Lower Pennsylvanian siliciclastic sedimentary rocks of the central Appalachian Basin consist predominantly of nonmarine, coal-bearing facies that developed within a fluvio-estuarine, trunk-tributary drainage system in a foreland-basin setting. Sheet-like, sandstone-mudstone bodies (up to 100 km wide and 70 m thick) developed in an axial trunk drainage system, whereas channel-like, sandstone-mudstone bodies (up to several km wide and 30 m thick) developed in tributaries oriented transverse to the thrust front. The origin of these strata has been debated largely because the paleogeomorphology and facies architecture of the New River Formation (NRF) are poorly understood. A sequence stratigraphic framework for the NRF, based on a combination of outcrop mapping and subsurface well-log analysis, reveals: 1) regionally significant erosional surfaces along the bases of sheet-like and channel-like sandstone bodies (sequence-boundaries), 2) fluvial- to estuarine-facies transitions (marine flooding surfaces), 3) erosionally based, framework-supported, quartz-pebble conglomerates (ravinement beds), and 4) regionally traceable, coarsening-upward intervals of strata (highstand deposits above maximum flooding surfaces). Using these criteria, both 3rd- and 4th-order sequences have been identified. An idealized 4th-order sequence consists of deeply incised, fluvial channel sandstone separated from overlying tidally modified estuarine sandstone and mudrock by a ravinement bed, and capped by coarsening-upward bayhead delta facies. The relative thickness of fluvial versus estuarine facies within a fourth-order sequence reflects a balance between accommodation and sediment supply within a 3rd-order relative sea level cycle. Lowermost 4th-order sequences are dominated by fluvial facies, whereas the uppermost sequences are dominated by estuarine facies. Therefore, 3rd-order sequence boundaries are interpreted to lie at the bases of the lowermost, fluvial-dominated fourth-order sequences. Coarsening-upward intervals that record the maximum landward extent of marine conditions are interpreted as highstand deposits of the composite third order sequence. Thus, the NRF consists of thick, superimposed fluvial sandstone of the lowstand systems tracts and anomalously thin transgressive and highstand systems tracts. Asymmetrical subsidence within the foreland basin resulted in westward amalgamation of multiple, 4th-order, fluvial valley-fill successions and sequence boundaries. The Early Pennsylvanian time period was characterized by global icehouse conditions and the tectonic assembly of Pangea. These events affected the geometry of the overall stratigraphic package, which can be attributed to high-magnitude, high-frequency, glacioeustatic sea-level fluctuations superimposed on asymmetric tectonic subsidence. / Master of Science

This study integrates sequence stratigraphy of the Late Permian Toolachee Formation in the non-marine intracratonic Permian-Triassic Cooper Basin, Australia with 3-D seismic attribute analysis to predict the extent of depositional environments identified on wireline and well core data. The low resolution seismic data (tuning thickness 23 - 31 m) comprised of six seismic horizons allowed the successful testing of sequence stratigraphic interpretations of the productive Toolachee Formation that were based on wireline data. The analysis of 29 well logs and three 20 m core intervals resulted in the identification of eleven parasequences that comprise the building blocks of an overall transitional systems tract, characterised by a gradual increase in accommodation. The parasequences reflect cyclic transitions between braided and meandering fluvial systems as a result of fluctuations in sediment flux, possibly driven by Milankovitch climatic-forcing. The seismic horizon attribute maps image mostly the meandering fluvial bodies within the upper parts of the parasequences, but some maps image the lower amalgamated sand sheets and show no channel structures. Categorisation of the fluvial bodies in the overbank successions reflects a gradual decrease in sinuosity, channel width, and channel belt width up-section, supporting the overall increase in accommodation up-section. Similar acoustic impedance values for shales and sands do not suggest successful seismic forward modelling between the two lithologies. Geological interpretations suggest most imaged channel fill to be made up predominantly of fine sediments, as channel avulsion and abandonment is common and increases with time. Seismic forward modelling resulted in the interpretation of carbonaceous shale as a possible channel fill, supporting the geological interpretations. The three major identified fluvial styles; braided, meanders, and distributaries are potential targets for future exploration. Extensive sand sheets deposited from braided fluvial systems require structural traps for closure. Meandering and anastomosing channel systems represent excellent stratigraphic traps, such as the basal sands/gravels of laterally accreted point bars.