ABSTRACT: Sedimentology of the Quartzose Lower Pennsylvanian Lee Formation, Central Appalachians: Fluvial Interpretation Using Architectural-Element Analysis

M. C. Wizevich, K. A. Eriksson

The Lower Pennsylvanian Lee Formation, central Appalachian basin, consists primarily of quartzose, often conglomeratic, laterally extensive sand bodies. Located stratigraphically between shallow-marine and fluvial-deltaic sediments, these nonfossiliferous sandstones have been interpreted as either barrier-island or fluvial deposited sediments. Detailed sedimentological analyses of outcrops in eastern Kentucky and northern Tennessee, using element analysis and hierarchical bounding surface concepts, demonstrate deposition in a bed-load-dominated fluvial system.

The Corbin Member, the best exposed Lee sand body, consists of multistory and multilateral, erosively based, fining-upward units that typically are truncated. A complete unit consists of conglomeratic base, overlain by strongly unimodal cross-bedded sandstones, capped by rippled fine-grained sandstones and laminated mudstones that contain in-place fossil tree roots. Individual units are interpreted as channel fills and primarily are composed of complex hierarchical associations of cross-bedding. Common features are large-scale, planar to sigmoidal foresets with superimposed, parallel to obliquely oriented small-scale cross-bedding. Planar and sigmoidal cross-strata represent downflow and lateral accretion deposits, respectively, of semi-repetitive lobate bed forms. Downflow dipping bo nding surfaces to the large-scale cross-beds indicate that the lobate bed forms were superimposed on larger mid-channel fluvial bars. An erosionally based, 1-3-m thick, massive bed with faint basal laminations is found within a channel-bar association. This is interpreted as a channel-transverse, gravity flow deposit caused by slumping of unconsolidated channel margins.

Overwhelming dominance of sand relative to mud, laterally extensive and low-angle erosional surfaces, and evidence for mid-channel bars and unconsolidated banks, suggests a bed-load-dominated fluvial system. Analyses of other less well-exposed sandstone members reveal similar facies relations and hierarchical cross-bedding and, therefore, represent deposition in a similar system.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990