Cenozoic Foraminifera from the South Atlantic, DSDP Leg 36

Abstract

Cenozoic foraminifera occur in four sites drilled during Leg 36, one in the Drake Passage (Site 326), one in the Falkland Outer Basin (Site 328), and two on the eastern end of the Falkland Plateau (Sites 327 and 329). A calcareous section containing a well-preserved fauna was cored at Site 329. Planktonic foraminifera show that four Tertiary intervals were recovered, upper Paleocene-lower Eocene, Oligocene, lower Miocene, and upper Miocene. Some calcareous planktonics and benthonics are found in the Paleocene-lower Eocene of Site 327. The carbonate-free sediments of Site 328 only yielded an upper Cretaceous-lower Eocene arenaceous benthonic fauna. Planktonic species diversity and faunal composition at Site 329 indicate a progressive warming during the latest Paleocene culminating with the invasion of mid-latitude angular acarininids and keeled morozovellids. Species diversity of Oligocene assemblages is high relative to the latitudinal position of the site. Intense cooling is inferred from extreme low-diversity assemblages in the late Miocene with predominance of Globigerina bulloides. Four distinct benthonic assemblages occur in the Paleocene, lower Eocene, Oligocene, and upper Miocene. Comparison with low and mid-latitude assemblages from the South Atlantic suggests bathyal depth during the Paleocene. The remarkable stability of benthonic assemblages all through the Cenozoic with great similarities (on generic level) in faunal composition is a further indication for the absence of any substantial subsidence of the Falkland Plateau during the Cenozoic. 'Contribution No. 3703 of the Woods Hole Oceanographic Institution. R. C. TJALSMA 60 c 65 C 60° 40°F igure 1. Location of Leg 36 drill sites. 20°P lanktonic foraminifera recovered at two levels show moderate dissolution and sorting as a result of winnowing. The assemblages are assigned to the late Pleistocene to Recent Globorotalia truncatulinoides Zone (sensu Kennett, 1970) based on the presence of the zonal marker which, according to Kennett, invaded the Southern Ocean south of 50°S late in the Brunhes Normal Epoch or about 0.2 m.y. ago. The poor assemblage which also contains Globorotalia inflata, Neogloboquadrina pachyderma (s), Globigerina bulloides, and G. cf. bulloides (sensu Keany and Kennett, 1972) is essentially similar to that reported from this area by Herb (1968).

Cenozoic Planktonic Foraminifers of the Falkland Plateau and Argentine Basin, Deep Sea Drilling Project Leg 71

“…Nannofossils of the D. multiradiatus Zone supports this conclusion (Wise and Wind, 1977). Tjalsma (1977) also attributed these sediments to the G. velascoensis Zone but assigned the basal layers (from Sample 329-33-4, 100-102 cm to Sample 329-33,CC) to the G. pseudomenardii Zone. In our opinion, the numerous A. acarinata and A. soldadoensis developed in these layers indicate the A. acarinata Zone (i.e., the G. velascoensis Zone).…”

“…All of these features relate these forms to Globigerina pachyderma. This connection was noted for the first time on Leg 36 by Tjalsma (1977), who referred both Globorotalia acostaensis and Globigerina pachyderma to the genus Neogloboquadrina. The atypical forms may be considered as transitional between the two species.…”

“…The assemblage of arenaceous benthic foraminifers, which is indicative of abyssal depth, dates the sediments as Late Cretaceous-late Eocene (Tjalsma, 1977).…”

“…Planktonic foraminifers from the Cenozoic sediments recovered by Leg 36 Sites and investigated by Tjalsma (1977) were referred to four Tertiary intervals: upper Paleocene-lower Eocene, Oligocene, lower-middle Miocene, and late Miocene. The combination of materials from Legs 36 and 71 provides an opportunity to widen our knowledge of Cenozoic planktonic foraminifers of the South Atlantic.…”

“…In the Pacific Ocean deposits with planktonic foraminifers are Danian, Oligocene, and Miocene in age (Sites 270,323,and 325); very complete Paleo-gene and Neogene sequences were discovered on the Campbell Plateau, Macquarie Ridge, South Tasman Rise, and the southern part of the Tasman Sea (Sites 277,278,(280)(281)(282)(283)(284) (Rögl, 1976;Kennett and Vella, 1975;Jenkins, 1975). In the South Atlantic, drilling at Sites 327 and 329 (Falkland Plateau) penetrated calcareous-siliceous oozes of the upper Paleocene, lower Eocene, Oligocene, and lower, middle, and upper Miocene that contained planktonic foraminifers (Tjalsma, 1977).…”