Global Change and the Biostratigraphy of North Atlantic Cainozoic deep water Ostracoda

Abstract

ABSTRACT. The biostratigraphical distribution of deep-sea (>1000m) Palaeocene to Recent benthonic Ostracoda, based on nannofossil NP and N N zones is presented. By excluding very rare species and those represented by juveniles, I84 species are used in constructing range tables from a total fauna for the interval of 230 species. The vertical distribution of these specimens clearly allows of the recognition of all the major stratigraphical units within the Cainozoic and is also sufficiently precise todistinguish most of the nannofossil zones. The principal criteria employed are the first and last appearances of taxa. While eminently possible to create a series of ostracod zones, it is argued that they are best employed in the recognition of particular levels within the existing nannofossil scheme. The interpretation of the range tables is complicated in places by large numbers of Lazarus taxa and also by the fact that many of the 'originations' actually record the arrival of immigrants from the Indo-Pacific.Graphs of both simple and cumulative species diversity, and of origination and extinction rates, are used to demonstrate major faunal events such as the first arrival in the area, during the Middle Eocene, of cosmopolitan deep-sea species, or the very marked, but stepped, Palaeogene-Neogene faunal turnover. ThedistributionpattemsoftheOstracodarecordsuchglobalchangesastheformationofthepsychrosphere and the inception of a marked thermocline but they do not, as other authors have suggested, indicate a dramatic faunal turnover at the Eocene-Oligocene boundary. The more vigorous circulation patterns of the Oligocene, related to the opening of the Drake Passage, are reflected in enhanced ostracod diversity at that time. Elevated late Oligocene extinction rates may be correlated with cooling consequent upon the growth of polar ice. Similarly, Lower Miocene low levels of diversity may be associated with the closure of the Iberian Portal and the effective isolation of the Tethys. The deep-sea ostracods do not, for the most part, record such events as the mid-Pliocene warming nor Quaternary climatic fluctuations.

A taxonomic and distributional survey of marine benthonic Ostracoda off Kerguelen and Heard Islands, South Indian Ocean

“…Its similarity with that genus seems to be rather superficial, however, since there are clear internal differences from Bosquetina in the present species, notably the accommodation groove, two frontal scars and a prominent anterior median hinge tooth. It appears to be closer to Pterygocythere, differing from that genus only in lacking an eyespot, and was assigned to Pterygocythere by Coles et al (1990), Whatley & Coles (1991) and Cronin (1996). Stratigraphical considerations also suggest a closer relationship to Pterygocythere as the oldest occurrence of P. mucronalatum is in the Early Palaeocene of the North Atlantic (Whatley & Coles, 1991) and the genus Pterygocythere is well known from the Late Cretaceous (Coles et al, 1990), whereas Bosquetina is confined to the Oligocene to Recent in relatively shallow-marine sediments.…”

“…It appears to be closer to Pterygocythere, differing from that genus only in lacking an eyespot, and was assigned to Pterygocythere by Coles et al (1990), Whatley & Coles (1991) and Cronin (1996). Stratigraphical considerations also suggest a closer relationship to Pterygocythere as the oldest occurrence of P. mucronalatum is in the Early Palaeocene of the North Atlantic (Whatley & Coles, 1991) and the genus Pterygocythere is well known from the Late Cretaceous (Coles et al, 1990), whereas Bosquetina is confined to the Oligocene to Recent in relatively shallow-marine sediments. Guernet & Moullade (1994) propose a new genus, Pseudobosquetina, for this species on the basis of hingment that, in the authors' opinion, is insufficient to support separation at the generic level.…”

“…2, figs 12, 13) Whatley & Coles (1991) record Bradleya normani from the Late Quaternary (NN 21) and Recent of the North Atlantic. Whatley et al (1996Whatley et al ( , 1997 watermasses.…”

“…ocularis) coincide with the upper boundary of the CDW watermass and characterize Assemblage Cluster 4a of CDW Upper watermass. From 1200 m, where temperatures are less than 2(C, Lower CDW (I) Assemblage Cluster 4b Whatley & Coles, 1991), the Southeast Atlantic off southwest Africa studied by , the Southwest Atlantic area including the Strait of Magellan and Scotia Sea (Whatley et al, 1996(Whatley et al, , 1998 and the Northeastern Indian and Southwest Pacific Oceans (Whatley & Ayress, 1988;Coles et al, 1990). Additional data on the distribution of Krithe species are taken from Coles et al (1994) and Ayress et al (1999).…”

“…This species is widely distributed in the Miocene to Recent of the North Atlantic, but only rarely recorded from elsewhere (Coles et al, 1990;Whatley & Coles, 1991;pers. obs.…”