FLUVIAL-ESTUARINE CHANNELS IN THE PARAGON FORMATION AND PENNINGTON GROUP, UPPER MISSISSIPPIAN, EASTERN KENTUCKY

In eastern Kentucky, the Pennington and partly equivalent Paragon Formation are exposed along the Cumberland Escarpment and on Pine Mountain. This stratigraphic interval consists of a wide range of depositional facies including channel facies. Some channel sandstones are thick (10 m) and extensive. The Stoney Gap Member on Pine Mountain is fine- to coarse-grained, quartzose, exhibits well-developed lags with fossil wood debris, and trough and planar crossbeds oriented unimodally down-dip. These features might suggest fluvial conditions, but shale-draped foresets, reactivation surfaces, and Arenicolites burrows upwards within channels indicates tidal and brackish-water influences and a position in the fluvial-estuarine transition. More locally restricted sandstones and heterolithic scour fills (2 to 6 m thick) also occur. These tend to exhibit more rhythmic lamination and less crossbedding than the thicker sandstones. One fine- to medium-grained, quartzose sandstone, exhibits cosets bounded by lateral accretion surfaces and rotated bedding. Down-dip oriented crossbeds occur toward the base of cosets, but are overlain by even or par¬allel lamination and rhythmites. Rhythmites are non-cyclic but show crude gradational thickening and thinning. Lateral accretion and rotated bedding indicates a meandering channel and slumping, which occur in both fluvial and tidal channels, but the shale-draped cosets and non-cyclic rhythmic lamination are more indicative of tidal influences and can be used to place the channel in the fluvial-estuarine transition. Smaller scale channel and scour fills (< 5m) with more definitive cyclic rhythmites are also noted. On Pine Mountain, two small scours are overlain by rhythmites with thick-thin laminae couplets indicative of semidiurnal tidal influences. Couplets exhibit vertical thickening and thinning, with 12 to 15 laminae couplets between sandstone laminae maxima, interpreted as neap-spring tidal cycles, and lunar monthly cycles.

The abundance of tidal-estuarine indicators in exposed channel facies has implications for understanding reservoir geology and compartmentalization in Pennington sandstone reservoirs, which are productive in the basin. The tidal indicators also have implications for basin geometry, supporting an elongate Late Missisippian embayment, which amplified tidal range and limited wave action.