Late Cretaceous through Neogene Deep-Sea Benthic Foraminifers (Maud Rise|Weddell Sea|Antarctica)

Abstract

Upper abyssal to lower bathyal benthic foraminifers from ODP Sites 689 (present water depth 2080 m) and 690 (present water depth 2941 m) on Maud Rise (eastern Weddell Sea, Antarctica) are reliable indicators of Maestrichtian through Neogene changes in the deep-water characteristics at high southern latitudes. Benthic foraminiferal faunas were divided into eight assemblages, with periods of faunal change at the early/late Maestrichtian boundary (69 Ma), at the early/late Paleocene boundary (62 Ma), in the latest Paleocene (57.5 Ma), in the middle early Eocene to late early Eo cene (55-52 Ma), in the middle middle Eocene (46 Ma), in the late Eocene (38.5 Ma), and in the middle-late Miocene (14.9-11.5 Ma). These periods of faunal change may have occurred worldwide at the same time, although specific first and last appearances of deep-sea benthic foraminifers are commonly diachronous. There were minor faunal changes at the Cretaceous/Tertiary boundary (less than 14°7o of the species had last appearances at Site 689, less than 9% at Site 690). The most abrupt benthic foraminiferal faunal event occurred in the latest Paleocene, when the diversity dropped by 50% (more than 35% of species had last appearances) over a period of less than 25,000 years; after the extinction the diversity remained low for about 350,000 years. The highest diversities of the post-Paleocene occurred during the middle Eocene; from that time on the diversity de creased steadily at both sites. Data on faunal composition (percentage of infaunal versus epifaunal species) suggest that the waters bathing Maud Rise were well ventilated during the Maestrichtian through early Paleocene as well as during the latest Eocene through Recent. The waters appeared to be less well ventilated during the late Paleocene as well as the late middle through early late Eocene, with the least degree of ventilation during the latest Paleocene through early Eo cene. The globally recognized extinction of deep-sea benthic foraminifers in the latest Paleocene may have been caused by a change in formational processes of the deep to intermediate waters of the oceans: from formation of deep waters by sinking at high latitudes to formation of deep to intermediate water of the oceans by evaporation at low latitudes. Benthic foraminiferal data (supported by carbon and oxygen isotopic data) suggest that there was a short period of in tense formation of warm, salty deep water at the end of the Paleocene (with a duration of about 0.35 m.y.), and that less intense, even shorter episodes might have occurred during the late Paleocene and early Eocene. The faunal record from the Maud Rise sites agrees with published faunal and isotopic records, suggesting cooling of deep to intermediate waters in the middle through late Eocene.

Methods

“…Taxonomic assignments follow Tjalsma andLohmann (1983), van Morkhoven et al (1986), Miller and Katz (1987), Thomas (1990), Van Marle (1991), Katz and Miller (1991), Kato (1992), Jones (1994), Nomura (1995), Hanagata (2003), Hanagata and Hiramatsu (2005), Kaminski and Gradstein (2005), and Holbourn et al (2013). The generic classification of Loeblich and Tappan (1988) was used and updated in some instances, in particular for uniserial taxa (Hayward, 2002).…”

Methods

“…Taxonomic assignments follow Tjalsma and Lohmann (1983), Miller and Katz (1987), Thomas (1990), Katz and Miller (1991), Jones (1994), Nomura (1995), and Holbourn and Henderson (2002). The generic classification of Loeblich and Tappan (1988) was used.…”

Palaeoenvironmental reconstruction of the Oligocene Afales Basin, Ithaki island, western Greece

“…Despite these problems, which require the comparison of modern and ancient foraminiferal fauna to be carried out cautiously, smaller benthic foraminifera are still indispensable in interpreting past environments and palaeoceanographic settings e.g. [32,[57][58][59][60]. Taking these complications into account, we attempt to estimate the palaeoenvironmental factors that controlled the distribution of small benthic foraminifera in the Oligocene foreland basin of Ithaki Island, using knowledge of modern foraminiferal ecology, morphology and microhabitats.…”

“…The ratio between epifaunal and infaunal groups (Figure 6) is used as an approximate measure of the degree of oligotrophy/eutrophy and related oxygen level in the Afales Basin, based on data derived from modern oceans [35,65,66] and similarly used for interpreting trophic and oxygen conditions in ancient seas [59,60]. The bulk of the samples, which contain 46-86% epifaunal taxa ( Figure 6), suggest more or less oligotrophic, welloxygenated bottom waters, where a significant amount of food is consumed at the sediment surface and only a smaller portion enters the sediment, restricting infaunal life.…”