Environmental stress and diagenetic modifications in inoceramids and belemnites from the Upper Cretaceous James Boss Basin, Antarctica

New petrographic and isotopic data from inoceramid bivalve shells and belem nite rostra from the lower Campanian and belemnite rostra from the mid-uppe r Maastrichtian of the Marambio Group, James Ross Basin, Antarctica are pre sented. Most of the inoceramid data were processed from shell fragments of the large form Antarcticeramus rabotensis (Crame and Luther) at the stratig raphic level marking the extinction of the inoceramids in the James Ross Ba sin (uppermost early Campanian-basal late Campanian). Standard transmitted light microscopy and cathodoluminescence (CL) studies in thin sections of A . rabotensis show clear evidence of environmental stress, which is reflecte d as marked growth breaks in the shell banding of this large inoceramid biv alve. At Redonda Point, CL and the mean oxygen isotopic value (delta O-18=- 3.11 parts per thousand (PDB); n=11; t degrees =25.4 degreesC) indicate a v aried degree of diagenetic modification, but without any evidence of neomor phism along the prismatic microstructures. Early Campanian belemnite rostra are much less diagenetically modified (at the Brandy Bay section; and the Santa Marta section; delta O-18=-0.50 parts per thousand (PDB); n=5; t degr ees =14.0 degreesC and delta O-18=-0.94 parts per thousand (PDB); n=21; t d egrees =15.8 degreesC) and are non luminescent except for localized, organi c-rich bands. The mean oxygen isotopic value for mid-late Maastrichtian bel emnite rostra (at the Seymour Island section; delta O-18=-0.11 parts per th ousand (PDB); n=5; t degrees =12.5 degreesC) indicates a substantial drop i n the sea-water paleotemperature, suggesting a causal relationship between the early extinction of the inoceramid bivalves in high latitudes of the So uthern Hemisphere and the falling sea-water temperature.