Mapping and structural investigations in an area bounded to to the west by by Grenvillian basement and to the east by allochthonous rocks emplaced during the medial Ordovician Taconic Orogeny led to division of the area into a Western Undeformed Zone and an Eastern Deformed Zone. The former consists of a thin, undeformed shelf sequence of upper Cambrian to lower Ordovician (Canadian) clastics and carbonates, which unconformably overlie Grenvillian basement and dip gently to the east.
The Eastern Deformed Zone consists of early to medial Ordovician carbonates folded about northnortheast trending axes with east to southeast dipping axial surfaces, overlain by likewise folded and sheared medial Ordovician shales. The rocks in the Eastern Deformed Zone form three eastward dipping, imbricated thrust sheets, from west to east the West Haven, the Forbes Hill, and the Carver's Falls Thrust Sheet. Evidence for east over west thrusting is presented. The initiation of folding predates thrusting, but further folding has probably occurred during the transport of the thrust sheets. Folding and thrusting are interpreted as early and late stages of tectonic movements caused by the emplacement of the Taconic Allochthon.
The consistent similar orientation of thrusts and axial planar cleavage and the large size of the carbonate sheets led to this new interpretation which contrasts with the existing one which viewed the Eastern Deformed Zone and its continuation along strike as an olistostrome.
Displacement estimates based on shelf geometry yield results on the order of 100 km for the thrust sheets in the field area. It is proposed that the boundary between the undeformed and the deformed part of the field area constitutes one of the southern continuations of the Champlain Thrust, the location of which was hitherto unknown that far to the south. Post-thrusting normal faulting in the field area may possibly be an expression of reactivated rift related basement faults in geologically recent time.
Steinhardt, C.K., 1983. Structure and Stratigraphy of West
Unpublished MSc. thesis, State University of New York at Albany. 167 pp., +x; 4 folded plates (maps)
University at Albany Science Library call number: SCIENCE Oversize (*) QE 40 Z899 1983 S74
Steinhardt MS thesis scanned
text pdf - 14MB
Plate 1 - Geology
of West Haven, VT 16 MB pdf file
(coloured geological outcrop map, scale 1:10,000)
Plate 2 - Geologic cross-sections of West Haven, Vermont 1MB pdf file
Plate 3 - Stratigraphic nomenclature chart, west-central Vermont 1.4MB pdf file
Plate 4 - Geological profile of imbricated thrust stack in roadcut on VT route 22A, north of Fair Haven (scale 1:38.5) 1.7MB pdf file
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