John C. Ridge

Late Wisconsinan, pre-Valley Heads glaciation in the western Mohawk Valley, central New York, and its regional implications

The history of late Wisconsinan, pre- Valley Heads glaciation (about 18-15.5 ka) implies that major glaciological controls, as well as overall climatic warming, influenced the pattern of deglaciation in the western Mohawk Valley. The Middleville Formation in the West Canada Valley contains the most complete record of pre-Valley Heads ice recession in central New York. The lithostratigraphic succession was determined through detailed mapping and logging of measured sections, provenance study of diamicton units, and the analysis of declination of detrital remanent magnetization (DRM) in laminated lacustrine silt and clay. The initial recession of southwest-flowing ice from the Adirondacks and at least two glacial re-advances of the Mohawk Lobe are recorded in these units. Glacial Lake Newport, impounded in the West Canada Valley during ice recession, attained levels that required ice-damming by coalescent Ontario and Mohawk Lobes and a subglacial outlet across the Mohawk Valley to the Susquehanna drainage basin. Initial ice recession in the Mohawk Valley was mostly by calving of active valley lobes in deep-water (up to 350 m) embayments and not by regional stagnation and simple downwasting. A shift of ice flow from the Adirondacks to ice flow from the Mohawk Lobe marks the development of low-land lobes during pre-Valley Heads time before the complete uncovering of the Adirondacks. The later dominance of the Ontario Lobe in Valley Heads time may have been the result of (1) a reduced supply of ice to the Mohawk Lobe from a diminished Adirondack ice dome, (2) changing ice-flow conditions in Quebec associated with an eastern St. Lawrence ice stream and calving bay, and (3) nonsynchronous surging of the Mohawk and Ontario Lobes as these lobes became fronted by deep lacustrine waters at different times.

A model of late quaternary landscape development in the Delaware Valley, New Jersey and Pennsylvania

Abstract In the Delaware Valley of New Jersey and eastern Pennsylvania the late Quaternary history of colluviation, fluvial adjustment, and soil formation is based on the ages of pre-Wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid-latitude climate changes indicated by marine oxygen-isotope records. The area is divided into four terranes characterized by sandstone, gneiss, slate and carbonate rocks. Since the last pre-Wisconsinan glaciation (> 130 ka, inferred to be late Illinoian), each terrane responded differently to chemical and mechanical weathering. During the Sangamon interglacial stage (∼ 130-75 ka) in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep, highly weathered soil and saprolite, and dissolution of carbonate rocks. Cold climatic conditions during the Wisconsinan, on the other hand, induced erosion of the landscape at rates faster than soil development. Upland erosion during the Wisconsinan removed pre-Wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium, grezes litees, and alluvial fans on footslopes. Fluvial gravel and overlying colluvium in the Delaware Valley, both buried by late Wisconsinan outwash, are inferred to represent episodes of early and middle Wisconsinan (∼ 75-25 ka) upland erosion and river aggradiation followed by river degradation and colluvium deposition. Early-middle Wisconsinan colluvium is more voluminous than later colluvium despite colder, possibly permafrost conditions during the late Wisconsinan ∼ 25-10 ka). Extensive colluviation during the early and middle Wisconsinan resulted from a longer (50 kyr), generally cold interval of erosion with a greater availability of easily eroded pre-Wisconsinan surficial materials on uplands than during the late Wisconsinan. After recession of late Wisconsinan ice from its terminal position, soil formation and landscape stability were delayed until the Holocene by a lingering cold climate, slope erosion, colluvium and alluvial fan deposition, and eolian sedimentation. Late Quaternary erosion in the Delaware Valley was dominated by glacial and periglacial processes during glacial stages. During the warm interglacial stages, soils developed on a more stable landscape. These souls were easily colluviated by periglacial erosion during periods of intermittent cold climate.

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.

Shed Brook Discontinuity and Little Falls Gravel: Evidence for the Erie interstade in central New York

The Shed Brook Discontinuity in the western Mohawk Valley region of central New York is an unconformity separating lacustrine beds of the Valley Heads drift (Port Bruce stade) from pre–Valley Heads lacustrine deposits (Nissouri stade). The Little Falls Gravel is a fluvial unit that can be found draped by Valley Heads lacustrine deposits in the Mohawk Valley. The discontinuity and gravel represent subaerial erosion and braided river deposition in response to initial late Wisconsinan ice recession and lake drainage in the Mohawk Valley. These events were followed by Valley Heads lake impoundment and glacial readvances. The Shed Brook Discontinuity and Little Falls Gravel have a 14 C age constrained to 17–14.1 ka on the basis of stratigraphic relationships in central New York and the correlation of paleomagnetic declination records from central New York and the 14 C-calibrated New England varve chronology. The Shed Brook Discontinuity and Little Falls Gravel appear to be features equivalent in age to the Erie interstade (about 14.5–16 ka), an interval during which eastward drainage to the Mohawk Valley has been inferred for lakes in the Erie basin. Evidence for a river in the Mohawk Valley (Little Falls Gravel) indicates that it may have served as an eastern outlet for the Erie and Ontario basins, and thus allowed the first eastward diversion of meltwater away from the Mississippi Valley during the last deglaciation. Drainage down the Mohawk Valley entered Lake Albany in the Hudson Valley, which drained into Long Island Sound and not along the present Hudson River course to the New Jersey continental shelf. Meltwater drainage across New York during the latest stages of the Erie interstade may have introduced large volumes of meltwater directly to the western Atlantic, creating a situation that needs to be more fully explored in terms of its possible influence on thermohaline circulation in the North Atlantic and climatic change marked by the Port Bruce stade.

Chapter 11 – Glacial Environments

Glacial environments are subject to drastic oscillations in energy regime that rapidly modify the local environment. The impact of glacial phenomena on the distribution, abundance, and evolution of biota based on trace-fossil evidence is the focus of this chapter. Arthropod trackways, shallow horizontal burrows, and fish trails dominate the glacial and periglacial trace-fossil assemblages preserved in terrestrial and glaciolacustrine sedimentary sequences, while nonspecialized feeding burrows that are diminutive when compared to normal-marine settings comprise glaciomarine ichnofaunas. As a consequence of rapid meltwater discharge, freshwater conditions prevail in some fjord settings during deglaciation, allowing for the establishment of suites more typical of freshwater or brackish-water conditions. Despite changes in the composition of the trace making community through time, ichnofacies relationships and ecological niche occupation are similar between the Paleozoic and Cenozoic, an indication of the constancy of the interplay between the biotic community and glacial processes.

The rise of varves

Institut National de la Recherche Scientifique, Centre Eau, Terre, Environnement, Québec, QC, Canada G1K 9A9; pierre.francus@ete.inrs.ca Department of Earth and Ocean Sciences, Tufts University, Medford, MA 02155, USA; jack.ridge@tufts.edu Department of Earth Sciences, University of Gothenburg, Box 460, SE-405 30 Göteborg, Sweden; mark@gvc.gu.se Manuscript received 8 July 2013. Revised manuscript accepted 3 August 2013.

The use of paleomagnetic declination to test correlations of late Wisconsinan glaciolacustrine sediments in central New York

Detrital remanent magnetization (DRM), recorded in laminated glaciolacustrine silt and clay of the western Mohawk Valley of central New York, was used to construct a secular variation record of geomagnetic declination for parts of the late Wisconsinan in the interval 12.5-18 ka B.P. Remanent declination has been used for time-stratigraphic testing of correlations between laminated fine-grained glaciolacustrine sediments at different exposures in the western Mohawk Valley. A discontinuity in the remanent-declination record supports the interpretation that an observed lithostratigraphic discontinuity in the region represents an unconformity. Diamicton units, composed of till and proximal proglacial diamictons, are overlain by laminated clay and silt units that have time-transgressive lower contacts. The clay and silt units exhibit stratigraphic onlap in the direction of ice recession, a characteristic that is recognizable in their paleo-magnetic records. The use of a secular variation record of remanent declination has an advantage over lithostratigraphic and morphostratigraphic correlation techniques in that it is time dependent. For a part of the late Pleistocene, it provides a powerful tool for correlating physically disjunct stratigraphic assemblages in New York and New England, where no other dating technique has provided interregional correlations with comparable resolution. Sampling of different exposures of contemporaneous sediment was used to demonstrate the fidelity of remanent declination as a recorder of geomagnetic declination. The remanent inclination record was not useful for testing correlations because inclinations in strata known to be contemporaneous were different. As compared to remanent inclinations from other contemporaneous lacustrine sequences in the eastern United States, the average remanent inclination of the western Mohawk Valley sediments is at least 11 degrees too shallow. Shallow inclinations may be the result of errors acquired at the time of deposition or compaction resulting from drying of the sediment, consolidation by overriding ice, or lithostatic load of overlying sediment. Subglacial deformation, dewatering, and some outcrop conditions, especially ground-water seepage, were recognized as processes that may cause or facilitate postdepositional disturbance of remanent magnetization.