Facies Variability of Transgressive and Regressive Systems of Gravity Deposits in Deep-Water Carbonates (Mesozoic, French Alps)

FERRY, SERGE, and GILLES DROMART, University of Lyon, France

From the several tens of depositional sequences that can be platform-to-basin traced in the Mesozoic of the Vocontian Trough and nearby

platforms, the following rules may be set: (1) there are two basic systems of gravity deposits--a regressive one and a transgressive one--but unequally developed depending on sequences; (2) thick bundles of bioclastic turbidites, tied to parasequence channels and representing "shingled turbidites," are emplaced mainly at the basis of lowstand systems tracts, but may last the whole lowstand; the complex organization of siliciclastic fans is not found; (3) debris-flow deposits, as a result of catastrophic margin collapses, are almost always within transgressive systems tracts; (4) slumps deposits are scattered throughout when frequent; when scarce, they are mainly within transgressive systems tracts, and replace debris flow deposits; (5) Upper Jurassic to Berriasian "resedimentation bre cias," a peculiar type of gravity deposits, are emplaced at both rises and falls in relative sea level, and cannot be used as reliable markers of sequence boundaries; and (6) both transgressive and regressive gravity systems are more developed during second order lowstands in sea level marked by strong carbonate platform progradation. As a whole, third order transgressive gravity systems are often more developed than regressive ones. Comparisons with siliciclastic depositional systems suggest that sandstone turbidites could be transgressive systems, as a result of stronger parasequential (?glacio-eustatic) high-frequency oscillations during third order rises in relative sea level.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)