Mapping a buried bedrock valley in North field, Vermont, using geophysical methods
- Norwich Univ., North field, VT (United States). Dept. of Geology
A flat playing field at Norwich Univ. in central Vermont in the north flowing Dog River Valley, has bedrock exposed at slightly higher elevations on both the east and west sides. This study area is located within the Dog River fault zone in the easternmost unit of the Green Mountain Anticlinorium, just west of the Connecticut Valley--Gaspe Trough. Outcrops on the eastern edge of the field (Cram Hill formation) are dark gray to black phyllite with minor interbedded quartzite, all exhibiting well-developed salty cleavage (N15E, 85E) and a younger spaced crenulation cleavage. The western outcrops (Harlow Bridge quartzite) are light gray to green, dirty micaceous chloritic quartzite with primary cleavage trending N21E, 84W. The buried bedrock valley is filled with more than 20 m of magnetite-rich glaciolacustrine and ice-contact stream deposits consisting of pebbly sands and gravels under well-sorted fine- to medium-grained sands that accumulated first during ice retreat, then in glacial Lake Roxbury, and finally in glacial Lake Winooski. Efforts to locate the covered bedrock contact by magnetics revealed a positive anomaly trending parallel to regional strike (NNE) over the magnetite-rich sediments. A gravity study showed an elongated negative gravity anomaly mirroring the pattern of the magnetics. Seismic data collected near the main axis of the buried valley revealed three distinct velocity layers. Stratigraphically, the top layer is undersaturated sands above the water table, the next layer is saturated sands and gravels, and the third layer is bedrock. Although the playing field surface slopes very gently toward the north (0.92[degree]), the seismic data shows that the water table slopes to the south at 0.51[degree] with depth increasing from 6.55 to 7.93 m, while the bedrock slopes at 1.28[degree], also to the south.
- OSTI ID:
- 5723461
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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