Abstract

The Grandfather Mountain formation is a succession of arkosic conglomerate, sandstone, and siltstone interbedded with basalt and rhyolite. The unit is between 3,000 and 9,000 m thick and is exposed only within the Grandfather Mountain window in the Blue Ridge province of North Carolina. Radiometric age determinations, stratigraphic position, and a lack of fossils suggest a late Precambrian age of about 800 to 900 m.y., making the unit possibly contemporaneous with the Ocoee Series of the Great Smoky Mountains area, the Ashe Formation of North Carolina, and several late Precambrian stratified assemblages exposed along the axis and northwestern and southeastern flanks of the Blue Ridge anticlinorium in Virginia and adjacent states. The Grandfather Mountain formation was deposited in a variety of environments typically found together as the "alluvial-fan (or piedmont) association." This association consists mainly of alluvial-fan and braided-river deposits. The sediments filled a basin rimmed by mountainous areas composed of crystalline rocks (mainly granite and gneiss) which today make up the Cranberry Gneiss and other units of the Blue Ridge basement complex. Interior drainage predominantly from the northwest and southeast define a broadly centripetal current system. Overall the basin resembles both the Triassic basins of eastern North America (such as the Newark Basin) and present day Death Valley. If the Grandfather Mountain basin originated in a fashion similar to these, previous suggestions postulating episodes of late Precambrian continental rifting in the central and southern Appalachians are reinforced.

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