Abstract In contrast to the Triassic–Jurassic boundary, there is no consensus on the definition and age of the Norian–Rhaetian boundary (NRB), which hampers the global correlation of Rhaetian strata and thus interpretation of the patterns and driving mechanism of the end-Triassic mass extinction. Recent works show that a significant negative carbon isotope excursion (N-CIE) occurs in the NRB interval ( c. 205.7 Ma), which probably provides a physical marker for the NRB. However, no such records have so far been reported from high-latitude continental deposits. Here we present high-resolution bulk organic carbon isotope data from the Upper Triassic continuous lacustrine-to-fluvial deposits in the Haojiagou section of the high-latitude continental Junggar Basin in northwestern China. A significant N-CIE is shown at an age of c. 205 Ma, which is most probably the expression of the NRB N-CIE in the Junggar Basin owing to their very close occurrence times. The NRB is thus probably along the N-CIE in the Haojiagou section, and a short Rhaetian stage is then supported. The Late Triassic climate in the high-latitude Junggar Basin was consistent with the global changes in climate, characterized by a long-sustained cooler and humid climate interrupted by the late Norian and latest Rhaetian warm events.

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 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.

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 Rift basins are complex features defined by several large-scale structural components including faulted margins, the border faults of the faulted margins, the uplifted flanks of the faulted margins, hinged margins, deep troughs, surrounding platforms, and large-scale transfer zones. Moderate- to small-scale structures also develop within rift basins. These include: basement-involved and detached normal faults; strike-slip and reverse faults; and extensional fault-displacement, fault-propagation, forced, and fault-bend folds. Four factors strongly influence the structural styles of rift basins: the mechanical behavior of the prerift and synrift packages, the tectonic activity before rifting, the obliquity of rifting, and the tectonic activity after rifting. On the basis of these factors, we have defined a standard rift basin and four end-member variations. Most rift basins have attributes of the standard rift basin and/or one or more of the end-member variations. The standard rift basin is characterized by moderately to steeply dipping basement-involved normal faults that strike roughly perpendicular to the direction of maximum extension. Type 1 rift basins, with salt or thick shale in the prerift and/or synrift packages, are characterized by extensional forced folds above basement-involved normal faults and detached normal faults with associated fault-bend folds. In Type 2 rift basins, contractional activity before rifting produced low-angle thrust faults in the prerift strata and/or crystalline basement. The reactivation of these contractional structures during rifting created the low-angle normal faults characteristic of Type 2 rift basins. In Type 3 rift basins, preexisting zones of weakness in the prerift strata and/or crystalline basement strike obliquely to the direction of maximum extension, leading to oblique rifting. Type 3 rift basins are characterized by faults with strike-slip, normal, and oblique-slip displacement and with multiple trends. Contractional activity followed rifting in Type 4 rift basins. These inverted rift basins are affected by late-formed contractional structures including normal faults reactivated with reverse displacement, newly formed reverse faults, and contractional fault-bend and fault-propagation folds. Structures within rift basins affect depositional patterns by creating sites of uplift and erosion, by controlling pathways of sediment transport, and by defining the accommodation space for sediment deposition and preservation. The relationships among basin capacity (structurally controlled), sediment supply, and water supply determine the primary depositional regime in nonmarine rift basins, fluvial or lacustrine. Changes in basin capacity resulting from the growth of a rift basin may yield a tripartite stratigraphy (fluvial, deep lacustrine, and shallow lacustrine-fluvial) common to many nonmarine rift basins.

Abstract The Newark Basin Coring Project (NBCP) has recovered over 6730 m of continuous core from 7 coring sites. Cores spanning the 4800 m of Lockatong and Passaic formations are characterized by cyclic lacustrine mudstone and shale, which reflect rise and fall of lake level in response to climatic fluctuations at intervals of 20,000 years and larger patterns of 100,000- and 400,000-year intervals. Sedimentary structures in the mudstones include: 1. Organic-rich laminites with thin, flat, continuous lamination; thick lamination with diffuse or irregular boundaries; silty or sandy laminae; or crystal-rich lamination. 2. Mudcracked, thin-bedded mudstone with lenticular sandstone layers; graded sandstone layers; mudstone layers with sharp contacts; muddy siltstone curls; or crystal-rich layers. 3. Massive mudstones with angular breccia fabric; vesicular fabric; rounded breccia fabric; root-disrupted fabric; or crystal-rich fabrics. These structures define five types of cycles: 1. Cycles dominated by thick, organic-rich laminites deposited in deep lakes and rounded breccias, reflecting deflated, salt-encrusted mudflats. 2. Cycles similar to the previous, but with more thin-bedded mudstone and massive mudstone with upward-fining crystal sequences reflecting saline mudflats. 3. Cycles with mudcracked thin beds grading to brecciated mudstone, then vesicular fabric reflecting shallow lakes drying up to dry playa mudflats. 4. Cycles similar to the previous, but with more organic-rich laminites or thin beds and root-disrupted mudstone at top, indicating wetter conditions and vegetation growth before lake transgressions. 5. Cycles dominated by root-disrupted mudstone and thin, organic-poor laminites or thin beds reflecting thick soils superimposed on shallow lake deposits. The abundance of each cycle type changes through the stratigraphic section, reflecting the change from arid conditions in a narrow basin upward to semi-arid to subhumid conditions in a broad basin. The use of climatic patterns and tectonic setting can provide important information toward modeling source and reservoir rocks in rift basin lacustrine deposits.