Lithostratigraphy and recent sedimentation history of Little Manitou Lake,Saskatchewan, Canada

Little Manitou Lake is a topographically closed, hypersaline lake that occupies a long, linear glacial meltwater channel in the northern Great Plains of western Canada. Most of the modern and late Holocene sediment in the lake has been generated from within the basin itself, either by endogenic inorganic precipitation or by other authigenic processes. These endogenic and authigenic precipitates, composed of mainly very soluble sulfate salts and sparingly soluble carbonates, provide an explicit record of the past chemical and hydrological fluctuations that have occurred in the lake. Although detailed chronostratigraphy is incomplete, preliminary¹⁴C dating indicates an age of about 2000 years for the oldest sediment recovered from the basin.Five subsurface sedimentary facies are identified in offshore cores. From the base these are: (i) structureless, gray clay, (ii) gypsiferous mud, (iii) structureless, organic-rich mud, (iv) finely laminated aragonitic mud, and (v) Na and Mg sulfate salts. The lithostratigraphy and variation in the mineralogical composition of the sediment indicate that Little Manitou Lake experienced significant water level changes and compositional fluctuations during the past several millennia. The basal clays indicate a relatively deep, freshwater lake existed about 2000 years ago, but was soon followed by a period of low water/playa sedimentation and a negative hydrological budget in the basin. Water levels gradually increased after about 1500 years ago in response to a cooler and wetter climate. This resulted in development of a meromictic, saline to hypersaline lake characterized by periodic carbonate (aragonite) whitings. Water levels again decreased about 1000 years ago, resulting in a breakdown of meromixis and initiation of subaqueous evaporitic salt precipitation. Although the brine in Little Manitou Lake has fluctuated between Na-SO₄ and Mg-Na-SO₄ -Cl types during the past 1000 years, water levels and overall salinities have remained relatively constant.Palliser Triangle Global Change Contribution No. 16.