Testing the Cretaceous Glaciation Hypothesis Utilizing Nd Isotopes of Southern Ocean Sediment

Evidence from paleosols and carbonate weathering models indicate that the Late Cretaceous had a super greenhouse climate due to atmospheric CO2 concentrations two to four times greater than modern levels, tropical sea surface temperatures exceeding 35°C, and high-latitude temperatures exceeding 20°C. Despite the warmth of this super greenhouse climate, benthic foraminifera δ18O records suggest continental ice sheet emplacement and marginal marine stratigraphic architectures indicate eustatic sea level fluctuations of > 25 m and a tempo of <<1 million year that punctuate the Late Cretaceous. These changes suggest a glacio-eustatic control, which we attribute to the growth and decay of continental ice sheets on Antarctica. The most significant of these changes is the 71.2 Ma Campanian-Maastrictian boundary event (CMBE). Because continental glaciation tends to increase the weathering of bedrock and production of sediment delivered to the oceans, circum-Antarctic marine sediment flux would be expected to increase during periods of glaciation. Here we present results of Sm-Nd analysis of the fine-grained terrigenous fraction (<20 μm) of Ocean Drilling Project site 690C across the CMBE to evaluate the controversial hypothesis of Late Cretaceous glaciation of Antarctica. The Sm-Nd system is ideal for assessing the problem of hidden glaciations as 1) the region of East Antarctica adjacent to site 690C is dominated by Archean-Proterozoic crust, thus the ɛNd signature of sediment delivered to the ocean during glaciations would be more negative (e.g., -15, -20) than non-glacial background levels (e.g.,-9) and 2) Nd isotopes from terrigenous sources are robust in ocean sediments as they are not readily influenced by weathering processes, sediment transport, or diagenic reactions.