Bioclastic Wackestone-packstone Research Articles

Microfacies of the San Juan Formation (lower Darriwilian) in the Rio Francia, Central Precordillera, Argentina

In this contribution, we describe and interpret the microfacies of the upper levels of the San Juan Formation in the Río Francia section of the Central Precordillera, Argentina, for the first time. Several studies in this section identified the Lenodus antivariabilis, Lenodus variabilis, Lenodus crassus, and Lenodus pseudoplanus zones, thereby limiting this stratigraphic interval to the early Darriwilian age. Five microfacies were recognized: M1 burrowed bioclastic wackestone, M2 bioclastic mudstone-wackestone, M3 intrabioclastic grainstone, M4 crinoidal wackestone-packstone, and M5 bioclastic wackestone-packstone. These microfacies indicate a shallow subtidal inner platform environment with variations in hydrodynamic energy ranging from low to moderate conditions below the fair-weather wave base level. The vertical arrangement of these sub-environments suggests a gradual transgressive setting during the lower Darriwilian for the carbonate beds of the San Juan Formation. The Baños de Talacasto, Ancha Creek, and Don Braulio sections are correlated with the section studied in this work, where conodont zones were documented, and microfacies analyses revealed shallow subtidal environments with low-energy conditions and occasional high-energy episodes. Differences in redox conditions were observed between the Don Braulio section (anoxic) and the Río Francia section (well-oxygenated), interpreted as the result of a rapid sea-level rise, though diachronic across the platform. Microfacies analysis, combined with precise conodont biostratigraphy, provides a powerful tool for reconstructing the Middle Ordovician carbonate platform.

Depositional Environment and Microfacies Analysis of Yamama Formation in North Rumaila Oil Field, South Iraq

Yamama Formation is an important sequence in southern Iraq. Petrographic analysis was used to determine and analyze the microfacies and pore types. The diagenetic processes and the impacts on the petrophysical properties of the rocks were also identified. The petrographic identification was based on data of 250 thin sections of cutting and core samples from four wells that were supplied by the Iraqi Oil Exploration Company (O.E.C). The present study focuses on the depositional environment and the microfacies analysis of Yamama Formation. The results revealed several types of microfacies, including peloidal wackestone-packstone, algal wackestone-packstone, bioclastic wackestone-packstone, foraminiferal wackestone, bioclastic wackestone, and mudstone. The latter was divided into two submicrofacies, namely argillaceous lime mudstone and sparse fossiliferous lime mudstone. The study showed that Yamama Formation was deposited through various settings within the carbonate platform; these comprise inner ramp, middle ramp, and outer ramp settings. The inner and middle ramp settings, characterized at the top and middle Formation, have high effective porosity and low clay volume, due to dominant packstone.

Sedimentology and carbonatogenesis of the Upper Campanian limestones in Jebel Berda (south central Tunisia)

The Berda Formation corresponds to an inner-shelf stratigraphic equivalent of the Campanian-Maastrichtian outer-shelf Abiod Formation of Tunisia. The present work aims to carry out a sedimentological study of the lower unit (Upper Campanian) of Berda Formation limestones in order to interpret the limestone depositional environment and the origin of the associated micrite particles. This work is based on the study of a geological section surveyed in the Jebel Berda, typic locality, completed by microscopic observation of thin sections that allowed us identifying different carbonate facies and interpreting their depositional environments. The micrite particles have been examined with the SEM. The mineralogical and geochemical proportions and the magnetic susceptibility of the Berda Formation limestone, have been evaluated using respectively XRD, Atomic Absorption Techniques and KLY-3 Kappabridge susceptometer. The studied succession of Berda Formation includes five carbonate facies that developed within different depositional environments (1) calcisphere-rich bioclastic mudstone-wackestone within a circalittoral environment, (2) echinoderm-rich bioclastic wackestone-packstone within a shallow-marine environment (3) bioclastic rudstone within an open-marine environment, (4) peloid-rich bioclastic grainstone within high energy littoral shallow-water marine environment and (5) bioclastic dolomicrite-dolomicrosparite within a continental to marine transition environment. The studied limestones are composed of two kinds of micrite particles, (1) irregularly shaped particles resulting from fossils and micro-fossils desintegration and (2) regularly shaped polyhedral particles resulting from inorganic chemical precipitation. The carbonate facies are arranged into shallowing-up parasequences. The sedimentary facies variation and carbonate accumulation are controlled by eustatic sea-level fluctuation. In this way the biodetrital micrite occurred mainly during the transgressive intervals whereas the inorganic chemical micrite is related to the regressive intervals.

Depositional environment and diagenesis of Late Cretaceous-Early Paleogene carbonates on the Benin flank, southwestern Nigeria

Carbonates of Late Cretaceous-Early Paleogene occur on the Benin Flank, southwestern Nigeria. Depositional environment and diagenetic history of the carbonates have not been extensively described. Outcrop sections and cores on Benin Flank were logged, sampled and analyzed in order to determine the depositional environment and diagenetic history of the carbonate rocks, through field-based studies, petrographic studies (employing both optical and scanning electron microscopy, SEM) and mineralogical studies using XRD (X-ray powder diffraction) analytical technique. Based on field studies, core description and petrographic investigations, two lithofacies have been identified, namely: wackestone (associated with mottled dolomite) and bioclastic wackestone-packstone. The Late Cretaceous-Early Paleogene limestone on the Benin Flank is interpreted to have been formed in low-energy environment along the shelf. Mineralogical composition of the analyzed limestone samples indicate that calcite was the original carbonate mineral in the limestone. The observed diagenetic fabrics of the analyzed carbonate samples suggest that the Late Cretaceous-Early Paleogene carbonates on the Benin Flank have been subjected to some post-depositional alterations, namely micritization, development of microspar, compaction, dissolution, dolomitization and calcite-filled microfractures.

Abiod Formation in Boukhil section (Jebel M'rhila, Central Tunisia): Facies, geochemistry, mineralogy and deposition sequences

The field study and the petrographic observations of the limestone samples particularly from the Boukehil section allowthe identificationof four carbonate facies: (1) calcisphere-rich mudstone-wackestone, (2) Conglomeratic limestone, (3) bioclastic wackestone-packstone, and (4) siliceous dolostones. According to the vertical change of the deposition facies and the occurrence of unconformities, it was possible to divide the AbiodFormation in this area into three third-order depositional sequences bounded either by subaerial exposure surfaces or by submarine erosional surfaces. These sequences include only transgressive and highstand systems tracts. The SEM observation of the limestone shows three types of micrite: bio-detrital, biological and chemical. Despite poor occurrence in our samples, the existence of some biological structures similar to bacterial fabrics highlights the role of bacteria in the carbonatogenesis. The XRD mineralogy and the calcimetry analyses show that the limestone of the Abiod Formation is very rich in calcium carbonate. The CaCO3 concentrations vary with the systems tracts and the depositional sequences controlled by the sea-level fluctuation. For instance, higher concentrations of CaCO3are recorded in the transgressive intervals of the eustatic cycles (with some samples yielding 100 wt% of CaCO3), whereas through highstand intervals, the CaCO3 concentration falls to 83 wt %. The atomic absorption geochemical analysis of limestones shows that the major elements concentrations change with systems tracts and thus with sea level fluctuation. For example the highest concentrations of Fe in the carbonates are observed in the marine highstand and regressive intervals, and those of Mg and Ca observed in the transgressive intervals.

First microbial-archaeocyathan boundstone record from early Cambrian erratic cobbles in glacial diamictite deposits of Namibia (Dwyka Group, Carboniferous)

This study records the first occurrence of a lower Cambrian archaeocyathan fauna in limestone cobbles from Carboniferous glacigenic deposits of the Dwyka Group of the Aranos Basin in Namibia. Petrographic and microfacies analysis of 17 large, middle and standard thin sections reveals two distinctive limestone cobble facies: (a) bioclastic wackestone-packstone (hyoliths, trilobites, chancelloriids, crinoids and archaeocyaths); and (b) microbial-archaeocyathan boundstone dominated by calcimicrobes (Epiphyton and Renalcis), neomorphosed microbial crusts and crypto-fibrous calcite crusts around mainly regular archaeocyaths such as Polycoscinus scutatus, where encrusting ?sponges are accessory. The published stratigraphical and palaeocurrent data from the Dwyka Group, as well as published ages and the tectonothermal history of the underlying Nama Group, have been used in this study to establish the provenance of these lower Cambrian cobbles. The archaeocyaths from the Aranos Basin are: Favilynthus contractus, Ajacicyathus aequitriens, Kisasacyathus subacutus, Plicocyathus sp., Erismacoscinus endutus, Erismacoscinus ganigobisensis sp. nov., Erismacoscinus cf. stephensoni, Polycoscinus scutatus, Chabakovicyathus sp., Loculicyathidae gen. et sp. indet., Dictyocyathus aranosensis sp. nov., Graphoscyphia sp., Archaeopharetra irregularis and Syringocnema favus. The presence of Syringocnema favus and other species allows us to determine a precise upper Stage 3 or early-mid Botoman age for the erratic cobbles of the Dwyka Group from the Aranos Basin. The Namibian fauna reported here provides a key record in Cambrian palaeobiogeography based on archaeocyathan assemblages. The archaeocyath faunal assemblage from the Dwyka cobbles is diverse and has an analogous richness to allochthonous assemblages from Permo-Carboniferous glacigenic deposits of other localities in south-western Gondwana. Thus, the archaeocyath-bearing cobbles from the Dwyka Group of Namibia could provide a better understanding of the different palaeo-ice flow direction models of the Permo-Carboniferous glacial deposits in future palaeogeographical reconstructions of south-western Gondwana.http://zoobank.org/urn:lsid:zoobank.org:pub:0365EE4C-D7FA-4C09-89DF-27C9E1F55511

The ups and downs of Diplocraterion in the Glen Rose Formation (Lower Cretaceous), Dinosaur Valley State Park, Texas (USA)

Diplocraterion, a U-shaped burrow attributed to infaunal invertebrates, is normally a shallow-marine trace fossil and not part of a continental vertebrate ichnoassemblage. Hence, the Glen Rose Formation (Aptian–Albian) of Texas (USA) presents an opportunity to study Diplocraterion associated with a world-class dinosaur tracksite. Most Diplocraterion are in a bioclastic wackestone–packstone bed just above the Taylor Tracklayer, a significant dinosaur track horizon. Diplocraterion are consistently sized, but with variable depths; most have protrusive spreiten and northeast–southwest trends. Smaller Arenicolites co-occur with Diplocraterion, and other trace fossils include Rhizocorallium and a large theropod trackway. Based on our analysis, a sea-level rise buried the Taylor Tracklayer, with a shallow-marine carbonate mud colonised by Diplocraterion and Arenicolites tracemakers. Protrusive Diplocraterion, eroded burrow tops, Rhizocorallium, and other criteria point towards firming and net erosion of the bed caused by a stillstand. The depositional environment of the Diplocraterion bed was possibly a subtidal lagoon that covered shoreward sediments impacted by large theropods. Burrow orientations suggest bidirectional currents consistent with trends of theropod trackways, implying each were controlled by a shoreline. The results of our study demonstrate how marine invertebrate and continental vertebrate trace fossils can be used together to define fine-scale changes in former carbonate shorelines.

Microfacies and environmental study of the lower cretaceous yamama formation in Ratawi field

The Yamama Formation is the main Lower Cretaceous (late Berriasian–Valangenian) carbonate reservoir in southern Iraq. Petrographic study from thin-section examination shows that the skeletal grains included calcareous algae from both red and green algae. Red algae is concentrated in the upper part of the Formation, and the most important of this algae species is Permocalculus ssp. Green algae is less common, and its concentration is in the middle part of the Formation. The most species found in the Yamama Formation is dasycladeans, and both small and large species of benthonic foraminifera such as Nautiloculina, Textularia, Trocholina, Pseudocyclammina, and Everticyclammina are also present. The non-skeleton grains included oolites, pellets, and micrite. Six cyclic type microfacies have been recognized for Yamama Formation in Ratawi-3 (Rt-3) and Ratawi-4 (Rt-4) Wells, namely peloidal packstone–grainstone, algal wackestone–packstone, oolitic–peloidal grainstone, bioclastic wackestone–packstone, foraminiferal wackestone, and mudstone microfacies. The latter has been divided into two submicrofacies: argillaceous lime mudstone and fossiliferous lime mudstone. The lateral extension of these microfacies has been identified by integrating the thin-section data and well logs’ character variations with similar characteristic for microfacies. The Yamama Formation was affected by five diagenetic processes, which are micritization, cementation, recrystallization, silicification, and stylolites. The Yamama Formation was deposited during a regressive period within the outer ramp, shoal, and inner ramp setting.

Ferruginous microstromatolites related to Middle Jurassic condensed sequences and hardgrounds (Bucegi Mountains, Southern Carpathians, Romania)

Integrated analyses of ferruginous laminated crusts and macro-oncoids associated with Middle Jurassic (Bathonian-Callovian) hardgrounds and condensed horizons cropping out in the Bucegi Mountains (Southern Carpathians) allowed an assessment of their microbial origin and the paleoenvironmental context of their genesis. The ferruginous microstromatolites reveal different morphological types (or macrofabrics): ferruginous microstromatolites representing the hardgrounds crusts, ferruginous endostromatolites and oncoidal ferruginous microstromatolites. The last are associated with ooidal bioclastic grainstone, ooidal bioclastic grainstone-packstone, bioclastic ooidal packstone-grainstone, oncoidal floatstone and rudstone, stromatolitic bindstone, bioclastic wackestone-packstone and bioclastic wackestone microfacies. The host mineral of the ferruginous microbialites is calcite, but microbially induced iron oxyhydroxides (goethite and magnetite) prevail in the ferruginous laminae. Petrographical and scanning electron microscope (SEM) investigations revealed that these ferruginous microstromatolites were formed by the activity of microbial mats dominated by putative bacterial and fungal filaments. Locations with reduced or no sedimentation, in relatively deep-water, open-marine shelf environments, below fair-weather wave base or near to storm wave base, within the deep euphotic zone, were favorable for the hardening of the seafloor and the development of the microbial mats. The scarcity of an autochthonous benthic fauna and of burrowing, as well as the presence of framboidal pyrite suggest dysaerobic conditions. In such an environment, iron would have been in its soluble state (Fe2+) and the activity of micro-aerophylic iron-oxidizing bacteria appears to have been particularly intensive at the dysoxic-anoxic interface, inducing the precipitation of iron oxyhydroxides and the formation of diverse ferruginous microstromatolites.

A NEW DINOSAUR TRACKSITE IN THE CENOMANIAN OF ISTRIA, CROATIA

The new locality with dinosaur footprints has been discovered in the port of Karigador village in Istria. The site is situated in peritidal limestones of late Cenomanian age. The track-bearing horizon is bioclastic wackestone-packstone deposited in a subtidal environment. A single trackway which consist of 28 pairs of footprints and a group of 4 track pairs was registered at the site. Trackways belong to quadrupedal dinosaurs and are assigned to sauropods. Oval-circular shaped footprints represent the pedal prints and horseshoe-semicircular shaped ones represent the manus prints. The trackway is of narrow-gauge type with outwardly rotated manus and pedal prints. The average length of the pedal prints is 33 cm what indicates the length of the individual of app. 10 m. The preferred gait of the individual was a normal walk, taking normal strides with a speed of around 3 km/h. The trackmaker was a non-titanosaurian sauropod. Together with the other late Cenomanian sauropod localities in Istria (Fenoliga and Ladin Gaj), the Karigador site represents an example of sauropod tracks in a carbonate platform environment which can be assigned to Brontopodus ichnofacies.

A foraminiferal assemblage as a bioevent marker of the main Ladinian transgressive stage in the Betic Cordillera, southern Spain

The Betic Cordillera comprises the mountain range in the southern Iberian Peninsula that extends from Cadiz to Alicante, which displays typical features of alpine cordilleras. The Betic Cordillera includes two large geological tectonic domains, namely an External Zone, and an Internal Zone. The External Zone is essentially composed of epicontinental Triassic rocks that consist of the Buntsandstein, Muschelkalk and Keuper facies. The Buntsandstein facies rarely occur in outcrops, whereas the Keuper stratigraphic successions are truncated. The Muschelkalk facies frequently displays complete successions that are very useful for interpreting the Ladinian stage palaeogeography. The Muschelkalk facies consists of a lower carbonate member formed by three thick, massive limestone beds with intervals of thin-bedded marly limestone, and an upper marly member with intercalation of distinct beds of limestones and marls, where tempestites predominate. The first member has been interpreted as a transgressive systems track in which subtidal and ramp deposits can be identified. The second member is related to a highstand systems track, and consists of marine-platform and coastal deposits, which correspond to a shallowing-upward sequence. We describe and interpret a distinct bioclastic limestone bed with high concentrations of Involutinidae benthic foraminifers, that has been found in the Muschelkalk of several distant sections. This unusual bed is just above the third bed of massive Muschelkalk limestone, and consists of a bioclastic wackestone–packstone, up to 8 cm thick, with many Involutinidae of Ladinian age. The most abundant species are: Lamelliconus gr. biconvexus– ventroplanus, Lamelliconus cordevolicus and Triadodiscus eomesozoicus. These foraminiferal concentrations form a well-defined marker bed that may be related to a bioevent. The appearance of these foraminiferal taxa, which are also very common in the Triassic Alpine realm, coincides with the maximum flooding interval of a transgressive sequence. We surmise that these Tethyan foraminifers moved into newly developed coastal zones during maximum transgression and, at times, produced prolific shallow-water communities, which were reworked by storm currents that caused their unusual concentrations in deeper water. These concentrations thus generated the marker beds of foraminiferal packstones that can be found over distant outcrops in the region. Similar involutinid foraminiferal assemblages occur in the upper Muschelkalk of the Iberian Ranges and Catalan Coastal Ranges, as well as in the upper part of the transgressive systems track of the UAA-2.2 third-order cycle identified in the Muschelkalk of the Pyrenees Basin. Thus, this foraminiferal assemblage can be considered as an extensive bioevent marker related to an important transgressive stage of Ladinian age.