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Origin and formation of the Valley Heads Moraine system, central New York

Ming Qin Yang, University of Nebraska - Lincoln

Abstract

The Valley Heads Moraine (VHM) is a 280 km-long interrupted and discontinuous band of glacigenic sediment in central New York. It forms the most extensive morainic system in the State and separates southward and northward-flowing streams that follow partly filled "through valleys" in the bedrock. Deposits comprise diamict, ice contact, outwash, and lacustrine sediment. Landforms include kames, kame terraces, kettles, outwash fans and deltas. Named by Fairchild in 1932, it has received little attention in spite of its geomorphic, geologic, and hydrologic importance. The result of this study provides knowledge of the glacial episodes involved, the mechanisms of drift emplacement, and the relation to other contiguous moraines east, west, and south.^ The purpose of this study has been to determine the method of emplacement of the VHM. There are four different glacier-process models that have been used in northeastern United States to explain sediments and landforms at the Laurentide Ice Sheet margin: (1) morphosequence model, (2) hydraulic pump model, (3) inwash model, and (4) backwash model. Each is evaluated and its relative importance assessed. To do this hundreds of glacial outcrops were examined in the field, and 39 special sites were mapped and sediment samples evaluated in the laboratory. Mineral analysis showed a remarkable sediment composition consistency throughout the area. Scanning electron microscopy indicated that both glacial and fluvioglacial transport processes took place during the VHM deposition.^ The VHM formed during recessional events of the Laurentide Ice Sheet about 14,000 ybp. Drift was deposited in a dead ice environment at the ice margin after adjacent uplands had become ice-free. Ice tongues up to 20 km in length and 300 m in thickness occupied major through valleys of the Alleghany Escarpment. During early stages of drift emplacement, sediment sources came as a result of hydraulic movements through decaying ice masses and inwash when ice ablated from the adjoining deglaciated terrain. Ice retreat from the drainage divide provided avenues for materials to backwash into the kame moraine and also produced thick lacustrine sediments in the proglacial lakes. Thus all the evidence generated in this investigation leads to the conclusion that the VHM was formed principally by three interacting sets of process mechanisms. They are hydraulic pump, inwash, and backwash transport processes. The relative importance of each debris transport process is likely to vary from valley to valley depending on topography (landform and relief), glacier geometry, and the thermal regime of the glacier. ^

Subject Area

Geology

Recommended Citation

Yang, Ming Qin, "Origin and formation of the Valley Heads Moraine system, central New York" (1992). ETD collection for University of Nebraska - Lincoln. AAI9314447.
http://digitalcommons.unl.edu/dissertations/AAI9314447

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