Population Dynamics, Paleogene Abyssal Benthic Foraminifers, Eastern South Atlantic

Abstract

Benthic foraminifers from Holes 522, 523, and 524 of DSDP Leg 73 (eastern South Atlantic) were quantitatively analyzed by using three methods: analysis of local originations and extinctions, factor analysis of species relative abundances, and population structure analyses of species diversity and equitability. The results of all three forms of analysis are compatible and show a sharp faunal change in the late Eocene. This change involves an almost complete cessation of local originations, a small increase in local extinctions, a dramatic shift in species relative abundances, and a sharp increase in species equitability. Sporadic small-scale variations in the same parameters during the middle Eocene precede the major change. These results indicate initiation of the psychrosphere in the latest Eocene, with precursor events in the middle Eocene. The faunal evidence is consistent with a northeast Atlantic source for the cold bottom water.

On the occurrence of Early Pliocene marine deposits in the Ierapetra Basin, Eastern Crete, Greece

“…This is also supported by the lack of shallow water fauna and the absence of pri- mary sedimentary structures. The minor percentage of frequency, throughout the section, of the species Elphidium crispum, E. advenum and Ammonia beccarii, which usually live not deeper than 100 m (Parker 1958, Chierici et al 1962, Jorissen 1988, Sgarrella & Moncharmont-Zei 1993, are probably linked to transport. The near absence of the taxa with a tolerance for salinity fluctuations, e.g., Ammonia, Elphidium and Nonion, and quite diverse character of planktonic foraminiferal assemblages indicate an open marine environment with normal value of salinity.…”

Plio-Pleistocene Benthic Foraminifera Stratigraphic Distribution in the Deep-Sea Record of the Tyrrhenian Sea (ODP Leg 107)

“…Unexpectedly, Hyalinea baltica is present and common in several samples of Site 654 and in some samples of Site 653. This species, living today from 50 to about 1000 m in depth (Parker, 1958;van Morkhoven et al, 1986), had evidently a wider bathymetric range during the early Pleistocene. In both sites the appearance level of this species just predates the base of the large Gephyrocapsa nannofossil biozone (Glacon, Rio, and Sprovieri, this volume) and therefore this event in the deep-sea sequences is well comparable with the same event in land-based sequences, where it first occurs in the same biostratigraphic position (Rio, 1982;Ruggieri et al, 1984).…”

“…In both sites the appearance level of this species just predates the base of the large Gephyrocapsa nannofossil biozone (Glacon, Rio, and Sprovieri, this volume) and therefore this event in the deep-sea sequences is well comparable with the same event in land-based sequences, where it first occurs in the same biostratigraphic position (Rio, 1982;Ruggieri et al, 1984). The last occurrence of Oridorsalis umbonatus, a species not living today in the Mediterranean basin (Parker, 1958;Blanc-Vernet, 1969;Blanc-Vernet et al, 1983) is recorded in Sample 3R-3, 68 cm in Site 654; in Site 653 it is present up to the uppermost sample (1H-1, 75 cm), belonging to the Emiliania huxleyi acme nannofossil biozone (Rio, Raffi, and Villa, this volume; Glacon, Rio, and Sprovieri, this volume) …”

“…Many species that disappear in land sections at this level are missing or have disappeared at lower levels, and many species which appear at this level are not represented or first occur higher in the sections. (Parker, 1958;Bizon and Boroulet, 1984) from 80 m to a maximum depth of about 1000-1200 m. The delayed disappearance from Site 652 to Site 653 and Site 654 (from east to west and from the deepest to the shallowest part of the Sardinian escarpment) may indicate the different time interval in which the three sites exceeded the depth of approximately 1200 m. Site 652 became deeper in an older interval than Site 653 which, in turn, crossed this depth before than Site 654. In Sites 653 and 654 Gyroidinoides altiformis appears, with rare specimens, in the upper part of MP15 biozone, respectively just above and below the base of the Discoaster brouweri nannofossil biozone.…”

“…This event may be correlated with the increasing well-oxygenated bottom conditions recognized at the base of the Pleistocene (Hasegawa, Sprovieri, and Poluzzi, this volume). Articulina tubulosa is a bathyal species (Parker, 1958;Blanc-Vernet, 1969;Wright, 1978a), and therefore the basal boundary of this biozone is better recognized in deep-sea and bathyal sequences. In sequences deposited in shallower depth environment this boundary can be approximated by the appearance level of Bulimina elegans marginata (Colalongo and Sartoni, 1979;Colalongo et al, 1982;d'Onofrio, 1983) and Uvigerina costato-caudata (Sprovieri, 1981) slightly below, and by the appearance of Bulimina etnea (Sprovieri, 1978;Colalongo and Sartoni, 1979;Colalongo et al, 1982;d'Onofrio, 1983) above.…”