Phanerozoic patch reefs are extensively studied because they are abundant and are potential reservoirs for valuable fluids. In contrast, geologic studies of modern reefs have largely focused on platform margins, leaving patch reefs comparatively neglected. What conditions favour patch-reef development? What is their potential as reservoirs or as coral refugia under deteriorating environmental conditions? Where other environmental conditions are favourable, the availability of lithified Holocene sediment or Pleistocene rock as substrates for coral colonization appears to control patch-reef distribution in The Bahamas. A census of patch reefs from satellite imagery of the eastern Great Bahama Bank (GBB) tallies 23 reefs/km2, for a total of 70,000 reefs over 3,000 km2. Higher resolution images of favorable areas tally up to 80 reefs/km2. Patch reefs accumulate sediment typically 3 m, and exceptionally 10 m, above the surrounding sea floor and amalgamate into complexes up to 2150 m long, illustrating their potential to form reservoirs. Patch-reef corals have adapted to conditions of elevated suspended sediment, salinity and temperature, suggesting they could provide refuge for corals as platform-margin reefs are decimated by climate change. Data on the distribution, abundance, morphology and health of patch reefs on the GBB may stimulate further research on modern patch reefs.

Carbonate platforms with automicritic boundstone slopes differ from detrital platforms in their architecture and reservoir properties. The controls on the occurrence of automicritic boundstone slopes are poorly constrained, but they have generally been associated with depleted reefs and other metazoan-algal benthic ecosystems. To test this association, we investigated automicritic boundstone occurrence across the end-Permian extinction and Triassic biotic recovery on the Xiliang slope of the Great Bank of Guizhou (GBG), an isolated carbonate platform in southern China. Our findings indicate that automicritic boundstone accumulation was not enhanced by depleted Early Triassic benthic ecosystems. Instead, detrital sediment dominated the GBG slope, and automicritic boundstone was absent until the late Spathian (latest Early Triassic), 4-5 million yr after extinction. Beginning in upper Spathian strata, automicrite forms small (<1.5 cm) and sparse (<15% estimated volume) masses in slope boundstone, coinciding with an early stage of benthic ecosystem recovery. When a metazoan-algal reef subsequently formed during more advanced recovery in the middle Anisian (lower Middle Triassic), automicrite occurrences were more abundant (up to 40% estimated volume) and larger (up to similar to 10 cm). The proportions of automicrite and metazoan-algal fossils within samples are also positively correlated (Spearman's r = 0.70; P < 0.0001). Our findings suggest that the controls on slope automicrite accumulation and metazoan- algal benthic ecosystems are similar or that benthic metazoans and algae enhance, rather than inhibit, automicrite accumulation. Our results imply that concept-driven predictions of automicritic boundstone occurrence should be modified-automicritic slopes are not more likely to occur during geologic intervals with depleted benthic ecosystems.

The sedimentary parameters that are most important in modeling sedimentary sequences and geometry are accumulation rate, lag time, and accommodation space. Each parameter incorporates several other variables. Accumulation rate is the net result of sediment input and in situ production (for carbonates) less export through bypass or erosion. The appropriate accumulation rate to be chosen from the vast amount of data available will depend on depositional environment, basinal asymmetry, climate, tectonic setting, and the time increment being modeled. Lag time expresses the necessary condition for a transgressive sequence: that the initial sediment accumulation rate is less than the rate of submergence or accommodation. Mechanisms are not well understood; the potential for sediment production in shallow-water carbonate environments, for example, generally exceeds known rates of submergence. Biologic factors may reduce sediment production rates in shallow water, but a physical threshold, such as the wave base, above which accumulation is suppressed, seems more probable. Accommodation space is the increment of room available for sediment accumulation as determined by eustasy, subsidence, and erosion. Subsidence, in turn, incorporates tectonism, isostasy, and physical and chemical compaction. Lag time, compaction rates induced by pressure solution, and the interaction of siliciclastics and carbonates are probably the least constrained variables.

The Yangtze carbonate platform (Southern China) recorded a long sedimentary evolution from Neoproterozoic to the basal Upper Triassic. During the Early and Middle Triassic, this platform was dominated by shallow-water carbonates. In various sectors of the platform, the Middle Triassic (Anisian-Ladinian) succession contain abundant assemblages of benthic foraminifera and calcareous algae. Following a previous paper about the Middle Triassic dasycladalean algae from SW Guizhou Province, the present study describes algae and microproblematic organisms from three sections: Honyan, Longtou and Guanling. Some dasycladalean algae are well known from the Alpine-Dinaric domain: Diplopora annulatissima, D. annulata, Euteutloporella triasina, Macroporella dinarica, Oligoporella minutula, O. pilosa pilosa, Poncetella hexaster and Pseudodiplopora proba. However, the dasycladalean association is dominated by species belonging to the genus Kantia, including K. cf. dolomitica and K. cf. comelicana. New Kantia species (K. intusannulata n. sp., K. granieri n. sp., K. muxinanii n. sp.) are characterized by the presence of intusannulation, a feature unknown from the Kantia species in the Alpine domain. The dasycladalean association also contains new species of the genus Mizzia and specimens belonging to the organo-genus Acicularia and/or Terquemella. Besides, rare specimens of "Solenopora" and Rivularia-type cyanobacteria are also present. The algal association is accompanied by microproblematic organisms including Tubiphytes sp., Zorniella obscura, Plexoramea cerebriformis, Ladinella porata, and Baccanella floriformis. Anisian-Ladinian foraminifera complete the micropaleontological spectrum of the sections studied. The most important are Meandrospira dinarica, Endotriadella wirzi, Paleolituonella meridionalis, and Turriglomina mesotriasica. The microfossils from the Middle Triassic Yangtze carbonate platform of south China belong to the Eastern Tethys province. Some of these species are also present in the Western Tethys (Alpine Domain). The new species presented in this study are absent from the Alpine Domain and probably represent endemic species for the Eastern Tethys.

The Great Bank of Guizhou (GBG) is a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of southern China. The GBG is exposed in cross-section by exhumation and erosion along a syncline, providing an essentially continuous record of platform initiation, development and drowning across platform to basin palaeoenvironments. Platform evolution spanned the Palaeozoic to Mesozoic transition associated with physical, chemical and biological evolution of marine environments and ecosystems, including the end-Permian extinction and Triassic biotic recovery. Consequently, the GBG records the influence of late Palaeozoic to early Mesozoic carbonate factory evolution on the stratigraphic architecture of an isolated carbonate platform, facilitating examination of the close relationship among ocean environments, marine ecosystems and carbonate depositional systems.

Lofer cyclothems of the Alpine Upper Triassic have many features in common with Holocene sediments of Florida Bay. The modal ‘complete’ Lofer cycle is essentially symmetrical, having a deepening and shoaling phase, as does the cycle‐in‐progress in Florida Bay. Lateral discontinuity and thickness variations within members of the Lofer cyclothems indicate syn‐depositional relief, possibly in the form of mud banks, the signature feature of Florida Bay sedimentation. Spatial and temporal dimensions, although poorly constrained, appear comparable. Analogous depositional textures, biota and sedimentary structures, while not unique to either environment, strengthen the inferences that can be made about the Triassic depositional environment and regarding future evolution of the modern environment. The striking similarities between the Holocene icehouse sediments and the Late Triassic greenhouse deposits suggest that sedimentation patterns at the scale of individual cycles or parasequences may be largely independent of the global climate regime.

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.

The Triassic Dachstein platform limestone at Steinernes Meer, Salzburg, Austria, includes 611 m of limestone with 222 peritidal cycles overlain by 273 m of subtidal, non‐cyclic and weakly cyclic limestone. Cycle patterns include both shoaling and deepening upward, symmetrical, truncated, and couplets without a depth vector. Beds are laterally discontinuous, and cycle bounding surfaces are laterally variable in the studied strata. Of 558 subtidal and intertidal beds measured, 121 (21.7%) disappear laterally. An additional 73 beds (13.1%) show significant (>10%) lateral variations in thickness. Mean thickness variation is 49%. Both lateral variations and terminations appear to lack a spatial vector. Disappearances toward the inferred platform interior (west) total 10% of the beds. East, toward the platform margin, 11.6% of the beds disappear. Thickness changes occur in 6.5% of beds in each direction. The lack of lateral continuity of beds precludes a simple allocyclic forcing model and is consistent with a non‐eustatic component to stratification. Erosion of intertidal intervals is the process that can be most readily documented. Non‐uniform rates of production, transport and distribution of sediments, superposed on stratigraphic sequences driven by eustasy, probably also contributed to the complex cycle patterns recorded in the Dachstein. Such composites of autocyclic and extrabasinal factors should not be uncritically interpreted as exclusive records of orbital forcing. Lateral discontinuities and thickness variations would also produce inaccuracies in spectral analysis of thickness patterns, typically conducted in search of ‘Milankovich frequencies’, as well as in construction of Fischer plots to analyse long‐period oscillations in accommodation. Any section subjected to cycle analysis should be examined for lateral changes, to the extent permitted by the exposures, in order to produce the most complete (composite) section possible.

The Late Permian to Late Triassic Great Bank of Guizhou (GBG) in southwest China is one of the few isolated carbonate platforms in the world that exposes an essentially complete record of initiation, development, and drowning across multiple platform-tobasin transects. The platform is exceptionally exposed in cross section at the surface by a faulted syncline that rotated strata to a dip angle of approximately 65 degrees. Platform development spanned the end-Permian extinction and Triassic recovery that marks the transition from Paleozoic to Mesozoic styles of carbonate sediment production, providing a rare opportunity to assess the impact of global changes in carbonate factory types at a single locality. In addition, regional basin controls such as differential siliciclastic sediment input and varied antecedent topography provided mechanisms for lateral variability in platform morphology that can be investigated along exposures in several geographic sectors. Consequently, the GBG preserves a record of temporal and spatial variability in platform architecture that offers an unparalleled opportunity to investigate the controls on isolated carbonate platform morphology. A better understanding of these mechanisms is critical for improving predictive geologic models in exploration and field-development settings. The GBG also serves as a key outcrop analog for Early Triassic oolite reservoirs in the Middle East and China, the steep microbialboundstone slopes of Carboniferous platforms in Kazakhstan, and the Permian platforms of Texas and New Mexico.

Abstract The long-lived Yangtze platform (YP) drowned abruptly and was buried by pelagic facies and siliciclastic turbidites in western Guizhou Province during the Late Triassic (Carnian). The uppermost carbonate platform facies are peritidal cyclic limestone and dolostone containing a restricted biota and having fenestral laminate caps. Equivalent margin facies consist of intraclastic, grapestone, oolitic grainstone, and lenses of coral-Tubiphytes algal boundstone indicating high-energy shoals and patch reefs. The drowning horizon is a laterally variable sharp surface or gradational shift to dark, nodular-bedded, pelagic lime mudstone to wackestone. The contact lacks hardgrounds, phosphatized, or glauconitic surfaces that would indicate drowning by excess nutrient flux. Uppermost platform carbonates have a tropical photozoan biota and lack siliciclastic content, indicating neither climate cooling nor clastic flux played a role in drowning. Rare bioturbation and benthic biota in the lower part of the drowning interval indicate dysaerobic conditions with an upward shift to anoxic conditions. Syndepositional faults had a significant impact on the evolution of the western sector of the Yangtze platform and controlled three local accommodation cycles. Faults developed during the last accommodation cycle tip out at the drowning horizon and include a flower structure upon which a pinnacle reef developed as the rest of the platform drowned. Lateral variability in the drowning horizon and thickness of the post-drowning pelagic facies point to differential tectonic subsidence causing sinking of the platform into deep water along faults. Magnetic susceptibility and paleomagnetic reversal correlation demonstrates that the western sector of the platform drowned while shallow marine mixed carbonate-siliciclastic sedimentation continued in the eastern sector to be terminated later in shallow water by increasing rates of clastic flux. Starved black shale horizons in the basin indicate persistent water stratification and bottom water anoxia; elevated trace metal concentrations indicate dysaerobic to anoxic conditions and enhanced preservation of organic matter. Tectonic subsidence likely submerged the western sector into deep, toxic waters of the stratified basin causing the killing of benthic marine carbonate production.

Abstract Comparative analysis of platform evolution recorded along multiple 2D platform-to-basin transects of the Triassic Yangtze carbonate shelf and several isolated platforms in the Triassic Nanpanjiang basin, south China, indicates that laterally variable tectonic subsidence, rate of basinal clastic deposition at the toe of slope, antecedent topography, and changes of carbonate factory type controlled the evolution, large-scale sequence stratigraphic architecture, and geometry of the platform margin and slope. Lateral and temporal changes in these parameters, and their various combinations during the Middle and early Late Triassic, were responsible for the remarkable vertical and along-strike variability in the observed platform architecture and slope profile. Timing and rates of subsidence largely controlled along-strike variability, timing of drowning, back-step geometries, and pinnacle development. Antecedent topography and timing of clastic basin fill dictated differences in platform-margin stability and geometries such as slope angle, relief above basin floor, development of collapse scars, and progradation at basin margins. Changes in slope profile through the Early and Middle Triassic reflect changes in carbonate-factory type and evolving seawater chemistry following the end-Permian extinction. Eustasy, in contrast, had very little influence on platform morphology and large-scale architecture. Process-based depositional models derived from the Nanpanjiang basin of south China present an important analog for understanding, quantifying, and predicting facies distribution and architectural styles at the basin scale in other systems, particularly in areas of active tectonism and temporal variations in oceanic conditions, such as, for example, the prolific Tertiary carbonates reservoir province of southeast Asia.

Under favorable conditions sedimentary structures may be preserved in high-grade metamorphic rocks to yield valuable clues about the depositional and paleogeographic setting of the protolith. Two examples from gneisses of the Greater Himalayan Sequence of Bhutan demonstrate this potential. Laminated, channeled dolostone within gneiss of upper amphibolite facies indicates tidal-flat deposition and thus proximity of a paleoshoreline. The type Takhtsang Gneiss, within granulite facies, consists of alternating millimeter bands rich in quartz and biotite, interpreted as silt and clay interlaminations, respectively, in the protolith, typical of tidal deposits or varves. The gneissic banding drapes around isolated “lenses” of contrasting and varied compositions, interpreted as dropstones. This combination suggests deposition in a varved glacial lake. Published comparisons of Takhtsang lithologies indicate a minimum dimension of 315 km for the postulated lake. These examples demonstrate the potential of relict sedimentary features in reconstructing geologic history, even in high-grade metamorphic terrains.

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. 34m, 9m and 1.8mcycles, which are consistent with the ratios of orbital-climate oscillations caused by long-eccentricity (405kyr), short-eccentricity (~100kyr) and precession (20kyr). The magnetostratigraphy of all sections is consistent with the cyclicity and characteristic SGR features, thereby enabling a cycle-tuned magnetic polarity scale spanning ~2.4myr. 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.

The chronostratigraphy of Guandao section has served as the foundation for numerous studies of the end-Permian extinction and biotic recovery in south China. Guandao section is continuous from the Permian-Triassic boundary to the Upper Triassic.Conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows. Changhsingian-Griesbachian: first Hindeodus parvus, and first appearance of foraminifers Postcladella kalhori and Earlandia sp. Griesbachian-Dienerian: first Neospathodus dieneri, and last appearance of foraminifer P. grandis. Dienerian-Smithian: first Novispathodus waageni and late Dienerian first appearance of foraminifer Hoyenella ex gr. sinensis. Smithian-Spathian: first Nv? crassatus and last appearance of foraminifers Arenovidalina n. sp. and Glomospirella cf. vulgaris. Spathian-Aegean: first Chiosella timorensis and first appearance of foraminifer Meandrospira dinarica. Aegean-Bithynian: first Nicoraella germanica and first appearance of foraminifer Pilammina densa. Bithynian-Pelsonian: after last NeogondolelIa regalis, prior to first Paragondolella bulgarica and first appearance of foraminifer Aulotortus eotriasicus. Pelsonian-Illyrian: first Pg. excelsa and last appearance of foraminifers Meandrospira? deformata and Pilamminella grandis. Illyrian-Fassanian: first Budurovignathus truempyi, and first appearance of foraminifers Abriolina mediterranea and Paleolituonella meridionalis. Fassanian-Longobardian: first By. mungoensis and last appearance of foraminifer A. mediterranea. Longobardian-C ordevolian: first Quadralella polygnathiformis and last appearance of foraminifers Turriglomina mesotriasica and Endotriadella wirzi.The section contains primary magnetic signature with frequent reversals occurring around the Permian-Triassic, Olenekian-Anisian, and Anisian-Ladinian boundaries. Predominantly normal polarity occurs in the lower Smithian, Bithynian, and Longobardian-Cordevolian. Predominantly reversed polarity occurs in the upper Griesbachian, Induan-Olenekian, Pelsonian and lower Illyrian. Reversals match well with the GPTS. Large amplitude carbon isotope excursions, attaining values as low as -2.9 parts per thousand delta C-13 and high as +5.7 parts per thousand delta C-13, characterize the Lower Triassic and basal Anisian. Values stabilize around +2 parts per thousand delta C-13 through the Anisian to Carnian. Similar signatures have been reported globally. Magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the Lower Triassic and an overall decline in magnitude of fluctuation through the Middle and Upper Triassic. The largest spikes in magnetic susceptibility and gamma ray, indicating greater terrestrial lithogenic flux, correspond to positive delta C-13 excursions. High precision U-Pb analysis of zircons from volcanic ash beds provide a robust age of 247.28 +/- 0.12 Ma for the Olenekian-Anisian boundary at Guandao and an age of 251.985 +/- 0.097 Ma for the Permian-Triassic boundary at Taiping. Together, the new U-Pb geochronology from the Guandao and Taiping sections suggest an estimated duration of 4.71 +/- 0.15 Ma for the Early Triassic Epoch. (C) 2015 Elsevier Ltd. All rights reserved.

The Nanpanjiang Basin occurs in a key position for resolving controversies of basin tectonics and patterns of plate assembly at the junction between south China and Southeast Asian plates. Paleocurrent measurements indicate that siliciclastic turbidites in the basin were sourced by the Precambrian Jiangnan uplift to the northeast, the Precambrian Yunkai uplift to the southeast and the Triassic Songma suture to the south. Detrital zircon geochronology reveals Archean (2500 Ma), Paleoproterozoic (1800-1900 Ma), Neoproterozoic (900-1000 Ma) and Paleozoic (420-460 Ma) ages consistent with derivation from the Jiangnan and Yunkai uplifts. A large Permian-Triassic peak of 250 Ma is present in the southern basin and attenuates northward suggesting derivation from an arc developed along the Songma suture. Sandstone QFL compositions average 65/12/23% and plot in the recycled orogen field except for a few samples in the southern basin that fall in the dissected arc field. The compositions are consistent with derivation from Precambrian basement that includes orogenic complexes. In the southern basin, Middle Triassic turbidites contain greater lithics and feldspars and Lower Triassic turbidites have volcaniclastic composition consistent with derivation from a southerly arc. Our preferred interpretation is evolution from remnant basin to a large peripheral foreland with southward subduction and convergence with Indochina along the Songma suture. The previously proposed Dian-Qiong zone is not a suture as its map location places it within carbonate platforms bounded by identical stratigraphy. The Nan-Uttaradit zone is too distant to have provided voluminous siliciclastic flux to the basin. The Nanpanjiang Basin provides an example of the evolution of an exceptionally large foreland with far-field rejuvenation of Precambrian uplifts and carbonate platforms that were significantly influenced by siliciclastic flux. The timing and pattern of turbidite basin fill impacted platform evolution by enabling margin progradation in areas proximal to siliciclastic sources, whereas platforms distant from sources were driven to aggradation and extreme relief with large-scale gravitational sector collapse.

The Yangtze Platform drowned and was buried by pelagic facies and siliciclastic turbidites in western Guizhou Province during the Late Triassic, Carnian. The uppermost platform facies of the Ladinian Yangliujing Fm. consists of peritidal cyclic carbonate. Ladinian margin facies of the Longtou Fm. consist of grainstone and lenses of coral-Tubiphytes algal boundstone indicating high-energy shoals and patch reefs. The drowning horizon is laterally variable; it is either a sharp surface or a gradational shift to dark, nodular-bedded lime mudstone and wackestone of the Zhuganpo Fm. The contact lacks phosphatized or glauconitized hardgrounds that would indicate drowning by excess nutrient flux. Uppermost platform carbonates have a tropical photozoan biota and lack siliciclastic content indicating neither climate cooling nor siliciclastic flux played a role in drowning. The Zhuganpo Fm. contains a dominantly pelagic biota of ammonoids, planktonic bivalves, pseudoplanktonic crinoids, conodonts, and the marine reptile Keichousaurus. Rare bioturbation and benthic biota in the lower part indicate dysoxic conditions with an upward shift to anoxic conditions. The overlying Wayao Fm. is a pyritic, laminated, black argillaceous lime mudstone that grades to black shale with an exclusively pelagic fauna and marine reptile lagerstattes indicating anoxic deep-marine sedimentation.Syndepositional faults played a significant role in the evolution of the western sector of the Yangtze Platform and controlled three local, backstepped accommodation cycles in the Zhenfeng area. Faults that developed during the last accommodation cycle tip out at the drowning horizon and include a flower structure upon which a pinnacle reef developed while the rest of the platform drowned. Lateral variability in the drowning horizon and thickness of the post-drowning pelagic facies suggest that differential tectonic subsidence caused the platform to sink into deep water along faults.Magnetic susceptibility and paleomagnetic-reversal correlations demonstrate that the western sector of the platform drowned while shallow-marine, mixed carbonate siliciclastic sedimentation continued in the eastern sector which later terminated in shallow water by increasing siliciclastic flux. Starved black shale horizons in the basin indicate recurrent bottom-water anoxia. Elevated trace-metal concentrations in the pelagic facies of the Zhuganpo and Wayao formations indicate dysoxic to anoxic conditions and enhanced preservation of organic matter. Tectonic subsidence likely submerged the western sector into deep, toxic waters of the basin, killing benthic carbonate production.Previous studies have implicated the Carnian pluvial event as a cause of drowning of the Yangtze Platform and the shift to siliciclastic turbidites of the Laishike Fm., but the Yangtze Platform drowned earlier than western Tethys platforms and siliciclastics were already rapidly infilling the basin in the Anisian and Ladinian, indicating that the events are probably unrelated. Siliciclastics of the Laishike Fm. that overlapped and buried the platform only after the basin was filled are better interpreted as a response to tectonics than to a shift in climate.