Triassic Limestone Research Articles

Using Clumped Isotopes to Reconstruct the Maximum Burial Temperature: A Case Study in the Sichuan Basin

For strata that have experienced continual burial in the early stage and uplift in the late stage, the present-day temperature is lower than the maximum burial temperature (MBT), which is a key parameter for studying the hydrocarbon generation history of source rocks in petroliferous basins. In this paper, a new method for reconstructing the MBT is proposed based on the solid-state reordering model of carbonate clumped isotopes (Δ47). The MBT reconstructed using the Δ47 was compared with the MBT constrained using the traditional Easy%Ro model. The clumped isotope temperature (TΔ47) of the Permian micritic limestone from the Xibeixiang outcrop (about 62°C) is much higher than its initial formation temperature (20–25°C), suggesting that the limestone experienced partial solid-state reordering during the late burial process. The MBT of the calcite obtained from the solid-state reordering model is 139–147°C, which is quite similar to the MBT determined using the Easy%Ro model (139.5–147.5°C). TΔ47 of the Permian and Triassic limestone and calcite cements in the Puguang gas field are 150–180°C, while TΔ47 of the micritic dolostone is about 70°C, suggesting that the Δ47 of the limestone and calcite cements experienced complete solid-state reordering and the dolostone only experienced partial solid-state reordering. The MBT of the dolomite determined using the solid-state reordering model is 200–220°C, which is also similar to the MBT determined using the Easy%Ro model (202–227°C). Therefore, the case studies from the Sichuan Basin suggest that Δ47 can be used to reconstruct the MBT of ancient carbonate strata lacking vitrinite and detrital zircon data. However, different types of carbonate samples should be used to reconstruct the MBT for strata that have experienced different temperature histories. Micritic limestone and very finely crystallized dolostone can be used to reconstruct the MBT of strata that have experienced MBTs of <150–200°C and >200–250°C, respectively.

The disappearance of inland dunes landscape – a case study from southern Poland

Abstract The paper presents changes in the landscape of inland dunes in one of the basins in the eastern part of Silesian Upland. Based on the analysis of archival maps and historical sources, the former dune landscape of Dąbrowa Basin was reconstructed. The current state of its preservation was determined based on contemporary cartographic materials and field research. It was established that the dunes occur on the floodplain, under-slope flattening, and cuesta escarpment (Ząbkowice Hummock)). The source of aeolian sands was fluvioglacial and alluvial deposits, which, as a result of aeolian transport, were moved to higher and higher morphological levels and stabilized on a substrate of different lithology and age. The impermeability of the bedrock – tills, clays, mudstones, siltstones had a significant influence on the dune landscape. It resulted in the presence of wetlands and peat bogs in the vicinity of most dunes. Consequently, the landscape of the valley was distinguished by a lot of contrast in terms of vegetation - dry pine forests or grassy areas on the dunes and moisture-loving vegetation in their surroundings. However, this landscape was under strong human pressure. Most of the dunes (3/4) have been destroyed in the last hundred years due to sand mining and industrial and residential construction. One of the largest dune fields in the Przemsza River basin and most floodplain and under-slope flattening dunes were utterly destroyed. In addition, an interesting dune at Triassic clays was almost fully exploited, and a rare case on the Silesian Upland where a dune entered the Triassic limestones was partially covered with concrete. There are only 25 dunes in the study area - they deserve protection both as the last fragments of the inland dunes landscape in this part of the Silesian Upland and for historical and natural reasons.

Rb–Sr dating and S–Sr–Nd isotopic constraints on the genesis of the Hehuashan Pb–Zn deposit in the Middle–Lower Yangtze River Metallogenic belt, China

The Hehuashan sediment-hosted Pb–Zn deposit is a large-scale (Pb + Zn＞1 Mt) deposit hosted in the Tongling mining district of the Middle-Lower Yangtze River belt (MLYB). The Pb–Zn ore bodies are composed of two main mineralization types, namely breccia type and massive type. The breccia type ore bodies are hosted by the Triassic limestone and dolostone, while the massive ore bodies are hosted by marble dolostone which are close to the diorite intrusions. The previous research showed that the Hehuashan Pb–Zn deposit is a Mississippi Valley-type (MVT) deposit formed in Middle Triassic and overprinted by late mineralization of magmatic-hydrothermal fluids in Yanshanian period. In this research, we aimed to declare the age of the late mineralization and it's relationship with diorite intrusions. The mineralization age (132.8 ± 3.1 Ma) of the massive ore rocks (late mineralization) is similar to the zircon U–Pb age of the diorite (133–130 Ma), showing that this type mineralization is contemporaneous to the Yanshanian intrusive events. Furthermore, similar initial 87Sr/86Sr values between sphalerite and diorite indicating a magmatic fluid was involved during the mineralization process and the emplacement of diorite also might have provided ore-forming materials. The heavy sulfur compositions (δ34S = +8.6‰ to +12.8‰) of the sphalerite in massive ore rocks indicate that the sedimentary sulfate may have provided reduced sulfur for sulfides precipitation by sulfate thermochemical reduction process. Sr–Nd isotopic compositions of the diorite in the Hehuashan deposit area showed that the massive Pb–Zn mineralization was related to the intrusion of diorite in an extensional tectonic setting. In summary, the Hehuashan Pb–Zn deposit composes a late Yanshanian Pb–Zn mineralization event and represents a younger Pb–Zn mineralization in the Tongling district and MLYB. The Triassic carbonates have the potential for Pb–Zn deposit exploration in the Tongling district and Middle–Lower Yangtze River belt.

Upper Triassic–Lower Jurassic continental carbonates from the Apuseni Mountains, Romania: facies, lithology and paleoenvironments

We studied deposits belonging to the Bihor Unit from the Northern Apuseni Mountains (Romania). The described outcrops are located in the SW of Șes Mountain and the northeastern Pădurea Craiului Massif. We determined the depositional environment and the mechanisms controlling the accumulation of Upper Triassic–Lower Jurassic continental deposits. The sedimentary formations contain carbonate breccia and calcretes embedded in continental clay deposits. Late Triassic–Early Jurassic depositional processes were influenced by the inherited paleobasement of the subaerially exposed Middle Triassic deposits. Numerous fragments of Anisian and Ladinian carbonate deposits are encased in weathered clay deposits accumulated on karstification surfaces developed at the top of Middle Triassic limestones. We integrated facies analysis and clay mineralogy to obtain an accurate interpretation of the continental processes acting at the Triassic–Jurassic boundary in the northern part of the Apuseni Mountains. The composition of the carbonate pebbles is described in terms of the carbonate facies, whereas the clay mineralogy was determined by applying X-ray powder diffraction. Thirteen facies associations are described consisting of carbonate, siliciclastic and ferilitic rock types. Such facies indicate sediment accumulation in a continental, mixed carbonate-siliciclastic depositional environment. A Late Triassic exposure event was followed by an Early Jurassic (Hettangian) transgression. Two major facies types are identified on the basis of their depositional environment. The first category includes subaerially exposed Triassic carbonates and ferilitic facies, while the second category consists of transgressive siliciclastic facies from the basal Lower Jurassic (Hettangian) sediments. The existing data suggest continental deposition in alternating, arid–humid warm climate conditions at the Triassic–Jurassic transition.

Neoproterozoic evolution of northern Gondwana recorded in detrital zircon grains from the Gheshlagh bauxite deposit, Alborz Mountains, Iran Block

When the Cimmerian Continent separated from Gondwana and drifted northward to equatorial latitudes, sedimentary rocks on the continent underwent intense weathering, resulting in the formation of bauxite deposits. Gheshlagh is one such bauxite deposit, located in the Alborz Mountains in northern Iran. The bauxite deposit at Gheshlagh, 12–18 m in thickness with a strike length > 4 km, is hosted by Permian strata and unconformably overlain by Early Triassic limestone. Detrital zircon grains in the bauxite deposit yielded U-Pb ages ranging from 2.5 Ga to 0.5 Ga, with most ages between ca. 0.9 Ga and 0.5 Ga. The detrital zircon grains with age populations between ca. 0.9 Ga and 0.6 Ga are tabular and rounded with sharp oscillatory zoning, and most likely derived from igneous rocks in the northern part of the Arabian-Nubian Shield. The detrital zircon grains with ages of ~1 Ga are long and rounded in shape with slightly obscure growth zoning and probably originated from metamorphic rocks of the Sinai basement in the northernmost part of the shield. Detrital zircon with ages between 1.8 and 2.5 Ga are smoothly rounded in shape with faint internal zoning, suggesting long transport from a metamorphosed source(s), possibly including the Saharan Metacraton, and/or the Kabul Block. The Gheshlagh deposit contains minor needle-like to prismatic-shaped zircon grains, with U-Pb ages ranging from ca. 571 to 521 Ma, corresponding to the timing of the Cadomian magmatic event in northern Gondwana. The occurrence of such proximal sourced zircons at Gheshlagh supports the notion that northern Gondwana was an active margin in response to southward subduction of Prototethys during late Neoproterozoic to Early Cambrian. Our data also suggest that the Cimmerian Continent was still located on the northern margin of Gondwana during deposition of the bauxite protolith in the Permian.

Implications of giant ooids for the carbonate chemistry of Early Triassic seawater

Abstract Lower Triassic limestones contain giant ooids (>2 mm) along with other precipitated carbonate textures more typical of Precambrian strata. These features appear to have resulted from changes in seawater chemistry associated with the end-Permian mass extinction, but quantifying the carbonate chemistry of Early Triassic seawater has remained challenging. To constrain seawater carbonate saturation state, dissolved inorganic carbon, alkalinity, and pH, we applied a physicochemical model of ooid formation constrained by new size data on Lower Triassic ooids from south China, finding that the Triassic giant ooids require a higher carbonate saturation state than typifies modern sites of ooid formation. Model calculations indicate that Early Triassic oceans were at least seven times supersaturated with respect to aragonite and calcite. When combined with independent constraints on atmospheric pCO2 and oceanic [Ca2+], these findings require that Early Triassic oceans had more than twice the modern levels of dissolved inorganic carbon and alkalinity and a pH near 7.6. Such conditions may have played a role in inhibiting the recovery of skeletal animals and algae during Early Triassic time.

Microfacies and biostratigraphy of an Upper Triassic Dachstein limestone fore-reef block in the Jurassic Sirogojno carbonate-clastic Mélange (Zlatibor Mt., SW Serbia)

In the late Middle to early Late Jurassic carbonate-clastic Sirogojno Melange in the Zlatibor Mountain there is one roughly 35 m thick overturned block with an intact Late Triassic fore-reefal Dachstein Limestone succession studied for its biostratigraphic age, content and microfacies characteristics. The succession starts with coarse-grained rudstones followed by meter-sized reefal blocks intercalated in partly layered resedimented grainstones and packstones with abundant reef-building organisms like calcareous sponges, corals and encrusting organisms. Inside this part of the succession open-marine influenced layers are rare. The succession continues with a partly turbiditic sequence and chaotic rudstones, densely packed with reef-derived material like broken reefbuilding organisms and shallow-water material like gastropods, bivalves and foraminifers. Grainstones with clear open-marine influence (e.g., thin-shelled bivalves, crinoids, conodonts) appear in between those rudstones, in cases lumachelle layers be composed of halobiids were deposited. To the end of the succession some layers show turbiditic bedding with mixed shallow-water and deep-marine grains and organisms, i.e. filaments and crinoids. On base of conodonts, foraminifers, calcareous algae, holothurians and halobiids throughout the whole studied succession, a middle Norian (Alaunian) to Rhae tian 1, most probably a late Norian (Sevatian) age can be assigned to this fore-reefal Dachstein Limestone succession, with a similar sedimentation pattern like Late Triassic Dachstein fore-reef limestone facies, e.g., in the Northern Calcareous Alps or the eastern Southern Alps. The study of this block in the Sirogojno Melange closes an important gap in knowledge about the extent, facies and stratigraphy of the Dachstein Carbonate Platform evolution in the Dinarides.

Paleoenvironments and geochemistry across a continuous Permian–Triassic boundary section at Bűkk Mountains, Hungary

The Bálvány North Permian-Triassic boundary sediments were deposited on a carbonate platform in the tropical part of the western PaleoTethys ocean. The overall elemental geochemistry of the detailed two-metre-thick section across the boundary that we studied shows that the clastic content of the sediments came from dominantly silica-rich continental sources though with some more silica-poor inputs in the uppermost Permian and lowest Triassic limestones as shown by Ni/Al and Nb/Ta ratios. These inputs bracket, but do not coincide with, the main extinctions and associated C, O and S changes. Increased aridity at the Permian-Triassic boundary with increased wind abrasion of suitable Ti-bearing heavy minerals accounts for both the high Ti/Al and Ti/Zr ratios. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the Permian–Triassic extinction boundary. The lack of consistent element geochemical changes across the Permian-Triassic boundary occur not only in adjacent shallower-water marine sections, and in other marine sections along the SW Tethys margin such as the Salt Range sections in Pakistan, but also in deeper shelf and oceanic sections, and in non- marine African and European continental sediments. In the absence of significant changes in physical environments, chemical changes in the atmosphere and oceans, reflected in various isotopic changes, drove the Permian–Triassic extinctions.

Geological Characteristics and Genesis of the Jiamoshan MVT Pb–Zn Deposit in the Sanjiang belt, Tibetan Plateau

AbstractThe carbonate‐hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust‐fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst‐controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore‐forming fluids belonged to a Mg2+–Na+–K+–SO42––Cl−–F−–NO3−–H2O system at low temperatures (120–130°C) but with high salinities (19–22% NaCl eq.). We have recognized basinal brine as the source of the ore‐forming fluids on the basis of their H–O isotopic compositions (–145‰ to –93‰ for δDV‐SMOW and –2.22‰ to 13.00‰ for δ18Ofluid), the ratios of Cl/Br (14–1196) and Na/Br (16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite (–5.0‰ to 3.7‰ for δ13CV‐PDB and 15.1‰ to 22.3‰ for δ18OV‐SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34S values are low in the galena (–3.2‰ to 0.6‰) but high in the barite (27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo‐seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples (18.3270–18.3482 for 206Pb/204Pb, 15.6345–15.6390 for 207Pb/204Pb, and 38.5503–38.5582 for 208Pb/204Pb) are similar to those of the regional Triassic volcanic‐arc rocks that formed during the closure of the Paleo‐Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.

One of the oldest polychelidan lobsters from Upper Triassic (Carnian) beds at Kozja dnina in the Julian Alps, Slovenia

Upper Triassic limestones at Kozja dnina in the Julian Alps have long been known to yield an exceptionally preserved Carnian fauna. In the present study, we discuss three specimens of polychelidan lobsters found on bedding planes of platy limestones during recent years. Polychelidan lobsters have a very patchy fossil record and every new specimen increases the palaeo biodiversity of the group. Eopolycheles cornuaureus gen. nov., sp. nov. constitutes one of the oldest species of the family Polychelidae to date. Its affinities to the Polychelidae, the only family of polychelidan lobsters that survived to the present day, suggest an earlier diversification of polychelidan lobsters during their evolutionary history than previously assumed.

Behavioural responses of Rhizocorallium to storm events: Evidence from the Middle Triassic of SW China

Large numbers of densely distributed Rhizocorallium provide a window to understanding the behavioural and functional changes of the trace maker after extreme environmental events. This study focuses on the analysis of Rhizocorallium from the Middle Triassic (Anisian) limestones in the Boyun section, Yunnan Province, Southwest China to investigate the ecological strategies and ethological signatures of its producers before and after storm events. Based on its morphological features, the studied Rhizocorallium is attributed to two ichnospecies Rhizocorallium jenense and R. commune, the latter showing two varieties R. commune var. auriforme and R. commune var. irregulare. In addition to Rhizocorallium, the trace fossil assemblage consists of Arenicolites, Palaeophycus, Planolites and Thalassinoides, which allows assignation to the Cruziana ichnofacies associated with the shallow marine environment. The studied ichnofossil-bearing intervals in the Boyun section are usually high bioturbated, with BPBI (bedding plane bioturbation index) around 5. The ichnoassemblage has a relatively low ichnodiversity and shows high density of Rhizocorallium, which is interpreted as the result of the opportunist strategy when the Rhizocorallium trace makers exploited the quiet, nutrient-rich substrates after storm events. Crosscutting relationships between multiple levels of Rhizocorallium indicate that earlier burrows were reworked by later ones due to successive storm events and erosion of the shallow-tier burrows. Orientation of the marginal tubes of Rhizocorallium jenense shows a bidirectional pattern at 295°NW and 160°SE, which may record the changes of the main flow direction. Diameter measurements support the total recovery of the macrobenthic trace makers during the Middle Triassic (Anisian).

Geological Heritage, Geotourism and Local Development in Aggtelek National Park (NE Hungary)

We examine how geoconservation and geotourism can help the local development of an economically underdeveloped karst area. First, we briefly present the geoheritage of Aggtelek National Park, which largely overlaps the area of the Aggtelek Karst. The area is built up predominantly of Triassic limestones and dolomites. It is a typical temperate zone, medium mountain karst area with doline-dotted karst plateaus and tectonic-fluvial valleys. Besides caves, the past history of iron mining also enriches its geoheritage. Aggtelek National Park was set aside in 1985. The caves of Aggtelek Karst and Slovak Karst became part of the UNESCO World Heritage in 1995 due to the high diversity of cave types and morphology. Socially, the area of the national park is a disadvantaged border region in NE Hungary. Baradla Cave has always been a popular tourist destination, but visitor numbers fell significantly after 1985. Tourism is largely focused on Baradla Cave, and thus it can be considered “sensu lato” geotourism. Reasons for the changes in visitor numbers are discussed in this paper. Tourist motivations, the significance of geotourism and other tourism-related issues were explored in our study by questionnaire surveys and semi-structured interviews. Furthermore, the balance of geoconservation versus bioconservation is also examined. Finally, the relationship of geotourism, nature protection and local development is discussed. We conclude that the socio-economic situation of the Aggtelek Karst microregion is relatively better than that of the neighbouring regions, and this relative welfare is due to the existence of the national park and Baradla Cave.

Diversity of vertebrate remains from the Lower Gogolin Beds (Anisian) of southern Poland

Middle Triassic (Muschelkalk) limestones and dolostones of southern Poland contain vertebrate remains, which can be used for palaeoecological and palaeogeographical analyses. The results presented concern vertebrate remains uncovered at four localities in Upper Silesia and one on Opole Silesia, a region representing the south-eastern margin of the Germanic Basin in Middle Triassic times. The most abundant remains in this assemblage are fish remains, comprising mostly actinopterygian teeth and scales. Chondrichthyan and sauropsid remains are less common. Reptilian finds include vertebrae, teeth and fragments of long bones, belonging to aquatic or semi-aquatic reptiles, such as nothosaurids, pachypleusorosaurids, and ichthyosaurids. Also, coprolites of possibly durophagous and predacious reptiles occur. In the stratigraphic column of Mikolow, actinopterygian remains are the most numerous and no distinct changes of the taxonomic composition occur. Although this assemblage differs from those described at other localities (Ząbkowice with numerous chondrichthyans, Żyglin, and Plaza with common sauropsid fossils), sampling bias has to be considered.

Upper Triassic limestone clasts of the polymictic limestone conglomerate in the Mino Belt, the northwestern Nanjo Mountains, Fukui Prefecture, central Japan

Upper Triassic limestone clasts of the polymictic limestone conglomerate in the Mino Belt, the northwestern Nanjo Mountains, Fukui Prefecture, central Japan

Distribution of Triassic Foraminifers in the Limestone Massifs of the Dalnegorsk District, Primorsky Krai

Foraminifer assemblages from five massifs of the Triassic limestones of the Dalnegorsk District have been described for the first time, and images of these foraminifers are provided. Foraminifer associations are found here on all the known stratigraphic levels, except for the Rhaetian. In the massif of Mount Verkhnii Rudnik, four foraminifer assemblages have been recorded within the interval from the Carnian to the top of the Norian. The foraminifer assemblages in the Dalnegorsk limestones are comparable to the coeval foraminifer associations of the Carpathians and the Alps. The research results make it possible, for the first time, to compare the foraminifer assemblage composition between various limestone massifs and different stratigraphic levels.

Determination of rockfall design blocks in Upper Triassic limestones and dolomites (Dachstein Formation, Northern Calcareous Alps)

Design block size is of vital importance for rockfall countermeasure design. According to the Austrian normative document ONR 24810, the design block is specified as fractile (V95-V98) of the block size distribution depending on rockfall frequency. For rock formations, which form very large rockfall blocks (> 10 m3), the use of fractiles V95–V98 appears too high with regard to economically justifiable protective measures. The paper deals with the determination of design blocks for the Dachstein Formation on the basis of data from three Austrian test regions. The formation’s bedded limestone represents a key rock of the eastern part of the Northern Calcareous Alps and is very common along some major transport routes. A range of design blocks is derived from a synopsis of block size distributions, magnitude-frequency relations, and considerations about the rockfall barriers’ service life. In the process, the knowledge of the return period of the determinated design block is considered more important than the overall rockfall frequency. Analyzing available rockfall event data and block size distributions, it is possible to identify a return period of 21–26 years for a rockfall event ≥ 1 m3/1000 m route section. Thus, such events are rare. Events that affect the V97–V100 fractiles of the block size distribution are even rarer; they yield very large design block volumes, which show return periods > 100 years. For the bedded Dachstein limestone of the test areas, the application of the fractiles V95–V96 (0.15–2.25 m3) is useful for adapting the return period of the design block to the working life of the rock fall barrier (25–50 years).

Modelling long-term and short-term evolution of karst in vicinity of tunnels

Tunnel construction offers unique insights into the interior structure of rock massifs. Soluble rocks encountered during tunnel construction, however, pose a substantial challenge. Especially classical karst rocks such as limestone, dolostone, gypsum, and anhydrite are unpredictable during tunnel excavation. The enlarged voids created by the long-term dissolution of the soluble rocks in contact with water pose risks because of possible uncontrollable water inflow and of instability of the encountered cave voids, which often requires expensive remediation measures. We model the long-term development of karst features and the evolution of phreatic and epi-phreatic caves below the Schalkau Plateau in the Triassic limestone with a numerical karst evolution model. With hydrological boundary conditions derived from local meteorological data and karst springs, and a simplified model of the local lithology, our model predicts the increase in secondary permeability in the karst aquifer. Enlarged fracture zones develop at locations, where cave systems have been explored. Thus our long-term evolution model can successfully predict karst features in the Schalkau Plateau. Applying the karst evolution model on a short-term period, we assess the effect of consolidation measures taken to stabilise the tunnel cross section in vicinity of the Bleßberg Cave and its longer-term stability. Our model results suggest that flow through the cave section beneath the tunnel, which has been filled with concrete and blocks, is blocked and that during flood events the impounded water will accelerate the development of by-passes around the artificial infill.

Petrophysical properties of the Muschelkalk from the Soultz-sous-For\xeats geothermal site (France), an important lithostratigraphic unit for geothermal exploitation in the Upper Rhine Graben

The Muschelkalk, composed of Triassic limestones, marls, dolomites, and evaporites, forms part of the Permo-Triassic cover of sedimentary rocks that directly overlies the fractured granitic reservoir used for geothermal energy exploitation in the Upper Rhine Graben. Petrophysical data for this lithostratigraphic unit are sparse, but are of value for reservoir prospection, stimulation, and optimisation strategies at existing and prospective geothermal sites throughout the Upper Rhine Graben. To this end, we present here a systematic microstructural, mineralogical, and petrophysical characterisation of the Muschelkalk core (from the Middle to Lower Muschelkalk; from a depth of ~ 930 to ~ 1001 m) from exploration borehole EPS-1 at Soultz-sous-Forêts (France). First, we assessed the microstructure and mineral content of samples from six depths that we consider represent the variability of the available core. The majority of the core is composed of fine-grained, interbedded dolomites and marls; however, anhydrite and a dolomitic sandstone bank were found in the Upper and Lower Muschelkalk core, respectively. A larger suite of samples (from fifteen depths, including the six depths chosen for microstructural and mineral content analysis) were then characterised in terms of their petrophysical properties. The matrix porosity of the measured Muschelkalk samples is low, from ~ 0.01 to ~ 0.1, and their matrix permeability is below the resolution of our permeameter (≪ 10−18 m2). P-wave velocity, thermal conductivity, thermal diffusivity, specific heat capacity per unit volume, Young’s modulus, and uniaxial compressive strength range from 2.60 to 5.37 km/s, 2.42 to 5.72 W/mK, 1.19 to 2.46 mm2/s, 1.63 to 2.46 MJ/m3 K, 9.4 to 39.5 GPa, and 55.1 to 257.6 MPa, respectively. Therefore, and despite the narrow range of porosity, the petrophysical properties of the Muschelkalk are highly variable. We compare these new data with those recently acquired for the Buntsandstein unit (the Permo-Triassic unit immediately below the Muschelkalk) and thus provide an overview of the petrophysical properties of the two sedimentary units that directly overly the fractured granitic reservoir.

FACIES ASSOCIATIONS AND MICROFOSSILS FROM THE MIDDLE-UPPER TRIASSIC LIMESTONES OF THE TRANSILVANIAN NAPPES (PERȘANI MOUNTAINS, EASTERN CARPATHIANS, ROMANIA)

Triassic limestones that belong to the Transilvanian Nappe system, form extensive outcrops in the central part of the Persani Mountains, near Racos locality, on the southern and northern sides of the Olt Gorges. Triassic carbonate olistoliths were sampled in four distinct locations belonging to the Transilvanian Nappe: the Old Racos Quarry, Olt Gorges, Tipia Racosului Hill and Tipia Ormenisului Hill. The identified facies types include brecciated limestones with encrusting organisms and cyanobacteria, packstone-grainstone with sponges and encrusting organisms, boundstone with grainstone internal sediment, peloidal wackestone-packstone, peloidal packstone-grainstone, intraclastic grainstone-rudstone. Such microfacies characterize reefal bioconstructions or fore-reef domains located in the vicinity of shelf crest areas. They share common features with similar Wetterstein facies carbonates from Italy, Austria or Hungary. The micropaleontological assemblage indicates the Anisian-Ladinian to Carnian ages for the studied limestones, the present study bringing new data concerning the age of these carbonates. In addition, the presence of some foraminifera and dasycladalean algae are mentioned for the first time in this area.

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

Recent exploration of the Gorno Zn-Pb-Ag deposit in northern Italy identified 3.3 Mt of sulfides at 4.9% Zn, 1.3% Pb, and 27.2 g/t Ag (indicated+inferred resources), and a further mineralized nucleus of mixed sulfides-nonsulfides in the Val Vedra area, currently under evaluation. The ores are hosted in Triassic limestone and shale. Sulfides (sphalerite, Ag-bearing galena, minor pyrite, and chalcopyrite) paragenetically follow Mn-Fe-bearing saddle dolomite and sparry calcite. The mineral association, and the carbon and oxygen isotope ratios of the sparry calcite (avg. δ13C = 1.0 ± 0.6‰ V-PDB; avg. δ18O = 19.63 ± 1.25‰ V-SMOW), are in agreement with precipitation from hydrothermal fluids in a deep burial setting. Sulfide emplacement occurred before the Alpine orogeny, likely during the Early-Middle Jurassic, in analogy to other Alpine-type deposits. The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. The C-O-isotope values of the early generations of Zn-carbonates are characterized by δ18O between 24.1 and 26.8‰ V-SMOW and δ13C ratios between − 3.1 and 1.7‰ V-PDB. The later generations have lower δ18O (21.9 to 23.9‰) and lower δ13C (− 6.2 to − 3.9‰). These compositions, as those measured on cerussite (δ13C = −6.3 and − 7.7‰; δ18O = 14.0 and 15.3‰), agree with the formation of the nonsulfides in a supergene environment, under climatic conditions warmer than today. The δ18O decrease from early to late generations suggests progressive involvement of meteoric water sourced from higher altitudes. These characteristics indicate that the nonsulfides formed during the exhumation of the Gorno area from Miocene to Pliocene.