MASTODONS, MARL AND GROUND PENETRATING RADAR: A CASE STUDY OF SEDIMENT-LANDFORMS AND PALEOECOLOGIC RECONSTRUCTIONS IN SOUTHEASTERN NEW YORK

An accidental discovery of two large diameter mastodon tusks protruding from a stream bank in Orange County, NY in the Walkill Valley Lowland led to multiple ground penetrating radar (GPR) surveys to ascertain site stratigraphy and possible distribution of additional disarticulated faunal remains. In addition three 17 meter deep exploration borings were collected to investigate regional stratigraphy. The survey location was in a former proglacial lake basin of the Hudson Lobe of the Laurentide Ice Sheet.

Observations made during the initial site visits indicated that the tusks were 1.8 meters below the ground surface in close association with a marl unit overlain by peat and underlain by a massive silt-clay. Two GPR surveys were completed using a GSSI SIR-3000 data acquisition system with 400 MHz and 200 MHz monostatic antennas. Data acquisition was completed using an 8 meter by 17 meter survey grid with a 0.25 meter line spacing and sampling interval of 40 scans per meter. Amplitude-slice maps were produced using RADAN processing software to produce a three-dimensional image of anomalies and stratigraphic relationships.

Surveys results suggested the marl and peat interface occurs as a sharp contact at a depth of 1.6 meters. While both GPR surveys produced multiple anomalies and delineated the tusks and site stratigraphy, the 200 MHz antenna clearly produced the best combination of penetration and resolution.

Results of the GPR surveys were used to guide a 3meter by 3meter excavation to extract and salvage the tusks. Excavation of the site confirmed the marl contact at a depth of 1.6 meters that draped onto the tusks. The total thickness of the marl containing the tusks was 0.3 meters. In addition to the tusks a 0.3 meter long fragment of tree was found at the contact of the marl interface. Abundant plant macro-fossils and spruce needles were also recovered from the excavation. The botanical and faunal remains recovered will provide detailed information and chronologic context for paleoecologic and deglacial reconstructions in the region.