Sequence Stratigraphy of the Lower Mississippian in Ohio and West Virginia: Origin of the Black Hand Sandstone as Incised Valley Fill
MATCHEN, DAVID L.
West Virginia Geological Survey, Morgantown, 26507,
KAMMER, THOMAS W.
West Virginia University, Morgantown, 26506
Lower Mississippian sandstones of the Appalachian Basin have been primary exploration targets since the late 19th Century. These distinct, north-south trending sandstones have been interpreted as everything from delta fronts to fluvial channels. The Black Hand Sandstone of central Ohio may shed some light on the origin of these sandstones. The Black Hand in outcrop is the stratigraphic equivalent of the Big Injun sandstone of the subsurface. A coarse-grained, conglomeratic sandstone surrounded by finer-grained marine clastics, the Black Hand has always been an anomaly. Interpretations range from distributary mouth bar to shoreline sand. The Big Injun and Black Hand share several characteristics- lithology, narrow linear geometries, anomalous thickness, sharp basal contacts - commonly associated with incised valley deposits.
To reach a thickness of 500 feet, as seen in central Ohio, the Black Hand was probably deposited during a series of drops and recovery in relative sea level. Several factors may have contributed. Isostatic rebound of the Appalachian Foreland Basin during the Early Mississippian changed the basin geometry, resulting in rapid southwesterly progradation and contributed to lowering relative sea level and initiating incision. An unconformity at the Kinderhookian-Osagean boundary in the mid-continent also implies a drop in relative sea level. The cause is unclear, but may be related to glaciation of Gondwana suggested by tillites in South America. Available biostratigraphic data points to late Kinderhookian incision followed by a subsequent transgression during the early Osagean. The Black Hand and Big Injun sandstones were deposited as valley fill during this transgression.