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The occurrence of Precambrian stromatolites is closely related to the ancient seawater composition and the evolution of life. It is also a potential oil and gas reservoir. In what kind of environment the stromatolites of the upper Ediacaran Qigebulak Formation in the Tarim Basin developed, and whether they constitute potential hydrocarbon reservoirs, remained unclear. Stromatolites occur in 1–5 m thick layers, interbedded with thrombolites and dolostones. Distinct stromatolite morphologies were observed, including columnar, sinuous, short columnar, domal, and conical shapes. The δ13C values of the stromatolites (6.1‰ on average) are slightly lighter than those of the dolostones, and the δ18O values (− 1.4‰ on average) are significantly heavier than that of the dolostones. The stromatolites have a relatively high content of rare-earth elements and a minor Ce anomaly. The geochemical results imply that the stromatolites formed in an evaporative hypersaline lagoon environment. The presence of barrier dams near the coast led to the formation of lagoons, where hypersalinity was achieved when evaporation was greater than marine or freshwater input. High salinity conditions inhibited the growth of Ediacaran metazoans, allowing the buildup of stromatolites in the restricted lagoons. The stromatolites are rich in primary fenestral pores and sheet-like cavities along the laminae, and the secondary dissolution pores and vugs are related to meteoric karstification. The stromatolites, together with dolostones and thrombolites, constitute the majority of the hydrocarbon reservoirs in the Upper Ediacaran in the Tarim Basin. The results clarify the environment where the stromatolites could still flourish and be well preserved whereas they significantly declined globally throughout the Neoproterozoic elsewhere. The results imply that extensive stromatolites in the Proterozoic strata are potentially important reservoir rocks of Precambrian petroleum systems.

The main goal of the paper is the reconstruction of a Middle Triassic buildup cropping out in the central part of the Southern Apennines. Middle Triassic reefs of the western Tethys realm are well known in the Northern and Southern Alps. In contrast, few studies of the Anisian–Ladinian carbonate platforms of the southern Apennines are available, due to the diagenetic alteration and tectonic disruption that hinder their paleoenvironmental and stratigraphic reconstruction. In an attempt to fill this gap, and to improve the knowledge on the Anisian–Ladinian carbonates of central Mediterranean area, this research is focused on a carbonate buildup cropping out in the “La Cerchiara” area, Sasso di Castalda (Basilicata, Southern Italy). The buildup, affected by intense tectonic deformation associated with the development of the Apennine thrust and fold belt, was studied using a statistical evaluation of the quantitative microfacies data. The research enabled a reconstruction of the original stratigraphic relationships of the various buildup fragments. A positive linear regression between the sample positions vs the percentage of autochthonous carbonates indicates an increase of the autochthons carbonate toward the top of the succession. The allochthonous fabrics (packstone/wackestone) at the base of the section (Unit IIIa) pass gradually upward into autochthonous (boundstones) facies (Units IIIb, I), consisting of microbialites (clotted peloidal micrite, microbial-derived laminae, and aphanitic micrite), microproblematica and cyanobacterial crusts, with few encrusting skeletal organisms. Statistical data suggest that units IIIa, IIIb, and I are in stratigraphic order while unit II appears to have been moved by tectonic dislocation from its original position at the base of the succession. The absence of metazoan reef framework, and the richness of micro-encrusters, autochthonous micrite and synsedimentary cements, suggest a mud-mound style of growth for the carbonate bodies of the Southern Apennine during the Anisian.

Alternations of thin-bedded limestone and shale, or ribbon rock, commonly occur throughout lower Palaeozoic carbonate successions; however, their formative processes are still unclear. In this study, we discuss the origin of the ribbon rocks of the upper Cambrian Hwajeol Formation, Korea, based on detailed microfacies analysis of a ~ 2-m-thick interval. Five sedimentary microfacies were identified: normally graded calcarenite to shale; parallel-laminated shale; lime mudstone; wackestone-to-packstone; and bioclastic–intraclastic packstone-to-conglomerate. Shale facies were most likely formed by frequent storm-induced bottom currents, whereas, lime mudstone facies were deposited in situ by suspension settling of micrite, mudflows, or growth of keratose sponges on the seafloor, and/or formed by early diagenetic growth. Conglomerate/packstone/wackestone indicate infrequent, larger-scale events, e.g., mega-storms, tsunamis, or earthquakes. We propose a new formative model for tempestite-type ribbon rock based on the Hwajeol example, and suggest that this model can be differentiated from the other types of ribbon rocks—tidalite, turbidite, and diagenetic types. Formation of the tempestite-type ribbon rocks would have been promoted by the characteristic environmental conditions of the early Palaeozoic, in particular sea-water chemistry that promoted calcite precipitation and the paucity of burrowers. Detailed microscopic observations can thus provide clues to elucidate previously unknown sedimentary processes in the deeper parts of carbonate platforms.

The Upper Ordovician Zhe-Gan Platform was a short-lived carbonate platform that formed near the northern margin of the Cathaysian Land of the South China Block. The Zhe-Gan Platform is less well understood than the adjacent Yangtze Platform due to the absence of detailed sedimentological study as well as the structural complexity of the area. The aim of this study was to reconstruct the Zhe-Gan Platform based on detailed facies analysis of the middle to upper Xiazhen Formation. A total of 24 shallowing-upward depositional cycles (C1–24) are identified and subdivided into three types based on the vertical association of facies: (1) mixed carbonate–clastic subtidal cycles; (2) carbonate subtidal cycles; and (3) peritidal-capped subtidal cycles. The reconstructed depositional model indicates a ramp-type, mixed siliciclastic–carbonate platform, generally similar to other Late Ordovician carbonate platforms characterised by dominant skeletal grains, less common ooids, and an absence of skeletal barrier reefs. The newly developed Late Ordovician ramp-type carbonate platforms could have been induced by the evolution of skeletal organisms and the accompanying palaeoceanographic changes prior to the Hirnantian glaciation. The complex palaeogeography of the South China Block would have influenced the co-occurrence of the Xiazhen carbonate platform and black shales of the adjacent Yangtze Platform on the same block during the Late Ordovician.

The lower member of the Poleta Formation is well known for its abundant archaeocyaths, including an exceptionally preserved reef at Stewart’s Mill in Nevada. Large archaeocyath-bearing reefs are relatively uncommon, with most occurring as small nearshore patch reefs. Here, we describe a new 70 m-thick archaeocyath reef from the lower Poleta Formation, herein referred to as the Gold Point Reef, located near the townsite of Gold Point, Nevada. In spite of broad similarities with the Stewart’s Mill exposure, the Gold Point Reef shows an interplay between shoal and reef development over the ~ 70 m exposure that differs from what is observed at Stewart’s Mill. This reef also preserves a small shelly fauna in its uppermost 10 m, dominated by Hyolithellus. Three successive ecological stages of reef development are observed here: the pioneer stage characterized by a single rare frame-building species; the diversification stage involving about nine species of both frame-building and mud-sticking archaeocyaths; and the final foundering stage represented by one to two species of archaeocyaths and facies indicating reef demise, including abundant grainstone/packstone shoals and a silicified upper bed with a settlement of hyolitheminthes. During the apex of reef development here, there are large modular archaeocyaths, which were able to produce thick secondary skeletal tissue for a firm attachment; these archaeocyaths were capable of building large reefs in a variety of settings. Additionally, the carbon isotope profile recorded in the Gold Point Reef shows similarities to nearby exposures of the equivalent lower Poleta Formation, with the exception of a small negative downturn at the top of the reef that is not found in other locations. Combined with the documentation of facies changes over short lateral distances, the isotope data suggest that archaeocyathan reefs may have been time-transgressive across the shelf during deposition of the lower Poleta. Additionally, our work suggests that both here and globally, the specific biotic assemblage reflected the local influences of the environment on reef development, creating highly variable coeval paleocommunities even within a restricted area.

The Mediterranean red coral, Corallium rubrum (L.), has been a valuable economic resource for more than 2000 years. The Sicily Channel and surrounding areas are one of the most famous red coral fishing grounds of the whole region, hosting the deepest ever found living colonies and large sub-fossil red coral deposits; the so-called Sciacca banks are a unique location in the whole Mediterranean Sea. In this paper, a morphometric description of this sub-fossil population is presented for the first time from studies of colonies in the collection of several coral factories from Torre del Greco (Naples), with radiocarbon age estimations and growth rate evaluations. From the results of this study, after several thousand years Sciacca red coral colonies maintained the organic matrix structure with evident annual discontinuities, allowing estimations of the annual growth rate (about 0.3 mm/year) and the average population age (about 33.5 years). These resulting data are similar to the values determined for deep-dwelling living red coral populations. The radiocarbon dating evidenced a range of ages, from 8300 to 40 years before 1950 CE, mostly falling between 2700 and 3900 YBP, suggesting that colonies accumulated over a wide span of time. In view of the tectonically active nature of the area, several catastrophic events affected these ancient populations, maintaining them in a persistent state of early-stage, structurally similar to the those in current over-exploited areas.

We propose a new facies classification scheme of the cyclic lacustrine carbonates of the Bernburg Formation (Lower Triassic, Induan), with a major focus on the microbial biota and grains. Our data are based on a detailed bed-by-bed outcrop study in Central Germany, within a robust (litho)stratigraphic framework. We concentrate on two intervals of the Bernburg Formation: one around the Calvorde/Bernburg Formation boundary (including the HRZ – „Hauptrogensteinzone“), and a second around the ninth cycle near the upper formation boundary. The textural and mineralogical composition of the two endmember components: skeletal stromatolites and oolites, and the macro-, meso-, and microstructural characteristics (supplemented by μ-XRF-data) allow to classify the carbonates into five lithofacies types. They are interpreted with respect to the development of an ideal lacustrine depositional cycle, embedded between a lake level rise and a lake level fall. The microfacies attributes of the microbialites include various lamination types, shrubs, spherulites, and laminated/clotted/fenestral microfabrics. All sedimentologic (macro-, meso, and microscale) and geochemical data of this study indicate nearshore deposition of the carbonates at marginal shoals in a major endorheic lake (playa lake) with high alkalinity and salinity, and strongly fluctuating lake levels, under arid climates. The lacustrine carbonates are associated with maximum lake expansions, and are laterally interfingering with fan deltas, as indicated by abundant clastic grains in the intercalations of the skeletal stromatolites. The Bernburg Formation microbial buildups reflect changes in lake-level, hydrodynamics and grain supply, and therefore offer insights for the paleoenvironmental interpretation of lacustrine microbialites elsewhere.

The siliciclastic Jhuran Formation of the Kachchh Basin, a rift basin bordering the Malagasy Seaway, documents the filling of the basin during the late syn-rift stage. The marine, more than 700-m-thick Tithonian part of the succession in the western part of the basin is composed of highly asymmetric transgressive–regressive cycles and is nearly unfossiliferous except for two intervals, the Lower Tithonian Hildoglochiceras Bed (HB) and the upper Lower Tithonian to lowermost Cretaceous Green Ammonite Beds (GAB). Both horizons represent maximum flooding zones (MFZ) and contain a rich fauna composed of ammonites and benthic macroinvertebrates. Within the HB the benthic assemblages change, concomitant with an increase in the carbonate content, from the predominantly infaunal “Lucina” rotundata to the epifaunal Actinostreon marshii and finally to the partly epifaunal, partly infaunal Eoseebachia sowerbyana assemblage. The Green Ammonite Beds are composed of three highly ferruginous beds, which are the MFZ of transgressive–regressive cycles forming the MFZ of a 3rd-order depositional sequence. The GAB are highly ferruginous, containing berthieroid ooids and grains. GAB I is characterized by the reworked Gryphaea moondanensis assemblage, GAB II by an autochthonous high-diversity assemblage dominated by the brachiopods Acanthorhynchia multistriata and Somalithyris lakhaparensis, whereas GAB III is devoid of fossils except for scarce ammonites. The GAB are interpreted to occupy different positions along an onshore–offshore transect with increasing condensation offshore. Integrated analyses of sedimentological, taphonomic, and palaeoecological data allow to reconstruct, in detail, the sequence stratigraphic architecture of sedimentary successions and to evaluate their degree of faunal condensation., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Department of Science and Technology, Ministry of Science and Technology http://dx.doi.org/10.13039/501100001409, Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)

Petrofacies and taphofacies defined for the Morro do Chaves Formation (Late Barremian/Early Aptian) outcropping in the Sergipe-Alagoas Basin (NE Brazil) enable the interpretation of the biostratinomic and fossil-diagenetic processes that acted on the abundant bivalve shells and enclosing sediments. Such processes played an important role in the circulation of fluids within the coquina deposits and therefore on the resulting porosity–permeability of the rocks. Ten taphofacies and four lithofacies are recognized, allowing 36 petrofacies to be defined, based on the nature of the sedimentary and taphonomic processes. Five of these petrofacies are distinguished for those showing almost total replacement of the original constituents. The relationship between petrofacies with the geometry of sedimentary bodies and their lateral and vertical variations, forms the basis of a stratigraphic model for the depositional system of the coquinas of the Morro do Chaves Formation that reflects the spatial and temporal distribution of the identified petrofacies. The integration of the evolutionary taphonomic analysis of the unit with the analysis of multiscale properties through the CAMURES Methodology allowed us to develop a theoretical model for the alteration and modification of taphonomic elements and coquinas, which reflect the rise and fall of the relative base level in a lacustrine to the restricted marine setting. This model leads to more accurate identification and classification of coquina reservoir facies, as well as the delimitation of reservoir zones for 3D geocellular modeling and flow simulation of hydrocarbon-producing reservoirs, thus improving predictive analyses.

Fossil bioerosion traces at a new site of Les Bez (Jura Department) and those already known from Verrieres-de-Joux (Doubs Department) in the central French Jura record an ancient Miocene cliffed shoreline cut into Lower Cretaceous limestones. Both localities are at about 900 m above the present sea level. Caulostrepsis, Gastrochaenolites and Circolites are the ichnogenera identified at Les Bez, whereas only Gastrochaenolites is present at Verrieres-de-Joux. This ichnoassociation identifies the Entobia ichnofacies, which corresponds to the upper infralittoral marine environment, biologically associated with the biocenosis of photophilic algae. By means of digital analysis of high-resolution field images, the percentage of the surface affected by the erosive activity of polychaete worms, bivalves and echinoids has been calculated. This information permits a better evaluation of their biological activity, thus complementing the data on the number of specimens per surface area. The cliff preserved at Les Bez was more affected, showing Gastrochaenolites with diameters smaller than those at Verrieres. The Circolites–Caulostrepsis association is well developed at Les Bez, where polychaete borings are located within echinoid bowl-shaped pits with particular patterns, suggesting an ecological relationship between involved organisms. Moreover, the distribution of the borings along this outcrop is not uniform and digital analysis at three sections (A, B and C) suggests a lower and an upper zone developed on the outcrop under slightly different environmental conditions within the upper infralittoral. The exceptional preservation of the Les Bez fossil cliff-site demands protection in order to ensure its future existence and accessibility.

The Miocene genus Rzehakia, an endemic brackish bivalve that lived in the Paratethys Sea, recorded in late Ottnangian sediments deposited during the regression of the Central Paratethys Sea in the semi-enclosed Alpine-Carpathian foreland basin, is closely related to the Rzehakia found hundreds of kilometres away in the early Badenian transgressive sequence situated in the Western Carpathians hinterland. The finding of the “Rzehakia beds” from the Malý Krtis site in the Novohrad-Nograd Basin provides insight into the palaeobiogeography of the Central Paratethys. The present study documents Rzehakia-bearing deposits of an alternating wave-dominated, river-influenced environment and of a fluvial-dominated, tide-influenced, wave-affected environment, probably located on the prodelta slope of a compound deltaic clinoform. Corresponding calcareous nannofossil assemblages, marked by the absence of Sphenolithus belemnos and the co-occurrence of Helicosphaera ampliaperta with Sphenolithus heteromorphus without Helicosphaera waltrans, indicate the NN4 Zone. Furthermore, the presence of the regional benthic foraminiferal marker Uvigerina graciliformis indicates a Karpatian age and the planktic Globorotalia transsylvanica restricts the profile stratigraphic range to the upper Burdigalian-Langhian part of the NN4 Zone (i.e., upper Karpatian-lower Badenian). In accordance with updated palaeogeographic data, these results led us to the conclusion that the “Rzehakia beds” in the Novohrad-Nograd Basin are synchronous with or younger than those from the Alpine-Carpathian Foredeep and are possibly related with their middle Miocene (late Kotzakhurian–early Tarkhanian) occurrences in the Eastern Paratethys.

Being the main oil-bearing basin of Argentina, the Neuquén Basin contains a well-documented stratigraphic record of continental and marine sedimentation during the Jurassic and Cretaceous in the western margin of Gondwana. Marine sedimentation started in the Early Jurassic with the deposition of the ofshore to prodelta shales of the Los Molles Formation, the basal unit of the Cuyo Group. A palynological study of outcrop samples of the Los Molles Formation at two localities,Puente Picún Leufú, southern Neuquén Basin, and Cordillera del Viento, central basin area, is presented. The palynological evidence allows inferring two diferent palaeoceanographic contexts during the deposition of the Los Molles Fm. At Puente Picún Leufú and the lower part of the Cordillera del Viento localities, the record of acritarchs and prasinophytes suggests a stratiied water column, suboxic-to-anoxic bottom conditions, and a reduced salinity within the photic zone, associated with a marginal marine environment under restricted oceanic circulation. These conditions would have last at least until the Early Bajocian. Conversely, at the middle and mainly the upper part of Cordillera del Viento locality, the predominance of dinocysts in the assemblages indicates a hydrographically unstable shelf (non-stratiied water mass column) with welloxygenatedbottom waters developed under open-marine settings with non-restricted oceanic circulation. The abundance and diversity of dinocyst assemblages are comparable with those observed in the Late Callovian Lotena Formation. These evidences suggest an open oceanic circulation due to the establishment of diferent seaways in the Neuquén Basin, during the inal accumulation of the Los Molles Formation (Early Callovian). Fil: Olivera, Daniela Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina Fil: Martinez, Marcelo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina Fil: Zavala, Carlos Alberto. Universidad Nacional del Sur. Departamento de Geología; Argentina. GCS Argentina; Argentina Fil: Di Nardo, Juan. Universidad Nacional del Sur; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina Fil: Otharán, Germán Aníbal. Universidad Nacional del Sur; Argentina. GCS Argentina; Argentina

The Early Permian (Kungurian) Khao Khad Formation of Central Thailand consists mostly of carbonates deposited on the western margin of the Indochina Terrane. This formation has yielded unusual microbial-fusulinid limestones with large gastropods which contribute most to the rock volume. With a height of more than 6 cm, the gastropods are amongst the largest Early Permian gastropods ever reported. Gastropods as major rock formers are rare in the Palaeozoic. This, and other recently reported invertebrate faunas from Thailand show that gastropods may dominate Permian fossil assemblages not only in diversity, but also regarding abundance and in some cases also regarding biomass. Besides gastropods, fusulinids, various calcareous algae, intraclasts and thick microbial-cyanobacterial (Girvanella and Archaeolithoporella) coatings and reticular microbial patches as well as thick inter- and intragranular radial fibrous cement crusts are present. The gastropods represent at least four species and belong probably to undescribed taxa. The fusulinid genus Pseudofusulina and Misellina (M.) termieri are reported from the Khao Khad Formation for the first time and indicate a Bolorian age. Calcareous algae are dominated by dasycladaceans followed by gymnocodiaceans and solenoporaceans. The studied limestone almost completely lacks metazoan reef builders such as corals and sponges. Likewise, brachiopods and bivalves are absent in the studied samples and echinoderms are very scarce. The carbonate is interpreted as product of shallow water, back-reef lagoonal platform community with a high productivity providing the large gastropods with sufficient food. However, conditions were too eutrophic for sessile filter feeders including metazoan reef builders.

Microfacies analyses of twenty-five samples collected from three outcrops located in the northwestern part of the Transylvanian Basin offered new insights into the structural architecture and diagenetic features of the nummultic accumulations in this region. The data from thin-section observations revealed the fact that diagenetic processes (mainly pressure dissolutions) played a crucial role in the fabric development, porosity evolution and general morphology of these build-ups. A high degree of compaction was observed with respect to the abundance of stylolitic structures, fissure sets, and numerous fragmented nummulitic particles within the matrix. Such features allowed the identification of several phases of stylolitization which affected the nummulitic accumulations during burial diagenesis. Moreover, these compactional traits can provide clues for understanding the ratio variations between N. perforatus A (microspheric) and B (macrospheric) forms in such deposits. Combining our results with previous data we better constrained the autochthonous and/or para-autochthonous provenance of the nummulithoclasts. Our results offer a new perspective into the development and preservation of nummulitic accumulations deposited in the Eocene tropical/sub-tropical shallow-marine settings of the central Neotethyan realm.

The Jurassic–Lower Cretaceous successions cropping out in three different parts of Central Anatolia (Turkey) were deposited in local basins developed under tectonic influence from the Hettangian to the Oxfordian. Pelagic carbonate platforms (PCPs) were formed in the region during two separate phases in which synsedimentary faulting was active in the basins. Prior to the first tectonic phase, fluvial and tidal sediments, Hettangian-Sinemurian in age, were deposited unconformably on the low-grade metamorphic substrate of the Karakaya Complex (Upper Triassic), with Sinemurian crinoidal limestones above. At the end of the Sinemurian, the PCPs were developed as a result of fragmentation of shallow-marine platforms by normal faults. Across hanging-wall basins and footwall-blocks, the PCP facies: pelagic/hemipelagic nodular and marly Ammonitico Rosso facies, brachiopod-bearing limestone facies with hardgrounds, red fossiliferous mudstone, and calcareous Ammonitico Rosso facies containing blocks, were deposited with marked lateral thickness variations. The platform, which gradually became shallower in relation to the clastic sediments (180 m thick) filling the basin, was fragmented again at the end of the Bathonian. The opening of fractures in the platform is documented by neptunian dykes developed within the clastic facies, filled with Callovian ammonite-bearing mudstone. During the Callovian–Oxfordian, widespread ammonite-bearing red marl draped the clastic facies, although nodular pelagic and oolitic/ammonite limestones are locally present. Moreover, Oxfordian pelagic oolitic facies rest unconformably on Upper Triassic sandstone (Karakaya complex), which is locally intercalated between the metamorphics and the Jurassic cover, wherever these had been unroofed at the footwall of Jurassic normal faults. As a result of the tectonic activity during the Callovian–Oxfordian time, the Ankara region totally became a PCP in the Oxfordian. Condensed, nodular, pelagic oolitic–ammonitic limestones were deposited across the major uplifted blocks in an open-marine environment, previously called the Ankara seamount. These facies constitute an important key level in the Ankara region. Laterally continuous deep-marine sediments overlying the Late Oxfordian–Early Cretaceous PCP deposits indicate the rapid foundering of this sector.

The diagenesis of travertine and tufa is rarely considered an issue due to the common difficulty of distinguishing what is primary from secondary, as in most of cases these diagenetic changes occur very early. The main diagenetic features of travertine and tufa formed within a volcanic ravine in the north of Gran Canaria (Canary Islands, Spain) are cementation within pores and cavities, and of micropores (

The Ladinian Pseudozilian formation in the central part of the Sava Folds, Slovenia, was deposited in a deeper marine basin situated among the carbonate platforms lining the western margin of the Neotethys. The formation consists of shale and sandstone, hemipelagic limestone, volcanics, and volcanoclastics. At Dole pri Litiji, tuffaceous sandstone contains metre-scale olistoliths dominated by microbialites, solenoporacean algae, sponges, microproblematica and, to a minor extent, corals. Six types of fossil reef associations were recognized based on different proportions of these components. The presence of Ladinella porata Ott, dasycladaceans, and solenoporacean algae suggests the olistoliths originate from within the photic zone, perhaps the platform margin or the upper slope. Similar or even identical associations can be found in other Anisian to early Carnian reefs, suggesting the perseverance of reef associations that established themselves during the Middle Triassic recovery. Rather than replacing the older associations, new associations were added through time. The Anisian–early Carnian reef associations thus probably remained present even after the Late Triassic rise of scleractinian corals to dominance.

An important interval for reef evolution occurs in the Triassic Period. However, Late Triassic reefs along the edge of the Panthalassa Ocean receive much less attention than their Tethys region counterpart. To improve our understanding of reef evolution along the Panthalassa, we present a quantitative microfacies analysis to characterize reef facies types from a central Nevada locality. We point counted thin sections to quantitatively assess the relative abundance of reef and interstitial components from six Carnian reef mounds. Reef mound formation occurs at three different stratigraphic intervals. Each interval records a different reef mound size and shape. The oldest stratigraphic interval consists of four separate reef mounds; each mound is approximately 3–12 m wide and 2–4 m high. The second youngest stratigraphic interval consists of one large ~ 10-m wide and 15.5-m high domal reef mound. The third, and youngest, reef mound is smaller in comparison (i.e., 1-m wide and 1.5-m high). We recognize two reef facies types within these reef mounds. Different calcareous sponges, bound together by microproblematica and clotted micrite, form the overall reef framework. We suspect that changes in relative sea level affect the initial colonization, different growth capacities, and overall preservation of the South Canyon reef mounds. When South Canyon reefs are compared to other Panthalassa reefs, it seems that “Wetterstein-type” reef–sponge bindstone facies containing biogenic crusts dominate and corals are less abundant and persist generally in both shallow and deeper water environments. However, significant differences in primary and secondary framebuilder abundances exist due to differences in where the reefs grew in relation to fair-weather wave base (FWWB). Thus, changes in relative sea level may affect the initial colonization, different growth capacities, and overall preservation of reef but water depth may also control the primary and secondary reef builders. Consequently, quantitative assessment of reef ecosystems within a sequence stratigraphic framework undoubtedly facilitates fewer problematic comparisons between reefs but it also enhances our understanding of reef development.

The new crustacean microcoprolite Broennimannia persica n. ichnogen., n. ichnosp., is described from the Paleocene (Danian-Selandian) of eastern Iran. The new microcoprolite is characterized by a bilateral symmetrical system of longitudinal “canals” that in transverse sections display an irregular (labyrinthine) outline with concave infoldings and rounded protuberances. The crescentic outline of parts of the canal system recalls the long-ranging ichnogenus Palaxius Bronnimann & Norton (Carboniferous to Pleistocene). In the latter ichnogenus, however, the canals are isolated. A general determination key for microcoprolites in transverse section is provided. The new microcoprolite occurs in poorly sorted foram-algal grainstones/packstones with a fine-grained siliciclastic content. The associated microfauna and –flora includes common miliolids, among the agglutinating Haymanella, Stomatorbina sp., serpulids, and dasycladalean algae (Cymopolia sp., Trinocladus atacis Segonzac). From Iran, fossil microcoprolites have been described so far only from the Upper Jurassic, Lower Cretaceous, and Miocene. Broennimannia persica represents the first Paleocene record from this area.

A comprehensive study of the palaeoenvironmental and post-mortem conditions of Cenozoic clypeasteroids from the Miocene (Aquitanian) of the Qom Formation in the Esfahan–Sirjan Basin (central Iran) is based on test morphology, taphonomy, test surface preservation, echinoid abundance and echinoid sedimentary fabrics (density, orientation, and cluster), and facies analysis. The deposit-feeding clypeasteroids lived in deeper open-marine, shallow open-marine and shoal settings in a sublittoral environment. The low–moderate energy, deeper open-marine facies contain the lowest population of clypeasteroids, including rare shallow infaunal Parascutella and rare semi-infaunal Clypeaster. The moderate to high energy shallow open-marine facies contains the highest abundance and diversity of Clypeaster. The shallow open-marine and high-energy shoal facies are dominated by epibenthic Clypeaster individuals with robust, inflated and commonly dome-shaped tests. Differences in the abundance and diversity of the living clypeasteroids were related to water depth, food sources and energy levels. Different food sources, life-styles and burrowing depths are indicated by the particular morphologies of the echinoids. Dead echinoids, especially the robust and inflated Clypeaster individuals, were used as substrates and domiciles by skeletozoans and other epibiontic organisms. Disarticulation, fragmentation, bioerosion, test outline distortion and radial cracking affected the preservation of the dead clypeasteroid tests. The clypeasteroid shells in the deposits accumulated as 1—an almost autochthonous assemblage (Parascutella), 2—a moderately transported and reworked assemblage (Clypeaster and Parascutella) and 3—transported and multiple reworked assemblages (Clypeaster) affected by storms.

In the eastern Yangtze Platform of South China Block, Tremadocian (Early Ordovician) stromatolites in southern Anhui Province occur along a palaeoenvironmental transect from the shallowest intra-platform setting through to deeper platform margin. The intra-platform and platform margin belts of Tremadocian rocks in the eastern platform are carbonate-dominated marine environments favourable for calcimicrobes. However, stromatolites are absent in siliciclastic-dominated slope facies. Shallower carbonate facies are represented by the upper member of the Lunshan Formation, composed of a hundred metres thickness of stromatolite-bearing carbonates. Such stromatolites at the Beigong section of Jinxian county are characterized by stratiform and dome-shaped laminations. Girvanella filaments are ubiquitous in thin sections. Crinoids grew on the surfaces of the microbialites. In contrast, towards the deeper carbonate platform margin, stromatolites in massive-bedded limestones of the upper member of Lunshan Formation of the Ma’anshan section at Shitai occur as dense columns of bindstones; macrofossils and bioclasts are rare in those stromatolites, indicating a lower energy and deeper marine setting. Water depth at the platform margin of the Ma’anshan section is interpreted as being above the base of the euphotic zone favorable for photosynthesis in the calcimicrobial community; however, benthic fauna notably declined. In contrast to shallower settings, in clastic-dominated locations interpreted as deposited in deeper water, stromatolites are absent, represented by the middle member of Dawuqian Formation at the Ziliqian section. This work, therefore, supports that Early Ordovician reef systems were still microbial-dominated, representing the last golden age of stromatolites.

In the Late Jurassic, the rifting process led to the disintegration of the southern margin of the North European Platform and to the opening of the Outer Carpathian flysch basin sedimentary system. The initial sediments accumulated in the northern part of the basin are related to both the destruction and resedimentation of older platform deposits. Since the sedimentary succession of this pre-flysch phase was consumed by the Miocene subduction, its only traces are represented, nowadays, by clasts preserved as exotics in the succeeding flysch deposits. Our analysis of foraminifers as well as calcareous and organic dinoflagellate cysts found in these exotics confirms the Oxfordian–early Kimmeridgian timing of the platform phase that preceded the opening of the flysch basin. The exotics are represented by three main facies types: sponge–microbial limestones, oncoid–intraclastic–Crescentiellalimestones and fine-grained, biodetrital limestones withSaccocoma. These deposits are related to mid-ramp to outer-ramp settings. The land influence was rather weak, and these sedimentary settings were dominated by pelagic/hemipelagic accumulation. The studied facies are similar to facies types widely distributed over the northern shelf area of the Western Tethys (e.g., extra-Carpathian southern Poland, Carpathian Foredeep basement, southern Germany). In turn, coeval strata known from the part of the Magura Basin and of the Penninic–Pieninic Ocean, which were situated in more southern part of the Tethys, yielded different microfacies reflecting significant differences between the sedimentary settings of the study area and its southern extensions.

Of all the Devonian stratigraphic boundaries, the Frasnian–Famennian transition (372.2 ± 1.6 Ma) preserves the record of one of the most significant crises in the history of life, the final stages of which lie buried in the distinctive Kellwasser limestone. The Kellwasser facies occur in Western and Central Europe and the commonly cited Płucki area of Poland’s geologically rich Holy Cross Mountains is the only site in that region where the Frasnian–Famennian boundary is considered to occur within Kellwasser facies. At this locality, the limestone contains slump structures, comprising contorted beds and folds. Actually the Kellwasser-like limestone from Płucki is composed of a mixture of three distinct types of sediment, occurring as clasts, commonly deformed and sheared, and matrix, rather than being one homogenous bed, as previously considered. Thus, earlier studies and interpretations of this limestone may need revising. This paper documents the evidence for sediment erosion and reworking, debris flows, sliding and soft-sediment deformation on a submarine slope, and suggests that seismic events were the likely triggering mechanism for slumping and resedimentation.

The Aptian lacustrine carbonates of the Barra Velha Formation, offshore Brazil, have undergone a highly unusual paragenetic and diagenetic history and present significant terminological problems if current textural classifications are applied. Existing limestone classifications invoke the concept of textural maturity, whereby the ratio of matrix to grain is a critical property and can be used to infer energy levels and the degree of transport prior to deposition. In the Barra Velha Formation, some critical carbonate grains grew in a matrix which later dissolved, congruently, producing what appears to be primary intergranular porosity. In addition, apparent boundstone textures occur, not due to organic trapping or binding, but ones which can be shown to be diagenetic, and were also related in part to the former presence of labile matrices. Thus, applying some terms in existing classifications can lead to false interpretations, and to avoid misinterpretations criteria for identifying ghost (former) matrices are provided.

Margins, slopes, and toe-of-slopes represent regions of sediment transfer and bypass from shallow-water settings to the basin. They are zones of sediment flux triggered by different types of physical process including sediment-gravity flows, storm-driven currents, unidirectional currents, and oscillatory flows. As a consequence, they are zones where sediment can be remobilized and strongly reworked from inner environments to offshore settings and deposited as a mixture of autochthonous/allochthonous sediments. In the Monte La Serra and Monte Torretta (Central Apennines) lower-to-upper Eocene reworked sedimentary succession, two main facies associations are differentiated on textural characteristics and tested for robustness by hierarchical cluster analysis: a grain-supported (packstone-to-grainstone) facies FA1 and a mud-supported (mudstone-to-wackestone) facies FA2. The outcrops allow investigation of the transition zone between the margin of the Latium–Abruzzi platform and the adjoining basin and especially the identification of the carbonate factories that supplied the sediment to the slope zone of the Latium–Abruzzi platform. During the Paleogene, this platform was a shaved isolated platform under the action of waves, with sediment deposition during the transgressive and highstand phases of sea level, and erosion of this material during a subsequent lowstand phase. During these phases, storm-driven currents acted on the carbonate platform, remobilizing, resuspending, and reworking sediments. The remobilized material was transferred from the inner platform on to the slope, generating a mixture of detrital shallow- and deep-water biotic assemblages and depositing autochthonous/allochthonous units mainly constituted by alveolinids, large rotaliids, hooked gypsinids, nummulitids, and orthophragmines (discocyclinids and orbitoclypeids) assemblages. This mixture of shallow- and deep-water biotic assemblages demonstrates that a systematic study of the provenance of carbonate-producing biota, even if they are not preserved in their original context, can be useful in palaeoenvironmental reconstruction of the original carbonate factory system.

Archaeocyathan sponges were the dominant metazoan framework builders during Series 2 of the Cambrian. After their near extinction during the Toyonian stage (middle Stage 4), this important ecological role was eventually filled by robustly skeletonized lithistid sponges. However, the exact timing of ecological restructuring is not well understood and was likely not contemporaneous across different paleocontinents. For example, reefs from the Wuliuan of China appear to show rapid replacement of archaeocyaths with lithistid sponges, yet the earliest occurrence of lithistids in Laurentia is not until the early Furongian. In this study, we explore the Mule Spring Limestone of Nevada, which contains shallow water carbonate environments from the immediate aftermath of the regional archaeocyathan extinction, for signs of reef-building activity. Within this formation, we find evidence of sparse microbial-built leolites and some potentially poorly preserved metazoan organisms. However, the totality of our field observations and thin-section point counts suggest that there was no substantial reef-building activity by either microbial or metazoan organisms within our study locality. Our data suggest the occurrence of a local reef eclipse during this interval for the locality investigated. We also incorporate geochemical proxies to determine paleoredox conditions, which suggest well-oxygenated marine conditions through the period of interest. Lack of hardground substrate is proposed as the cause for this gap in the reef record. These results show that a temporary loss of framework-building activity occurred after the regional extinction of archaeocyaths and demonstrates the ecological impact of losing framework builders on a reef environment.

Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-like platform to intrashelf basinal setting under the controls of tectonics and eustasy. Coated grains (oncoids and pisoids) are abundant and show different textures and internal microstructures depending on the stratigraphic position. These Aptian coated grains are divided according to their texture, cortex composition, morphology, type of biota and internal structure, based on petrographic (routine petrography, cathodoluminescence and scanning electron microscope) and geochemical analyses. Accordingly, four types of oncoid and a pisoid group are identified. Oncoid types 1 and 2 along with pisoids typically formed during phases of relative sea-level fall developed within the regressive systems tract (RST). They are commonly associated with shallow-marine (inner ramp), high-energy shoal facies and occur below exposure horizons, at sequence boundaries. Oncoid types 3 and 4 show micro-encrusters (i.e. Lithocodium aggregatum and Bacinella irregularis) and usually occur in a wackestone texture that indicates deposition in a low-energy lagoonal setting with low sedimentation rate during rises in relative sea level (i.e. a transgressive systems tract: TST). Stable carbon and oxygen isotopes are used to define the OAE1a and its environmental effects in the Dariyan Formation. Palaeoenvironmental proxies reflecting energy level, sedimentation rate and trophic level are evaluated for Aptian sedimentary sequences deposited on the southern margin of the Neo-Tethys Ocean.

The Late Ordovician succession of the Baltic Basin contains a characteristic fine-grained limestone, which is rich in calcareous green algae. This limestone occurs in surface outcrops and drill-cores in an extensive belt reaching from Sweden across the Baltic Sea to the Baltic countries. This limestone, which is known in the literature under several different lithological names, is described and interpreted, and the term “Baltic limestone facies” is suggested. The microfacies, from selected outcrops from the Åland Islands, Finland and Estonia, consists of calcareous green algae as the main skeletal component in a bioclastic mudstone-packstone lithology with a pure micritic matrix. Three types of calcitarch, which range in diameter from c. 100–180 μm, are common. Basinward, the youngest sections of the facies belt contain coral-stromatoporoid patch reefs andPalaeoporella-algal mounds. The Baltic limestone facies can be interpreted as representing the shallow part of an open-marine low-latitude carbonate platform.

The depositional setting for northern most Atlantic coral reef development during the Mid-Pliocene Warm Period is a gentle sloping mixed carbonate–siliciclastic ramp. Five core transects document the distribution of the reef complex in an area approximately 65 by 12 km, and nine repetitive depositional facies are identified. Paleoecological and sedimentological evidence documents facies development along a water depth–energy gradient. The mid-Pliocene Tamiami Formation is characterized by coral boundstone developed over level skeletal rudstone depositional units dominated by mollusks. Hyotissa haitensis (Sowerby), one of the last Gryphaeid oysters, is the dominant fossil found in the most continuous skeletal facies and overlies deeper water green clay facies, the only facies with pelagic foraminifera. Ground penetrating radar documents reef depositional topography, onlapping stratigraphy and two episodes of reef growth. Two cycles of deposition are recognized, separated by subaerial exposure. The coral boundstone and the skeletal rudstone exhibit both high primary and secondary porosity and overlie the impermeable clay facies. The upper surface of the coral boundstone lies at ~ 4 m in elevation whereas contemporaneous estuarine deposits are found to the north at elevations of 20–25 m. High porosity bank reef complexes along a shallow dipping ramp provide an alternative to the standard model of reef and porosity development along the outer shelf margin. Understanding the differences in associated facies between these two depositional environments permits better interpretation of observed heterogeneities in subsurface geobodies associated with inner shelf and platform settings.