Sedimentology of pennsylvanian quartzose sandstones of the lee formation, central appalachian basin: fluvial interpretation based on lateral profile analysis

Abstract

Lateral profiling, including bounding surface and architectural-element analyses, are utilized to demonstrate a fluvial origin for the quartzose sandstones of the Lee Formation. Internal architecture of the sandstones consists primarily of multistorey and multilateral channel bodies. Individual channel elements, up to 20 m thick, contain a complex hierarchy of bedform deposits. The primary depositional elements within the channels were downstream-accreting (mid-channel?) macroforms; channel elements frequently contain deposits of more than one macroform. Reconstruction of the macroforms reveals accretion primarily by superposed bedforms that migrated down a low-angle front. Steeper, giant foresets, transitional along flow with the low-angle facies, indicate that the macroform episodically developed a steep slipface. The uppermost channels within the Rockcastle Member contain macroform elements with components of lateral accretion, interpreted as deposits of alternate bank-attached macroforms. Other depositional elements recognized within channel-fill deposits are minor-channel, sandy-bedform, gravity-flow (attributed to bank slumping), and channel-bottom elements. The latter element is contained within a facies sequence that suggests rising- to flood- to waning-stage deposition. In general, deposition probably occurred during relatively high stage; little evidence of low-stage flow was recognized. Subordinate fine-grained facies are interpreted as levee and overbank deposits. The greater part of the Lee Formation was deposited in deep, low-sinuosity, bedload-dominated fluvial channels. Strongly unimodal paleocurrents, lack of facies that suggest low-stage reworking and paucity of lateral-accretion features indicate deposition in a single-channel system (i.e., a low braiding index).