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This work firstly presents a newly compiled literature-based database of global playas (Part 1) and later reviews geomorphological aspects of lake margin calcium carbonate (CaCO3) landforms (CCLs) and recommends research priorities (Part 2). In Part 1 literature data reveal that playa occurrence is not limited by topography per se but is mainly constrained by climatic factors and the excess of evaporation over total inflow. Playa evaporation rates vary between ∼4200 mm/yr and ∼760 mm/yr. Evapo-concentration effects take place along with increasing salinity or Total Dissolved Solids (TDS). pH values vary between pH 2 to pH 10, although globally most playas comprise carbonate and soda lakes. Part 2 compiles CCL data from large bioherms to crusts, marginal calcretes, tufa pinnacles and mounds. The literature shows that, for example, while playa marginal calcretes occur most dominantly in southern Africa and Australia, further research is required to establish the role of groundwater incursions in relation to the land-palustrine-playa interface. In contrast, work on mostly biogenic carbonate precipitation resulting in bioherm and crust formation is more advanced. Nonetheless the review highlights the need for more research to establish direct links between (micro) textural fabrics and mound or crust building processes as similar carbonate fabrics may result from different pathways of precipitation and diagenetic replacement. [ABSTRACT FROM AUTHOR]

“Nubecularia bioherms” represent unique foraminifera dominated buildups which are restricted to the late Middle Miocene (late Serravallian) of the Paratethys. They occur in the Central Paratethys in the late Sarmatian and in the Eastern Paratethys in the Volhynian–Bessarabian, both regional stages of the respective Paratethyan areas. The generic assignment of the main constituent of the bioherms changed in time from Spirorbis to Nubecularia and Sinzowella. No clear diff erential diagnosis has been provided for the establishment of the genus Sinzowella by Cushman (1933) and the diff erence between both porcelaneous taxa was reported to be the agglutination of foreign particles in Nubecularia (Loeblich and Tappan 1964, 1987). Since in studied Central Paratethyan material agglutinated particles occur frequently in the test wall a separation of Sinzowella from Nubecularia is not justifi ed based on this character and Sinzowella is considered synonymous with Nubecularia. At the species level the situation is even more confusing since a variety of species (nodulus, novorossica, caespitosa), subspecies or/and “types” (e.g., nodulus, solitaria, deformis) have been described. All these taxa are considered to be subjective junior synonyms of Nubecularia nodulus which is the only Nubecularia species in the Central Paratethys since all described morphotypes co-occur even in a single rock thin section. [ABSTRACT FROM AUTHOR]

Morphology, internal structure, and in situ facies distribution of mesophotic Halimeda bioherms from the Queensland Plateau (NE Australia) are presented based on hydroacoustic and oceanographic data, seafloor observations, and discrete sediment sampling carried out during RV SONNE cruise SO292 in 2022. Halimeda buildups consist of cone-like mounds up to 500 m in diameter and 3–10 m high, with gentle slopes (2°–5° on the top of Tregrosse Bank). Bioherms occur in water depths of 10–70 m, with most bioherm between 50 and 65 m. Their internal structure consists of aggrading low-amplitude reflections at the core of the bioherm interfingering with high-amplitude reflections to the flanks. Surface facies distribution displays one to four facies belts, from distal to proximal: Halimeda rudstone, Halimeda rudstone with living plants, Halimeda rudstone with coralgal debris, and coralgal boundstone (when present, occupied the top of the bioherms). It is proposed that the alternation of two key processes contributes to the formation of these bioherms: (1) in situ accumulation of Halimeda debris and (2) episodic dismantling of the mesophotic coralgal boundstone at the centre of the bioherm by severe storms. These storms may dismantle the mesophotic reef and export coralgal rubble to the flanks. Flanks may be recolonized by Halimeda during fair-weather periods. Due to their different geomorphic expressions, complex internal structure, and surficial facies distribution, we suggest that the buildups of the Queensland Plateau represent a new Halimeda bioherm morphotype, distinct from previously described bioherms on the adjacent Great Barrier Reef and elsewhere globally. [ABSTRACT FROM AUTHOR]

The revision of the lithostratigraphic scale of southern Belgium, based on the revised geological map of Wallonia and recent stratigraphic and sedimentological works, has led to the re-definition of 63 lithostratigraphic units for the Middle Devonian Series. Although most of the units described in the present overview are classical subdivisions of the Belgian lithostratigraphic scale, updates on their definition, boundaries and age were required and are provided herein. New terms are introduced for remarkable beds and facies. Groups are introduced to gather formations that are difficult to separate on geological maps, whereas some previously described formations are here retrograded to member status. The Middle Devonian units recorded the development of the carbonate factory in the Eifelian, interrupted by siliciclastic deposits followed by the development of a wide carbonate shelf during the Givetian. Reefs occur both in the Eifelian (offshore bioherms, biostromes on platforms) and in the Givetian (biostromes). The vertical succession and lateral correlation of the lithostratigraphic units allow to reconstruct the evolution of the shelf from the early Eifelian to the demise of the carbonate shelf at the end of the Givetian. [ABSTRACT FROM AUTHOR]

Stromatolite bioherms were found in the Lower Ordovician sediments of the Moyero River section (Tunguska syneclise, Eastern Siberia). Their structure is considered based on the example of their typical buildup and adjacent sediments. It is revealed that the studied sediments were formed during the development of both bacterial communities (primarily cyanobacteria) and calcareous algae. The presence of remains of calcareous algae Nuia of different preservation in bioclastic–oolitic and oolitic–bioclastic limestones underlying stromatolite buildups and composing interbioherm sediments is established. It is assumed that the formation of stromatolite bioherms and surrounding sediments was controlled by sea level fluctuations that were reflected in the transgressive–regressive cyclicity and changes in sedimentation conditions. [ABSTRACT FROM AUTHOR]

Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen—Zollhaus, Vienna—Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia‐coralline algal boundstone, stromatolitic/thrombolitic boundstone and serpulid‐nubeculariid‐microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross‐bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbonates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia‐coralline algal to stromatolitic/thrombolitic boundstone. The serpulid‐nubeculariid‐microbial boundstone reflects an internal succession with a decrease of the same parameters. Water depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline. The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic! [ABSTRACT FROM AUTHOR]

Parkinson, F.; Douglas, K.; Li, Z.; Meijer, A.; Stacey, C.D.; Kung, R., and Podhorodeski, A., 2024. A generalized semiautomated method for seabed geology classification using multibeam data and maximum likelihood classification. Journal of Coastal Research, 40(1), 1–16. Charlotte (North Carolina), ISSN 0749-0208. This paper presents a GIS-based model to perform semiautomated seabed classification that can act as a first-pass, pseudoclassified surficial geological map. The user can then edit the output into a finalized map in less time than by manual classification. The model uses maximum likelihood classification with unsupervised classification through iterative self-organizing clusters. This model is fully contained within the ArcGIS software suite as a ModelBuilder workflow composed of geoprocessing tools and Python script tools. Model inputs tested include different combinations of multibeam echosounder–derived data: slope, backscatter, and terrain ruggedness. Furthermore, to test the assumption of Gaussian distribution of input data required for maximum likelihood classification, Box–Cox power transformations were applied to slope and backscatter data and were used as model inputs. To illustrate the performance of the model, two locations are highlighted as case studies: Milbanke Sound and Spiller Channel, located on the central coast of British Columbia, Canada. Association between model outputs and ground-truth classes was generally weak to moderate when measured using Cramér's V association scores. Overall, the slope and backscatter parameter model had the highest scores of association. Results from an overlay analysis comparing model outputs with user-confirmed polygons show that the slope and backscatter model performs best in regions with distinct changes in the hardness of sediments but that in fjord regions dominated geologically by steeper bathymetric change, the slope parameter model may perform better. However, all model outputs had difficulty delineating bedrock units. The model has the flexibility to identify certain seabed habitat features as well, including glass sponge reefs—biologically active bioherms that have led to marine protected area designations in other areas of British Columbia. [ABSTRACT FROM AUTHOR]

We present previously unknown stacked bowl-shaped bioherms reaching a size of 45 cm in diameter and 40 cm in height from weakly solidified peloidal sand from the upper Sarmatian of the Paratethys Sea. The bioherms were mostly embedded in sediment, and the "growth stages" reflect a reaction on sediment accretion and sinking into the soft sediment. The bioherms are spirorbid–microclot–acicular cement boundstones with densely packed Janua tubes surrounded by microclots and acicular cement solidifying the bioherm. The surrounding sediment is a thrombolite made of peloids and polylobate particles (mesoclots) which are solidified synsedimentarily by micrite cement and dog-tooth cement in a later stage. The shape of the bioherms reflects a series of growth stages with an initial stage ("start-up stage") followed by a more massive "keep-up stage" which grades into a structure with a collar-like outer rim and a central protrusion and finally by a termination of growth ("give-up stage"). The setting was a shallow subtidal environment with normal marine or elevated saline, probably oligotrophic, conditions with an elevated alkalinity. The stacked bowl-shaped microbialites are a unique feature that has so far been undescribed. Modern and Neogene microbialite occurrences are not direct analogues to the described structures, but the marine examples, like in The Bahamas, Shark Bay and the Persian Gulf, offer insight into their microbial composition and environmental parameters. The microbialites and the surrounding sediment document a predominance of microbial activity in the shallow marine environments of the Paratethys Sea during the late Middle Miocene, which was characterized by a warm, arid climate. [ABSTRACT FROM AUTHOR]

Organic reefs are largely calcareous build‐ups of sessile organisms, commonly in shallow marine ecosystems, with a long Precambrian to Modern history. Despite a long history of study, the reef classification is still open to development due to reefs encompassing diverse organic and inorganic components with various imprecise and synonymous terms. In this study, a new classification model for organic reefs is expressed in two hierarchical levels. Level 1: Reef outline geometry has two major forms: bioherms (prominent relief and laterally constrained) and biostromes (low relief and large lateral extension interbedded with non‐reef sediments), within which constructional components highly vary. Level 2: Four reef constructor groups form end‐members in a pyramid diagram: macroskeleton (S), microbia (Mi), matrix (Ma) and cement (C). Thus five reef types are recognized depending on the composition and structure of these constructors: (i) S‐supported reef; (ii) Mi‐supported reef (calcimicrobial and agglutinated microbial); (iii) Ma‐supported reef (cluster and carbonate mud mound); (iv) C‐supported reef; and (v) hybrid component‐supported reef (comprising two or more major types of reef components). This arrangement makes a more streamlined and accessible reef classification than prior schemes. Two associated non‐reef habitats that may grade into reefs are relevant: debris biostromes/banks and level‐bottom communities containing taxa found in adjacent reefs. Based on this 'SMiMaC' model, the structural evolution of reef ecosystems is demonstrated for the Phanerozoic, characterized by S‐supported and hybrid‐supported, and Mi‐supported and Ma‐supported structures under cooling and intense warming climates, respectively. [ABSTRACT FROM AUTHOR]

The depositional period of the early Miaolingian Maozhuang Formation in the North China Platform (NCP) is characterized by sediments of a restricted tidal-flat facies zone, i.e., transgressive red bed (sabkha facies) and highstand dolostone, and by sediments of an open tidal-flat facies zone, i.e., transgressive red bed and highstand limestone. The Maozhuang Formation at the Jinzhouwan section is composed of sediments of an open tidal-flat facies in which highstand limestone is marked by a set of bioherms that represent rare examples of microbial carbonates in the NCP. They consist of stromatolites and leiolites with intercalations of oolitic grainstones that can be categorized into four units: Unit [1] encompasses large-scale columnar stromatolites, small quartz grains and trilobite fragments; Unit [2] consists of structureless leiolites that contain trilobite fragments, quartz grains, and few dark and dense clumps of micrite dominated by calcified sheaths of filamentous cyanobacteria which probably grew in relatively thick cyanobacterial mats; Unit [3] comprises radial ooids that contain abundant fossils of calcified sheaths of filamentous cyanobacteria that might be genetically involved in the formation of ooids; Unit [4] contains small columnar stromatolites and small-scale micritic clumps dominated by filamentous cyanobacteria. The filamentous fossils in units [3] and [4] provide useful information regarding the origin of radial ooids and stromatolites in normal marine environment. Further, the large and small columnar stromatolites of early Miaolingian age in units [1] and [4] represent a unique example because they belong to the first episode of cyanbacterial calcification at the base of Phanerozoic. [ABSTRACT FROM AUTHOR]

Historically, the Helderberg Group has been an important unit including some of the earliest paleontologic and stratigraphic studies in North America. Once interpreted as a series of coeval facies, most formations and even some members of the Helderberg Group are separated by disconformities and regionally angular unconformities. The Green Vedder Member (new) is defined within the Manlius Formation and the Dayville Member is reassigned from the Coeymans to the Manlius Formation. The name Ravena member of the Coeymans Formation is abandoned because it coincides entirely with the redefined Coeymans Formation. Two new members, Jefferson Heights and Leeds Gorge, are recognized within the New Scotland Formation. A cluster of tephra beds occurs in the Kalkberg Formation, the upper Jefferson Heights and lower Leeds Gorge members of the New Scotland Formation. Strata formerly described as an "upper tongue of the Kalkberg Formation" are referred to as the Old Stone Fort Member (new) of the Becraft Formation. The Deansboro, formerly a member of the Coeymans Formation, is raised to formational rank owing to its physical and biostratigraphic separation from the Coeymans Formation. Reef-bearing strata may still comprise a part of the Deansboro Formation or may be removed and referred to as the Mosquito Point Formation (new). Strata that overlie the Deansboro Formation in central New York that had been regarded as part of the Kalkberg Formation differ lithologically and are significantly younger than the Kalkberg. They are therefore redefined as the Buckley Mill Formation (new). Major unconformities occur between the Chrysler Member of the Rondout Formation and the Thacher Member of the Manlius Formation (Mine Lot Falls Unconformity), between the Thacher and Green Vedder members of the Manlius Formation (Clockville Unconformity), and between the Green Vedder Member and the Olney and Dayville members (Terrace Mountain Unconformity). The Columbia Center Unconformity separates the Olney from the overlying Dayville Member. The Howe Cave Unconformity marks the base of the Coeymans Formation and is basin-wide in its extent. The Punch Kill Unconformity caps the Coeymans Formation and is onlapped by four subunits of the Kalkberg Formation. The Getman Corners Unconformity marks the base of the Deansboro Formation and erosionally separates this unit from the Helderberg Group. The Silurian-Devonian boundary interval (base of the Lochkovian Stage) occurs in the upper portion of the Green Vedder Member of the Manlius Formation. The co-occurrence of scyphocrinitid loboliths and a positive δ13C excursion (Klonk Event) in facies that represent deeper, dysoxic conditions characterize the boundary interval. The Judds Falls Bentonite Bed is constrained to the middle Lochkovian (upper bohemica Zone) by a somewhat diverse chitinozoan fauna. A mid- to late Lochkovian age for the Becraft and Alsen formations is indicated by chitinozoans. Additional chitinozoan data suggest that the Lochkovian-Pragian boundary occurs in the Port Ewen Formation. Pragian conodonts from the Deansboro Formation mark a maximum age for the bioherms that have been grouped with the Deansboro. A Pragian age is also likely for the Buckley Mill Formation that overlies the Deansboro Formation, but chitinozoan studies from this unit are not yet completed. Seven epiboles of various crinoids and cystoids are recognized and are important marker horizons in the revised stratigraphy. The sequence stratigraphic framework of the Helderberg Group suggests that the stratigraphic architecture is strongly controlled by episodic, tectonically-driven subsidence produced by crustal loading during a pre-Tectophase I episode of Acadian orogenesis. During deposition of the Thacher Member of the Manlius Formation, maximum subsidence occurred in the region around Cherry Valley, New York. During deposition of the overlying Green Vedder Member, a low arch developed in this region, separating two sub-basins. The Cherry Valley Arch disappeared during deposition of the Dayville Member of the Manlius Formation and maximum subsidence was centered near Columbia Center, New York. The Cherry Valley Arch was reactivated and broadened to extend between Cherry Valley and the area around West Berne during deposition of the Elmwood through Jamesville members of the Manlius Formation. The Cherry Valley Arch disappeared as subsidence increased during deposition of overlying Helderberg units. Post-Manlius formations document eastward migration of the axis of maximum subsidence and bathymetric axis of the basin through time. This pattern reversed during deposition of the lower part of the Becraft Formation in which deeper water facies (Old Stone Fort Member) were deposited in the Schoharie region and shallower environments developed in the Hudson Valley. This transposition was short-lived as maximum subsidence migrated into the Hudson Valley region once again and persisted during deposition of the upper Becraft and the overlying Alsen and Port Ewen formations. The newly developed sequence stratigraphy and biostratigraphy in the Appalachian Standard Succession (New York State) enable revised correlations within the Central Appalachian Basin. [ABSTRACT FROM AUTHOR]

Bryozoan–serpulid–algal–thrombolite bioherms of up to 50 cm size are described from the Sarmatian (upper Middle Miocene) of the Central Paratethys. They occur on top of lower Sarmatian carbonate sediments of high-energy conditions and the individual bioherms settle on crests of ripples. The buildups are overlain and partly truncated by cross-bedded oolites of late Sarmatian age. Buildup growth starts with a Cryptosula/Hydroides (bryozoan/serpulid) pioneer community, followed by nodular Schizoporella (bryozoan) colonies overgrown by coralline algae/microbial mats and a thrombolite with calcareous algal filaments. All these constituents form a framestone fabric which is overall dominated by bryozoans labeling them as bryoherms. Inside the bioherms ecological successions of higher frequencies occur which are interpreted to reflect short-time environmental fluctuations such as nutrient availability, oxygenation (possible anoxia), salinity (possible brackish water), temperature and water level. The internal succession in individual bioherms is related to long-term environmental changes including general shallowing, increasing nutrient supply and decreasing water circulation and oxygenation. The described bioherms are most similar to modern bryostromatolites of the Coorong lagoon in S Australia and also similar to structures in the Netherlands. The widespread occurrence of bryoherms/bryostromatolites in the Central Paratethys suggests a phase of considerable eutrophication during the early Sarmatian. [ABSTRACT FROM AUTHOR]

Calcareous green algae bioherms have recently gained significant attention in the scientific community, as they serve as valuable stratigraphic and paleoecological archives, comparable to the most studied coral reefs. Currently, the genus Halimeda , which is very abundant in tropical settings and common in temperate ones, contributes significantly to the production of sediments rich in CaCO 3. This is due to a rapid calcification process that occurs in its peculiar internal structure. Halimeda bioherms represent a key case because of their non-continuous distribution in the stratigraphic record and in the Modern oceans. In fact, the presence of the green alga Halimeda is widely documented in present-day reefs throughout the entire tropical belt, although extensive bioherms are limited to areas such as the Indonesian K-Bank, the Caribbean, and particularly along the Australian Great Barrier Reef (GBR), where they reach remarkable extensions exceeding 6000 km2. Discontinuous distribution is also noted during the Miocene, with Halimeda bioherms reported only in three main localities within the Mediterranean basin, all dating to the pre-evaporitic Messinian. In this study, we present data obtained from detailed stratigraphic and sedimentological analyses of two small Halimeda bioherms (with a maximum thickness of 5 to 6 m), located in the southernmost portion of the Apulia Carbonate Platform (Salento Peninsula, Italy). Field observations, coupled with thin sections analysis show that despite these two sections being ascribed to different stratigraphic intervals, both record the same facies, with an alternation of shallowing-deepening cycles. While it is documented that different Halimeda species currently inhabiting carbonate systems respond variably to factors such as light, temperature, and salinity, the input of large quantities of nutrients via upwelling currents has recently become the most widely accepted hypothesis to support the occurrence of wide bioherms such as along the GBR. We infer that the occurrence of Salento Messinian Halimeda -rich facies could be related to upwelling of cool, nutrient-rich waters, possibly enhanced by the occurrence of internal waves (IWs). Such processes are well documented in the Salento Peninsula and in many areas of the Mediterranean throughout the Tortonian and likely still acting during the early Messinian. • The occurrence of Halimeda bioherms in the stratigraphic record is often discontinuous. • Halimeda contributes significantly to the production of CaCO3-rich sediments. • Nutrient supply and hydrodynamics influence Halimeda bioherm development. • Halimeda bioherms in tropical regions mitigate global warming by capturing CO2. [ABSTRACT FROM AUTHOR]

Fossil caddisfly larval cases (CLCs) are of great significance for reflecting the habits of ancient caddisfly and indicating the paleoenvironment. Multiple layers with bioherms formed by fossil CLCs and stromatolites were found to be distributed in the Lower Cretaceous in Liupanshan Basin, Central China. In order to deeply understand the characteristics and formation environment of the CLCs-stromatolite bioherms, a series studies were conducted on the Yaoshan section in the northeastern of the basin. Morphological anatomy, mineralogy, element geochemistry, and isotope geochemistry are included in the studies. It reveals that the CLCs-stromatolite bioherms in Yaoshan are mainly composed of calcite and dolomite mineralogically, and CLCs and stromatolite morphologically. In the bioherms, a large number of fossil CLCs stacked orderly, with a conical shape perpendicular to the stratum distribution. The bioherms were deposited in a semi-enclosed saline lake in hot and dry paleoclimate, and they were mainly formed during the periods when the evaporation increased, the water body became shallower, and the supply of terrestrial material increased. [ABSTRACT FROM AUTHOR]

The lower Maeotian carbonate encrustation of bryozoan bioherms and local problematic carbonate buildups at Cape Kazantip (Kerch Peninsula) were studied to elucidate their genesis. Analytical (lithological and mineralogical, X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry, and isotopy) studies have shown that hardness of the bryozoan framework is related to the syndepositional, biologically induced cement around bryozoans and carbonate encrustation of bioherms. In addition to fossilized traces of products of the microbiotic vital activity (bacteriomorphic structures, mineralized biofilms, glycocalyx—an exopolymer substance (IPS), and framboidal pyrite), the carbonate crusts on bryozoan bioherms and mollusk–polychaete minibioherms contain abundant bitumen, strontianite, barite, celestine, Mn-rich calcite (kutnohorite), Mg-calcite, aragonite, dolomite are widespread. Mineralized biofilms include trace elements Fe, Si, Mg, Al, K, Na, Cl, Ba, S, Ni, and Co. The isotopic composition of different carbonate rock types is marked by wide variations of carbon (–2.76...7.17‰) and oxygen (24.20–33.01‰) and manifested in fluctuations of water salinity (16.67–39.74‰). The chemical composition and mineral specificity of rocks, confinement of carbonate crusts and minibioherms to saline waters, and local pattern of their formation suggest the manifestation of near-bottom cold gas-fluid seeps, probably, of a complex chloride-sodium-sulfate-magnesium composition or various modifications of these components in a shallow sea basin, whereas the bryozoan biohermal complex is most likely a near-hydrothermal oasis. [ABSTRACT FROM AUTHOR]

Reef communities changed dramatically during the Early Jurassic as they recovered from the End-Triassic Mass Extinction. The Atlas Rift Zone in Morocco provided expansive shallow water substrate, which allowed a variety of reef communities to develop, such as lithiotid bivalves that established themselves as new and prolific reef builders alongside corals, microbialites, and sponges in the Sinemurian and Pliensbachian stages. To better understand the dynamics between these reef builders and their environments, a detailed facies analysis of upper Pliensbachian reefs and a quantitative analysis of their composition was undertaken. We describe two distinct environmentally controlled reef types in the Central High Atlas Mountains. Lithiotid bivalves dominated reef construction in lagoonal environments and, together with phaceloid corals, commonly built bioherms and biostromes that ranged from 1 to 2 m tall and up to several hundred meters wide. Meanwhile, on the platform edge, microbialites, corals, and sponges constructed patch reefs up to 7 m tall and 20 m wide. These two reef types share common facies, as many of the same reef inhabitants, and some framework builders, grew in both environments. Despite the facies overlap, the communities in these two environmental settings are distinct, which is likely a result of environmental controls on the dominant reef framework builders. Moderately turbid waters and soft substrate in lagoons were ideal conditions for lithiotids but excluded many corals, sponges, and microbialites. Conversely, the clear, oligotrophic waters at the platform edge allowed photosynthetic and photosymbiotic organisms to thrive (e.g., coral and microbial reefs), while firmer substrate and higher wave energy may have prevented lithiotids from establishing dense populations. • Lithiotid bivalves, corals, sponges, and microbialites constructed late Pliensbachian reefs in the Atlas Basin. • These reef builders formed two distinct reef types depending on the carbonate setting. • Lithiotid bivalves and corals built bioherms and biostromes in lagoonal environments. • Corals, sponges, and microbialites built patch reefs on the platform edge. • Ecologic preferences of each organism determined the location and morphology of each reef type. [ABSTRACT FROM AUTHOR]

Megapodius reinwardt, the orange-footed scrubfowl, belongs to a small family of birds that inhabits the Indo-Australian region. Megapodes are unique in incubating their eggs in mounds using heat from microbial decomposition of organic materials and solar radiation. Little is known about the microorganisms involved in the decomposition of organic matter in mounds. To determine the source of microbes in the mounds, we used 16S and 18S rRNA gene sequencing to characterize the microbial communities of mound soil, adjacent soil and scrubfowl faeces. We found that the microbial communities of scrubfowl faeces were substantially different from those of the mounds and surrounding soils, suggesting that scrubfowls probably do not use their faeces to inoculate their mounds although a few microbial sequence variants were present in both faeces and mound samples. Further, the mound microbial community structure was significantly different to the adjacent soils. For example, mounds had a high relative abundance of sequence variants belonging to Thermomonosporaceae, a thermophilic soil bacteria family able to degrade cellulose from plant residues. It is not clear whether members of Thermomonosporaceae disproportionately contribute to the generation of heat in the mound, or whether they simply thrive in the warm mound environment created by the metabolic activity of the mound microbial community. The lack of clarity in the literature between designations of heat-producing (thermogenic) and heat-thriving (thermophilic) microbes poses a challenge to understanding the role of specific bacteria and fungi in incubation. [ABSTRACT FROM AUTHOR]

We once took my ten-year-old son Calvin and his fourteen-year-old cousin Ethan into a slot canyon so narrow that only Calvin could shuffle through at the bottom. Tomorrow, I'll walk upstream instead of downstream and see what I can find in the canyon carved by the South Fork of Robber's Roost Creek, a canyon Louis and I never descended. But it's always there, waiting: approaching the Dirty Devil anywhere from the east or west, the ground suddenly peels back and cracks open, exposing a sea of sandstone cliffs and dozens of canyon complexes more than a thousand feet deep. Calvin wriggled up out of the hole, Ethan grabbed the shoe, and we continued on until the canyon opened a hundred yards downstream, where we collapsed in the sun, laughed for a good ten minutes, and duct-taped the shoe back together. [Extracted from the article]

The Cambrian stratigraphic succession of the Pyrenees (SW Europe) has undergone a complex Variscan and Alpine tectonothermal history leading to marked metamorphism and development of cleavage networks, which might partly explain the lack of Cambrian fossiliferous beds. This gap has traditionally precluded its paleobiogeographic and biostratigraphic relationships with other neighboring peri-Gondwanan units. Correlations are only based on lithostratigraphic comparisons and radiometric constraints. In this general scheme, the Terrades inlier (Gerona Province, Spain) provides the only significant and indisputable 'early Cambrian' fossil record of the Pyrenees. This predominantly siliciclastic outcrop consists of multiple patch reefs and bioherms having yielded archeocyaths dated at Cambrian Epoch 2, Age 3. This paper describes, for the first time, the microfossil assemblage included in the archeocyathan-microbial reefal complex that crops out in the Terrades inlier to clarify its age and affinities with surrounding tectonostratigraphic units. Reefal flanks of patch reefs have yielded bradoriids, brachiopods, molluscs, tommotiids, chancelloriids, hyoliths, and the problematic fossil (and chronostratigraphically significant) Rhombocorniculum cancellatum Cobbold, 1921. In addition to confirming the previously assigned age of the succession, the recovered fauna emphasizes strong affinities with the surrounding Occitan Domain (Montagne Noire, southern Massif Central, France) and Sardinia (Italy). Along with lithostratigraphic comparison and tectonic considerations, this further supports the recent reconstructions positioning the Pyrenean domain between the Montagne Noire (to the southwest) and Sardinia (further to the northeast) on the Gondwana margin during Cambrian times. [ABSTRACT FROM AUTHOR]

The Cambslan strata of Zhucaoying Section in Qinhuangdao, Hebsi are intact and continuous, and stromatolltes are developed in the top of Zhangxla Formation of Mlaoling Series. Based on field data and microscopic observation, the characteristics and sedimentary envtronment of columnar(domal) stromatolltes are studied. The results show that stromatollte bioherms and high energy oolltic shoal limestones are developed in the forced regressive system at the top of the Cambslan Zhangxla Formation in Qinhuangdao, Hebsi, which are produced in an interactive manner, representing the carbonate deposition during the slow sea ievel delline in the North Chma Platform during the Cambrian. The well-pre-served filamentous calcified cyanobacteria sheath fossils and window-like fabrics can be found in the dense micrite of the stromatolites from the Zhangxia Formafion, suggesfing that the stromatolites were formed by the complex calcification of photosynthesis microbial mats or microbial membranes. A small amount of pyrite residue associated with precipitation induced by sulfate reducing bacteria was observed. The results provide an important case for studying the sedimentary environment of Cambrian stromatolites. [ABSTRACT FROM AUTHOR]

I Tarbellastraea i and I Porites i constituted an important element in the reef-building process in the Mediterranean Messinian, as in the case of the Sidi Safi reef. 1990; 56: 1-366 16 Vinn O, Naimi MN, Cherif A. The endobiontic serpulids in corals and other reef associated fauna from the Messinian of Algeria. Coral reefs are among the most productive and biologically diverse ecosystems in the world. [Extracted from the article]

Aims: Climate warming is predicted to increase permafrost degradation and soil carbon (C) loss, while changes in microrelief and vegetation cover can also influence soil C storage at local scale. Black spruce forests develop lichen/moss-covered organic mounds on permafrost. Recalcitrance of lichen and moss litters, as well as cold climate, is hypothesized to increase C storage in hummocky soils. Methods: We compared the decomposition rates of lichen and moss litters, spruce root litter, and cellulose at hummocky clayey soils, non-hummocky clayey soils, and non-hummocky sandy soils in northwest Canadian subarctic. Results: Lichen/moss-covered hummocky clayey soils displayed greater C stocks than non-hummocky clayey and sandy soils. Lichen and moss litters decomposed more slowly than did spruce root litter and cellulose. Recalcitrant litter inputs of lichen and moss contributed to greater C stocks of hummocky clayey soils, compared to non-hummocky clayey and sandy soils. Lower temperature dependency of lichen and moss litter decomposition, compared to vascular plant litter, suggests stronger resistance of lichen and moss litters to decomposition. Conclusion: Permafrost degradation by climate warming would reduce hummocky microrelief covered by lichen and moss, major contributors to soil C, and decrease the high potential for C storage of black spruce forests on permafrost. [ABSTRACT FROM AUTHOR]

Side‐scan sonar and Compressed High Intensity Radar Pulse mapping of Great Salt Lake, Utah, linked to reprocessing of acoustic data from bathymetric surveys, has enabled the distribution of microbial bioherms to be assessed. Bioherms occupy an estimated area >700 km2 in the south arm and >300 km2 in the north arm. Distributions vary from statistically dispersed to clustered, and in this latter case, are predominantly located on metre‐scale, fault‐controlled topographic highs, with sediment infilling intervening lows between adjacent offsets. Individual bioherms are circular to oblate and range from centimetres to over 2 m in diameter. In some areas, bioherm heights were measured at more than 1.5 m above adjacent substrate. Sublittoral bioherms are made of aragonite, calcite and minor dolomite precipitated due to physico‐chemical, biologically induced and influenced carbonate mineralization processes in association with microbial mats. Bioherm fabrics vary at the millimetre to centimetre‐scale and consist of leiolitic and clotted peloidal micrite‐grade carbonate, sinuous threads of spherulitic fibrous aragonite crystals, laminated micrite boundstone and internal carbonate mud sediment with peloids and ooids. The identification of factors that influence microbial bioherm occurrence and spatial distribution in Great Salt Lake is limited to a set of collinear physical, chemical and biological variables that are confined to a localised closed system, such as salinity, water depth, wave energy, stable substrate and sediment accumulation. Anthropogenic modifications to Great Salt Lake resulting in increased salinity have exceeded the salinity range in which bioherm‐mediating microbial communities can survive, effectively defining an upper limit of salinity for bioherm microbial community viability. The better understanding of the distribution of microbial bioherms has significant implications for managing and protecting the lake ecosystem and may provide insights into the physical and chemical controls that existed during the formation of fossil microbialites in deep time. [ABSTRACT FROM AUTHOR]

More accurate global volumetric estimations of shallow-water reef deposits are needed to better inform climate and carbon cycle models. Using recently acquired datasets and International Ocean Discovery Program (IODP) Expedition 325 cores, we calculated shallow-water CaCO3 volumetrics and mass for the Great Barrier Reef region and extrapolated these results globally. In our estimates, we include deposits that have been neglected in global carbonate budgets: Holocene Halimeda bioherms located on the shelf, and postglacial pre-Holocene (now) drowned coral reefs located on the shelf edge. Our results show that in the Great Barrier Reef alone, these drowned reef deposits represent ca. 135 Gt CaCO3, comparatively representing 16–20% of the younger Holocene reef deposits. Globally, under plausible assumptions, we estimate the presence of ca. 8100 Gt CaCO3 of Holocene reef deposits, ca. 1500 Gt CaCO3 of drowned reef deposits and ca. 590 Gt CaCO3 of Halimeda shelf bioherms. Significantly, we found that in our scenarios the periods of pronounced reefal mass accumulation broadly encompass the occurrence of the Younger Dryas and periods of CO2 surge (14.9–14.4 ka, 13.0–11.5 ka) observed in Antarctic ice cores. Our estimations are consistent with reef accretion episodes inferred from previous global carbon cycle models and with the chronology from reef cores from the shelf edge of the Great Barrier Reef. [ABSTRACT FROM AUTHOR]

Biostromes and low‐relief bioherms, some of which are characterized by exceptionally large, flat specimens of larger benthic foraminifera, are common in Palaeogene and Miocene carbonates, most notably those deposited along the Neotethys Seaway and tropical Pacific islands. By incorporating insights from palaeoceanographic research and the biology of living larger benthic foraminifera, a scenario is proposed that can account for palaeontological and sedimentological features while augmenting previous interpretations. Sexual reproduction by gamete broadcasting is common in foraminiferal taxa, including extant Nummulitidae and Amphisteginidae. Resultant zygotes can develop into tiny, resistant, easily dispersed propagules that recruit in suitable benthic‐environmental conditions. The role of algal symbiosis in the biology of larger benthic foraminifera is well‐documented. Palaeoceanographically, such taxa proliferated during times of reduced thermal stratification of the oceans. In regions with exceptionally clear, nutrient‐depleted waters, 'twilight‐zone' light penetration was sufficient, at least intermittently, to support some photosynthesis. On outer‐shelf or promontory sites at depths of ca 100 to 200 m, the tiny propagules of larger benthic foraminiferal species, incorporating algal symbionts with the lowest light requirements, could have settled and recruited, growing very slowly, nourished by feeding on bacteria and the limited photosynthate produced by their algal symbionts. Under such conditions, thin microspheric individuals of one or two larger benthic foraminiferal taxa could have survived and grown slowly over several years to very large shell diameters, seldom reproducing asexually. Resulting carbonate accumulation rates would have been very slow, such that even rare disturbances by currents, major storms or internal waves could have produced evidence of winnowing and sedimentary structures. The fossil evidence of such habitats should include biostromes or possibly low‐relief bioherms of low diversity assemblages characterized by abundant, exceptionally large, flat, microspheric larger benthic foraminifera. [ABSTRACT FROM AUTHOR]

In the central-eastern Sirt Basin, enigmatic Intisar domal structures host significant hydrocarbon accumulations. These structures have been commonly interpreted as pinnacle reefs/bioherms occurring in the open-marine basinal environment. Generally, pinnacle reefs/bioherms are mainly characterized by in situ carbonates. The current study challenges the Intisar pinnacle reef/bioherm model by examining one of the domal structures in terms of biostratigraphy, microfacies and depositional environment. These structures were dated using larger benthic foraminifera, which yielded a Middle to Late Paleocene age (Selandian–Early Thanetian). Thirteen microfacies types representing different carbonate ramp environments ranging from outer ramp to inner ramp, were defined. Outer ramp deposits have been observed adjacent to the domal structure, represented mainly by wackestone with small benthic and planktonic foraminifera. The outer ramp deposits are most likely isochronous to the domal structures. The lower part of the domal structures is composed mainly of foraminiferal–algal–echinodermal packstones. The upper part is characterized by foraminiferal–algal–echinodermal packstones with intercalated microbialite–coral boundstones. The euphotic inner ramp deposits are preserved on the crest of the domal structure, consisting of grainstone and packstone rich in Glomalveolina. As a result of this study, the Intisar domal structures are seen as erosional relics of a carbonate ramp and no evidence for pinnacle reef/bioherm model was found. [ABSTRACT FROM AUTHOR]

The last interglacial (MIS 5) transgressive-regressive deposits of the Capo Colonna marine terrace provide a good fossil example of a Central Mediterranean infra/circa-littoral setting, characterized by both calcareous coralline algae-dominated low-relief bioherms and biostromes, equivalent respectively to the modern coralligenous and mäerl habitats. The skeletal primary framework of the bioherms, consists of laminar to massive encrusting coralline red algae acting as main bioconstructors, with minor bryozoans, encrusting foraminifera, and serpulids as secondary frame-builders. Whereas, the autochthonous mäerl tabular beds are mainly composed of free-branched coralline red algae rudstone. A variable amount of sandy bioclastic sediment is laterally interbedded with the bioconstructions and tends to be entrapped in their cavities and pockets. All sedimentary sub-facies of the bioconstructions and associated sediment are rich in autochthonous syn-sedimentary microbial-mediated micrite, forming aphanitic, peloidal, clotted peloidal, and filamentous fabrics. Microbial micrite can also trap and bind a variable amount of grains, or be a secondary component of the sandy sediment as micritic rims surrounding the clasts. All these early-lithified micrites show the typical nanostructure of the primary microbial-mediated carbonates, rather than a detrital mud particles accumulation, as they consist of nanospheres coalescing into subhedral microcrystals that replace both microbial cells (present with several morphological types) and extracellular substances. This in turn implies the original widespread presence of benthic lithifying microbial biofilms which colonized both the cavities of the skeletal framework of the bioconstructions, and the intergranular space of the associated sediment. These microbial communities, thanks to the metabolic processes of the microorganisms that induced the carbonate precipitation, significantly contributed to the early cementation of all the studied deposits. • Capo Colonna MIS 5 bioconstructions are typified by calcareous red algae, metazoans, and autochthonous microbial mediated micrites. • Lithifying microbial biofilms are found on the seabed, within bioconstruction skeletal framework and associated sediment. • The early hardening of microbial micritefavored the bioconstructions strength and growth and the sediment stabilization. • All micritic fabrics derive from the mineralization of organic substrates by submicron calcite nanospheres. • Microbial communities were dominated by heterotrophs taking advantage of organic matter deriving from dead organisms. [ABSTRACT FROM AUTHOR]

A multi-proxy field and laboratory study was conducted to investigate the impact of a regional fault zone on Devonian carbonate geothermal reservoir properties. The outcrop analogue chosen is exposed in the Steltenberg quarry (North Rhine-Westphalia, Germany) and provides access to Devonian lime- and dolostone units affected by branches of the Ennepe Thrust Fault zone. Data presented include (i) field evidence from sedimentological and structural data, (ii) petrographic and mineralogical analyses, and (iii) geochemical and petrophysical data. Although the interpretation of the depositional environment is not trivial, the carbonate facies present generally reflect the shedding of reefal material from large bioherms to the west of the study areas as well as localised, small bioherms prone to storm disintegration. The inherited properties of these carbonates at deposition, and a clear understanding of their diagenetic history, are the prerequisite for extrapolation between outcrop analogues and their corresponding subsurface units. We document a detailed interpretation of the paragenetic sequence that affected these rocks from deposition, burial, subsequent hydrothermal overprint related to rock disintegration and fluid circulation along the fault zone, and finally, late-stage meteoric overprint. Emphasis is placed on various forms of dolomitisation and its effect on rock properties and reservoir quality. The resulting scenario is complex, and when comparing the data from the Steltenberg quarry with nearby outcrops, significant regional heterogeneity is observed. It is important to separate between: (i) diffuse, locally distributed dolomitisation, (ii) replacive dolomitisation (fronts), spatially separating lime- and dolostones, and (iii) fault-bound, hydrothermal dolomitisation. The Devonian carbonates in the Steltenberg quarry examined here have higher thermal conductivity compared to the Jurassic (Malm) carbonate units in the Munich area, with some even higher than the values of massive limestone facies of the Munich area. As a large portion of North Rhine-Westphalia's territory is underlain by Devonian carbonates, this is considered significant. However, emphasis is placed on the fact, that data shown here document the spatially complex organisation of rock types and their reservoir properties. This presents a warning against oversimplifications when extrapolating observations from outcrops into subsurface rock bodies. [ABSTRACT FROM AUTHOR]

The calcareous Halimeda bioherms of the northern Great Barrier Reef, Australia are the largest actively accumulating Halimeda deposits worldwide. They contribute a substantial component of the Great Barrier Reef neritic carbonate factory, as well as the geomorphological development of Australia's northeast continental shelf. Halimeda bioherm geomorphology is complex, expressing three distinct variations in morphotype patterns: annulate, reticulate and undulate. Similar regular and irregular geomorphological patterning often results from scale‐dependent biophysical feedback mechanisms. Therefore, a better understanding of morphotype differentiation can inform the biotic and abiotic drivers of spatial heterogeneity in the bioherm ecosystem. Here, 3D LiDAR bathymetry is integrated with 2D sub‐bottom profile datasets to investigate surface topography and internal sedimentary architecture of Halimeda bioherms through space and time. Using the ESRI ArcGIS 3D Analyst and Benthic Terrain Modeller extensions, the bioherm surface and subsurface geomorphometric characteristics were quantified for the annulate, reticulate and undulate morphotypes. Significant variation was found between the three bioherm morphotypes in their surface topography, internal structure, volume, slope gradients and terrain complexity. Therefore, their geomorphology is probably influenced by differing processes and biophysical feedback mechanisms. The complex surface topography does not appear to be inherited from the antecedent substrate, and preferred aspect orientations resulting from hydrodynamic forcing appear to be limited. It is suggested here that autogenic dynamics or biotic self‐organization similar to patterns and processes in other marine organo‐sedimentary systems modulates Halimeda bioherm geomorphology, and some hypotheses are offered towards future studies. Morphotype differentiation has implications for the development of the Halimeda bioherm carbonate factory, rates of sediment aggradation and progradation, and variable capacity to fill accommodation space. Self‐organization dynamics and morphology differentiation in Modern bioherm systems could potentially inform palaeo‐environmental interpretations of fossil bioherms and phylloid algal mounds on geological timescales. [ABSTRACT FROM AUTHOR]

Eight bryozoan species are described from the Hanchiatien Formation (lower Silurian, Telychian) of southern Chongqing, South China. Four species are new: the trepostomes Asperopora sinensis n. sp., Trematopora jiebeiensis n. sp., and Trematopora tenuis n. sp., and the fenestrate Moorephylloporina parvula n. sp. One species, the cystoporate Hennigopora sp. indet., is described in open nomenclature. Moorephylloporina parvula n. sp. is eurytopic, occurring in all types of facies within the bioherms. Erect Moorephylloporina Bassler, 1952, Trematopora Hall, 1852, and Leioclema Ulrich, 1882 formed pioneering communities on weakly cemented substrata, whereas encrusting Fistulipora M'Coy, 1849, Hennigopora Bassler, 1952, and Asperopora Owen, 1969 occurred on hardgrounds and formed densely compact framestones. Robust branched Trematopora and Leioclema tend to occur out of the reef core (framework) where they could have formed reef-flank thickets in more agitated conditions. The generic composition of the studied fauna correlates with other localities in South China, and they show general paleobiogeographic relations to Siberia and Indiana, USA. UUID http://zoobank.org/3326dd2f-7c9e-43bc-9dab-84047b274f89 [ABSTRACT FROM AUTHOR]

The northern Great Barrier Reef (GBR) Halimeda bioherms have accumulated on the outer continental shelf from calcium carbonate algal sediments over the past ∼10,000 years and cover >6,000 km2 of shelf area. As such, Halimeda bioherms play a key role in the shallow marine carbon cycle over millennial timescales. The main source of nitrogen (N) to these bioherms is thought to be westward transport of upwelled NO3‐‐rich water from the Coral Sea. However, the primary N source has not been traced geochemically, and we have no understanding of any temporal variation. Here, we reconstruct patterns of N supply to Halimeda bioherms in the GBR since the mid‐Holocene using the 15N/14N ratio of skeletal‐bound organic N (δ15N‐skeletal organic material [SOM]) in modern and fossil Halimeda sediment cores. Average Halimeda skeletal δ15N‐SOM was 6.28 ± 0.26‰, consistent with δ15N‐NO3‐ from western tropical South Pacific (WTSP) thermocline waters. Thus, geochemically validating shelf‐break upwelling of an oceanic N source that regulates bioherm spatial distribution. Halimeda δ15N‐SOM decreased by 1‰–2‰ from 5,000 to 2,000 cal. yr BP, reaching a minima of 5.5‰ that persisted for almost 1,000 years. The Halimeda δ15N‐SOM variation reflects mid‐ to late Holocene changes in regional climate and intensified El Niño activity that likely facilitated elevated N2 fixation in the WTSP, thereby lowering thermocline δ15N‐NO3‐. Thus, Halimeda skeletal material provides a valuable high‐resolution geochemical archive of past oceanographic and climatic processes over centennial to millennial timescales, complementing existing paleoclimate proxy records. Key Points: Well‐preserved fossil Halimeda is a valuable geochemical proxy archive of millennial‐scale oceanographic and climatic processesNitrogen (N) supply to Halimeda bioherms originates from western tropical South Pacific thermocline waters since at least the past 5,000 yearsHalimeda15N signature records a 1‰–2‰ change in δ15N‐skeletal organic material (SOM) concurrent with regional climate variation and the El Niño Southern Oscillation [ABSTRACT FROM AUTHOR]

The Vema Fracture Zone orthogonally intersecting the Mid-Atlantic Ridge along 11° N is a complex tectono-sedimentary system, through which bottom water is transferred from the western to the eastern Atlantic. The southern surrounding of the fault valley is an extended (about 320 km) transverse ridge. At the early stages of the Vema System evolution, the ridge was located at shallow depths in the photosynthesis zone, which led to the formation of extensive biogenic carbonate buildups on its surface. Spreading, general sinking of the system, and associated movements along faults caused disintegration of ultramafic basement and bioherms with subsequent fractionation of colluvial–pelagic sediments and their eastward transport by bottom currents. The formation of coarse-grained residual sands completely devoid of pelitic material is associated with the high flow rates of Antarctic bottom waters. The presence of rounded pebbles of organogenic limestones and ultramafic rocks with traces of bioproductivity indicates that clastic material was transferred over a few hundred kilometers. [ABSTRACT FROM AUTHOR]

The complex of modern physical methods for studying authigenic carbonate crusts in the Miocene bryozoan bioherms of the Kazantip Cape (Kerch Peninsula) has made it possible to reveal fossil biofilms and glycocalyx for the first time. These finds indicate that methanotrophic carbonate-precipitated bacteria during their activity strengthened brittle bryozoan skeletons. The presence of cavities in bioherms incrusted with goethite crusts, the presence of bitumen, pyrite, strontianite, barite, kutnagorite in the composition of carbonate crusts, and traces of the vital activity of methanotrophic bacteria are associated with the significant influence of near-bottom local gas–fluid seeps. This situation was determined by the occurrence of a discharge zone of rising gas–fluid flows in the Kazantip Cape area as a result of activation of mud volcanism, typical of the Neogene–Holocene interval of the Kerch–Taman Region. [ABSTRACT FROM AUTHOR]

Oxfordian (Upper Jurassic) coral buildups developed widely in Tethys and Atlantic realms, during a time when paleoclimate potentially swung between greenhouse climate and cold snaps. Buildups were constructed by platy and branching corals, sponges and microbialites. Although their initiation is commonly linked to the Upper Jurassic global transgression, a number of global and local factors may have influenced buildup growth and demise (e.g. climate, shelf geometry, detrital input). Extensive outcrops of Oxfordian buildups in Morocco provide an opportunity to investigate the relationship between external drivers and buildup fauna and architecture. Here we show that the interplay of local accommodation changes, rising sea water temperature, and increasing pCO 2 linked to the onset of the Middle Oxfordian global transgression were the main drivers for buildup initiation, which was synchronous across the basin. The demise of the coral buildups in Morocco was linked to a regression, dated no later than Upper Oxfordian, the establishment of partly evaporitic conditions across the basin, and to localized influx of coarse-grained siliciclastics, the latter likely driven by synsedimentary tectonic activity. Serial logged sections, outcrop panoramas and detailed facies analysis show that low-relief deeper-water buildups of Dimorpharaea platy corals evolved into higher-relief diversified buildups where shallower-water reworking produced coral rubble and large clinoforms. Buildup diachronicity is apparent, with younger coral bioherms growing in the depressions created between the initial bioherms. Size of buildups ranges from 2 m wide and 0.5 m thick, to 700 m wide and 80 m thick. The outcrops provide constraints on geobody architecture and heterogeneity in the subsurface of Morocco and North America, where facies-controlled dolomitization of high-energy buildup and clinoform facies is a main driver for porosity development. • Coral buildups started to develop synchronously in the Middle Oxfordian. • Evolution from deeper-water platy corals to diverse coral fauna in shallow water. • Buildups controlled by global and local factors: transgression-regression, temperature, pCO 2. • Complex internal architecture serves as analog for subsurface geobodies. [ABSTRACT FROM AUTHOR]

Although Late Cambrian microbial build‐ups were recognized in the Point Peak Member of the Wilberns Formation in Central Texas (USA) nearly 70 years ago, only a few studies focused specifically on the build‐ups themselves. This study focuses on the interpretation of the regional (15 measured sections described in literature representing an area of 8000 km2) and local (field and drone photogrammetry studies in a 25 km2 area from within south Mason County) microbial build‐up occurrence, describes their growth phases and details their interactions with the surrounding inter‐build‐up sediments. The study establishes the occurrence of microbial build‐ups in the lower and upper Point Peak members (the Point Peak Member is informally broken up into the lower Point Peak and the upper Point Peak members separated by Plectotrophia zone). The lower Point Peak Member consists of three <1 m thick microbial bioherms and biostrome units, in addition to heterolithic and skeletal/ooid grainstone and packstone beds. One, up to 14 m thick, microbial unit associated with inter‐build‐up skeletal and ooid grainstone and packstone beds, intercalated with mixed siliciclastic–carbonate silt beds, characterizes the upper Point Peak member. The microbial unit in the upper Point Peak member displays a three‐phase growth evolution, from an initial colonization phase on flat based, rip‐up clast lenses, to a second aggradation and lateral expansion phase, into a third well‐defined capping phase. The ultimate demise of the microbial build‐ups is interpreted to have been triggered by an increase of water turbidity caused by a sudden influx of fine siliciclastics. The lower Point Peak member represents inner ramp shallow subtidal and intertidal facies and the upper Point Peak member corresponds to mid‐outer ramp subtidal facies. Understanding the morphological architecture and depositional context of these features is of importance for identifying signatures of early life on Earth. [ABSTRACT FROM AUTHOR]

Subsurface sedimentary strata in northern Switzerland, such as the Middle Triassic Upper Muschelkalk, are attracting interest as potential reservoirs for CO2 sequestration and for geothermal energy production. Characterizing facies in such strata aids prediction of reservoir properties in unexplored areas. Although well studied elsewhere, the Swiss Upper Muschelkalk has received little attention despite containing the southern-most deposits of the Central European Basin. The Upper Muschelkalk represents the deposits of a storm-dominated, homoclinal carbonate ramp, developed during a basin-wide 3rd-order transgressive–regressive cycle. Our facies analyses of nine boreholes across northern Switzerland reveal 12 lithofacies, eight lithofacies associations and four types of metre-scale 5th-order cycles corresponding to at least 23 short orbital eccentricity cycles. During the 3rd-order transgression, crinoidal bioherms developed across Switzerland followed by deep-ramp environments. Subsequently, tempestites were deposited up to and after the basin-wide maximum flooding surface. Lateral tempestite correlations indicate that Switzerland lay within an open-marine, mid-ramp environment during almost half of the depositional history. Mid-ramp deposits pass upwards to prograding shelly shoals, which sheltered a back-shoal lagoon containing patchy oolitic shoals. At the top of the Upper Muschelkalk, back-shoal sediments give way to coastal sabkha facies, which were overlain by oolitic shoals during a marine transgression. Shortly thereafter the top of the Upper Muschelkalk was dolomitized by brines from an overlying hypersaline environment that was later removed by a basin-wide erosive event. Overall, the paucity of porous shoal facies, unlike in southern Germany, has resulted in poor primary reservoir properties in the Upper Muschelkalk of Switzerland. [ABSTRACT FROM AUTHOR]

This paper presents a case study of the sublacustrine precipitation of hydrothermal silica ± TiO2 in the Ediacaran Mançour Group of the Saghro inlier, Anti‐Atlas, Morocco. Lacustrine carbonates containing stromatolitic mats and bioherms occur in ephemeral ponds developed within the Oued Da'ra caldera. Its syn‐eruptive infill consists of pyroclastites, ashflow tuffs, and subsidiary lava flows and sills, whereas inter‐eruptive deposition is mainly represented by slope‐related debris‐flow breccias and landslides, alluvial fans and fluvial channels. Carbonate production took place in a mosaic of differentially subsiding, fault‐bounded intra‐caldera blocks controlled by episodic collapse‐induced drowning, pyroclastic blanketing and migration of alluvial/fluvial environments. After microbial carbonate production, the carbonates recorded several early‐diagenetic processes, punctuated by polyphase fissuring (controlling secondary permeability) locally linked to hydrothermal influx. Three generations of carbonate cements are recognisable: (i) fibrous, botryoidal and blocky/drusy mosaics of calcite; (ii) idiotopic mosaics of dolomite caused by flushing of hypersaline Mg‐rich brines; and (iii) euhedral to drusy calcite via dedolomitization. The δ13C and δ18O values from carbonate cements broadly become successively isotopically lighter, as a result of meteoric and hydrothermal influence, and were probably overprinted by the Panafrican‐3 phase that affected the top of the Mançour Group. Two mechanisms of silicification are involved: (i) early‐diagenetic occlusion of interparticle pores at the sediment/water interface of pyroclastic substrates and reefal core and flanks; and (ii) hydrothermal precipitation of silica ± TiO2 lining fissures and vuggy porosity encased in the host rock. Silica conduits cross‐cutting lacustrine mats and bioherms exhibit high potential of preservation in collapsed volcanic calderas. Primary fluid inclusions of hydrothermal silica contain brine relics with NaCl/CaCl2 ratios of 2·1 to 4·4, representing minimum entrapment temperatures of about 142 to 204°C, and abiotic hydrocarbons (heavy alkanes) related to serpentinization of the volcanic and volcanosedimentary basement of the Oued Dar'a caldera. [ABSTRACT FROM AUTHOR]

Microbialites are studied for their sedimentary features in stratigraphic relationship to the surrounding facies to determine the depositional environments suitable for dissemination of calcimicrobes. This study examines the stratigraphic position and distribution of microbial fabric in the Lower Furongian Changshan Formation exposed in Kouquan section of Datong City in the North China Platform. The formation is comprised of the first third-order carbonate depositional sequence of the drowning unconformity-type in Furongian. A variation tendency of sedimentary facies characterized by a generally shallowing upward succession can be noticed across the formation, ranging from the calcareous mudstone and shale of shelf facies at the bottom to massive micrites in the middle, and to thick-bedded oolitic grainstone of shallow-ramp facies in the top part. Inside a bed of microbial carbonate composed of massive micrites in the upper part of the formation, developed the dense undifferentiated microbial boundstones as a result of forced regression in response to the third-order relative sea-level falling, which can be grouped into leiolitic bioherms. A variety of well-preserved calcified cyanobacteria fossils recognizable as Epiphyton, Girvanella, and Renalcis developed inside the leiolite. These aerobic calcified microorganisms contribute to the calcification of mucilaginous sheaths by uptake of CO2 and/or HCO3− during photo-assimilated photosynthesis and participate in the first episode of cyanobacteria calcification event in Phanerozoic. The current macroscopic and microscopic analyses provide significant implications for the future understanding of the origin of leiolitic bioherm and their paleodepositional environment in the North China Platform. [ABSTRACT FROM AUTHOR]

Globally significant geoheritage features of the Cliefden Caves area, in the Belubula River Valley between Orange and Cowra in central western New South Wales, comprise a richly fossiliferous shallow-water limestone succession of Late Ordovician age (the Cliefden Caves Limestone Subgroup) overlain by deep-water laminites and allochthonous limestones of the Upper Ordovician Malongulli Formation. Key features of the Ordovician geology of the Cliefden Caves area that have been identified using the Geoheritage Toolkit as being of international significance are the abundance of unique and exceptionally diverse fossils in the Fossil Hill Limestone (forming the lower part of the Cliefden Caves Limestone Subgroup), which supplement detailed interpretation of carbonate-dominated deposition within an Ordovician volcanic island setting. The fossiliferous limestones preserve biostromes and local small bioherms of stromatoporoids and corals, and recurrent in situ and disarticulated/imbricated Eodinobolus shell beds formed in shallow, quiet-water, dominantly muddy carbonate sediments that passed up-sequence to clay-free carbonate environments. These mud-dominated carbonate sediments are interspersed with higher-energy conditions, represented by skeletal, lithoclastic and calcrete-ooid grainstones overlying disconformities, leading to the identification of subaerial disconformities and associated diagenesis in the Fossil Hill Limestone. The Fossil Hill Limestone is succeeded by massive limestones in the middle part of the Cliefden Caves Limestone Subgroup and then, in turn by the Vandon Limestone and the deeper-water graptolitic laminites of the Malongulli Formation—this completes a succession that is rarely preserved in the geological record, further enhancing the geoheritage significance of the Cliefden Caves area. [ABSTRACT FROM AUTHOR]

During the Late Jurassic, the Jura platform was the site of major carbonate production involving various reef building components, particularly corals and microbialites. The existence of a detailed stratigraphic framework for the French Jura sedimentary succession during the Late Oxfordian–Early Kimmeridgian interval makes it possible to analyse the nature and distribution of these reefs within a high-resolution time frame, the Bimammatum Zone. Even though these reefs developed in a wide range of settings, their development was never optimal, indicating the presence of limiting factors. When the supply of terrigenous material was lower, the inner platform was characterized by strong carbonate production, with the development of a large ooidal shoal complex including ten-meter scale coral-microbialite patch reefs. The large size and high-density skeletal structure of some colonies indicates a favourable environment for coral and reef development (shallow, agitated, well-oxygenated waters with high light levels), despite the coral assemblage being poorly diversified and characterized by a mixed photo-heterotrophic association. The autocyclic character of the sedimentary system (i.e. major migrations of the ooidal dunes after big storm events) recurrently interrupted reef development. When the French Jura platform was subject to significant terrigenous input, the coral assemblages became well-diversified and characterized by mixed or heterotrophic-dominated associations. In the shallow and proximal areas of the inner ramp, limited available space imposed strong constraints on the reef growth, which only developed biostromal morphologies. Along the mid ramp, the reefs were composed firstly of plurimetric bioherms, then metric patches and finally coral meadows, highlighting the inversely proportional relationship of reef size to water depth. Once a certain depth was reached on the mid ramp, the presence of corals with heterotrophic feeding patterns could explain their reduced capacity to grow and build up a reef framework. Periods of greater terrigenous input, causing high turbidity and eutrophic conditions, led to frequent interruptions in reef growth both in the inner and more proximal mid ramp positions. This terrigenous influence is less pronounced in the central part of the mid ramp, where storms could alternatively stop reef development by causing migration of oncoidal sediments that then covered the small coral patches. In the distal part of the mid ramp, reef growth was reduced and relatively stable. Here, periods of reef development were controlled by long-term allocyclic processes that triggered the migration of oncoidal facial belts resulting from variations in relative sea level. [ABSTRACT FROM AUTHOR]

Microbial carbonate has been increasingly recognized as an important player for sediment production and building up of organosedimentary deposits. The integrated spatio‐temporal pattern of microbial facies is important for understanding carbonate production processes in a carbonate platform. This paper focuses on the sedimentary facies and development of a microbe‐dominated platform in the Cambrian North China Platform (the Zhangxia Formation of the Cambrian Series 3) in Shandong Province, China. In the entire Zhangxia platform, deposition started with oolite‐dominated shoal‐lagoon system with rare microbialites. The shoal‐lagoon system in the western part of the study area kept up with sea‐level rise and formed a flat‐topped platform, whereas that in the eastern part failed to keep up and thus drowned. The platform top then changed to a microbe‐dominated carbonate platform consisting of thrombolite, stromatolite, dendrolite, and Epiphyton framestone. The initial significant microbialites were biohermal thrombolite and dendrolites, which subsequently changed into wider biostromal forms. The morphologic change was largely due to initial rapid rise in sea level and the following deceleration. Extensive biostromes of laterally coalesced thrombolite–Epiphyton bioherms occur in the shale‐dominated eastern part. These microbialites then perished by platform‐wide drowning. The vast initial development of microbialite facies of the Zhangxia Formation in the Shandong area was important for the establishment of an extensive microbialite‐dominated carbonate factory made by combination of an absence of reef‐building metazoans and possible transition of seawater chemistry from aragonite sea to calcite sea in the Cambrian Series 3. It is comparable to the other carbonate environments lacking dominant metazoan reef builders after the mass extinctions. [ABSTRACT FROM AUTHOR]

The Eifelian lithostratigraphic succession of southern Belgium is here revised based on new field investigations and reconsideration of biostratigraphic data. The Couvin Formation is divided into four members: the Villers-la-Tour Member recorded the onset of stromatoporoid biostromes, the Petigny Member is a dark fine-grained limestone that recorded the Choteč event, the Cul d'Efer Member is dominated by stromatoporoid-coral biostromes. These first three members were previously united in the Foulerie Member and correspond to the transgressive and highstand system tracts of the Middle Devonian 3rd-order sequence MD1. The argillaceous and bioclastic successive units of the Abîme Member recorded the sequence MD2. Laterally, this sequence is only composed of siliciclastic deposits of the Vieux Moulin, Station and Cimetière members of the Jemelle Formation. The highstand system tract is the newly introduced carbonate Vierves Member. Large bioherms, newly described as the Wancennes Formation, recorded the first two sequences MD1 and MD2. A major sequence boundary caps the Couvin Formation and is overlaid by the transgressive and diachronous Chavées Member of the Jemelle Formation with a depositional gap increasing eastwards. The highstand system tract of sequence MD3 is recorded in the bioherms of the Tienne Sainte-Anne Member (upper part of the Jemelle Formation), also capped by a sequence boundary. These bioherms probably acted as highs around which the sandy deposits of the Lomme Formation accumulated as lowstand system tract of sequence MD4. The Hanonet Formation and its crinoidal Wellin Member form the transgressive system tracts of sequence MD4 that terminates in the bioclastic and biohermal Trois-Fontaines Formation (Givetian). The Kačák event is identified in the transgressive system tract of this sequence. The geographic distribution of facies and of reefs in particular led to the recognition of at least six sedimentation areas corresponding most probably to synsedimentary faulted blocks here defined as the Eau Blanche, Viroin, Lesse, Ourthe, Condroz and Sambre blocks. These sedimentation areas structured the Namur-Dinant Basin and recorded distinct depositional history and were probably active during the Devonian and Carboniferous interval. [ABSTRACT FROM AUTHOR]

Coral bioherms of the Vršatec Limestone that formed massive, several tens of meters thick complexes during the Jurassic were important sources of carbonate production, with carbonate sediment exported to deeper parts of the Pieniny Klippen Basin (Western Carpathians). However, the age of these carbonate factories remains controversial. New analyses of benthic foraminiferal assemblages occurring in coral bioherms and peri-biohermal deposits of the Vršatec Limestone at five sites in the western Pieniny Klippen Belt (Vršatec-Castle, Vršatec-Javorníky, Malé Hradište, Malé Hradište-Kalvária, and Drieňová Hora) show that these sediments were deposited during the Bajocian and were lateral equivalents of crinoidal limestones and breccias, in contrast to previous studies suggesting that they were deposited during the Oxfordian. First, all sites are characterized by similar composition of foraminiferal assemblages on the basis of presence–absence data, although foraminiferal assemblages in biosparitic facies at Vršatec are dominated by miliolids whereas biomicritic facies at Malé Hradište are dominated by the spirillinid Paalzowella. The composition of foraminiferal assemblages does not differ between the lower and upper parts of the Vršatec Limestone. Second, foraminifer species that were assumed to appear for the first time in the Oxfordian already occur in the Middle Jurassic sediments of the northern Tethyan shelf. Third, the first and last appearances of foraminifers documented in other Tethyan regions are in accordance with stratigraphic analyses and ammonoid occurrences, demonstrating that bioherm-forming coral communities developed on the Czorzstyn Ridge during the Bajocian. Several species of foraminifers of the Vršatec Limestone appeared for the first time during the middle or late Aalenian (Labalina occulta, Paalzowella feifeli) and during the Bajocian (Hungarillina lokutiense, Radiospirillina umbonata, Ophthalmidium caucasicum, O. terquemi, O. obscurum, Paalzowella turbinella, Cornuspira tubicomprimata, Nubecularia reicheli) or appeared for the last time in the Bajocian (Tethysiella pilleri) or Early Bathonian (Ophthalmidium caucasicum, O. obscurum). The composition and diversity of communities with benthic foraminifers of the Vršatec Limestone is similar to the composition of foraminiferal communities on carbonate platform environments with corals of the French Jura and Burgundy during the Bajocian. [ABSTRACT FROM AUTHOR]

Eight Bessarabian (Sarmatian) serpulid bioherms located among aragonite sediments of the Topola Formation in section Zelenka (Northeastern Bulgaria) have been studied to elucidate their macro- and microscopic characteristics. It is concluded that these bioherms were formed under identical arid climatic conditions as the associated aragonite sediments. [ABSTRACT FROM AUTHOR]

When the modern features of large-scale Asian monsoonal circulation were set-up is poorly constrained and pre-Neogene monsoonal archives are rare. This study investigates the temporal evolution of neritic carbonates in the proto-South China Sea to reconstruct East Asian monsoonal currents and winds during the middle to late Paleogene. Analysis of three-dimensional seismic and well core data from the North-West Palawan block reveals the occurrence of a set of thick (>125 m), aggrading Halimeda bioherms, early Oligocene in age. By analogy with Holocene green algal buildup counterparts, they are interpreted to form in nutrient-rich areas subject to upwelling currents and reflect the early presence of a strong coastal jet in the Proto-South China Sea, as seen today during the summer monsoonal season. The analysis of the underlying mixed carbonate–siliciclastic ramp shows that mesotrophic conditions already prevailed during the late Eocene, thus suggesting that modern-like summer East Asian Monsoon large-scale circulation was possibly active as early as the late Eocene in the Proto-South China Sea. Evidence for upwelling currents vanishes in late early Oligocene carbonate-producing biota, that are characterized by the significant development of euphotic hermatypic coral communities reflecting lower nutrient concentrations. This turnover coincides with the opening of the modern South China Sea and is interpreted to result from the southward drift of the North-West Palawan block which placed the area away from the Chinese margin and the coastal jet. Our results highlight therefore that many of the features of the summer East Asian Monsoon large-scale circulation are rooted in the middle Paleogene. • Many of the features of the summer East Asian Monsoon large-scale circulation are rooted in the middle Paleogene. • Early Oligocene Halimeda bioherms from offshore NW Palawan record nutrient-rich areas subject to upwelling currents. • They reflect the early presence of a strong coastal jet in the Proto-South China Sea. • Euphotic hermatypic coral communities have developed from the late early Oligocene revealing the demise of upwelling currents. • This turnover coincides with the opening of the modern SCS and the southward drift of the North-West Palawan block. [ABSTRACT FROM AUTHOR]

Abstract: The cold-water Volkhov and warm-water Keila hardgrounds of the Ordovician Baltic Basin represent a specialized product of cyanobacterial communities of the seafloor, another member in a group containing stromatolites and microbially induced sedimentary structures. The leading role of cyanobacterial communities in the development of hardgrounds is suggested by their macrofeatures, structure, and elemental composition revealed by SEM equipped with a microprobe microanalyzer. During the formation of the hardgrounds, the cyanobacterial films were of considerable thickness (up to 4-5 mm), but lacked vertical zonation of bacterial communities, thereby being at an intermediate stage between the mature biofilms and true mats. The soft substrate underlying hardgrounds was inhabited by an abundant infauna. Thanks to bioturbation, the cyanobacterial film was in places destroyed, which prevented the development of hardgrounds. In the warm Late Ordovician basin of northern Estonia, cyanobacterial films formed hardgrounds on the surface of ripple marks. Abundant peloids and warm pore waters facilitated further cementation and hardening of the substrate underneath the hardground before the burial of the ripple marks and the hardground. Cyanobacterial films appeared simultaneously over large areas of the seafloor due to settling of planktonic bacteria. The extracellular polymeric substances (EPSs) released by these bacteria were rapidly mineralized within a maximum of one season, apparently at a depth of 15-25 m, below the fair weather wave base. The formation of hardgrounds in bioherms occurred in a shallower environment and was patchy due to the alternation of living and dead cyanobacterial mats, mineralizing mats and resulting hardgrounds. Inhabitants of biohermal hardgrounds were producers of carbonate detritus, including of micritic size, over vast areas of the seafloor surrounding the bioherm. [ABSTRACT FROM AUTHOR]

Lower Cretaceous (Valanginian) dendritic microfabrics occur in karstic cavities within fine-grained shallow-marine platform carbonates at San Lorenzello, southern Italy. They form dense micritic masses and clusters, generally oriented perpendicularly to cavity surfaces, surrounded by layered sparry cement. Individual dendrites, typically sub-millimetric in size, have highly irregular margins and form distinctive shrub-like masses ranging from compact and squat, to elongate and highly branched. The centimetric and irregularly elongate cavities appear to have formed through subaerial exposure, and are almost entirely filled by the micritic dendrites and associated sparry crusts. In size, shape and micritic composition, the dendrites broadly resemble a variety of similar fabrics, including hot spring travertine shrubs and calcified microfossils such as Cambrian Angusticellularia , which has analogs in present-day lacustrine calcified cyanobacteria. However, the San Lorenzello dendrites differ in occupying small cavities. This cryptic microkarstic dripstone setting, together with the often regular spacing and appearance of these dendritic fabrics, may be more consistent with an abiotic origin. These comparisons underscore the challenge of interpreting microdendritic carbonates fabrics in general. [ABSTRACT FROM AUTHOR]

The Lower Cretaceous Devils River Trend on the northeast margin of the Maverick Basin in southwest Texas contains unique deposits of large domal, thrombolitic, microbial biostromes that have not been identified elsewhere in the Albian of the onshore Gulf of Mexico. These microbial biostromes are overlain by microbial-dominated, moderate-energy grainstones to mud-free rudstones. Above the grainstone to rudstone section is a hiatus (the Albian-19, high-frequency-sequence maximum flooding surface), and above this hiatus are large caprinid rudist bioherms. The overall setting for these carbonate deposits is the moderate- to high-energy north rim of the intraplatform Maverick Basin that is approximately 150 mi (240 km) behind the Stuart City Reef Trend. Four levels of description are necessary to describe the biostromes: (1) megalevel (overall external form)—domal biostromes, (2) macrolevel (larger internal form or layering)—sinuous convex-up layers within domes, (3) mesolevel (basic growth morphology—clotted thrombolites [subvertical to vertical]), and (4) microlevel (microbialite basic texture)—microbial peloids and mesoclots (clots of microbial-mediated material—mainly packed clusters of dark, micritic peloids). The thrombolitic peloids and mesoclots are arranged in digitate to randomly branching growth forms. The thrombolites are very microporous. Growth-framework cavities with sediment fill are common and are filled with mesoclots, peloids, clasts, miliolids, ostracods, echinoid fragments, bivalve fragments, and gastropods. The microbial biostrome is not continuous but has gaps (channels) filled with microbial-dominated grainstone and mud-free rudstones. The microbial-dominated grainstone and mud-free rudstone strata above the microbial biostrome are continuous, although irregularly bedded, with some beds being cross-stratified, and they are composed of fossiliferous, peloidal, mesoclot grainstone with abundant biota encrusted in a microbial coating. The domal, thrombolitic, microbialite biostrome is interpreted to have been deposited on a moderate-energy, semirestricted intraplatform rim at the northeast edge of the Maverick Basin during a higher order transgression. The microbial-dominated strata may have been associated with high nutrient concentrations and initial low sedimentation rates, followed by low to moderate sedimentation rates. The microbial-dominated grainstones and mud-free rudstones above were laid down in a moderate-energy environment during continued transgression. A sharp break exists with the shelf-interior, high-frequency highstand cycle above, which contains abundant rudist bioherms but no microbialites. Most of the primary megapores (growth-framework cavities and interparticle pores) are cemented with equant calcite. Nano- and micropores are extremely abundant within the microbial-related strata. These deposits would make good microporous reservoirs in the subsurface. [ABSTRACT FROM AUTHOR]

The distribution and changing pattern of stromatolites in the Vempalle Formation of the Cuddapah Basin, India, have been investigated with emphasis on external morphologies, internal fabrics, growth patterns and sediment associations. The stromatolitic limestone occurs in a low angle ramp type carbonate platform, with complete exposures from shallow shelf to basinal facies, provides record of changes in reef-building capacity of stromatolites with change in the depositional milieu. Changing pattern and style of the stromatolites clearly reflect depth partitioned growth of the microbial community. Small and scattered stromatolites, commonly with wavy parallel laminations or stratifications occurred in inner-ramp settings, where they are build up to the sea level. Tepee structure and desiccation cracks in associated sediments and salt pseudomorphs point to shallow water to occasional exposure condition. Large bioherms with columnar and conical stromatolites developed in the headland (mid ramp), which were in continuous interaction with strong waves of the open sea. Growth of the bioherms changed the landform with time and generated a high sloping edge with a sheer drop that extended out into the sea, forming distally steepened ramp. Outer ramp lithofacies characterized by thick layers of shale succession with thin beds of laterally persistent stromatolitic beds with low synoptic relief build-ups. These biotic components, along with the absence of wave-related structures, place the outer ramp below the base of wave action zone. Ooid banks developed in the mid ramp area are in the high surfing zone. High flux of nutrients and high-light show positive correlation; thus the high growth pattern is best observed within the photic zone where wave action is maximum. The ability to change from low synoptic relief algal laminites to high synoptic relief columnar stromatolites point to their adaptive power. The key factor that controlled the shape of these Palaeoproterozoic stromatolites is the dynamic interactions between mat growth, currents and sediment supply. Presence of concentric and radial fibrous ooids indicates change in climate and salinity of the sea. [ABSTRACT FROM AUTHOR]