Northeast-trending facies of the James Limestone of the East Texas basin reflect three depositional settings. From northwest to southeast they include (1) an area of quartz-sandstone deposition, most of which can be inferred to be of continental origin, (2) a reef and skeletal-oolitic grainstone belt that formed under high-energy conditions in nearshore shallow water, and (3) a broad area of open-marine shelf on which argillaceous lime mudstone and calcareous shales formed under relatively quiet-water conditions.

Three depositional trends and their associated carbonate bodies can be differentiated in the reef and carbonate grainstone belt. One is an east-northeast-trending oolitic grainstone ridge of "dune" which can be mapped for at least 30 mi. A second is marked by northwest trending rudistid-reef complexes, one of which forms a conspicuous salient projecting southeastward from the main grainstone belt (Fairway reef) and another within the main grainstone belt (Quitman reef). The third depositional trend is also in the northwest and is seen as very large skeletal-oolitic grainstone bars separated from one another by channels. The northwest-trending channels, reefs, and oolitic grainstone bars strongly suggest that tidal currents from the ancestral Gulf in the southeast played an important r le in the deposition of the James reef and grainstone belt.

Porosity and permeability distribution within the reef and grainstone belt were controlled profoundly by a sequence of three diagenetic events. In the first event, subaerial exposure of the reef and grainstone belt shortly after deposition resulted in the development of solution or moldic porosity and the precipitation of an iron-free calcite cement. Maximum development of solution or moldic porosity is in the thickest reef and oolitic buildups indicating that (a) areas of higher relief played an important role in the gathering and movement of meteoric water, and (b) areas of higher relief contained enough unstable carbonate (probably aragonite) so that the solution by meteoric water was maximized. Although a calcite cement was precipitated during this first diagenetic event, it did n t seriously occlude void space and, therefore, did not significantly lower porosity and permeability.

In contrast to the first diagenetic event, a second event of ferroan calcite cementation and a third event of ferroan dolomite cementation resulted in widespread elimination of porosity and permeability, especially in areas between the thickest carbonate buildups and in limited zones within the carbonate buildups. The textural relations of these second and third cements clearly indicate that they were precipitated some time following subaerial exposure and prior to migration of hydrocarbons into the producing reservoirs. However, fundamental problems remain, the foremost of which is the determination of the source, or perhaps sources, of the fluids from which the cements were precipitated.

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