A STRATIGRAPHIC FRAMEWORK FOR PREDICTING SANDSTONE BODY GEOMETRY IN FLUVIAL AND ESTUARINE DEPOSITS OF THE NEW RIVER FORMATION, WEST VIRGINIA

The New River Formation (NRF) consists of thick (up to 70 m) and areally extensive (up to 120 km wide) sandstone bodies that are gas reservoirs in southern West Virginia. Despite the economic importance of the NRF, existing depositional models fail to adequately explain the large scale distribution of sandstone body geometry and interconnectivity.

A detailed depositional framework based on outcrop and subsurface data has been developed for the middle part of the NRF. This study demonstrates that the Lower Raleigh, Upper Raleigh, and Guyandot sandstone bodies occupy trunk/tributary incised valley fill (IVF) systems. Tributary systems occur along and immediately west of the present day outcrop belt. These sandstone bodies are separated by fine grained deposits and/or well developed coal beds. Trunk systems occur to the northwest (mainly in the subsurface), where they amalgamate to form thick bodies, often called ‘salt sands’ by well drillers. Fine grained deposits and coal seams near the trunk system are either partially removed by erosion or not developed.

Two end member types of trunk/tributary IVF’s occur, fluvial-dominated and estuarine-dominated. The Upper Raleigh is the fluvial-dominated end member. Coarse grained fluvial deposits completely fill the tributary systems, whereas thin estuarine deposits occur on top of fluvial deposits in the trunk system. The complete infilling of this IVF is represented by the Sewell coal. The Guyandot Sandstone represents the estuarine-dominated end member. Both trunk and tributaries are incompletely filled by coarse grained fluvial deposits and are overlain by fine grained estuarine deposits and thin, tidally influenced sandstones. The complete infilling of this paleovalley is represented by the Iager coal. The Lower Raleigh is probably estuarine-dominated, but is incomplete due to truncation along the base of the Upper Raleigh.

Stratigraphic and paleogeomorphic position within the trunk/tributary system determines sandstone body geometry and interconnectivity. In general, southeastern parts of the study area correspond to tributary paleovalleys and have a low degree of sandstone body interconnectivity. Conversely, trunk paleovalleys to the northwest have the highest degree of sandstone body interconnectivity due to sandstone body amalgamation.