STRATIGRAPHY AND STRUCTURE OF THE OAK HILL SUCCESSION IN VERMONT

Abstract

North of the Winooski River, Vermont, the Oak Hill succession occupies the region between the eastern margin of the Champlain Lowland and the western foot of the Green Mountains. The lithologic units are traceable into southern Quebec, and some are traceable southward into west-central Vermont. Lower and middle Cambrian ages have been assigned to all units. The strata below the Gilman quartzite are tentatively correlated with the Mendon series in the Rutland-Brandon region. All units above the Gilman have stratigraphic equivalents in the adjoining Rosenberg succession. The earliest recorded differential downwarping of the local geosynclinal area immediately preceded the beginning of deposition of the Pinnacle sediments. The distribution of the shaly, sandy, and conglomeratic facies of the Pinnacle and West Sutton formations indicate a western source for the sediments and also that the sea was encroaching westward. The Gilman quartzite marks the first occurrence of reworked sands; reworked sediments formed practically all of the elastics sediments thereafter. A prominent anticlinorium occupies much of the southern part of the area. Northward it fades into a westward-dipping homocline. The western margin of the succession is formed in most places by a series of thrust faults, which may be continuous. The Oak Hill thrust, considered the western boundary of the succession in southern Quebec, has not been recognized in Vermont. The strata were strongly folded before thrusting; the thrusts are subsequent shear thrusts. Several klippen, related genetically to the thrusts, form prominent hills west of the western margin of the succession.