Coral Buildups Research Articles

Resilient coral reef ecosystems: The case study of turbid-mesophotic coral buildups during the Late Oligocene Warming Event (Tertiary Piedmont Basin, NW Italy)

Nowadays, but also in the geological record, coral communities living in marginal conditions (i.e. low light, high turbidity, extreme temperatures, high nutrients and sediment input) are quite common and there is evidence that some of these reefs, often associated with mesophotic environments, may be more resilient to the current global warming trend, thus serving as possible ecological refugia.As an attempt to understand the response and resilience to past warming events of marine calcifying organisms, such as zooxanthellate corals of marginal reefs, herein we reconstruct the palaeoenvironment of an Oligocene mixed siliciclastic‑carbonate system in the Tertiary Piedmont Basin (NW Italy), where a suite of coral assemblages formed small buildups at the edge of a coarse-grained delta system. Geochronological dating by strontium isotope stratigraphy places the coral buildups in the middle Chattian, thus within the Late Oligocene Warming Event (LOWE): a crucial climatic event for coral reefs as characterised by substantial warming coincident with declining atmospheric CO2.The depositional model that we propose is ascribed to a fan-delta system, deposited within a narrow valley cutting through the metamorphic basement, where small and laterally discontinuous coral buildups grow-up in the prodelta setting, thus suggesting a mesophotic environment. In this context, the coral buildups appear to have been intermittently deactivated or smothered by fine-grained terrigenous input during flood phases or shifts in distributary channels until their final suffocation by fluvial sediments input.Within the coral buildups, the four distinguished coral facies (branching Stylophora floatstone, Acropora-Stylophora floatstone/rudstone, Goniopora/Caulastraea pillarstone, and mixed-coral domestone) are characterised in general by sediment-resistant corals and by specific taphonomic features.These coral facies shifted in time and space during the LOWE, highlighting the noteworthy adaptability and resilience of Oligocene corals to a complex interplay of environmental stressors such as turbidity, hydrodynamic energy, sediment and nutrient supply within a mesophotic setting.

Architecture of Oxfordian coral buildups along the Atlantic margin of Morocco

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 pCO2 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.

A new sedimentary and biostratigraphic framework for the Callovian-Oxfordian transition on the Atlantic margin of Morocco

A major global marine transgression occurred during the Callovian to Early Kimmeridgian, which was interrupted locally by a hiatus during the Late Callovian to Early Oxfordian. The transgression may have been a major driver for extensive coral buildup development in the Oxfordian. The depositional hiatus may be related to a combination of eustasy, local tectonic activity and hinterland movements, highlighting the potential influence of tectonism on sedimentary evolution in sedimentary basins. Whilst a regional Late Callovian-Early Oxfordian hiatus has been recorded extensively in the Tethys realm, this study has improved the biostratigraphic and sedimentary record from Morocco, and for the first time documents the Late Callovian-Early Oxfordian depositional hiatus in the Atlantic realm. Detailed sedimentary facies analysis of Callovian to Oxfordian carbonates and siliciclastics (Ouanamane Formation) demonstrates a major transgression from continental and coastal sediments, through oolitic mid-inner ramp deposits, brachiopod-rich middle ramp deposits, and ultimately to outer ramp marls, sharply overlain by Middle Oxfordian coral buildups across the basin. Repeated hard- and firmgrounds and bioturbated bed tops highlight transgressive surfaces traceable basinwide, which suggests low sedimentation rates in the upper Ouanamane Formation. Localized siliciclastic input is evidence for episodes of erosion in the same interval. Collection of new fossil specimens (ammonites, brachiopods, echinoderms, foraminifera) and revision of existing fossil material suggest this interval corresponds to a hiatus or condensed section in the Callovian-Oxfordian transition. The uppermost part of the Ouanamane Formation is of early Middle Oxfordian age and is directly overlain by Middle Oxfordian coral buildups. Onset of buildup construction is considered synchronous based on the new biostratigraphic data. Observations in Moroco compare with the sedimentary evolution around the Tethys, and in particular with the Arabian Plate. The Callovian-Oxfordian depositional hiatus corresponds to eustatic sea level changes, which were possibly driven by global cooling, and was likely overprinted by local tectonics.

The Miocene record of the Betic Cordillera uplift in Los Guájares valley (Granada province, S Spain)

The Los Guájares valley is located about 35 km south of Granada in the Internal Zones of the Betic Cordillera. The Miocene deposits in this area consist of six sedimentary units separated by unconformities, which are exposed in small and laterally discontinuous outcrops overlying metamorphic rocks of the Alpujárride Complex. The lowest unit comprises upper Serravallian marls with planktonic foraminifera filling neptunian dykes and covering Triassic dolomitic marbles of the Alpujárride Complex. These marls reflect deep marine deposition on the Betic basement under a local extensional regime. Uplift of the region led to emergence and deposition of continental red alluvial-fan conglomerates and foothill breccias. The overlying unit, a shoreline conglomerate with small oyster banks, indicates relative sea-level rise. Shallow-marine conditions continued during the deposition of the following unit, early Tortonian in age, which consists of calcareous sandstones with hermatypic corals. Small patch reefs developed in the overlying unit composed of sandy limestones with corals (Porites, Tarbellastraea, Thegioastraea) and oysters, and sandy limestones with coralline algae in the most distal areas. The coral reefs in Los Guájares and some coral heads in Albuñuelas, a near locality, are the only record of early Tortonian coral buildups in the Mediterranean. The last marine unit comprises lower Tortonian conglomerates, sandstones and siltstones accumulated in the front of a small delta. Oyster banks and concentrations of Turritelines suggest high nutrient levels in the delta-front paleoenvironments. The Los Guájares valley area emerged afterwards, following the onset of a compressional geodynamic regime in the central Betic Cordillera and since the early Tortonian only small bodies of foothill and alluvial-fan deposits formed in a predominantly erosional context.

The Eocene carbonate platforms of the Ghomaride Domain (Internal Rif Zone, N Morocco): a segment of the westernmost Tethys

The Eocene platform deposits in the Moroccan Ghomarides have been studied. These marine carbonate platforms were located in the westernmost Tethys approximately 30°N and 0°–10°W during the Cuisian to Bartonian. The study includes observations from fossiliferous assemblages (such as larger benthic foraminifera and colonial corals), their palaeoenvironment as well as rock texture and fabric. Eight microfacies were identified that represent different ramp environments in a ‘distally-steepened carbonate ramp’ type of platform. The studied deposits are organised into a transgressive succession composed of three sedimentary cycles: lower Cuisian, middle Cuisian and middle Lutetian to Bartonian. In the lower cycle, photic inner to mid ramp environments in mesotrophic conditions were prevalent. In the second cycle, photic inner ramp (sea-grass) to mid ramp environments in mesotrophic to oligotrophic conditions were observed. The upper cycle, which is more extensive and variable, represents mesophotic mid ramp to aphotic slope environments and changes gradually from oligotrophic to eutrophic conditions. During the Eocene, larger benthic foraminifera were dominant overtaking the zooxanthellate corals in the Tethys regions. Nevertheless, our study and the performed comparison with other Tethyan sectors have revealed that in some areas both coexisted in similar proportions. In some western Tethys regions close to the Atlantic Ocean, coinciding with areas influenced by upwelling currents, larger benthic foraminifera and coral build-ups were replaced by oyster reefs. The Ghomaride Domain represents an intermediate case between fossil assemblages of the northern Tethyan margin and eastern sector of the southern margin of the Tethys, with a dominance of larger benthic foraminifera but with a certain presence of corals as well. A good correlation exists between Eocene warm intervals and carbonate platform deposits in these domains. Contrarily, during cooling ones shallowing and gaps in the sedimentation are registered. Two anomalies have been detected in the Ghomaride Domain during Ypresian and Bartonian times indicating particular climatic conditions or local tectonic interferences.

The Impact of Seasonal Weather Changes on the Accumulated Sediments within Back-Reef Environment around Umm Al-Maradim island- Kuwait

This study is based on petrographic, geochemical and mechanical analysis of all collected samples from the intertidal zone around the southern Umm Al-Maradim Island in Kuwait. The objective is to interpret the impact of seasons conditions on coral buildups around the island. Petrographic study revealed that the intertidal area is a part of a back-reef environment which is composed of the accumulation of broken up coral debris, coralline algae, foraminifera, echinoderms particles, bivalves, and gastropods. Generally, most abundant grain sizes along the shores are coarse and very coarse sand size, indicating short distance of transport and high wave action. Short transportation distance and fast sedimentation resulted in the accumulation of poorly sorted and strongly coarse to coarse skewed sediments. Detailed study of the samples shows variations in grain size parameters as well as type of accumulated sediments between the different seasons and locations along the island, which is mainly related to the differences in wind intensity, changes in prevailing wind direction, and biological activities affecting the coral reefs. Geochemical study suggests an aragonitic and low-Mg calcite composition for the coral fragments, as well as a pathetic relationship between all tested major elements within the collected sediments.

Chemical composition of late Eocene–early Oligocene corals in reef buildups from the Thrace basin, Bulgaria–Greece: Paleoenvironmental implications

Coral whole-rock geochemistry and in situ LA-ICP-MS analyses of coral skeletons were performed on late Eocene–early Oligocene coral reef buildups from the Eastern Rhodope–Thrace region of Bulgaria and Greece. Coral reefs are locally associated with voluminous Oligocene volcanism in the region. The reefs are subdivided into (i) eruption-associated reefs (Krumovgrad); (ii) pre-eruption reefs (Ivaylovgrad); and (iii) Metaxades-Didymotycho reefs from field relations, trace element and rare-earth element (REE) abundances. Coral assemblages are dominated by Cladocora sp., which is accompanied by Porites sp., Colpophyllia sp., Favites sp. and Leptoseris sp. Eruption-associated reefs are characterized by their higher REE content than the lower in all REE contents of pre-eruption reefs showing negative Ce anomaly, and Metaxades-Didymotycho reefs that have lower middle-heavy REE contents compared to previous groups. Trace element and REE geochemistry of the coral skeletons indicates volcanic contribution to seawater, mostly evident in the eruption associated reefs, and contribution from terrestrial input in the site of coral buildup deposition. Contribution from a different source of prior diagenetic nature, along with subsequent diagenetic modification, is inferred. The increase in REE+Y (ΣREY) from pre-eruption to eruption-associated reefs is well correlated with elevated amounts of terrigenous elements like Al and Fe.

Multi-scale analysis of shallow-water carbonate depositional geometries from a reservoir perspective: Insights from outcrop (Middle Jurassic, Portugal) and subsurface (Lower Cretaceous, U.A.E.) contrasting case studies

Outcrop observations offer valuable insights into depositional architecture as a primary control on facies and reservoir properties variability, in contrast to subsurface cases, where observation points are limited to well locations. Two dominantly high-energy shallow-water carbonate case studies were analysed, including outcrops of a Bathonian-Callovian (Middle Jurassic) carbonate succession in the Maciço Calcário Estremenho (MCE) region, central Lusitanian Basin, Portugal and a Barremian (Lower Cretaceous) subsurface carbonate reservoir from Abu Dhabi (U.A.E.). The MCE succession comprises a range of inner ramp deposits, which consist of oobiointraclastic grainstones, biointraclastic grainstone-rudstones and coral/algal boundstones, mostly defining sandbody and coral biostrome units which represent potential reservoir facies, as suggested by their textural types and locally significant porosity, though now mostly occluded by calcite cements. The succession is exposed in recently-cut quarry faces showing minimal weathering, hence allowing for detailed observations on depositional geometries. The U.A.E. case study is a world-class reservoir characterized by mid-ramp to high-energy inner-ramp facies, ranging from biomicritic wackestones to biointraclastic packstones, bioclastic packstones, grainstones and rudstone-grainstones, interpreted using core and thin section data from four onshore wells.In the analysed outcrops, strong continuity of main major bedding surfaces is observed at larger scales (dozens to hundreds of metres), with strong spatial variability seen at smaller centimetre to metre scales and depositional geometries varying from tabular, wedge-like, lensoid bodies and coral buildups. The subsurface case also shows strong continuity of larger-scale depositional packages (at kilometre scale) and moderate to strong small-scale heterogeneities at centimetre to metre scales. Discontinuity-bounded intervals are observed in the younger section of this reservoir generally showing stronger vuggy porosity and coarser skeletal grains at the base, while the youngest set of these intervals are characterized by an abundance of rudist fragments. The interpreted depositional geometries in this reservoir consist of tabular, wedge-like and lenticular geobodies of limited lateral extension.The multi-scale heterogeneity in both these case studies is strongly influenced by depositional factors related to hydrodynamics and the balance between carbonate factory productivity and accommodation space, affecting lateral facies migration and creating complex depositional patterns. This study illustrates how the perception of heterogeneity, though reflecting an intrinsic property of carbonate rocks, is influenced by the scale of observation and, from a reservoir perspective, both cases show that addressing small-scale heterogeneities and associated geological factors in higher detail is vital in defining conceptual geological models for a better understanding of the reservoir.

Systematics and distribution of decapod crustaceans associated with late Eocene coral buildups from the southern Pyrenees (Spain)

A new decapod crustacean assemblage associated with late Eocene coral reef deposits in northeast Spain (southern Pyrenees) is recorded; it includes Gemmellarocarcinus riglosensis sp. nov., Daira corallina sp. nov., Lobogalenopsis joei sp. nov., Liopsalis cf. anodon (Bittner, 1875) and Galenopsis crassifrons A. Milne- Edwards, 1865. The genera Gemmellarocarcinus, Daira and Lobogalenopsis are here recorded for the first time from Eocene strata of the Iberian Peninsula, extending their palaeobiogeographical distribution. Detailed sampling from three different coral reef facies within the La Peña buildup, here referred to as branching, tabular and massive, suggest that the core of the reef, which was dominated by branching corals, hosted the highest diversity and abundance of decapod crustaceans. Daira corallina sp. nov. predominated in the branching corals facies, while G. crassiforns was the most abundant taxon within the tabular coral facies and carpiliids showed preferences for environments with massive corals. Thus, this constitutes a good example of primary ecological zonation among decapod crustaceans within a discrete reef.

Paleocene-Lower Eocene carbonate platforms of westernmost Tethys

The Paleocene-lower Eocene succession is well exposed in Sierra Espuña-Mula Basin (Betic Cordillera, S Spain) and carbonate platforms are well represented as part of this succession. The study of the paleoenvironmental evolution of these platforms has allowed to cover an important gap in the knowledge in the westernmost Tethys. Thirteen microfacies (Mf1 to MF13) were recognized based mainly on the fossil assemblage (principally larger benthic foraminifera), texture and fabric of the microfacies. The fossiliferous assemblage of the entire succession shows a mixture of photozoan and heterotrophic biogenic elements, typical of an inner to outer ramp environment of a warm temperate biogeographic province. Fragments of hermatypic corals have also been detected in the lower part of the succession (Paleocene) allowing thinking in propitious conditions in this period. The succession evolves upwards (Lower Eocene) to low-energy shallow marine protected environments (lagoon) in inner ramp settings. In addition, abundant porcelaneous larger benthic foraminifera such as alveolinids and soritids are indicative of euphotic shallow marine conditions in moderately oligotrophic upper subtidal environments. In the upper part of the succession, hermatypic corals as displaced fragments and in situ isolated coral phaceloid colonies also appear together with other biogenic components indicating warm shallow and euphotic marine conditions (coral-maërl environment). Lenticular larger benthic foraminifera, characterizing marine mesophotic and oligotrophic habitats can be found in the upper part of the middle ramp, and flattened larger benthic foraminifera forms indicating lowermost mesophotic conditions in a distal middle ramp. The obtained results have been compared with other similar Tethyan sectors obtaining a broader view. The biogenic marine association is characterized by the absence of the ‘Lockhartia community’ of the Tethyan domain, together with the dominance of alveolinids, nummulitids and orthophragminids. During most of the Paleocene, northern Mediterranean Tethys platforms were located in the middle paleolatitudes and characterized by coral-reef and coralgal biofacies. The studied platforms (located at a latitude close to 25°N) show, in a ramp-like context, underdeveloped in situ coral constructions probably of patch-reef type. In the early Eocene the expansion and abundance of the larger benthic foraminifera and the practical disappearance of coral took place in the sedimentary platforms through the entire Tethys. However, in the study area small reef coral build-ups have also been observed in the lower Cuisian beds, indicating that in westernmost Tethys coral construction continued at these latitudes.

Regional stratigraphy, facies distribution, and hydrocarbons potential of the Oligocene strata across the Arabian Plate and Western Iran

Major global events during the Oligocene epoch included a climatic change from warm “greenhouse” to a cooler “icehouse” that was accompanied by the onset of Antarctic glaciation. These events led to decline in water temperature, salinity, nutrient supply and oxygen levels, and the extinction of some major fauna and flora. Within the study area, during this epoch, the shrinkage of the Neotethys and the development of the Paratethys, the collision of Arabia with Eurasia and the development of the Zagros mountains and opening of the Red Sea which led eventually to the separation of Arabia from Africa were witnessed. Oligocene sediments are absent from most parts of the Arabian Plate but are well-preserved in western and southwestern Iran. The most well-developed strata are the coral reefs of the Kirkuk Group in northern Iraq and the shallow water carbonates of the Asmari Formation in southwestern Iran. The study area also represents the birthplace of commercial hydrocarbons production in the Middle East from these sediments in Masjid-i-Sulaiman Field in Iran and Kirkuk Field in Iraq at the first decade of the last century. Future exploration for hydrocarbons potential should focus on identifying subsurface coral buildups or clastic strata that are equivalent to the Asmari Formation in Iran.

Depositional architecture and sequence stratigraphy of the Oligo–Miocene Asmari platform; Southeastern Izeh Zone, Zagros Basin, Iran

In the easternmost part of the main Izeh Zone of the Zagros Mountains, Iran, the Asmari carbonate platform system of Oligo–Miocene age is superbly exposed in three-dimensional outcrops displaying a variety of carbonate facies associated with well-preserved depositional geometries. The main biogenic components of the Asmari Formation are large benthic foraminifera, corals, coralline algae, and planktonic foraminifera. The Asmari carbonate platform system, based on dating by large benthic foraminifera, biogenic components, and depositional geometries, is divided into four distinct intervals of carbonate platform growth. This depositional system during the Rupelian and Rupelian/earliest Chattian was a carbonate ramp. During the Chattian, the system was dominated by coral buildups, and later, porcellaneous benthic foraminifera and coralline algae were prominent during late Chattian–early Miocene time. Six major depositional sequences are distinguished, with an overall systematic progradation from NE to SW. These progradations are evidenced in the Rupelian and lower Chattian by major changes in facies and stratal architectures, whereas such complex geometries are not observed in the upper Chattian and lower Miocene carbonates, since only platform-top facies are exposed and there are no outcrops of the platform margin. Comparison of the proposed depositional sequences with those reported in the Dezful Embayment and adjacent areas suggests a correlation with the global sea-level curve.

Growth and demise of a Burdigalian coral bioconstruction on a granite rocky substrate (Bonifacio Basin, southeastern Corsica)

During the Early Miocene, coincident with the Sardinia–Corsica block rotation, mixed carbonate–siliciclastic sediments of the Cala di Labra Formation were deposited on the southern margin of the Bonifacio Basin (southeastern Corsica, France). The Burdigalian marine transgression is spectacularly represented by a peculiar coral bioconstruction, unconformably lying on the eroded Variscan granitic basement. Superb exposures allowed detailed, three-dimensional field mapping, lithofacies analysis, and characterization of the Cala di Labra coral bioconstruction. As a result of the extremely irregular and articulated substrate, the coral buildup appears as an organized lens-shaped structure, and its core is constituted by a relatively dense coral domestone with a moderate increase of platy corals in the upper part. A coral rubble associated with granitic cobbles and pebbles is locally present at the base. The inter-coral sediment consists of poorly sorted bioclastic wackestone to packstone. Results from this study clearly show evidence for the occurrence of a former submerged granitic substrate that, as very rarely documented in the geological record, is here interpreted as the subtidal substrate for growth of a small bioconstruction under relatively high energy and clear water conditions. The Cala di Labra bioconstruction is overlain by a fining-upward quartzose conglomerate and sandstone succession interpreted as deposited in a coastal setting near fluvial point sources. The demise of coral growth was caused by a regressive event and by the consequent quite-sudden burial and related changes of trophic conditions.

Thrombolitic and coral buildups in the Upper Albian of the Fahdene basin (North Tunisia): stratigraphy, sedimentology and genesis

AbstractWithin the Upper Albian marl/limestone pelagic to hemi-pelagic successions of Fahdene basin (northern Tunisia), small-scale thrombolitic and coral buildups were recognized for the first time. The exceptionally well-exposed and well-preserved buildups (i.e. Oued Siliana and Jebel Srassif buildups) were investigated for their biostratigraphic, petrographic, and genesis character. The vertical succession is characterized as shallowing upward and comprise four to nine conical and/or lenticular bioherms/biostromes (up to 4 m in diameter). Basal buildups consist of four to six deep water microbial thrombolites and are generally associated with the uppermost organic-rich black shale of the Mouelha member which corresponds to the Oceanic Anoxic Event OAE1d. These buildups change stratigraphic upward into three hermatypic hexacorallian thrombolites with abundant fossils and bioturbation traces. The geometry and the observed internal structures of the thrombolites suggest that microbial activity thrived carbonate precipitation and subsequent lithification, which in turn favoured preservation of the original structure of the buildups. The microbial thrombolites formed within or near the anoxic zone (related to the Oceanic Anoxic Event OAE1d) whereas the coral thrombolites grew in the photic zone. We suggest that the onset of the microbial thrombolites was induced by the presence of an eutrophic, hypersaline, and anoxic environment which is enhanced by the Late Albian sea level rise. Nevertheless, flourishing of metazoans that lead to the coral thrombolites was associated with an oxygenated and oligotrophic environment. Halokinetic dynamics and tilted-block fault systems provided conduits for nutrient-rich fluids and hydrocarbons which fueled chemosynthetic-based communities.

Mesophotic coral buildups in a prodelta setting (Late Eocene, southern Pyrenees, Spain): a mixed carbonate–siliciclastic system

AbstractLower Priabonian coral bioherms and biostromes, encased in prodelta marls/clays, occur in the Aínsa‐Jaca piggyback basin, in the South Central Pyrenean zone. Detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups. Coral lithosomes occur either isolated or amalgamated in larger buildups. Isolated lithosomes are 1 to 8 m thick and a few hundred metres wide; clay content within coral colonies is significant. Stacked bioherms form low‐relief buildups, commonly 20 to 30 m thick, locally up to 50 m. These bioherms are progressively younger to the west, following progradation of the deltaic complex. The lowermost skeletal‐rich beds consist of bryozoan floatstone with wackestone to packstone matrix, in which planktonic foraminifera are abundant and light‐related organisms absent. Basal coral biostromes, and the base of many bioherms, consist of platy‐coral colonies ‘floating’ in a fine‐grained matrix rich in branches of red algae. Corals with domal or massive shape, locally mixed with branching corals and phaceloid coral colonies, dominate buildup cores. These corals are surrounded by matrix and lack organic framework. The matrix consists of wackestone to packstone, locally floatstone, with conspicuous red algal and coral fragments, along with bryozoans, planktonic and benthonic foraminifera and locally sponges. Coral rudstone and skeletal packstone, with wackestone to packstone matrix, also occur as wedges abutting the buildup margins. Integrative analysis of rock textures, skeletal components, buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth. The bathymetric position of the buildups has been constrained from the light‐dependent communities and lithofacies distribution within the buildups. The process‐product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the Late Eocene and until the Late Miocene. Comparative analysis with some selected Upper Eocene coral buildups of the north Mediterranean area show similarities in facies, components and textures, and suggest that they also grew in relatively low light (mesophotic) and low hydrodynamic conditions.

Organic (coral) buildups in the carboniferous at the southwestern margin of the East European Platform

Organic buildups (biostromes and bioherms) were established for the first time in the coal-bearing formation of the Lvov-Volynsk coal basin. Colonial rugose corals of the Siphonodendron genus represented the main bioherm-builders. Coral buildups were formed under shallow marine conditions and located within the active tectonic region at the southwestern margin of the East European Platform. The region represents a northwest-trending band (10–12 km wide) extending over more than 70 km. The studied late Visean coral bioherms and biostromes are similar to coeval ones from some European regions.

Mosaic of environments recorded by bryozoan faunas from the Middle Miocene of Hungary

The marine sediments of the Badenian (Middle Miocene) of Hungary (Pannonian Basin, Central Paratethys) are composed of abundant bryozoan skeletal grains. Seventy-one bulk samples collected at 18 localities (outcrops and boreholes) yielded a total number of 238 bryozoan species. In order to reconstruct the Badenian palaeoenvironments, the present study investigates the composition of this very diverse fauna using a combination of statistical and palaeoecological methods. The statistical analyses make use of Cluster Analysis and Non-metric Multi-Dimensional Scaling. The palaeoecological approaches are based on the known ecological requirements of the bryozoan colonial growth forms and of the numerous extant species. Five facies have first been differentiated on the basis of sedimentological and palaeontological features: coral buildups, coralline algal limestones, biocalcarenites, sands, and marls. Each of them is characterized by the abundance, the diversity and the types of growth forms of the bryozoans. The palaeoecological, statistical and facies analyses further permitted to identify four depositional settings: carbonate platform (distal and proximal), terrigenous platform, slope, and basin. These environments developed at depths between 0 to about 300 m in a mixed carbonate–siliciclastic depositional system. Skeletal production and spatial distribution of carbonate factories were predominantly controlled by terrigenous input. This resulted in a complex mosaic of facies/habitats where rich bryozoan faunas could thrive. Many warm-water organisms, among them foraminifers, zooxanthellate corals, molluscs, bryozoans, and echinoids, were recorded from the study sites. The coexistence of coralgal and bryomol carbonate skeletal assemblages in this subtropical setting is explained mostly by variations in the productivity of surface waters. Periods of nutrient enrichment and increased benthic eutrophication affected coral diversity and abundance in favour of bryozoans.

Seismic expressions of a Miocene prograding carbonate margin, Mut Basin, Turkey

The detailed stratigraphic architecture of a Miocene intraplatform prograding carbonate margin, outcropping in Mut Basin, Turkey, was used to build two-dimensional synthetic seismograms by normal ray-tracing and finite-difference, exploding-reflector methods. The synthetic seismic models at various frequencies display the overall prograding architecture of the 1.5-km (0.95-mi) 250-m (820-ft) prograding margin, even at 40-Hz frequency; however, most of the complex stratigraphic architecture is below standard seismic resolution. Sigmoidal outcrop geometries create complex, shingled, seismic reflections that contain pseudodownlap, pseudotoplap, and various truncations at 40-Hz frequency. In addition, reflections that do not correspond to any impedance contrast are generated by a tuning effect within the clinoform. Interference patterns created by the complex impedance distribution create reflections that change phase laterally and cross stratigraphic timelines. Several high-impedance coral buildups at the slope break and on the platform top cause reflections to change phase and amplitude along the timeline. In addition, lateral-impedance variations generate mounded reflections that, in places, cross timelines and resemble seismic images for buildups or anticlinal structures.Several of these resolution problems and interference patterns are reduced by an increase of the frequency. For example, at 80 Hz peak frequency, the sigmoidal geometries are better imaged. Improved resolution was also achieved on the synthetic seismic data simply by dividing trace spacing from 25 to 12.5 m (82 to 39 ft) but keeping the modeling frequency constant, indicating that for stratigraphic interpretation, horizontal seismic resolution is at least as important as vertical seismic resolution. This implies that adjusting the acquisition geometries would improve the seismic resolution without compromising depth by increased frequency. For seismic interpretation, this study shows how little of a complex stratigraphic architecture is truly imaged on seismic data and how complex impedance distribution can create false seismic reflection geometries that impede a correct seismic facies and sequence-stratigraphic interpretation.

Les constructions coralliennes du Badénien (Miocène moyen) de la bordure occidentale de la dépression de Transylvanie (Roumanie)

The Badenian (Middle Miocene) Gîrbova de Sus Formation rests upon the basement in a transgressive trend (West of the Transylvanian depression). For the first time, an algal-rich carbonate platform with coral build-ups is described in this area. These build-ups underline clearly a retrograding sequence. The coral assemblage is dominated by Faviidae and Porites colonies. Five types of coral build-ups without any zonation are distinguished. Their unusual width and their palaeogeographical situation testify to the generalization of subtropical conditions and the complexity of the marine connections in the Paratethian area.

First Mesozoic record of the scleractinian Madrepora from the Maastrichtian siliceous limestones of Poland

The objective of the present article is to document the first stratigraphic occurrence of the colonial oculinid Madrepora, known from the modern seas as an azooxanthellate taxon that contributes to the formation of deep-water coral reefs. The Upper Cretaceous specimens of Madrepora sp. reported herein from Poland were recovered from Upper Maastrichtian (Nasilow and Bochotnica localities) and Lower Maastrichtian (Blizow locality) siliceous limestones. The corals are preserved as imprints of the branch fragments and molds of the calices. Despite their moldic preservation, the coral remains exhibit key generic features of the genus Madrepora; including (1) sympodial colony growth form with calices arranged in opposite and alternating rows in one plane of the branch, and (2) imprints of the granular coenosteum texture, occasionally showing peculiar reticulate patterns. Some features of the Cretaceous Madrepora sp., such as the reticulate coenosteum texture, the range of the corallite diameter (2.8–4 mm), and the arrangement of the septa in three regular cycles resemble the skeletal features of the modern, typically constructional, species M. oculata (type species). The lack of any evidence of coral buildups and related debris in the whole Upper Cretaceous/Paleogene sequences from Poland and the sparse occurrence of colony fragments, suggests that the Cretaceous Madrepora sp. formed small, isolated colonies.