Algal Boundstone Research Articles

Nubecularia-coralline algal-serpulid-microbial bioherms of the Paratethys Sea-Distribution and paleoecological significance (upper Serravallian, upper Sarmatian, Middle Miocene).

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!

Using Biofacies Analysis of a Tertiary Algal Reef (Pinnacle Reef - Middle Eocene IIA), at Burton Guyot (IODP Site U1376) to Determine Transition from Greenhouse to Icehouse

Twenty-five samples were collected at 30 cm intervals from the studied cored interval within the limestone unit (AII) reported at IODP Site U1376 on Burton Guyot. The purpose of this research is to examine and identify the coral and algae suites in the studied core concerning sea level fluctuation during the Eocene time. This reef is isolated by being between two volcanic units in the Southwest Pacific Ocean. Eleven biofacies units have been established based on the fabric of the grains. The biofacies units are as follows; Algal-coral grainstone, foraminiferal algal-coral grainstone (Alabaminabed), foraminiferal algal-coral packstone to grainstone (Heterostegina bed), algal-coral grainstone, foraminiferal algal boundstone, foraminiferal algal grainstone (Lagena bed), foraminiferal algal grainstone (Cibicidoides micrus-bed), foraminiferal algal boundstone to grainstone, foraminiferal algal-coral grainstone, algal echionoidal packstone, and foraminiferal algal coral wacke-packstone. This is the first study to use both algae and coral in differentiating the units mentioned above. The only coralline red algae recognized in the samples is Lithothamnion camarasae. This species is a good indicator of the warm climatic conditions during the middle-late Eocene. The only species of coral found in these units is Isopora togianensis, a scleractinian reef builder. The high percentage of algae compared to coral indicates a climatic change from a greenhouse to an icehouse climate. The faunal trend during this time also indicates a tectonic change.

Holocene, mesophotic, carbonate sedimentation, Bermuda atoll margin; a submersible study

Bermuda is an atoll-like reef system and associated islands bathed by the Gulf Stream at the cool, northern margin of coral reef growth in the North Atlantic Ocean. This study documents observations from and samples acquired by submersible on the shallow slope between 60 and 400 m water depth on the southern side of the structure. The mesophotic bathymetry is like other such carbonate margins, a shallow slope, an escarpment, and a lower slope, but the sectors are deeper than elsewhere, and interpreted to be due to underlying volcanic topography. The seafloor limestones are almost wholly mid-Holocene in age, 4.0 ka to 7.7 ka implying that the present depositional system at these depths is largely moribund. Facies are dominated by intensely bioeroded, encrusting coralline algal boundstones with associated bryozoans, serpulids, and hydrozoans with a wackestone matrix containing abundant bioeroded sponge chips. This facies also forms numerous rhodoliths. There are only two samples of intertidal algal cup reef facies, and both are clearly allochthonous in water depths of 106 and 384 mwd. Their presence and ages of ∼5.0 ka does, however, confirm the presence of such cup reefs that grew coeval with the mesophotic boundstones. The age of most facies coincides with the mid-Holocene thermal. This is one of the few analyses of Holocene mesophotic deposition at the boundary between the Holocene photozoan and heterozoan depositional realms during the Holocene and illustrates the importance of subtle, if somewhat unresolved oceanographic change in determining accretion.

Geomorphology of the Mirador-Calakmul Karst Basin: A GIS-based approach to hydrogeologic mapping

This paper classifies the karst landscapes of the Petén Plateau and defines the Mirador-Calakmul Karst Basin by illustrating the distribution of its karst hydrologic features. Archaeological and spatial research of the Mirador-Calakmul area of Guatemala and Mexico has shown it to be a karst basin with geopolitical implications. Current research characterizes the karst landscapes of the Petén Plateau, maps the distribution of karst hydrologic features, and delineates the basin in geomorphological terms. To further this aim, multiple forms of remote sensing data including orthophotographs, a satellite Digital Elevation Model, satellite multispectral images, and Light Detection and Ranging (LiDAR) data have been integrated to interpret the karst features in the study area. Outcrop study and thin section analysis of the upper Buena Vista Formation document that the dominant lithologies are a shallow water algal boundstone interbedded with terrestrial caliche. Karst landforms have been mapped over the Petén Plateau and we identify five karst landscapes, the largest of which is a fluviokarst landscape dominated by karst valleys. We further map karst hydrologic features including seasonal swamps, dolines, intermittent lakes, intermittent streams, solution-enhanced fractures, and springs all of which are characteristic of drainage basins. Boundaries of the karst basin are mapped from multiple lines of evidence including distribution of the karst valleys, a line of springs along the western boundary of the fluviokarst landscape, and a surface drainage analysis. We capture and classify hydrologic data points and develop a regional groundwater map that indicates subsurface flow from east to west within the basin. A drainage map illustrates the extensive system of karst valleys, boundaries, and inferred groundwater flow paths of the Mirador-Calakmul Karst Basin. It was within this geomorphological setting that the ancient Maya developed an extensive civilization during the Middle and Late Preclassic periods (1000 BCE-150 CE).

Facies and geometry of drowning steps in a Miocene carbonate platform (Maldives)

The study of the Miocene carbonate platform of the Maldives allows understanding the controlling factors triggering the stepwise drowning of carbonate platforms. This research presents high-resolution seismic profiles and sediment cores retrieved from Sites U1465, U1469, and U1470 drilled during International Ocean Discovery Program (IODP) Expedition 359. A microfacies analysis of the platform deposits was conducted and correlated with a sequence stratigraphic analysis of seismic reflection data. The Neogene evolution of the Maldives encompasses a series of drowning steps. Two of these steps are compared with regard to the carbonate factory type to unravel if fossil assemblage surviving the first drowning step are different from younger assemblages. In both cases the shallow water carbonate facies are formed by coral-coralline algal boundstone and foralgal floatstone that change basinwards into slope facies dominated by large benthic foraminifera grainstone to packstone, locally floatstone and rudstone. The red algae and large benthic foraminifera assemblages are similar before and after the first drowning step. After this first drowning, the carbonate platform developed under enhanced bottom current conditions, as deduced by the coeval drift deposits. The carbonate platform and the drift deposits were balanced for circa 2 Myr, until a global sea-level fall at 10.6 Ma and later reflooding of the platform, which destroyed the equilibrium between both depositional systems, favouring the current-controlled deposits. The drowning of the Miocene carbonate platform of the Maldives was the result of the combined effect of the fluctuating sea-level during the Neogene and the intensification of oceanic currents due to the invigoration of the South Asian Monsoon during the middle Miocene.

Stratigraphy and Microfacies Analyses of The Al Faidiyah and Benghazi Formations at Al Fatiah, Al Huarry and Al Abyar Quarries, NE Libya

Three quarries named Al Fatiah Cement, Al Huarry Cement, and Al Abyar are located in the northeastern part of Libya and consist of carbonate rocks of Miocene age. The main objectives of this study based on microfacies analyses are to construct the depositional environment with a comprehensive stratigraphical correlation of the study areas. The Al Fatiah Quarry has been divided into three microfacies which are operculinid packstone microfacies, algal packstone microfacies, and moluskan packstone grading to grainstone microfacies, one species of large benthic foraminifera is found to be abundant (Operculina complanata). Accordingly, the Al Faidiyah Formation was deposited in a continental shelf (outer to middle neritic zones) environment. Al Huarry Cement Quarry has been divided into five microfacies which are algal boundstone microfacies, amphisteginid - algae packstone microfacies, amphisteginid grainstone microfacies, algal - bryozan packstone microfacies and amphisteginiid - bryozoan - algal boundstone microfacies, one species of large benthic foraminifera is found to be abundant and well preserved (Amphestegina cf. lessonii). Accordingly, the Benghazi Formation was deposited in an inner self to open a marine shelf environment. On the other hand, the Al Abyar Quarry has been divided into two microfacies which are pelloidal packstone microfacies and miliolid wackestone–packstone microfacies, suggesting that the sedimentation was of low energy under very shallow marine to the restricted environment.

BURIAL RATE DETERMINES HOLOCENE RHODOLITH DEVELOPMENT ON THE BRAZILIAN SHELF

Abstract The structure and composition of rhodoliths in two regions of the Brazilian shelf, Abrolhos Continental Shelf (ACS) and South Espirito Santo State (SES) were examined and compared. Rhodoliths were sampled at depth ranges of 10–20 m and 50–60 m in SES, and 20–30 m and 50–75 m in ACS. Rhodoliths in SES are algal boundstones, built mainly of melobesioid corallines, with subordinate bryozoans and encrusting foraminifers. They show high porosity and the sediment infill of borings and voids contains a relatively high amount of siliciclastics (up to 8%). Rhodoliths from ACS are formed by a structureless carbonate mass covered by a thin veneer of encrusting coralline algae. The massive interior was produced by multiphase boring and infilling of an original boundstone. The infillings consist of a micritic matrix with bioclasts and low amounts of siliciclastic grains. Coralline assemblages are reduced to fragments of thin crusts. Rhodoliths from shallow depths are small (< 8 cm) whereas rhodoliths from the...

Lateral variability of shallow-water facies and high-frequency cycles in foreland basin carbonate platforms (Pennsylvanian, NW Spain)

The kilometer-sized and 100-meter-thick carbonate platforms of the Escalada Fm. I and II (Middle Pennsylvanian) accumulated in the foredeep of a marine foreland basin during the transgressive phases of 3rd-order sequences and were buried by prograding siliciclastic deltaic systems in the course of the subsequent highstand. The carbonate successions show a general upward trend from grain- to mud-supported carbonates, interfingering landwards with siliciclastic deposits of a mixed siliciclastic-carbonate shelf (Fito Fm.) adjacent to deltaic systems. The spatial variability of the carbonate facies and the high-frequency (4th–5th order) cycles, from the platform margin-outer platform to the deltaic systems, has been interpreted from basin reconstruction. Carbonate facies include skeletal grainstone to packstone, ooidal grainstone, burrowed skeletal wackestone, microbial and algal boundstone to wackestone forming mounds, various algal bafflestone and coral biostromes in areas with siliciclastic input. These high-frequency transgressive–regressive cycles are interpreted to record allocyclic forcing of high-amplitude glacioeustasy because they show characteristic features of icehouse cycles: thickness >5 m, absence of peritidal facies, and in some cases, subaerial exposure surfaces capping the cycles. In the mixed cycles, siliciclastics are interpreted as late highstand to lowstand regressive deposits, whereas carbonates as transgressive-early highstand deposition. The lateral and vertical variability of the facies in the glacioeustatic cycles was a response to deposition in a rapidly subsiding, active foreland basin subjected to siliciclastic input, conditions that might be detrimental to the growth of high-relief carbonate systems.

Cyanobacterial diversity and related sedimentary facies as a function of water flow conditions: Example from the Monasterio de Piedra Natural Park (Spain)

The River Piedra in the Monasterio de Piedra Natural Park (NE Spain) is a modern tufa-depositing river that encompasses various depositional environments that are inhabited by different cyanobacterial populations. Molecular (16S rDNA) and morphological analyses of the cyanobacteria from different facies showed that Phormidium incrustatum dominates in the fast-flowing water areas where the mean depositional rate is 1.6cm/year. Stromatolites in these areas are formed of palisades of hollow calcite tubes (inner diameter of 6.0–7.5μm, walls 2–12μm thick) that formed through calcite encrustation around the filaments followed by decay of the trichomes. In contrast, in slow-flowing water areas with lower depositional rates (mean depositional rate of 0.3cm/year), Phormidium aerugineo-caeruleum is the dominant species. In these areas, randomly oriented calcite tubes (inner diameter of 5–6μm, walls 3–8μm thick) formed by calcite encrustation, are found in thin and uneven laminae and as scattered tubes in the loose lime mud and sand-sized carbonate sediment. Although this species did not build laminated deposits, it gave cohesiveness to the loose sediment. In the stepped and low waterfalls, with intermediate deposition rates (mean depositional rate of 0.9cm/year), both species of Phormidium are found in association with spongy moss and algal boundstones, which is consistent with the variable flow conditions in this setting.The calcite encrustations on the cyanobacteria from different environments exhibit irregular patterns that may be linked to changes in the calcite saturation index. The physicochemical conditions associated with extracellular polymeric substances may be more significant to CaCO3 precipitation in microbial mats in slow-flowing water conditions than in fast-flowing water conditions. These results show that flow conditions may influence the distribution of different cyanobacteria that, in turn, leads to the development of different sedimentary facies and structures in fluvial carbonate systems.

Drowning of the Triassic Yangtze Platform, South China, By Tectonic Subsidence Into Toxic Deep Waters of An Anoxic Basin

Abstract The Yangtze Platform drowned and was buried by pelagic facies and siliciclastic turbidites in western Guizhou Province during the Late Triassic, Carnian. The uppermost platform facies of the Ladinian Yangliujing Fm. consists of peritidal cyclic carbonate. Ladinian margin facies of the Longtou Fm. consist of grainstone and lenses of coral–Tubiphytes algal boundstone indicating high-energy shoals and patch reefs. The drowning horizon is laterally variable; it is either a sharp surface or a gradational shift to dark, nodular-bedded lime mudstone and wackestone of the Zhuganpo Fm. The contact lacks phosphatized or glauconitized hardgrounds that would indicate drowning by excess nutrient flux. Uppermost platform carbonates have a tropical photozoan biota and lack siliciclastic content indicating neither climate cooling nor siliciclastic flux played a role in drowning. The Zhuganpo Fm. contains a dominantly pelagic biota of ammonoids, planktonic bivalves, pseudoplanktonic crinoids, conodonts, and the marine reptile Keichousaurus. Rare bioturbation and benthic biota in the lower part indicate dysoxic conditions with an upward shift to anoxic conditions. The overlying Wayao Fm. is a pyritic, laminated, black argillaceous lime mudstone that grades to black shale with an exclusively pelagic fauna and marine reptile lagerstattes indicating anoxic deep-marine sedimentation. Syndepositional faults played a significant role in the evolution of the western sector of the Yangtze Platform and controlled three local, backstepped accommodation cycles in the Zhenfeng area. Faults that developed during the last accommodation cycle tip out at the drowning horizon and include a flower structure upon which a pinnacle reef developed while the rest of the platform drowned. Lateral variability in the drowning horizon and thickness of the post-drowning pelagic facies suggest that differential tectonic subsidence caused the platform to sink into deep water along faults. Magnetic susceptibility and paleomagnetic-reversal correlations demonstrate that the western sector of the platform drowned while shallow-marine, mixed carbonate siliciclastic sedimentation continued in the eastern sector which later terminated in shallow water by increasing siliciclastic flux. Starved black shale horizons in the basin indicate recurrent bottom-water anoxia. Elevated trace-metal concentrations in the pelagic facies of the Zhuganpo and Wayao formations indicate dysoxic to anoxic conditions and enhanced preservation of organic matter. Tectonic subsidence likely submerged the western sector into deep, toxic waters of the basin, killing benthic carbonate production. Previous studies have implicated the Carnian pluvial event as a cause of drowning of the Yangtze Platform and the shift to siliciclastic turbidites of the Laishike Fm., but the Yangtze Platform drowned earlier than western Tethys platforms and siliciclastics were already rapidly infilling the basin in the Anisian and Ladinian, indicating that the events are probably unrelated. Siliciclastics of the Laishike Fm. that overlapped and buried the platform only after the basin was filled are better interpreted as a response to tectonics than to a shift in climate.

Growth Dynamics of Pennsylvanian Carbonate Mounds From A Mixed Terrigenous-Carbonate Ramp In the Puebla De Lillo Area, Cantabrian Mountains, Northern Spain

Abstract Carbonate mounds are widespread in many places around the world and are especially well exposed in the Cantabrian Mountains, northern Spain. This study focuses on the composition and growth dynamics of two large mound complexes well exposed near the village of Puebla de Lillo, 70 km northeast of Leon, and evaluates the impact of sea level, accommodation, and siliciclastic input on mound growth. The mound substrate consists of bedded dark skeletal bindstone. The core facies exhibits patchy growth forms of alternating massive microbial–algal boundstone and skeletal and nonskeletal wackestone, reflecting the overall mound internal composition of smaller coalescent bodies. Microbial activity, as inferred from the volumetrically important clotted peloids, appears to be the main factor leading to the high accumulation rate in the cores. The steeply dipping flanks presumably resulted from early cementation and subsequent lithification and stabilization induced mainly by microbial activity. In the intermound strata, carbonate beds and small mounds alternate with fine-grained sandstone, siltstone, and shales. The intermound carbonates consist of skeletal and intraclastic mudstone to wackestone, whereas algal–microbial boundstone is a minor component. Overall, facies transition from the mound core towards the flanks or the mound-capping beds is gradual. However, the volume of bioclasts and intraclasts increases towards the flank and capping facies, inversely to amount of clotted peloids or micrite. The substrate and the cores of the two mound complexes likely formed in the photic zone, as inferred from the common calcareous algae. Carbonate precipitation favored by microbial activity and algal growth along with gain in accommodation space led to mound-core accretion. The growth of the small mound complexes was most likely stopped by recurrent sea-level fall and siliciclastic input. The large, high-relief mound complex actually kept growing until reaching shallow-water and high-energy conditions. Unlike many late Paleozoic counterparts, these mounds were not subaerially exposed during growth. The great thickness and the aggradational mound growth are indicative of a high subsidence rate. At a later stage, however, siliciclastic input also buried the large mound complex. Rapid subsidence, sea-level fluctuations, and siliciclastic input were thus decisive factors controlling carbonate production. This study reveals that mound complexes nucleated and grew on preexisting paleohighs, maintaining consistent growth in these specific settings. Paleohighs, recurrent sea-level fluctuations (presumably linked to glacio-eustasy), and episodic siliciclastic input are the principal factors that controlled the shape, size, and growth evolution. Furthermore, the internal architecture as a mosaic of juxtaposed small bodies composing the complexes represents an important finding for better understanding of mound growth and, thus, for better constraining reservoir heterogeneity, particularly for upper Paleozoic deposits.

High frequency subtidal-peritidal cycles of the Callovian Calabozo Formation (Neuquén Basin, Western Argentina): Preliminary approach

The Calabozo Formation (Cuyo Mesosequence, Neuquen Basin) is made up by a thin, up to 30-m thick Middle Jurassic carbonate-dominated sequence. The minor, thin siliciclastic facies in this formation (i.e. lowermost granule-pebble shoreface conglomerate and fine-grained sandstones interbedded among the lower carbonates) record early transgressive shoreline and shallow lagoonal-subtidal sedimentation, respectively. The major carbonate deposits have been split into six facies and seven microfacies on the base of macroscopic field observation and petrological analysis. The carbonate facies have been grouped into three major assemblages: 1) Tidal flat facies assemblage (including the planar laminated algal boundstone facies; 2) Inner platform facies assemblage (including peloidal and bioclastic wackestone, coral floatstone and bioclastic and intraclastic packstone facies; and 3) Platform margin assemblage (including oolitic-peloidal packstone-grainstone facies). Afossil algal record made up by dasycladacean species (Salpingoporella annulata, Cylindroporella sp. and Heteroporella sp.) and blue-green algae (Cayeuxia (Rivularia) piae, and Cayeuxia (Rivularia) kurdistanensis) has been reported for the first time in this unit. The analysis of the intracycle facies and microfacies arrangements, as well as the nature of the cycle bounding surfaces, enabled one to identify two kinds of cycles. 1) Widespread subtidal cycles capped by shallow to intermediate subtidal facies, with no evidence of subaerial exposure at cycle tops; and 2) a minor subtidal cycle with similar shallowing-upward trend but capped by peritidal facies. The stacking pattern and thickness trend of these cycles was studied to determine possible allocyclic and autocyclic controls on their evolution. The Fischer plots reveal that the deposition of the Calabozo Formation subtidal-peritidal cycles took place under upward decreasing accommodation space conditions which may be related to eustatic lowering.

An assessment of the calcination characteristics of the mfamosing limestone for quality commercial lime production.

High quality lime is an essential raw material for many industries (such as steel, chemical, sugar etc) all over the world. In Nigeria most of the demand for this chemical product is met through importation. The Cretaceous Albian carbonate of the Calabar Flank - the Mfamosing limestone is hereby assessed for production of quality lime. The limestone is fine-grained, fossiliferous and composed dominantly of algal boundstone and lenses of oolitic wackestone and packstone. X-ray fluorescence (XRF) and X-ray diffraction (XRD) were employed in its chemical and mineralogical investigations. The suitability of the limestone for commercial lime production depends on its chemical purity (66.69% CaCO3) and calcination process. Consequently the limestone was calcined through a range of temperature (9500C, 10000C, 10500C and 11000C) for varied retention times (60, 90, 120 minutes) and the burning characteristics were determined. Thus technological tests such as loss on ignition of lime, decrepitation, mechanical strength, and reactivity with water (slaking test) were carried out. The 10500C/90 minutes calcine yielded best quality product - a compact, soft burned, porous and highly reactive lime (>400C rise) desired by lime manufacturers. The Mfamosing limestone is highly recommended for commercial lime production.KEY WORDS: Lime, calcinations, soft-burned, purity, commercial

Microfacies analysis of Wadi Waqb member (Miocene) in Wadi Aynunah, northwest of Saudi Arabia

Easier access to most of spectacular sedimentological features of Midyan region along the northern coast of Red Sea has enabled a more detailed examination of the Miocene succession that could not have been possible except from deep subsurface drilling. The Wadi Waqb member of Jabal Kibrit Formation hosted the Wadi Waqb reservoir in this region. In this study the microfacies of the exposed discontinuous fringing rhodolith and coral reef complex of Wadi Waqb member that seated unconformably on steep cliffs of granitic basement are investigated. Four microfacies were recognized as follows: MF-1) Quartz-peloid packstone and Red algal bioclastic boundstone, MF-2) Bioturbated rhodophyte-bioclastic grainstone, MF-3) Calc-allochemic sandstone, and MF-4) Intraclastic wackestone.

Facies and Stratigraphic Anatomy of a Temperate Carbonate Sequence (Capo Colonna Terrace, Late Pleistocene, Southern Italy)

Abstract Accurate interpretation of ancient non-tropical carbonate systems requires the development of appropriate facies and sequence stratigraphic models. These models should account for the marked differences in sedimentation style among non-tropical carbonates formed under different energy settings. This paper presents data and a conceptual model of the sequence architecture of non-tropical carbonates of moderate energy environments based on the late Pleistocene deposits of Capo Colonna marine terrace (Calabria, southern Italy). These deposits have the advantage of being continuously exposed along a proximal–distal transect across the paleo-shelf and their geometry has not been disturbed by later tectonic activity. They consist of a transgressive–regressive (T–R) cycle whose genesis can confidently be related to one of the interstadial glacio-eustatic fluctuations of marine isotope stage (MIS) 5. Eight different mixed carbonate–siliciclastic and carbonate facies are present in the studied sequence. Of these, biogenic-dominated facies are invariably made up of skeletal remains of light-independent organisms plus or minus red calcareous algae (the heterozoan association). The relatively young age of the deposits allows calibration of the paleoecological significance of observed facies by direct comparison with modern analogues from the Mediterranean Sea. Four laterally persistent discontinuity surfaces were identified along the transect, and interpreted, from bottom to top, as (1) a basal ravinement surface, (2) a submarine hardground locally acting as a substrate for algal boundstones, (3) a regressive surface of marine erosion, and (4) a surface of subaerial exposure. Sequence stratigraphic analysis indicates that the preserved T–R cycle is asymmetric, with a thicker regressive portion. Highstand deposits can be subdivided into a shore-connected sandy prism and more distal autochthonous and parautochthonous skeletal accumulations and algal boundstones. During forced regression, a thin, sharp-based, strongly progradational unit of calcarenites was deposited above the regressive surface of marine erosion. The deposits of Capo Colonna terrace document the response of non-tropical, moderate-energy carbonate ramps to sea-level fluctuations during icehouse conditions. Their architecture can facilitate the interpretation of other successions from similar settings and provide an end member to be compared and contrasted with high-wave-energy cool-water carbonates.

Facies de patch reefs en la Formación Picún Leufú (límite Jurásico/Cretácico) en la región de Zapala, Cuenca Neuquina

Patch reefs facies in the Picun Leufu Formation (Jurassic/Cretaceous boundary) in the Zapala region, Neuquen Basin, Argentina. In the locality of Cerrito Caracoles, situated in the nearby of Zapala city, in the western central region of the Neuquen province, Argentina, the basal part of the Picun Leufu Formation (Jurassic/Cretaceous boundary) crops out. The facies and microfacies association analysis points out to an inner shelf margin environment, with development of well preserved patch reefs. The description of these bodies (coral and algae bafflestone, bryozoan bafflestone and algal boundstone), and of a low relief mound reef (skeletal algal packstone) are presented in this paper. The associated facies are represented by low energy deposits (mudstone), bar complexes (sandy skeletal packstone and skeletal packstone) and channels (skeletal intraclast floatstone and intraclast skeletal ooidal floatstone).

Marine Red Staining of a Pennsylvanian Carbonate Slope: Environmental and Oceanographic Significance

Abstract Red-stained platform facies are a common feature of many carbonate settings throughout the geological record. Although the mechanisms involved in red staining of subaerially exposed or argillaceous, peri-platform limestones are reasonably well understood, the environmental and oceanographic significance of red carbonates often remains uncertain. Here, sedimentological, sequence stratigraphic, geochemical, paleontological, and quantitative bathymetric data from Pennsylvanian red intervals across a well exposed carbonate platform top and slope are documented and interpreted in a process-oriented context. On the upper slope (80–350 meters below the shelf break), red intervals alternate with gray, mainly microbial algal boundstones. On the lower slope (350–600 meters below the shelf break), redeposited red-stained mud builds matrix-supported breccia tongues interbedded with predominantly redeposited, clast-supported carbonate debris. The presence of large volumes of fibrous calcite biocementstones as well as firmgrounds point to low sedimentation rates or omission. In terms of sequence stratigraphy, red intervals occur within maximum flooding intervals and reflect near platform drowning. Elevated δ18O values (2–3‰) and an essentially cool-water, heterotrophic biotic association in red intervals on platform top and slope suggest deposition during sea-level highs, associated with colder water masses and high nutrient levels. The most likely drivers are an elevated thermocline and upwelling. The red staining is the result of iron oxidation which occurred during early diagenesis, likely by iron bacteria. These red intervals provide an important bathymetric benchmark against which other (mainly Paleozoic) red facies can be tested and calibrated.

Peritidal sedimentary depositional facies and carbon isotope variation across K/T boundary carbonates from NW Adriatic platform

The K/T boundary in the Karst region (Italy and Slovenia) is well documented in correspondence to shallow water limestones. Its evidence is usually related to palaeontological data (disappearance of Cretaceous taxa and subsequent appearance of Tertiary ones), palaeomagnetism (Ch 29r) iridium anomaly and negative shift of δ 13C. In Italy, the Padriciano section highlights the K/T boundary included in the basal breccia of a peritidal cycle. Recent investigations brought to light a short well exposed new stratigraphic sequence containing the K/T boundary, 100 m east of Padriciano, as demonstrated by lithological, palaeontological and new isotopic data. The recording of a new peritidal setting denotes stressed environmental conditions. The findings of the biota mostly correspond to the lagoonal limestones of the peritidal cycle. It consists of small opportunistic thin shelled foraminifers, ostracods and gastropods. At Padriciano, the environmental stability occurred after episodes of strong fresh water influence. The intraclasts, oncolites and stromatolites have been observed in the Padriciano section. The broken shell fragments, algae and foraminifera have been found associated with fenestral fabric. These features indicate deposition in a shallow marine (intertidal to supratidal) environment. Algal boundstones and microbial (stromatolitic) laminae, crenulated domal laminae and crenulated conical laminae have been studied in petrographic sections for microstructures. The K/T boundary section has been analysed for the carbon and oxygen isotopic ratios. The δ 13C values range from − 3.62 to − 10.01‰ (V-PDB) and the δ 18O values range from − 3.85 to − 5.47‰ (V-PDB). This extreme depletion in the δ 13C record has already been reported from other K/T boundary sections both in the Padriciano area (Italy) and in Slovenia (Dolenja Vas sections) and may be related to global climate change but also to local environmental changes occurring in the NW Adriatic Platform.

230Th/234U and 14C dating of a lowstand coral reef beneath the insular shelf off Irabu Island, Ryukyus, southwestern Japan

Abstract High‐resolution seismic reflection profiles delineated the distribution of mound‐shaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral–algal boundstone suggesting a small‐scaled coral reef. High‐precision α‐spectrometric 230Th/234U dating coupled with calibrated accelerator mass spectrometric 14C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3–2. The existence of low‐Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific.

Microfacies and depositional environments of the Asmari Formation, at Dehdez area (a correlation across central Zagros basin)

The predominant microfacies of the Asmari Formation at Dehdez area are: (1) globigerinid bioclastic wackestone to packstone, (2) globigerinid laminated wackestone, (3) coral and coralline algal boundstone, (4) bioclastic-lithoclastic wackestone to packstone, (5) foraminifera bioclastic wackestone to packstone, (6) foraminifera grainstone, (7) peloid wackestone to packstone, and (8) peloid bioclastic grainstone.