APPS, GILLIAN M., British Petroleum, Houston, Texas, USA; and TREVOR ELLIOTT, University of Liverpool, England

ABSTRACT: Tectonic and Sea Level Controls on the Initiation, Development and Termination of a Turbidite Basin: The Tertiary Gres D'annot Basin, French Alps.

The Eocene-Oligocene Gres d'Annot basin is an extensive thrust-sheet-top basin created during the early phases of Alpine deformation in southern France. The main basin fill succession commences with a transgressive carbonate unit (Calcaires Nummulitiques) which is overlain by marls, recording a progressive deepening of the basin (Marnes Bleues). This deepening, sediment-starved phase of the basin fill is diachronous, younging westwards (Lutetian-early Priabonian), which reflects combined flexural subsidence and rising eustatic sea level, with the shifting locus of flexural subsidence accounting for the diachronism.

Alpine deformation produced structural bathymetry on the basin floor, which is onlapped by siliciclastic turbidites (Gres d'Annot). Slope/turbidity current interactions caused significant thickness and facies variations. The initiation of coarse, siliciclastic deposition cannot be explained with reference to tectonics and instead is considered to reflect the prevalence of falling eustatic sea level during the Priabonian. The base of the turbidite succession appears to young westwards and therefore, it is a compound sequence boundary, defining a lowstand sequence set. The turbidite basin was terminated by two synchronous structural events: the emplacement of thrust sheets which filled the remaining available accommodation space and the tectonic rotation of the sediment source away from the basin (back arc spreading of Corsica-Sardinia).

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.