Late Cretaceous (Cenomanian to Campanian) Dinoflagellate Cyst Assemblages and Palaeoproductivity Signals from the Kanguk Formation, Sverdrup Basin, Nunavut, Canada

Abstract

The response of the polar sea to Cretaceous carbon perturbations is poorly understood and palaeotemperature data from the Arctic are limited. To help understand high latitude palaeoceanographic dynamics, sediment samples containing dinoflagellate cysts (dinocyst) assemblages were collected from a composite Cenomanian to Campanian section from the Bastion Ridge and Kanguk formations within the Sverdrup Basin at Glacier Fiord, Axel Heiberg Island, and at Slidre Fiord, Ellesmere Island. Dinocyst assemblages were compared to recent carbon isotope and benthic foraminiferal age data taken from the same lithographic section.These multiproxy correlations allowed for a more constrained placement of dinocyst biozones, palaeoenvironmental changes, planktic/benthic coupling, and indicate that local age ranges for several Late Cretaceous dinocyst taxa need regional revision within the Sverdrup Basin. At Glacier Fiord a change from a restricted marine to an open marine setting before the Cenomanian/Turonian boundary and a polar expression of the globally recognized OAE 2 is revealed through a turnover in dinocyst and acritarch assemblages, an increase in relative abundance of angiosperm and bisaccate pollen, and an increase in amounts of gelified, dark amorphous organic matter derived from microbial degraded terrestrial material. At Slidre Fiord, depositional settings transition from open marine to deltaic; recognized by an overall increasing sporomorph index trend. Taxa-specific dinocyst peaks are recognized in the Coniacian (Chatangiella sp.), late Santonian (Heterosphaeridium difficile) and middle Campanian (Manumiella sp.). The Coniacian Chatangiella acme is a correlative event across the CanadianArctic that likely contributed to an increased organic matter supply, causing dysoxic to anoxic benthic redox conditions, which resulted in an increase in the benthic foraminifera iii Trochammina. Correlations between δ 13 Corg, peridiniod dinoflagellate cysts occurrences and cooling global sea-surface temperatures, calculated from the tropical Atlantic, indicate an increase in palaeoproductivity during a Coniacian to Campanian cooling trend. Multiproxy correlations allow for accurate dinocyst first and last occurrences dates, which resulted in newly proposed biozonations for the Sverdrup Basin. In ascending order, these include the Cenomanian to Turonian Surculosphaeridium longifurcatum Zone, Coniacian to Santonian Chatangiella ditissima Zone and the Upper Santonian to Middle Campanian Arvalidinium scheii Zone. These will aid future regional pan-Arctic biostratigraphic event correlations and studies of paleobiogeographic pattern.iv