Ocean Drilling Program, United States

Sediments recovered from Ocean Drilling Program Leg 210 Hole 1276A range in age from Early Cretaceous (earliest Albian) to Paleogene (earliest Oligocene). In this study, samples were processed and analyzed for micropaleontological and palynological content, as well as sedimentary components. Core recovery from this site was good (85% between 800 and 1725.16 meters below seafloor), and the majority of samples processed yielded microfossils of some nature. Although none of the major groups are consistently present in all samples, calcareous nannofossils, agglutinated benthic foraminifers, and radiolarians do occur in many samples. The best age constraints for Hole 1276A are provided by calcareous nannofossils and dinoflagellate cysts. Age-diagnostic planktonic foraminifers are more commonly found in redeposited turbidite sandstones rather than in the autochthonous pelagic mudrocks. The depositional environments of the sediments have been interpreted as varying in oxygenation but having been deposited at abyssal depths (>2000 m) near or below the calcite carbonate depth (CCD). Almost uninterrupted deepwater deposition since the Aptian is evidenced both by the evolutionary succession of biota recovered from the sediments and by the sedimentary history of turbidites and gravity flow deposits derived from neritic and bathyal sources on the adjacent margin. A condensed interval recorded in the Turonian-Maastrichtian is likely associated with sediment starvation at times of high global sea level. A disconformity and condensed interval in the lower middle Eocene ( approximately 48.5-43.7 Ma) is associated with a change in global sea level and may be associated with invigorated deepwater current activity. Anoxic conditions affected the deep seafloor of the North Atlantic during Oceanic Anoxic Event (OAE) 1b (earliest Albian, approximately 112 Ma) and OAE2 (Cenomanian-Turonian boundary interval, approximately 93.5 Ma). Cooling during the early Turonian followed the vast carbon burial associated with OAE2 based on calcareous nannofossil assemblages. The recovery of a nearly complete Cretaceous-Paleogene boundary transition represents one of the deepest-water records of the end-Cretaceous event known. Another important paleontological discovery from Hole 1276A was the redeposited large-size benthic foraminifers of Campanian-Maastrichtian and latest Paleocene-early Eocene ages, which point to a nearby source of shallow, warmwater carbonates during these two periods of global warmth.