SEDIMENTOLOGY AND STRATIGRAPHY OF THE UPPER ORDOVICIAN BLACK RIVER AND TRENTON GROUPS, WELLS OUTLIER, ADIRONDACK MOUNTAINS, NEW YORK

Cambrian to Upper Ordovician strata are present within the Wells, NY outlier, surrounded by the Mesoproterozoic igneous and metamorphic basement rocks of the Adirondack Massif. The Upper Ordovician Black River and Trenton Groups are exposed in the active Graymont Quarry. Recent drill cores available for study at the site document the presence of the Upper Cambrian Potsdam and Galway Formations beneath the Upper Ordovician sequence. One core includes Upper Ordovician Utica Formation down-faulted beneath Upper Cambrian Galway Formation. This faulting is consistent with regional fault patterns within the Adirondack/Mohawk Valley region related to late Ordovician-Devonian evolution of the northern Appalachian Basin.

The Black River and Trenton Group interval at Wells is correlative to the sequences exposed at Crown Point Peninsula, NY and Roaring Brook, NY and cored intervals in the Mohawk Valley. Carbonate facies typical of the Lowville and Chaumont Formations of the Black River Group, and the Napanee and Kings Falls Formations of the Trenton Group, are present in the Wells exposures. The Black River and Trenton carbonate sequence includes coarse siliciclastic sand intervals and angular cobbles and pebbles of local basement lithologies are present. Carbonate clast breccias within the sequence also suggest syndepositional faulting. The interval at Wells includes the M3-M4 depositional sequence boundary (Brett et al., 2004) and a prominent calcitized K-bentonite tentatively identified as the M/H K-bentonite (Cornell, 2008). U-Pb geochronological analyses of zircon from the bentonite are underway.