DEVELOPMENT OF MODERN AND HOLOCENE LACUSTRINE MICROBIALITES FROM A CANADIAN GREAT PLAINS LAKE

The Canadian Great Plains region contains many saline lakes that precipitate endogenic carbonates. However, studies of carbonate lacustrine microbialites from the region are scarce. West Reflex Lake is an alkaline, hypersaline lake on the Alberta-Saskatchewan border in the Canadian Great Plains. A decrease in water level over the past several decades has exposed carbonate microbialites along the lake’s shore. West Reflex Lake is located 22 km from Manito Lake, the only other lake in the region with microbialites that have been studied in detail. Despite the proximity of the lakes, their chemistries are very different. Thin section petrography, epifluorescence, cathodoluminescence, and scanning electron microscopy were used to describe the fabrics and textures in the microbialites and interpret the processes involved in their deposition.

Thrombolitic and stromatolitic microbialites occur in West Reflex Lake. The thrombolites occur as isolated structures or large bioherms and are associated with sites of groundwater inflow. The stromatolites occur on hard substrates, such as cobbles and thrombolites. The thrombolitic microbialites have a porous framework of clotted micrite and micrite-coated filaments. Fibrous and botryoidal aragonite and calcite cements are deposited on the other components. The stromatolitic microbialites are composed of alternating couplets of micrite and microspar with fenestral porosity.

Biologically-induced calcification alternates with inorganic precipitation in the formation of the carbonates. The thrombolites form as a result of groundwater percolating through the porous structures, while the stromatolites form as result of the development of microbial mats on the exterior surface. Investigation of the properties of these carbonate microbialites will improve our understanding of the processes of formation of lacustrine microbialites in the Canadian Great Plains region.