GSA Connects 2022 meeting in Denver, Colorado

Paper No. 169-7
Presentation Time: 9:00 AM-1:00 PM


GADSON, Olivia, Biology, Georgetown University, 3700 O st, Washington, DC 20052, HUBER, Brian, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, JONES, Matthew M., Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109, FARFAN, Gabriela, Department of Geology, SUNY New Paltz, New Paltz, 12561 and PETERSEN, Sierra, University of MichiganEarth and Environmental Sciences Dept., 1100 N University Ave, Ann Arbor, MI 48109-1005

Remarkably well-preserved lower-middle Turonian (~92-93 Ma) and middle Campanian (~75-77 Ma) foraminifera samples from a Tanzania Drilling Project (TDP) drill site (~35°S paleolatitude) were analyzed for their carbonate clumped isotope (Δ47) composition to compare with previous oxygen isotope (δ18O) paleotemperature estimates and assumptions about the oxygen isotope composition of the regional seawater (δ18Osw). Reduced sample size requirements for Δ47 analyses using a cold finger configuration on a Nu Perspective dual inlet mass spectrometer (<2 mg) enabled us to measure paleotemperature data for multi-species separates of benthic and planktic foraminifera from each stratigraphic interval sampled. Foraminiferal test wall preservation was documented using light microscope and SEM imaging of whole and dissected specimens. External appearance of nearly all Turonian and Campanian tests indicated good to excellent (glassy) preservation, but some infilling was observed following test dissections. Using a water flotation method to concentrate hollow, non-infilled tests, samples were pipetted into a sieve and dried for analysis.

Preliminary Δ47 results are consistent with the expectation of cooler temperatures for benthics compared with co-occurring planktics and warmer Turonian surface and bottom water temperatures compared to the Campanian, with all Δ47 temperature data considerably warmer than at present day. A subset of samples exhibits very high Δ47 temperatures (>35°C) and considerably depleted d18O values, consistent with diagenetic alteration and infilling of some specimens.

These results highlight that when shallowly buried and well-preserved specimens are available, Δ47 analyses of foraminifera can quantitatively resolve paleotemperature and δ18Ow values for geologic time intervals of greenhouse paleoclimate, such as the Late Cretaceous.