Jurassic and Triassic units of the northern Gulf Coast do not crop out, and Cretaceous units do so only along narrow discontinuous belts, comprising small fractions of their known extent. Nevertheless, our thinking concerning stratigraphy sedimentation, and geological history has been dominated by surface-oriented concepts of such nearshore phenomena as onlap, offlap, and shoreline position. A much broader, more truly three-dimensional view of geological history is possible through the use of much more extensive subsurface control.

"Peripheral" tectonic elements (e.g., Ouachitas and "Ouachita-Monroe Trend"), on the landward edge of the Mesozoic depositional area, affected nearshore clastic distribution, shoreline relations, etc. "Shelf" tectonic trends, particularly at the Gulfward edge ("shelf-edge"), strongly affected deposition in offshore areas by controlling marine circulation, direction and competency of currents, etc. Both types of structures have variously combined to produce such phenomena as: 1) trends of porous limestone or massive sandstone; 2) evaporite lagoons; and 3) "direct-source" and "indirect-source" facies patterns, i.e., Gulfward and landward decrease, respectively, in grain size and clastic-ratio.

A tectofacies classification is proposed to show the effect of structural patterns on sedimentary environments. Greater weight is placed on lithofacies data (reflecting water depth, and position in reference to dominant tectonic trends) than on thickness, per se. Four tectotopes are recognized in Gulfward sequence, each with its own characteristics: backshelf, foreshelf, shelfedge, and basin. The shelfedge migrated, commonly by shifting from one structural trend to another, as depositional cycles progressed. Each "stand" of the shelfedge produced a characteristic environmental regime. A tectofacies map of each of these regimes would produce an episodal history of the Mesozoic of the Gulf Coastal Plain.

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