ISOTOPE DATA FROM CRETACEOUS CHALKS AND FORAMINIFERA - ENVIRONMENTAL OR DIAGENETIC SIGNALS

Scanning electron microscopy of sediments, microfossils, and polished thin sections from the Cenomanian-Turonian boundary section at Dover, England, demonstrates that cement is concentrated within large pores s uch as foraminifera and calcispheres, whereas the surrounding coccolit h-rich sediments are largely lacking in cement. Isotope analysis of si ngle microfossils and cement samples indicates the presence of mixing lines between primary (paleoceanographic) compositions and cements. Co nsequently, paleoceanographic and stratigraphic interpretations of the se sediments, and perhaps other similar sediments based on similar dat a, may be suspect.