Date of Award
Master of Science (MS)
The Precambrian (?) to medial Ordovician rocks of the Taconic Allochthon are characterized by argillaceous and arenaceous sediments with lesser associated carbonates, carbonate breccias, and cherts of predominantly deep-water aspect. These allochthonous rocks tectonically overlie an autochthonous to parautochthonous coeval sequence of dominantly shallow marine clastics and carbonates of the Champlain and Vermont Valley sequences. Facies, thickness, sedimentologic, and paleontologic considerations suggest that these coeval sequences represent a carbonate shelf continental rise pair of the east-facing early Paleozoic Atlantic-type margin of North America. This margin formed by the opening of an ocean in latest Precambrian time. The stratigraphy of the shelf suggests that it experienced a complex transgressive-regressive history which is recorded on the rise by marked changes in type of sediment and mode of sedimentation. This Atlantic-type margin was destroyed in the medial Ordovician by eastward subduction and consequent collision beneath the Ammonoosuc volcanic arc. This resulted in the progressive east to west stacking of the rise sequence and subsequent obduction onto the shelf. Obduction involved an exceedingly complex deformation history of folding and imbrication of the shelf, Allochthon and Grenville basement.
The stratigraphy of the study area varies considerably across strike. Regions of different, though comparable stratigraphy occur in thrust bonded slices. In the west a stratigraphy closely similar to that defined by Jacobi (1977) is observed. All units, including Bomoseen, Truthville, Browns Pond, Mettawee, Hatch Hill-West Castleton, Poultney, Indian River, Mount Merino, and Pawlet are present. A central region with a similar stratigraphy is recognized, but characterized by less carbonate, thinner and commonly more fine-grained quartzites, which among other aspects suggests that it represents a somewhat more distal (easterly) facies. To the east, the sequence is Bullfrog Hollow Lithozone, Poultney, Indian River (?), Mount Merino (?), and Pawlet. The name Bullfrog Hollow Lithozone is introduced for the basal, apparently thick sequence of purple, green and gray slates and argillites, with associated minor thin quartzites. A thin gray slate with interbedded quartzite and black calcareous quartz wacke lies within the Bullfrog Hollow and is tentatively correlated with the Browns Pond. A new name is used because direct correlations with the Truthville and Mettawee slates of western regions was not possible and other names, such as Bull, St. Catherine, or Mettawee were considered inappropriate because of misuse, poor definition, or the inclusion of untis not observed in this area. Pawlet and Poultney are usually in stratigraphic contact, but locally Indian River and/or Mount Merino are also observed. The Poultney-Pawlet contact appears to be a disconformity. Pawlet and Bullfrog Hollow are locally juxtaposed, but their contact is everywhere interpreted to be structural.
Structurally, the study area is quite complex. Four phases of tectonic deformation associated with at least three generations of thrust faults are recognized. Earlier, pre-tectonic, syndepositional deformation features (DO) are also recognized. The earliest tectonic deformation (Dl) is only locally recognizable. It involves macroscopic isoclinal and initially recumbent folds (Fl) and axial surface-parallel thrusts (T1). F1 folds and T1 thrusts are refolded by prominent west-verging, asymmetric, overturned folds (F2) with an axial surface slaty cleavage (S2). Thrusting (T2) parallel or somewhat less steep than F2 axial surfaces imbricates and dismembers the F2 folds. These structures pre-date the Giddings Brook Thrust. Mesoscopic refolding of D2 and earlier structures by F3 folds which are associated with an axial surface crenulation cleavage (S3) is observed, but is not macroscopically significant. A third generation of thrusts (T3) that dip significantly less steeply east than F2 axial surfaces are prominent in this area and may be temporally associated with F3 folds, but this cannot be proven. T3 thrusts may be of the same age as the Giddings Brook Thrust. Rare vertical kink bands (F4) represent the fourth tectonic deformation and are not considered to be significant to the regional structure.
Rowley, David B., "Complex Structure and Stratigraphy of Lower Slices of the Taconic Allochthon Near Middle Granville, New York" (1980). Geology Theses and Dissertations. 77.
Plate 1 - Geological map of the Middle Granville (NY) - Lake St. Catherine (VT) area (coloured outcrop map, scale 1: 12,000)
rowleymspl2.pdf (1505 kB)
Plate 2 - Geological Sections of Middle Granville-Lake St. Catherine area NY-VT (uncoloured geological cross-sections, scale 1: 12,000)
rowleymspl3.pdf (3795 kB)
Plate 3 - Lithounit-age stratigraphic chart for eastern New York-western New England (uncoloured stratigraphic columns)