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

Abstract

Just as glaciers worldwide left a record of past advances and retreats that shifted latitudinally in response to oscillating Quaternary climate changes, so too have cold-climate conditions and permafrost left topographic and sedimentary signatures in former periglacial environments. This review documents widespread occurrence of past permafrost and intense frost action that led to rock fracturing, regolith production, and regolith-mantled slopes in the mid-Atlantic region of the United States during late Pleistocene cold-climate conditions. Strong signatures of thermal contraction cracking and brecciation from frost cracking exist where rocks and sediments are most frost susceptible, as with fissile shales. On sandstone hillslopes, frost weathering produced boulder-rich sediment that episodically flowed slowly downslope during permafrost thaw, resulting in solifluction lobes and terraces in which colluvium moved cumulatively at least a kilometer. Radiocarbon dating, optically stimulated luminescence age control, and cosmogenic isotope studies constrain some periglacial features to the Last Glacial Maximum but also indicate longer residence times of regolith. ▪ Former permafrost and areas of intensive frost cracking extended over much of the mid-Atlantic region of the eastern United States during late Pleistocene cold glacial periods. ▪ Cold-climate conditions and permafrost left long-lasting topographic and sedimentary records with limited post-depositional erosion in the formerly periglacial mid-Atlantic region. ▪ Prominent relict periglacial landforms include polygon networks and frost wedges that are the result of thermal contraction cracking and brecciated rock formed by segregated ice and frost cracking. ▪ Widespread solifluction landforms are a topographic signature of freezing, thawing, and mass movement of mobile regolith produced by frost cracking, and some were active during the Last Glacial Maximum. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Hillslope and vegetation response to postglacial warming at Bear Meadows Bog, Pennsylvania, USA

“…The distribution of boulders both at the surface and below the Sphagnum at Bear Meadows is consistent with the solifluction lobe activity documented elsewhere in central Appalachia (Merritts and Rahnis, 2022). Preservation of a sandy matrix within boulders under peat is a rare glimpse into the nature of these lobes at the time of their activity, because solifluction lobes at the surface today often lack interstitial grains, which presumably have been lost to erosion (Del Vecchio et al, 2018).…”

“…21 ka (Watts, 1979; Clark et al, 2009; French and Millar, 2014; Vandenberghe et al, 2014). Evidence for periglacial surface processes (e.g., solifluction, ice wedge polygons) is widespread from Pennsylvania to northernmost Virginia (Merritts et al, 2015; Merritts and Rahnis, 2022). Landforms and deposits from multiple Pleistocene cold periods are preserved across central Appalachian landscapes (Braun, 1989; Denn et al, 2017; Del Vecchio et al, 2018, 2022).…”

“…Landforms and deposits from multiple Pleistocene cold periods are preserved across central Appalachian landscapes (Braun, 1989; Denn et al, 2017; Del Vecchio et al, 2018, 2022). Compared to modern processes, these relict landforms (Del Vecchio et al, 2018; Merritts and Rahnis, 2022) are interpreted to reflect a combination of high regolith production driven by frost cracking during colder glacial periods (Hales and Roering, 2007) and accelerated hillslope transport during permafrost thaw due to slope failure (Matsuoka, 2001). Yet, there are few constraints on the timing and mechanisms of hillslope response to warming that are detailed enough to inform studies of ongoing permafrost thaw.…”

Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

“…Due to physical constraints of drilling equipment, we drilled at the ridgetop (Well 1) and on an interfluve (Well 2) that is 10 m below the ridgetop but not contained within the original soil hillslope transect. The soil morphology at the interfluve indicates that colluvium filled this position in the landscape, likely as periglacial mass movement during the Last Glacial Maximum (Carter and Ciolkosz, 1986;Merritts and Rahnis, 2022). After the colluvial influx the landscape experienced erosion that formed gullies in many parts of the forest, including our sampling location.…”

Periglacial resurfacing of hillslopes and channels with large boulders in the Virginia Appalachians

“…A model of frost cracking intensity across unglaciated North America during the LGM indicates that the Virginia Blue Ridge and Valley and Ridge provinces experienced porosity increases as high as 0.34 mm annually down to depths of ~2 m because of frost cracking (Marshall et al, 2021). In addition to boulder deposits, other relict morphologic features, such as patterned ground, terraces, and large alluvial fan systems, across the mid‐Atlantic and southern Appalachians have been assigned an origin tied to periglacial processes (Clark & Ciolkosz, 1988; Marsh, 1987; Merritts & Rahnis, 2022; Potter & Moss, 1968; Whittecar & Ryter, 1992). Recent work from Pennsylvania using geochronology suggests that Appalachian periglacial features may be multigenerational in origin, persisting through multiple Quaternary glacial stages (e.g., Del Vecchio et al, 2018; Denn et al, 2018).…”