SUBSURFACE FACIES ANALYSIS OF DELTA FRONT ENVIRONMENTS IN THE SILURIAN “CLINTON SANDSTONE” IN SOUTHEASTERN OHIO

The “Clinton Sandstone” is an informal name for a series of related sandy intervals located exclusively in Ohio and not related to the Silurian Clinton Group. This study investigated the depositional history of the unit in southeastern Ohio (Fairfield, Perry, and Vinton counties) from six wells, using core descriptions, thin section analysis, and geophysical logs. The primary bedding units are multistory trough or planar-tabular cross-bedded fine-grained sandstone (lithofacies St and Sp) ranging from 0.5-1.5 m thick. By association, massive bedded sandstones (Sm) are interpreted as having cross bedding that is difficult to see in core slabs. Many of these sandstones contain small mudstone intraclasts or organic fragments. Individual cross-bedded sets 10-30 cm thick are separated by thin mud-drapes (Mm or Ml), micro-erosion surfaces, and small-scale rippled sandstones. These are interpreted as reactivation surfaces and related tidally-influenced (i.e., reversed flow) deposits on subaqueous dunes. Some of the thicker sandstone bodies are separated by finer-grained deposits up to about 2 m thick. These include heterolithic sandstone-mudstone or siltstone-mudstone deposits with planar lamination (SMl), flaser bedding (SMf), wavy bedding (SMw), or lenticular bedding (SMk), collectively interpreted as tidal rhythmites.There are also numerous burrows and escape burrows, and minor convoluted bedding. Rare thin limestones can be found in some of these thicker intervals of finer-grained clastics. These thicker intervals probably represent abandonment and reworking of small-scale deltaic distributary channels.