The Oxford Clay is notable for its diverse and well preserved fossil assemblages as well as for the abundance and state of preservation of organic matter in the unit. Kosmoceras is a genus of ammonite with an aragonite shell.
Belemnites are calcitic.
Both Kosmoceras and belemnites were nektonic in habitat. Nuculacean bivalves and Gryphaea were benthic. Nuculacean shell is composed of aragonite, while Gryphaea is calcitic. The left figure shows the calculated carbon isotopic composition of dissolved bicarbonate in equilibrium with those fossil groups. The right figure shows the calculated oxygen isotope paleotemperatures of the fossil groups.