--> Tidal Depositional Systems in Pennsylvanian Strata in the Anadarko Basin, Northeast Texas Panhandle

Southwest Section AAPG Annual Convention

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Tidal Depositional Systems in Pennsylvanian Strata in the Anadarko Basin, Northeast Texas Panhandle


A thick (>6,000-ft [>1,830-m]) succession of Desmoinesian to Virgilian (Pennsylvanian) strata in the northwest part of the Anadarko Basin contains a variety of tidally modified deposits. This succession, which encompasses the Marmaton Group (Upper Desmoinesian), Cleveland Formation (Missourian) and Douglas Group (Virgilian), records progradation of highstand tidally modified delta and shorezone systems punctuated by lowstand incised-valley deposits. Tidal stratification in this succession includes asymmetric, double-draped ripples, reactivation surfaces, flaser bedding, rhythmic, laminar stratification, UFR (upper flow regime) planar stratification, and minor herringbone stratification.

Tidal amplification and reworking of deltaic and shorezone sediments was controlled by (1) basin configuration, consisting of a broad, shallow shelf merging northward with an extensive epicontinental seaway in the U.S. Midcontinent, and (2) the formation of embayments during periods of relative sea-level fall, notably in the Cleveland Formation, in which an east-west-trending lowstand paleovalley contains a vertical succession of coarse-grained fluvial-channel, tidal-channel, sandy tidal flat, muddy tidal flat, and transgressive facies associated with late-stage estuarine deposits. Local paleogeography was an important factor in the preservation of tidal signatures in the Marmaton to Douglas succession, where the relative weakness of wave and fluvial processes in areas between depocenters resulted in preservation of rhythmic bedding and bi-directional, double-draped ripples. A macrotidal setting is inferred for parallel, narrow and dip-elongate, upward-coarsening sandstone bodies in highstand-shelf systems in the Marmaton Group. In contrast, absence of large-scale bedforms such as estuarine-floor tidal sand bars in lowstand incised-valley fill systems in the Cleveland Formation instead suggests upper-microtidal to lower-mesotidal regimes.

Gross-sandstone-thickness maps of highstand versus lowstand systems tracts within the Cleveland Formation and Marmaton Group document systematic changes in sandstone-body thickness, continuity, and regional extent through time. These variations in sandstone-body geometry are a function of a unique paleogeomorphologic setting within each systems tract. Abrupt changes in sandstone-body geometry between each systems tract control variations in reservoir continuity and permeability pathways that should be considered in future resource development