Allogenic and Autogenic Controls in Appalachian Basin, Middle Pennsylvanian Allegheny Formation, Central – Northern West Virginia
Allogenic controls, including paleoclimate, tectonics and glacio-eusatcy, have long been debated as dominant controls in the deposition of cyclic coal-bearing strata. However, recent research has questioned the validity of this cyclicity and may indicate major influence from autogenic controls. To further investigate allogenic controls on stratal order, we analyze the facies architecture, geomorphology, and the stratigraphic framework of the Middle Pennsylvanian Allegheny Formation (MPAF), a classic “cyclic” coal bearing interval in the Appalachian basin, to test for the dominant allogenic and/ or autogenic controls during deposition.
Two outcrop locations with preservation of the MPAF members was used for facies architectural analysis. Measured sections and 3D photogrammetry were used to acquire sedimentary data from the MPAF outcrops; while paleohydrology estimates, was used for paleo-geomorphological analysis of MPAF fluvial transport systems. Preliminary results from the facies architectural analysis reveals 12 lithofacies, grouped into 6 facies associations. The depositional environment interpreted from facies of the MPAF members evolve upward from the unconformable contact at the base as follows: anastomosing fluvial, lacustrine-deltaic, swamp, and meandering fluvial. Meandering fluvial sandstone deposits above the Lower Kittanning Coal (LKC) are quartz rich and contain significant abundance of mafic lithic minerals. In contrast the meandering fluvial sandstone deposits at the base of the LKC contains less mafic lithic minerals. The change in source area may reflect allogenic response to changes in paleoenvironmental conditions. Geomorphological analysis of fluvial members above and below the Lower Kittanning Coal (LKC) revealed similar channel dimensions. Estimated average flow depths and channel widths below LKC is 5.45m (±1.93) and 203.17m (±125.02) respectively, whereas above the LKC, estimated average flow depths and channel widths for fluvial sandstone is 5.19m (±1.84) and 186.41m (±114.15) respectively. Similarity in estimated channel dimensions above and below the LKC may indicate similar allogenic controls on deposition. Information from facies and geomorphological analysis of the MPAF members will be combined with subsurface data to develop a stratigraphic framework of the MPAF members. Outcrop-based modeling of the MPAF for allogenic versus autogenic influence on fluvial deposits can serve as an analog for subsurface reservoirs.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018