An early Maastrichtian organic-walled phytoplankton cyst assemblage from an organic-rich black mud in Core Fl-533, Alpha Ridge: evidence for upwelling conditions in the Cretaceous Arctic Ocean

Abstract

A diverse assemblage of acritarchs, prasinophytes and dinoflagellate cysts occurs in an organic rich black mud in Core Fl-533, taken from the Alpha Ridge, Arctic Ocean. Similarities between this assemblage and others described from the Canadian Arctic allow this black mud to be dated as early Maastrichtian, based primarily on the presence of Cerodinium leptodermum, and the absence of exclusively Campanian and upper Maastrichtian taxa. The high abundance of Comasphaeridium and marine derived amorphous organic matter may indicate a shelf to upper slope environment, possibly deposited during a marine transgression. An abundance of prasinophyte algal cysts, a moderately high peridinioid/gonyaulacoid dinoflagellate cyst ratio, and high species diversity indicate high paleoproductivity, most likely associated with upwelling conditions. When interpreted within the context of two nearby biosiliceous-rich Maastrichtian cores also taken from Alpha Ridge, and from paleogeographic reconstructions, these results indicate that an upwelling region probably existed along the eastern Arctic Ocean during at least part of the Maastrichtian, and formed different sedimentary facies in shelf to slope environments, similar to facies patterns recognized in lower latitude paleo-upwelling regions.