UNLOCKING THE LATE PALEOZOIC SUBTROPICAL DEPOSITIONAL REALM: ENVIRONMENTAL TRANSITION IN EARLY PERMIAN CARBONATES OF THE CANADIAN ARCTIC

The Sverdrup Basin, a late Paleozoic rift in the Canadian Arctic Archipelago, hosts early-Carboniferous to Permian age rocks that change with time from Carboniferous photozoan limestones and evaporites to Permian heterozoan carbonates and siliceous spiculites. Carboniferous rocks have typical tropical attributes, with numerous and diverse colonial corals, calcareous green algae, fusulinid foraminifers, ooids, and synsedimentary marine cements. The late-Sakmarian to early-Kungurian transition from warm to cool-water is recorded by the Raanes (RF) and Great Bear Cape (GBC) formations. The change in water temperature in the Sverdrup Basin was not, however, unidirectional, but was complicated by concomitant changes in sea-level and oceanography. Initial cooling is recorded in mid to outer ramp argillaceous sediments of the RF, wherein large colonial rugose corals remained, but other photozoan components were replaced by brachiopods, bryozoans, and crinoids. Overlying GBC limestones are mainly mid to inner-ramp rocks dominated by heterozoan facies rich in crinoids and lacking colonial rugosans. A return to warmer-water conditions is recorded in the middle to upper GBC, and marked by the return of large colonial corals and large benthic foraminifers (fusulinids). The return to inferred warmer-water conditions was, however, brief, and in upper GBC, all warm-water components had permanently disappeared, and the entire neritic setting, even the shallowest environments, had become cool-water. The change in biota in the RF and GBC is accompanied by the appearance of glauconite implying increased trophic resources, and the disappearance of abiotic calcareous precipitates. Middle to late Permian time units post-dating the RF-GBC system are entirely heterozoan with siliceous spiculites becoming progressively more important with time. The biota of these late Paleozoic transitional rocks is strikingly similar to modern and Cenozoic subtropical carbonate sediments, confirming the supposition that transitional facies across the spectrum of water temperatures should be identifiable in Phanerozoic rocks, and more common than thus far recognized.