IAPETAN RIFT-RELATED TURBIDITE-FAN DEPOSITS FROM THE CENTRAL APPALACHIAN PIEDMONT

Late Proterozoic-Early Cambrian extension of Grenvillian lithosphere t o produce the Laurentian margin and Iapetus ocean resulted in rift bas ins filled with siliciclastic sediments that presently form part of th e crystalline core of the Appalachians. Metasedimentary rocks related to this rift event occur in the Peters Creek Formation of southeastern Pennsylvania and northern Maryland. There are three Peters Creek Form ation lithofacies: (1) metamorphosed graded sandstone beds, (2) quartz ose metapelite, and (3) discrete massive metasandstone lenses within t he graded bedded sequences. Greenstone interlayered with feldspathic m etasandstone in the uppermost part of the Peters Creek Formation sugge sts rift-related deposition. Rift clastics of the Peters Creek Formati on consist of two submarine turbidite-fan systems represented by thick sequences of interlayered feldspathic metasandstone and schist, separ ated by a region underlain by quartzose schist. The Peters Creek Forma tion contains some lithofacies similar to Upper Proterozoic rift seque nces in the southern and northern Appalachians, and its presence in th e Piedmont of Pennsylvania certainly narrows the gap between the south ern and northern rift basins.