Sequence Stratigraphy of the Predominantly Nonmarine Lower Pennsylvanian New River Formation, Appalachian Basin, USA
J. T. Korus
Virginia Tech, Dept. of Geological Sciences, Blacksburg, VA
Nonmarine sequence stratigraphy is based on the recognition of facies indicative of high accommodation during maximum flooding. Tidally influenced facies in fluvial-dominated incised valley-fill deposits represent the up-dip equivalent of condensed sections, thus, they separate the transgressive systems tract from the highstand systems tract. Where tidal facies are not developed identification of systems tracts is problematic. Some workers have used changes in coal bed thickness and lateral extent to identify systems tracts because significant volumes of peat accumulate to form coal when rates of base-level rise are relatively high. Unlike tidal facies, however, direct marine influence is equivocal.
The New River Formation contains both well-developed tidal and coal facies in association with erosionally based sandstone to bodies that are interpreted as incised valley-fill deposits. Depositional response to a rising relative sea level is suggested by a change from fluvial to tidally influenced facies in incised valley fills. In places where tidal facies are present, the position and geometry of coal seams relative to the position of tidal facies will be investigated to provide an understanding of the conditions that controlled coal formation. A consistent relationship between coalbed development and tidal facies will allow for identification of systems tracts using coal beds alone where tidal facies are not developed.
A better understanding of nonmarine sequence stratigraphy will be gained by studying the genetic relationships between tidal, coal, and fluvial facies through combined outcrop and subsurface work. This will improve the effectiveness of nonmarine sequence stratigraphy as a predictive tool and provide better models for coal, gas, and oil exploration.
AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid