Planktonic Foraminiferal Biostratigraphy and Paleoenvironmental Interpretation of Paleogene Faunas from the Subantarctic Transect, Leg 114

Abstract

Paleogene planktonic foraminifers recovered during ODP Leg 114 in the subantarctic region exhibit a cosmopolitan character at the opening of the Paleocene, and then they evolve similarly to faunas from lower latitudes. They begin to differentiate from lower latitude faunas by the early late Paleocene when large morozovellids disappear from the region and cool deep-water-dwelling Globorotaloides appear much earlier than at lower latitudes. By early Eocene time large morozovellids immigrate into the subantarctic area during the warmest episode of the entire Eocene. From that time up to the end of the middle Eocene planktonic foraminiferal faunas exhibit a temperate character, as indicated by the abundance of common acarininids. At the same time dissolution at depth causes depauperated planktonic faunas at the deeper sites. A new warming episode during the late Eocene is marked by the immigration of Globigerinatheka luterbacheri into the subantarctic region. The cooling trend during the late Eocene causes a progressive decrease in species richness, which only sporadically is less than 10 species. The early Oligocene is also characterized by relatively rich planktonic faunas, but after that time the western subantarctic region is occasionally invaded by few planktonic foraminiferal species. These immigrations coincide with the warmer episodes on the climatic curve, such as Zones P21a and P22-"N4."Beginning in late early Eocene and through the Oligocene eastern subantarctic planktonic foraminiferal faunas exhibit a much warmer character than those from the western side and are more similar to warm temperate faunas. Therefore, the eastern faunas provide a more refined biostratigraphy. Oligocene time is characterized by a trend toward a warmer climate; however, this trend was reversed in the early Miocene.A dissolution event, possibly coeval with an erosional event, occurs within Zone P21b across the subantarctic region.

Oligocene Planktonic Foraminifer Biostratigraphy of Hole 803D (Ontong Java Plateau) and Hole 628A (Little Bahama Bank), and Comparison with the Southern High Latitudes

“…Paragloborotalia opima, Globigerina ciperoensis, and Globigerinella obesa are also noted in the South Atlantic holes (Nocchi et al, 1991). Globigerina labiacrassata was not observed in upper Oligocene sediments from either of the low-latitude sites, and Tenuitella munda occurs only sporadically in Hole 803D.…”

“…Nearly all samples had to be washed twice to free the foraminifer tests from the chalky matrix. Sites 698-704 (Nocchi et al, 1991) Sites 689 & 690 • 113…”

“…Recent studies of planktonic foraminifers from subantarctic Oligocene deep-sea sequences have been published by Stott and Kennett (1990) from the Maud Rise in the Weddell Sea, Huber (1991) from the southern Kerguelen Plateau, and Nocchi et al (1991) from the South Atlantic (Fig. 1).…”

“…Both sites contain rich assemblages of planktonic foraminifers. Recent ODP drilling in the southern high latitudes has provided new Oligocene records of planktonic foraminiferal populations for comparison with our low-latitude results (e.g., Stott and Kennett, 1990;Huber, 1991;Nocchi et al, 1991). Our purpose here is to document planktonic foraminiferal distribution through the uppermost Eocene-basal Miocene interval of Holes 628 A and 803D, to compare assemblage composition between these two low-latitude sites, and to examine the similarities and differences in assemblage composition between the low latitudes and southern high latitudes based on recent ODP results.…”

Morphology and Affinity of the Planktonic Foraminifer Cassigerinelloita amekiensis Stolk and Reclassification of Cassigerinelloita Stolk

“…Since this report was written, we have been informed that Cassigerinelloita amekiensis also occurs in a level equivalent to Zones P9 (upper part) and P10 at Holes 698A, 699A, 700B, 702B, 703A, and 704B in the subantarctic South Atlantic Ocean (Nocchi et al, 1991).…”