Stratigraphy, petrography, and correlation of late Cenozoic middle Atlantic Coastal Plain deposits: Implications for late-stage passive-margin geologic evolution

摘要

Regional chronostratigraphic correlation of middle Atlantic upper Coastal Plain and Fall Zone fluvial deposits, long thought to represent the updip, proximal facies of a well-dated, post-Oligocene marine sequence in the Salisbury Embayment, remains incomplete, in part, because of the paucity of biostratigraphic data. Petrography-based lithostratigraphic correlations provide an opportunity to extend age control present in downdip marine deposits, updip to fluvial deposits, thus establishing the means for a regional chronostratigraphic correlation. Previous stratigraphic studies in New Jersey, Delmarva, southern Maryland, Virginia, and the central Appalachian Piedmont are linked by a crucial sequence of fluvial deposits at the head of Chesapeake Bay. Here petrography-based lithostratigraphic correlations demonstrate (1) late Oligocene-late Miocene, Susquehanna River-dominated, polygenetic, quartzose fluvial aggradation (Bryn Mawr Formation); (2) Pliocene, heterolithic, but quartz-dominated fluvial-terrace and alluvial-fan deposition (Perryville formation); (3) Pliocene-early Pleistocene, paleo-Delaware-Hudson River- dominated, lithic- and feldspathic-rich, fluvial aggradation (Pensauken Formation); and (4) the initiation of estuarine conditions (Turkey Point beds) by early Pleistocene time. These results are synthesized to propose a new late Cenozoic regional chronostratigraphic correlation and depositional history for the Salisbury Embayment. The correlation elucidates a complex interaction between passive margin isostasy, tectonics, eustasy, and sediment source.