The association of feldspar-rich alluvial-fan deposits with lake sediments formed in anoxic conditions is one of the most intriguing and least understood settings for sedimentary uranium accumulation. The Triassic-Jurassic basins formed during early rifting of North America's eastern margin all contain extensive accumulations of alluvial deposits which intertongue with basin-center black shales and, in places, coals. These basins lie adjacent to, or just beneath, the prograded seaward-thickening sedimentary coastal plain wedge which blankets the trailing continent margin. Many analogies in basinal development, sedimentary fill, climatic controls, and presence of evaporites can be drawn between these basins and the spreading centers of the Red Sea and Gulf of California-Sa ton Trough.

In addition to extensive interfingering between oxidized and reduced sedimentary deposits, the Triassic-Jurassic basins contain the first major rock groups in the Phanerozoic of the Appalachian region having ubiquitous feldspar and feldspar-weathering products. These basins apparently received significant input from exposed Acadian and younger Paleozoic batholiths and granitic intrusions developed during the terminal evolution of the Appalachian geosyncline. Wide variations in source-rock types are directly reflected in both the sediment fills and uranium potentials within and among these Triassic-Jurassic basins.

End_of_Article - Last_Page 827------------