Abstract The Triassic Songpan-Ganzi Complex (SGC) of central china is one of the world’s largest ancient turbidite systems, containing a thick succession of Anisian through Norian (∼240-210 Ma) turbidites. Geotectonically, the Songpan-Ganzi complex is situated at the juncture of several tectonic blocks: North china, Qiadam, South china, and North Tibet (i.e., Qiangtang; Figure 1 ). Songpan-Ganzi basin closure and inversion occurred during early Jurassic time and was later intruded and locally metamorphosed by Jurassic to Cretaceous plutons. Few studies document the nature of these turbidites due to the limited nature of outcrop exposures, steep topography, steep dip angles (70-90°) associated with isoclinal folds, and thick vegetation. A stratigraphic framework has recently been established for the Songpan-Ganzi terrane based on field mapping, lithology, and fossils. The fossils are sufficiently abundant to permit stage-level age assignments and correlation throughout much of the SGC basin (Figure 2). The succession of Middle to Upper Triassic turbidites within the Songpan-Ganzi complex is an estimated >10 km (>6 mi) thick, locally reaching a thickness of 15 km (9 mi), and cover a triangular area >200,000 km 2 (77,000 mi 2 ), an area about the size of the U.S. state of Colorado.

Abstract The Songpan–Garzê terrane is the largest Triassic remnant flysch basin on Earth and formed as the Palaeo-Tethys Ocean closed during the final amalgamation of the Pangaea supercontinent. However, the origin of the Songpan–Garzê terrane is highly controversial. A synthesis of the tectonic evolution of the Palaeo-Tethys Ocean and its branches surrounding the Songpan–Garzê terrane is presented, which clarifies the nature and relationships among the many Palaeo-Tethys sutures. Provenance analyses suggest that branches of the Palaeo-Tethys near the Songpan–Garzê terrane closed before the Early Triassic. In contrast, the main Palaeo-Tethys Ocean (Longmu Co-Shuanghu) did not close until the beginning of the Late Triassic. This study argues against the Songpan–Garzê terrane being a remnant ocean basin, and proposes that it was a back-arc basin of the main Palaeo-Tethys Ocean. It initially underwent extension by the combined effects of the main Palaeo-Tethys Ocean subduction and the Emeishan mantle plume in the Late Permian, and subsequently developed into a back-arc basin in the Triassic, into which huge turbiditie units were deposited derived from all surrounding terranes and orogens. The final closure of the main Palaeo-Tethys Ocean in the beginning of the Late Triassic and subsequent continent–continent collision led to basin inversion in the Late Triassic.

Abstract China presently comprises several independent tectonic palaeoplates or terranes and parts of other blocks, which have been assembled over geological time. In the Ordovician, these blocks included South China, North China, Tarim, Qaidam, Junggar, Qiangtang-Qamdo, Lhasa and partially Himalaya, Sibumasu and Indochina, as well as the Altay-Xing'an and Songpan-Garze fold belts, which were discrete but near-adjacent. Twelve stratigraphic megaregions bounded by tectonic sutures or major fault zones can be recognized. Some of them are further differentiated into several regions according to the lithological and biotic facies or distinct stratigraphic sequences. Here, the palaeontologic features and biostratigraphic framework of these stratigraphic megaregions and regions are summarized. The unified biostratigraphic framework presented herein is supported by 33 graptolite biozones and 27 conodont biozones, together with supplementary biozones, communities or associations of brachiopods, trilobites, cephalopods, chitinozoans, acritarchs and radiolarians. With constraints of integrative chronostratigraphy, biostratigraphy, chemostratigraphy, cyclostratigraphy and magnetostratigraphy, along with some geochronologic data, our understanding of the temporal and spatial distribution of the Ordovician lithostratigraphic units on these major blocks has been significantly advanced. Vast amounts of new data accumulated in recent decades also constrain the major Ordovician geological and biotic events evident in China, such as marine anoxia, faunal turnovers and tectonic orogenies.