Late Cretaceous ecosystem dynamics in the southern incipient Arctic Ocean: A micropaleontological and geochemical perspective

Micropaleontological and geochemical analyses in samples from the Coniacian-Maastrichtian-aged Smoking Hills and Mason River formations in the Anderson Basin of the northern mainland coast of Arctic Canada provide a refined picture of the environmental conditions occurring in the incipient southern Arctic Ocean at the end of the Cretaceous. These units were deposited within a 22 myr time span in an outer shelf setting characterized by relatively stable tectonic conditions and low sedimentation rates. The Coniacian-middle Campanian Smoking Hills Formation was deposited during times of marine transgression and water column stratification. Surface waters were highly productive and dominated by dinoflagellates, red algae, green algae and likely diatoms and silicoflagellates. Bottom waters were predominantly anoxic-euxinic, but the presence of benthic foraminifera and variations of geochemical signatures in some intervals indicate episodic ventilation. The deposition of the Smoking Hills Formation is temporally consistent with the Oceanic Anoxic Event 3 (OAE3), but the duration of these anoxic conditions is much longer in the Anderson Basin. During the middle Campanian, relative sea level reached a highstand, fostering the expansion of planktic siliceous microorganisms, including diatoms, silicoflagellates and radiolarians. During the late Campanian to at least the Maastrichtian, sediments of the Mason River Formation were deposited during a regressive sedimentation phase characterized by high productivity fueled by river run-off and the proliferation of diatoms, red and green algae. Despite high productivity, bottom waters were oxygenated. This study highlights the importance of data integration to reconstruct the environmental conditions of the past as many, if not all, of the proxies utilized to this end are subjected to preservational and diagenetic bias. • Micropaleontology and geochemistry reveal Late Cretaceous Arctic Ocean conditions. • Smoking Hills Fm. shows long-term anoxia during Oceanic Anoxic Event 3 • Mason River Fm. shows high productivity, oxygenated waters, driven by river run-off • Data integration critical for reconstructing past environmental conditions.