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The Pennsylvanian is characterized by intense paleoenvironmental changes related to glacio-eustatic sea-level fluctuations and major tectonic events, which affected the evolution of biocommunities. Most known Pennsylvanian tropical reefs and mounds are predominantly composed of calcareous algae (e.g. phylloid algae, Archaeolithophyllum), calcareous sponges, fenestrate bryozoans, Tubiphytes, and microbialites. However, in Houchang (southern China), the Late Pennsylvanian carbonate platform records a large coral reef lacking any analogs in age (Gzhelian), size (80–100 m thick) and composition (high biodiversity). The large coral reef developed at the border of the Luodian intraplatform basin. The intraplatform basin is characterized by the deposition of green algal grainstone, coated grain grainstone and bioclastic packstone, grainstone, floatstone and rudstone in shallow-waters. In the deep-water shelf, lithofacies are composed of burrowed bioclastic wackestone, microbioclastic peloidal packstone, grainstone, and fine-grained burrowed wackestone and packstone. In this context, the coral reef developed on a deep-shelf margin, in a moderate to low energy depositional environment, below the FWWB. The scarcity of Pennsylvanian coral reefs suggests global unfavorable conditions, which can be attributed to a complex pattern of several environmental factors, including seawater chemistry (aragonite seas), paleoclimatic cooling related to continental glaciation, and the biological competition with the more opportunistic and adaptive phylloid algal community that occupied similar platform margin paleoenvironments. The existence of the large Bianping coral reef in southern China, as well as a few additional examples of Pennsylvanian coralliferous bioconstructions, provides evidence that coral communities were able to endure the Late Paleozoic fluctuating paleoenvironmental conditions in specific settings. One of such settings appears to have been the deep shelf margin, where low light levels decreased competition with the phylloid algal community. [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]

Volcanic atolls host exceptionally important marine ecosystems in the modern oceans. Yet, due to limited exposures, fossil atolls are poorly constrained. Multiple drowned Cretaceous volcanic atolls have been reported in the Pacific, but less information exists regarding those in the Tethys. Here we report on two early Cenomanian age volcanic atolls outcropping in Mt. Carmel (northern Israel), along the eastern Levant margin. These atolls are a few kilometers in diameter and differ significantly in facies from their surroundings, which are dominated by chalky calcareous mudstone and wackestone. The atolls are composed of grainstone, floatstone, rudstone and bafflestone facies, which are dominated by molluscans, notably gastropods, rudists, oysters and other bivalves. Corals and green algae are absent throughout these atolls. The studied sections of these atolls display a full succession, beginning with aggradation and ending with drowning. Age constraints for the volcanic phases suggest that deposition occurred within a relatively short time interval (<1 Myr) and the sequence represents a keep-up to give-up transition, within rising global and local sea-level trends. The inability of these atolls to keep up with rising sea level is attributed here to a suppressed carbonate factory, either due to drowning, turbidity and/or nutrient excess. Our study sheds new light on the dynamics of carbonate buildups during the Late Cretaceous and their ability to persist. • We describe two km scale Cenomanian volcanic atolls from northern Israel. • These atolls offer a unique window into the details of succession in Late Cretaceous atolls. • The atolls exhibit a heterotrophic assemblage which was sustained for a relatively short time. • Data point to reef demise due to factors other than light limitation. [ABSTRACT FROM AUTHOR]

Organic geochemical, palynological and palynofacies analyses were carried out on 79 selected samples from four sedimentary basins (Mayo-Rey, Mayo-Oulo-Lere, Hamakoussou and Benue) in northern Cameroon. Rock-Eval pyrolysis and Total Organic Carbon results indicate that most of the samples of the studied basins are thermally immature to mature. The organic matter consists of terrestrial components (peat, lignite, bituminous coal, and anthracite) associated with organic matter of marine origin. Based on the appraisal of multiple parameters: Total Organic Carbon (TOC), maximum Temperature (T-max), Hydrogen Index (HI), Oxygen Index (OI) and Production Index (PI), some samples are organically rich both in oil and/or gas-prone kerogen Type-II, II/III and III. The source rock quality ranges from poor to very good. The source material is composed of both algae and higher plants. Samples from these basins yielded palynological residue composed of translucent and opaque phytoclasts, Amorphous Organic Matter (AOM), fungal remains, algal cysts pollen and pteridophyte spores. Abundance and diversity of the palynomorphs overall low and include Monoporopollenites annulatus (= Monoporites annulatus ), indeterminate periporate pollen, indeterminate tetracolporate pollen, indeterminate tricolporate pollen, indeterminate triporate pollen, indeterminate trilete spores, Polypodiaceoisporites spp., Biporipsilonites sp., Rhizophagites sp., Striadiporites sp., Botryococcus sp. (colonial, freshwater green algae), and Chomotriletes minor (cyst of zygnematalean freshwater green algae). Age assigned confidently for all these basins the palynological data except for one sample of Hamakoussou that can be dated as Early to Mid-Cretaceous in age. Callialasporites dampieri , Classopollis spp., Eucommiidites spp. and Araucariacites australis indicate, an Aptian to Cenomanian age. The other pollen and spores recovered may indicate a Tertiary or younger age (especially Monoporopollenites annulatus ), or have arisen from modern contamination. Geochemical data show that sediments are wackes, arkose, iron-sandstone and iron-shale. The Chemical Index of Alteration (CIA-K) is low moderate to high, suggesting a shorter exposure time and fast erosion and transport. The studied sequences cover various depositional settings ranging from wetlands to dry environment inside island arc, passive margin or active continental margin. This study reveals new data and the economic potential of this part of Cameroon. [ABSTRACT FROM AUTHOR]