SIGNIFICANCE OF THE EARLY MAASTRICHTIAN BELEMNITE BELEMNITELLA AMERICANA FROM THE PEE DEE FORMATION IN SOUTH CAROLINA (ADOPTED AS AN ISOTOPIC STANDARD) FOR OXYGEN ISOTOPE PALAEOTEMPERATURE MEASUREMENTS

Oxygen and carbon isotope ratios were measured on well-preserved molluscs collected from the Pee Dee, Coon Creek and Fox Hills formations in South Carolina, South Dakota and Tennessee to compare their relative depth habitats. Judging from calculated palaeotemperatures (13.1-22.4 ^oC), all investigated Late Campanian-Early Maastrichtian bivalves and ammonoids from these areas inhabited warm waters of epipelagic depths, which is in an agreement with the previously published data. Anomalously light δ¹⁸O signatures preserved in an aragonitic ammonoid Sphenodiscus lenticulata shell from the Fox Hills Formation confirm Tsuita and Westermann’s (1998) and Cochran’s et al. (2003) suggestion that some well-streamlined ammonoid shells have been secreted in brachyhaline shallow waters of the WIS. In contrast, measurements of δ¹⁸O on high-resolution samples across growth bands of the Early Maastrichtian B. americana from South Carolina indicate that its representatives were inhabitants of deeper, cooler waters of mesopelagic depths: palaeotemperatures varied mainly between 9.4 ^oC to 12.0 ^oC, occasionally (taking into account Lowenstam and Epstein’s (1954) analyses newly revised) to 17.8 ^oC, on average to 12.3 ^oC. Similar original results have been received from Late Maastrichtian and Early Campanian belemnite rostra from Poland and Germany (10.6 ^oC and 12.9 ^oC respectively, whereas Late Maastrichtian bivalve Dhondtichlamys from Poland shows palaeotemperature of 20.7 ^oC). These evidences are consistent with findings suggesting a considerable vertical range of the migration of belemnites in the seawater column and therefore the assessment of belemnite-derived palaeotemperatures for any reconstructions should be made with caution. δ¹⁸O values in samples from B. americana were found to be positively correlatable with δ¹³C through its successive growth portions, with the exception, however, of the latest one, which possibly indicates minor diagenetic alterations in near surface portions of belemnite rostra. It is particularly noteworthy because B. americana was adopted in the 1950s as a reference standard PDB for oxygen and carbon isotope analyses (Urey, 1948; Craig, 1957). We are indebted to the FEB of Russian Academy of Sciences for a grant 09-III-A-402 (Russia), which has made this work possible.