The Madygen Formation (Russian: Madygen Svita) is a Middle–Late Triassic (Ladinian–Carnian) geologic formation and lagerstätte in the Batken and Osh Regions of western Kyrgyzstan, with minor outcrops in neighboring Tajikistan and Uzbekistan. The conglomerates, sandstones and mudstones of the 560 m (1,840 ft) thick formation were deposited in terrestrial lacustrine, alluvial, fluvial and deltaic environments.

The formation, extending across the Fergana Valley and Fergana Range, is unique for Central Asia, as it represents one of the few known continental deposits and the Madygen Formation is renowned for the preservation of more than 20,000 fossil insects, making it one of the richest Triassic lagerstätten in the world. Other vertebrate fossils as fish, amphibians, reptiles and synapsids have been recovered from the formation too, as well as minor fossil flora.

The lake sediments of the Lagerstätte provided fossil cartilaginous fishes and their egg capsules and unusual Triassic reptiles like Sharovipteryx and Longisquama. The wide diversity of insect fossils was first discovered in the 1960s and first described by Russian paleontologist Aleksandr Sharov, with a notable example being Gigatitan.

The Madygen Formation is a 560 metres (1,840 ft) thick succession of predominantly siliciclastic rocks accumulated in a tectonically induced basin, covering parts of the Fergana Range and Fergana Valley of Kyrgyzstan with minor outcrops in Tajikistan and Uzbekistan. The Middle-Late Triassic layers rest on top of Paleozoic basement with local Permo-Triassic molasse sediments. They are likewise overlain by latest-Triassic to Early Jurassic sediments, some of which host their own arthropod faunas.

The formation consists of a wide and multicolored variety of siliciclastic rocks: mudstones, sandstones, conglomerates, fanglomerates, and rare coal layers. This diversity of sediment types reflects the a complex set of depositional environments through time and space, including alluvial fans, sandflats, swamps, back-swamp areas, and littoral to profundal lake zones. The fluvio-lacustrine deposits of the Madygen Formation belong to one of only a few occurrences of continental Triassic beds in Central Asia.

Isotope analyses of fish teeth confirm that the lakes and rivers represented by the formation were entirely freshwater and deep inland, about 600 km from the nearest coast. Though fossils can be found throughout the entire formation, the most extensive fossil deposits occur in the northern area, known as Dzaylyaucho (also spelled Dzhayloucho or Dzhailoucho), which is dominated by brown and grey claystones and mudstones. The abundance of burrows and absence of darker sediments in this area indicate that it was a well-oxygenated lacustrine environment, such as a large oxbow lake.

The environment represented by the Madygen Formation was positioned on the Cimmerian microcontinent, a slab of crust that collided with Laurasia during the Cimmerian orogeny in later Mesozoic times. This orogeny led to the disappearance of the Paleo-Tethys Ocean. The Madygen Formation was emplaced at warm temperate latitudes (34° to 40° north) in a rift basin surrounded by old, eroded mountains, the ancestral Tien Shan Mountains. The climate was likely humid and moist year-round, as drying features such as mudcracks and evaporite deposits are absent.

The formation grades from bottom to top from alluvial to fluvial into a thick succession of lacustrine mudstones, followed by an alluvial package, on top of which lacustrine, fluvial, deltaic and alluvial layers were deposited.