One of the most underestimated factors influencing carbonate platform development and its internal architecture is the role of syndepositional tectonics, either in the form of high-frequency, regional tectonic "flexing", for example, tectonic reversals within strike-slip settings, or local uplift/subsidence related to underlying movement of mobile lithologies such as evaporites or shale. In many, if not all, passive margin settings, thick layers of evaporite (principally halite or "salt") accumulate above the regional break-up unconformity above the syn-rift section, such as the divergent Mesozoic margins of the Gulf of Mexico, west Africa (Angola/Congo) and South America (Brazilian margin).

In all of these Mesozoic divergent margin examples (and many Paleozoic examples as well), widespread carbonates overlie these evaporites, for example: (1) the Upper Jurassic Smackover/ Buckner/Haynesville ramp carbonate complex of the US Gulf of Mexico rests upon mobile Middle Jurassic Louann salt; (2) the Albian carbonate systems of both west Africa (Congo and Kwanza Basins offshore Angola) and Brazil (Santos and Campos Basins) overlie thick Lower Aptian salt associated with the breakup of Pangaea.

Inspection of offshore seismic data is replete with numerous examples of syn-depositional salt tectonism that was active during the development of the carbonate ramp and rimmed shelf systems. Typically, two modes of salt-influenced activity occur:

(1) Pillowing and diapiric uplift of mobile salt can create topographic highs that are favorable sites for carbonate accumulation (high-energy grainstones and reefs; e.g., the Holocene of the Persian Gulf);

(2) Gravitationally driven extension and downdip lateral migration of incipient thin carbonate deposits that occur over the mobile salt unit in the form of "raft tectonics:'

In both scenarios, carbonate sedimentation is active while the local substrate is affected by salt-induced uplift, enhanced subsidence, and/or lateral sliding. The common occurrence of such phenomena in many Mesozoic divergent margins indicates that the role of syndepositional salt tectonics is very much a factor controlling the evolution of carbonate systems, something that is almost universally excluded in summaries of carbonate depositional models and stratigraphic evolution.

End_of_Record - Last_Page 19---------------