ORIGIN OF RHYTHMITES IN THE LOWER KANAWHA FORMATION (LOWER PENNSYLVANIAN), WYOMING COUNTY, WEST VIRGINIA

Well-developed rhythmites occur in parallel-laminated very fine sandstone above the Glenalum Tunnel coal. The succession of sedimentary facies in the 10 m interval above the coal indicates that the peat swamp was drowned by rising water table forming a freshwater lake. Avulsion diverted a deltaic distributary channel into the lake. Deactivation of the distributary led to tidally influenced hydraulic conditions. Unimodal paleocurrents and the absence of burrowing suggest freshwater conditions. The distributary channel complex is truncated by a burrowed, sideritic transgressive lag that formed during transgression of the Oceana sea.

The rhythmites occur over a 2.1 m stratigraphic interval in a diamond drill core recovered in 2012. Sand-mud couplets are well defined and appear to be grouped in bundles separated by thicker, prominent carbonaceous shale bands. Preliminary results indicate the sand laminations are 0.09-0.70 mm thick. Where cyclicity is well-developed, bundles typically contain 8-14 clay-draped sand lamina. These may represent attenuated spring-neap cycles where competence was insufficient to move sand during the neap portion of some cycles. This would have resulted in amalgamation of daily clay layers to form thicker, more prominent carbonaceous shale bands.