Distribution of an Arctic Ostracod Fauna in Space and Time

Abstract

A fossil locality on the Pembina Upland, in southern Manitoba (L. D. Delorme, Geological Association of Canada, Special Paper9, 301–304, 1971), contains three ostracod species near the base of the deposit. Two of these ostracods, Candona rectangulata and Cyclocypris globosa, are found alive only in the northern parts of the Northwest and Yukon territories of Canada. Both species are indicative of subarctic forest tundra and alpine tundra. Their position in the lower 69 cm of the deposit indicates that, as the glacier ice thinned over the upland and retreated from the Lake Agassiz basin, an arctic-subarctic environment could have existed with the potential for tundra vegetation to develop. A reverse situation occurred in the Northwest Territories based on seven fossil ostracod species from a peaty marl deposit. As reported by L. D. Delorme, S. C. Zoltai, and L. L. Kalas. (Canadian Journal of Earth Science14, 2029–2046, 1977) for other similar sites, the striking element is the absence of true arctic ostracods. The majority of the species live very successfully further south in Manitoba and Saskatchewan at present. At both sites, the fossil assemblage is different than the modern assemblage. This indicates a dislocation in space and time which is the basis for the change in paleoenvironmental interpretation.