Abstract
When compared with their modern counterparts, the internal morphologies and external geometries of flood-tidal-delta and tidal-channel deposits in Carboniferous rocks of eastern Kentucky suggest mean tidal ranges of 1 to 2 m. Tidal-inlet, tidal-channel, and tidal-delta deposits of modern barriers each display characteristic vertical sequences; their relative proportions within barrier lithosomes vary consistently with tidal range. Increasing tidal range is accompanied by: (1) thicker inlet sequences; (2) changes in back-barrier deposits from thin, extensive flood-tidal-delta sheets intercalated with lagoonal muds to tidal-creek channel fills intercalated with marsh sediments; and (3) the increasing predominance of ebb-tidal deltas. Stratigraphic recognition of these environments provides an estimation of paleotidal range. Moreover, if basin geometry is known, tidal-wave-propagation theory allows evaluation of relative paleotidal range on a basin-wide scale, enabling prediction of sand-body-geometry pattern along depositional strike. Several Carboniferous exposures in eastern Kentucky are composed of well-sorted fine to medium-grained orthoquartzites arranged in linear, lenticular bodies up to 14 m thick, 1 to 2 km wide, and 40 km long. They intertongue basinward with red and green shales and carbonate rocks containing marine faunas, and landward with dark shales and siltstones bearing brackish faunas. Two thin (< 4 km) lithosomes display obvious flood-tidal-delta characteristics. These erosionally based sheets compose gently landward-dipping to subhorizontal accretion surfaces that bound cosets 1 to 2 m thick of decimeter-scale cross strata with bimodal/bipolar orientations. Washed-out ripples, ladder-backs, rill marks, and bubble sand textures attest to intertidal exposure; extensive root casts typify suprati al areas. Biogenic structures are similar to those on modern flood-tidal deltas. These lithologic and stratigraphic characteristics resemble those of back-barrier components transitional between microtidal and mesotidal environments. End_of_Article - Last_Page 415------------
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