THE BLUEBERRY BARRENS OF DOWNEAST MAINE LAID BARE WITH GROUND-PENETRATING RADAR

Ground-penetrating radar (GPR) has become an invaluable tool in our ongoing study of the Pleistocene deposits of SW Washington County, Maine; due to their agricultural use, these features have few excavations revealing their internal stratigraphy and sedimentary structures. GPR provides a means of identifying the subsurface architecture of these deposits and, in conjunction with core logs, allows us to interpret origins and depositional environments.

This poster will present a compilation of data from three years of research in SW Washington and easternmost Hancock Counties (Tary, et al., 2000, 2001). Landforms studied in past years and whose data and interpretations will be presented include: Pineo East, a large, E-trending, elongate ice-contact delta; Pineo West, a SE-trending, streamlined, flat-topped, kettled rise with deltaic foresets radiating outward from the feature’s central axis; the Deblois Blueberry Barrens, a prograding braided stream deposit overlying marine clays; and the Deblois West Barrens and associated features, a landform containing rapidly-shifting small-scale prograding deltaic deposition. This year, we have begun work on the Pork Brook Delta and other features along the county line near the towns of Beddington and Deblois.

Radar profiles along a small flat-topped, steep-sided plain (el. 74 m) near the W bank of the Narraguagus River show little delineation of stratigraphic features below ~3 m depth. Above that depth, shallow dipping reflectors (~8°) and small U-shaped reflectors suggest a prograding braided stream environment. This is supported by a core log, which records 9 m of clay overlain by 3 m of coarse, gravelly sand.

GPR transects from the Pork Brook Delta (Hooke, 2001) show rhythmic sigmoidal reflectors, indicative of deltaic clinoforms. This marine-limit delta (el. 83 m) has a GPR signature similar to that seen at Pineo Ridge. Foresets here dip SE at 9-19°. Bedding visible at one small gravel pit exposure has been correlated to a GPR record run atop the pit; sediments range from cobble to pebble gravel to coarse sand.

GPR lines were also run along a small, flat-topped U-shaped landform (el. 85 m) NE of the Pork Brook Delta. Rhythmic reflectors here dip SE at 14-23°, and the feature is interpreted to be a delta. The landform’s shape and elevation suggest that it is a small ice-contact delta.