PALYNOLOGY AND AGE OF POST-ERUPTIVE LAKE SEDIMENTS FROM THE WOMBAT KIMBERLITE LOCALITY, NORTHWEST TERRITORIES, CANADA

An exploration drill-core containing over 140 m of laminated mudstone was retrieved from the Wombat kimberlite pipe in the Lac de Gras region of the Slave Province, N.W.T., Canada. The crater lake formed after kimberlite emplacement following phreatomagmatic volcanism, and represents one of many kimberlite pipes emplaced regionally between the late Cretaceous and late Oligocene. The age of the Wombat post-eruptive sequence, however, has been elusive to date. Abundant terrestrial palynomorphs from the Wombat core provide useful preliminary age constraints. Results from lower and upper Wombat lacustrine facies indicate two distinct palynological assemblages. The lower assemblage includes seven types of angiosperm pollen, eight types of gymnosperm pollen, and one type of spore. Important angiosperm pollen include Momipites coryloides, Momipites tenuipolus, Triporopollenites bituitus, Fraxinoipollenites variabilis and Caryapollenites imparalis. The upper assemblage is significantly more diverse, including 14 types of angiosperm pollen, 10 types of gymnosperm pollen, and nine types of spores. Important angiosperm pollen include Ericaceiopollenites sp. and Alnipollenites sp., Caryapollenites veripites, Betulaceoipollenites sp., and Plicatopollis triradiatus. The absence of late Cretaceous index taxa Aquilapollenites and Wodehouseia suggests the sediments are younger than Maastrichtian, whereas the occurrence of Ericaceiopollenites and Alnipollenites, coupled with the absence of the Eocene indicator Platycarya, lead us to conclude that a Paleocene age is most likely for the Wombat post-eruptive sequence.