Controls on the Inception of Early Senonian Tethyan Rudist-Bearing Carbonate Platforms

Gabriele Carannante, Roberto Graziano, and Lucia Simone
Napoli University, Napoli, Italy

Coniacian-Santonian limestones from north-western Sardinia and southern Apennines (Italy), evidenced the dominance of foramol lithofacies over chlorozoan-chloralgal ones. The large spreading of the foramol assemblages in tropical/subtropical sedimentary settings would be consistent with changing in the environmental conditions which developed due to different types of stress in the water mass. The resulting depositional contexts were open-shelves prone to the more opportunistic forms of the foramol assemblages. They were characterized by the diffusion of the rudists that covered, with their detritus, increasingly larger sectors of the shelf without building real reefs. The different nature and organization of the sediment-producer assemblages as well as the abundance of the bioerosion-derived skeletal detritus resulted in sheets of loose bioclastic sediments that covered bottoms lacking protective rims. The large spreading of molluscs (rudists), which became dominant in the whole shelf, coincided with a reduction of the corals. These latter persisted in the marginal and deep sectors of the shelf as subordinated forms. Both the studied examples refer to post-emersive sedimentary contexts. A tectonically-related topography controlled the inception of the carbonate factories which suffered the effects of local induced upwellings and/or hyperproductivity by terrestrial runoff on post-emersive and/or tectonized transgressed substrata. These local controls superimposed on global fluctuating environmental conditions.The resulting major turning points in the stratigraphic record strictly are coincident with major variation in the global scale chemical/phisical parameters of the Hydrosphere/Atmosphere System.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005