Petrographic Characteristics Research Articles

Sedimentology and Diagenetic Evolution of Maastrichtian Fugar Sandstone, Western Flanks of Anambra Basin, Nigeria

Diagenetic studies unravel the different diagenetic processes a rock has been subjected to and this plays an important role in the formation of sedimentary rocks, therefore the detailed study of the sedimentology and diagenetic evolution of the Fugar Sandstone depicts the diagenetic history and the paragenetic sequence of the cements present. The Fugar sandstone is an extension of the Upper Cretaceous Ajali Sandstone unit of the Anambra Basin in South western Nigeria and this study was aimed at understanding the sedimentological and petrographical characteristics of the sandstone with a view to model the sandstone diagenesis. The field study and granulometric analysis results reveals that the sandstones are unconsolidated, friable, fine to medium-coarse grained, poorly sorted, planar and herringbone cross-bedded and exhibits a repeated succession of fining upward cycles with the inferred depositional environment of fluvial to marginal-marine. The samples were analyzed using a range of techniques: X-ray diffraction, X-ray fluorescence and Optical microscope which shows that the sandstone is quartz arenite with an average of 95% quartz consisting of subangular to subrounded grains and this implies that the sandstone is mineralogically matured but texturally immature. Detailed diagenetic study using thin section petrography reveals that the rocks have undergone different diagenetic processes; compaction, cementation, dissolution, alteration and replacement, and the paragenetic order of the cementing minerals were from authigenic quartz which occurs as quartz overgrowth, clay and then Iron oxides which serves as the predominant mineral cements in the rocks.

Detrital zircon U–Pb ages of the Miocene clastic sedimentary succession in the Shidara Basin, central Japan: Implications for provenance changes and timing of collision between the Izu–Ogasawara and Honshu arcs

• Zircon U–Pb dating revealed provenance change in the middle of Miocene succession. • Deposition of Miocene strata was associated with the initial collision of two arcs. • Collision between the two arcs was initiated at around 17.4 ± 0.4 Ma. Collision of the Izu–Ogasawara and Honshu arcs occurred during the Miocene. The Miocene Hokusetsu Subgroup in the western part of the Izu collision zone is considered to be a key formation that might record the timing of the initial collision. To clarify the timing, we conducted provenance analysis based on detrital zircon U–Pb ages of the Hokusetsu Subgroup. Zircon ages show a Late Cretaceous peak in the strata below the Umedaira Sandstone Member and a peak around 100 Ma in the lower Umedaira Sandstone Member. Furthermore, the proportions of Jurassic to Proterozoic ages increase in the upper part of the sandstone member and the overlying horizons. The zircon ages and the petrographical characteristics of detritus suggest that the formations below the lower Umedaira Sandstone Member were derived from the Ryoke Plutonic Rocks, but the formations above the upper Umedaira Sandstone Member were derived from a Jurassic accretionary complex. Deposition of the Umedaira Sandstone Member suggests uplift of the provenance areas, which are inferred to have been the 100 Ma Ryoke Plutonic Rocks to the northeast and east of the Shidara Basin and Jurassic accretionary complexes farther to the northeast and east. The provenance change during deposition of the Umedaira Sandstone Member was caused by collision of the Izu–Ogasawara and Honshu arcs. Therefore, the collision is considered to have begun around 17.4 ±0.7 Ma constrained by depositional age of the Umedaira Sandstone Member.

An explanation of the field and petrographic features of granitic rocks in Narsapur area of medak District, Telangana, India

The study area, Narsapur Mandal in Medak district, Telangana State, is at a distance of 60 km NW of Hyderabad. The area covers geological out crops in and around Narsapur.To research the petrographic variations in the rocks, a total area of around 44 square kilometres has been covered. This area represents the geology of the investigated area. It is primarily composed of Precambrian granite and its varieties, such as quartz syenite, quartz monzonite and alkali feldspar granite. Alkali feldspar granite dominates the NE, W, SE, S and SE regions of the area, alkali feldspar and quartz syenite dominates the NW and SE regions, quartz monzonite and quartz syenite dominate the middle region. From all of the nearby outcrops, the nine most representatives in-situ, fresh and unweathered samples were gathered. These plutons' variations in structure and mineral makeup are sufficiently diverse that the name “migmatite” must be used and their mutual field interactions always remain mysterious. The structural fabrics also demonstrate the batholiths' complexity. It is included that differences in mechanical dilution of mafic magma, fractional crystallisation, and diffusive fractionation are responsible for the variability in compositional variation of medak granite. The geochemical data support the idea that subduction had a part in the formation of these rocks.

Genetic mechanism of multi-scale sedimentary cycles and their impacts on shale-oil distribution in Permian Lucaogou Formation, Jimusar Sag, Junggar Basin

Complex lithofacies of Lucaogou Formation in Jimusar Sag promote strong heterogeneity of oil distribution in fine grained sedimentary rocks. It is of great significance to define the formation mechanism of fine-grained sedimentary rocks for favorable reservoir prediction and exploration target selection in Jimusar Sag. Based on detailed petrographic characterization, in-situ geochemical parameter testing, and high-resolution cycle analysis, sedimentary cycles on the micron to meter scales were successfully identified in Lucaogou Formation from Jimusar Sag. Precession-forced paleo-environmental evolution mainly induces the deposition of meter-scale sedimentary cycles. In the period of low precession, the paleo-environment is cold and dry, the lake level falls. Silt-grained particles advance toward the center of the lake basin carried by gravity current, thus siliciclastic sediments are mainly deposited. In the period of high precession, the climate is warm and humid, the lake level rises. The inputs of siliciclastic sediments are limited and the temperature increases, which are conductive to the carbonate deposition. On this basis, high-frequency paleo-environmental evolution caused by solar activity (70–110yr cycle) further induces the formation of sedimentary cycles on micron-centimeter scale. When the precession is low, the rise and fall of lake level controlled by solar activity is contribute to the deposition of tuff-rich lamina and silt-grained felsic lamina, respectively. The period of high precession is under the background of overall high lake-level, the rise and fall of lake level, along with fall and rise of temperature, controlled by solar activity finally induce the deposition of tuff-rich lamina and carbonate lamina, respectively. The development of multi-scale sedimentary cycles controlled by Milankovitch cycle and solar activity cycle have important implications for shale oil enrichment. The fine-grained sediments deposited during the period of low precession and intense solar activity dominate feldspar dissolution pores and intergranular pores, which are favorable for shale oil enrichment.

나주읍성 동점문 성벽부재에 대한 암석학적 연구 및 산지 추정

This study is based on the mentorship course in CNU Science Education Institute For the Gifted. The Naju Eupseong Dongjeommun Gate, which was built in the Goryeo Dynasty, was restored in 2002, but a heterogeneous stone material that showed a significant difference from the original stone of the fortress wall, was used as the restoration stone. This study aims to clarify the difference between raw stones and restored stones by the investigation of the petrological features of the stone materials for the Naju Eupseong Dongjeommun Gate, and to estimate the provenances of the raw stones through the geologic survey. In addition, replacement stones that can be used for when the Naju Eupseong Dongdaemun Gate is renovated are presented. As a result of measured magnetic susceptibility and visual observation, the stone materials of the Naju Eupseong Dongjeommun Gate consist of granodiorite, and granite gneiss. Compared to the original stone, the restored stone is judged to be a granite, which shows a clear difference in the petrographical features such as the results of visual observation and the magnetic susceptibility. As a result of the geologic survey around Naju Eupseong Walled Town, the area of Geumseongsan Mountain in Naju is presumed to be the source of the original stones. Granite diorite is considered appropriate as a substitute stone if the restoration of Naju Eupseong Dongjeommun Gate is carried out.

CHARACTERIZING THE PAINTED WALL RELIEFS FROM THE ANCIENT EGYPTIAN ROCK TOMBS OF MEIR AT ASSIUT, EGYPT

The present research was designed to characterize the main components of ancient Egyptian wall reliefs of Meir rock tombs at Assiut of Egypt using severalµ-destructive analytical methods. The microscopic characterization included optical examination on painted surfaces and petrographic examination on thin sections of rock fractions. The morphology of pigments and their chemical structure were investigated by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM-EDX). Fourier transform infrared spectroscopy (FTIR) was used for the investigation of the molecular composition of the render layer and the blue pigment. The mineralogical composition by X-ray diffractometry (XRD) helped to study the stone, underlying preparation layer, and some pigments. The results showed that the petrographic features of the rock samples are based mainly on fine calcite grains. The identified pigments were Egyptian blue (synthetic cuprorivaite), red ochre (iron oxides and clay minerals), and carbon black. While for the green colour, a mixture of Egyptian blue and yellow ochre was created. Since the materials used in the abovementioned tombs were never been previously analyzed, this research will be a valuable start for a future complex study related to painting materials used in the Meir necropolis of ancient Egypt

Geochemistry and organic petrology of the bituminite shales from the Kapurdi mine, Rajasthan of NW India: implications for waxy oil generation potential

This study examines the geochemical and petrographic characteristics of seven bituminite shales from the Kapurdi mine in the Rajasthan, NW India, in order to assess their organic matter inputs and evaluate the oil-prone potentials. These bituminite shale samples exhibit high total organic carbon (TOC) content (up to 45.11 wt.%). The high TOC contents were correlated with low total sulfur content of less than 1 wt.% and suggest that these bituminite shales were deposited in a fresh lacustrine environment. The dominance of such lacustrine environmental setting was confirmed by the presence of the Botryococcus algae. The analyzed bituminite shales are characterized by a bimodal distribution of normal alkanes and relatively low isoprenoid Pr/Ph, Pr/n-C17 and Ph/n-C18 ratios. These characteristics suggest that these bituminite shales contain a blend of organic matter that was derived primarily from algal lacustrine and other aquatic organic matter, with terrigenous land plants and deposited under suboxic to anoxic environmental conditions. Such findings of the organic matter (OM) input and environmental conditions are consistent with mainly Types I and II kerogen and small amounts of Type II/III kerogen, thus yielding both oil and gas prone to higher concentrations of oil generation potential. The dominance of hydrogen-rich kerogen and oil generation potential is in agreement with the findings of high hydrogen index (HI = 240–425 mg HC/g TOC) and H/C atomic ratio of more than 1.20. The abundance of n-alkene and n-alkane doublets in the pyrolysis–gas chromatography (Py–GC) also indicates that these bituminite shales have potential to generate high concentrations of paraffinic waxy oil. Most of the maturity indicators show that the bituminite shales from the Kapurdi mine have not yet entered the main stage of oil generation window, exhibiting a range of immature stages. Therefore, as highlighted in this study, these bituminite shales can be considered as a good candidate for oil shale reoterting processes to release commercial amounts of oil upon using artificial heating techniques such as hydrothermal conversion.

Periodic paleo-environment oscillation on multi-timescales in the Triassic and their significant implications for algal blooms: A case study on the lacustrine shales in Ordos Basin

The Triassic climate has been a relatively neglected topic and conventionally considered a “hot-house” world. Using detailed petrographic characterization, in situ geochemical testing, and high-resolution cycle analysis, the Triassic lacustrine shale in the Ordos Basin was studied to confirm that periodic oscillations of the paleo-environment occurred at different timescales during the Triassic. On the millennial scale, increased obliquity induced enhanced transfer of heat and moisture to high latitudes, which then recharged continental aquifers, resulting in an increase in temperature, humidity, and levels of lakes in the mid-latitudes of the Northern Hemisphere. In contrast, decreased obliquity induced temperature and humidity reduction, followed by lake-level decline. Variations in eccentricity further regulated the magnitude of obliquity-forced paleo-environmental evolution. On the decadal–centennial scale, solar activity, including the 360–500 yr cycle I, 81–110 yr cycle II, and 30–57 yr cycle III, caused high-frequency oscillations of humidity and lake level. In the mid-latitudes of the Northern Hemisphere, intense (weak) solar activity promoted the decline (rise) in humidity and lake level. On the interannual scale, in the coastal area of western Panthalassa, El Niño-Southern Oscillation (ENSO)-like cycles also induced significant fluctuations in humidity and reducibility on a 2–8 yr scale. Whether complex paleo-environmental oscillations at different timescales occurred worldwide during the Triassic remains to be verified at other places. It is also noteworthy that high-frequency paleo-environmental oscillations in the Triassic stimulated algal blooms over a short period. The increase in rainfall caused by solar activity and ENSO-like cycles led to a frequent influx of nutrients into the Ordos Basin. The 30–57 yr cycle III induced red algae enrichment at intervals of decades. ENSO-like cycles also promoted algal bloom on 2–8 yr scale to form organic layers in lacustrine shale.

Structural and petrographic characterization of the Fotouni-Kekem Shear Zone: implication for P–T-t regional metamorphism and mylonitic evolutions along the Central Cameroon Shear Zone

Structural and petrographic characterization of the Fotouni-Kekem Shear Zone: implication for P–T-t regional metamorphism and mylonitic evolutions along the Central Cameroon Shear Zone

Petrographic Characterization of Geological Settings in the Locality of Mabuku in the Territory of Beni, DRC

The geology of the DRC has already been studied on regional plans, on the scale of a province or territory. But these studies are too synthetic and they do not consider the variations of petrographic facies that can occur at the scale of a locality or a village. Thus, to overcome this possibility, the present study aims to make a petrographic characterization of the rocks of the locality of Mabuku in the territory of Beni. To achieve this, we proceeded by a microscopic analysis of 10 field samples (selected on the basis of the variability of the petrographic characteristics of the rocks). Analyzes of these samples at the petrographic laboratory of the University of Nairobi in Kenya at the LPA and LPNA revealed that the lithology of the Mabuku locality consists of orthogneiss, schists, dolerite and diorite intrusions, quartzites , laterite and sandstones. However, there are four dominant formations. These are the orthogneiss found to the north; schist, dominant in the eastern part; doleritic intrusions in the northwest part; and the sandstones which are distributed along a SW-NE diagonal. Nevertheless, important gaps remain to be completed from the geochemical and metallogenic point of view in the locality of Mabuku.

Petrogenesis and geochronology of the bronze fox porphyry Cu-Au deposit: Implications for the geodynamic evolution of the Gurvansaykhan Island arc, southern Mongolia

ABSTRACT A diversity of Devonian-Carboniferous volcanic arcs and granitoid intrusions are exposed in the Gurvansaykhan arc terrane of southern Mongolia. Several giant porphyry Cu-Au-Mo deposits are associated with intrusions within these arcs. The Bronze Fox deposit located in the central part of the Gurvansaykhan arc terrane is an example of a potentially economic deposit with affinity of adakite-like granitoid porphyry (i.e. 428 Mt grading 0.26% to 0.30% Cu for up to 2,437 Mlb of copper and 0.84 Moz gold). The genesis and magmatic evolution of the causative rocks of the Bronze Fox porphyry Cu-Au hosting rocks are poorly understood, and different models are still under debate. In the current study, we present new field observations and petrographic, geochemical, and geochronological data to describe the magmatic evolution and geodynamic settings. In addition, the mineral chemical data are reported from some selected rock-forming minerals to identify crystallization conditions of the studied rock suites by employing geothermobarometric methods. Zircon chronological data reveal the emplaced age at 331 ± 3.4 Ma for the volcanic lava, followed by mineralized granodiorite and monzodiorite with intruded ages of 326.5 ± 3.4 Ma and 326.5 ± 2.7 Ma, respectively. The studied intrusive and extrusive rocks are high-K-alkaline and metaluminous, characterized by high Mg#. They are enriched in large ion lithophile elements (Sr and Ba) and light rare earth elements (LREEs) and depleted in high field strength elements (Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The highly mineralized granodiorite intrusion yields zircon crystallization temperatures ranging from 631.8 to 779.4°C, and the monzodiorite intrusion, which contains relatively low-grade mineralization, has a wider range (599.0 to 803.4°C). The formation pressures of the former range from 0.5 to 0.2 kbar, which is equivalent to a depth of 1.38 km based on amphibole geochemical calculations. The results of mineral chemistry indicate that the unmineralized diorite unit was formed under medium pressure (~50 MPa) and high temperature (~750°C) at depths of 6.8 to 7.5 km. Similarities in geochemistry and petrographic features suggest that the igneous rocks probably originated from a similar magma source (i.e. from the melting of ancient oceanic crust and sediments) but experienced different degrees of partial melting or mixing with lower juvenile crust melts. The estimated fO2 values obtained by amphibole chemistry in the granodiorite and quartz diorite of the Bronze Fox copper-gold mineralization range from −13.0 to −11.8 and −13.2 to −10.8, respectively, confirming that these igneous rocks probably crystallized under relatively oxidized conditions above the nickel-nickel oxide (NNO) buffer. Such results yield an overall range between NNO +2.6 and NNO +1.4, which are characterized by high oxygen fugacities and high Ce4+/Ce3+ ratios that reflect oxidizing magma, thus indicating quite promising potential for porphyry Cu-Au mineralization in the region. Based on the findings of this work, we suggest a new tectonic model of arc magmatism that is a response to the subduction of the Paleo-Asian Ocean in the early Carboniferous period.

Intricate Regolith Reworking Processes Revealed by Microstructures on Lunar Impact Glasses

AbstractGlasses cooled from impact melt and vapor are a common component in lunar regolith, carrying important information about protolith composition, regolith formation, and impact flux on the Moon. Interpretations, however, are frequently challenged due to widespread ambiguity in determining their provenances. Regolith samples returned by China's Chang’E‐5 mission provide a unique opportunity to study the microscopic mechanism of regolith reworking on the Moon, because as evidenced by the coherent radioisotope ages and petrographic characteristics of basaltic clasts in the regolith, the Chang’E‐5 regolith was mainly evolved from local mare materials, containing minor exotic components. Here, we report 153 glass particles larger than 20 μm in diameters that were screened from 500 mg of Chang’E‐5 regolith. Most glass particles have rotational shapes and contain structural and/or compositional heterogeneities in interiors, and geochemical analyses reveal a dominant origin as impact melt of local mare materials. Surfaces of the impact glasses are observed to have abundant protruded and dented microstructures, which are classified as different groups based on their morphology and geochemistry. Similar microstructures were observed on impact spherules collected by the Apollo and Luna missions, but those on the Chang’E‐5 impact glasses were formed without substantial involvement of exotic ejecta. Microstructures such as silicate melt pancakes that frequently exhibit flow spikes at margins, nano‐phase iron‐rich mounds that are arranged with semi‐equidistant spaces in curves and patches, spatially clustered microcraters that are indicative of secondary impacts, and blunt linear scratches with terminal particles all suggest that regolith reworking mainly occurred among local materials at low speeds.

Ceramic artifacts from the archaeological site “Biser”, Eastern Rhodopes, Bulgaria – new data about composition and manufacturing technology

Ceramic artifacts from the archaeological site “Biser”, located near the village of Biser, Haskovo region are studied. The artifacts from the Early Iron Age (EIA) have been characterized by optical, XRD, and SEM-EDS methods. The main part of the cherds shows similar composition. The raw material used for their manufacturing is well-washed clay. The temperature of the firing is in the interval between 500–550 °С to 800–850 °С. According to the petrographic characteristics and technological features of the production of the pottery, we supposed a local source of the raw material. The results for the composition of minerals such as plagioclase and amphibole (the main mineral inclusions) in ceramic artifacts confirmed the local source as well. The obtained data will help to identify the characteristics of the local ceramic production during EIA in the region.

Geochemical and petrographic investigation of the provenance of white marble decorative elements from the Roman Villa Armira in south-eastern Bulgaria

The paper presents evidence of Roman marble production in the Balkan region, specifically from the south-eastern Rhodope Mountain area (modern Bulgaria) and Armira. Although the Roman marble trade and production in antiquity are well known in Prokonnesos, Thasos, and several other production sites, marble deposits from inland Thrace have received far less attention. In 2018–2019, a systematic survey of south-eastern Bulgaria (Roman Thrace) was carried out by our team in collaboration with the National Archaeological Institute with Museum in Bulgaria. White marble quarries and outcrops were investigated in situ with the goal of characterizing the macroscopic qualities of the stone. Quarry samples were collected and analyzed through various techniques—petrography, isotopic, and chemical analyses—and compared with the architectural decorative marble and artifacts from the Roman villa at Armira. We demonstrate that the geochemical and petrographic features of these samples indicate a marble provenance restricted to a few selected sources. We conclude that the local marble from the Armira and Kamilski Dol quarries was widely used for the complete architectural program of the Roman villa of Armira.

Impact of Lithologic Heterogeneity on Brittleness of Cenozoic Unconventional Reservoirs (Fine-Grained) in Western Qaidam Basin

In order to understand the impact on reservoir brittleness of lithologic heterogeneity in the continental mixed fine-grained sedimentary rocks in the western Qaidam Basin, the mechanical properties of the rocks and their correlation with mineral composition and petrographic characteristics were studied. A total of 20 samples from two parallel groups (10 samples in each group) were analyzed by triaxial stress test mineralogy, and morphology. The results show that the reservoir rocks can be divided into five different types according to the mechanical properties of the reservoir (characterized by stress–strain curves), among which Types I and III belong to a similar elastoplastic failure model, Type II shows a special pulse failure mode for plastic material, Type IV shows a failure mode of mixed characteristics, and Type V exhibits a typical plastic failure model. The correlation between minerals and mechanical properties indicates that quartz and feldspar, which are often considered brittle minerals, do not contribute much to the brittleness of these continental fine-grained sedimentary rocks. The main minerals affecting the reservoir brittleness are dolomite and clay minerals, contributing positively and negatively to it, respectively. The petrographic analysis results prove that the abnormal correlation between rock mechanical properties and quartz and feldspar is caused by the different rock fabrics. When dolomite forms a rock skeleton, it typically exhibits greater strength, brittleness and physical properties than other minerals. Based on the results, a brittleness evaluation standard for continental unconventional reservoirs (fine-grained) is proposed, and the validity of the standard is verified by the spatial correlation between the lithology probability model and the micro-seismic monitoring data. This indicated that the spatial heterogeneity of the dolomite-rich rock is the main controlling factor for the effective development of the Cenozoic continental unconventional reservoirs (fine-grained) in the Western Qaidam Basin.

Geochemical, mineralogical and petrographical characteristics of the domanik formation from north samara region in the volga-ural basin, Russia: Implication for unconventional tight oil reservoir potential

This paper comprehensively analyzes the geochemical, mineralogical and petrographical properties combined with bulk kinetics modeling of the Domanik organic-rich carbonate from various depth intervals in Kuzminovsky oilfield (well № 26 R), Volga-Ural Basin, Russia. The results show that, the Domanik carbonate-rich samples are characterized by high content of the total organic matter (TOC) up to 13.31 wt %, and contain mainly Type II kerogen with a slight II/III kerogen type, reaching very good to excellent oil generation potential. Moreover, the studied samples contain hydrogen-rich kerogen, which expected to generate paraffin, naphthene and aromatic (P–N-A) oil with low wax content as demonstrated by the Py-GC Pyrolysis combined with the abundance of fluorescent alginite, amorphous organic matter, and bituminite as established from investigations via microscope. The maturity indicators demonstrated that, most of the examined Domanik carbonate-rich samples, with a burial depth between 1726.5 m and 1784.9 m, have generally reached low thermal maturity stages; thus, defining an immature to moderate-mature of oil generation window. The results of the kinetic models suggested that, Domanik carbonate-rich rocks with vitrinite reflectance (VRo) values in the range of 0.60–0.71%, have reached relatively low kerogen transformation ratio in the range of 10–20%, indicating low probability oil generation. These finding are confirmed by the presence of low oil saturation index of less than 100 mg HC/g rock (19.64–69.97). In addition, the results of thin section, scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) showed that the studied samples are characterized by low porosity (up to 3.29%) with a wide pores size range, including interparticle, cavities, cracks and organic matter pores. The development of these pore types and their quality in the studied samples is mainly controlled by high mineralogical brittleness (i.e., carbonate and quartz) together with the high organic matter inputs. Therefore, according to the obtained results, characteristics and observations, the Domanik Formation has a high potential for commercial oil production, which typically requires hydraulic fracturing followed by an in-situ retort, mainly by thermal methods such as steam injection and in situ combustion process.

Middle-Late Jurassic chronology and source-to-sink system of the Sikeshu section in the southern margin of the Junggar Basin, Xinjiang

With the improvement of isotopic testing technology, high-precision dating methods such as SHRIMP or LA-ICP-MS of detrital zircon have been used to analyze and infer the formation age of sedimentary basins, the source of detrital materials, and the tectonic background of the formation and widely used. The LA-ICP-MS zircon U-Pb dating method was used to study the detrital zircon in the Middle-Late Jurassic sandstone in the Sikeshu section of the southern margin of the Junggar Basin, Xinjiang. The results show that the detrital zircon ages are mainly 270~447Ma,240~440Ma,245~432Ma, and 286~360Ma. There are also several ancient zircon ages, mainly 945~1080Ma. Combined with zircon mineralogical characteristics, CL images, Th/U ratio, sandstone petrographic characteristics, and regional chronological data, the primary provenance of the Middle-Late Jurassic sandstone is mainly from the Yilinghabilga Mountains in the North Tianshan, and Carboniferous-Permian volcanic rocks, pyroclastic rocks and Carboniferous granites exposed in the Borokonu Mountains of the Central Tianshan Mountains. By comparing the age changes between the four sampling points, the change process of the North Tianshan-Middle Tianshan source-sink system is obtained. From west to east, the upper Devonian glutamate, the Middle Devonian carbonate, and the large granite bodies of the Carboniferous series constituted the early watershed. From the middle to late period of the Toutunhe Formation to the Xishanyao Formation, from east to west, the Cambrian and Silurian carbonate rocks and the large granites and other rocks formed the late water line.

Křídové pískovce u Ždírce nad Doubravou (Českomoravská vrchovina): materiál pro gotické sakrální stavby v širokém okolí

The narrow, 40 km long belt of the Cretaceous sediments called „The Dlouhá mez“ has been preserved along the NW-SE-striking Železné hory fault within crystalline rocks in the Eastern Bohemia (Fig. 1). The youngest relic of this belt corresponds to the middle part of Jizera Fm. of middle Turonian age. In the southeastern part of the „Dlouhá mez“ belt, these deposits have fine-grained, glauconitic sandstone nature. Near the town of Ždírec nad Doubravou, the sandstone had been exploited for a long time in several presently abandoned quarries and used as a building material. The old quarry at the margin of Ždírec nad Doubravou was founded in the end of the 13th century, and it was replaced by new quarries between Ždírec nad Doubravou and the village of Nový Studenec in the second half of the 19th century. This sandstone was discovered in four gothic buildings in the wide surroundings of these quarries within the course of the macroscopic investigation by the author. To confirm this discovery, the author carried out microscopic investigation of ten sandstone samples taken both in the quarries and in the gothic buildings. Petrographic features of the sandstone were also specified. Microscopic study confirmed the identical character of all studied samples. The identity of sandstone exploited in the quarries and sandstones used in gothic buildings was also demonstrated by the analysis of total SiO2 content. The sandstone is fine-grained, with matrix-supported texture, variable content of glauconite grains and fragments of silicisponge spicules and rare foraminifera tests. Muscovite and feldspars occur in accessory amounts. The sandstone is silicified and exhibits a porosity from 6–8 to 20 %. The pores with very elongated, needle-like form originated by diagenetic dissolution of silicisponge spicules while the diagenetic quartz penetrated the original clayey and possibly also calcareous matrix. The foraminifera tests were also silicified during this process. Within subordinate thin layers in sandstone, the content of terrigenous quartz grains drops below 25 % (20–22 %) while the content of silicisponges fragments increases to 10–12 %. These layers can be classified as spiculitic, sandy silicite. The sandstone from Ždírec nad Doubravou was documented in two village churches (Krucemburk, Havlíčkova Borová), in a big church in the town of Havlíčkův Brod and in the chapel in the Lipnice Castle in the town of Lipnice nad Sázavou. These buildings originated in the last quarter of the 13th and in the 14th century. These localities are from 4 to 32 km away from the quarries near the town of Ždírec nad Doubravou (Fig. 1). The sandstones were used as ashlar masonry, window jambs and tracery, vault ribs and also in sculptures (figural corbels). A further investigation can probably reveal the Ždírec nad Doubravou sandstone in a higher number of medieval buildings.

Petrographic characterization of historic mortar as a tool in archaeologic study: Examples from two medieval castles of Aosta Valley, Northwestern Italy

In the present work is reported the study of historical mortars sampled in the two medieval castles of Châtel Argent and Quart (Aosta Valley, NW Italy), which in recent years are subject to restoration projects.All the samples were subjected to a petrographic analyses with an optical microscope, in order to recognize and compare the minerals constituting the main aggregates with the geological formations surrounding the areas where the castles stand.Four mortar samples were analyzed for each castle with the scanning electron microscope (SEM-EDS system). This procedure allows us to know the composition of the binder (not distinguishable on the basis of a petrographic analyses under an optical microscope), to calculate indices related to the composition of the binder, to analyze the composition of the main minerals present in the aggregate.Then, compositional X-ray maps were performed, in order to investigate the relative abundances of the different elements and calculate other important information of the mortars such as the hydraulic index, the porosity distribution and the abundance of aggregate with respect to the binder.The analytical protocol allowed us to define not only the characteristics of the individual mortars, but also to detect the area of provenance of the raw materials used for their realization, guiding the choice of the best materials for future restoration operations.

Field and Petrographic Characteristics of Photang Thrust Sheet of Zanskar Tethys Himalaya, Ladakh, India

The Photang thrust sheet is a distinct complex of rocks that lies under the Spongtang ophiolite, showing almost complete ophiolite sequences. The pre-collision tectonic setting, emplacement age, mechanism of association of diverse litho-units within Spongtang klippe, and their regional correlation is still debatable and partially known. The controversy exists as to whether the ophiolite was obducted onto the northern passive margin of the Indian plate during the Eocene or the late Cretaceous. Moreover, the fundamental question emerges whether the Photang thrust sheet is a part of the independent Spong arc, has been tectonically derived from the Ophiolitic Melange Zone in the Dras island arc, or is a representative of the accreted seamounts of the Indus suture zone. This paper presents the application of fundamentals of field geology and petrography to understand the pre-collision tectonic setting of the Photang thrust sheet, Spongtang ophiolite, and associated rock sequences in the Photoksar region of the Zanskar Himalaya. Keywords: Photang thrust sheet, Spongtang ophiolite, Tectonic setting, Obduction, Ophiolitic Melange Zone, Indus suture zone, Himalaya