resistant species in relation to the Upper Cretaceous calcium carbonate compensation depth (CCD). Douglas (1973), in his study of Pacific deep-sea sediments (DSDP Leg 17), concluded that there is generally a successive improvement in preservation from miliolids through agglutinated

taxa to rotaliids, where rotaliids are thus generally best preserved. Corliss and Honjo (1981) have shown that different species of Recent deep-sea benthonic foraminifers are differentially susceptible to calcite dissolution. Borings in the foraminiferal test wall due to predators may increase dissolution. Sliter (1971) showed the existence of predation on the basis of studies of in situ benthonic foraminifers and in laboratory experiments. He also compared the results with borings in Holocene and Cretaceous foraminifers, and found that borings often occur in specimens of only a few, but identical or related genera. Compositions of fossil deep-sea benthonic foraminiferal assemblages are probably affected by dissolution; individuals of species that are susceptible to dissolution are reduced in abundance or may be eliminated from the sediment, whereas individuals of resistant species are concentrated. The effect of dissolution must, therefore, always be taken into consideration in the context of stratigraphical and paleoenvironmental interpretations based on fossil benthonic foraminiferal assemblages. As far as is known, no detailed quantitative study has been carried out on differential dissolution of pre-Cenozoic benthonic foraminifers from the deep South Atlantic. In the present study, an upper Maastrichtian section from the deepest site (Site 527) of DSDP Leg 74 from the Angola Basin, South Atlantic (Fig. 2) was investigated quantitatively for differential dissolution of benthonic foraminifer. Malmgren (1987) established a dissolution index for this core segment based on the degree of fragmentation of planktonic foraminifers. The site was rotary-drilled and provided 341.5 m of Maastrichtian to Quaternary sediments. During the terminal Maastrichtian, the paleodepth is estimated to have been about 2700 m at this site (Moore et al., 1984). The relative abundances of the 28 most common taxa (at the species or genus level) were compared between groups of samples exhibiting strong and less prominent

49

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S i t e 527.

dissolution to determinate their responses to dissolution, and to establish a ranking of the order of dissolution susceptibility. Material and methods Twenty-four core samples of Maastrichtian age from Hole 527 were analyzed for benthonic foraminifers (Table I). All samples were collected from the interval 289.34-284.69 m, which belongs to the Abathomphalus mayaroensis planktonic foraminiferal zone (Malmgren, 1987). Lithologically the sequence consists of nannofossil chalk and ooze (Moore et al., 1984). The same core segment was used by Malmgren (1987) in his study of differential dissolution of planktonic foraminifers. From the

paleomagnetic data of Hole 527 ( Chave, 1984), Malmgren estimated that the rocks were deposited during a time interval of about 190 ka (66.85-66.66 Ma; Fig. 3). The time scale used is that of Berggren et al. (1985). Malmgren (1987) established two "dissolution regimes", one of moderate dissolution and the other of stronger dissolution, on the basis of the degree of fragmentation of planktonic foraminifers (Fig. 4 ). He ( Malmgren, 1987 ) showed that an increase in relative abundance of planktonic foraminiferal fragments in the sediment is accompanied by a decrease in the ratio of planktonic to benthonic foraminifers (P/B ratio) and a decrease in the percentages of the coarse fraction ( > 63 # m ) , which supported the utility of the degree of fragmentation as an index of dis-

50 TABLEI

Site 527

Upper Cretaceous samples from D S D P Site 527 (Leg 74) studied for differentialdissolution of benthonic foraminifers.Abbreviations S 1-S 12 denote samples referableto the regime of stronger dissolution;abbreviations M 1 3 - M 2 4 indicate samples from the regime of moderate dissolution. "Weight" is totaldry sample weight. Abbr.

Sample

Int.

Depth (m)

Weight (g)

S 1 S 2 S 3 S 4 S 5 S 6 S 7 S 8 S 9 S10 Sll S12

33-1 33-1 33-1 33-1 33-1 33-1 33-1 33-1 33-1 33-2 33-2 33-2

18- 20 37- 39 57- 58 69- 71 84- 86 95- 97 109-111 123-125 139-141 4- 6 22- 23 40- 41

284.69 284.88 285.08 285.20 285.35 285.46 285.60 285.74 285.90 286.05 286.23 286.41

8.22 6.49 10.16 9.12 7.07 7.60 8.30 10.25 12.32 8.76 4.34 5.61

M13 M14 M15 M16 M17 M18 M19 M20 M21 M22 M23 M24

33-2 33-2 33-2 33-2 33-2 33-2 33-3 33-3 33-3 33-3 33-4 33-4

58- 59 76- 77 94- 95 111-113 116-118 144-146 23- 26 67- 69 110-112 145-147 29- 31 33- 35

286.58 286.77 286.95 286.12 287.17 287.45 287.74 288.18 288.61 288.96 289.30 289.34

5.10 5.07 9.20 7.53 8.98 7.99 7.95 7.27 6.93 6.50 8.51 7.40

s o l u t i o n in t h e s e s t r a t a ( A r r h e n i u s , 1952; Berger, 1970). O n e m i g h t a n t i c i p a t e b e n t h o n i c f o r a m i n i f e r a l f r a g m e n t s to r e s p o n d to dissolut i o n in a similar w a y as p l a n k t o n i c f o r a m i n i f eral f r a g m e n t s , as d e m o n s t r a t e d b y M a l m g r e n (1987). H o w e v e r , t h e f r a g m e n t s o f b e n t h o n i c f o r a m i n i f e r s s h o w n o s i g n i f i c a n t r e s p o n s e to d i s s o l u t i o n in t h e m a t e r i a l studied. T h e dissolution regimes established b y M a l m g r e n (1987) are u s e d in t h e p r e s e n t s t u d y as a f r a m e w o r k for t h e a n a l y s i s o f d i s s o l u t i o n in b e n t h o n i c foraminifers. T h e s a m p l e s were i m m e r s e d in d e - i o n i z e d w a t e r a n d p l a c e d o n a r o t a r y table for a b o u t 24 hr. T h e y were w a s h e d over a 6 3 / ~ m sieve; t h e

A

B

Fig. 3. Magnetochronology of the middle-upper Maastrichtian and lowermost Paleocene (P) of Site 527 (A), and a close-up of the upper Maastrichtian sequence used in the analysis of differential dissolution of benthonic foraminifers (B). Details on the stratigraphy and recovery of the sediments are from Moore et al. (1984), and data on magnetic anomalies are from Chave (1984). Ages of magnetostratigraphic boundaries are calibrated to the time scale of Berggren et al. (1985). Maastrichtian material was recovered down to Core 44, but material below Core 38 consists mostly of basalt. Twenty-four samples were analyzed from a 4.65 m long interval within the zone of Abathomphalus mayaroensis (Malmgren, 1987). Note that the top of Magnetic Anomaly 30 lies within the segment analyzed. (Modified from Malmgren, 1987. ) coarse fraction ( > 63/~m) was sieved over a 125 # m s c r e e n a n d q u a n t i t a t i v e l y a n a l y z e d for b e n t h o n i c foraminifers. T h e s a m p l e s c o n t a i n e d b o t h c a l c a r e o u s a n d a g g l u t i n a t e d taxa. N o s p l i t t i n g o f t h e s a m p l e s was n e c e s s a r y b e c a u s e o f t h e relatively low a b u n d a n c e s o f b e n t h o n i c f o r a m i n i f e r s in t h e m , generally below 3.0% of the total foraminiferal content (Malmgren, 1987). T h e n u m b e r o f c a l c a r e o u s s p e c i m e n s in

51

Depth, Age, m

Ma

0

10 i

20

30

i

i

66.65. 285. 66.70.

287

40

50

60

70

80

i

i

i

L

i

?

--V-

o

286 •

-o

== o

Upper Cretaceous benthonic foraminiferal taxa identified at species or genus level in the interval of DSDP Site 527 analyzed here for differential dissolution (527-33-4; 33-35 cm-527--33-1; 18-20 cm). Identified taxa that occurred in at least 75% of the samples in either of the two dissolution regimes distinguished here were selected for further investigation. Selected for dissolution study

36.75' o

288

T A B L E II

Fragments of planktonic foraminifera, %

~

56.80

289 66.85"

\ 8

Fig. 4. Dissolution regimes established by Malmgren (1987) on the basis of the degree of fragmentation of planktonic foraminifers (fragments in relation to entire and fragmented t e s t s ) . Horizontal bars show 95% confidence intervals (from Malmgren, 1987 ).

each sample ranged between 120 and 388 (sample weights were between 4.3 and 12.3 g; Table I). The number of agglutinated specimens was between 6 and 47 per sample. In all 60 calcareous and eight agglutinated taxa were identified at the species or genus level (Table II ). Some specimens, for example, most of the nodosariids, were impossible to assign to species because of their low abundances precluding the study of intraspecific variation. Even though some calcareous specimens could not be identified as to species or genera, they were assigned to one of the following superfamilies: Nodosariacea, Buliminacea, Discorbacea, Orbitoidacea, or Cassidulinacea. Unidentified specimens were between 5.6 and 14.4%. Those taxa that were present in at least 75% of the samples in either of the dissolution regimes were selected for investigation of differential dissolution. The selected taxa include two taxa of Nodosariacea, four taxa of Buliminacea, three taxa of Discorbacea, three taxa of Orbitoidacea, eleven taxa of Cassidulinacea, and five agglutinated taxa ( Table II). Taxonomic notes on the taxa selected are given in Appendix I.

Suborder ROTALIINA Superfamily NODOSARIACEA Astacolus spp. Dentalina aff. cylindroides Reuss Dentalina spp. "Fissurina" spp. Globulina lacrima (Reuss) Globulina I. horrida (Reuss) Guttulina cretosa? Yoshida Guttulina spp. Lagena cf. globosa Montague Lagena spp. Lagena cf. sulcata (Walker and Jacob) Lenticulina cf. rotulata (Lamarck) Lenticulina spp. Nodosaria cf. limbata d'Orbigny Nodosaria velascoensis Cushman Oolina apiculata Reuss Superfamily BULIMINACEA Bolivinoides peterssoni Brotzen Brizalina limonense (Cushman) BulimineUa? beaumonti Cushman and

X X

X

aenz

Praebulimina sp. inflated form Praebulimina sp. spinose form Praebulimina sp. fusiform Pyramidina spp. Reussella sp. nonspinose form Reussella szajnochae (Grzybowski) S tilostomella spp.

X X

X

Superfamily DISCORBACEA Nuttallides truempyi ( Nuttall ) Nuttallides sp. a Nuttallinella sp. a

X X X

Superfamily ORBITOIDACEA Eponides? spp. Neoeponides hillebrandti Fisher Neoeponides sp. intermediate form Neoeponides lunata (Brotzen )

X X X

Superfamily CASSIDULINACEA Alabamina sp. a Allomorphina minuta Cushman Allomorphina trochoides ( Reuss ) Anomalina praeacuta Vasilenko

X

X

52 (Table II cont. )

Selected for dissolution study

Anomalina sp. a Aragonia ouezzanensis (Rey) Aragonia velascoensis (Cushman) Cibicidoides? spp. EUipsobulimina spp. EUipsodimorphina spp. Ellipsogladulina? spp. Ellipsoidella? spp. GavelineUa beccariiformis (White) GavelineUa hyphalus (Fisher) GavelineUa velascoensis (Cushman) Globorotalites spp. Gyroidinoides quadratus (Cushman

X

X

X X

X

and Church)

Gyroidinoides spp. Nonion havense (Cushman and

X

Bermudez

Nonionella spp. Oridorsalis? umbonatus? (Reuss) Osangularia spp. Pleurostomella spp. PuUenia coryeUi White Pullenia quinqueloba (Reuss) Pullenia spp. Quadrimorphina aUomorphinoides

X X

X

( Reuss ) Suborder T E X T U L A R I I N A

Bolivinopsis ? spectabilis

nated benthonic foraminifers on the other. The differences in average relative abundance for each selected taxon, calcareous superfamily, and total number of agglutinated specimens were compared between dissolution regimes using univariate generalized distance analysis (Marcus, 1969 ). The statistical significance of generalized distances (D) was tested using t-test. Variances for raw relative abundances were heterogeneous in many cases, hence relative abundances were arcsine-transformed (Sokal and Rohlf, 1969, p. 386) before computations of the generalized distances. This transformation produced homogeneous variances for most taxa and calcareous superfamilies (Tables III-V). The generalized distance for a taxon that decreases from the regime of moderate to that of stronger dissolution is here said to be "negative", whereas one that increases is said to be "positive". A taxon showing a significantly "positive" D-value is interpreted as resistant to calcite dissolution, and a taxon with a significantly "negative" Dvalue is interpreted as susceptible. Generalized distances and their significance are summarized in Tables III-V.

( Grzybowski )

Dorothia buUetta ( Carsey ) Dorothia pupa (Reuss) Dorothia trochoides ( Marsson ) Gaudryina pyramidata C u s h m a n Spiroplectammina dentata (Alth) Spiroplectammina spp. Tritaxia spp.

Results X X X X X

The relative abundances of selected calcareous taxa, calcareous superfamilies, and selected agglutinated taxa were calculated as follows: calcareous taxa in relation to total number of calcareous specimens, whereas agglutinated taxa were calculated in relation to total number of specimens (calcareous and agglutinated). The definitions of relative abundance for calcareous taxa and agglutinated taxa are different, because of the probable different response to dissolution of calcareous benthonic foraminifers on the one hand and the aggluti-

As a first step in the analysis, a correspondence analysis, based on 21 calcareous taxa, was carried out to determine whether benthonic foraminiferal taxa at all respond to dissolution. Figure 5 shows a plot of the scores of the samples of the first axis against core depth. The change in scores coincides with the change from moderate to stronger dissolution, which suggests that the composition of the calcareous benthonic foraminiferal fauna is altered as an effect of differential dissolution. The changes in faunal composition could possibly have been caused by ecological change affecting the bottom water. However, a more reasonable explanation is probably that the faunal changes are due to dissolution, since absolute concentrations of planktonic foramini-

53 T A B L E III Summary of univariate statistics (generalized distances) of calcareous taxa that occurred in at least 75% of the samples in either of the regimes of dissolution. All values in this table are based on relative abundances {percentages); the relative abundances are arcsine- transformed. F-values show the significance of the heterogeneity of standard deviations (the degrees of freedom are 11 and 11, respectively, in all analyses). D-values are generalized distances for the differences in relative abundance between dissolution regimes. A "negative distance" marks greater abundance for moderate dissolution, and a "positive distance" marks greater abundance for stronger dissolution, t-values show the significance of this difference (the degrees of freedom is 22 in all analyses). The significance level of F and t (if any) is marked by asterisks: * denotes the 5% level, ** denotes the 1% level, and *** denotes the 0.1% level. "Res." marks the response to dissolution and indicate whether a taxa is interpreted as resistant (R) or susceptible (S) to calcite dissolution on the basis of significant t-values. Taxa that do not show significant difference between regimes are interpreted as unaffected to dissolution.

Dentalina app. Globulina lacrirna BulimineUa? beaumonti Praebulimina sp. inflated form Praebulimina sp. fusiform ReusseUa szajnochae NuttaUides truempyi Nuttallides sp. a Nuttallinella sp. a Neoeponides hiUebrandti Neoeponides sp. intermediate Neoeponides lunata Alabarnina sp. a Anomalinapraeacuta Anomalina sp. a Cibicidoides? app. Gavelinella beccariiformis GaveUneUa hyphalus Gyroidinoides quadratus Gyroidinoides app. Oridorsalis? umbonatus? Osangularia? app. PuUenia app.

Strong Moderate F mean mean

D

t

0.05 0.06 0.17 0.15 0.19 0.14 0.37 0.18 0.15 0.19 0.18 0.13 0.12 0.18 0.09 0.06 0.42 0.30 0.11 0.19 0.07 0.10 0.09

-0.72 - 0.45 -0.65 - 0.09 - 1.28 +0.51 +2.37 +0.05 - 1.40 -0.60 + 1.53 +0.39 -1.14 +0.42 -1.28 +0.20 + 0.37 +0.31 +0.72 + 0.52 +0.07 -0.15 - 1.02

1.75 1.11 1.59 0.21 3.13"* 1.24 5.81"** 0.12 3.59** 1.48 3.76** 0.94 2.79* 1.03 3.13"* 0.48 0.91 0.76 1.76 1.27 0.16 0.36 2.51"

0.08 0.08 0.22 0.14 0.93 0.90 0.24 0.18 0.26 0.22 0.09 0.12 0.17 0.16 0.16 0.07 0.40 0.28 0.06 0.16 0.06 0.11 0.14

1.11 1.57 1.27 4.06* 2.12 1.75 2.03 1.97 1.80 2.36 1.64 1.35 1.31 2.34 2.01 1.30 2.23 1.17 1.80 1.20 2.96* 1.33 1.86

Res.

S R S R S S

S

T A B L E IV

Summary of univariate statistics (generalizeddistances) of benthonic foraminiferalgroups of higher taxonomiclevel (rotaliid superfamiliesand agglutinatedspecimens).For details,see caption of Table Ill.

NODOSARIACEA BULIMINACEA DISCORBACEA ORBITOIDACEA CASSIDULINACEA Agglutinated

Strong mean

Moderate mean

F

D

t

Res.

0.25 0.31 0.46 0.39 0.78 0.32

0.30 0.36 0.41 0.37 0.77 0.30

1.65

- - 1.57 -0.88 +0.86 + 0.64 +0.14 +0.47

3.83*** 2.15" 2.12" 1.57 0.35 1.15

S S R

1.38 2.42 1.07 2.16 8.74***

54 TABLE V Summary of univariate statistics(generalizeddistances) of agglutinated selectedtaxa. For details,see caption of Table III.

Dorothia trochoides Gaudryina pyramidata Spiroplectammina dentata Spiroplectamminea spp. Tritaxia spp.

Strong

Moderate

mean

mean

0.15 0.15 0.08 0.06 0.14

285 t- •j

Strong

o~e ~ • 286 E lZ T I--

287 -

/

W 0

I

,./

UJ nO

./

I

Moderate

288 -

1

, / I \ I 289,

I -0.4

I -0.2

i

I l I

0

I

+0.2

I

+0.4

FIRST AXIS

Fig. 5. Plot of scores of f'h-st correspondence analysis axis

against depth in Site 527. The correspondence analysis was based on 21 calcareous benthonic foraminiferal taxa in the 24 samples analyzed in this study. The change in scores coincides with the change from moderate to stronger dissolution (compare Fig. 4), which suggests that the calcareous b e n t h o n i c foraminiferal fauna is altered as a n effect of differential dissolution.

F

D

t

Res.

0.12 0.86

2.40 2.62

+0.70 + 1.30

1.72 3.33**

R

0.10 0.09 0.12

1.41 1.29 1.01

-0.46 -0.59 +0.48

1.13 1.45 1.17

fers (number of tests per gram of sediment) decrease from values in the range of 1.2-15.1 × 103 in the regime of moderate dissolution to values between 0.03-3.5 × 103 in the regime of stronger dissolution (Malmgren, 1987). This is overwhelming evidence that dissolution exerted a major control on the foraminiferal relative abundances, because if the change had been ecologically induced, we would have expected change in relative abundances without concomitant decrease in absolute abundance. Nyong (1985) stated that absence of strong bottom-water circulation in the Cretaceous ocean prevented provincialism of benthonic foraminiferal faunas, but aided uniform and broad distributions of faunas. He, therefore, concluded that species compositions in the Upper Cretaceous deep-sea basins are chiefly the product of differential dissolution. In the following, the degree to which our various taxa are affected by dissolution will be analyzed. The dominating faunal element in the material studied is represented by the suborder Rotaliina, which constitutes 81.4-95.2% of the total number of benthonic foraminifers in the samples studied (the rest consists of agglutinated forms). Among the calcareous superfamilies Cassidulinacea dominates (42.8-61.0%), followed by Discorbacea (9.8-29.4%) and Orbitoidacea (8.3-17.4%). Nodsariacea is rare in all samples, especially in those of strong dissolution. Gavelinella beccariiformis (6.9-23.0%) and Nuttallides truempyi (2.2-21.8%) are the most abundant species (Appendix II).

55

Ranking of taxa Calcareous taxa: Two taxa, namely Neoeponides sp. intermediate form and Nuttallides truempyi (Fig. 6), are regarded as resistant to dissolution because they increase in relative abundance with increasing dissolution. A majority of the taxa (sixteen out of the 23 analyzed; Figs. 6 and 7) show no significant difference in relative abundance between regimes, which is interpreted as evidence of no response to dissolution (Table III). The remaining five taxa are regarded as susceptible since they show a decrease in relative abundance from the regime of less prominent dissolution to the regime of stronger dissolution: Alabamina sp. a, Anomalina sp. a, Pullenia spp. (Fig. 7), NuttaUinella sp. a, and Praebulimina sp. fusiform (Fig. 6; Table III). Generalized distances (D) are used to rank the selected calcareous taxa within each group with regard to their response to dissolution. Resistant taxa (from most to less resistant) are: Nuttallides truempyi and Neoeponides sp. intermediate form; unaffected taxa (without ranking) are: Dentalina spp., Globulina lacrima, BulimineUa? beaumonti, Praebulimina sp. inflated form, Reussella szajnochae, Nuttallides sp. a, Neoeponides hillebrandti, Neoeponides lunata, Anomalina praeacuta, Cibicidoides? spp.,

GavelineUa beccariiformis, Gavelinella hyphalus, Gyroidinoides quadratus, Gyroidinoides spp., Oridorsalis? umbonatus?, and Osangularia? spp.; susceptible taxa (from less to most susceptible) are: PuUenia spp., Alabamina sp. a, Anomalina sp. a, Praebulimina sp. fusiform and Nuttallinella sp. a, (see Table VI ). Agglutinated taxa: The relative abundance of the total number of agglutinated specimens was between 4.8 and 18.6% in the samples studied here. The most abundant species are represented by Dorothia trochoides and Gaudryina pyramidata with relative abundances of 0.0-4.1% and 0.0-5.6%, respectively. One might anticipate that agglutinated foraminifers with arenaceous tests would all be

highly resistant to dissolution. However, only one of the five agglutinated taxa analyzed here, Gaudryina pyramidata (Fig. 8), shows a significant increase in relative abundance with stronger dissolution and is, therefore, interpreted as being resistant to dissolution. All of the remaining agglutinated taxa, Do-

rothia trochoides, Spiroplectammina dentata, Spiroplectammina spp., and Tritaxia spp. (see Table V; Fig. 8), show no changes at all. The insignificant changes in relative abundances for the remaining agglutinated taxa could probably be due to the low representation in the samples studied. The total number of agglutinated specimens shows a clear tendency for increase in relative abundances with stronger dissolution (Fig. 8). The high F-value in Table IV is caused by the high values of relative abundances of three samples at the bottom of the regime of moderate dissolution (Appendix II). Superfamilies: Calcareous benthonic superfamilies also display a differential response to dissolution. Two superfamilies, Nodosariacea and Buliminacea, decreased in relative abundance with stronger dissolution and are interpreted as being susceptible to dissolution (significance at the 0.1% and 5% level, respectively; Fig. 8). One superfamily, Discorbacea, was interpreted as resistant on the basis of a significant increase in relative abundance with stronger dissolution (at the 5% level; Fig. 8). One might expect this superfamily to belong to the resistant group, because it is composed of only three taxa (and unidentified Discorbacea), among which Nuttallides truempyi is a dominating species that shows great resistance to dissolution (Table III; Fig. 6). The remaining two superfamilies, Orbitoidacea and Cassidulinacea (Fig. 8), show no difference between regimes and are, therefore, interpreted as unaffected by dissolution. In conclusion, one superfamily, Discorbacea, is found to be resistant, two superfamilies, Cassidulinacea and Orbitoidacea, are unaffected,

56

Dentalina spp.

Globulina lacrima

o15

-0

Bu mine a'~ beaumonti

;

1'.5

;

P. sp. inflated form

1'o

285-

•o

S

286-i J

M

: 287-

•e

288 -

289 -

D= - 0 . 4 5

• D= - 0 . 7 ~

P. sp, fusiform

Reussella s z a j n o c h a e

D= - 0 . 6 5

Nuttallides sp. a

D= - 0 . 9

Nuttailides truempyi

1'o

1'5

2'0

285"

286-

%

S

I

. . . . . . . .

M 287-

|

288,

289'

OD=_ 1.28 °o

Nuttallinella sp. a 0

u

I

5

10

D= +0.51

°De= +0.05

Neoeponides hillebrandti

N, sp. intermediate form

D= * 2 . 3 7

Neoeponides lunata

~

~

6

285

DO

° °

286

•

s M

287

288

289 -

D= -1.47

•

D= - 0 . 6 0 '

D= . 1 . 5 3

• D= *0.39

Fig. 6. Plots of relativeabundances (percentages) of selectedspecies and genera of Nodosariacea, Buliminacea, Discorbacea, and Orbitoidacea. Relative abundances are plotted against depth in site.The intervalof strong dissolutionis denoted S, and the intervalof moderate dissolution is denoted Air.Percentages are scaled at the upper part of each diagram. Significance of generalized distances (D) is shown by asterisks; *=significance at the 5 % level, **=significance at the 1% level,and *** --significanceat the 0.1% level.The signs of significantD-values indicate whether a taxon is susceptible (negative sign) or resistant (positive sign) to calcitedissolution.

57

~

C i b i c i d o i d e s ? spp.

A n o m a l i a sp. a

Anomalina praeacuta

A l a b a m i n a sp. a

'

u

,;

015

0

;

1~5

285-

:.

•0

g

286 "

s

i •%

287-

O•

288

J

289 •

t(-

G~v~l nella b e c c a r i f o r m i s

lb

D = +0.42

D= - 1 . 1 4

•

1~

•

Gavelinella hyphalus

- 1.28

O s a n g u l a r i a ? spp. i 0

2'o

D =

, 2

i 4

D = +0.20

Oridorsalis? umbonatus?

I 6

285-

286-

s M

__1 287

-

288-

289-

•

D = +0.31

D =•+0.37

Gyroidinoides quadratus

G y r o i d i n o i d e s spp.

D= -0.15

•

D = +0.07

Pullenia spp.

285 -

t s M

286-

287

i,

288-

2894~

D= +0.72

D = +0.52

D= - 1 . 0 2

Fig. 7. Plots of relative abundances (percentages) of selected species and genera of Cassidulinacea. For details, see caption of Fig. 6.

58 T A B L E VI Ranking of dissolution susceptibility of Upper Cretaceous calcareous taxa selected for analysis. For details, see caption of Table III. The resistant taxa are ranked from most to least resistant; the unaffected taxa are without ranking, and the susceptible taxa are ranked from least to most susceptible to dissolution.

Resistant taxa

NuttaUides truempyi Neoeponides sp. intermediate form Unaffected taxa

Dentalina spp. Globulina lacrima Buliminella? beaumonti PraebuIimina sp. inflated form Reussella szajnochae Nuttallides sp. a Neoeponides hillebrandti Neoeponides lunata Anomalina praeacuta Cibicidoides? spp. GavelineUa beccariiformis GavelineUa hyphalus Gyroidinoides quadratus Gyroidinoides spp. Oridorsalis ? umbonatus? Osangularia? spp. Susceptible taxa

Pullenia spp. Alabamina sp. a Anomalina sp. a Praebulimina sp. fusiform NuttallineUa sp. a

and two superfamilies, Nodosariacea and Buliminacea, are susceptible to dissolution. Among the susceptible superfamilies, Buliminacea appears to be less susceptible than Nodosariacea (Table IV; Fig. 8). Discussion In his study of benthonic foraminifers from the Pacific (DSDP Leg 17), Douglas (1973) concluded that miliolid species are less preservable than rotaliid species, and that agglutinated species seem to be intermediate between the former two groups of benthonic foraminifers.

Also, species with the thickest test walls and lowest porosity seem to be best preserved, whereas thin-walled and rectilinear forms with numerous pores seem to be the least preservable. Douglas (1973) further stated that agglutinated taxa with smooth textures generally show a high degree of selectivity in their use of building material, and that these foraminifers seem to be better preserved than species that are less selective in this respect. Among the taxa studied by Douglas (1973), Valvulina and KarrerieUa were suggested to be the most resistant genera, whereas Bolivinopsis and Hyperammina-like genera were suggested to be the most susceptible. Corliss (1985) showed that test morphology in rotaliid taxa can be correlated with the microhabitat of the living benthonic foraminifer as epifaunal or infaunal species. Furthermore, infaunal species are stratified with respect to the depth of habitat (some may be found living down to a depth of 15 cm; Corliss, 1985). Corliss noted that piano-convex and biconvex forms with a sharp periphery in side view represent epifaunal habitat, and more rounded forms with less sharp periphery in side view represent infaunal habitat. Also, the size and distribution of the pores are directly related to the microhabitat. Epifaunal species have fewer and larger pores; the pores are more often distributed over only one side of the test. Alternatively, the pores may form a patchy pattern. Infaunal species have pores more equally scattered over the whole test. Borings of the tests by predators may affect the composition of fossil benthonic foraminiferal assemblages. Sliter (1971) concluded that some Holocene and Cretaceous benthonic foraminiferal species show a preferred area of attack by boring predators. Trochospiral genera (such as Gyroidina, Gyroidinoides, Hoeglundina, Laticarinina, and Rosalina) are often bored on the dorsal surface. Sliter (1971) noted that the preference of borings most likely is related to the aperture-down life position, which caused the dorsal surface to be more exposed to

59 Nodosariacea

10 285

Orbitoidacea

Discorbacea

Buliminacea 10

1'5

115~

210

2'5

1'0

3'0

1'5

• ° ~.

-

286 -

S

. . . .

J

_

M 287oo

288-

289-

~e

D= - 0 . 8 8

• D ~ -1.67

Cassidulinacea 4'5

5'0

5'5

D = +0.64

D= +0.86

Gaudryina p y r a m i d a t a

Dorothia t r o c h e i d e s

Spiroplectammina dentat~

6'0

285-

286-

S •

M

287-

288-

289•o

D = +0.70

D = +0.14

T r i t a x i a spp.

Spiroplectammina spp.

2

3

D = +1.36

•

[~= - 0 . 4 6

Agglutinated specimens

1'o

4

1~

285Q oo 286-

s M 2s7

I

o o

0 o

288-

289-

t

o•

D = -O.59

•

~)= + 0 . 4 8

D= +0.47

Fig. 8. Plots of relative abundances (percentages) of calcareous superfamilies such as Nodosariacea, Buliminacea, Discorbacea, Orbitoidacea, Cassidulinacea, agglutinated selected taxa at species or genus level, and totals of agglutinated specimens. For details, see caption of Fig. 6.

60 the predators. Elongate genera (such as Bulimina, Colomia, Praebulimina, and Uvigerina ) are occasionally bored on the apertural half of the test, or bored parallel to t h e long axis of the test (Sliter, 1971 ). Sliter (1971) suggested that both location patterns may be a result of the life position or accessibility of the prey to benthonic predators. Sliter (1971) stated that evidence of predation also provides information on the living habit, habitat, and community structure of the foraminiferal prey. Predation can directly influence the interpretation of foraminiferal production and rates of sedimentation based on foraminiferal production (Sliter, 1971). In the present discussion, an attempt is made to explain the differential sensitivity to dissolution in terms of the two major factors controlling preservation of benthonic foraminifers, namely test morphology and microhabitat of the living foraminifer (Fig. 1 ). The third factor, borings by predators, is not evaluated because of the difficulty in quantifying the intensity of borings.

Calcareous taxa Corliss (1985) noted that Cibic~doides kullenberqi (Parker), Hoeglundina elegans ( d'Orbigny), Oridorsalis tener (Brady), and Planulina wuellerstorfi ( Schwager ) are epifaunal, and that Chilostomella oolina ( Schwager), Globobulimina a/finis (d'Orbigny), and Melonis barleeanum ( Williamson ) are infaunal. In the present material, most of the calcareous taxa analyzed could be interpreted as epifaunal or infaunal on the basis of their test morphology by comparison with the morphotypes shown in Corliss (1985; table 7 herein). As mentioned before, Gavelinella beccariiformis and Nuttallides truempyi are the most frequent species in the material studied. Together they dominate the fauna but show different patterns of change with time (Figs. 6 and 7, respectively). According to the results of Corliss (1985), N. truempyi with its strongly plano-

convex outline in side view, sharp periphery, and small pores could be interpretated as an epifaunal species (Table VII). An epifaunal habitat would result in greater exposure of the test to dissolution than an infaunal habitat. It may, therefore, be anticipated that N. truempyi should decrease in relative abundance with stronger dissolution, but the observed change is in the opposite direction. In contrast to Nuttallides truempyi, Nuttallinella sp. a of the same superfamily (Discorbacea) shows an opposite pattern in decreasing in relative abundance with stronger dissolution. Nuttallinella sp. a is interpreted as representing an epifaunal habitat (strongly pianoconvex and sharp periphery). If the microhabitat were the main factor controlling dissolution, this species thus changes in the way expected. Gavelinella beccariiformis and G. hyphalus seem to be unaffected by dissolution in the sense that they show no clear difference in relative abundance between regimes of dissolution. The morphology of these species, characterized by a rounded trochospiral test with large pores, especially on the umbilical side, may suggest an epifaunal habitat (B.H. Corliss, pers. comm., 1987). Two taxa (PuUenia spp., and Praebulimina sp. fusiform) exhibit "infaunal" test morphologies, but show susceptibility in that they decrease in relative abundance with stronger dissolution. The pores are minute and distributed over the whole test; these taxa are morphologically similar to Chilostomella oolina and Globobulimina a/finis, which were found by Corliss (1985) to be infaunal (Table VII). Alabamina sp. a is suggested to be epifaunal by Corliss (pers. comm., 1987), and this form, decreasing in relative abundance in relation to increased dissolution, conform to the hypothesis that epifaunal species are more exposed to dissolution. The borings in the specimen of Alabamina sp. a (see Plate III, la) indicate an epifaunal habitat whereas epifaunal biconvex species are suggested to provide a preferred area

61 TABLE VII Various benthonic characters suggested by Corliss (1985) to vary between epifaunal and infaunal species, and interpretations of microhabitats of calcareous taxa analyzed here. In cases where interpretations of microhabitat is doubtful, the presumed habitat is marked with a question mark. Epifaunal characters Planoconvex

Corli~, 1 9 8 5 Cibicidoides hullenbergi Hoeglundina elegans Oridorsalis tener Planulina wueUerstorfi Chilostomella oolina Globobulimina a/finis Melonis barleeanum Present study Alabamina sp. a Anomalina sp. a Anomalina praeacuta Cibicidoides? sp. Gavelinella beccarii/ormis Gavelinella hyphalus Gyroidinoides quadratus Gyroidinoides spp. Neoeponides lunata NuttaUides sp. a Nuttallides truempyi NuttaUineUa sp. a Oridorsalis ? umbonatus ? Osangularia? spp. Neoeponides sp. intermediate

Infaunal characters

BiPores one convex side

Pores absent

X X X

X

X

X

X

Periphery Pianosharp spiral

Pores small

X X

X

X

X X

X X X X

X X X

X X

(X) (X) (X)

X

X

X

X X X

E E E E I I I

E E E

E X X

X X

X X

X

X (X) X (X) (X)

Periphery rounded

(X ) (X ) X (X ) X

X X

Pores large

Habitat

(x)

X

X X X X X X

E E E E E E E E E E E?

form

Neoeponides hiUebrandti BulimineUa? beaumonti Dentalina spp. Globulina lacrirna Praebulimina sp. inflated form Praebulimina sp. fusiform Pullenia spp. ReusseUa szajnochae

X

of attack to predators (Sliter, 1971). In summary, 11 of the 16 taxa that are interpreted as epifaunal, are here found to be unaffected by dissolution; two are resistant, and three are susceptible to dissolution. Among those interpreted as infaunal, five taxa are unaffected, two taxa are susceptible, and none is resistant to dissolution (Table IX). This suggests that in this case the microhabitat plays a minor part in controlling the pattern of differential dissolution of benthonic foraminifers. For evaluating the other main factor that may

X X

X X X X X X

X X X X X X X

E? I I I I I I I?

control differential dissolution of benthonic foraminifers, the calcareous taxa analyzed were visually allocated to three different groups with respect to wall thickness: thick-walled, "intermediate"-walled, and thin-walled ( Table VIII ). Pullenia spp., Alabamina sp. a, Anomalina sp. a, and Praebulimina sp. fusiform are all interpreted as susceptible to dissolution. They are all more or less thin-walled, which might e x plain this susceptibility. The majority of taxa that are interpreted as unaffected by dissolution (Reussella szajno-

62 TABLE

VIII

Visually estimated allocationof analyzed Upper Cretaceous calcareous benthonic foraminifers into three groups on the basis of the thickness of the test walls. "Response" denotes whether a taxon is interpreted as unaffected by dissolution (U), resistantto dissolution (R), or susceptible to dissolution (S).

Wall thickness

Thick

Reussella szajnochae Neoeponides hillebrandti Anomalina praeacuta Cibicidoides? spp. GavelineUa beccariiformis GavelineUa hyphalus Gyroidinoides spp. Oridorsalis? umbonatus? Buliminella? beaumonti Nuttallides sp. a Nuttallides truernpyi Neoeponides sp. intermediate

X X X X X X X X

Intermediate

Thin

Response

U U U U U U U U U U

X X X X

R R

form

Neoeponides lunata Anomalina sp. a Gyroidinoides quadratus Osangularia? spp. Dentalina spp. Globulina lacrima Praebulimina sp. inflated form Praebulimina sp. fusiform Nuttallinella sp. a Alabamina sp. a PuUenia spp. TABLEIX Summary of the relation between microhabitat and differential benthonic foraminiferal dissolution based on analyzedcalcareous taxa and susceptibletaxa (percentsare givenin brackets). Microhabitat is suggestedto have a minor influenceon differential benthonicforaminiferaldissolutionbecausethe resistanttaxaare within the groupof epifaunal habitat and the susceptible taxa are nearly equally distributed between epifaunal -and infaunal, respectively. Microhabitat Resistant Unaffected Susceptible Total Epifaunal Infaunal

2(12.5) 11(68.8) 3(18.8) -(0.0) 5(71.4) 2 (28.6)

16(100.0) 7(100.0)

chae, Neoeponides hillebrandti, Anomalina preacuta, Cibicidoides? spp., Gavelinella beccariiformis, Gavelinella hyphalus, Gyroidinoides spp., a n d Oridorsalis? umbonatus?), are all m o r e or less t h i c k walled. Buliminella? beaumonti, NuttaUides sp. a, Neoeponides lunata, Gyroidinoides quadratus, a n d Osangularia? spp., re-

X X X X X X X X X X X

U S U U U U U S S S S

g a r d e d t o h a v e a wall t h i c k n e s s i n t e r m e d i a t e b e t w e e n t h e g r o u p s of t h i c k - w a l l e d a n d t h i n walled t a x a , are i n t e r p r e t e d t o be u n a f f e c t e d b y dissolution. Dentalina spp., Globulina lacrima, a n d Praebulimina sp. i n f l a t e d f o r m are all m o r e or less t h i n - w a l l e d a n d are i n t e r p r e t e d as b e i n g u n a f f e c t e d b y dissolution. One o f t h e t a x a , i n t e r p r e t e d as r e s i s t a n t to dissolution, Neoeponides sp. i n t e r m e d i a t e f o r m is r e g a r d e d to h a v e t e s t walls o f i n t e r m e d i a t e thickness. Nuttallides truempyi, t h e o t h e r t a x o n i n t e r p r e t e d as being r e s i s t a n t to dissolution, also h a s t e s t walls of i n t e r m e d i a t e t h i c k n e s s . T h i s t a x o n possesses a n o t h e r f e a t u r e t h a t m a y control dissolution, n a m e l y a poreless h y a l i n e boss at t h e c e n t e r of t h e umbilical side. M a n y speci m e n s o f N. truernpyi w o u l d h a v e d i s a p p e a r e d as a r e s u l t of d i s s o l u t i o n or w o u l d h a v e b e e n c o u n t e d as f r a g m e n t s if t h e boss h a d n o t pre-

63 TABLE X Summary of the relation between test morphology ( i.e. wall thickness) and differential benthonic foraminiferal dissolution based on analysed calcareous taxa that are referable to each of the categories of resistant, unaffected, and susceptible taxa (percents are given in brackets). Test morphology is suggested to be a major factor controlling differential benthonic foraminiferal dissolution because no one of the susceptible taxa are thick-walled and no one of the resistant taxa are thin-walled. Watlthickness Resistant Unaffected Susceptible Total Thick Intermediate Thin

-(0.0) 2(25.0) -(0.0)

8(100.0) 5(62.5) 3(42.9)

-(0.0) 1(12.5) 4(57.1)

8(100.0) 8(100.0) 7(100.0)

vented total dissolution of the specimens. In summary, all the calcareous taxa that are thick walled (eight in number), are here found to be unaffected by dissolution. Among the taxa, which have intermediate wall thickness, two taxa are resistant, five are unaffected, and one is susceptible to dissolution. The thin-walled taxa are all within the groups of unaffected or susceptible taxa (three and four, respectively; Table X). This suggests that wall thickness plays a more important part in controlling the differential dissolution of benthonic foraminifers than the microhabitat. The tendency would probably have been even more obvious if a sufficient number of nodosarian specimens had been available in the material.

Calcareous superfamilies No taxa of the Nodosariacea analyzed here show any response to dissolution. Only two taxa ( Dentalina spp. and Globulina lacrima ) were present in a sufficient number of samples to permit analysis of differential dissolution. It is well known that nodosariids are rare in deepsea sediments; in "normal" DSDP samples (about 3-5 cc) they are represented by a few specimens per species (Dailey, 1983). The susceptibility to dissolution among the nodosariids might be explained by the relatively homogeneous test structure, for example, wall

thickness and porosity. Douglas (1973) noted that thin-walled, rectilinear forms with a large number of pores seem to be the least preservable, a condition that would be applicable to most nodosariids. This suggestion is supported by the fact that Nodosariacea is decreasing in relative abundance and therefore interpreted as susceptible to dissolution. Buliminacea as a group is susceptible to dissolution. The response to dissolution is not so obvious as in Nodosariacea, which might be explained by the more robust test morphology. Predation by boring predators (such as marine nematodes and gastropods) may enhance the susceptibility in the superfamilies of Nodosariacea and Buliminacea. Sliter (1971) reported that, among 14 Upper Cretaceous calcareous bathyal genera containing bored specimens, 10 genera belonged to Nodosariacea and Buliminacea. Nuttallides truempyi, a dominating form in the present material, is one of the three taxa of Discorbacea identified here. This species constitutes between 11 and 93% of all Discorbacea. Since N. truempyi is highly resistant to dissolution (Fig. 6), the Discorbacea as a whole is also ranked as resistant. The remaining two superfamilies, Orbitoidacea and Cassidulinacea, show no obvious response to dissolution. Apart from unidentified specimens, Orbitoidacea is represented by three taxa. Neoeponides hillebrandti, which shows no response to dissolution, dominates the superfamily to a lesser extent (relative abundances between 1.5 and 8.2% ). The two other, N. sp. intermediate form and N. lunata have relative abundances between 0 and 7.2% and between 0.4 and 5.0%, respectively. An explanation for the lack of a clear trend in Cassidulinacea, the dominating superfamily in this material, could be the heterogeneous and highly variable test morphologies (e.g. wall thickness) within this superfamily, as well as the wide variety of microhabitats in which the cassidulinacean taxa once lived.

64

Agglutinated taxa Gaudryina pyramidata is the only species that responds to dissolution through an increase in relative abundance in the regime of stronger dissolution. The walls of this species are rather compact, smooth, and built up of small particles. The pores are rare or absent, and this, together with its finely grained wall texture, may contribute to the resistance of G. pyramidata (Douglas, 1973 ). One might expect that the areno-agglutinated benthonic foraminifers would be resistant to dissolution. This may be so at the suborder level, because a tendency towards enrichment with stronger dissolution is evident ( Fig. 8). Three samples near the bottom of the regime of moderate dissolution have at least twice as high values of relative abundance as the remaining samples in this regime. Nevertheless, the diversity of agglutinated taxa is low in the material studied, probably because of the susceptibility of the wall cement, which causes some agglutinated specimens to disaggregate (Douglas and Woodruff, 1981; Corliss, 1985).

Summary An Upper Cretaceous sequence of the Deep Sea Drilling Project (DSDP) Site 527 from the Angola Basin, South Atlantic Ocean, was analyzed in an attempt to determine whether benthonic foraminiferal taxa from these strata are differentially sensitive to calcite dissolution, and, if so, to rank their order of susceptibility. Two regimes of dissolution, established by Malmgren (1987), representing stronger and less prominent dissolution within the segment analyzed, were used as a framework for this study. A total of 60 calcareous and eight agglutinated benthonic foraminiferal taxa were identified at species or genus level. The fauna is dominated by a single calcareous suborder, Rotaliina, and the most abundant superfamily is represented by Cassidulinacea. Gavelinella beccariiformis and NuttaUides truempyi are the

most common species in the material studied. The diversity and number of agglutinated benthonic foraminifers is low. Twenty-three calcareous and five agglutinated taxa were selected for analysis of differential calcite dissolution. A taxon that increases in relative abundance with stronger dissolution is interpreted as resistant to dissolution, whereas a taxon that decreases in relative abundance is interpreted as susceptible to dissolution. Taxa that did not show any significant change in relative abundances between regimes of dissolution were interpreted as unaffected. A ranking was made to establish an order of precedence of the responding benthonic foraminiferal taxa from less to most susceptible, using generalized distances. (1) Two taxa, Nuttallides truempyi and Neoeponides sp. intermediate form are interpreted as being resistant to dissolution (Table VI). Five taxa, PuUenia spp., Alabamina sp. a, Anomalina sp. a, Praebuliminasp. fusiform, and NuttaUineUa sp. a are interpreted as being susceptible to dissolution (Table VI). A majority oftaxa (16 in number) are interpreted as being unaffected by dissolution (Table VI). (2) Among the agglutinated taxa analyzed, one ( Gaudryina pyramidata) is interpreted as resistant to dissolution, whereas the remaining four taxa are interpreted as unaffected by dissolution (Table V). (3) At the superfamily level one calcareous superfamily (Discorbacea) is interpreted as resistant, two (Orbitoidacea and Cassidulinacea) are interpreted as unaffected, and two (Nodosariacea and Buliminacea) are interpreted as susceptible to dissolution ( Table IV). (4) An evaluation is made of two factors controlling differential dissolution, wall thickness and microhabitat, to assess which one that has the greatest influence. Wall thickness is suggested to be the major factor controlling dissolution, whereas the habitat (epifaunal or infaunal) is suggested to be of minor importance (Tables I X - X ) . (5) Studies of differential dissolution are

65 more complex in benthonic foraminifers than in planktonic foraminifers because benthonic foraminifers are more heterogeneous with respect to shell material and shell microstructure. Benthonic foraminifers are divided into different suborders and superfamilies, which are distinguished by differences in these characters. In contrast, planktonic foraminifers all belong to a single superfamily (Globigerinacea) within the suborder of Rotaliina, and they exhibit greater homogeneity with respect to shell material and microstructure. Acknowledgements

This paper is part of J.G.V.W.'s Doctoral Dissertation. J.G.V.W. is responsible for the taxonomy, census counts, interpretations of the data, and conclusions; B.A.M. initiated and supervised this project. We thank Dr. Bruce Corliss, Duke University, and Dr. William Sliter, U.S. Geological Survey, for kindly reviewing the manuscript, and for providing valuable comments on it. Additional thanks go to Professor Richard A. Reyment, University of Uppsala, and Dr. Peter Bengtson, University of Uppsala, who scrutinized the manuscript. We also wish to thank Birgit Jansson, University of Uppsala, for preparing the samples, Dagmar EngstrSm, University of Uppsala, for drafting assistance, Eva Reyment and Martin Feuer, University of Uppsala, for photographic assistance. Deep-sea samples used in this study were generously supplied through the assistance of the Ocean Drilling Program (ODP). Appendix I -- Taxonomical lected taxa

notes

on se-

The systematics in this study follows that of Loeblich and Tappan (1964). Previous studies on Maastrichtian deep-sea benthonic foraminifers from the South Atlantic by Beckmann (1978), Dailey (1983), and Sliter (1977) are also taken into consideration.

Order FORAMINIFERIDAEichwald, 1830 SuborderTEXTULARIINADelageand Herouard, 1896 SuperfamilyLITUOLACEAde Blainville,1825 FamilyTEXTULARIIDAEEhrenberg,1838 SubfamilySPIROPLECTAMMINIAECushman, 1927 Genus Spiroplectammina Cushman,

192 7

Spiroplectammina dentata (Alth) ( Plate V, 4 ) 1850 TextularinadentataAlth, p. 262, pl. 5,13. Specimens possessing the typical spines at the border of the periphery are included in this species. Some specimens with poorly preserved typical spines are also included in this species. The species is previously reported from the Maastrichtian of the South Atlantic by Beckmann (1978), Sliter (1977) and Dailey ( 1983 ).

Spiroplectamminaspp. Various forms of Spiroplectammina that do not agree with the concept ofS. dentata'as used here are included in this taxon. Some calcareous-agglutinated specimens of Spiroplectammina are also included. FamilyATAXOPHRAGMIIDAESchwager,1877 SubfamilyVERNEUILININAECushman, 1911 Genus Gaudryina d'Orbigny, 1839

Gaudryina pyramidata Cushman (Plate V, 5) 1926 GaudryinalaevigataFranke var. pyramidata Cushman, p. 431,pl. 16,8. This is a characteristic species with early triserial chamber arrangement, becoming biserial in later ontogeny. It is reported by Beckmann (1978), Sliter (1977) and Dailey (1983), from the Maastrichtian of the South Atlantic Ocean. Genus Tritaxia Reuss, 1860

Tritaxia spp. (Plate V, 6) Representatives of this form are mostly small

66

PLATEI

67

and juvenile. It was impossible to consistently assign the specimens to a species. Species such as T. globulifera (ten Dam and Sigal) and T. trilatera Cushman are probably included in this taxon. Subfamily GLOBOTEXTULARIINAE Cushman, 1927 Genus Dorothia Plummet, 1931 Dorothia trochoides (Marsson) (Plate V, 3a-b)

1878 Gaudryina crassa Marsson var. trochoides Marsson, p. 158, pl. 3,27.

This form is the most abundant agglutinated taxa in the material studied. Dorothia trochoides resembles D. oxycona (Reuss) but is smaller and possesses a globular, rounded initial end, a n d the two latest chambers are more inflated. This species is previously reported from sediments of Maastrichtian age from the South Atlantic by Beckmann (1978). Suborder ROTALIINA Delage and Herouard, 1896 Superfamily NODOSARIACEA Ehrenberg, 1838 Family NODOSARIIDAE Ehrenberg, 1838 Subfamily NODOSARIINAE Ehrenberg, 1838 Genus Dentalina Risso, 1826

single specimen in the material studied is assigned to Dentalina aft. cylindroides Reuss and not included in this taxon. Family POLYMORPHINIDAE d'Orbigny, 1839 Subfamily POLYMORPHININAE d'Orbigny, 1826 Genus Globulina d'Orbigny, 1826 Globulina lacrima (Reuss) (Plate I, 2)

1845 Polymorphina (Globulina) lacrima Reuss, p. 40, pl. 12,6; pl. 13,83.

This species is distinguished from other unilocular forms by its hardly visible, but for this species characteristic sutures. Previously reported from the Maastrichtian of the South Atlantic by Dailey (1983) and Sliter (1977). This species is also reported by Beckmann (1978), who used the name G. l. lacrima ( Reuss ) . Superfamily BULIMINACEA Jones, 1875 Family TURRILINIDAE Cushman, 1927 Subfamily TURRILININAE Cushman, 1927 Genus BuUmineUa Cushman, 1911 BulimineUa? beaumonti Cushman and Renz (Plate I, 3)

1946 Buliminella beaumonti Cushman and Renz, p. 36, pl. 6,7a-c.

Dentalina spp. (Plate I, 1 )

This form includes all specimens with the genus characteristics given by Loeblich and Tappan (1964). The specimens of Dentalina spp. occur by a single specimen in most samples. One

Forms with distinct, sinuous, and translucent sutures are included in this species. The aperture possesses a toothplate. Closely related species such as B. grata (Parker and Bermudez) are also included within the synonymy of this

PLATEI

Sample 74-527-33-3,145-147 1. Dentalina spp., side view, 125 X, specimen JWl-1. 2. Globulina lacrima, side view, 255 X, specimen JWl-2. 3. Buliminella? beaumonti, side view, 250 X, specimen JWl-3. 4. Praebulimina sp. inflated form, side view, 185 X, specimen JWl-4. 5. Praebulirnina sp. fusiform, side view, 195 X, specimen JWl-5. 6. ReusseUa szajnochae, side view, 265 X, specimen JWl-6. 7a. Nuttallides truernpyi, a. Umbilical view, 185 X, specimen JWl-7. b. spiral view, 170 X, specimen JWl-8 c. side view, 170 X, specimen JW2-1.

68

PLATE II

69

species. This species is previously reported from the Maastrichtian of the South Atlantic by Beckmann (1978). He used the name Praebulimina cf. beaumonti (Cushman and Renz).

Genus Nuttallides Finlay, 1939

NuttaUides truempyi (Nuttall) (Plate I, 7a-c) 1930 Eponides truernpyi NuttaU, p. 287, pl. 3,5.

Genus P r a e b u l i m i n a Hofker, 1953

Praebulimina sp. inflated form (Plate I, 4)

This taxon includes specimens of Praebulimina with rapidly inflaring chambers. The last whorl overlaps about 3/4 of the test. Praebulirnina sp. fusiform (Plate I, 5)

This form includes specimens of Praebulimina with fusiform test shapes, which may be difficult to separate. Praebulimina sp. fusiform includes species such as P. carseyae (Plummet), P. laevis (Beissel ), and P. obtusa ( d'Orbigny ). Genus Reussellu Galloway, 1933

ReusseUa szajnochae (Grzybowski) (Plate I, 6) 1896 Verneuilina szajnochae Grzybowski, p. 287, pl. 9,19.

This species is easy to recognize by its spiny outgrowths at the edges of the triangular test. It is previously reported from the Maastrichtian of the South Atlantic by Beckmann (1978), Dailey (1983), and Sliter (1977). Superfamily D I S C O R B A C E A Ehrenberg, 1838 Family E P I S T O M A R I I D A E Hofker, 1954

This well-known species is one of the most frequent in the sediments analyzed here. A relatively wide species concept was used by Tjalsma and Lohmann (1983), who also included morphotypes such as N. bronnimanni (Cushman and Renz) and N. carinotruempyi (Finlay) in the concept of N. truempyi (Nuttall). A wide species concept of N. truempyi is also applied in this study. This species is previously reported from the Maastrichtian of the South Atlantic by Daily (1983) under the name of N. truempyi and by Beckmann (1978) under the name of N. bronnimanni. Sliter (1977) figured a specimen, which he named Osangularia cordieriana (d'Orbigny), which possesses small chamberlets around the center of the umbilical side and a slitlike aperture, extending from "umbilical boss" to the periphery, which rather suggests that the specimen should be referred to Nuttallides. Nuttallides sp. a (Plate II, 1 )

This form resembles N. truempyi, but is more lenticular in section, has a less developed umbilical boss, and curved rather than sinuous sutures on the umbilical side.

PLATE II Sample 74-527-33-3, 145-147 1. NuttaUides sp. a, umbilical view, 175 X, specimen JW2-2. 2a. Nuttallinella sp. a, side view, 255 X, specimen JW2-5. b. NuttaUineUa sp. a, umbilical view, 170 X, specimen JW2-3. 3a. Neoeponides hiUebrandti, umbilical view, 140 X, specimen JW2-8. b. N. hiUebrandti, 150 X, side view, specimen JW2-6. 4a. Neoeponides sp. intermediate form, umbilical view, 175 X, specimen JW3-2. b. N. sp. intermediate form, spiral view, 280 X, specimen JW3-1. 5a. Neoeponides lunata, spiral view, 185 X, specimen JW3-4. b. N. lunata, umbilical view, 175 X, specimen JW3-3.

70

PLATE III

71 Genus NuttaUineUa Belford, 1959 NuttaUinella sp. a (Plate II, 2a-b)

This is a minute form whose taxonomic status is uncertain. Dailey (1983) reported a Nuttallinella sp. from Rio Grande Rise, which was documented by SEM-photographs. Nuttallinel/a sp. a resembles the specimen ofN. sp. given by Dailey {1983). Superfamily ORBITOIDACEA Schwager, 1876 Family EPONIDIDAE Hofker, 1951 Genus Neoeponides Reiss, 1960 Neoeponides hillebrandti Fisher (Plate II, 3a-b)

1969 Neoeponides hillebrandti Fisher, p: 196. (This reference is Fisher's renaming of Eponides whitei Hillebrandt ).

This form is strongly piano-convex, with a flat to weakly concave umbilical side, and a strongly convex spiral side.This species is previously reported from the Maastrichtian of the South Atlantic by Dailey (1983). The figured specimen in Dailey (1983) has more strongly convex umbilical side than the specimens here referred to this species. The specimens found here show close resemblance to the figures of N. hillebrandti Fisher shown by Tjalsma and Lohmann (1983). Neoeponides sp. intermediate form (Plate II, 4a-b)

This form is intermediate between N. hillebrandti and N. lunata. Neoeponides sp. intermediate form is biconvex, with a spiral side resembling that of N. hillebrandti and an umbilical side resembling that of N. lunata. Tjalsma and Lohmann (1983) reported a species named N. cf. lunata, which shows close resemblance to N. sp. intermediate form. Neoeponides lunata (Brotzen) (Plate II, 5a-b)

1948 Eponides lunata Brotzen, p. 77, pl. 10,17-18.

To this species are only specimens included, that closely resemble the figure of the holotype of Eponides lunata (Brotzen, 1948). Brotzen's species is nearly piano-convex, with an almost flat spiral side and a strongly convex umbilical side. This species is previously reported fore the Maastrichtian of the South Atlantic by Dailey (1983) and Sliter (1977); the later used the name Gyroidinoides lunata ( Brotzen ). Superfamily CASSIDULINACAE d'Orbigny Family NONIONIDAE Schultze, 1854 Subfamily NONIONINAE Schultze, 1854 Genus PuUenia Parker and Jones, 1862 Pullenia spp. (Plate V, 2)

Several species of Pullenia are included in this taxon; these are difficult to separate. Species such as P. cretacea (Cushman) and P. jarvisi (Cushman) are referred to this group.

PLATE III Sample 74-527-33-3, 145-147 la. Alabamina sp. a, spiral view (showing borings), 230 X, specimen JW3-6. b. Alabamina sp. a, umbilical view, 150 X, specimen JW3-5. 2. Anomalinapraeacuta, umbilical view, 120 X, specimen JW6-8. 3. Anomalina sp. a, umbilical view, 155 X, specimen JW3-8. 4a. Cibicidoides? spp., spiral view, 125 X, specimen JW4-1. b. Cibicidoides? spp., umbilical view, 125 X, specimen JW4-2. 5a. GavelineUabeccariiformis, spiral view, 140 X, specimen JW4-4. b. G. beccariiformis, side view, 145 X, specimen JW4-5. c. G. beccariiformis, umbilical view, 120 X, specimen JW4-3.

72

PLATE IV

73 Family OSANGULAIIDAE Loeblich and Tappan, 1964

Gyroidinoides spp. (Plate IV, 3)

Genus Osangularia Brotzen, 1940

This taxa includes several species such as G. globosus (Hagenow) and G. octocamerata (Cushman and Hanna).

Osangularia ? spp. (Plate V, 1a-b)

In this taxon are probably at least three different species lumped together. The specimens are very small with poorly preserved apertural features. The species included in this group are O. cordieriana (d'Orbigny), O./ens Brotzen, and O. velascoensis (Cushman). Genus Gyroidinoides Brotzen, 1942 Gyroidinoides quadratus (Cushman and Church) (Plate IV, 2a-c) 1929 Gyroidina quadrata Cushman and Church, p. 516, pl. 2,5.

This species is well known from Upper Cretaceous deep-sea sediments from the South Atlantic. Gyroidinoides quadratus is easy to recognize on the basis of its concavo-convex outline in side view and its "tulip-petal" shaped chambers in the last whorl of the umbilical side. This species is previously reported from the Maastrichtian of the South Atlantic by Beckmann (1978), Dailey (1983), and Sliter (1977). Beckmann (1978) used the genus name Gyroidina for this species.

Family ALABAMINIDAE Hofker, 1951 Genus Aiabamina, Toulmin, 1941

Alabamina sp. a (Plate III, la-b)

This is a fairly stable form in the material studied. Its taxonomical position is, however, uncertain. Only two species of Alabamina from the Maastrichtian of the South Atlantic are reported in the three papers considered here, namely A. creta (Finlay) by Dailey (1983) and A. dorsoplana (Brotzen) by Sliter (1977). The specimens found here resemble the figures of A. creta (Finlay) given by Dailey (1983) and the original figures of Eponides creta Finlay given by Finlay (1940). Genus Oridorsalis Andersen, 1961

Oridorsalis? urnbonatus? (Reuss) (Plate IV, 4a-b) 1851 Rotalina umbonata Reuss, p. 75, pl. 5,35

This taxon is represented by shiny, biconvex forms, with a large umbo, and a narrow last

PLATE IV Sample 74-527-33-3, 145-147 la. Gavelinella hyphalus, spiral view, 140 X, specimen JW4-6. b. G. hyphalus, side view, 160 X, specimen JW4-8. c. G. hyphalus, umbilical view, 195 X, specimen JW4-7. Sample 74-527-33-1,139-141 2a. Gyroidinoides quadratus, spiral view, 180 X, specimen JW5-3. b. Gyroidinoides quadrutus, side view, 145 X, specimen JW5-1. c. Gyroidinoides quadratus, umbilical view, 140 X, specimen JW5-2. 3. Gyroidinoides spp., umbilical view, 175 X, specimen JW5-4. 4a. Oridorsalis? umbonatus?, umbilical view, 90 X, specimen JW5-7. b. 0. ? umbonatus?, spiral view, 95 X, specimen JW5-6.

74

PLATE V

75 whorl on the spiral side. T h e sutures on the umbilical side are weakly sinuous. Specimens of O. ? umbonatus? were difficult to separate from different forms of Eponides? spp. in the material studied. Oridorsalis umbonatus ( R e u s s ) is previously reported from the Maastrichtian of the South Atlantic by Dailey (1983). Family ANOMALINIDAECushman, 1927 SubfamilyANOMALININAECushman, 1927

Genus Cibicidoides Thalmann, 1939

Cibicidoides? spp. (Plate III, 4a-b)

Most of the specimens referable to this taxa are juveniles, and therefore, its taxonomical position is uncertain. A few larger specimens could possibly be referred to Cibicidoides dayi (White).

Genus A n o m a l i n a d'Orbigny, 1826

Anomalina praeacuta Vasilenko (Plate III, 2)

1950Anomalina praeacuta Vasilenko,p. 208, pl. 5,2a-c. This species is separated from similar forms in possessing a nearly evolute spiral side, gradually increasing chamber size on the spiral side, and characteristic umbilical features. The specimens show close resemblance to the specimens shown in figures given by Tjalsma and Lohm a n n (1983). Anomalina praeacuta is not reported in any of the papers by B e c k m a n n (1978), Dailey (1983), or Sliter (1977). Anomalina sp. a (Plate III, 3)

This form resembles A. praeacuta, but differs in having a more trochospiral coiling, weakly involute spiral side and distinct, narrow, and straight sutures on the umbilical side.

Genus GavelineUa Brotzen, 1942

Gavelinella beccariiformis {White) (Plate III, 5a-c)

1928 Rotalia beccariiformis White, p. 287, pl. 39,2-4. This is a characteristic species of the Maastrichtian-Paleocene deep-sea South Atlantic and the most abundant one in the material studied. In the Paleocene, G. beccariiformis represents a member of a "relict" Mesozoic deepsea fauna, which became extinct near the Paleocene/Eocene boundary (Tjalsma and Lohmann, 1983). This species is previously reported from the Maastrichtian of the South Atlantic by B e c k m a n n (1978) and Dailey (1983). GavelineUa beccariiformis was not reported by Sliter (1977), but he reported a similar species, G. whitei ( M a r t i n ) . This species was established on the basis of one of the varieties of Rotalia beccariiformis White by Martin (1964) as Anomalina whitei Martin. Tjalsma and Loh-

PLATE V Sample 74-527-33-1,139-141 la. Osangularia? spp., spiral view, 105 X, specimen JW6-1. b. Osangularia? spp., umbilicalview,90 X, specimenJW5-8. 2. PuUenia spp., side view, 190 X, specimenJW6-2. 3a. Dorothia trochoides, apertural view, 95 X, specimen JW6-3. b.D. trochoides, side view, 185 X, specimenJW6-4. 4. Spiroplectammina dentata, side view, 120 X, specimenJW6-6. 5. Gaudryinapyramidata, side view, 150 X, specimenJW6-5. 6. Tritaxia spp., side view,66 X, specimen JW6-7.

76

Appendix II - - Relative abundances (percentages) of benthonic foraminiferal taxa in the interval of stronger dissolution (see Table I for depths and abbreviations of samples). B e n t h o n i c forams/sample

Sl

$2

$3

$4

$5

$6

$7

$8

$9

$10

Sll

$12

0.0 0.5 0.0 0.9 1.9 0.9 12.7 8.5 0.9 4.7 2.8 1.9 1.9 1.9 0.9 0.0 17.0 7.1 1.4 4.2 0.5 6.6 0.5 4.2 5.2 22.2 15.6 52.8

0.9 0.0 6.9 3.2 0.0 0.9 11.9 5.5 3.2 3.7 2.3 5.0 1.8 1.4 1.4 0.5 17.9 12.8 0.0 0.5 0.5 0.9 0.5 7.3 11.5 20.6 16.5 44.0

0.8 0.0 0.8 2.4 0.0 7.3 12.1 3.2 4.0 5.6 4.0 0.8 4.8 4.8 0.0 1.6 12.1 9.7 1.6 4.8 0.8 0.0 0.8 7.3 10.5 19.4 15.3 47.6

0.7 0.0 3.3 3.3 0.0 5.8 14.5 5.1 4.3 1.8 7.2 3.3 1.4 1.4 3.3 0.4 12.7 6.5 2.5 2.2 0.4 0.7 0.0 4.7 12.3 24.3 15.9 42.8

0.4 0.0 3.1 2.2 0.0 4.8 21.8 0.4 1.3 5.7 2.6 2.6 0.4 3.5 0.0 0.4 20.1 6.1 4.4 2.6 0.9 0.0 0.0 5.7 10.5 23.6 15.3 45.0

0.0 1.2 2.4 1.2 0.0 9.4 15.3 2.4 4.1 4.7 2.4 1.2 1.2 2.4 1.2 0.6 12.4 9.4 0.0 5.9 0.6 1.8 2.9 5.9 14.7 22.9 11.8 44.7

0.4 1.1 0.8 1.5 0.0 3.1 16.8 4.6 7.6 1.5 3.8 0.4 1.5 1.1 1.5 1.1 17.2 9.9 0.0 3.8 0.4 1.5 1.1 7.3 5.3 29.4 10.3 47.7

0.3 0.3 2.6 2.3 0.0 0.3 14.8 5.5 0.9 1.7 2.9 1.2 1.2 3.8 1.4 0.6 21.7 8.4 1.4 3.8 1.2 1.7 0.3 5.5 5.5 21.2 12.2 55.7

0.3 1.0 1.8 2.8 0.0 0.0 12.4 2.6 0.0 1.8 4.4 1.8 0.8 3.6 1.3 0.8 23.0 11.1 5.4 3.6 1.3 0.8 2.1 6.7 5.7 15.0 11.6 61.0

0.0 0.0 4.1 1.4 0.9 0.5 15.6 1.4 0.5 6.4 5.5 0.9 3.2 7.8 0.0 0.0 6.9 4.1 1.4 5.0 0.5 6.9 2.8 4.1 11.5 17.4 17.4 49.5

0.0 1.6 11.4 2.4 0.0 0.0 7.3 1.6 0.8 5.7 0.0 1.6 0.8 6.5 1.6 0.8 18.7 11.4 1.6 4.9 0.0 0.0 1.6 5.7 15.4 9.8 14.6 54.5

1.4 1.4 3.6 3.6 0.0 0.7 6.4 2.9 5.7 3.6 4.3 2.9 0.7 4.3 1.4 0.0 22.9 7.9 0.7 2.1 0.0 0.0 1.4 9.3 9.3 15.0 17.1 49.3

Total of agglutinated T o t a l i d . specimens Total unid. specimens

2.5 1.7 0.8 1.3 1.7 10.5 91.1 8.9

3.3 2.1 0.4 0.0 1.7 9.5 89.6 10.4

1.5 1.5 0.7 1.5 1.5 8.1 92.6 7.4

2.3 1.9 1.3 0.3 2.3 10.4 91.9 8.1

0.8 2.0 0.0 2.4 3.5 9.8 92.1 7.9

1.6 2.2 1.6 1.6 1.1 8.1 93.0 7.0

2.1 2.4 0.0 0.3 1.0 9.7 89.7 10.3

1.3 1.6 1.6 0.3 1.8 9.2 88.4 11.6

2.5 2.5 0.9 0.2 2.3 10.8 88.7 11.3

4.0 4.0 0.8 0.0 1.6 12.1 90.7 9.3

3.5 5.6 0.0 0.0 0.7 13.4 90.8 9.2

3.2 1.3 1.3 0.0 3.8 10.8 92.4 7.6

Total of fragments

23.3

27.2

25.0

25.2

21.6

28.8

28.9

30.0

22.4

31.5

27.9

29.9

Dentalina spp. Globulina lacrima Bulirninella?beaumonti Praebulirnina sp. inflated form Praebulimina sp. fusiform Reussella szajnochae Nuttallidestruempyi NuttaUides sp. a Nuttallinella sp. a Neoeponides hillebrandti Neoeponides sp. intermediate form Neoeponides lunata Alabamina sp. a Anomalinapraeacuta Anomalina sp. a Cibicidoides? spp. GavelineUabeccariiforrnis Gavelinellahyphalus Gyroidinoides quadratus Gyroidinoides spp. Oridorsalis? umbonatus? Osangularia? spp. PuUenia spp. Total Total Total Total Total

of Nodosariacea of Buliminacea of Discorbacea of Orbitoidacea of Cassidulicea

Dorothia trochoides Gaudryinapyrarnidata Spiroplectammina dentata Spiroplectammina spp. Tritaxia spp.

mann (1983) were of the opinion that the typical threadlike depressions around the umbilicus of G. whitei may be due to poor preservation. GavelineUa hyphalus ( F i s h e r ) ( P l a t e IV, l a - c ) 1969 Anornalinoides hyphalus Fisher, p. 197, text-fig. 3.

This is a common species in the material studied here. It is distinguished by its convex involute spiral side with numerous chambers. The umbilical side is nearly flat, almost evolute, and possesses numerous large pores. This species is previously reported from the Maastrichtian of the South Atlantic by Dailey (1983).

77 (Appendix II cont.)

Benthonicforams/sample

M13

M14 M15

M16

M17

M18

M19

M20

M21

M22

M23

M24

Dentalina spp. Globulina lacrima Buliminella? beaumonti Praebulimina sp. inflated form Praebulimina sp. fusiform Reussella szajnochae Nuttallides truempyi Nuttalides sp. a NuttaUineUa sp. a Neoeponides hiUebrandti Neoeponides sp. intermediate form Neoeponides lunata Alabaminasp. a Anomalinapraeacuta Anomalinasp. a Cibicidoides? spp. GavelineUa beccariiformis Gavelinella hyphalus Gyroidinoides quadratus Gyroidinoides spp. Oridorsalis? umbonatus? Osangularia? spp. Pullenia spp.

0.0 1,5 7.6 1.5 0.0 0.0 6.8 1.5 13.6 5.3 0.8 0.8 2.3 1.5 0.8 0.8 14.4 5.3 0.0 6.8 0.0 0.0 5.3 6.8 9.1 22.0 15.2 47.0

0.0 0.8 10.8 3.3 2.5 0.8 5.8 1.7 8.3 4.2 0.0 0.8 2.5 3.3 2.5 0.0 15.0 9.2 2.5 3.3 0.0 0.0 3.3 5.8 17.5 15.8 8.3 52.5

1.1 0.5 3.7 2.6 0.5 4.8 5.3 5.8 5.8 4.8 1.6 0.5 3.2 3.7 3.7 1.1 8.5 5.3 0.5 1.1 2.1 1.1 3.2 9.0 14.8 16.9 14.3 45.0

0.7 0.0 5.1 3.6 1.8 3.6 4.3 3.3 4.3 5.1 0.4 0.7 1.4 4.0 4.3 0.7 15.2 8.3 1.1 3.3 1.4 3.6 1.8 8.3 16.7 12.0 10.1 52.9

0.6 0.8 5.6 1.4 1.7 3.7 4.5 3.1 6.2 3.4 0.6 1.1 2.5 4.2 4.8 0.3 18.6 9.9 0.6 2.3 0.3 3.4 1.1 5.9 14.1 13.8 10.7 55.5

0.6 1.0 8.0 2.3 3.9 1.0 9.0 2.9 2.6 4.5 2.3 0.6 2.6 2.3 2.9 0.0 18.3 4.5 0.6 2.6 0.6 2.9 1.9 8.7 18.0 14.8 12.5 46.0

1.1 0.4 6.1 1.9 0.8 0.8 8.7 2.7 3.8 4.6 1.1 1.1 1.5 1.5 1.9 1.1 15.6 9.5 0.0 3.0 1.1 5.7 1.5 8.7 12.9 15.2 11.8 51.3

1.0 2.1 6.8 3.6 0.0 0.0 7.3 3.6 5.7 4.7 2.1 1.6 5.7 3.1 2.6 1.0 9.9 7.8 0.0 1.0 0.0 1.6 1.6 12.0 12.0 17.2 15.6 43.2

1.1 0.5 3.8 4.3 0.5 0.0 7.0 4.3 7.5 2.7 0.5 1.6 2.2 1.6 1.6 0.5 14.0 12.4 0.0 3.2 0.0 0.0 0.5 9.7 11.3 18.8 15.1 45.2

1.1 1.1 4.3 3.8 1.1 1.1 4.9 1.1 4.9 6.5 2.2 3.2 4.3 1.1 2.7 1.6 17.3 7.6 0.0 1.6 2.2 1.6 3.2 10.8 13.0 10.8 15.1 50.3

1.6 0.0 0.8 0.0 0.0 0.0 6.6 4.9 5.7 8.2 0.0 2.5 4.9 4.1 0.8 1.6 15.6 9.0 0.8 3.3 0.0 1.6 1.6 13.1 7.4 17.2 13.9 48.4

0.9 0.9 0.4 0.4 2.6 0.4 2.2 5.6 11.7 3.9 0.4 3.5 2.2 2.2 3.0 0.0 18.6 6.5 1.7 1.7 1.3 0.4 1.7 10.4 8.2 19.5 12.6 49.4

Total of agglutinated Total id. specimens Total unid. specimens

2.2 0.0 2.2 0.0 0.7 5.0 92.8 7.2

0.0 1.0 0.0 1.5 1.6 1.0 0.8 1.0 0.8 1.5 4.8 7.4 94.4 89.2 5.6 10.8

1.7 0.7 0.0 0.3 1.0 5.8 88.7 11.3

1.3 0.0 0.5 0.3 0.8 5.1 92.5 7.5

1.8 1.2 0.3 0.3 2.7 7.4 91.1 8.9

1.7 0.7 1.0 1.0 0.7 8.7 88.2 11.8

3.4 2.5 1.7 3.0 1.7 18.6 88.1 11.9

4.1 0.9 2.8 2.8 2.8 14.7 93.1 6.9

0.5 2.3 2.8 1.9 1.4 14.0 85.6 14.4

1.5 0.8 0.0 0.8 3.0 8.3 88.7 11.3

1.2 2.0 2.0 0.8 1.2 9.1 90.6 9.4

Total of fragments

31.5

29.6 31.3

33.7

25.1

27.6

24.6

36.9

19.0

28.6

31.4

22.8

Total Total Total Total Total

of Nodosariacea of Buliminacea of Discorbacea of 0 r b i t o i d a c e a of Cassidulicea

Dorothia trochoides Gaudryina pyramidata Spiroplectammina dentata Spiroplectammina spp. Tritaxia spp.

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