Abstract

A Middle Ordovician submarine-channel deposit in the southern Appalachians is capped by an interval of fine-grained, predominantly cross-laminated sandstones that are interpreted as internal-tide deposits. Two facies are recognized: (1) bidirectional cross-laminated, very fine grained sandstones, and (2) unidirectional cross-bedded and cross-laminated, medium- to fine grained sandstones. Facies 1 is dominated by bidirectional cross-laminations that dip both landward and seaward parallel to the paleochannel axis. This facies is related to up-channel and down-channel currents caused by internal tides. Facies 2 has both low-angle, tabular cross-beds and cross-laminations that dip landward. The formative up-channel currents are attributed to superimposition of internal waves on internal tides. The vertical transition from high-concentration gravity-flow deposits to intercalated low-concentration turbidites and internal-tide deposits is related to a rise in sea level that resulted in storage of coarse debris landward of the submarine channel.

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