STRUCTURES ALONG THE EASTERN MARGIN OF THE CATSKILL MOUNTAINS AND THEIR RELATIONSHIPS TO THE HUDSON VALLEY FOLD THRUST BELT, EASTERN NEW YORK

The Hudson Valley fold-thrust belt (HVB) of eastern New York is a narrow 018° trending west-verging, thin-skinned belt between the Hudson River and the Catskill Mountains. An angular unconformity between Silurian and Ordovician strata is deformed by HVB, demonstrating a post-Taconic (Middle Ordovician) age. An Acadian (Devonian) age is suggested by its location between the Devonian Catskill delta, and the Acadian orogeny of New England. However, HVB appears continuous to the south with the Alleghanian (late Paleozoic) central Appalachian fold-thrust belt. The lack of definitive overprinting structures led to a focus on the Catskill Mountains west of HVB, where structures are less complex, and where joints should record stress trajectories associated with HVB. Over 1800 joint orientations have been compiled, including data from Isachsen et al. (1977), and give two well defined maxima at 278°, 90° (J1) and 014°, 89° (J2). Joint intersection geometries suggest that J1 are older, although mutually crosscutting relationships occur, thought to be due to joint reactivation. Plumose structures, and the absence of slickensides, indicate the joints are extensional and record maximum paleo-stress trajectories. In addition, shear zones, slickensides, duplexes, and localized cleavage zones occur, notably within the Marcellus Subgroup, at the base of the Catskill sequence, but also higher in the section. Such structures appear similar to features described in the Mohawk Valley, and may be evidence of a regional décollement. These give a displacement direction of 295°, similar to J1 orientations. It is suggested that J1 and J2 joints represent stress trajectories associated with HVB and Alleghanian compression respectively. It is hypothesized that stress trajectories from both the Acadian and Alleghanian Orogenies are recorded in the Catskill Mountains, and that HVB is Acadian in age. Further work is in progress to test this hypothesis.