Using ostracodes and sediments in paleolagoons behind the Upper Campbell Beach of glacial Lake Agassiz to reconstruct its history during the Emerson Phase

Abstract

Four small lakes, modern remnants of Upper Campbell level backbeach lagoons (each separated by several tens of kilometers), were investigated to (1) obtain radiocarbon dates that constrain the age of the Upper Campbell beach, (2) provide a stratigraphic record of sedimentation from Lake Agassiz through the Holocene, and (3) provide paleohydrological insight--by using ostracodes--into conditions (e.g. water depth and temperature) in the lagoon during its periodic connection to Lake Agassiz, and through time thereafter. The main sites studied include Brokepipe Lake (near Dauphin, Manitoba), Ruby Lake (near Hudson Bay, Saskatchewan), Jay Jay Lake (southeast of La Ronge, Saskatchewan), and Gregory Lake (northwest of La Ronge, Saskatchewan). Because the Gregory Lake site is located northwest of an area where correlation of the Upper and Lower Campbell beaches is questionable, a regional analysis was undertaken of high resolution Global Positioning System beach elevations and isobases. The interpretation of the Gregory lake site is presented from two perspectives; one that the site is located behind the Upper Campbell beach and the other that the site is located behind the Lower Campbell beach. Unfortunately, only Brokenpipe Lake provided a relatively continuous record of sedimentation and ostracodes from its inception in Lake Agassiz to the present. Ostracodes such as Cyclocyris ampla, Cypridopsis vidua, Candona ohioensis, and C. rawsoni in the lower clayey-silt and silty-clay in the Brokenpipe core suggest that the lagoon was separated (though certainly periodic beach overwash was common) from the main body of Lake Agassiz, where species like Candona subtriangulata occur. (Abstract shortened by UMI.)