The Middle Triassic Guanling Formation: A Crucial Window into Marine Ecosystem Recovery after the End-Permian Mass Extinction

The profound end Permian Mass Extinction (EPME) killed 81% of marine species and led to completely collapse of marine ecosystems. The full recovery of marine life took about 8–10 Myr. The Triassic succession in the South China Block is especially important internationally because it documents a long time from the Late Permian to middle–late Triassic. The Middle Triassic Guanling Formation, which is widely distributed across eastern Yunnan and western Guizhou in southwestern China, plays a key role in understanding the recovery of marine ecosystems after the end-Permian mass extinction. Lithologically, the Guanling Formation is subdivided into two members. Member I is approximately 300 m thick and consists mainly of mudstone and argillaceous dolomite, with a volcanic ash bed (green pisolite) at its base. Member II is composed of nodular limestone, cherty limestone, micritic limestone, and dolomite bands, reaching a thickness of over 500 m in most localities. The paleoenvironments of the Guanling Formation range from tidal flats and open platforms to intraplatform basins. Notably, two fossil Lagerstätten—the Luoping biota in Yunnan and the Panxian biota in Guizhou—have been recovered from the Guanling Formation. Although both occur within the same conodont zone (the Nicoraella kockeli Zone) of Member II, the Luoping biota is slightly older than the Panxian biota. Fossils of the Luoping biota have been recovered mainly from two areas, Luoping and Luxi, both representing intraplatform basin deposits. The biota yields exceptionally preserved and diverse fossils, including marine reptiles, fishes, arthropods, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts, foraminifers, and plants. Of particular significance are the 15 species of marine reptiles, 33 species of fishes, and 15 species of arthropods, making the Luoping biota one of the most diverse Triassic marine fossil Lagerstätten. The Luoping biota is considered a classic example of full marine ecosystem recovery after the end-Permian mass extinction. It demonstrates that a mature, typical Mesozoic marine ecosystem had already become established by the Anisian substage of the Middle Triassic, approximately 8 million years after the EPME. Further investigation of the Luoping biota and the Guanling Formation will shed new light on the recovery and radiation of Triassic life in the aftermath of the end-Permian mass extinction.