Mineralogy, lithostratigraphy and geochemistry of North Ingebright Lake, Saskatchewan, Canada
North Ingebright Lake, containing Canada's thickest known Holocene terrestrial salt sequence, is a small (1.25 km2), hypersaline playa basin located in the Great Sand Hills area of southwestern Saskatchewan. Because of its remarkably thick lacustrine sedimentary fill, the basin offers considerable potential for providing a high resolution record of past environmental changes in a region that has few other sources of Holocene paleoenvironmental information. Until recently, efforts to acquire cores of this thick sequence of well-indurated but very soluble salt have been unsuccessful using conventional coring techniques. However, exceptional sediment recovery was achieved using a compressed-air diamond drilling technique that permitted collection of continuous, large-diameter, undisturbed and chemically unaltered cores. The 10,000 year long lacustrine sequence recovered from the basin consists of well-indurated salt, with only minor dispersed mud and organic debris. Indeed, the section is remarkable in its lack of obvious bedding, colour variation or other visible sedimentary structures. The mineral suite of these Holocene salts consists mainly of hydrated Na, Mg, Ca, and Mg+Na sulfates, carbonates, and chlorides. Minor amounts of nitrate evaporitic minerals also occur. This long uninterrupted sequence of soluble salts implies that the lake was characterized by high salinity throughout its Holocene history. However, variations in the mineralogy of the salts suggest that the basin experienced significant changes in brine composition. These evaporites, which allow a detailed reconstruction of specific ion activities and ratios in the brine through time, provide our evidence of the complexity of brine evolution in a closed-basin lacustrine environment in western Canada.