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.