Sections Of Rocks Research Articles

Source rock potential and depositional environment of Upper Cretaceous sedimentary rocks, Abu Gharadig Basin, Western Desert, Egypt: An integrated palynological, organic and inorganic geochemical study

The Abu Gharadig Basin in the northern part of the Western Desert, Egypt is among the most important petroleum provinces in Egypt. Here, Cenomanian to Santonian rocks of Bahariya Formation and Abu Roash A-G members from the GPT-3 well were investigated for their depositional environment, kerogen quality, petroleum generation potential and thermal maturity by geochemical, petrological and palynological methods. The sediments of the Bahariya and Abu Roash formations excluding the Abu Roash “F” Member represent variable shallow marine environments with poor preservation of marine organic matter, whereas there is an excellent preservation in the Abu Roash “F” Member. The basal part of this member is characterized by anoxic, carbonate-rich depositional conditions, high TOC values up to 7%, high HI up to 700 mgHC/gTOC and liptinite-dominated organic matter. Depletion of iron leads to sulfur incorporation into organic matter which is reflected in high thiophene/benzene ratios. Above, sediments are enriched in “terrestrial elements” Fe, Ti, as well as K and Mn. This pattern and the occurrence of the fresh/brackish water algae Botryococcus suggests a regression phase during deposition. The upper part of the Abu Roash “F” Member is again characterized by fully marine, suboxic conditions and a lower thiophene/benzene ratio. The source rock section demonstrates lower thermal maturity compared to the above and below sections based on all microscopic, pyrolysis and biomarker data. This indicates thermal maturity retardation/suppression most likely due to a different organic facies and early diagenetic transformation of kerogen as indicated by the geochemical and palynological data. The source rock heterogeneity indicates a relatively shallow marine environment where the changes in bottom water conditions are very sensitive to sea level fluctuations. Residual oil characterization reveals two reservoir compartments, which are in the Abu Roash “D” and “C” members.The Abu Roash “F” source rocks are compared with time-equivalent sediments in the Tarfaya Basin in Morocco, which represent more distal settings. The more proximal group (A) is characterized by S/Fe ratios between 0.57 and 0.67 indicating suboxic conditions. It has TOC and HI values not exceeding 4% and 600 mgHC/gTOC, respectively, at variable CaCO3 contents. The more distal Tarfaya sediments (group B) have higher TOC and HI as well as high organic sulfur contents. Group A is higher in terrigenous element concentrations. The Tmax of immature source rocks ranges from 410 to 415°C in organic‑sulfur rich samples and from 420 to 430°C in organic‑sulfur poor samples revealing an important impact of organic facies on maturity parameters. Furthermore, there is an inverse relationship between S/Fe and Al2O3/TOC which might become an important tool in paleoenvironmental reconstructions as well as petroleum source rock studies.

Trace element and stable (C, O) and radiogenic (Sr) isotope geochemistry of stromatolitic carbonate rocks of the Mesoarchaean Pongola Supergroup: Implications for seawater composition

The Mesoarchaean Pongola Supergroup hosts one of the oldest well-preserved stromatolitic carbonate successions. Major- and trace-element geochemistry along with C, O, and Sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment, and to unravel the chemical characteristics of contemporaneous seawater. The carbonate rocks consist mainly of dolomite and, to a lesser extent, ankerite. Their variable Sr concentrations of ~95 to 450mg/kg are interpreted as resulting from early to late dolomitization of metastable carbonates (aragonite and/or high-Mg calcite), facies control and calcitization during meteoric diagenesis. δ18O values range from −19.6 to −12.0‰ VPDB and reflect recrystallization of carbonates caused by high water-rock interactions during diagenesis and metamorphism. A δ13C value of 2.5‰ VPDB was measured in carbonate samples least affected by alteration, and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater. The samples display variable 87Sr/86Sr isotopic ratios, from as low as 0.708 to 0.777. These ratios are considerably higher than those expected in Archaean open-ocean water masses buffered by hydrothermal interaction with the mantle. We interpret the highly radiogenic Sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic Sr from siliciclastic/volcaniclastic components in the samples and fluids from clay-rich layers intercalated with the carbonates. The least radiogenic Sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the Kaapvaal Craton. The dolomitic carbonate samples show shale-normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive LaSN, GdSN and YSN anomalies, superchondritic Y/Ho ratios, a small negative CeSN anomaly and depleted light rare earth elements relative to the heavy rare earth elements. These anomalies are not as pronounced as expected for an open marine setting, which together with the Sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions. A convex-upward shale-normalized rare earth element and yttrium pattern is probably a result of several factors, including organic matter complexation, and element fractionation during estuarine mixing. The small negative CeSN anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity.

Investigating a Rock Art Site in Paraná State, South of Brazil

AbstractJaguariaíva 1 is a sandstone rockshelter located in Jaguariaíva, Paraná State, Brazil, with rock art on the surface of the walls and ceiling. A stratigraphic analysis of the soil within the shelter showed six occupational layers and a superficial disturbed layer with evidence from the end of the 19th century. The establishment of a rock-art chronology became possible using fallen painted rock sections incorporated into three sedimentary levels underlying this rock shelter. These show superimpositions of several pictures of differently sized animals, such as deer, and lattice motifs, which are generally associated with the Planalto rock art tradition. The chronological study was performed based on radiocarbon (14C) analysis of charcoal collected from six excavated subsurface archaeological contexts. The two oldest layers, associated with hunters and gatherers of the Umbu tradition, were dated to 7680–7516 cal BP and 6913–6656 cal BP. There are four occupational layers from ceramists and farmers related to the south Jê linguistic family, and linked to the Itararé-Taquara archaeological tradition: layer 3 linked to the oldest of such occupation, dated to 3058–2796 cal BP, followed by layer 4, dated to 2080–1701 cal BP. Layers 5 and 6, dated to 1995–1526 cal BP and 540–152 cal BP, respectively.

Sr chemostratigrphy, δ13C, and δ18O of rocks in the Crimean carbonate platform (Late Jurassic, northern Peri-Tethys)

The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The 87Sr/86Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ18O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in 18O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ13C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ13C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.

Automated mineralogy based on micro-energy-dispersive X-ray fluorescence microscopy (µ-EDXRF) applied to plutonic rock thin sections in comparison to a mineral liberation analyzer

Abstract. Recent developments in the application of micro-energy-dispersive X-ray fluorescence spectrometry mapping (µ-EDXRF) have opened up new opportunities for fast geoscientific analyses. Acquiring spatially resolved spectral and chemical information non-destructively for large samples of up to 20 cm length provides valuable information for geoscientific interpretation. Using supervised classification of the spectral information, mineral distribution maps can be obtained. In this work, thin sections of plutonic rocks are analyzed by µ-EDXRF and classified using the supervised classification algorithm spectral angle mapper (SAM). Based on the mineral distribution maps, it is possible to obtain quantitative mineral information, i.e., to calculate the modal mineralogy, search and locate minerals of interest, and perform image analysis. The results are compared to automated mineralogy obtained from the mineral liberation analyzer (MLA) of a scanning electron microscope (SEM) and show good accordance, revealing variation resulting mostly from the limit of spatial resolution of the µ-EDXRF instrument. Taking into account the little time needed for sample preparation and measurement, this method seems suitable for fast sample overviews with valuable chemical, mineralogical and textural information. Additionally, it enables the researcher to make better and more targeted decisions for subsequent analyses.

Klasifikasi Batuan Beku Gabbro Pada Citra Sayatan Tipis Menggunakan Multilevel Otsu’s Thresholding

Citra sayatan tipis batuan merupakan metode pengaman yang digunakan untuk menentukan jenis batuan dan nama dari batuan berdasar pada mineral penyusun. Melakukan pengamatan sayatan tipis sulit dilakukan jika hanya menggunakan bantuan mikroskop polarisasi karena kemampuan mata manusia tidak dapat melakukan identifikasi secara mendetail. Oleh karena itu analisis dan identifikasi mineral menjadi lebih mudah dilakukan dengan bantuan pengolahan citra digital dengan menggunakan algoritma Multilevel Otsu’s Thresholding untuk mengetahui kelimpahan mineral batuan beku. Data yang digunakan dalam penelitian ini menggunakan citra sayatan tipis batuan beku yang diakuisisi dari penggunaan mikroskop polarisasi dengan perbesaran 10x. preprocessing yang dilakukan dengan 2 perlakuan yang berbeda yaitu garyscale dan grayscale dengan k-means untuk mengetahui hasil yang maksimal. Selanjutnya tahap pengolahan dilakukan segmentasi Multilevel Otsu’s Thresholding dengan dua nilai ambang. Selanjutnya analisis pada hasil segmentasi untuk mengetahui kelimpahan mineral. Hasil perhitungan dan analisis yang telah dilakukan pada preprocessing yang menggunakan grayscale dan grayscale dengan k-means yang kemudian di lakukan segmentasi Multilevel Otsu’s Thresholding memiliki akurasi paling tinggi 40% dan 33,57%. Dari kedua perlakuan dapat disimpulkan bahwa penggunaan k-means pada preprocessing memiliki pengaruh pada pengolahan citra sayatan tipis batuan beku jenis gabbro dengan nilai akurasi tertinggi dari dua perlakuan yaitu 40% dengan menggunakan preprocessing k-means dengan nilai k=7.

Whole rock and spinel compositions of serpentinized peridotites from the Divriği-Sivas region, eastern Turkey: Implications for their tectonic setting

In this study we investigate the spinel and whole rock chemistry of ultramafic rocks in the Divriği-Sivas region hosting one of the largest ophiolite suites in Turkey, which were emplaced following the convergence between the African and Eurasian plates in the Late Cretaceous. The ophiolitic mélange (Güneş Ophiolite) in Divriği is composed of ultramafic rocks, amphibolites, sub-ophiolitic metamorphic rocks and calc-silicates. The ultramafic rock section is made up of serpentinized wehrlites overlain by irregular segregations of pyroxenite levels.Whole rock chemistry of Divriği wehrlites resembles serpentinized peridotites in Himalayas. They have high MgO (average 31.27 wt%) and low Al2O3 (average 0.56 wt%) concentrations and Mg/Si and Al/Si ratios imply that peridotites formed in a supra-subduction zone environment. The U-shaped REE patterns of serpentinized wehrlites are formed by partial melting, coupled with interaction between peridotite and hydrous melts in the mantle wedge. The spinels collected from serpentinized wehrlites show compositions ranging from chromite in the core to ferritchromite and Cr-magnetite at the rims and have high Cr2O3 (46.5–56.2 wt%) and very low TiO2 contents (<0.3 wt%). Cr# values (0.71–0.84) of studied spinels are consistent with those of selected spinels from Anatolian peridotites but their Mg# values (0.26–0.46) are significantly lower. Cr# values of Divriği spinels correspond to SSZ peridotites and indicate high-degree partial melting (>%35). Parental melt compositions computed (8.69–11.71 wt% for Al2O3 and 0.1 to 0.37 wt% for TiO2) from chromite-melt equilibrium conditions yield a boninitic affinity. Our data suggest that spinels from serpentinized wehrlites in the Divriği area are similar to peridotite xenoliths from the Kamchatka arc and West Bismarck.

Cyclogenesis and mineragenic features of Early Permian sediments of the western part of Peredovoi range (North Caucasus)

Ritmostratigrafic complexes of Early Permian sediments of Belorechenskaya depression of the western part of the Peredovoy range (Front Range) have been distinguished. Single cycles of the accumulation of the red continental molasses have been established in sections of Aksautskaya and Kinyrchadskaya formations. The cyclic recurrence is associated with the differentiation of the water-flow accumulation in the intermountain trough within wandering channels and extensive debris cones in enclosed shallow basins. The sedimentation occurred in the continental environment of the intermountain accumulative plains under fluvial sedimentation conditions. It refers to the migration-mutation sedimentation type and corresponds to the upper continental molasses. Both, the mineragenic features of copper and gold in the Early Permian red sediments and the confinedness of the mineralization to the specific parts of the rock sections within the limits of the distinguished rhythms, have been shown.

New understandings of the lithofacies paleogeography of the middle assemblage of Majiagou Fm in the Ordos Basin and its exploration significance

Accurate lithofacies-paleogeographic reconstruction is of great significance in predicting the dolomite reservoir distribution of the middle assemblage of Ordovician Majiagou Fm in the Ordos Basin. In this paper, the controlling effects of palaeotectonic background over sedimentation were first analyzed. Then the sedimentary mode of the middle assemblage was established and the lithofacies-paleogeography was reconstructed objectively for three intervals (Ma55, Ma57 and Ma59), based on the observation results of a large number of drilling cores and rock sections, together with the results of logging interpretation of rock composition and structure, single factor maps analysis and seismic data interpretation. The following findings were obtained. First, the middle assemblage of Majiagou Fm presents the uplift-depression alternation; two secondary low uplift zones extending in NS, i.e. Wushen Banner–Wuqi and Shenmu–Yulin–Yan'an, are developed in the eastern side of the central paleo-uplift, between which there is intraplatform depression, and lagoons are deposited in the Mizhi area in the east of the basin. Second, in the Ordos Basin, four NE-trending rift troughs are developed in the Proterozoic, which greatly affects the Ordovician sedimentary pattern and controls the distribution of intraplatform grain banks. Third, influenced jointly by the uplift-depression alternation and the intraplatform rift troughs of the Proterozoic, the intraplatform grain banks in the middle assemblage are mainly developed in the two low uplift zones, i.e. Shenmu–Yulin–Yan'an and Wushen Banner–Wuqi, trending NE in a similar echelon distribution. In conclusion, the two low uplift zones are the main development areas for high-quality carbonate reservoirs within the middle assemblage of Majiagou Fm in the basin.

Reflectance Spectroscopy and Hyperspectral Imaging of Sapphire-Bearing Marble From the Beluga Occurrence, Baffin Island, Nunavut

Abstract Baffin Island (Nunavut, Canada) is located in the remote arctic where geological exposure is high, terrain is expansive, and field seasons are short. Metacarbonates in the Lake Harbour Group, southern Baffin Island, are considered to be prospective for sapphire (corundum), lapis lazuli (lazurite), and spinel gem deposits. This research is an investigation of the hyperspectral signature of rocks from the Beluga sapphire occurrence near Kimmirut, Nunavut. Thirty-five rock and thin section offcut samples from the Beluga corundum occurrence were studied in a laboratory setting using high spatial resolution imaging spectroscopy in the shortwave infrared region (SWIR, ∼975 to 2500 nm). Analysis of hyperspectral imagery successfully reproduced mineralogical and textural information relevant to gem mineralization previously assessed through thin section petrography and scanning electron microscopy. Scapolite, phlogopite, and muscovite from these rocks are shown to have distinct spectral responses from the host marble that is dominated by calcite. Furthermore, spectrally distinct prehnite and zeolite, both locally associated with corundum mineralization, are readily distinguishable. From the perspective of regional exploration, the small footprint of colored gemstone deposits in combination with their unique mineralogical makeup, unusual settings, and unfamiliarity to most geoscientists has resulted in very few discoveries in this remote but otherwise fertile area. These factors, in combination with the unique spectral responses observed from hand samples and thin section offcuts, provide a positive case for mapping and exploration of gem corundum targets by high spatial resolution hyperspectral imaging as part of regional surveys.

Comparative palynofacies, magnetic susceptibility and cyclicity of the Middle Devonian Müllertchen Section (Eifel area, Germany)

The recognition of subtle small-scale cycles in “monotonous” calcareous mudstone intervals requires a multi-disciplinary approach. In the classical Eifel area of Germany, a section of lower Givetian calcareous rocks is exposed in the well-known Mullertchen Quarry near Uxheim-Ahutte. Lying on top of limestones of the Lahr Member of the Ahbach Formation, a succession of calcareous mudstones (marlstones) is developed. This succession contains diverse brachiopods, corals and bryozoans, which are mostly small, especially in the lower part. In the present study, we focus on the combination of lithology, palynological content and magnetic susceptibility in order to evaluate whether a cyclic pattern is developed and can be mirrored by these methods. The lithological succession shows a rather homogenous marly sequence interrupted by a few more rigid calcareous beds; two of them are known as the Lower and Upper Wurmweide beds, which yield traces of Chondrites on the upper surface. For palynological analyses, 19 samples were obtained from a 4-m interval in the marly succession. Eighty samples were collected at regular spacing through the same interval, for magnetic susceptibility analysis. Palynofacies analysis has been carried out, and the assemblage of leiosphaerids, acritarchs, scolecodonts and miospores reflects the lithology. In particular, the distribution pattern, abundance and ratios of leiosphaerids and miospores can be applied for palaeoenvironmental interpretation. Patterns of change in proportion of these two groups match that of the magnetic susceptibility. These combined data indicate small-scale cyclicity, even within a relatively monotonous, thin stratigraphic interval.

Dinoflagellate cyst assemblages, biostratigraphy and paleoenvironment of a Paleocene-Early Eocene sedimentary succession in the northern Niger Delta Basin: Comparison with low, mid and high latitude regions

This study represents a contribution to the Late Paleocene-Early Eocene biostratigraphy in a low latitude stratigraphic setting where, published studies are few in comparison with mid- and high latitude regions. We generated data for 62 dinoflagellate cysts from a comprehensive analysis of 33 samples covering a 713-m interval in the Alo-1 Well in the northern Niger Delta (Anambra) Basin, Nigeria. Dinoflagellate cyst recovery in the samples varies from very good to poor, and the specimens are commonly well preserved. We calibrate the dinoflagellate cyst data with recent biozonation schemes for ODP Hole 959D, Côte d'Ivoire-Ghana Transform Margin in the eastern Equatorial Atlantic, which allowed for a valid comparison with published studies in well-dated rock sections in northwestern Europe, the Mediterranean region, New Zealand, and Tasmania. Our observations show that there is better correlation between tropical and mid latitude dinoflagellate cyst assemblages compared to those in high latitude regions.We use the last occurrence and/or last abundance events of dinoflagellate cysts to identify four biostratigraphic zones (zone E to zone H) in the Alo-1 Well. Lithostratigraphic and biostratigraphic analyses suggest a late Selandian age for the contact between the Imo and Nsukka formations. Abundant thermophilic taxa that include the Cordosphaeridium group and Apectodinuim dominate the assemblage recovered in the depositional succession. The late Selandian to early Thanetian sediments are dominated by the Cordosphaeridium group, and are succeeded by abundant to superabundant marker species of Apectodinium in the late Thanetian to Ypresian. The superabundance of Apectodinium is significant because it is indicative of the global intense climatic warming that characterized the late Thanetian to early Ypresian. The Alo-1 Well dinoflagellate cyst data also suggest deposition under proximal, inner neritic conditions that preserved an assemblage dominated by species of Cordosphaeridium, Damassadinium, Ifecysta and Polysphaeridium.

Stratigraphic record of Pliocene-Pleistocene basin evolution and deformation within the Southern San Andreas Fault Zone, Mecca Hills, California

A thick section of Pliocene-Pleistocene nonmarine sedimentary rocks exposed in the Mecca Hills, California, provides a record of fault-zone evolution along the Coachella Valley segment of the San Andreas fault (SAF). Geologic mapping, measured sections, detailed sedimentology, and paleomagnetic data document a 3–5Myr history of deformation and sedimentation in this area. SW-side down offset on the Painted Canyon fault (PCF) starting ~3.7Ma resulted in deposition of the Mecca Conglomerate southwest of the fault. The lower member of the Palm Spring Formation accumulated across the PCF from ~3.0 to 2.6Ma during regional subsidence. SW-side up slip on the PCF and related transpressive deformation from ~2.6 to 2.3Ma created a time-transgressive angular unconformity between the lower and upper members of the Palm Spring Formation. The upper member accumulated in discrete fault-bounded depocenters until initiation of modern deformation, uplift, and basin inversion starting at ~0.7Ma.Some spatially restricted deposits can be attributed to the evolution of fault-zone geometric complexities. However, the deformation events at ca. 2.6Ma and 0.7Ma are recorded regionally along ~80km of the SAF through Coachella Valley, covering an area much larger than mapped fault-zone irregularities, and thus require regional explanations. We therefore conclude that late Cenozoic deformation and sedimentation along the SAF in Coachella Valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault-zone complexities. We further propose a kinematic link between the ~2.6–2.3Ma angular unconformity and a previously documented but poorly dated reorganization of plate-boundary faults in the northern Gulf of California at ~3.3–2.0Ma. This analysis highlights the potential for high-precision chronologies in deformed terrestrial deposits to provide improved understanding of local- to regional-scale structural controls on basin formation and deformation along an active transform margin.

Swelling potential of clay-sulfate rocks in tunneling in complex geological settings and impact of hydraulic measures assessed by 3D groundwater modeling

Swelling of clay-sulfate rocks is a feared problem in tunneling in such rock, causing heave of the tunnel invert and leading to swelling pressures that seriously damage the tunnel lining. Prediction of the swelling potential of rocks in different tunnel sections and tools to evaluate measures that aim at reducing the swelling risk would be a major aid for designers of tunneling projects and rehabilitation works in order to respond adequately to the swelling problem. The study presents a hydrogeological approach to assess the swelling potential of clay-sulfate rocks in tunneling, using the Belchen tunnel in Switzerland as a case study. It shows that this approach can be applied to complex geological settings using structurally consistent 3D numerical models to simulate groundwater flow influenced by tunneling. The models are in particular used to evaluate hydraulic measures that aim at preventing or minimizing water inflow into clay-sulfate rocks after tunneling. Analyzed hydraulic measures include pumping shafts connected to the tunnel drainage, sealing structures applied to the rock zone around the tunnel damaged by the excavation process (excavation damaged zone), as well as groundwater level drawdown in aquifers crossing the tunnel. A sensitivity study addresses model uncertainties and evaluates the impact of model parameters on the swelling potential. Promising measures include the installation of pumping shafts in tunnel sections of clay-sulfate rocks at the border to aquifers and permeable fault zones. The study shows that monitoring of hydraulic heads as well as of groundwater volumes drained by the tunnel would increase the predictive capability of the models. Presented results are site specific. However, the approach to assess the swelling potential of clay-sulfate rocks in tunneling, and to assess hydraulic measures to respond to the swelling problem, can be transferred to other tunneling projects.

Estimation of carbonates permeability using pore network parameters extracted from thin section images and comparison with experimental data

Petrography and image analysis have been widely used to identify and quantify porous characteristics in carbonate reservoirs. This paper uses the thin section images of 200 carbonate rock samples to predict the absolute permeability using intelligent and empirical methods. For each thin section, several pore network parameters are extracted from thin section images of rocks including the average pore size, average throat size, average throat length and average 2-D coordination number of pore network. A neural-based model successfully predicts the permeability of samples using pore network parameters as the inputs. Second neural network is applied for predicting absolute permeability considering lithology, pore type and fabric of the rock samples. Finally, an empirical formula containing porosity and average coordination number as inputs is proposed to predict the permeability. It has been found that the porosity and coordination number can directly describe the permeability of carbonates while pore and throat sizes extracted from a single 2-D cross section of rock cannot explain the permeability of carbonates very well. The results of this study indicate the better performance of pore network extraction method compared to the simple regression analysis for prediction of the permeability.

Source potential and depositional environment of Oligocene and Miocene rocks offshore Bulgaria

Abstract Oligo-Miocene (‘Maikopian’) deposits are considered the main source rocks in the Black Sea area, although only a few source-rock data are available. Geochemical logs from nine wells are used together with age constraints provided by calcareous nannoplankton, well and seismic data to determine vertical and lateral changes of the source potential. Oligocene rocks overlie Eocene deposits with a major unconformity on the western Black Sea shelf in Bulgaria. A west–east-trending erosional structure (the Kaliakra canyon) developed during Lower Oligocene time and was filled with Oligo-Miocene deposits. Potential source rocks are present in different stratigraphic units, but the most prolific intervals accumulated during time intervals when the isolation of the Paratethys resulted in oxygen-depleted, brackish environments with high bioproductivity. These include Lower Solenovian rocks related to blooms of calcareous nannoplankton, which form an extensive layer outside the Kaliakra canyon. This unit hosts a good potential to generate oil and gas. Diatom-rich, very good oil-prone source rocks accumulated during a second isolation event in the Kozakhurian. Thick sections of these diatom-rich rocks occur within the canyon and are present in thin layers outside of it. High productivity of siliceous organisms is attributed to upwelling within the canyon. All studied units are thermally immature on the shelf.

Landslide hazard zonation mapping and cut slope stability analyses along Yercaud ghat road (Kuppanur\u2013Yercaud) section, Tamil Nadu, India

In the present study, the macro landslide hazard zonation (LHZ) mapping and slope stability analyses of selected rock slope (RS) sections were carried out along Kuppanur–Yercaud ghat road section. The macro LHZ map was prepared on 1:50,000 scale using landslide hazard evaluation factor (LHEF) rating scheme proposed by Bureau of Indian Standard IS 14496 (Part-2) 1998. The study incorporated predefined ratings for different causative factors viz. lithology, structure, slope morphometry, relative relief, land use and land cover, and hydrogeological condition as well as triggering factors like seismicity and rainfall. The total estimated hazard (TEHD) was evaluated by adding ratings of all the causative factors. On the basis of TEHD values, the facet 3 with TEHD value 6.25 was classified as high hazard zone (HHZ). The facet 2 and 4 with TEHD values 5.50 and 5.40 respectively was classified as moderate hazard zones (MHZ). The facet 1 and 5 with TEHD values 2.20 and 3.15 was categorized as very low hazard zone (VLHZ). The slope stability analyses were carried out in six RS sections using rock mass rating (RMR) and slope mass rating (SMR) systems and the factor of safety (FOS) was evaluated for critical discontinuity sets. The results of RMR show that RS sections 1, 2, 4, 5, and 6 fall in class-III fair rock category, whereas the RS section 3 falls in class-IV poor rock category. The SMR method involves field measurement of slope and discontinuity orientation. These structural values were plotted in the stereonet and identified possible direction and mode of failure. The results of SMR show that the rock sections 1, 2, 4, 5, and 6 falls under partially stable condition, while the rock section 3 comes under unstable condition. The FOS of the critical discontinuity sections was evaluated for planar as well as wedge failure modes. The results based on planar failure analysis, the RS-2 and RS-3 having FOS < 1 are more unstable for slope failure. The wedge failure analysis shows that all the RS sections having FOS > 1 fall in safe conditions.

Late Ordovician deep-water brachiopod fauna from Raheen, Waterford Harbour, Ireland

The Raheen Formation at Newtown Head in Waterford Harbour is a small isolated section of Ordovician rocks, dominated by volcanics of the Duncannon Group, but with interbedded fossiliferous shales. Although a brachiopod and trilobite dominated fauna has been known since the mid-nineteenth century, only the trilobites and cystoids have been assessed in modern terms. This paper describes the brachiopod fauna for the first time. The assemblage from Raheen is overwhelmingly dominated by the dalmanelloid Onniella, with the small plectambonitoid Sericoidea comprising the second most numerous species; both are represented by new species. This revision has also identified a wide range of other genera, but all in very small numbers. These include an obolid, a paterulid, Paracraniops and Orthisocrania divaricata (M‘Coy) amongst the non-articulated brachiopods. Articulated genera present include the orthoids Nicolella, Ptychopleurella, Sulevorthis, Skenidioides and the plectambonitoid Leptestiina. Very rare forms include Idiospira? and Palaeostrophomena, together with possibly Biscuspina and Sowerbyella. The brachiopod revision supports the late Caradoc (early Katian) age indicated by the trilobite fauna. The trilobite fauna generally indicates a probable deeper-water environment and the brachiopod assemblage confirms an outer-shelf environment. Although elements of the assemblage indicate affinity with the well-defined Late Ordovician Foliomena fauna, it probably occupied a more shoreward position. (Less)

Enrichment of 88Sr in continental waters due to calcium carbonate precipitation

δ88/86Sr data published over the last few years suggest that continental waters are enriched with 88Sr as compared to the rocks in their drainage basins. In an attempt to understand this phenomenon, this study established the fractionation in the 88Sr/86Sr ratio during precipitation of continental carbonates (i.e., carbonates precipitated on land from surface, pedogenic, or ground waters), and evaluated the contribution of this process to the 88Sr-enrichment in rivers. For this, stable and radiogenic Sr isotopes (88Sr, 87Sr and 86Sr) were measured in calcite samples and their precipitating waters collected in various continental environments, such as soil, cave, streams and groundwater.The results indicate that continental carbonates are 88Sr-depleted relative to their precipitating waters, placing them as one of the most 88Sr-depleted reservoirs on earth. The average difference in δ88/86Sr values between waters and solid CaCO3 (tufas or speleothems) that they precipitate is Δcarb-water=−0.218±0.014‰ (1SD). An even larger fractionation (εcarb-water=−0.285±0.02‰) was measured in groundwater with particularly high carbonate-alkalinity and high carbonate precipitation rate that depleted ∼65% of the Sr in the groundwater, resulting in substantial 88Sr-enrichment in the residual dissolved Sr (δSr88/86=0.656‰). Results also suggest that pedogenic carbonate precipitation in soil profile removes 50–85% of the Sr from the recharging soil–water, thereby increasing the δ88/86Sr value of the soil-water from ∼0.18‰ to 0.3‰–0.6‰. Similar 88Sr-enrichment was observed in drip water from a karst cave.A maximum removal flux of Sr into continental carbonates of about 20 Gmol(Sr)⋅y−1 is required to yield the reported 88Sr-enrichment in global rivers (δSr88/86=0.32‰) relative to their rock sources when using the fractionation factor derived in this study, Δcarb-water=−0.218‰, and the published δ88/86Sr composition of marine carbonates of 0.16‰. This surprisingly large flux requires that ∼40% of the originally weathered Sr should co-precipitate with continental carbonates. This calculation may suggest that CaCO3 precipitation is a significant mechanism in the continental Sr cycle. It is possible however that other mechanisms such as Sr uptake by plants or incongruent weathering of silicates, could also contribute to the riverine 88Sr-enrichment. Alternatively, the average δ88/86Sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature. It is concluded that additional δ88/86Sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine δ88/86Sr.

A microfluidic approach to water-rock interactions using thin rock sections: Pb and U sorption onto thin shale and granite sections

The feasibility of using microfluidic tests to investigate water-rock (mineral) interactions in fractures regarding sorption onto thin rock sections (i.e., shale and granite) of lead (Pb) and uranium (U) was evaluated using a synthetic PbCl2 solution and uranium-containing natural groundwater as fluids. Effluent composition and element distribution on the thin rock sections before and after microfluidic testing were analyzed. Most Pb removal (9.8mg/cm2) occurred within 3.5h (140 PVF), which was 74% of the total Pb removal (13.2mg/cm2) at the end of testing (14.5h, 560 PVF). Element composition on the thin shale sections determined by μ-XRF analysis indicated that Pb removal was related primarily to Fe-containing minerals (e.g., pyrite). Two thin granite sections (biotite rich, Bt-R and biotite poor, Bt-P) exhibited no marked difference in uranium removal capacity, but a slightly higher amount of uranium was removed onto the thin Bt-R section (266μg/cm2) than the thin Bt-P section (240μg/cm2) within 120h (4800 PVF). However, uranium could not be detected by micro X-ray fluorescence (μ-XRF) analysis, likely due to the detection limit. These results suggest that microfluidic testing on thin rock sections enables quantitative evaluation of rock (mineral)-water interactions at the micro-fracture or pore scale.