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Complete 3-D Reconstruction of an Early Paleozoic Fore-Reef Succession in Yukon, Canada

Abstract

Carbonate reefs provide an excellent paleontological record of marine biodiversity and can also contain significant hydrocarbon accumulations. In particular, fore-reef and reef margin successions preserve the sedimentary record of environmental change in reef systems and also host many prolific hydrocarbon reservoirs. However, there are few exposures of reef margin depositional systems which provide appropriate outcrop analogues to subsurface equivalents containing hydrocarbon accumulations.

A remarkable exposure of the Cambrian-Devonian Bouvette Formation at Nadaleen Mountain in Yukon, Canada was discovered in 2017, and reconnaissance observations suggested a fore-reef succession was preserved at the margin of the Ogilvie Platform. In August 2018, we measured 24 closely spaced stratigraphic sections of the Bouvette Formation along depositional dip and strike and carefully mapped the region to test the hypothesis that the exposure at Nadaleen Mountain represents a fore-reef depositional system. To aid in mapping and visualization of the depositional system, an Unmanned Aerial Vehicle (UAV) was employed to collect imagery and create a high-resolution digital elevation model (DEM) of the entire Bouvette Formation exposure. Approximately 100 strike and dips were measured with accompanying GPS points, so that in combination with the UAV imagery and DEM, a 3-D depositional model can be constructed.

The measured stratigraphic sections and UAV imagery revealed several important stratigraphic features at Nadaleen Mountain. Notably, two 5-30 m thick stacked clinoformal wedges of fossiliferous packstone composed of crinoid and reef fossil debris thicken to the NW in the study area. A third more massive unit ~15-100 m thick composed entirely of reef debris and topped by domal tabulate and rugose coral reef buildups also thickens to the NW in a clinoformal geometry.

Sedimentary facies and unit geometries observed suggest the Bouvette Formation at Nadaleen Mountain comprises a fore-reef depositional environment and records significant environmental change along the margin of the Ogilvie Platform in the early Paleozoic. The study will allow for a complete 3-D reconstruction of a fore-reef depositional system that can be use in reservoir modeling of analogous petroleum systems. Furthermore, these data will also provide an exceptional record of early Paleozoic sequence stratigraphy, carbonate sedimentology, reef ecology, and carbonate geochemistry.