ABSTRACT
The Taconic Allochthon is located in eastern New York, western
Vermont, western Massachusetts, and western Connecticut and
extends about 200 kilometers north-south and east-west for about
25 kilometers. It contains rocks of Late Proterozoic, Cambrian and
Ordovician age. The rocks are predominantly slates with lesser
amounts of arenites, wackes, limestone, chert, and conglomerates.
All rocks have been subjected to chlorite or biotite grade
metamorphism and at least two generations of deformation. The
emplacement of the Taconic Allochthon onto the coeval shelf took
place during the Middle Ordovician Taconic Orogeny.
The study area lies at the western margin of the Taconic
Allochthon. Field mapping indicates that in the present area the
stratigraphy of the Taconic allochthonous sequence and the
lithological characteristics of individual rock units match the
descriptions of Jacobi (1977) and Rowley et al. (1979) in the
Granville area and in central Washington County. The stratigraphic
units observed include the Bomoseen Formation, the Truthville
Formation, the Browns Pond Formation, the Indian River Formation,
the Mount Merino Formation and the Snake Hill Formation. The
well-known Diamond Rock Quartzite was found to lie near the base
of the Browns Pond Formation and a correlation with the Mudd Pond
Quartzite
in the northern Taconics is suggested. It is also demonstrated
that the "Troy Shale" of Ruedemann actually lies at the same
stratigraphic level as his "Nassau Beds".
The most remarkable structural features of the mapped area are the
widespread distribution of commonly tight, westward-leaning or
overturned folds, the presence of the basal thrust of the Taconic
Allochthon and the development of peculiar anastomosing cleavages
in the Taconic Melange beneath the Allochthon. Anastomosing
cleavages were produced after the formation of slaty cleavages
parallel to the axial plane of mesoscopic folds. Observations at
the outcrop scale and under the microscope suggest that the
anastomosing cleavage surfaces are possibly conjugate shears
arranged in various orientations oblique to the normal to the
axial plane cleavages.
Xia, Z., 1983. Geology of the western boundary of the Taconic
Allochthon near Troy and the anastomosing cleavage in the Taconic
Melange. Unpublished MSc. thesis, State University of New York at
Albany. 189 pp., +xiii; 3 folded plates (maps).
University at Albany Science Library call number: SCIENCE
Oversize (*) QE 40 Z899 1983 X53
thesis (scanned text) - 15.3MB pdf file
Geological Map (uncoloured outcrop map,
cross-sections, scale 1:2,400)
Plate
1
- Geological Map of part of the North Troy area -
10.7MB pdf file
Plate
2 - Cross sections (North Troy area) - 3.1MB pdf file
Plate
3 - Enlargement of a thin section containing anastomosing
cleavage 1.8MB pdf file
Return to MS Theses completed in the
Geological Sciences Program, University at Albany