Trent A. Rehill

Based on interpreted seismic, lithostratigraphic, and biostratigraphic analyses, a detailed stratigraphic framework is presented for the thick (>10 km) succession of Late Carboniferous strata preserved in the offshore portion of the Maritimes Basin. The offshore comprises more than 70% of the total area (~215 000 km2) of the Maritimes Basin and was previously poorly understood in terms of regional tectono-stratigraphic history. Consequently, although the 20 exploration wells drilled in the offshore area had strong indications of gas, there is little understanding of regional petroleum potential and documentation of play types.

Offshore, the Late Carboniferous stata was deposited in an asymmetrical basin that developed within a Continental Wrenched Foldbelt tectonic regime. The majority of the restricted-marine to alluvial basin fill consists of a thick (>8 km) succession of Cumberland and Pictou Group strata that can be subdivided into 7 newly proposed, formation level, lithostratigraphic units.

Within the post Namurian basin fill, four 2nd-3rd order depositional sequences are recognized, bounded by regionally identifiable sequence boundaries. Each sequence consists of a basal coarse grained facies overlain by a fine grained facies. The 200-500m thick sequences contain smaller, higher frequency sequences, hence are divided into sequence sets. The progradational basal facies are interpreted to be forestepping systems sets. Retrogradational backstepping systems sets overlie both the basal unit and a transgressive surface. These cyclic sequences developed in response to episodic allocyclic tectonic processes related to renewed Alleghanian thrusting in the Appalachians and increased tectonic subsidence. Interaction of these mechanisms controlled relative rates of change of accommodation and sediment supply in the basin.

The derived stratigraphic framework, used in conjunction with modern basin analysis techniques, allowed the reconstruction of subsidence, compaction, thermal and maturation histories for 14 exploration wells. Burial rates on the order of 100-200 m/My led to rapid organic maturation and expulsion of hydrocarbons (ca 310-280 Ma). This timing information confirms that a viable petroleum system developed in the basin with favourable source, reservoir, seal and overburden dynamics. Hydrocarbon play types include; subsalt, salt piercement, fault related, basin-centre gas, stratigraphic pinchout, and unconformity.

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Supervisor: Martin Gibling