This paper presents different interpretations of the structural and/or stratigraphic criteria which are the bases for understanding evaporite-basin sedimentation and its subsequent role in oil exploration.

The gross profile and configuration of Devonian Famennian, Givetian, and Eifelian evaporite basins in North America have induced the a priori conclusion that these lenses and wedges are the result of differential sedimentary tectonics with contemporaneous evaporite-carbonate deposition. Such basins are viewed as culminating in uniform subsidence and conformable deposition of superjacent successions--generally of open-marine and nearshore facies.

Although this hypothesis deserves equal consideration with any other as a basis for interpreting evaporite-basin sedimentation, its preponderant acceptance without benefit of local and regional detailed stratigraphic studies hardly endows it with any real validity. In testing, this hypothesis should be examined seriously by the following considerations: (1) Walther's Law of Correlation of Facies demands that an unconformity must be recognized between the evaporites and the overlying transgressive redbed, sand, and/or carbonate succession; (2) related to Walther's Law--contemporaneous carbonate-evaporite deposition generally is impossible; the concept of cyclical superposition is much more rational; and (3) the offset "basin" axes of superjacent successions demand

End_Page 550------------------------------

interdepositional tectonics and not subsidence contemporary with sedimentation.

The above three points support the validity of the concept that the Devonian Famennian, Givetian, and Eifelian evaporite-basin configurations are not simply the result of differential sedimentary tectonics but are mainly eroded structural remnants. Supporting this concept are detailed stratigraphic subdivisions suggesting that these basins or lenses are only remnants of originally much more expansive evaporite depositional regions.

These basins are analogous to structural basins in contemporaneous open-marine sedimentary provinces. Post-depositional epeirogenic movement and vast areal erosion have left thick broad lenses or wedges of evaporite sections--regionally defined as evaporite provinces of deposition.

In searching for hydrocarbon accumulations among structural and stratigraphic traps within the evaporite complex, one has to consider these critical factors--the supra-evaporite basin unconformities and their tectonic origin.

End_of_Article - Last_Page 551------------