CHARACTERIZATION OF VARIATIONS IN OPTICALLY STIMULATED LUMINESCENCE RESPONSE IN DIFFERENT PRO-GLACIAL ENVIRONMENTS; FORT DRUM, NY AS A PROVING GROUND

Optically stimulated luminescence (OSL) dating is an increasingly vital Quaternary dating technique for numerous stratigraphic settings. OSL is used to estimate the burial duration of sand-sized grains since the last exposure to light during transport. As in all chronologic methods, there exist more extensive considerations for sample collection and in “it depends” scenarios. OSL methods have been progressively utilized in glacial environments to date the deposition of sediments, but with varying success. A consideration with OSL is partial bleaching, or incomplete resetting, of the OSL signal prior to deposition, resulting in inherited luminescence from previous burial and ages older than expected based on an existing stratigraphic framework. Environments prone to partial bleaching are from reworked sub-glacial sediments deposited into a sediment laden pro-glacial lake devoid of sunlight. This has led to the strategic sampling of sediments from glacial environments that are “Distal (maximum bleaching potential), High (above water level) and Dry (minimum ground water interference to gamma radiation)” relative to the glacier front.

During ongoing USGS Quaternary geologic mapping of Fort Drum Army Base, NY we sampled pro-glacial environments to estimate the age of sediment deposition and to characterize OSL measurement variations across a range of depositional environments: 1) an ice contact lacustrine fan, 2) an ice contact lacustrine delta, 3) a meteoric delta prograding into Glacial Lake Iroquois, and 4) post-glacial eolian dunes resting on the drained bed of glacial Lake Iroquois. Sampling locations were determined based on geologic mapping and the stratigraphic relationship of the units from oldest to youngest, respectively. These deposits are bracketed within known ice front positions, and variations in the OSL measurements are compared with sedimentological analyses, portable OSL and IRSL luminescence grids, elemental abundances, single aliquot regenerative OSL/IRSL measurements, and sediment source variations.