Bivalve palaeoecology in an Early Cretaceous carbonate ramp, central Argentine Andes

DAMBORENEA, S.E.; MANCEÑIDO, M.O.; RICCARDI, A.C.

Cambridge, Gran Bretaña

Simposio; International Meeting on the Biology and Evolution of the Bivalvia; 1999

Malacological Society of London

On the eastern slope of the central Argentine Andes crop out extensive Early Cretaceous deposits accumulated within the Neuquén basin. This study is focused on the benthonic faunas from the Berriasian-Hauterivian interval that occur in mostly carbonate units of the Mendoza Group. Eighteen localities were sampled over a N-S strip, 230 km long, between Diamante and Grande rivers in southern Mendoza Province, western Argentina, and the qualitative faunal composition along the stratigraphic sections surveyed was recorded. Although the identified fauna also includes cephalopods, brachiopods, gastropods, corals, echinoderms, serpulids and crustaceans, bivalves are by far the most abundant and diverse invertebrate group, thus allowing the characterisation of various assemblages of palaeoecological significance. The biostratigraphic control was provided by co-occurring ammonites. On this basis, the distribution in time and space of about fifty bivalve species was subjected to multivariate analysis and sets of recurrent groups of taxa were recognized. Interpretation of such fossil associations was based on the analysis of biofacies, trophic groups, spatial distribution of guilds, as well as relationships to lithofacies and inferred oxygen levels. One of the main fossil associations showing a localized occurrence is related to coral buildups, whereas several oyster-dominated associations are widespread in most other carbonate lithofacies. On the other hand, mud grade lithofacies bear distinctive, thin-shelled bivalve associations, which developed basinward. A palaeoenvironmental model for this part of the basin during Berriasian-Hauterivian times involves a carbonate ramp with occasional development of organic banks.