The Melvillian Disturbance: Repeated Pulses of Early Permian Structural Inversion following Initial Rifting of the Sverdrup Basin

Benoit Beauchamp
Department of Geoscience, University of Calgary, Calgary, AB, Canada.

The Melvillian Disturbance was the name given to the tectonic event that led to an angular unconformity between the flat-lying Middle Permian Trold Fiord Formation and underlying variably-inclined strata of the Upper Carboniferous to Lower Permian Canyon Fiord Formation on Melville Island, Sverdrup Basin (Arctic Canada). The sub-Trold Fiord unconformity (STFU) was later shown to be related to the inversion of rift structures and to the partial exhumation of half-graben fills. The unconformity was also shown on seismic profile to correspond to a major reflector below which syn-sedimentary faults terminate. The Melvillian Disturbance was thus viewed as a short-lived compression tectonic event that marked the transition from rift-related fault-controlled subsidence below and the onset of regional passive subsidence above. Subsurface seismic work on Prince Patrick Island, however, suggested that the Melvillian Disturbance may have resulted from several Early Permian compressional pulses alternating with intervals of tectonic quiescence. A new map and geological compilation from the Blind Fiord and Trold Fiord area, SW Ellesmere Island, shows that the syn- and post-rift Upper Carboniferous fill (Canyon Fiord Formation) of a 10 km-wide down-to-the-basin half graben - the North Trold Fiord Depression (NTFD) - was variably exhumed through compressional forces acting on a number of reactivated Ellesmerian structures. The geometry of the STFU varies along the width of the graben ranging from concordant to highly angular. Only minor inversion occurred along the NTFD-bounding master listric fault which lies 4-5 kms east of the head of Trold Fiord. The near complete exhumation and erosion of the NFTD occurred through the reactivation of a major Ellesmerian thrust, which appears to have been associated with a mid-graben roll-over anticline immediately east of Trold Fiord. Chert pebbles and cobbles within the basal Trold Fiord Formation attests for the erosion of Upper Carboniferous syn-rift conglomerates nearby. Just west of Trold Fiord, the syn- and post-rift succession is repeated beneath the STFU and decoupled along the sub-Carboniferous unconformity with the shale-dominated Devon Island and Danish River formations. West of the NTFD, a series of Ordovician limestone-cored thrusts popped through the post-rift succession, leading to locally-developed steep angular unconformities. Intra-Canyon Fiord minor angular unconformities between second-order sequences beneath the STFU suggest that structural inversion resulted from more than one Early Permian compressional pulses. More subtle evidence of crustal deformation in the form of differential uplift and subsidence is recorded in the thicker and more complete Lower Permian succession southwest of the NTFD (west and east of Blind Fiord), confirming that episodic compressional tectonics influenced sedimentation pattern in the study area as it did throughout the Sverdrup Basin.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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