Age of Loess on Long Island
Loess is unconsolidated, wind deposited sediment composed largely of silt-sized particles with the modal diameter between 15-50 µm. Loess is very homogeneous and shows little or no stratification. Loess deposits on Long Island range from a few centimeters to several meters in thickness. Provenance o...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.511.7659 http://www.geo.sunysb.edu/lig/Conferences/abstracts-03/kundic.pdf |
| Summary: | Loess is unconsolidated, wind deposited sediment composed largely of silt-sized particles with the modal diameter between 15-50 µm. Loess is very homogeneous and shows little or no stratification. Loess deposits on Long Island range from a few centimeters to several meters in thickness. Provenance of Long Island loess was previously studied by Zhong (Zhong, 2000) using single mica grain Ar/Ar ages. Her mica ages fell within the age range of the Connecticut bedrock and she concluded that most loess on Long Island was derived from basement rocks typical of Connecticut. Our working hypothesis is that Long Island loess is derived from the glacial sediments deposited on the bottom of the present day Long Island Sound. As the ice sheet retreated from Long Island a proglacial lake formed in the Long Island Sound basin between the ice and the Harbor Hill Moraine. This lake was trapping the sediment produced by the glacial grinding. Around 15.5 ka proglacial Lake Connecticut was completely drained and its bottom was exposed. Strong catabatic winds were blowing down from the ice sheet whose margin was then at the Connecticut-Massachusetts border. The lake bottom sediments were entrained by the wind and deposited on Long Island. By 12.4 ka the sea level raised enough to completely cover the bottom of the sound and the lake bottom was no longer available as the loess source (Lewis and Stone, 1991). 17,500 years ago 15,500 years ago 15,000-5,000 years ago |
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