The Karabastau Formation () is a geological formation and lagerstätte in the Karatau Mountains of southern Kazakhstan whose strata date to the Middle to Late Jurassic. It is an important locality for insect fossils that has been studied since the early 20th century, alongside the rarer remains of vertebrates, including pterosaurs, salamanders, lizards and crocodiles. Lithology and depositional environment The primary lithology consists of 1 mm thick varve laminations of claystone, with a dark part and a light dolomitic part, which probably correspond to a wet and dry season respectively, alongside rare, several cm thick sandstone interbeds. These were deposited within an ancient freshwater paleolake, that given the number of laminations has been suggested to have existed for over 150,000 years. The top of the formation shows the laminations becoming wavy, likely as a result of microbial interactions, and the top of the formation is capped by a conglomerate predominantly composed of black Carboniferous limestone pebbles. History of discovery The Karabastau Formation was first discovered in 1921 by Soviet geologists, and was declared a protected paleontological reserve in 1924. Paleofauna Vertebrates Invertebrates Hundreds of species of insects are known from several localities within the formation, primarily Karatau-Mikhailovka Flora See also List of pterosaur-bearing stratigraphic units List of fossiliferous stratigraphic units in Kazakhstan References Geologic formations of Kazakhstan Jurassic System of Asia Jurassic Kazakhstan Kimmeridgian Stage Oxfordian Stage Shale formations Dolomite formations Lacustrine deposits Lagerstätten Fossiliferous stratigraphic units of Asia Paleontology in Kazakhstan