Date of Award

Fall 1991

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Geology

Committee Director

G. Richard Whittecar

Committee Member

Dennis A. Darby

Committee Member

Joseph H. Rule

Call Number for Print

Special Collections LD4331.G4D84

Abstract

Large coalescing alluvial fans mantle the carbonate and shale formations west of the Blue Ridge mountains near Stuarts Draft, Virginia. Fan sediments are predominantly boulder and cobble gravels derived from the Antietam Quartzite, The fan complex consists of three alluvial units of significantly different ages. The surface of each fan unit was mapped using relative geomorphic position, soil color, clay content and thickness of Bt horizons, clast weathering, and degree of removal of depositional surfaces by stream incision. A five-category quartzite clast weathering scale developed for this study was very effective as a measure to distinguish map units. Stratigraphic data and statistical analyses of pedalogic data indicate that fluvial deposition on these fans occurred during discrete pulses separated by long periods of weathering and landscape stability.

The map pattern of the three fan units show old fan remnants cluster near the distal margins of the fan complex and younger surfaces lie near the mountain front. Much of this spatial distribution results from the periodic capture of upland streams by piedmont streams. In addition solutional lowering of fan surfaces overlying the Shady Formation probably generated space for young fan sediments high on the fan complex.

Order-of-magnitude age estimates are based upon comparisons of soil development and clast weathering criteria in these sediments with dated Coastal Plain deposits. This analysis suggests that the youngest fan deposits are late Pleistocene in age, the intermediate-age deposits are middle Pleistocene or older, and the oldest deposits are Pliocene or older.

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DOI

10.25777/rvwf-5f59

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