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Exploration for "tight" gas (F.E.R.C. Section 107) production from the Schuler Formation (Cotton Valley sands) has provided recent data for the recognition of the lower Schuler (Shongaloo member) shoreface facies and delineation of the upper Schuler (Dorcheat member) delta plain complex in Upshur Country.
Shoreface facies within the lower Schuler have a typical funnel-shaped log pattern (coarsening-upward clastic), with individual sequences ranging from 90 to 100 ft (27 to 30 m) thick. In core, the corresponding coarsening-upward sequence grades from offshore to upper shoreface facies. Upper offshore sediments are dominated by a heavily bioturbated and intercalated sandstone/shale sequence with numerous trace fossils, escape traces, and shell debris. Intensity and diversity of this bioturbation decrease toward the upper shoreface. The lower shoreface is a very fine-grained quartz sandstone with horizontal to slightly inclined stratification. Climbing vertically in the sequence, the upper shoreface is interbedded fine-grained quartz sandstone and biomodal, pebbly carbonate cemented quar z sandstone exhibiting a steep inclined stratification with low-angle truncations.
Associated facies overlying the upper shoreface are lagoonal. Thin marsh deposits are characterized by carbonaceous shales with visible root traces cutting across partings. Subaerially exposed mottled red and green siltstone and red mudstone show evidence of root penetration and are interpreted as coastal plain to tidal flat. The marsh deposits (green siltstones and red mudstones) gradationally interbed with a subtidal lagoonal facies containing dark gray, fossiliferous, argillaceous, limestone containing oysters, echinoid fragments, and annelid worm tubes.
In an effort to tie the limited core data (4 wells) to a countywide environmental interpretation, sand percent interval slice maps were constructed above and below the ubiquitous subtidal lagoonal "marker." These maps and core data in the lower Schuler delineate a strike-oriented, linear clastic shoreline (ENE-WSW). Within Upshur County, lower Schuler sediments were deposited as interdeltaic, shoreface facies. Slice maps and sample logs indicate a significant environmental discontinuity exists between the upper and lower Schuler. The upper member is characterized by a dip-oriented sandstone trend interpreted as an aggradational delta plain complex associated with the Lone Oak delta system.
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