Chronostratigraphic and paleoenvironmental constraints derived from the 87Sr/86Sr and δ 18O signal of Miocene bivalves, Southern McMurdo Sound, Antarctica

Abstract: 87Sr/86Sr measurements were carried out on samples of various macrofossil taxa recovered from the SMS AND-2A core with the main goal of improving age control of the core, and provide insight on marine climate at the time of carbonate precipitation. Shell material was carefully screened using cathodoluminescence (CL) to discern optimum areas for microdrilling. Powders thus obtained were in addition analyzed for Ca, Mg, Sr, Mn, and Fe contents to further evaluate the possibility of diagenetic alteration of the skeletal carbonate before measuring their Sr isotope compositions. Bivalves turned out to be the best candidates for isotopic determinations. Unaltered calcitic bivalves produced reliable 87Sr/86Sr age ranges. Aragonitic material, on the other hand, produced less radiogenic 87Sr/86Sr than anticipated, an unexpected result. Preliminary oxygen isotope determinations in calcite samples confirm contrasting marine climate conditions between the late Early Miocene (16.5–16.0 Ma), and the early Late Miocene (~11 Ma). [Copyright &y& Elsevier]