Abstract The Junggar Basin, NW China, hosts continuous and well-exposed Late Triassic and Jurassic continental strata. Extensive coal, oil and gas deposits occur within the basin and, together with the high-palaeolatitude locality and continental records of several Mesozoic geological events, make the sedimentary successions globally important. This special publication focuses on these successions, presenting recent advances in palaeontology, geology and palaeoenvironments. The contents span various topics, including studies of fauna, flora, stratigraphy, geochemistry, palaeogeography, palaeoclimate, petroleum reservoir quality, the end-Triassic mass extinction, the Toarcian Oceanic Anoxic Event, Triassic–Jurassic seasonal freezing and true polar wander. To provide continuity throughout the various papers, where possible, bed numbers for all stratigraphic units are provided, enabling findings to be compared among studies and tested in the future. This special publication highlights that the sediments of the Junggar Basin provide important long-term records of continental life and environmental changes through the Triassic and Jurassic.

Abstract The vast, widely exposed terrestrial (lacustrine to fluvial) Upper Triassic–Jurassic (except Tithonian) successions of the Junggar Basin not only record most of the stratigraphic boundaries of the Upper Triassic and Jurassic, including the Triassic–Jurassic boundary and the Hettangian–Sinemurian, Sinemurian–Pliensbachian, Pliensbachian–Toarcian, Lower–Middle Jurassic, Middle–Upper Jurassic and Oxfordian–Kimmeridgian boundaries, but also record a range of geological, organic, palaeogeographic and palaeoclimatic events known to have happened globally in the Late Triassic and Jurassic. The Triassic–Jurassic boundary is placed in the stratigraphic interval of the first occurrence of Retitriletes austroclavatidites and Callialasporites dampieri and the last occurrence of Lunatisporites rhaeticus . The end-Triassic mass extinction is characterized by the disappearance of most of the sporomorph and macro-plant taxa. The end-Triassic mass extinction occurred before the first occurrence of the sporomorph Cerebropollenites thiergartii , and ended after its appearance when life began to revive. The Junggar Basin was situated at a high latitude during the Late Triassic–Early Jurassic Pliensbachian ‘hothouse’ and ‘greenhouse’ periods. The Late Triassic–Mid Jurassic Bajocian was humid and warm, and rich in coal swamps, except the Toarcian, which yields little coal because it was relatively warmer and drier. It became arid from the early Late Jurassic Oxfordian.

Abstract Vertebrate assemblages from the Junggar Basin in Xinjiang, China, are the only ones known from palaeo-Arctic continental strata of Late Triassic and Early Jurassic age. Here we present a preliminary description of these new assemblages, focusing on the underappreciated Arctic palaeolatitude and winter freezing of this coal-bearing sequence. Mostly collected during NIGPAS-led stratigraphic studies in the 2016–17 field seasons, new assemblages include: (1) small to large sculptured palaeonisciform cranial elements and scales, small associated palaeonisciforms, a sauropterygian tooth, large-dinosaur bioturbation and additional unidentified small vertebrate bones from the Haojiagou Formation (?upper Norian–Rhaetian); (2) a medium-sized brontozoid dinosaur footprint and a previously described possible Anomoepus track from the Badaowan Formation (Hettangian–?Pliensbachian); and (3) a hybodont shark egg case of the form taxon Palaeoxyris (only the third reported from Early Jurassic age strata of China), numerous associated and fragmentary small palaeonisciform remains (including one partial skull and several small skeletons), and another possible Anomoepus track and associated dinoturbation from the Sangonghe Formation (?Pliensbachian–Toarcian). A possible ash associated with the aforementioned lower Sangonghe fish skull has produced a laser ablation inductively coupled plasma mass spectrometry age of roughly 186 Ma, consistent with a Pliensbachian age. We are optimistic that there will be many additional discoveries from early Mesozoic age strata of the Junggar Basin, the importance of which for understanding Earth system processes cannot be overemphasized.

Abstract We show that the Late Triassic–Early Jurassic continental Arctic experienced wintertime freezing conditions, despite the exceptionally high atmospheric CO 2 levels, by quantifying common lake ice-rafted debris (L-IRD) identified in the Junggar Basin of Xinjian, NW China. This L-IRD consists of outsized (0.1–12 mm) lithic clasts ‘floating’ in otherwise fine-grained, profundal lake sediment matrix. Laser-diffraction grain-size analysis demonstrates that the grain-size distribution for lacustrine strata of Junggar Basin is very similar to modern sediments from the seasonally ice-covered Sea of Okhotsk, reflecting a similar depositional mechanism. Three-dimensional computed tomography and two-dimensional thin sections demonstrate that the outsized clasts are dispersed, rather than confined to sand lenses or layers. These results are inconsistent with alternative methods of bimodal sediment deposition such as mud flows, algae rafting or root rafting. The discovery of Triassic–Jurassic continental freezing provides new context for understanding global climate during periods with high-CO 2 conditions and climate and biotic changes in the Mesozoic Era.

Abstract The middle Mesozoic of the southern Junggar Basin is a source of abundant Late Triassic–Jurassic non-marine and Early Jurassic marine–littoral bivalves. The bivalve chronology provides a framework for dating the strata and documents Early Jurassic transgressions and the end-Triassic mass extinction in the Junggar Basin. The first occurrences (FOs) and last occurrences (LOs) of Utschamiella cf. tungussica and Utschamiella cf. obrutschevi lie in the basal upper Rhaetian. The FOs of Ferganoconcha sibirica , Ferganoconcha subcentralis , Unio manasensis , Unio mirabilis and Waagenoperna are at, and the FOs of Margaritifera isfarensis , Tutuella rotunda and Tutuella chachlovi adjoin, the base of the middle Sinemurian. The LOs of Yananoconcha hengshanensis and Waagenoperna are at the Lower–Middle Jurassic boundary. The LOs of Psilunio , Cuneopsis and F . subcentralis are near the Middle–Upper Jurassic boundary. Non-marine bivalves disappeared in the late Rhaetian, due to a sudden Norian–Rhaetian temperature drop. New forms did not return until the Sinemurian, when the climate warmed. The transgressions created low-relief terrestrial environments, in which organisms including bivalves thrived, leading to the formation of large quantities of coal, oil and gas. The Junggar Basin shifted from Arctic to subtropical latitudes in the Northern Hemisphere between the Early and Middle Jurassic.

Abstract Twenty taxa of fossil plants are described from the Sangonghe Formation (Lower Jurassic) of the Haojiagou section in the Junggar Basin, Xinjiang, NW China. The Sangonghe flora consists of Equisetales, ferns, bennettitaleans, ginkgoes, conifers and gnetales, but is dominated by ferns. It is a low-species-diversity but extraordinary flora as it has a high proportion (45%) of thermophilous or arid-tolerant (xerophilous) elements, in comparison to 0% in the underlying Badaowan Formation and c. 2% in the overlying Xishanyao Formation. These thermophilous or arid-tolerant (xerophilous) elements include Marattiopsis asiatica Kawasaki, Phlebopteris polypodioides Brongniart and Dictyophyllum sp. (ferns), Otozamites leckenbyi Harris, Otozamites sp., Zamites sp. and Dictyozamites sp. (bennettitaleans), Brachyphyllum (Hirmeriella ?) sp. (conifers) and Cadmisega ephedroides Krassilov and Bugdaeva (gnetales). Based on the geological ranges of the known species and comparisons with coeval floras in Eurasia, the age of the Sangonghe flora is Toarcian (Early Jurassic). The flora reveals a climatic warming and aridification event that occurred during the Toarcian in the Junggar Basin. Palaeontological (including palaeobotanical and palynological), sedimentological and geochemical data demonstrate that warming and aridification occurred widely across the north of China during the Toarcian, and that this might be the response of the terrestrial ecosystem to the Toarcian Oceanic Anoxic Event.

Abstract Mesozoic continental basins of northern China, including the Junggar Basin, provide some of the most spectacular and important fossil assemblages in the world, but their climatic and environmental contexts have been shrouded in uncertainty. Here we examine the main factors that determine those contexts: palaeolatitude; the effects of changing atmospheric gases on the radiative balance; and orbitally paced variations in insolation. Empirical evidence of these factors is accumulating rapidly and promises to upend many long-standing paradigms. We focus primarily on the Junggar Basin in Xinjiang, NW China, with the renowned Shishugou Biota, and the basins in Liaoning, Hebei and Inner Mongolia with their famous Jehol and Yanliao biotas. Accurate geochronology is necessary to disentangle these various factors, and we review the Late Triassic to Early Cretaceous U–Pb ages for these areas and supply a new laser ablation inductively coupled plasma mass spectrometry age for the otherwise un-dated Sangonghe Formation of Early Jurassic age. We review climate-sensitive facies patterns in North China and show that the climatic context changed synchronously in northwestern and northeastern China consistent with a previously proposed huge Late Jurassic–earliest Cretaceous true polar wander event, with all the major plates of East Asia docked with Siberia and moving together since at least the Triassic when the North China basins were at Arctic latitudes. We conclude that this true polar wander shift was responsible for the coal beds and ice-rafted debris being produced at high latitudes and the red beds and aeolian strata being deposited at low latitudes within the same basin. The climatic and taphonomic context in which the famous Shishugou, Yanliao and Jehol biotas were preserved was thus a function of true polar wander, as opposed to local tectonics or climate change.