Palaeoenvironment of Maastrichtian ostracods from ODP Holes 1049B, 1050C and 1052E in the Western North Atlantic

Stefan Majoran

doi:10.1144/jm.18.2.125

Abstract

Abstract. The Maastrichtian ostracods recovered from ODP Holes 1049B, 1050C and 1052E on the Blake Nose, Western North Atlantic, are investigated. The three sites are located on a depth transect encompassing middle to lower bathyal, Late Cretaceous palaeodepths. Fourteen samples ranging in age from early to late Maastrictian are investigated from Hole 1052E, which is the shallowest site. The early Maastrichtian G. falsostuarti–G. gansseri Zone of Hole 1052E yields rare ostracods. The species richness, abundance and faunal density are on average considerably higher in the late Maastrichtian R. fructicosa and A. mayaroensis Zones of Hole 1052E, possibly, at least partly, as a result of palaeoceanographical changes that were also responsible for the disappearance of the inoceramid bivalves at this location. A palaeobathymetrical comparsion among the late Maastrichtian ostracod assemblages recorded from Holes 1049B, 1050C and 1052E shows that the faunal density and mean number of taxa are inversely correlated with palaeodepth; however, the dominance of the platycopid genus Cytherella increases with palaeodepth. A dominance of platycopids may signify environmental stress related to low oxygen content. The dominance of the benthic foraminifer Nuttalides trumpeyi in the Late Cretaceous of Holes 1049B and 1050C provides additional evidence of oxygen deficiency. From a total of 28 genera recorded from Holes 1049B, 1050C and 1052E, 14 were previously recorded from Hole 689B, a high latitude hole in the Southern Ocean, and show that many ostracod genera display a wide latitudinal distribution in the Late Cretaceous deep sea, although more geographically restricted genera are also present, analogous with modern and Tertiary oceans.

Highlights

During the Maastrichtian, world-wide biotic changes occurred which included the global extinction of the inoceramid bivalves (MacLeod, 1994; MacLeod et al, 1996) and the tropical rudist reef faunas (Johnson & Kauffman, 1990)
The replacement of the depleted ostracod assemblage of the G. .falsostuarti-G. gansseri zones by the generally richer and more diversified ostracod assemblage of the R. fructicosa and A . mayaroensis zones in Hole 1052E occurs near the top of magnetostratigraphic subchron C31R
The replacement seems to post-date the short-lived global palaeoceanographic episode observed in southern high latitudes in the early Maastrichtian between about 71 and 70 Ma

Summary

INTRODUCTION

During the Maastrichtian, world-wide biotic changes occurred which included the global extinction of the inoceramid bivalves (MacLeod, 1994; MacLeod et al, 1996) and the tropical rudist reef faunas (Johnson & Kauffman, 1990). Superimposed on this trend, there is isotopic evidence of a temporarily short event in the early Maastrichtian (between 71 and Ma) during which the oceanic circulation may have become more typical of the Recent thermohaline pattern with an intensified production of cool, well-oxygenated bottom and intermediate waters at high latitudes (MacLeod & Huber, 1996; Barrera et al, 1997) Before and after this event, the oceanic circulation was probably more typical of the Late Cretaceous pattern with a stronger influence of warm saline plumes formed at low latitudes (Barrera et al, 1997). Partly or completely focused on Late Cretaceous deep-sea ostracods (i.e. from a palaeodepth > 500 m) of the Atlantic and Southern Oceans include Benson (1975, 1977), Benson et al (1984, 1985), Damotte (1979, 1988), Dingle (1981), Swain (1973, 1978, 1983), Majoran et al (1997), Majoran et al (1998) and Majoran & Widmark (1998)

METHODS

DISCUSSION