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Sector‐collapse structures ranging up to 27 km wide with up to 7.7 km bankward erosion (scalloped margins) and linear escarpments occur along the east‐north‐east‐trending, south‐facing margins of the Yangtze Platform and Great Bank of Guizhou. Exposure of one of the structures on the rotated limb of a syncline displays the geometry in profile view. Declivities range from 65° to 90° in the upper wall and decrease asymptotically to the toe. Catastrophic collapses of the margins in both platforms occurred during the late Ladinian as constrained by the ages of strata truncated along the margins and the siliciclastic turbidites that onlap collapse structures. Middle Triassic Anisian and Ladinian platform‐edge reef facies and platform‐interior facies were truncated along both the Yangtze and Great Bank of Guizhou margins. Lower Triassic facies were also truncated along the Great Bank of Guizhou margin. Gravity transport during the main episodes of collapse occurred as mud‐rich debris‐flows and as mud‐free hyper‐concentrated flows. Clasts, several to tens of metres and, exceptionally, hundreds of metres across, were transported to the basin. Following collapse, talus, carbonate turbidites and periplatform‐mud accumulated at the toe of slope. Shedding of skeletal grains and carbonate mud indicates active carbonate factories at the margin. Preserved sections of the margins demonstrate that the platforms evolved high‐relief, accretionary escarpments prior to collapse. High‐relief, without buttressing by basin‐filling sediments, predisposed the margins to collapse by development of tensile strain and fracturing within the margin due to the lack of confining stress. The linear geometry of margins and active tectonics in the region supports tectonic activity triggering the collapse. Collapse is thus interpreted to have been triggered by fault movement and seismic shock. Comparison with other systems indicates that evolution from high‐relief accretion to tectonic collapse of largely lithified margins resulted in large sector‐collapse structures and deposition of a coarse, generally mud‐poor breccia apron. [ABSTRACT FROM AUTHOR]

Thrombolite and stromatolite habitats are becoming increasingly recognized as important refuges for invertebrates during Phanerozoic Oceanic Anoxic Events (OAEs); it is posited that oxygenic photosynthesis by cyanobacteria in these microbialites provided a refuge from anoxic conditions (i.e., the "microbialite refuge" hypothesis). Here, we test this hypothesis by investigating the distribution of ~34, 500 benthic invertebrate fossils found in ~100 samples from a microbialite succession that developed following the latest Permian mass extinction event on the Great Bank of Guizhou (South China), representing microbial (stromatolites and thrombolites) and non‐microbial facies. The stromatolites were the least taxonomically diverse facies, and the thrombolites also recorded significantly lower diversities when compared to the non‐microbial facies. Based on the distribution and ornamentation of the bioclasts within the thrombolites and stromatolites, the bioclasts are inferred to have been transported and concentrated in the non‐microbial fabrics, that is, cavities around the microbial framework. Therefore, many of the identified metazoans from the post‐extinction microbialites are not observed to have been living within a microbial mat. Furthermore, the lifestyle of many of the taxa identified from the microbialites was not suited for, or even amenable to, life within a benthic microbial mat. The high diversity of oxygen‐dependent metazoans in the non‐microbial facies on the Great Bank of Guizhou, and inferences from geochemical records, suggests that the microbialites and benthic communities developed in oxygenated environments, which disproves that the microbes were the source of the oxygenation. Instead, we posit that microbialite successions represent a taphonomic window for exceptional preservation of the biota, similar to a Konzentrat‐Lagerstätte, which has allowed for diverse fossil assemblages to be preserved during intervals of poor preservation. [ABSTRACT FROM AUTHOR]

Small-scale synsedimentary folds in the Eagle Ford Formation in southwest Texas formed during deposition in a shallow epicratonic basin on the North American craton. These folds formed by slumping (i.e., gravity-driven deformation) and are characterized by (i) plastic deformation of limestone beds, (ii) discontinuous bedding and thickness changes of limestone beds, (iii) horizontal compactional fabric at high angle to folded bedding, (iv) low-angle or recumbent axial surfaces, and (v) erosion of slumped intervals and/or onlapping by resumed sedimentation. Exposures of the Eagle Ford near the northwest margin of the Maverick Basin reveal slump folds in 1–2 m thick zones with observed lateral extents of 10's to 100's of meters to >1 km – actual extents are likely much larger. Curvilinear fold hinges changing trend by >90° over short distances, indicating markedly non-cylindrical fold geometries. Bed thickness changes reflect flowage of unlithified sediment during slumping, and subsequent compaction. Previous descriptions of slump folds in the Eagle Ford Formation have focused on examples from the hydrodynamic facies of the basal portion, but slump folds are also present in pelagic facies of the upper Eagle Ford. Slump folding locally represents significant shortening (e.g., 50%) and thickening (e.g., 100%) of slumped intervals, with up-dip absence of the same interval represented by missing section, bed terminations, boudinage, and/or extensional faulting. Repeated slumping can result in significant cumulative updip thinning and downdip thickening along depositional slopes. Our experience working unconventional reservoirs in a variety of North American epicratonic basins indicates that slump folding is common and underrepresented in the literature. Criteria for recognizing slumping in the subsurface include a combination of discontinuous and contorted beds, thickening into fold hinges, compactional fabric postdating folds, and inverted or repeated section. Natural fracture networks may be less regular than in similar but flat-lying beds. Occurrence of slump folded intervals adds complexity and unpredictability to unconventional reservoirs, with implications for reservoir quality, drilling, and optimal stimulation during completion. • Synsedimentary slump folding is under-recognized in epicratonic basins, and influences unconventional reservoirs. • Slump folds in outcrops of the Eagle Ford Formation occur in both hydrodynamic and pelagic facies. • Slump folds are dominated by plastic deformation, even in layers that later became competent and brittle. • Compaction resulted in vertical thinning and locally an axial planar fabric in recumbent folds. • Outcrop fracture networks in slumped intervals are less regular than in similar but flat-lying beds. [ABSTRACT FROM AUTHOR]

Thick successions from the margins of the Triassic Yangtze Platform of the South China Block record a transition from carbonate-rich facies (Zhuganpo Formation and equivalents) to clastic-rich facies (Xiaowa Formation and equivalents) during the Carnian (early Late Triassic) that mark the final phase of termination of this long-lived platform. Cyclostratigraphy derived from spectral gamma-ray (SGR) intensity curves was combined with magnetostratigraphy of two sections in Guizhou Province (Wayao transect and its upward extension into the Geopark Wayao in Guanling county and the Laishike section in Zhenfeng county) and one location in Sichuan Province (Hanwang section). The cyclostratigraphy from all the Guizhou sections indicates a persistent suite of ca. 34 m, 9 m and 1.8 m cycles, which are consistent with the ratios of orbital-climate oscillations caused by long-eccentricity (405 kyr), short-eccentricity (~ 100 kyr) and precession (20 kyr). The magnetostratigraphy of all sections is consistent with the cyclicity and characteristic SGR features, thereby enabling a cycle-tuned magnetic polarity scale spanning ~ 2.4 myr. The main feature is a 1.3-myr interval of reversed polarity containing brief normal-polarity subchrons, and this reversed-polarity chron appears to correspond to the significant reversed-polarity-dominated interval spanning the upper half of the Trachyceras aonoides through the lower half of the Austrotrachyceras austriacum ammonoid zones of the upper Julian (the lower substage of Carnian). This magnetostratigraphic correlation implies that the termination of the Yangtze Platform is coeval with the beginning of the mid-Carnian episode of climatic disruption in Europe, which is locally called the “Carnian Pluvial Event” or “Wet Intermezzo”, and with the temporary cessation of the platform carbonates in the Dolomites. The cycle-scaled magnetic-polarity time scale supports the “Short-Tuvalian/Long-Norian” age model of the Late Triassic in which the base of the cycle-tuned polarity pattern from the Newark Group of eastern North America is younger than the end of the Julian substage. [ABSTRACT FROM AUTHOR]