FAUNAL TURNOVER AND CHANGING OCEANOGRAPHY: LATE PALEOZOIC WARM-TO-COOL WATER CARBONATES, SVERDRUP BASIN, CANADIAN ARCTIC ARCHIPELAGO

The carbonate succession in the Sverdrup Basin contains a record of changing paleoceanography and faunal turnover. The composition of the biotas, their biogeography and nutrient levels, provide the means to determine changes in regional oceanic circulation through the late Paleozoic.

Carboniferous and earliest Permian inner ramp carbonates are a photozoan association of colonial corals, fusulinids, algae and ooids, with sparse heterozoan elements that based on modern analogues reflect warm-water oligotrophic marine environments. Warm, nutrient poor, waters were sourced from the tropical Paleo-Tethys Ocean to the east. Contemporaneous mid-ramp and basin heterozoan biotas (solitary corals, crinoids, bryozoans and brachiopods) reflect cooler deeper waters, perhaps below a thermocline.

The first phase of cooling began in the early Artinskian. Along with the northward drift of Pangea, the Arctic-Russian link to the Paleo-Tethys Ocean was closed and warm shallow Arctic waters were supplemented by cool waters derived from the Panthalassa Ocean to the west. The resultant sub-tropical marine biota was heterozoan (crinoids, bryozoans, brachiopods and sponges) with photozoan elements (fusulinids and colonial corals) in inner ramp facies. This mixed photozoan-heterozoan biota, along with slightly elevated trophic resources, produced the greatest faunal diversity seen in the Sverdrup Basin succession.

During the Kungurian, the final transition to cool-water saw a wholly heterozoan biota (brachiopods, bryozoans, crinoids and sponges) with no remaining photozoan elements. Nutrient levels were elevated as indicated by phosphate and glauconite, numerous infaunal foraminifers, and a diverse shelly biota, that during times of high siliciclastic input was replaced by a profuse Zoophycos infauna.

Through the Middle Permian, continued cooling and increased nutrients (abundant glauconite and phosphate) resulted in an abundant heterozoan biota of reduced diversity and local gigantism. The faunas are part of the cool-water boreal Arctic-Uralian province, open only to the Panthalassa Ocean. The succession ends with Late Permian biosiliceous spiculitic cherts containing accessory heterozoan components (brachiopods, bryozoans and few crinoids) of low diversity.