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

摘要

Late Proterozoic-Early Cambrian extension of Grenvil-lian lithosphere to produce the Laurentian margin and lapetus ocean resulted in rift basins filled with siliciclastic sediments that presently form part of the 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 Formation lithofacies: (1) metamorphosed graded sandstone beds, (2) quartzose metapelite, and (3) discrete massive metasand-stone lenses within the graded bedded sequences. Greenstone interlay-ered with feldspathic metasandstone in the uppermost part of the Peters Creek Formation suggests rift-related deposition. Rift elastics of the Peters Creek Formation consist of two submarine turbidite-fan systems represented by thick sequences of interlayered feldspathic metasandstone and schist, separated by a region underlain by quartzose schist. The Peters Creek Formation contains some lithofacies similar to Upper Proterozoic rift sequences in the southern and northern Appalachians, and its presence in the Piedmont of Pennsylvania certainly narrows the gap between the southern and northern rift basins.