Paper No. 302-1
Presentation Time: 8:00 AM
BENTHIC FORAMINIFERAL MORPHOGROUP RESPONSE TO PALEO-REDOX CONDITIONS ACROSS THE CONIACIAN TO SANTONIAN “OAE 3” INTERVAL IN THE KANGUK FORMATION, CANADIAN ARCTIC ARCHIPELAGO
The Upper Cretaceous Kanguk Formation, comprising of mainly shales and siltstones deposited in the Sverdrup Basin, was investigated at two localities on Ellesmere Island, Arctic Canada. Faunal assemblages were compared to chemostratigraphic, lithologic, and geochemical records to demonstrate a response to spatial and temporal changes in the paleoenvironmental conditions. At each study site, major and trace element geochemistry was predominantly influenced by sediment source proximity and diagenetic processes and allows for the distinction of two informal members. Correlation of chemostratigraphy to a low-latitude composite curve revealed Late Cretaceous global transgressive-regressive cycles in the Kanguk Formation, which correspond to changes of morphogroup assemblages and diversity of benthic foraminifera. Within the Coniacian to Santonian interval, infaunal species tolerant of lower oxygen conditions dominate the assemblage during transgressive phases. Continued oxygen depletion, due to increased primary production and elevated organic matter flux to the seafloor, caused the expansion of the oxygen minimum zone (OMZ) in the mid-Coniacian highstand interval and a shift to predominantly small, dysoxia-tolerant taxa of the Trochammina genus. Regressive intervals brought back oxygenated conditions to the benthos and assemblages became more diverse. Elevated molybdenum concentrations during the Coniacian were only recorded in the more proximal locality studied, supporting the case for OMZ expansion and local dysoxia in portions of the basin. A positive carbon isotope excursion is associated with a highstand interval at the Santonian to Campanian boundary, but low Mo values at all study sites suggest that the benthos was oxygenated. The highstand interval with elevated organic matter flux and local dysoxia in the Coniacian to Santonian recorded in this study corresponds to the “OAE 3” interval recognized within the Western Interior Sea and Atlantic Ocean. Therefore, the Canadian Arctic portion of the Polar Sea may have also contributed to the continued CO2 drawdown and cooling after the Cenomanian/Turonian temperature maximum.