REVISITING THE EARLY DEVONIAN REEF KNOLLS OF LOWTHER ISLAND, NUNAVUT TERRITORY, ARCTIC CANADA: A RETROSPECTIVE ON THE RESEARCH OF ERIC C. PROSH

Eric Charles Prosh (1957–2013) was a respected Canadian paleontologist and geologist well known for his many years of service to the government of Nunavut in the fields of mineral exploration and mining. Less widely known is his still mostly unpublished Ph.D. research on the Early Devonian reef knolls of the Disappointment Bay Formation on Lowther Island, 120 km SW of Resolute, Cornwallis Island. Because of the relative inaccessibility of the area and because Early Devonian reefs are globally uncommon, the results of his 1982–1984 field investigations of Lowther and Young Islands are of especial significance and worthy of further attention.

During the Early Emsian, Lowther Island was part of a protected, tropical marine, shallow-shelf embayment receiving limited input of clastic sediments from arid lands nearby. A deepening ocean basin lay toward Young Island, some 30 km to the southwest where the Disappointment Bay Formation consists only of a few meters of grey-black calcareous mudstone containing the chemoautotrophic solemyid bivalve, Acharx.

On Lowther Island the Disappointment Bay consists of upward shoaling limestones and dolomites up to 90 m thick, the upper 50 m of which crop out as exhumed reef knolls. Lying disconformably above a sequence of redbeds, the Disappointment Bay preserves a vertical succession of carbonate facies representing the growth and senescence in of a reef knoll complex in response to passive sedimentary shoaling. Nucleating on brachiopod aggregations, the vertical facies succession is as follows: F1) a basal stromatactis-rich dark mudstone-to-wackestone (~5 m); F2) an algally bound wackestone (20-30 m) with a lateral subfacies consisting of steeply dipping beds of reef-marginal, bioclastic, spill-over debris; F3) a dolomitic, stromatoporoid-tabulate coral framestone-to-rudstone (10-15 m); and F4) dolomitized crinoidal grainstone (<5m). Dolomitization, confined to F4 and the upper part of F3, is of the burial stage, partially penetrative type, affecting the reef peripheries but not their cores.

In addition to calcareous algae, stromatoporoids and tabulate corals, portions of the reef succession contain diverse shelly faunas, mostly of Old World paleobiogeographic affinities, dominated notably by brachiopods (32 species) and gastropods (30+ species).