ACADIAN OROGENY AND SEQUENCE DEVELOPMENT IN THE UPPER LOWER--LOWER MIDDLE DEVONIAN (UPPER PRAGIAN--EIFELIAN), APPALACHIAN FORELAND BASIN AND COMPARISON WITH NORTH GONDWANA SUCCESSIONS

The late Pragian, Emsian, and Eifelian succession of the Appalachian foreland basin consists of six depositional sequences that represent approximately 24 m.y. (Tucker et al., 1998). These comprise the Oriskany (1); Oriskany--Esopus (2); Schoharie (3): lower to middle Onondaga (4); upper Onondaga--Union Springs (5); and Oatka Creek (6) formations of New York and correlative strata across the basin. The six sequences were deposited prior to and during two tectonically active to quiescent phases of Acadian orogenesis on the eastern Laurentian margin. Recent basinwide stratigraphic synthesis indicates correlatability of sequences or associated unconformities throughout the Appalachian foreland basin. Anomalous patterns of sequence development include: 1) Local to regional modification of basin topography of the foreland basin through time. Flexural development of foredeep, forebulge, and back-bulge basin features and relatively restricted distribution of "deeper," more proximal, clastic-dominated sequences characterize tectonically active phases of the orogeny (e.g., sequences 2, 5, 6). Periods of relative quiescence are characterized by flattened basin topography and widespread distribution of relatively "shallower", carbonate-/quartz arenite-dominated sequences (e.g., sequences 1, 4). A transitional active to quiescent stage in the orogeny (sequence 3) is characterized by erosional bevelling of the forebulge and partial infilling of available accommodation that results in a leveling of foredeep, bulge, and backbulge topographic features; 2) Alternating cratonward and hinterlandward migration of foreland basin system forebulge through time; and 3) local to regional amalgamation of multiple sequence-bounding unconformities cratonward and/or over the forebulge of basin. These trends reflect a relatively complex stratigraphic history of sea level change across the basin, and clearly indicate a strong tectonic influence on the development of depositional sequences in the basin. However, preliminary examination and literature study of Pragian through Eifelian successions in North Africa and central Europe indicate overall correlation with the Appalachian Basin sequence-scale framework. Varying magnitudes of facies change between sequences in both areas appear to indicate an overprint of tectophase-scale flexural kinematics on eustatic trends in eastern Laurentia.