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Longitudinal petrographic variations in a Middle Ordovician trench deposit, Central Appalachian orogen
Author(s) -
LASH GARY G.
Publication year - 1987
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1987.tb00773.x
Subject(s) - geology , petrography , ordovician , detritus , provenance , terrane , paleontology , geochemistry , lithic fragment , clastic rock , sedimentary rock , petrology , tectonics
Petrographic analysis of Middle Ordovician turbidite sandstones of the Greenwich slice of the Hamburg klippe (eastern Pennsylvania), inferred to be part of a fossil subduction complex, define three coeval petrofacies. The Jonestown petrofacies was derived from felsic plutonic and less abundant metasedimentary rocks, whereas the Windsor Township, the most extensive petrofacies, and Werleys Corner petrofacies were derived from sources characterized by various proportions of sedimentary/metasedimentary, plutonic, and volcanic rocks. The presence of minor but conspicuous extrabasinal carbonate and microlitic volcanic lithic fragments together with higher percentages of polycrystalline quartz, serve to distinguish the Werleys Corner from the Windsor Township petrofacies. It is conceivable that sandstones of the Greenwich slice were derived from microplates inferred to have existed to the southeast of the proto‐North American plate in Early Palaeozoic time. The variations in sandstone composition along the length of the Greenwich slice may be explained by post‐accretion tectonic juxtaposition of petrofacies derived from various sources. An equally plausible explanation involves transverse infilling of a channelized longitudinal transport system (Windsor Township petrofacies) by sediment derived from compositionally diverse source terranes orthogonal to the trench (Jonestown and Werleys Corner petrofacies).