ABSTRACT: The terminal phase of Lake Ojibway in Northern Ontario as recorded in lacustrine sediment cores.

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Abstract

Sediment cores from multiple lakes constrain the stratigraphy of Glacial Lake Ojibway and its subsequent drainage to the Hudson Straits. North of the limit of the Cochrane ice advance there is a consistent and correlatable stratigraphy. Lacustrine sediment cores terminate on the Cochrane till. Above the till is a short series of glaciolacustrine varves (<30) that rapidly thin upsection. These varves cannot be correlated to the Lake Ojibway varve thickness time series. Above these varves is a dark gray, ice distal glaciolacustrine clay. This dark gray clay unit is characterized by numerous ice-rafted silt and clay pellets, but sedimentation rates are lower than within the varves and the flux of ice rated pellets generally decreases upsection. Low sedimentation rates resulted in the complete dissolution of calcite, and incomplete dissolution of dolomite. Ostracodes (Candona subtriangulata) occur within this unit. There is a sharp transition above the dark gray clay to a calcareous light gray clay, which is believed to reflect drainage of Lake Ojibway. Geochemically this light gray clay appears to be homogenized varved clay from lower in the section. This unit grades into post- glacial sediment, which varies depending on the site, but generally these sediments reflect a climate that was drier than modern. Dateable terrestrial macrofossils are absent in the immediate post-glacial sediments. South of the Cochrane ice limit the dark gray, ice distal clay is not conspicuous, but the overlying re-worked varves that occur during drainage are ubiquitous. The implications of this pattern are not yet fully realized.

Bibliography of Canadian Geomorphology