DELTA FRONT AND SHALLOW SUB-TIDAL FACIES IN THE LATE DEVONIAN BEDFORD SHALE AND BEREA SANDSTONE, NW OHIO

Facies analysis of outcrops of the Bedford Shale and Berea Sandstone in Cuyahoga and Medina counties (NE Ohio) has described 21 lithofacies. The units are entirely siliciclastic, ranging from mudstones and mudshales to coarse-grained and pebbly sandstones. There is a general coarsening- and thickening-upwards trend from the Bedford Shale to the overlying Berea Sandstone, consistent with previous interpretations of a prograding deltaic environment, however there is extensive local variation representing sub-environments such as: (1) storm-dominated clastic shelf deposits with tempestites (hummocky and swaley stratification); (2) extensive muddy shelf deposits below storm wave-base; (3) gravity-controlled slope deposits with extensive syndepositional slump structures and mud diapirs; (4) tidal sandwaves; (5) tidally-influenced deposits with heterolithic flaser, wavy, and lenticular bedded sandstones and mud drapes and tidal rhythmites; (6) distributary mouth bar deposits with climbing-ripple lamination; and (7) channel deposits with mud intraclasts, and tidally-influenced fluvial cross-bedded sandstones. On a larger-scale, deltaic distributary lobes exhibit both progradational and retrogradational trends (distributary channel abandonment, delta platform subsidence, and wave reworking), consistent with a dynamic environment affected by both autocyclic (distributary lobe switching and avulsion) and allocyclic controls (eustasy, subsidence, and sediment supply).