THE RELATIONSHIP OF COASTAL-SHELFAL TIDAL CLASTIC SYSTEMS TO RAMP CARBONATES IN THE UPPER STRAWN REVEALED FROM CORE AND WIRELINE LOGS IN STONEWALL AND KING COUNTIES, PERMIAN BASIN, TEXAS

Upper Strawn (Desmoinesian) cyclicity is well-documented. However, complex coastlines/shelves and the distribution of deposystems vary regionally. Active tectonics, fluctuating accommodation and sediment supply, and a low-latitude setting controlled shifting depocenters and carbonate reefs. Cyclicity varies depending on basinal location. We focus on uppermost Strawn cycles in Stonewall/King Counties, Eastern Shelf, Permian Basin to understand: 1) complex deposystems and underlying controls on stratal characteristics, and 2) the spatio-temporal relationship of clastic systems to carbonate factories.

We examined ~20 whole cores and 100+ wireline logs in Stonewall-King Counties. Clastic-rich, proximal-marine deposits in Katz Field, Stonewall County, contain interbedded quartz-rich and carbonate-clast-rich sandstone, and bioturbated, wavy-to lenticular bedded siltstone. Quartz-rich sandbodies are trough, current-ripple, and herringbone cross-stratified, or are heavily bioturbated (ii=6) with a diverse-abundant marine trace-fossil assemblage. Calcareous sandstones are trough-to ripple cross-stratified and contain mud drapes, mud inclusions, and fragments of crinoids, bivalves, carbonate, and ooids. Stratal characteristics and log character indicate tidally modified deposystems including flood-tidal deltas, bayhead deltas, tidal flats, backbarrier, and near-barrier shoreface. Increasing-upward gamma ray logs overlain by a blocky log record transgression of backbarrier deltaics by a shoreface in the uppermost Strawn cycle.

Contrastingly, Anne Tandy Field, King County and adjacent fields are carbonate dominated with cycles of interbedded mudstone and quartz-rich sandstone containing mud-drapes and mud inclusions. Carbonates record tidally modified to sediment-starved carbonate ramp, slope to ramp margin debris flows or grain flows, muddy outer ramp-slope, and ooid shoals. Clastics record interfingering tidal flats, deltas and/or estuaries, tidal/wave modified shelf, and muddy offshore-slope.

Overall, uppermost Strawn complex tidally modified deltaic transgressive shorelines to the east give way to interfingering clastic carbonate shelf-ramp-slope systems to the west.