DISTINGUISHING BETWEEN OXYGEN AND SUBSTRATE CONTROL IN FOSSIL BENTHIC ASSEMBLAGES

Low diversity benthic shelly assemblages occur under conditions of both low oxygen and very soft substrates. It is therefore important to be able to distinguish between these two environmental parameters. A declining oxygen gradient causes benthic diversity (including epibionts on hard benthic islands) to decline to a zero point. A transition from firm to soft substrates is also associated with a decline in overall benthic faunal diversity but, importantly, this has little affect upon epibionts. Functional morphological studies may also provide information about substrates. for example, thin-shelled bivalves of the 'paper pecten' morphology may represent super-soft substrate strategists.