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Cenozoic Planktonic Foraminifera—DSDP Leg 39 (South Atlantic)

1977; Linguagem: Inglês

10.2973/dsdp.proc.39.126.1977

Anne Boersma,

Marine Biology and Ecology Research

Tertiary planktonic foraminiferal faunas were recovered at Sites 354, 355, 356, 357, 358, and 359 during DSDP Leg 39 in the western South Atlantic; faunas at Site 355 are considered redeposited.At Site 354 the Tertiary section is characterized throughout by strong dissolution; the low-latitude planktonic foraminiferal faunas indicate deposition above the CCD.Dissolution across the Miocene/Pliocene boundary has resulted in the unique "' Sphaeroidinellopsis fauna," typical of the circum-Mediterranean and equatorial Atlantic for this interval.An extensive middle Miocene hiatus occurs at this site.Site 356 contains the oldest Tertiary, basal "GlobigerincT eugubina Zone, which includes the ancestor to Globoconusa daubjergensis.An extensive middle Miocene hiatus also occurs at this site.Some unusual planktonic foraminiferal morphotypes with abundant spines characterize a temperature maximum in the early Miocene.The faunas at Site 357 contain a greater number of high latitude species than the adjacent Site 356, particularly in the early Tertiary.-There is a significant hiatus across the Eocene/Oligocene boundary, preceded by a marked drop in planktonic foraminiferal diversity; this is also the time of cooling bottom and surface temperatures in the South Atlantic.The very long lower Miocene section, so typical of the South Atlantic, is followed by a relatively short middle Miocene hiatus.Several unusual planktonic foraminifera occur at this site.The first appearance of Streptochilus, known previously only from the middle Miocene to Recent, was recorded here in the latest Oligocene.Unusual spiny morphotypes of Globoquadrina and Catapsydrax appear during a temperature rise in the early Miocene.Globorotalia miozea morphotypes have a long stratigraphic range, occurring from the early Miocene into the Pliocene.Because of the high latitude component it was difficult to zone the late Miocene; it was, however, possible to use these higher latitude elements to interrelate the Neogene temperate and high latitude zonations with the low latitude zonation of Berggren (1972).Site 358 contains an unusual sequence of moderately well preserved to poorly preserved Paleocene through middle Eocene planktonic foraminifera.This site, deep in the Argentine Basin, was apparently near the foraminiferal lysocline and CCD throughout the early Tertiary until it sank permanently below these levels in the middle Eocene.Using the paleodepth of the site during this time period, it is possible to estimate the depth of the paleo CCD in this part of the Southern Atlantic from the Maestrichtian through the Eocene.Site 359 faunas are similar to those at Site 357.Only intermittent coring was done and only Pliocene, Miocene, and upper Eocene intervals were recovered.Eocene samples are full of volcanic debris and displaced foraminifera; Hantkenina is very abundant at this site, which must have lain at about 1000 meters in the Eocene.'The author has expressed strong preference for using "foraminifera" rather than the common form "foraminifer."Although the DSDP editors feel that the common form of the word is preferable in English, and have decided for consistency to use it in the Initial Reports, they accede here to the authors wishes.