Medial Ordovician rocks exposed in westernmost New England and eastern New York State include thick sequences of marine sandstones which are part of a belt extending from Newfoundland to Tennessee. A petrographic study was made of 237 samples distributed across the entire outcrop belt (approx. 250 km. north-south along strike and 190 km. east-west across strike).
Two distinct types of sandstone are recognized, the oldest, and most widespread, is a deep water lithic wacke deposited by turbidity currents and found interbedded with shale (flysch). The younger sandstone is found only in the southeastern part of the study area and is a lithic to quartz arenite which was deposited in a shallower water environment (molasse).
The composition of these sandstones is mainly quartz (50-70%) along with minor amounts of chert, feldspar and lithic fragments all in a varying amount of matrix and cement. The lithic fragments (7-12% of a given sample) are mainly sedimentary (shale, siltstone, greywacke and sandstone) with minor amounts of metamorphics (phyllite, slate and schist), carbonates, volcanics (silicic to mafic) and volcaniclastics. No minerals indicative of medium to high grade metamorphism were found.
Paleocurrent evidence suggests that the oldest flysch was deposited from the east in a number of small overlapping fans while the younger flysch and the molasse appear to be part of a single large fan whose source is to the south. Along strike no significant change in composition is seen but across strike as the flysch grows younger an increase in K-feldspar and carbonate material is noted with the greatest increase occurring in the molassic sediments.
These clastic sandstones were deposited in an elongate basin which formed as the result of an arc-continent collision during the Taconic Orogeny. The flysch sands are thought to be derived from recycled continental rise sediments (eg. Taconic Allochthon) with a contribution of volcanics and volcaniclastics from the colliding island arc. The lack of ophiolitic detritus indicates ophiolitic obduction either did not take place or occurred to a much lesser degree than in the northern extension of this belt in Canada. The increase of K-feldspar and carbonate may indicate the progressive exposure of Grenville basement and covering shelf carbonates, by overthrusting.
Tanski, S.A., 1984. Provenance study of the Middle Ordovician
of New York and western Vermont. Unpublished MSc. thesis, State
of New York at Albany. 112 pp., +ix; 1 folded plate (map)
University at Albany Science Library call number: SCIENCE Oversize (*) QE 40 Z899 1985 T35
Tanski MS thesis (scanned
pdf - 13 MB)
Plate 1 - Sample
location and outline geological map (Middle Ordovician
sandstones of eastern NY and western VT)
(uncoloured map, scale 1: 250,000) - 2.4MB pdf file
Return to MS Theses completed in the
Sciences Program, University at Albany