Bart Reef: a Possible Early Permian Restricting Barrier of the Fosheim-Hamilton Evaporite Sub-Basin, Ellesmere Island, Arctic Canada
Sedimentologic and stratigraphic evidence suggests restriction by Bart reef promoted Early Permian evaporite deposition within the Hamilton-Fosheim sub-basin of the Canadian Arctic. The Fosheim-Hamilton sub-basin, a satellite basin of the Sverdrup Basin, was a site of subaqueous evaporite deposition during Late Pennsylvanian to Early Permian time.
Initial aggradational growth of Bart reef occurred during the Early Permian (middle Asselian) in fully marine, mid shelf conditions. Reef facies are extensively dolomitized, with remnant limestone composed of phylloid algae-peloidal boundstone-rudstone with occaisonal Girvanella. Correlative off-reef facies are argillaceous, organic rich echinoderm-bryozoan wackestone-packstone with sharp based, bioclastic lags, suggesting periodic disturbance by storm waves.
Transition to shallower, hypersaline conditions caused a hiatus in reef growth. Evaporitic facies appear to onlap only the eastern flank of Bart, which is proximal to the Fosheim-Hamilton sub-basin. Presence of bottom-nucleating gypsum pseudomorphs, dolostone, stromatolites, scour and brecciation within off-reef strata suggest a shallow ‘salina’ depositional environment, also implying that Bart Reef was subaerially exposed. Carbon and oxygen stable isotope analysis reveals heavy isotope enrichment of reef and off-reef dolostones with respect to co-eval limestones, implying an early dolomite precipitation mediated by evaporitic brines.
Marine sedimentation after evaporitic hiatus is asymmetric. Measured sections on the eastern side of Bart comprise lagoonal and shallow shelf facies. Airphoto analysis suggests resistant reef strata concentrate on the western, Sverdrup Basin flank. The facies transition between reef and lagoon/shelf facies is interpreted to occur around the reef crest. Reef growth exclusively on the western flank suggests Bart evolved geometrically from a reef-mound to a fringing reef.
Evaporitic facies which onlap the eastern flanks of Bart reef may constitute the western extent of the Fosheim-Hamilton sub-basin. This may imply Bart served as a temporary barrier to oceanographic circulation between Fosheim-Hamilton sub-basin and Sverdrup Basin during the Early Permian, promoting the last two episodes of evaporite deposition in the former during lowstand sea-levels. It is suggested that Bart reef and surrounding strata could form a functioning petroleum system within sub-surface sections of the Hamilton-Fosheim sub-basin.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009