HR: 15:30h
AN: H33E-06    [Abstracts]
TI: Use of Single Grain 40Ar/39Ar Mica Ages for Provenance Studies of Loess, Long Island, New York
AU: * Kundic, V
EM: vesna@kundic.com
AF: State University of New York, Department of Geosciences, Stony Brook, NY 11790, United States
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Columbia University, Lamont Doherty Earth Observatory, Palisades, NY 10964, United States
AU: Hanson, G N
EM: gilbert.hanson@sunysb.edu
AF: State University of New York, Department of Geosciences, Stony Brook, NY 11790, United States
AB: In this provenance study we used single-step laser fusion 40Ar/39Ar ages of single grains of muscovite and biotite in loess and sand to evaluate its potential for distinguishing provenance sources. Long Island provides a good setting to evaluate this method for provenance because, in the potential local sources of loess north of Long Island, the cooling ages for mica in the basement rocks change systematically from 200 Ma in eastern Massachusetts and Rhode Island, to 300 and 400 Ma in western Connecticut and western Massachusetts, to 800 Ma in New York, and to older than 1,000 Ma further to the west in North America. Muscovite is common in our loess samples and there is reasonable published coverage of 40Ar/39Ar and K/Ar ages of bedrock in the region. The deposition of loess on Long Island probably started as soon as the ice sheet retreated. The most likely sources of the sediment were stream deposits on the exposed lake beds of the drained Proglacial Lake Connecticut and Lake Hitchcock north of Long Island. Loess and sand samples were collected along the north shore and on the south fork of Long Island. Additionally, a sample was collected from the Lake Hitchcock bottom deposit. 40Ar/39Ar ages of muscovite in loess and eolian sand from the north shore of Long Island have a mode between 300 Ma and 400 Ma corresponding to the source rock in western Connecticut and western Massachusetts. In contrast, muscovite from the South Fork of Long Island has a mode between 200 Ma and 300 Ma suggesting derivation from a more easterly source in eastern Massachusetts and Rhode Island. Muscovite from Lake Hitchcock bottom deposits has a bimodal distribution of 40Ar/39Ar ages with a mode younger than 300 Ma and a mode between 300 Ma and 400 Ma. Biotite 40Ar/39Ar ages from the same sample, however, are overwhelmingly younger than 320 Ma.
DE: 1115 Radioisotope geochronology
DE: 1165 Sedimentary geochronology
SC: Hydrology [H]
MN: 2007 Joint Assembly