Mid-Maastrichtian Benthic Foraminiferal Isotope Record from Shatsky Rise, Northwest Pacific Ocean, Evidence for a Change in Oceanic Circulation

Schroeder, Eric J.¹, Tracy Frank¹ (1) University of Nebraska-Lincoln, Lincoln, NE

Ocean circulation plays a major role in governing the production and burial preservation of organic matter in the deep sea. Warm polar temperatures and relatively sluggish ocean circulation through much of the Cretaceous promoted extensive accumulations or organic matter in the marine sedimentary record. In the mid-Maastrichtian (c. 69 Ma), however, a latitudinal shift in areas of oceanic deep-water production led to improved ventilation of the deep sea and a corresponding decline in organic matter preservation. This event is marked globally by the abrupt extinction of inoceramids, a wide-ranging deep marine bivalve. Previous studies of this event have focused largely on sites in the Atlantic and Southern Oceans. Cores obtained during Ocean Drilling Program (ODP) Leg 198 provide an opportunity to examine a tropical Pacific record of this event. We examined the δ¹³C and δ¹⁸O values of well-preserved benthic foraminifera and Inoceramus fragments from cores drilled along a depth transect on Shatsky Rise. In these cores, inoceramid remains are common in lower Maastrichtian and absent from upper Maastrichtian sediments. The last appearance of inoceramid debris coincides with fluctuations in benthic δ¹³C and δ¹⁸O values, which are interpreted to reflect the displacement of warm intermediate water by colder, better ventilated water mass emanating from the Southern Ocean. These changes coincide with evidence from previous studies for accelerated cooling in the high latitudes at this time, which may have been driven in part by a global drop in sea level and associated changes in weathering rates and planetary albedo. Results illustrate the complexity of interactions between ocean circulation, climate, and sea level and their implications for the preservation of organic matter in the deep marine sedimentary record.