Orwell Limestone and Isle la Motte and Lowville Limestones

Orwell Limestone and Isle la Motte and Lowville Limestones - Smooth ledged, sublithographic and lithographic, dove gray weathered limestone commonly cut by veins of white calcite; beds filled with fossil shell fragments are characteristic. The Lowville is a thin, undifferentieated unit near the base of the Orwell that is characteristically ashen gray and contains abundant Phytopsis tubulosum. The Isle La Motte is about the equivalent of the Orwell in areas west of Champlain thrust, on Isle La Motte and near South Hero, Highgate, Swanton, and St. Albans; it is locally underlain by the Lowville, which is too thin to show on map. The Sawyer Bay is herein defined as a member of the Lowville Formation of the Black River Group. Occurs approximately in the middle of the Lowville throughout the Champlain Valley and represents a significant deepening event. Lower part of the Lowville was deposited in a shallow lagoonal environment, while the Sawyer Bay was deposited in a subtidal normal marine environment. Deposition probably the result of high angle block faulting in the Champlain basin. Member is very dark gray to black micrite to sparite in composition with irregular "lumpy" bedding, wavy lamination, cross-lamination, and ripple marks. Irregularly shaped, scattered chert nodules are concentrated in specific horizons. Contains a few large and small brachiopods, trilobite fragments and some fossil hash. Member is approximately 6 ft thick at Sawyer Point, South Hero Island, northwestern VT; thins to 2 ft at Arnold Bay, and becomes an indistinct rubbly unit at Crown Point, northeastern NY. The Lowville, at Crown Point, also contains the House Creek Member. The House Creek is also present in northwestern NY, southern Ontario, and the Black River Valley, but is not seen at Sawyer Point or Arnold Bay. The Lowville reaches a maximum thickness of 50 ft at Crown Point and a minimum of 24 ft at Sawyer Point. The Lowville overlies the Pamelia Formation and underlies the Chaumont Formation. Age is Middle Ordovician (Blackriveran). (Bechtel and Mehrtens, 1995).