The deformed belt of the Appalachians consists of the fold-and-thrust structures of the Valley and Ridge and the adjoining Appalachian Plateau provinces. The Blue Ridge and Piedmont provinces are excluded from this belt as being unprospective for petroleum. The deformed belt contains four morphostructural zones, from northwest to southeast, the folded foreland (southeastern Appalachian Plateau), the frontal imbricates (Nittany anticlinorium, Wills Mountain-Friends Cove anticlinorium), the interthrust syncline (Broadtop synclinorium, Greendale-Kimberling syncline) and the back imbricates (North Mountain-Pulaski system). Major types of potential hydrocarbon traps were formed by thrusting in these zones; these include opposed-thrust anticlines, step fold- and anticline-formi g thrust sheets, concentric folds, stack-thrust anticlines, and leading- and trailing-edge imbricates. The role of salt, rock competency, sheet thickness and length, tectonic transport, and thrust ramping are the critical factors in the formation of the traps.

Along the strike of the Appalachians, the deformed belt consists of three main arcs which are convex northwestward and display changes in strike and dominant structures. The southern arc extends southwest of Roanoke, Virginia; the central arc extends from Roanoke to the Hudson River; and the northern arc extends from New York to the Gulf of St. Lawrence. A fourth arc begins offshore of western Newfoundland and extends into the Atlantic Ocean where it terminates at the continental margin. Main and secondary arcs are linked at basement nodes. These include the Anticosti platform, the Quebec arch, and the Adirondacks in the north, and the Roanoke(?) and Cartersville recesses in the south.

The component arcs of the Appalachians evolved with different histories subsequent to the quiescent, carbonate-shelf deposition of the Cambrian and Early Ordovician Periods. The northern arc was deformed by the Taconian orogeny, has thick Upper Ordovician to Devonian flysch, and was intensely thrusted during the Acadian orogeny. The central arc was moderately deformed during the Taconian orogeny, was a source proximal, thick depocenter during the Late Paleozoic and principally was folded and thrusted during the Appalachian orogeny. The southern arc was an unstable platform until the Appalachian orogeny, when it was intensely thrust-faulted.

The petroleum potential of the deformed belt is described in relation to its structures and reservoirs. Beginning in the Ordovician, the southeast mobile flank of the Appalachians was deformed and uplifted. Hydrocarbons may have been trapped in the reservoirs of early formed folds which subsequently were relocalized by later thrusting into antiform traps. Thrust structures form large "slab" traps having a high drainage volume for early and late hydrocarbon accumulations. The structures considered

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the most prospective are those where the Trenton and Knox carbonate rocks are encased by Upper Ordovician shales in the frontal and back imbricate zones where up to four thrust sheets may be superposed. Reservoirs are studied in relation to the depositional trends of Cambrian, Ordovician, Silurian, and Devonian fairways, diagenesis, and the enhancement of porosity and permeability by fracturing. The deformed belt is considered to be a gas province because of the maturing of hydrocarbons through burial and migration. Despite the low calorific gases in some areas, Silurian and Cambro-Ordovician objectives are above the eometamorphic threshold. The deformed belt has been explored sparsely and many large structures and deep objectives remain to be drilled.

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