Late albian paleoceanography of the western subtropical north Atlantic

Abstract

A late Albian-early Cenomanian record (similar to 103.3 to 99.0 Ma), including organic-rich deposits and a delta C-13 increase associated with oceanic anoxic event 1d (OAE 1d), is described from Ocean Drilling Program sites 1050 and 1052 in the subtropical Atlantic. Foraminifera are well preserved at these sites. Paleotemperatures estimated from benthic delta O-18 values average similar to 14 degrees C for middle bathyal Site 1050 and similar to 17 degrees C for upper bathyal Site 1052, whereas surface temperatures are estimated to have ranged from 26 degrees C to 31 degrees C at both sites. Among planktonic foraminifera, there is a steady balance of speciation and extinction with no discrete time of major faunal turnover. OAE 1d is recognized on the basis of a 1.2 parts per thousand delta C-13 increase (similar to 100.0-99.6 Ma), which is similar in age and magnitude to delta C-13 excursions documented in the North Atlantic and western Tethys. Organic-rich "black shales" are present throughout the studied interval at both sites. However, deposition of individual black shale beds was not synchronous between sites, and most of the black shale was deposited before the OAE 1d delta C-13 increase. A similar pattern is observed at the other sites where OAE 1d has been recognized indicating that the site(s) of excess organic carbon burial that could have caused the delta C-13 increase has (have) yet to be found. Our findings add weight to the view that OAEs should be chemostratigraphically (delta C-13) rather than lithostratigraphically defined.