CLUMPED ISOTOPE PALEOTEMPERATURE ANALYSIS OF CAMPANIAN AND TURONIAN FORAMINIFERA FROM SOUTHEAST COASTAL TANZANIA

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 (δ¹⁸O_sw). 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 δ¹⁸O_w values for geologic time intervals of greenhouse paleoclimate, such as the Late Cretaceous.