Duane D. Braun

Glacial and periglacial erosion of the Appalachians

Abstract The marine 18 O record indicates that the first ice advance into the Appalachians equivalent to that of the late Wisconsin occurred in the Pliocene at about 2.4 Ma. Only periodic localized glacial and periglacial activity occurred in the northern Appalachians from 2.33 to 0.85 Ma. After 0.85 Ma (middle to late Pleistocene) eight out of ten glaciations covered the northern Appalachians and brought periglacial conditions to the southern Appalachians. During the last 850,000 years, glaciation extended to the late Wisconsin limit within the Appalachians for 15% of the time and extended to the early Wisconsin limit just north of the Appalachians for 25% of the time. Pleistocene glacial erosion of the Appalachians of 120–200 m is necessary to account for the estimated volume of Pleistocene ocean sediment derived from the Appalachians and the estimated volume of Pliocene-Pleistocene glaciogenic ocean sediment derived from the entire Laurentide ice sheet. This amount of glacial erosion, occurring over the maximum expectable duration of Pliocene-Pleistocene ice cover of 247,000 years, yields glacial erosion rates from 0.5–0.8 m ka −1 . Such depths of erosion by thick, warm-based ice streams were localized in the lowlands and estuaries of the northern Appalachians. In the Maritimes the presence of thin, cold-based ice caused minimal erosion of uplands. Periglacial landforms and tundra-boreal forest were distributed throughout the Appalachian Highlands and the northern Coastal Plain during the glacial maxima. Periglacial erosion of 0.15–0.30 m ka −1 near the ice in Pennsylvania decline to 0.1–0.2 m ka −1 in the southern Piedmont. Each cold period almost completely renewed the regolith by eroding slopes and filling valleys. The cumulative effect of the eight to ten major cold events could have produced as much as a few tens of meters of periglacial ridge-top lowering during the Pleistocene. Both estimated glacial and periglacial erosion rates greatly exceed estimated current fluvial erosion rates. Therefore glacial and periglacial processes should be considered the dominant processes in shaping the present Appalachian landscape. The northern Appalachians may be evolving towards a form where the landscape provides just the shape necessary to permit the least work conveyance of the ice across the region during glacial maxima. The southern Appalachians may be evolving towards a form where the landscape provides just the hillslope form necessary to transport the debris provided by periglacial conditions.

Does Altonian drift exist in Pennsylvania and New Jersey

Abstract From New Jersey to southwestern New York, Altonian colluvium and fluvial gravel have been recognized beneath Woodfordian drift, but the existence of Altonian till near or beyond the Woodfordian border has not been demonstrated. Reworking of weathered materials by Woodfordian ice has produced some drift with an “Altonian” appearance. Soil criteria, applied without regard for parent material differences, have been incorrectly used to infer an Altonian age for Illinoian deposits that have a redbed provenance. The currently mapped distribution of Altonian till and the occurrence of undisturbed Illinoian deposits within areas of inferred Altonian ice cover are incompatible with the behavior of ice sheets.

The Glaciation of Pennsylvania, USA

Publisher Summary There is evidence for at least four Pleistocene glacial advances into Pennsylvania. Each time the Laurentide ice sheet advanced, it entered Pennsylvania from the North-West and the North-East. The triangular shaped unglaciated area between the two lobes is called the Salamanca Re-entrant. In Northwestern Pennsylvania, the relatively low relief, shaly bedrock, and abundant debris from the Great Lake basins produced a dominance of deposition over erosion in each glacial advance. This produced multiple till-sheet sequences whose layers sometimes are separated by partly-preserved weathering profiles. These till sequences are well exposed in open pit coal mines. The chapter discusses that the pre-glacial stream drainage in north-western Pennsylvania was to the north-west. During glaciation this drainage was blocked and diverted to the south-west to form an ice marginal drainage system, the present Allegheny-Ohio River system. In north-eastern Pennsylvania the moderate relief on sandstone bedrock produced a dominance of erosion over deposition during each glacial advance. Each successive advance almost entirely removed the deposits of the previous advance and some bedrock. Other proglacial lakes were imponded along that limit, along younger limits, and North of the Late Pleistocene limit as ice receded from Pennsylvania.

Chapter 40 – The Glaciation of Pennsylvania, USA

Four early to late Pleistocene glaciers entered Pennsylvania. Large proglacial lakes were dammed in north trending valleys. Preglacial northerly drainage has been turned to the south. Periglacial colluvium mantles Pennsylvania outside the glacial limit. Early Pleistocene deposits on karst produce pseudo-moraine topography. Late Pleistocene till knobs form “beaded valleys”.