Figure 4
From: Biogenically induced bedded chert formation in the alkaline palaeo-lake of the Green River Formation
Schematic illustrations of the mechanism of lacustrine chert formation in the Green River Formation. (a) Abundant algal organic spheres were initially deposited within dolomite-rich sediments in the shallow and highly alkaline lake rich in dissolved Si. Subsequently, the algal organic spheres were decomposed and the pH of pore water in the sediment around the organic spheres became acidic. (b) The decreased pH of the pore waters would then cause the abundant dissolved silica to precipitate around the decomposed organic spheres.
