Rivers, glaciers, landscape evolution, and active tectonics of the central Appalachians, Pennsylvania and Maryland

Abstract

Welcome to the Appalachian landscape! Our fi eld trip begins with a journey across Fall Zone (Fig. 1), named for the falls and rapids on streams fl owing from the consolidated rocks of the Appalachians onto the unconsolidated sediments of the Coastal Plain. The eastern U.S. urban centers are aligned along the Fall Zone, the upstream limit of navigation. Typically, the rocks west of the Fall Zone are part of the Piedmont province. This province exposes the metamorphic core of the Appalachian Mountains exhumed by both tectonics and erosion. At least four major phases of deformation are preserved in Piedmont rocks, three Paleozoic convergent events that closed Iapetus, followed by Mesozoic extension that opened the Atlantic Ocean. A record of Cretaceous to Quaternary exhumation of the Appalachians is preserved as Coastal Plain sediments. Late Triassic and Jurassic erosion is preserved in the synextensional fault basins, such as the Newark basin, or is buried beneath Coastal Plain

Pleistocene Periglacial Processes and Landforms, Mid-Atlantic Region, Eastern United States

“…The main reasons are that blockfields are inactive under modern climatic conditions and no modern geomorphic processes produce such copious amounts of large boulders or transport them on low-gradient slopes. Middlekauff 1991;Snyder & Bryant 1992;Braun et al 1994;Marsh 1998Marsh , 1999Pazzaglia & Cleaves 1998;French 2000;Eaton et al 2003a;Pazzaglia et al 2006;Nelson et al 2007;Grote & Kite 2010;Newell & DeJong 2011;Merritts et al 2014Merritts et al , 2015Merritts et al , 2020Grote 2017;Del Vecchio et al 2018;Del Vecchio 2021). Thermal contraction polygons are highly common on some shale hillslopes in New Jersey (Walters 1978) and Pennsylvania (Merritts et al 2015(Merritts et al , 2020D.…”

Cosmogenic nuclides indicate that boulder fields are dynamic, ancient, multigenerational features

“…Glacial erratics are found south of Hickory Run (Pazzaglia et al, 2006;Sevon and Braun, 2000), indicating that it was covered by ice at least once, although the timing of ice advances is not well known (Braun, 2004), and we found no obvious erratics in the field. The last glaciation to override Hickory Run is mapped as Illinoian (ca.…”

“…Hickory Run boulder field is ~2 km south of the Last Glacial Maximum (LGM) Laurentide Ice Sheet boundary (Pazzaglia et al, 2006;Sevon and Braun, 2000) in east-central Pennsylvania, USA ( Fig. 1A), a temperate, forested, inland region of the Atlantic passive margin.…”