Year: 1984
Type: book-chapter
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-cm 3 samples from Hole 53OA were barren of foraminifers.Most of the foraminiferal populations recovered 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, ?lowerTuronian, 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, agglutinated 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, persistence, 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 belong to the Austral Bioprovince.Latitudinal and provincial properties seem to diminish with depth, and the Albian indigenous 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.Possible hiatuses occur at the base of the Maestrichtian-Campanian and at the base of the Santonian-Coniacian intervals. MAESTRICHTIAN-CAMPANIANThis interval extends from Core 50, Section 2, 10-14 cm through Core 80.Neither the Tertiary/Cretaceous nor the Campanian/ Santonian boundary is well documented by foraminifers.Globotruncanids occur above Sample 50-2, 10-14 cm, and Tertiary planktonic species occur as low as Core 62. Presumably the latter are cavings, although Tertiary specimens are common in residues as low as Core 57.The apparent sharpness of the base of this interval is questionable because of the lack of satisfactory samples immediately below the boundary.The correlation is based for the most part on very poorly preserved, rare, and infrequent globotruncanids and a restricted, also poorly preserved, but relatively persistent Paleogene to Campanian benthic assemblage.In the interval from Core 50-2, 10-14 cm to Core 61 (lithologic Units 5a and 5b), one or two broken and eroded specimens of Abathomphalus mayaroensis Bolli, Globotruncana gagnebini Tilev, G. contusa (Cushman), G. fornicata Plummer, G. area Cushman, Pseudoguembelina palpebra Brönnimann and Brown, Pseudotextularia difformis (Kikoine), and Rugoglobigerina sp. were found in residues of four samples.In the interval of Core 61 to Core 71 (Unit 5c), Globotruncana fornicata, G. linneiana (d'Orbigny), and Rugoglobigerina sp.occur with similar rarity.The volcanogenic interval of Core 71 to Core 75 (Unit 6) yielded no planktonic foraminifers, but the interval from Core 76 through Core 80 13° E
Author: C.L. McNulty
Institution: The University of Texas at Arlington
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: bronze
Funder: University of Texas at Arlington
OpenAlex ID: W2494524749