MORPHOLOGICAL ANALYSIS OF ALKALINE LAKE SEDIMENTS

Saline, groundwater-fed, lacustrine environments can host fine-grained carbonate sediments called “microbialites.” Offshore-Brazil “microbialite” reservoirs and reclassified lacustrine carbonate shales emphasize a need to better understand the sedimentology of “microbialite” facies. The lakes of the Sand Hills region, Nebraska, USA, are closed-basin, groundwater-fed lakes with water chemistries that vary both spatially and temporally. Numerous lakes in the region are alkaline, saline, and display signs of microbial activity. The mineralogy and morphology of sediments from alkaline lakes of the Sand Hills region were analyzed by SEM to better understand the sedimentology of saline, alkaline, groundwater-fed lakes in the context of water chemistry data. The data compile sediment morphology observations, mineralogical relationships, and observations regarding the presence of microbial forms. Key initial findings include the observation of aggregates of carbonate and clay minerals at the micron scale, and the intermixing of biological material such as photosynthetic algae among the sediments. Further work is needed to classify sediment textures and the role of microorganisms in mineral formation in “microbialite” facies deposits.