The Origin of Lacustrine Carbonates and Microbialites in Lake Basins
Accumulation and distribution of lacustrine carbonates and microbialites in tectonic basins must be assessed according to controls on input of calcium-rich waters within lake systems, including surface water, groundwater, and precipitation. Controls on input of calcium ions into a lake environment are dependent on volume of carbonate bedrock (surface and subsurface) in relation to the lake body along with hydrology (dependent on tectonics and climate) that determines the mode of water input. Water input controls the distribution of all carbonates within a lake system. Carbonate lakes can be classified as dominantly, partially, or sparsely carbonate-rich. Dominantly carbonate lakes have more than 60-70% carbonate source rocks in the drainage area so that a complete array of carbonate facies occurs from littoral to profundal environments. Examples include the Eocene Shulu Sag deposits (Hebei Province, China), the Eocene Green River Formation (Wyoming, USA), the Las Hoyas Lake in the Serrania de Cuenca basin in central Spain, and the Cretaceous Apache Canyon Formation (Bisbee Basin, USA). Lakes associated with catchment areas containing both siliciclastic and carbonate bedrock (perhaps 40-60% carbonate) contain carbonate facies limited to groundwater or surface input areas, such as the Shoofly oolitic delta of a Pliocene lake in Idaho (USA) or littoral lacustrine facies of the deep water phase of the Miocene Horse Camp Formation (Nevada, USA). If the carbonate provenance is limited relative to the volume of siliciclastic rocks in the drainage area, then carbonates accumulate in less significant quantities, as in fine carbonate laminae in profundal regions. Significant accumulation of bioherms in all these lake types is the result of large quantities of Ca-rich groundwater entering a lake environment, dependent upon subsurface carbonate aquifers.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013