Black Limestone Research Articles

The Bougrine Zn-Pb deposit, the largest salt diapir-related Mississippi Valley-type deposit in the Eastern Maghreb salt diapir province, Tunisia

The Bougrine Zn-Pb sulfide deposit (5.5 Mt @ 12 % Zn + 2.5 % Pb) in the Eastern Maghreb salt diapir province of Tunisia is located at the northeastern end of the Lorbeus-Bougrine diapir. The several-km large diapir is composed of Triassic evaporite that intruded about 10 km-thick Jurassic and Cretaceous marine sedimentary rocks during the Cretaceous and Tertiary. Mineralization occurs in breccia zones at the contact with the Triassic diapir and in the peridiapiric Cretaceous strata. Most of the ore is stratabound (F2 orebody) with microsphalerite disseminations in organic-rich laminated black limestone of the Cenomanian-Turonian Bahloul Formation, where sphalerite occurs as infill of Globigerina shells, as massive replacement of Globigerina-rich layers, as banded colloform sphalerite and in voids as euhedral, coarse-grained crystals together with skeletal galena and minor marcasite. Abundant degraded oil seepages in the orebodies and their host rocks testify to the existence of a (former) hydrocarbon reservoir.The various sphalerite generations have highly variable Mn and Fe contents; Cd has an average content of 445 ppm; As and Hg contents are in the 200 ppm range; Tl content is about 40 ppm; Ga content is about 10 ppm; and In content is consistently <1 ppm. Fluid inclusions in celestite, coarse-grained late-stage sphalerite and calcite indicate moderate fluid salinities (16 ± 2 wt% NaCl eq.) and moderate temperatures (85 to 146 °C). The empirical trace-element sphalerite geothermometer gives 184 ± 38 °C for the main-stage microsphalerite and the banded colloform sphalerite which have no measurable fluid inclusions.A wide range of δ13C (-13.6 to 5.6 ‰) and δ18O (-19.8 to 33 ‰) values is observed in ore-stage and post-ore calcite. Ore-stage calcite commonly has negative δ13C values reflecting involvement of carbon from organic matter; its δ18O composition with an average of 22.6 ± 2 ‰ (19.7 to 26.0 ‰) may be explained by a moderate-temperature hydrothermal fluid. There is no systematic δ34S variation between and across the different styles of mineralization. The range of δ34S of 6–19 ‰ with a mean of 13 ‰ is close to the δ34S value of local and regional Triassic marine sulfate (δ34S = 16 ‰). Thermochemical reduction of Triassic sulfate, likely mediated by hydrocarbons, is the most probable source for sulfur in the ores. Lead isotope data on galena are within a narrow field of upper crustal signature (206Pb/204Pb = 18.71–18.77; 207Pb/204Pb = 15.66–15.70; 208Pb/206Pb = 38.81–38.97) indicating a homogeneous ore fluid.The major characteristics of the Bougrine ore deposit are typical of Mississippi Valley type Pb-Zn deposits and indicate large-scale fluid circulation likely related to stacking and uplift in the northern Tunisian Nappes Zone during the Miocene. Both the hydraulic load of meteoric water and over-pressured basinal and basement fluids during compressional movements favored southward fluid migration along basement discontinuities and most permeable strata in the Mesozoic-Cenozoic sedimentary pile. Low-pressure domains around salt diapirs in a rifting environment allowed focused upward fluid flow, and the hydrocarbon reservoir of the Bahloul Formation then provided the geochemical trap for efficient base metal deposition.

Geochemistry and petrology of the Chandarpur-Raipur sandstones: Implications for the evolution of the Chattisgarh Basin, Central India

Depositional processes and stratigraphic evolution of the Chattisgarh basin exhibit a synergistic relation between sedimentation and tectonics. To interpret the sedimentation history and basin evolution, multiproxy approach including field studies, petrography, geochemical, and multivariate statistical analyses of the sandstones of Chandarpur and Raipur groups is employed. The study provides a detailed analysis of the time-connoted petrography and geochemistry of the sandstone units from each formation of the Chandarpur-Raipur sequence of Chattisgarh basin. The sandstones grade from immature wacke through submature arkose to mature quartzarenite from the bottom up the section. These sandstones are broadly characterized by felsic provenance, arid-humid palaeoclimate, and weak-intense palaeoweathering at the source. The assemblage of wacke-arkose-sublitharenite of the basal Lohardih Formation is characteristics of fan delta environment and represents initiation of rifting and basin formation stage. Subarkoses from the younging up sequence of Lohardih-Chaporadih-Kansapathar formations reflect prograding shelf environment that represents craton interior field of the continental block provenance and passive marginal tectonic setting, indicating gradual stabilization of the basin. Quartzarenites from Kansapathar Formation and stratigraphically younger Devsagar Member of Charmuria Formation also represent broadly similar provenance and tectonic setting indicating stable craton interior provenance in a passive marginal setting. Petrographic and geochemical analyses of some of the Kansapathar-Devsagar sandstones suggesting recycled orogen provenance, however, may be attributed to the orogenic activity and/or role of younger bimodal volcanic rock during rejuvenation of multistage basin opening faults. Rifting stage was followed by subsidence stage as indicated by the presence of black limestone capping the sandstone successions. Initiation of basin formation ∼1400 Ma and sedimentation can be correlated with the late-stage fragmentation of the supercontinent Columbia. The basin probably closed ∼1000 Ma during the assembly of the next supercontinent Rodinia. It is estimated that ∼87% of the 2.2-km-thick sedimentary succession in the eastern Chattisgarh basin, were already deposited within this time frame (∼1405 and ∼1007 Ma). The basin is correlatable with other Mesoproterozoic basins of Peninsular India like Vindhyan, Cuddapah basins, as well as with basins like Xiong’er rift basin of North China Craton, Espinhaco basin of eastern Brazil, that are related to the Columbia-Rodinia Supercontinent cycle.

Cenozoic evolution of the Tripolitza carbonate platform in the Tethyan realm: new age constraints on deposition, diagenesis, metamorphism and nappe emplacement based on U-Pb and Rb-Sr dating (External Hellenides, Crete)

AbstractWe present kinematic, radiometric, geochemical and PT data, which help to constrain the tectonometamorphic evolution of the Tripolitza Unit (TPU). The age of both the metamorphic peak (P = 0.4 ±0.2 GPa, T = ca. 310 °C) and top-to-the WNW mylonitic thrusting, attributed to the emplacement of the hanging Pindos nappe, has been constrained at 19 ±2.5 Ma using Rb-Sr on synkinematic white mica of a basal mylonite of NW Crete. This early tectonic event is also documented by the oldest generation of veins, which cut through less metamorphic (T = 240 ±15 °C) late Bartonian/Priabonian Nummulite limestone exposed as olistolith in TPU flysch of central Crete. Calcite of these veins yielded a similar U-Pb age at 20 ±6 Ma. U-Pb dating of matrix calcite, on the other hand, reflect the time of sedimentation (38.4 ±5.7 Ma and 37.6 ±1.2 Ma), which is in line with the faunal content of the black limestone. Geochemical data and U-Pb calcite ages of fibres of the Nummulite test (32.3 ±3.1 Ma and 34.6 ±0.9 Ma) suggest unexpected pseudomorphic fibre replacement during late Priabonian/early Rupelian diagenesis. Additional calcite veins, which developed at ca. 10–11 and 7 – 9 Ma (U-Pb on calcite), are attributed to top-to-the S thrusting and subsequent extension, respectively. The resulting anticlockwise rotation of the shortening direction within the TPU from WNW-ESE at ca. 20 Ma to N-S at ca. 10 Ma has significant implications for the geodynamic evolution of the External Hellenides.

Garau Formation as an unconventional hydrocarbon resource in southwestern Iran: a geochemical investigation

Due to the growing need for hydrocarbons and the limited conventional resources, paying attention to unconventional oil and gas resources is essential. The upper Jurassic-Lower Cretaceous in western and southwestern Iran contains the most crucial source rocks of the Zagros sedimentary basin. One of the richest source rocks is the shaly Garau Formation. Owing to geochemical and geological characteristics, the Garau Formation, with Neocomian to Coniacian age and periodicity of radiolore black limestones with black pyrite bituminous shales, ammonite, and chertite shale, is the suitable potential sweet spot as oil shale and gas shale. In this study, a comprehensive regional study was conducted on the entire Garau Formation basin using Rock–Eval parameters and organic matter maturity data. In addition to investigating the hydrocarbon generation potential of the Garau Formation as a source rock, the prospect of this Formation as oil and gas shales in the entire Garau basin was investigated. For this purpose, 31 fields in 5 important sub-basins of Zagros, including East Lorestan, West Lorestan, Izeh zone, Dezful Embayment, and Abadan plain were investigated. The study showed that total organic carbon varies between 0.17 and 24.6, and more than 75% of total organic carbon had values greater than 1. By examining the quantity, quality, and maturity parameters and considering the necessary thresholds, it was found that East Lorestan and West Lorestan have the conditions for oil and gas shales. The highest quantity and best quality of organic matter are related to Eastern Lorestan. By moving west and south of Garau Basin, the quantity and quality of organic matter decrease, and the hydrogen index proves the results. Vitrinite reflection studies indicated that the lowest and highest levels of organic matter maturity belong to East Lorestan and West Lorestan, respectively. Therefore, the northeast of Garau Basin (Eastern Lorestan) has the potential for oil shale, and the northwest of the Basin (Western Lorestan) has the potential for gas shale.

Sedimentary Environments and Age Determination of the Chia Gara Formation, Northern Iraq

The rock successions of the Chia Gara Formation were studied at two surface sections (Barsarin and Rania) from North-Eastern Iraq. The detailed sedimentological study reveals that the formation consists basically of thin-bedded black limestone, dolomitic limestone, marly limestone, bituminous shales, and Ammonitic limestone. The petrography results showed that the formation consists of various petrographic components as Ammonites, calcispheres, radiolarian, and silicate sponges in addition to the groundmass of micrite. Ammonite taxa are examined in the upper part of the Chia Gara Formation to find Ammonite species, of which seven species have been identified. One biozone is postulated based on the above assemblages, in order of age: Berriasella Jacobi, from a regional perspective, this biozone was connected with other Ammonite assemblages, leading to the conclusion that the Formation age is Early Cretaceous in age. The facies analysis demonstrates that the rock succession consists mainly of three microfacies. The main microfacies include lime mudstone, wackestone, and packstone. At the same time, the lithofacies comprise limestones and shales. The overall characteristics of these facies show that the Chia Gara Formation was deposited in three different environments; (1) the Lower part of the Upper bathyal (2) the Middle part of the bathyal, and (3) the Upper part of the outer shelf environment.

Origin of the vanadium-uranium geochemical anomalies in the limestones of the Puyango Formation, La Sota (Ecuador): preliminary results

Vanadium (V) and uranium (U) are critical elements for the energy and technology industry. They are characterized by low abundance in the earth crust´s rocks, but can be concentrated and give rise to sedimentary mineral deposits as a result of redox processes during sedimentation and diagenesis. The anomalies of V-U in La Sota, Ecuador, are found in black limestones and black calcareous shales of Cretaceous age. Here we present the results of a geochemical study and a multivariate geostatistical analysis, which enables us to infer four different associations: 1) disseminated organic matter in the limestones that hold V and Zn, probably in the form of organometallic complexes; 2) phosphatic minerals and concentrations of U, HREE and Ni, which may be incorporated as trace elements in the phosphates, compatible with sedimentation in an anoxic environment; 3) Ca in carbonates from a marine environment; and, 4) litophile elements associated with detritic minerals, such as quartz, plagioclase, feldspar, micas, clays and oxyhydroxides of Fe-Mn-Ti, produced by weathering and erosion. Our findings suggest that V is associated mainly with the organic matter of marine origin in the bituminous limestones, while U is associated with P, thereby indicating the formation of uraniferous phosphates during sedimentation.

Re-thinking the Trübner stele: pictorial forms and authenticity

ABSTRACT The Trubner stele, a large Chinese Buddhist stele displayed in the Metropolitan Museum of Art, is carved from grayish black limestone and commemorates the building of a Buddhist monastery in Qi county, Henan province, China. According to the inscription, it is dated 533 to 543 C.E. It was named after the art dealer Jorg Trubner (1902?-1930) who acquired the stele for the museum in 1929. Engraved in high relief, the stele contains numerous images, including the preaching Buddha with attendants, pictorial representation of the Vimalakirti Sutra, donor figures, small seated Buddha niches, spirit guardian kings, grooms and lions. Because of the excellent craftsmanship of the stele and the complexity of the composition, it has been referred to by previous scholars as a monumental, antique work now preserved in the West. However, some scholars doubt its authenticity, and, in this case, the leading scholar is Wai-kam Ho who published his article in 1999, since when the stele has been the subject of considerable controversy. In this article, focusing on Ho’s arguments, I compared this stele to other dated steles and images, considering textual sources, thematic content, iconography and style, and I have come to the conclusion that this stele is genuine.

Lower Permian (Artinskian) chondrichthyan tooth remains (Petalodontidae) from Dovje (Karavanke Mts., NW Slovenia)

Fossil remains of chondrichthyan tooth bases (roots) were found in Lower Permian beds exposed along the forest road between Dovje and Plavški Rovt. These layers are part of the clastic development of the Trogkofel Group beds. They are composed of an alternation of dark to light-grey shales, siltstone, and sandstone with rare beds of the conglomerate. Within the clastic succession, layers or lenses of dark-grey to black limestones (biosparitic, biomicritic and oolitic) and limestone breccias occur. The limestone consists remains of algae, fusulinids, brachiopods, and mostly crinoids (Palermocrinus and Entrochus). Detail study has shown that two remains of tooth bases belong to the genus Petalodus, one of them to the species Petalodus ohioensis. The bases are tongue-shaped and come to a rounded point in the distal (base end) edge. On the surface of the base, the typical oval-shaped foramina are visible. In addition, the osteodentine is visible on the cross-section of one specimen. Teeth of Petalodus are often the most common chondrichthyan fossil vertebrate remains reported from the Carboniferous and Permian rocks of the USA, Europe, and Russia. In Slovenia, Petalodus ohioensis has been recorded only from Upper Carboniferous beds. The new record of Lower Permian remains contributes to the knowledge of this cosmopolitan but still common genus of Late Paleozoic chondrichthyans.

Optimization of Acid Fracturing Process for Carbonate Reservoirs in Daniudi Gas Field

The Daniudi gas field is located in the Ordos Basin’s northern section of the Yishan slope. The intertidal–subtidal depositional environment dominates the lithology of the Ma55 sub-member, resulting in a stable, thick-layered dark gray–gray–black limestone and lime dolomite. The stratum is stable laterally as well as dolomite, with an average thickness of 26.8 m. Fractures, dissolution expansion pores, and inter-crystalline dissolved pores are the primary reservoir space kinds, with a minor number of karst caves and fractures generated as well. The main distribution ranges for porosity and permeability are 1–8 percent and 0.01–1 mD, respectively. Low porosity, tightness, and ultra-low permeability are common characteristics, and a single well typically has no natural productivity. Production stimulation technologies like pre-fluid acid fracturing, compound sand addition acid fracturing, and multi-stage injection + temporary plugging volumetric acid fracturing have been gradually optimized using the horizontal well development method, and breakthroughs in the development of tight and low-permeability carbonate rock reservoirs have been made. However, the conditions of different types of reservoirs are quite different, and the acid fracturing process is not matched and imperfect, resulting in large differences in the productivity of different horizontal wells after fracturing, as well as a high proportion of low-yield wells, which cannot meet the needs of cost-effective and effective development of this type of gas reservoir. In light of the aforementioned issues, a series of laboratory tests have been carried out to explore the stimulation effects of acid fracturing on different types of reservoirs and to optimize the acid fracturing process in the Daniudi gas field. The results show that the rock mechanical performances and the acid etching conductivities of the rock specimens are related to the types of reservoirs. The rock mechanical properties can be deteriorated after acidizing, but different types of reservoirs have different degrees of deterioration. According to the results of acid etching conductivity of different types of reservoirs, conductivities obtained by high and low viscosity and cross-link-gelled acid (two stage injection) processes are higher than those of high viscosity systems. The experimental results of process suitability suggest adopting high and low viscidity acid systems for pore type and fracture-dissolved pore type reservoirs, and cross-linked acid systems for fracture-pore type reservoirs. The findings of this study can help form a better understanding of the performance of different types of reservoirs under the various acidified conditions that can be used for the optimization of acid fracturing processes in carbonate formations.

BIOSTRATIGRAPHY AND SEDIMENTARY ENVIRONMENTS OF THE LOWER/UPPER CRETACEOUS BOUNDARY DEPOSITS BY SMALL FORAMINIFERA (PIENINY KLIPPEN BELT, UKRAINIAN CARPATHIANS)

The Pieniny Klippen Belt extends 600 km from the Slovakian Carpathians to the Romanian Carpathians. The Pieniny KIippen Belt narrows in the Ukrainian Carpathians. It is called the Pieniny Zone here. The Cretaceous succession of the Pieniny KIippen Belt in the Ukrainian Carpathians consists of the upper part of the Svalyava Formation (Titonian- Neocomian), Tyssalo Formation (Aptian-Senomanian), Puchov Formation (Turonian-Maastrichtian) and Yarmuta Formation (Maastrichtian). This succession is overlapped by the Eocene Vylhivchyk Formation with angular uncomformity. The Lower/Upper Cretaceuous boundary sediments of the Pieniny KIippen Belt in the Ukrainian Carpathians is located in the Tyssalo Formation. The paper presents the results of the analysis of foraminifera from the marls of the Tysalo Formation developed in the Tysalo tract, in the sections of the Tereblya and Luzhanka rivers, in the quarries of Perechyn and Pryborzhavske villages (Transcarpathians region). 27 species of foraminifera were identified in this study in the age range of Late Albian — earliest Turonian including 15 planktonic species and 4 benthic species. The biostratigraphic succession of foraminiferal subdivisions ranging from late Albian to Senomanian is identified. Upper Albian-Senomanian sediments of the Tyssalo Formation are divided into three lithological members. The lower member consists of black limestones and marls with dark grey limestones which correspond to early Late Albian. The middle member is represented by gray and gray-green marls with gray siltstones and sandstones which correspond to middle Late Albian. The upper member consists of light green-gray marls with pink marls which correspond to late Late Albian-Senomanian. The Hedbergella gaultina Zone (late Late Albian), Pseudothalmanninella ticinensis Zone (middle Late Albian) and Parathalmanninella appeninica Zone (late Late Albian) were identified in the Tyssalo Formation both by previous researchers and in the material presented. The layers with Thalmanninella globotruncanoides (early Senomanian), Thalmanninella reicheli Zone (middle Senomanian) and Rotalipora cushmani Zone (later Senomanian) are established in the Tyssalo Formation for the first time. The Lower/Upper Cretaceous boundary corresponds to the boundary between the Parathalmanninella appeninica Zone and the layers with Thalmanninella globotruncanoides, which are not found in the same section due to the intense deformation of the deposits in the Pieniny KIippen Belt. Changes in the generic composition of planktonic foraminifera in the boundary deposits of the Lower and Upper Cretaceous of the Tysalo Formation are gradual, from the dominance of small Biglobigerinella, Globigerinelloides, Hedbergella, Ticinella in the Upper Albian to the bloom of large complex-built Pseudothalmanninella, Rotalipora, Thalmanninella, Parathalmanninella, Praeglobotruncana Pseudothalmanninella, Rotalipora, Thalmanninella, Parathalmanninella, Praeglobotruncana in the Senomanian. The black marls of the lower member contain pyritized foraminifers, so it can be assumed that they were formed in oxygen-deficient botton-water conditions (early Late Albian). In the middle member change in the color of sediments from black to gray and green and the presence of calcareous benthic foraminifera belonging to genera Parella, Anomalina, Pleurostomella, Gavelinella indicate an improvement in oxygen conditions in bottom waters (middle Late Albian). The marl of the upper member is dominated by (70-100% of associations) planktonic foraminifera mainly from the genera Parathalmanninella, Rotalipora, Thalmanninella, Praeglobotruncana, which indicates the depth of the middle batial (late Late Albian-Senomanian).

Utilization of waste black limestone filler in short jute fiber reinforced epoxy composites: Influence on the mechanical behaviour

Natural materials-based composites with superior mechanical properties were produced by utilizing waste black limestone as a filler and jute fibers in the epoxy matrix. The present effort investigates the mechanical properties of the epoxy composite reinforced by varying the weight percentages of the black limestone and the length of the jute fibers. Nine composites comprising black limestone with weight percentages of 0%, 5%, 10%, and short jute fibers having different lengths of 15 mm, 30 mm, and 45 mm were fabricated by a hand lay-up technique. It was found that the composites with optimal content filler material exhibited better performance than higher filler content-based and without fillers composites. The ultimate tensile strength of the 5% black limestone filled with 30 mm jute fiber was 54.8 MPa, similarly higher ultimate flexural and compression strength values. Fractography studies were performed using a scanning electron microscope to elucidate the characteristics of the mechanically tested composite.

Doushantuo-Pertatataka—Like Acritarchs From the Late Ediacaran Bocaina Formation (Corumbá Group, Brazil)

Acritarchs, a polyphyletic group of acid-resistant organic-walled microfossils, dominate the eukaryotic microfossil record in the Proterozoic (2500–541 Ma) yet exhibit significant reduction in diversity and size at the transition to the Phanerozoic (541–520 Ma). Despite the difficulty of tracing phylogenetic relationships among acritarchs, changes in their complexity and diversity through time have allowed their use in paleoecological and biostratigraphic schemes. The Doushantuo-Pertatataka Ediacaran acritarch assemblage, for example, is usually considered as restricted to the early Ediacaran between 635 and 580 Ma. But similar, diverse acritarchs have been recovered from younger rocks in Mongolia and Arctic Siberia and are now reported here from phosphatized horizons of the upper Bocaina Formation (ca. 555 Ma), Corumbá Group, SW Brazil. In the overlying black limestones and shales of the latest Ediacaran Tamengo Formation (542 Ma) acritarch diversity is low, but the skeletal metazoans Cloudina and Corumbella are abundant. The Bocaina acritarch assemblage shares forms referable to the genera Leiosphaeridia, Tanarium, Asseserium and Megasphaera with the Doushantuo-Pertatataka assemblage, but also includes specimens similar to the Phanerozoic genus Archaeodiscina in addition to two new complex acritarchs. The first is covered by rounded low conical bumps, similar to Eotylotopalla but differs in having a distinct opening suggestive of greater (multicellular?) complexity. The second, identified here as Morphotype 1, is a double-walled acanthomorph acritarch with scattered cylindrical processes between the walls. The contrast in acritarch diversity and abundance between the Bocaina and Tamengo formations is likely due in part to paleoenvironmental and taphonomic differences (absence of the phosphatization window in the latter), as well as to the appearance of both suspension-feeding skeletal metazoans (Cloudina and Corumbella). The occurrence of Doushantuo-Pertatataka acritarchs in SW Brazil, northern Mongolia, and Arctic Siberia extend the biostratigraphic range of this assemblage up to the terminal Ediacaran Cloudina biozone.

Facies, magnetic susceptibility and timing of the Late Devonian Frasnian/Famennian boundary interval (Xom Nha Formation, Central Vietnam)

Upper Devonian carbonates deposited through the Frasnian/Famennian (F/F) stage boundary in the Xom Nha Formation, Central Vietnam, were studied. The section is mainly composed of fossiliferous, brecciated, and laminated limestone beds, while shale beds occur in a subordinate number. Microfacies generally suggests a hemipelagic setting on an outer shelf environment with low sedimentation rates. A sediment accumulation rate of 0.217 cm/kyrs for this section is calculated. The Xom Nha section does not exhibit characteristic black shales or black limestones through the F/F boundary, but instead shows a similar lithology in comparison to other F/F sections in Southeast Asia. The carbonates yielded abundant conodonts, which represent mainly cosmopolitan species but the section differs from most sections in Europe in showing relatively high numbers of Palmatolepis linguiformis species. Deposition through the F/F boundary interval reported here for the Xom Nha section appears to have occurred during a ~1.2 Ma, and shows well-defined climate cyclicity.

Organic petrological characterisation and facies interpretation of the Upper Triassic (Carnian – Julian) black limestone in the Lesno Brdo area (External Dinarides, Central Slovenia)

Upper Triassic (Carnian - Julian) bedded dark limestone in the Lesno Brdo area, more precisely in the Drenov Grič quarry (Central Slovenia), was investigated in this study to describe its carbonate facies, its geochemical characteristics of the inorganic and organic matter, and to estimate its hydrocarbons generative potential. The site was chosen as a well referenced location of previous lithological and paleontological studies with the aim to fill a gap in the up-to-date knowledge on organic petrology of the investigated rocks termed as the Julian “Carbonate Member” within the Lesno Brdo stratigraphic sequence. The study represents the first multi-analytical organic petrological investigation of Mesozoic carbonate rocks in Slovenia. In the Drenov Grič (DRG) section, 7 microfacies were defined. A total of 38 DRG samples of micritic limestones, marlstones, and a coaly sample were collected from the section. The average total organic carbon (TOC) content of the samples is 0.70 wt% with one outstanding sample DRG-28 with a TOC content of 15.56 wt.%. According to the TOC content, DRG samples are considered as a fair to good source rock for hydrocarbons generation. In addition, the samples with TOC >0.5 wt.% were characterised by the Rock-Eval S1, S2 and S3 peaks, hydrogen and oxygen indices (HI, OI), Tmax and production index (PI) values. According to these data, typical “black” Julian carbonate beds from the Drenov Grič locality are poor source rocks. Based on pyrolysis data (HI versus OI), the type of the organic matter could not be determined, so a micropetrographic examination was performed. . The predominant and the only clearly visible maceral in the DRG samples is vitrinite within the amorphous organic matter. Given the low S2 peaks, thermal maturity was determined by vitrinite reflectance. Vitrinite reflectance results (between 2.71 ± 0.19 %Ro and 3.89 ± 0.17 %Ro) indicate that the organic matter in the DRG samples is in a thermally mature to overmature stage, which is also consistent with the Thermal Alteration Index (TAI) (4- - 4). All 38 samples were also analysed on main and trace elements, focusing on the redox sensitive trace elements (Ni, Mo, Th, U, V and Zn) to supplementary interpret depositional conditions. Overall, the “black” carbonate rocks of the Drenov Grič section show a negligible potential for the generation of hydrocarbons. Their original dispersed organic matter was thermally strongly transformed. Therefore, the investigated carbonate rocks almost completely exhausted their ability to generate a considerable quantity of hydrocarbons. They can therefore be classified as “spent source rocks”, which could conditionally generate some dry gas.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Raman spectroscopy as a tool for provenancing black limestones (bigi morati) used in antiquity

AbstractAmong precious stones used in antiquity, bigi morati stand out for their importance. They consist in black limestones mainly employed in sculptures and architectural heritages and quarried from several sites through the Mediterranean area. Their provenance is difficult to assess due to their similar appearance to the naked‐eye observation and the possible confusion with black marbles (i.e., bigi antichi). Classical methods used for studying ancient marbles, such as minero‐petrographic and stable isotopes analyses (δ13C and δ 16O), resulted to be powerful in provenancing these black lithotypes. However, these methods are microdestructive and cannot be always applied in the case of precious artefacts for which sampling is not allowed. Bearing carbonaceous matter conferring them the typical black‐dark grey colour, Raman spectroscopy might support studies on these limestones, bringing important information about the structural state of organic/carbonaceous matter and their geological evolution. In this study, the potential of Raman spectroscopy in determining geological and geographic provenance of bigi morati was tested on quarry samples from six among the most famous ancient exploitation sources. The obtained results demonstrated that the use of Raman parameters typical of low‐ordered carbon matter is an effective tool in discriminating provenance. Moreover, the laboratory‐based approach lays the groundwork for future development and validation of the method for in situ measurements on artefacts by using portable equipment.

Lithic Raw Materials in the Lower Rio Grande Valley, South Texas and Northeast Mexico

ABSTRACT Analysis of 976 lithic artifacts from twelve museum and private collections in the Lower Rio Grande Valley revealed a preference for seven rock types. Sixty nine percent of all tools were made from gravel chert, which is locally the most abundant rock type on the Frio and Goliad Formations, as well as on the gravels of the Rio Grande. Representing less than 10% each were, the local El Sauz Chert, a black banded metamorphic rock, volcanic rocks, agates, silicified wood, limestone and black chert. Variations in the relative proportion of each rock type are observed by location, suggesting a tendency to use other suitable rocks that were locally available. Contrary to what has been suggested an abundance of lithic resources were available to stone tool makers in the Lower Rio Grande Valley. This study underscores the value of working with collectors in regions where little archaeological research has been conducted.

Drenov Grič black limestone: a heritage stone from Slovenia

Abstract Drenov Grič black limestone is considered to be one of the most beautiful Slovenian natural stones due to its black colour interwoven with white veins. Over the centuries, it has been extracted from two major quarries located west of Ljubljana. One of these quarries has been declared a valuable natural feature of national importance and is protected as a natural monument. This well-stratified, Triassic (Carnian) micritic limestone occurs in 10–80 cm thick beds with thin marl interlayers. The limestone occasionally contains abundant fossil bivalves, gastropods and ostracods. It is relatively rich in carbonaceous and bituminous organic matter, which is responsible for the black colour of the stone. The stone has been widely used in Slovenian monuments. Many indoor and outdoor architectural elements have been constructed using this limestone, particularly during the Baroque period, which was known for its extensive use of black limestones in other European countries as well. The most significant use of this limestone has been recorded in sculpted portals and altars. Some important buildings, which were decorated utilizing this stone, have been declared cultural monuments of local or national importance. Use of this limestone was also documented in other European countries (Italy, Austria, Serbia) and worldwide (USA). When exposed to climatic influences, chromatic and salt weathering are recognized as the main deterioration phenomena for this limestone when used in monuments.

Deep insights into the organic carbon role in selectivity and adsorption mechanism of phosphate and crystal violet onto low–cost black limestone: Modelling and physicochemical parameters interpretation

Herein, raw black limestone (RBL) and its activated form at 450 °C/5 h (ABL) were characterized and tested as adsorbents for phosphate and crystal violet (CV) at pH (2.0–10.0). The two adsorbents displayed nearly the same efficiency for phosphate uptake, while RBL was more effective for CV. Isotherm studies at 298–318 K indicated that Langmuir, Freundlich, and Dubinin–Radushkevich models described well the uptake results without determination of the physicochemical parameters governing phosphate and CV adsorption mechanisms. The application of five advanced statistical models (ASM) indicated that monolayer with one energy and monolayer with two energies fitted well the phosphate and CV adsorption, respectively. Phosphate adsorption was controlled by multi–docking mechanism, while multi–docking and multi‒molecular mechanisms were involved in CV uptake onto the RBL. The density of receptor sites (NM) was resulted to be an important factor controlling the phosphate and CV adsorption capacities. With temperature, the NM values increased from 149.62 to 215.52 mg/g and decreased from 340.13 to 208.97 mg/g for phosphate and CV, respectively. This confirmed the significant role of organic carbon interactions as n–π and π–π in enhancement of CV uptake. The adsorption energies exhibited the physical nature of the adsorption processes as endothermic and exothermic reactions for phosphate and CV, respectively. Thermodynamic studies confirmed the spontaneous nature of the phosphate and CV adsorption onto RBL. Based on this study, it can be concluded that RBL is an excellent and low–cost adsorbent for water contaminants, especially organic dyes. Furthermore, the interpretations of steric and energetic parameters indicated that the adsorption performance of RBL is mainly related to its organic carbon content.

Walking in the Streets of Pisa to Discover the Stones Used in the Middle Ages

This paper deals with the stones used as building materials in the centre of Pisa during the Middle Age. Most of the stones are quarried from the nearby mountains, Monte Pisano and Monti d’Oltre Serchio, but there are also other ones, coming from Apuan Alps, Elba Island, western Tuscan coast, and from other quarries opened in the Western Mediterranean area. Our goal is to enrich the classic concept of street photography by inserting, in an interpretative context, the analysis and the observation of the geoenvironment in which we are immersed, daily, for the journey home-office, home-school or just for a simple walk. The tools we have are the eyes, the light and an instrument: the camera. Five stops along a city route allow to describe the main types of stones that have been used to construct and ornate the buildings since the 10th and 11th centuries, when Pisa acquired its traditional fame as one of the four historical Maritime Republics of Italy. Monte Pisano marble is the most important stone in the medieval phase of construction of the city of Pisa, often used together with black limestones to give the typical decorative alternate bands, black and white, of the Pisan Romanesque style. Other types of stones were also used, such as Quartzites, Agnano breccia, Panchina, Macigno sandstone as well as Apuan marble, granitoid rocks from Elba Island and Sardinia, and some rocks from ancient quarries of the western Mediterranean area, such as precious marbles from Greece and Turkey.