Cyclothems, transgressions and faunal change in the lias of north-west Europe

Publisher Website
Google Scholar
Abstract
Lithofacies changes in the marine epicontinental Liassic successions of Britain, northern France and West Germany are referred to eleven stratigraphical units corresponding locally with cyclothems, which are expressions of more or less contemporaneous, widespread movements of sea level. These could be eustatic but are treated provisionally as due to regional epeirogenesis. These movements, which tended to be asymmetrical in the sense that gradual shallowing of the sea was often followed by rapid deepening, appear to have been independent of a complex pattern of basins and swells. It is suggested that the larger landmasses were perhaps downwarped less than the marine areas, since marine transgressions seemed to have been rather local and inconsiderable in extent, with the exception of one at the base of the Pliensbachian. An intimate correlation exists between cyclothems and evolutionary and migrational changes in the ammonites. Other faunal groups were less influenced by the environmental changes expressed in the sediments, but two profound changes are apparent. One, at the base of the Pliensbachian, was marked by a large influx of new forms. The other, in the Lower Toarcian, was marked by mass disappearance and renewal. This, the most significant faunal change in the whole of the Lias, coincides with a widespread and comparatively sudden deepening of the sea.

This publication has 29 references indexed in Scilit: