Mid-Cretaceous radiolarians from the eastern equatorial Atlantic and their paleoceanography

Abstract

Distinct intervals from cores recovered at Holes 959D and 962B of Ocean Drilling Program Leg 159 have yielded Cretaceous radiolarians. The recovered faunas are of late Albian to uppermost Cenomanian (in intervals 159-962B-8H-4, 85-86 cm, to 159-962B-10H-CC), late Turonian to Santonian (in intervals 159-962B-8H-4, 2-4 cm, to 159-962B-8H-4, 24-28 cm) and Campanian age (Sections 159-959D-61R-1 through 3). Preservation of the faunas is moderate to poor. While the Campanian fauna generally reflect the typical low- to mid-latitude associations known from the North Atlantic and Alpine realm, mid-Cretaceous radiolarian assemblages show certain differences to those known from the North Atlantic and Tethys. The similarities of the observed faunas to those from the North Atlantic and Tethys seem to increase with the ongoing opening of the Equatorial Atlantic Gateway. Differences between the late Albian faunas of both basins are significant. All of the observed faunas are of a remarkably low diversity. The diversity and the similarity to Tethyan faunas increase toward the late Cenomanian. As very little knowledge exists about late Turonian to Santonian assemblages, comparisons between the observed fauna and their definite ages remain difficult. Radiolarian-bearing intervals correlate well with the radiolarian-rich time intervals of other basins and, therefore, support former observations of a correlation of radiolarian intervals and mid-Cretaceous oceanic events. The observed radiolarian-rich intervals (late Albian, pre-Oceanic Anoxic Event [OAE] 1d; late Cenomanian, pre- OAE 2, and Campanian, OAE 3) correlate well with times of transgressive sea level.