Paleogeography and sedimentology of the MacKenzie Basin, Northwest Territories, Canada: An evaluation of Devonian sea-level change, paleoecological controls on Paleozoic reef growth, and early diagenetic conditions.

摘要

The MacKenzie Basin, located in the District of MacKenzie in the southern part of the Northwest Territories, Canada, includes a thick succession of Middle Devonian strata. This basin, bordered to the east by the Canadian Shield and to the south by the Tathlina Uplift, was directly connected to the open ocean that lay to the northwest. Comprehensive facies analyses of the Chinchaga Formation, Lonely Bay Formation, Horn Plateau Formation, and Horn River Formation, which formed in this basin during the Early and Middle Devonian, shows that sedimentation was largely controlled by eustatic sea level changes. Accordingly, these strata reflect a long period of sea level rise during which shallow water evaporite deposition in the Eifelian was followed by open marine conditions that led to reef growth in the Givetian, and ultimately pelagic shale deposition in the Frasnian.;The Horn Plateau Formation is comprised of numerous isolated reefs that are located along northeast-southwest direction over a distance of 350 km along the MacKenzie Basin ramp. Reefs in the southwest are dominated by stromatoporoids whereas those in the northeast are dominated by corals. Although difficult to prove, it appears that the distribution of the stromatoporoids and corals may have been controlled by nutrients coming from coastal upwelling or runoff from the exposed Canadian Shield.;Effects of early diagenetic processes were evident on the MacKenzie Basin ramp in an intensely bioturbated facies in the Lonely Bay Formation. Burrows from this facies are dolomite-filled further down the ramp and calcitefilled proximal to the Canadian Shield in the east. Anoxic conditions and the presence of sulphate reducing bacteria may have promoted early dolomite formation in the burrows located in deeper water. Burrows further up the ramp were oxygenated and show evidence of input from the exposed Canadian Shield, both of which may have inhibited low-temperature dolomite formation.