Paleoecology of an exceptionally preserved arthropod fauna from lake deposits of the Miocene Barstow Formation, southern California, USA

A unique aquatic arthropod Konservat Lagerstatte occurs in Lacustrine-deriv ed carbonate concretions within the Miocene Barstow Formation, of southern California. Faunal elements are primarily aquatic, salinity-tolerant, autoc hthonous predaceous diving beetle larvae, fly Larvae and pupae, mosquito an d thrip larvae, and fairy shrimp. Three-dimensional preservation of soft ti ssues is via replacement by silica-based minerals as well as calcite, celes tite, apatite, and gypsum. The fauna occurs in three beds (each 1-3 m thick) within an approximately 1 00 m sequence of predominantly microlaminated mudstone deposited in a salin e-alkaline lacustrine environment. Faunal composition is consistent between sites and concretion beds, but faunal composition and diversity changed si gnificantly during lake history, corresponding to differences in brine chem istry as well as preservational facies, resulting from the shift toward a m ore nearshore regime. The changes in lake chemistry and subsequent changes in fauna indicate lake shallowing as well as regional and global climate ch ange towards greater aridity during the Miocene that also is coincident wit h regional uplift.