Stanwell-Fletcher Lake lies in a post-Cretaceous graben on the east side of the Boothia Arch, Somerset Island, Northwest Territories. The lake site was formed by glacial excavation of a down-faulted block of relatively soft Cretaceous (?) rocks, and the history of the area can be traced through three stages as post-Pleistocene uplift progressed; marine, estuarine, and the present lacustrine stage. The last stage is believed to have commenced approximately 5,000 years ago.

Since that time, the saline water formerly occupying the lake site has been completely replaced by fresh water, largely through circulation during the estuarine stage. The lack of chemical stratification and the isothermal character of the lake indicate efficient circulation and hence oxygenation of the water in spite of the year-round ice-cover.

In general the bottom sediments of Stanwell-Fletcher Lake are unlaminated, fine-grained deposits oxidized to a reddish-brown colour at the surface. Poor sorting and positive skewness are the rule even in the seasonally ice-free, windagitated margins. Silt and mud predominate in the central portions of the lake, whereas the marginal areas are generally sandy. The distinctness of these two groupings of sediments is attributed to differing modes of transport and deposition, namely, bottom traction and seasonal deposition of the sand as opposed to slow, year-round settling out of the mud. Surface organic carbon averages 2.3%, and total carbonates less than 1%. The appearance downward in the cores of apparently detrital dolomite and in situ foraminiferal test is accompanied by an increase in mean grain size. The higher energy estuarine phase is believed to have been operative at that time.

The cold climate retards chemical weathering and limits the duration of sediment transport by streams. The rate of sedimentation in the lake is therefore low and sorting is poor because the ice-cover minimizes winnowing by wave activity. Chemical and biological processes in the water are inhibited by the low temperatures with the result that autochthonous sediments such as organic matter and precipitated carbonates (marls) are insignificant in the deposits. As chemical breakdown of clay-producing minerals is minimal, the clay minerals present were mechanically derived from source rocks in the area.

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