TEMPORAL AND SPATIAL FACIES CHANGES IN BARREMIAN-APTIAN DEPOSITS OF THE TETHYS, THEIR PALEOTECTONIC AND PALEOCEANIC SIGNIFICANCE

Carbonate platform deposits in different circum-tethyan domains show significant spatial and temporal variations since their widespread inception in the Jurassic. Comparison of these variations in Barremian/Aptian facies succession in southeastern France and northeastern Mexico, as reflected in their micro- and macrofaunal assemblages, and carbon-carbonate content, indicates influences associated with paleoclimatic forcing mechanisms on the oxygen level of the water column, as well as significant local paleophysiographic changes controlled by tectonism. Hence, organic carbon-rich sediments, and coeval anoxic events, which are widely reported within lower Cretaceous sequences, may occur differently in these tethyan domains due to their paleophysiography. In southeastern France, interruption of typical cyclic patterns of variation related to global forcing mechanisms and development of organic-rich limestones was caused by differential tectonics due to basement dislocation. This is characterized in variations of the urgonian facies from the upper Bedoulian to the Gargasian and Clansayesian, respectively. On the other hand, spatial and temporal distribution of cyclic and non-cyclic variations of inner and outer platform facies in northeastern Mexico is suggestive of controlling mechanisms consistent with punctuated development of emergent knolls and domes associated with salt diapirism, analogous to the modern western Gulf of Mexico (Ewing and Antoine, 1972). Thus, the tectonically-controlled subbasins created on the Mexican platform played a significant role in allowing coeval facies to develop within a same given domain. This is expressed in the apparent frequency of cycles, spatial and temporal distribution of relative percentages of C-organic and the ammonites.