Date of Award
Master of Science (MS)
The Taconic Allochthon contains rocks of Cambrian (?), Cambrian and Ordovician age. It measures approximately 200 kilometers by 25 kilometers and is located in contiguous sections of New York, Vermont, Massachusetts, and Connecticut. The rocks are predominantly slates with lesser amounts of arenites, wackes, limestone, chert, and conglomerates. All have been subjected to chlorite or biotite grade metamorphism and two tectonic deformations. The study area in central Washington County, New York, contains most of the Taconic sequence, and because of both natural and man-made exposure it is more accessible than most other locations. A lithostratigraphic column has been identified which has more detail than any single previous version. Because of the already excessive Taconic nomenclature pre-existing boundaries and names have been retained wherever appropriate. However, two new formations and four new members have been described and formally introduced. Extensive literature research suggests this column can be applied throughout the Giddings Brook Slice of the Allochthon as a reference section.
Analyses of horizontal and vertical rock type distribution, sedimentary structures, and coarse clastic sedimentary petrography indicate a depositional environment which varies both laterally and with time. The overall picture suggests intermediate depths, moderate distance from shore, and a slope between source and deposition site which is sufficiently steep to permit turbidity, debris, and channel flows. Comparisons with segments of a modern stable rifted margin indicates that only the upper and lower continental rise can accommodate this sedimentological variety on a comparable scale. Map pattern scale structural observations were consistent with previous work and showed that the major folds have an approximate north strike and are overturned to the west. Regional slaty cleavage is axial planar to these folds. Evidence of a second tectonic deformation, seen only sporadically, consisted of fracture or crenulation cleavage and associated folds. Even more infrequent were examples of soft sediment deformation.
Jacobi, Louise D., "Stratigraphy, Depositional Environment and Structure of the Taconic Allochthon, Central Washington County, New York" (1977). Geology Theses and Dissertations. 41.
Plate 1 - Geological Map (Taconic Allochthon near Granville NY) (coloured outcrop map, scale 1: 12,000)
delanogpl2o.pdf (9229 kB)
Plate 2 - Geological Cross Sections (Taconic Allochthon near Granville NY) (coloured cross sections, scale 1: 12,000)
delanogpl3o.pdf (9800 kB)
Plate 3 - Geological Columns (Taconic Allochthon) (part coloured lithounit stratigraphic thicknesses, scale 1: 1,200)
delanogpl4o.pdf (2426 kB)
Plate 4 - Historical comparative stratigraphic chart (uncoloured lithounit-age stratigraphic chart)