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Hybrid carbonates, defined as the combinations of in situ abiotic, microbial, and skeletal precipitates, have changed with the biological and environmental conditions throughout geological history. After a long interval of dual-hybrid carbonates, the triple hybrid carbonates became predominant in the late Pennsylvanian and lasted until the Middle Triassic. The organic reefs of the upper Moscovian–Kasimovian (mid–late Pennsylvanian) strata of Guizhou, South China, are composed of abundant microbial carbonates, abiotic marine cements, and skeletal organisms, which are classified as triple hybrid carbonates. Microbial boundstones consisting of aragonitic cements (e.g., botryoidal cements) and microbial micrite are the major contributors to the reefs, as framework constructors, cavity fillers, and hard substrate for the encrusting metazoans. Skeletal components (e.g., the colonial rugose coral Ivanovia) and stromatolitic microbial carbonates could build simple frameworks with the growth cavities filled by syndepositional marine cements, automicrite, and carbonate particulate sediments. In situ phylloid algae normally form patch reefs and biostromes with abundant microbial micrite and peloids, while algal fragments contribute to the skeletal–cement–microbial reefs as large grains encrusted by microbial carbonates or marine cements. Petrographic features suggest the reefs formed at a shelf margin or upper slope setting with active water circulation. The evolution of Carboniferous organic buildups was primarily driven by changes in reef-building organisms, closely linked to external conditions, specifically seawater chemistry and paleoclimate. The ubiquitous triple hybrid carbonates in South China reefs, in agreement with Pennsylvanian tropical shallow-water reefs in their components, are proposed to derive from the interaction between decreasing atmospheric CO2 concentration, high seawater Mg2+/Ca2+ ratio, warm tropical water, and the evolution of skeletal organisms in the Pennsylvanian. [ABSTRACT FROM AUTHOR]

The late Early Jurassic (Toarcian) terrestrial succession exposed in the Tianshifu Basin, eastern Liaoning Province, northeastern China, was examined for palynomorphs. This sequence is part of the upper Changliangzi Formation and is mainly composed of shale and siltstone intercalated with several sandstone layers. The palynoflora in the upper part of the Changliangzi Formation is dominated by pteridophyte spores (average of 64.01%) and gymnosperm pollen grains (average of 34.99%), while the bryophyte spores are less than 1%. The dominant component of this palynoflora alternates between pteridophyte spores and gymnosperm pollen. The vegetation reconstructed from the palynoflora mainly comprises lowland ferns and cycads/ginkgophytes accompanied by upland conifers in low amounts, which is similar to the macroflora components of the Changliangzi Formation. The composition and evolution of this palynoflora indicates that eastern Liaoning was dominated by hot and subhumid climatic conditions with several warm and moderately humid intervals during the late Early Jurassic (Toarcian). Compared to the lower part of the Changliangzi Formation with coal-bearing strata, which is characterised by a rather moist climate, the upper part of this formation might represent a drier climate, although the inferred difference in temperature is small. Although there are several records of warming and drought in some inland regions in northern China during that time, which might be associated with the famous global geological event called the Toarcian oceanic anoxic event, most areas in northern China were dominated by a hot/warm and moist climate, especially in the eastern coastal region. The warm and wet flows from the Proto-Pacific Ocean may be responsible for this hot and humid climate. [ABSTRACT FROM AUTHOR]

Bioconstructions (five biostromes, one patch reef, and one large reef) of the colonial coral Fomichevella are well exposed, if infrequent, in the Upper Pennsylvanian-lower Permian of the Houchang area (southern Guizhou, China). Though they are primarily built by the same species, different growth morphologies and internal constructions are evident, which indicate different factors controlling their formation and development. The coral biostromes alternate with shoal deposits, being attributed to level-bottom communities that were closest to the reef ecosystem. The patch reef consists of a simple coral framework and a low biodiversity community. In contrast, rigid skeletal frameworks of Fomichevella are common and the biodiversity of the community is relatively higher in the large coral reef. Comparing these coral biostromes, the patch reef, and the large coral reef, several factors controlling their formation and development are suggested: stable substrate, water turbulence, sea-level fluctuation, and community structure. Hard substrates can provide stable habitats for the coral larvae during the initial colonisation stage, while the frequently changing sedimentary conditions were not conducive to the healthy development of Fomichevella. The simple community (e.g. the biostromes, patch reef) lacking encrusters and binders was too fragile to tolerate a turbulent environment. In Houchang, though intrinsic and extrinsic factors influenced the development of the Fomichevella bioconstructions, the extrinsic factors seem more important, which may be the key aspects controlling the Carboniferous coral bioconstructions. [ABSTRACT FROM AUTHOR]

The genesis of dolomite is an intensively debated and extensively studied problem in the field of carbonate sedimentology. This study focuses on the dolomite of the Dapu Formation in the Guixinan area, with the aim of deciphering the mechanism of dolomitization in the Dapu Formation. Three types of sedimentary environment, including the open marine of inner ramp, the restricted marine of inner ramp, and the shoal of inner ramp, have been identified. Three types of dolostone (DI, DII and DIII) identified in the study area with massive structure had close relationship with fault structures, and contacted with limestone in curved diffuse way on the outcrop. Both of the above points indicated diagenetic dolomite. Three types of dolomite (D1, D2 and D3) displayed similar dark—light purple red luminescence, indicating that the characteristics of their diagenetic fluids were similar. The planar-s to nonplanar dolomite crystals indicated that the temperature was more than 50 °C. The mineral assemblage including D2, D3, and silicate minerals (feldspar, tremolite and actinolite) suggested contact metamorphism and tht the diagenetic fluid was rich in silicon and magnesium. The dolomitization process was not influenced by the leaching of meteoric water in surface or shallow buried environment and hydrothermal fluids, based on the corrected REE characteristics. The range of the δ18O of dolostone samples showed that the burial dolomitization had taken place in high-temperature environment. The lower 87Sr/86Sr ratio of the dolostone samples than the coeval seawater meant that the diagenetic fluid was derived from the alteration of mid-ocean ridge basalt. Based on the geologic setting, it was speculated that the burial dolomitization was driven by the hydro-tectonic processes in the passive margin burial diagenesis hydrologic realm. In brief, magnesium came from the low-temperature alteration of ocean basalts, the thermohaline and compactional flow supplied hydrodynamic condition, and the synsedimentary fault zones-supplied channels. [ABSTRACT FROM AUTHOR]

The beginning of the Late Paleozoic Ice Age was characterized by localized events with small ice depocenters occurring in South America and a series of cyclic shallow-water limestones in far-field regions, in late Visean to Serpukhovian. This paper documents two topmost Visean–Serpukhovian sections in Guangxi, South China: a stromatolite-bearing deep-water succession in Helv village and a shallow-water succession in Dujie village. Seventeen microfacies types have been recognized and grouped into six microfacies associations. The vertical evolution of the microfacies associations from deep-water to shallow-water depositional environments in both sections indicate a major relative sea-level fall in the latest Visean. The repetitive successions comprising different morphological stromatolites in Helv section and the cyclic alternation of subtidal and peritidal facies in Dujie section imply high-frequency sea-level fluctuations during latest Visean to Serpukhovian, most likely eustatic in origin. The carbon isotope data of Dujie limestone exhibit a pronounced positive δ13C excursion with ± 4.3‰ in the peritidal deposits. This shift is interpreted as the result of enhanced organic carbon burial in other regions and depletion of the ocean in light carbon. The widespread coeval cyclicity occurring in settings in South China, Western Europe, and North America is most likely the results of glacio-eustatic sea-level fluctuations, possibly with local influences of tectonic movements. This pattern is interpreted to represent the expression of the onset of the major glaciation during the LPIA in low-latitudinal successions. [ABSTRACT FROM AUTHOR]

Well-preserved encrusting chaetetids are widespread and easily observed in limestones of the Benxi Formation (Moscovian, Upper Carboniferous) in the Benxi area, eastern Liaoning Province, North China. Chaetetids and colonial corals were the framework-building organisms, with chaetetids as the most common fossils in several small-scale reefs of the study area. The common types of hard substrate encrusted by chaetetids include in situ carbonate hardgrounds, carbonate hardground clasts, calcareous bioclasts and coral skeletons. We have observed lamellar, low domical (mini-domal) and anastomosing lamellar chaetetid morphologies in this fauna. Chaetetids with thin, spreading lamellae are the most common growth forms. Chaetetids employed peripheral, medial and mixed growth strategies to occupy sufficient living space on the substrates. They favoured a shallow, warm and clear marine environment within the photic zone. Chaetetids were later usually smothered by sediments. The chaetetid fossil communities in the Benxi area have a relatively high species diversity, which is not typical of hard substrate marine communities in the Carboniferous. The most common spatial relationship between competing encrusters on hard substrates is the growth of one over the other in the study region. Chaetetids were superior competitors for hard substrate attachment space. This palaeoecological study of chaetetids offers a new example for encrusting organisms on hard substrates of the Carboniferous of China. This research may aid in studying other colonised substrates of the Late Carboniferous. [ABSTRACT FROM AUTHOR]

We collected, processed, identified, and analyzed the spores and pollen samples from the Zhuanchengzi Bed of the Yixian Formation in the Yingwoshan area of western Liaoning. As a result, we confirm a palynomorph assemblage of Cicatricosisporites-Protoconiferus. The pollen was primarily from gymnosperms, dominated especially by conifer pollen. Pteridophyte spores were less common and some questionable angiosperm pollen occurred occasionally. The age of the palynomorph assemblage is dated as the late Valanginian or Hauterivian-Barremian stage, the Early Cretaceous. The study applies the concept of Palynological Vegetation based on palynological spectra and the paleoecological characteristics of palynological taxa for the first time. Palynological vegetation type, climatic zone type, and humidity type are divided quantitatively for the Zhuanchengzi Bed in the Yixian Formation of western Liaoning. We then obtained the evolutionary trends. The results showed that the overall climate was warm and humid during the deposition period of the Zhuanchengzi Bed in the Yixian Formation. Palynological vegetation types are various and include coniferous forest, deciduous broadleaf forest, evergreen broad-leaved forest, grass, and shrubs. The local temperature changed from warm to much warmer and from a semi-humid to humid climate. Palynological vegetation types are always dominated by coniferous forest. The coexistence of deciduous broad-leaved forest, evergreen broad-leaved forest, shrubs, grass, and some xerophytic plants indicates vertical zonation and seasonal climate change The vertical vegetation types and the warm humid climate may imply a large geomorphological contrast in the Yixian Formation of western Liaoning. [ABSTRACT FROM AUTHOR]

A typical reef occurs in the eastern part of south Qinling Mountains in Sanlixia, Xunyang, Shaanxi Province. The reef, extending in north-south direction, was built up by various kinds of calcareous tubes including Girvanella, tubular cyanobacteria and problem microbials. The bioclastic bank, built up by algal clasts, foraminiferous, and fusulinids, formed the reef basement, on which dasyclads baffle bioclasts formed the original bafflestone at a small scale on the reef basement, and then a mass of bindstone was made up by all kinds of calcareous tubes and algae. On lateral part the reef is cryptalgal mudstone. The reef that occurred in the geosynclinal area is so familiar with one of the platforms in many respects, such as in reef structure, morphology and building mold. This indicates that building organisms have amazing adaptability and identity for building capacity in the two kinds of geotectonic background mentioned above. [ABSTRACT FROM AUTHOR]