Date of Award
Master of Science (MS)
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, Zong-Guo, "Geology of the western boundary of the Taconic Allochthon near Troy and the anastomosing cleavage in the Taconic Melange" (1983). Geology Theses and Dissertations. 100.