10. CRETACEOUS FORAMINIFERS OF HOLE 530A, LEG 75, DEEP SEA DRILLING PROJECT1 C. L. McNulty, University of Texas at Arlington, Texas ABSTRACT Hole 53OA of Leg 75 is located in the southeastern corner of the Angola Basin of the South Atlantic (19° 11.26' S; 9°23.15 'E), on the abyssal seafloor (4629 m depth), close to the Walvis Ridge and near its junction with the continental margin. The hole penetrated 503 m of Cretaceous (Maestrichtian to Albian) and bottomed in basalt at 1121 m. No other hole of Leg 75 was drilled below the Neogene. Most of the 10-cm3 samples from Hole 53OA were barren of foraminifers. Most of the foraminiferal populations re- covered were barren of planktonic specimens. Consequently, no correlation with established planktonic biozones was possible, and correlation with European stages was limited to Maestrichtian-Campanian, Santonian-Coniacian, ?lower Turonian, and Albian. Most of the benthic species were interpreted to be displaced—not reworked nor redrilled cavings. Recognition of the displaced faunas helped in recognizing indigenous benthic faunas and in interpreting their paleodepth and provincial implications. Displaced faunas have temporal and paleogeographical value but not Paleobathymetric value. The prevalent general properties at Site 530 of sparsity of specimens, rarity of planktonic specimens, low taxonomic diversity of indigenous benthic faunas, and etched, worn, and broken specimens combined to indicate deposition well below the lysocline and near to, if not below, the carbonate compensation depth (CCD), or in the abyssal realm, during most of the Maestrichtian to Albian. Such a depositional environment is also implied by the primitive, quartzose, ag- glutinated faunas from noncalcareous red and green claystones, which occur with increasing prominence from the lower part of the Maestrichtian-Campanian interval to the bottom of the sedimentary section. The prominence, per- sistence, and physical condition of the displaced faunas suggest transport by a submarine fan system at some distance from the continental margin. The faunas of Hole 53OA resemble those of other paleoabyssal sites of the South Atlantic and Indian oceans and be- long to the Austral Bioprovince. Latitudinal and provincial properties seem to diminish with depth, and the Albian in- digenous benthic fauna is cosmopolitan. It is quite different from the Albian planktonic fauna of Hole 53OA, which is definitely midlatitudinal and Austral, and from the Albian fauna reported from nearby Sites 363 and 364. The principal event of the sedimentary record is a medial Cretaceous lacuna, which includes most of the Turonian and Cenomanian and some of the Albian. Such a lacuna is widespread in DSDP sites of the southern hemisphere. Possi- ble hiatuses occur at the base of the Maestrichtian-Campanian and at the base of the Santonian-Coniacian intervals. INTRODUCTION and were excluded from the recurrent and presumably indigenous benthic faunas. They are not included in the Site 530 is located in the southeastern corner of the faunal lists of the chronostratigraphic intervals discussed Angola Basin of the South Atlantic Ocean (19° 11.26' S; below, but are presented separately in Table 1. 9°23.15'E), on the abyssal floor (4629 m depth), close In addition to the sparsity of all species and the per- to the base of the Walvis Ridge and near to its junction sistent recurrence of so few species, foraminiferal popu- with the continental margin (Fig. 1). After one core was lations are characterized by conspicuously poor preser- taken, the first hole was abandoned because of a me- vation, because of dissolution, abrasion, and distortion. chanical problem. The second hole, Hole 53OA, termi- Consequently, it has been impossible to obtain satis- nated in basalt at 1121 m sub-bottom. Hole 53OA pene- factory photomicrographs, although numerous attempts trated 503 m of Cretaceous, which was divided into four were made. Camera lucida drawings have been made to lithologic units (Fig. 2). supplement photomicrographs of the more important The recovery of foraminifers from Cretaceous sam- benthic species, but photographic documentation of the ples (10 cm3 volume) of Hole 53OA was poor. About 75% dissolved and fragmentary planktonic and displaced of all washed residues yielded few or no specimens. Of benthic species, and of the fragmentary and distorted, the residues with 1% or more foraminiferal specimens, quartzose, agglutinated species are not included in this about 75% were totally or dominantly benthic forms, chapter. except those approximately from the horizons of Cores Because of the rarity of planktonic species in samples 79, 88, and 94. About 75% of the total benthic fauna of other than those from Cores 79, 88, and 94, established a faunule or of a chronostratigraphic interval is not foraminiferal planktonic biozones could not be recog- recurrent. In other words, most benthic species occur in nized (Table 2). The chronostratigraphic intervals em- one or two samples only. Moreover, they are typically ployed (Fig. 2), namely, Maestrichtian-Campanian, San- represented by only a few specimens in the sample of oc- tonian-Coniacian, ?lower Turonian, and Albian, are currence. Such species were considered to be displaced based upon both the few, rare, and erratic planktonic species and a small number of long-ranging recurrent benthic species (Tables 3, 4). As a result, the boundaries Hay, W. W., Sibuet, J.-C, et al., Init. Repts. DSDP, 75: Washington (U.S. Govt. Printing Office). of intervals are questionable, and their differences from 547 C. L. McNULTY 18° S 19° 21° 8° 9° 10° 13° E Figure 1. Location map for Site 530, DSDP Leg 75 those based on nannofossils, as reported elsewhere in (upper Unit 7) provided more planktonic species than this volume, are also questionable. any other interval of the hole. The planktonic fauna of Cores 76 through 80 is dis- MAESTRICHTIAN-CAMPANIAN tinguished by simple and early globotruncanids, such as This interval extends from Core 50, Section 2, 10-14 G. area, G. fornicata, G. linneiana, and G. ventricosa cm through Core 80. White, by terminal marginotruncanids, including Mar- Neither the Tertiary/Cretaceous nor the Campanian/ ginotruncana (Dicarinella) asymetrica (Sigal) and M. Santonian boundary is well documented by foramini- sinuosa Porthault, by Planoglobulina glabretta (Cush- fers. Globotruncanids occur above Sample 50-2, 10-14 man), and by rare, infrequent, other species, including cm, and Tertiary planktonic species occur as low as Globigerinelloides asperus (Ehrenberg). Reworked spec- Core 62. Presumably the latter are cavings, although imens of Hedbergella planispira (Tappan), Praeglobo- Tertiary specimens are common in residues as low as truncana stephani (Gandolfi), P. delrioensis (Plummer), Core 57. The apparent sharpness of the base of this in- and Rotalipora apeninnica (Renz) are common, espe- terval is questionable because of the lack of satisfactory cially in Core 79. Despite its deficiencies of preservation samples immediately below the boundary. The correla- and diversity, the assemblage is indicative of the lower tion is based for the most part on very poorly preserved, Campanian and provides this interval with the best cor- rare, and infrequent globotruncanids and a restricted, relation in the hole. also poorly preserved, but relatively persistent Paleo- The persistent, recurrent (indigenous) species for the gene to Campanian benthic assemblage. Maestrichtian-Campanian interval include Aragonia In the interval from Core 50-2, 10-14 cm to Core 61 ouezzanensis (Rey), Dorothia trochoides (Marsson), (lithologic Units 5a and 5b), one or two broken and Gyroidina diversus (Belford), Lenticulina velascoensis eroded specimens of Abathomphalus mayaroensis Bolli, White, Nuttallides sp., N. truempyi (Nuttall), Nuttal- Globotruncana gagnebini Tilev, G. contusa (Cushman), linellai florealis (Cushman), N.I spinea (Cushman), G. fornicata Plummer, G. area Cushman, Pseudoguem- Pullenia coryelli White, Reussella szajnochae (Grzy- belina palpebra Brönnimann and Brown, Pseudotextul- bowski), Spiroplectammina dentata (Alth), and Valvul- aria difformis (Kikoine), and Rugoglobigerina sp. were inerial whitei (Martin). found in residues of four samples. In the interval of Core 61 to Core 71 (Unit 5c), Globotruncana fornicata, SANTONIAN-CONIACIAN G. linneiana (d'Orbigny), and Rugoglobigerina sp. oc- The upper part of this interval (Cores 81 through 86) cur with similar rarity. The volcanogenic interval of is composed of red and green claystones and vari-col- Core 71 to Core 75 (Unit 6) yielded no planktonic fora- ored turbiditic siltstones and sandstones, which appear minifers, but the interval from Core 76 through Core 80 to be a continuation of and are included in lithologic 548 CRETACEOUS FORAMINIFERS Lithology 500- J »!»»..Ti 53.5 m.y. 44 550 45 46 600 5a 70 m.y. 650 56T 5b 700 61 5c 750- 5c 78 m.y. 82 m.y. Major components CΛ 850- 77 H j- | Forams and nannos | Dolomite [ Nannos Λ ΛI Sandstone id Clay |Cnalk 900 prurjsilt and clay (mud) [VrrπVrlClastic limestone ( =silicified) ^ Black shale KVJ Basalt Minor components 950 ] Volcanic breccia | (?) | Pyrite I Chert 86 m.y. < 92 m.y. >92m.y. 1050 100 m.y. 1100- Figure 2. Columnar section showing lithologic units for Hole 53OA, DSDP Leg 75. (Revi- sions of stratigraphic ages are given in Steinmetz et al., this volume.) Unit 7. However, their foraminiferal content differs ilar lithology. Second, planktonic specimens are rare, from that of the upper part of Unit 7 (Cores 76 through