Publications Related to this Project
Many questions remain regarding the formation and diagenesis of lacustrine carbonate reservoirs, such as those in Angola and offshore Brazil (e.g. Wright, 2012). Using alkaline, saline lake environments as natural, modern analogues for carbonate reservoir systems, we can investigate processes impacting carbonate sedimentation and interactions with siliciclastic inputs. In this project, we are characterizing microbe:water:rock interactions in the Alkaline Lakes of Sand Hills, Nebraska, to better understand how variations in climate, groundwater input, and microbial activity impact carbonate and silicate mineral equilibria in this highly alkaline system.
Current lacustrine carbonate facies models do not account for complexities in microbialite carbonate sedimentation (e.g. Wright, 2012). Therefore, elucidating the formation of lacustrine carbonates in alkaline, saline environments—especially those with siliciclastic inputs—is important for understanding the interplay between carbonate and silicate mineral phases that control diagenetic products in microbialite reservoirs.
The Nebraska Sand Hills are a region of grass-stabilized dunes located in western Nebraska, in which microbialites form in part due to highly concentrated fluids. Lakes occur in interdunal areas where the water table intersects the land surface. Groundwater provides the majority of solutes to these lakes, and evaporation is the primary control on lake chemistry. The geochemistry of the Alkaline Lakes is compositionally diverse, with a wide range of Total Dissolved Solids (0.2 g/L to 384 g/L, e.g. Gosselin et al. 1994, Gosselin 1997), varying salinity (e.g. Gosselin et al. 1994, Gosselin 1997), and pH values typically between 9 and 10.
This study serves to characterize the physical environment of saline, alkaline lakes in the Sand Hills of western Nebraska, laying groundwork for further investigating the formation of lacustrine carbonates and associated silicate minerals in similar environments. We have generated preliminary data analyzing sediment mineralogy and morphology, geomicrobiological observations, and water chemistry. These data suggest that carbonate and silicate mineral equilibria are decoupled. Carbonate minerals remain supersaturated, while dilution driven by climatic variation significantly impacts silicate equilibria from season-to-season and from year-to-year depending on the amount of precipitation.
Collaborators: Randy Stotler, University of Kansas, Adam Yoerg, University of Kansas; Gwen Macpherson, University of Kansas; Shaun Frape, University of Waterloo