Lithic Fragments Research Articles

Geochemical characteristics of shoreline sediments from the Bay of Bengal, Bangladesh: Implications for provenance and source‐rock weathering

The detrital mode and geochemical composition of sediments from a coastal section of the Bay of Bengal, Bangladesh, were examined to identify sediment distribution, maturity, provenance and source‐area weathering. The sediments are quartz‐rich with little feldspar and few lithic fragments (Q78F10L12), indicating derivation from a quartzose recycled orogen. The sediments exhibit high SiO2 (88–94 wt%) and low Al2O3 (4–5 wt%) contents. SiO2 shows a marked linear trend and strong negative correlation with Al2O3 (r = −0.95), consistent with the high quartz content. The upper continental crust (UCC) normalization patterns for the sediments show marked depletion in Na2O, CaO, MgO, Sr, Sc and Fe–V, but slightly increased Th and SiO2, indicating a felsic UCC source. The sediments have low to moderate compositional maturity and are classified as sublitharenite. The Al2O3/TiO2 ratio (15–38) suggests that the sediments were derived from intermediate to felsic igneous rocks. Rare‐earth element profiles, discrimination diagrams and various elemental ratios are all consistent with the derivation of the sediment from a felsic igneous source area. The values of the chemical index of alteration (~65–69), chemical index of weathering (~75–84) and plagioclase index of alteration (~70–81) indicate that the source rocks underwent moderate chemical weathering. Comparison with potential Himalayan sediment sources and rocks support derivation of the investigated shoreline sediments from felsic quartzose recycled detritus of that area.

Research on Diagenetic Evolution and Hydrocarbon Accumulation Periods of Chang 8 Reservoir in Zhenjing Area of Ordos Basin

The Mesozoic Chang 8 Section in the Zhenjing area is a typical low permeability-tight sand reservoir and is regarded as the most important set of paybeds in the study area. Guided by the principles of basic geological theory, the diagenetic evolution process and hydrocarbon accumulation periods of the Chang 8 reservoir in the study area were determined through various techniques. More specifically, core observation, scanning electron microscopy (SEM), X-ray diffraction (XRD), and vitrinite reflectance experiments were performed in combination with systematic studies on rock pyrolysis and the thermal evolutionary history of basins, the illite-dating method, and so on. The Chang 8 reservoir is dominated by feldspar lithic and lithic feldspar sandstones. Quartz, feldspar, and lithic fragments are the major clastic constituents. In clay minerals, the chlorite content is the highest, followed by illite/smectite formation and kaolinite, while the illite content is the lowest. The major diagenesis effect of the Chang 8 reservoir includes compaction, cementation, dissolution, metasomatism, and rupturing. The assumed diagenetic sequence is the following: mechanical composition → early sedimentation of chlorite clay mineral membrane → early cementation of sparry calcite → authigenic kaolinite precipitation → secondary production and amplification of quartz → dissolution of carbonate cement → dissolution of feldspar → late cementation of minerals such as ferrocalcite. Now, the study area is in Stage A in the middle diagenetic period. Through the inclusion of temperature measurements, in conjunction with illite dating and thermal evolutionary history analysis technology in basins, the Chang 8 reservoir of this study was determined as the phase-I continuous accumulation process and the reservoir formation epoch was 105~125 Ma, which was assigned to the Middle Early Cretaceous Epoch.

Diagenesis and controlling factors of Oligocene Huagang Formation tight sandstone reservoir in the south of Xihu sag, the East China Sea Shelf Basin

Considerable amounts of efforts have been made in search of depositional sand quality and diagenetic processes on the quality of low-permeability and tight reservoirs mainly due to the realization that these multiple factors exert profound controls on reservoir quality. This study evaluated the role played by original components and diagenetic processes on reservoir quality evolution of Oligocene Huagang Formation reservoir in the south of Xihu sag from braided river delta (H3, H4 and H5) to meandering river delta (H6 and H7). By a multi-disciplinary approach of thin section identification, scanning electron microscopy, grain size analysis, mineral phase analysis, and X-ray diffraction, the petrological characteristics, grain structure, and diagenesis of five of the layers (H3, H4, H5, H6, and H7) of Huagang Formation in the Western slope belt (WSB), the Western sag (WS) and the Central uplift belt (CUB) were studied. It was determined that the reservoirs are mainly composed of fine-medium sandstone (94.1%) and feldspathic lithic quartz sandstone (Q65.6F15.8L18.6). The E3H reservoirs in WSB and CUB Ⅲ structural belt are of conventional types with an average porosity of 13.2% and permeability of 30 × 103 μm2, and reservoirs in WS, CUB Ⅰ and CUB Ⅱ are mainly tight sand with an average porosity of 7.8% and permeability of 2.9 × 103 μm2. Furthermore, quantified characterization of diagenetic factors on porosity was revealed by multiple regression analysis to find out the depositional and diagenetic controls on reservoir quality. The effect of sorting, grain size, rigid lithic fragment, argillaceous content, compaction and feldspar dissolution have been identified as main contributing factors for reservoir quality evolution of E3h sandstones, notably post-depositional processes on the deep (3500–4500 m) and ultra-deep (>4500 m) tight sandstone reservoirs (DUDTSR) with high degree of diagenetic stage. Therefore, a better understanding of diagenesis will provide an efficient approach for evaluation and prediction of the DUDTSR.

Provenance of Mesozoic sandstones from the northwestern Gulf of Suez, Egypt: new evidence from petrography and whole-rock geochemistry

New investigations of petrographic and geochemical characteristics of Mesozoic sandstones from the northwestern Gulf of Suez in Egypt have been undertaken, documenting dominance of quartzose sandstones containing on average ~ 5% of mostly sedimentary and subordinately metamorphic lithic fragments (siltstone, sandy siltstone, and, more rarely slate, metasiltstone, limestone, dolostone, quartz-muscovite schist, and gneiss). These sandstones are depleted in many chemical elements and display low Al2O3/SiO2 and K2O/Na2O ratios. Mineralogical and geochemical parameters point at extensive recycling from older (i.e., Paleozoic) siliciclastic strata. Relatively constant composition throughout the Mesozoic contrasts with successive palaeogeographic changes associated to the major events of rifting and dispersal, which may be explained by the widespread distribution of Paleozoic clastic wedges all across northern Gondwana.

Detrital zircon ages of Oligocene to Miocene sandstone suites of the Southern Apennines foreland basin system, Italy

U–Pb spot ages on detrital zircons from turbidite quartzarenites, quartz-feldspathic and volcaniclastic sandstones of the Tufiti di Tusa (TTF), Numidian Flysch (NF), Bifurto (BF), Gorgoglione (GF) and Serra Palazzo (SPF) formations, exposed in southern Italy, were detected to define their provenance signatures aiming to contribute to reconstructing the complex geodynamic evolution of the southern Apennine chain. The deposition ages of these sandstones range from Rupelian (TTF), Burdigalian p.p. -Early Langhian (NF and BF) and Langhian-Serravallian -Early Tortonian (GF and SPF). The detrital zircon ages in each deposit show different clusters. In TTF, the zircon age clusters are: 610 ± 6 Ma; 390 ± 4 Ma; 287 ± 3 Ma; 157 ± 2 Ma; 78 ± 1 Ma and 67 ± 1 Ma; 33 ± 1 Ma. In NF and BF formations, the prevalent zircon ages are clustered at 661 ± 10 Ma, 607 ± 8 Ma and 547 ± 8 Ma. In GF sandstones, the ages of detrital zircons are clustered around 672 ± 28 Ma, 458 ± 9 Ma, 297 ± 8 Ma and 24 ± 1 Ma. The sandstones of SPF contain zircons showing age clusters at 649 ± 10 Ma, 486 ± 7 Ma and 315 ± 5 Ma. Zircons and lithic fragments from TTF display a dominant provenance from Oligocene calc-alkaline effusive products located on western domains of the Mesomediterranean Microplate, and minor detritus from granitoids and metamorphic rocks of Variscan ages. Zircons of NF and BF indicate a provenance of detritus from the African Craton without evidence of Variscan or Alpine signatures. Zircons from GF and SPF show a provenance from both Variscan crystalline basement rocks forming the Alpine chain (Calabria-Peloritani Terranes) and Variscan magmatic and metamorphic rocks unaffected by Alpine tectonics, similar to Sardinia–Corsica (pro-parte) block. In addition, the Oligocene magmatic component dated at 24 Ma in GF sandstones is evidence for the maximum age of sedimentation for these deposits. In light of the recent and preliminary geochronological data acquired, a revised paleogeographic restoration could be inferred for the location of sedimentary basins during the Apennines tectonic evolution. The Rupelian sedimentation age of TTF suggests that the deposition domains of the Numidian sequences and the successive deposits of GF and SPF, were located in a more complex paleogeographic scenario along the orogenic system.

Identification and quantitative evaluation of pores and throats of a tight sandstone reservoir (Upper Triassic Xujiahe Formation, Sichuan Basin, China)

Pores and throats are the key parameters for determining the pore structure and fluid flow behavior in tight sandstone reservoirs. In this paper, pores and throats of the tight sandstone reservoir of the Upper Triassic Xujiahe Formation in the northern Sichuan Basin were investigated using classical petrography, scanning electron microscopy, and confocal laser scanning microscopy. In addition, a method of pore as well as throat identification and quantitatification using high-pressure mercury injection (HPMI) measurements was worked out. The results show that clay mineral-related pores are well developed in lithic sandstone and feldspathic lithic sandstone in addition to pores produced by dissolution of calcite cement and clastic grains. Intergranular pores are connected by lamellar, curved lamellar, and narrow pore throats. The pores and throats associated with intragranular dissolution and clay minerals are mostly tube shaped. The rapid-increasing and slow-increasing profiles of the mercury injection curves represent the dominance of pores and throats, respectively, allowing to differentiate pores and throats. Calculations show, in addition to fractured lithic sandstone, that has micron-sized pore–throat systems, the other lithic sandstones possess dominatly nano-sized pore–throat systems. In case of feldspathic lithic sandstones, micron-sized and nano-sized pore throat systems are equally important. In micron-sized pore throat dominated reservoirs, the pore volume is slightly larger than the throat volume, whereas for the nano-sized pore throat system, the pore volume is considerably larger than the throat volume. The key factors that are favorable for the formation of lithic sandstone pore throat systems are early calcite dissolution, lithic fragments dissolution, and early chlorite cementation. In contrast the key factors that are favorable for the formation of feldspathic lithic sandstone pore throat systems are dissolution of feldspars and lithic fragments.

Compositional and Geochemical Signatures of Oligocene volcanoclastic sandstones of Abbasabad-Kahak area, NE Iran: Implications for provenance relations and paleogeography

Petrography and geochemistry of sandstone for the lower Oligocene volcanic-related sandstones of Abbasabad-Kahak area, NE Iran, are detected to decipher provenance, tectonic setting and paleo-weathering of source areas. Lower Oligocene sandstones are grey in colour and host copper mineralization as bedded and lenticular, vein-veinlets and disseminated textures and structures. Texturally, sandstones are medium to coarse grained, moderately to poorly sorted and compositionally have abundance of volcanic lithic fragments. Sandstones are lithofeldspathic to feldspatholithic, leading to a provenance from the progressive dismantling of a magmatic arc. Geochemical signatures suggest a derivation from mafic-to-intermediate volcanic sources. CIA values (56–61 with the average of 57) indicate a low level of chemical weathering in source areas, which may reflect arid to semi-arid climatic conditions in source terrains. These sandstones, deposited in a remnant backarc basin, are the results of the post-Eocene extensional stage of a dismantling magmatic arc.

Hydrocarbon prospectivity of the miocene-pliocene clastic reservoirs, Northern Taranaki basin, New Zealand: integration of petrographic and geophysical studies

In this study, it is aimed to characterize the Early pliocene sandstone (EP-SD) and the Late Miocene-Early Pliocene Mangaa sandstone reservoirs and the efficiency of their sealing cap rocks using the petrographical and petrophysical data of these sandstone zones in northern Taranaki basin, New Zealand. The prospective potential reservoirs were studied using impregnated thin sections, XRD data analysis, and well log data (self-potential, gamma-ray, sonic, density, neutron, shallow\\deep resistivity and PEF) to characterize the reservoir zones, in addition to Mercury intrusion capillary pressure data (MICP) to check the efficiency of some potential seals. The EP-SD and the Mangaa sandstone units are typically poorly consolidated very fine sandstone to siltstone, with porosities averaging 25%. The sands are composed of quartz (38.3–57.4%), with common feldspars (9.9–15.2% plagioclase, and 2.7–6.3% K-feldspars) and up to 31.8% mica. In Albacore-1 well to the north of the Taranaki Basin, the Mangaa formation includes three separate for each of the EP-SD zones (EP-SD1, EP-SD2, and EP-SD3), and the Mangaa sequence (Mangaa-0, Mangaa-1, and Mangaa-2). The thin section studies indicate that, the studied samples are grouped into greywackes, arenites and siltstone microfacies with much lithic fragments and feldspars, sometimes with glauconite pellets. From the XRD data, it is achieved that the mineral composition is dominated by quartz, mica/illite, feldspars, and chlorite. The petrophysical investigation revealed absence of pay zones in the EP-SD zones, and presence of thin pay zone with net thickness 5.79 m and hydrocarbon saturation of about 25.6%. The effective porosities vary between 23.6 and 27.7%, while the shale volume lies between 12.3 and 16.9%. Although the shale content is relatively low, the relatively high API (50–112 API of average 75 API) is contributed by the relatively high K-feldspar content and intercalations with thin siltstone and muddy siltstone beds. Sealing units include the intra-formational seals within the Mangaa sequence, mudstones and fine grained units overlying the Mangaa and further intra-formational mudstones, within the shallower EP-SD units. The efficiency of these seals indicates the capability to trap 16.4–40.6 m gas or 17.4–43.0 m oil which is relatively low in correlation with their efficiency in the central parts of the Taranaki Basin Overlying the primary seals, mudstones of the Giant Foresets Formation provide additional regional seal.

Lithologic, geomorphic, and climatic controls on sand generation from volcanic rocks in the Sierra Nevada de Santa Marta massif (NE Colombia)

Tectonics, climate, and lithology are the three main factors controlling the generation and transfer of sediments as well as their textural and compositional signatures. In this paper, we investigate the generation of sands from volcanic rocks in nine drainages with mixed lithological assemblage in a high-relief – subtropical climate setting (Sierra Nevada de Santa Marta, NE Colombia). The integration of geomorphological analysis with sand petrography, and bulk-rock and clay geochemistry allows us to constrain the dynamics regulating the generation of sediments derived from felsic and mafic-intermediate volcanic basement rocks in relation to plutonic and metamorphic lithologies. The petrographic composition of modern fluvial sands from the area is extremely variable (litho-feldspatho-quartzose, feldspatho-quartzose, and quartzose-feldspatho-lithic), but it reveals a strong dilution of (especially mafic) volcanic compositional signals, and a consequent overrepresentation of plutonic and metamorphic lithologies. Traditional chemical weathering indices fail to represent the extent of chemical alteration, but instead seem to favour preservation of provenance signals. Chemical weathering primarily affects feldspars and the ferromagnesian groundmass of mafic volcanic rock fragments. Enrichment of ferromagnesian elements in the clay fraction supports the notion that mafic volcanic rock fragments are unstable relative to plutonic and metamorphic rocks. Drainage features (particularly river network and relief) control the abundance of volcanic lithic fragments and the rates and extent of chemical weathering. A linear log-ratio model permits us to quantify sediment generation from volcanic rocks in this mixed-lithology setting. The results indicate that even in the case where volcanic grains are practically absent in the sand fraction, there could still be up to 20% of volcanic rocks in the drainage basin, and in the case that 50% of the sand grains are volcanic, around 75% of drained lithologies are expected to be volcanic. Our results demonstrate that the contribution of volcanic detritus to modern sands systematically underrepresents the areal proportion of volcanics rocks in mixed source areas. Post-depositional diagenetic modifications are likely to alter and/or dissolve volcanic lithic fragments, making accurate reconstruction of sediment provenance even more difficult. Sediment-generation models based on a range of mixed lithologies in various tectonic and climatic settings will be needed to improve estimates of the abundance of volcanic rocks in drainage basins of ancient sediment routing systems.

Petrography and geochemistry of the Middle Jurassic Fort Member Sandstone, Jaisalmer Formation, Western India: Implications for weathering, provenance, and tectonic setting

Detrital mineralogy, major oxides, trace, and rare earth elements (REE) were examined in the Middle Jurassic Fort Member Sandstone (FMS) of the Jaisalmer Formation in Western India to understand palaeoweathering, provenance of sediments, and to decipher the tectonic setting. The sandstones are classified as arkose to sub‐litharenite types according to their relative percentages of quartz, feldspar, and lithic fragments, and major elemental ratios. The values of Chemical Index of Alteration (67–85), Plagioclase Index of Alteration (78–97) and Chemical Index of Weathering (83–97) along with A‐CN‐K diagram suggest moderate to intense chemical weathering in the source region. Presence of fresh feldspars and dominance of monocrystalline quartz, showing both parallel and undulose extinction, indicate plutonic and volcanic felsic igneous provenance. Contribution from metamorphic orogen sources is indicated by the lithic fragment population. Various geochemical parameters such as Th/Sc, Cr/Th, Ti/Zr, and Eu/Eu* support a dominant felsic provenance. Higher Zr/Sc ratios relative to the magmatic Zr/Sc‐Th/Sc trend, higher Zr and Hf concentrations in the FMS indicate some extent of sedimentary recycling and zircon sorting. LREE enrichment, flat HREE pattern, negative Eu anomaly and trace element ratios, in conjunction with palaeocurrent data, indicate a likely sediment contribution from basement source terrains including Erinpura‐Mount Abu‐Sirohi granites, Malani Igneous Suite, and Aravalli‐Delhi orogens. The major and trace element tectonic setting discrimination diagrams for the FMS indicate a passive margin setting.

Sedimentary environment and tectonic setting of the clastic formation of the Tanjianshan Group in the Tuomoerrite area, North Qaidam

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物，也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究，而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中，对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段，其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合；上岩性段包含海底扇内扇、中扇和外扇沉积，且以中扇环境的沉积为主。垂向上，它们呈现出粒度向上逐渐变细特征；空间上，具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩，其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩；长石主要为斜长石；石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主，并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育，呈现出典型的浊流沉积特征；同时在局部露头见有滑塌构造和波痕。区域上，这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧；古水流分析显示，它们的碎屑物质主要来自于其北东方向。这些结果表明，柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。;Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

The Design and Realization of Intelligent Classification of Rock Samples Based on Convolutional Neural Network

With substantial improvement of computer hardware performance and rapid development in artificial intelligence research, artificial intelligence recognition technology has been applied in many industries, such as medicine, education, industry, commerce, exploration and other professional fields. In geological exploration, the classification and identification of rock samples is an important link in geological analysis. However, the traditional manual classification faces high economic and time costs, and is vulnerable to subjective judgment which may affect the recognition result. In order to avoid these problems, research is carried out on the specific application of computer-based artificial intelligent recognition technology in recognition of rock images and the performance difference caused by different parameters. The sample data used in the experiment are lithic fragments and core samples capture by industrial cameras at the well logging site, with a total of 350 images which cover 7 types of rock samples. In this paper, the 350 rock images are divided into training set, validation set and test set based on certain proportion. Since the data set is too small and the quantity of each type of rocks varies, data augmentation technology is used to expand the original data before training. During the expansion, the quantity of different types of rock samples are balanced. At the training stage, the open-source deep learning framework Pytorch is used to construct a multi-layer convolutional neural network for learning and classification training on the training set. The best accuracy rate in the tests reaches 82.86%. However, the recognition rate is poor for stretched images, which required further optimization of the network structure. Based on the experimental results, the optimization orientations of neural network training are summarized, including improvement of data set quality, optimization of network structure, and adjustment of training strategies. In order to display the experimental data as intuitively as possible, data visualization tools such as PlotNeuralNet and Python matplotlib are used in the experiment for specific visualization work, after which the experimental data and model effect are analyzed from the perspective with combination of data and images.

Climate-driven drainage reorganization of small mountainous rivers in Taiwan (East Asia) since the last glaciation: The Zhuoshui River example

As an important component in East Asia sediment source-to-sink systems, small mountainous rivers in Taiwan deliver disproportionately large amounts of sediments to oceans. Although the modern fluvial sediment transport processes, discharge fluxes and sediment compositions have been well investigated, the drainage evolution of these mountainous rivers remains understudied and sediment fluxes are expected to vary greatly in glacial-interglacial cycles due to the tremendous climatic fluctuations. To define how the drainage of Taiwan mountainous rivers has evolved since the last glaciation, we target a sediment core (98 m in length) from the Zhuoshui River delta, western Taiwan and conduct sediment petrography, heavy mineral analysis, detrital zircon U Pb geochronology and clay mineralogy to investigate provenance variations and river basin evolution since 60 ka. Sediments of the last glaciation show comparatively high illite crystallinity index values, low metasedimentary lithic fragment and stable heavy mineral contents and similar detrital zircon U Pb ages with downstream signatures, indicating prominent sediment contributions from the Coastal Plain and Western Foothills regions (elevation <1 km) during the glaciation. However, characteristics of the deglacial and Holocene sediments indicate high contributions from the higher Hsueshan Range and Central Range regions (elevation >1 km). We suggest that headward extension and drainage capture since the deglaciation, which was most likely due to the increasing monsoon rainfall, account for the provenance variations in the discharged sediments. This implies a climate-driven drainage reorganization of the small mountainous rivers in Taiwan since the last glaciation. Our findings highlight the previously-overlooked, variable provenance information from Taiwan in glacial-interglacial cycles, and the dynamic source signatures are important to East Asia sediment source-to-sink studies. • The provenance of Zhuoshui River sediments has changed since the last glaciation. • The provenance variation was caused by climate-driven drainage reorganization. • The river system of Zhuoshui River was not developed during the last glaciation. • The Zhuoshui River headward extended and captured other basins in the Holocene.

The Provenance and Tectonic Settings of the Greywacke Member of the Late Neoproterozoic Hazara Formation Lesser Himalayas, Northern Pakistan: Evidence from Geochemistry and Petrography

The petrographic and geochemical analysis of the greywacke horizon of the late Neoproterozoic Hazara Formation from the Hazara Mountains has been investigated to determine the provenance, tectonic settings and weathering history of the sediments. The Late Neoproterozoic Hazara Formation is a thick sedimentary sequence comprising of greywacke, shale, argillites, siltstone, and limestone. The greywackes are characterized by fine to medium-grained, moderately sorted and sub-angular to sub-rounded framework grains. They are rich in quartz, lithic fragments and clay minerals. The petrographic investigation of the greywackes categorized them as feldspathic greywacke in the QFR diagram. The quartz content is higher in sandstone and may reach to 70%, which indicates a weathered felsic source. Chemical Index of Alteration values of greywacke suggests that the source region has experienced highly weathering conditions with a warm and moist climate. Various geochemical interpretations, elemental ratios like Th/Sc, La/Sc,Th/Cr, and positive Eu anomalies indicate that the greywackes of the Hazara formation derived from a felsic source and were deposited within an active continental margin tectonic settings. The main source area of the sediments of the greywackes was located to south to southeast, which may possibly be the Aravali orogeny, central Indian craton and Bundelkhand craton. Finally, the geochemical data of the major elements point to a felsic igneous provenance for the greywacke.

Lithofacies and petrochemical characterization of volcano-sedimentary sequence of Chandil Formation around Kharidih-Bareda area, Seraikela-Kharsawan District, Jharkhand: implications for uranium mineralization

Mesoproterozoic Chandil Formation (ca. 1600 Ma) of North Singhbhum Mobile Belt record numerous features of felsic volcaniclastics and felsic to intermediate volcanics preserved in the central sector of the fold belt around Kharidih-Bareda area, Seraikela-Kharsawan district, Jharkhand. The felsic volcanic rocks exhibit flow bands, autoclasts and layering of crystal mushes revealing viscous nature of eruptives. The volcaniclastic sediments comprise of significant proportion of volcanic epiclasts and accidental lithic fragments. These volcaniclastics have been categorized into five prominent lithofacies viz, stratified lapilli tuff, banded tuff, tuff with penecontemporaneous deformation, welded lapilli stones, vitric tuff and volcanic bombs by field and petrographic studies of outcrops and subsurface borehole cores. The welded lapilli tuffs display fiamme and eutaxitic texture. Interlayering of the volcaniclastics, which are most often pyrite-rich, with psamo-pelitic lithology like carbonaceous phyllite, variegated phyllite, quartzite and minor limestone is suggestive of marine euxenic depositional environment. Petrographic study of the volcaniclastics indicated presence of glass shards, garnet phenocrysts, spherules of tremolite, ovoid to lenticular accretionary lapilli along with devitrified glassy material. Compositionally these felsic volcanics and volcaniclastics are rhyodacitic to andesitic in nature with peraluminous to meta aluminous in character. A/CNK values vary from 0.52 to 2.42 in felsic volcanics and from 0.12 to 1.63 in volcaniclastics. Signatures of arc magmatism is indicated by low concentration of HFS elements such as Nb (5-17 ppm), Ga (11-17 ppm) and Y (5-28 ppm). Elevated intrinsic content of uranium (3-8 ppm), Th/U ratio ranging from 1.2 to 13.2, presence of metamict allanite and zircon in volcanics and volcaniclastics reveal their suitability as a prospective source for search of uranium mineralization. The volcanic-volcaniclastic-clastic association of the Chandil Formation provides an ideal situation where provenance and province both are available. Thus, suitable litho-structural locales such as the concealed shear zones sympathetic to the Dalma thrust and South Purulia Shear Zone within the volcano-sedimentary package of Chandil Formation may be targeted as preferable sites for locating concealed uranium mineralization.

A compilation and characterisation of lithics in kimberlite and common maar-diatremes and tephra ring deposits

Maar-diatreme volcanoes are the second-most common type on land, occurring in volcanic fields within all major tectonic environments. Their deposits typically contain an abundance of lithic fragments quarried from the substrate, and many contain large, deep-sourced lithic fragments that were erupted to the surface. Primary volcaniclastic deposits fill the diatreme structure formed during eruption. There is negligible inelastic deformation of diatreme-adjacent country rock, indicating that country rock is removed to create the diatreme structures, either by being shifting downward below observable levels, ejected upward to contribute to surficial deposits, or dissolved and hidden in magma erupted or intruded at depth. No previous study has systematically reviewed and analysed the reported lithic fragments of maar-diatreme systems. We present a comprehensive compilation from published work of lithic characteristics in maar ejecta rings and in diatreme deposits of both common and kimberlite maar-diatremes. For maar-diatremes and their tephra ring deposits, we find no correlations among lithic clast sizes, shapes, depositional sites, and excavation depths. This is difficult to reconcile with models involving systematic diatreme deepening coupled with tephra-ring growth, but consistent with those involving chaotic explosions and mixing. Larger amounts of data are needed to further examine how these types of volcanoes operate.

Petrofacies investigations of the Cretaceous Pab Formation Rakhi Gorge Eastern Sulaiman Range Pakistan - Implication for reservoir potential

Petrologic investigations of the sixty representative thin sections from the Pab Formation within Rakhi Gorge section Eastern Sulaiman Range Pakistan have been used to characterize different diagenetic patterns, identification of primary composition and reservoir characters. Sublithic, lithic and quartzose sandstones have been the principal constituents of the formation. The processes responsible for the late-stage alteration and diagenetic processes identified during the petrographic study include compaction of lithic fragments and mud clasts, formation of quartz overgrowth structures, feldspar replacement and alteration, cementation, and replacement of grains by clay minerals other ferrous elements and diagenetic minerals. The study shows that the initial porosity has been primary intergranular, but the secondary porosity has been originated in the rocks as a result of the alteration of the primary and secondary constituents, as well as fracturing. These facies characters replicate the reservoir quality including, good, medium, low-quality, and non-reservoir. Samples displaying average total porosity greater than 10 % have been declared as good quality. While rocks samples having 7 % or greater porosity are grouped as a medium reservoir. Those samples consisting of porosity values between 1 and 4% are considered as a low quality reservoir while those samples having porosity ranges low than 1% have been called non-reservoir. Based on the investigated parameters the studied samples from the Pab Formation displayed the characters of a medium reservoir that may hold significant hydrocarbon. This different quality including good and low quality zonation can be attributed to the facies and diagenetic change in the formation.

Lithofacies architecture and paleoenvironment of a Paleoproterozoic volcano-sedimentary sequence: Insight into rift-related volcanism during supercontinent assembly

The greenschist to lower-amphibolite facies, Proterozoic (Orosirian: ca. 1883–1848 Ma) Aillik Group in Labrador, Canada, comprises a well-preserved example of subaqueous to intermittently subaerial volcanism and sedimentation. The group consists of interlayered sedimentary, volcaniclastic, pyroclastic and bimodal volcanic units that exhibit well-preserved depositional and structural relationships. Cumulatively, these lithofacies significantly demonstrate the evolution of Paleoproterozoic volcanism during the assembly of the supercontinent Nuna. A minimum stratigraphic thickness of 14.9 km of the Aillik Group is exposed along the coast of Labrador and is divided into two successions. The western stratigraphic succession consists of subaerial to subaqueous sandstone, siltstone, conglomerate, resedimented tuffaceous sandstones, and tuffaceous conglomerate with lesser rhyolite flows and felsic tuff. The eastern stratigraphic succession is dominated by felsic tuff and rhyolite, lesser pillowed to massive mafic lavas, and in situ and resedimented mafic tuff. Mafic rocks are basaltic, whereas felsic rocks comprise high-silica rhyolites and tuffs. Primary subaqueous pyroclastic deposits are indicative of explosive activity, an observation also supported by the presence of accretionary lapilli and an abundance of lithic fragments in epiclastic deposits. The volcano-sedimentary lithofacies of the Aillik Group are consistent with that observed in modern intra-arc or arc-rift settings, and the succession is interpreted to have formed in a localized back-arc rifting environment within an overall complex convergent margin.

Mineral assemblage and provenance of the Pliocene Viviparus beds from the Area of Vukomeričke Gorice (Central Croatia)

Viviparus beds are sediments deposited in lacustrine and fluvial freshwater environments (Lake Slavonia) during the Pliocene and the earliest Pleistocene. A detailed field study and mineralogical, petrographic and chemical analyses were carried out to determine their composition and origin in the area of Vukomeričke Gorice, Central Croatia. Viviparus beds are characterized by the vertical and lateral exchange of mineralogically and chemically mature pelites and sands. Pelitic sediments consist mainly of detrital quartz, calcite, dolomite and feldspar grains, with smectite as the most common clay mineral. Quartz and the most resistant lithic fragments dominate the sandy detritus. The composition of the sediments indicates their origin from the recycled orogen, while their textural immaturity suggests a short transport distance. Most of the material was re-deposited from the underlying Upper Miocene sediments, originally of Alpine provenance. A lesser proportion originated from Palaeogene sediments, Triassic carbonate rocks, basic or acidic magmatic rocks and metamorphites. The Medvednica and Žumberak Mts. were the most important source areas, while a smaller proportion of the material could have come from the Moslavačka gora Mt. and Banovina region. The uniform composition of the Viviparus beds over the entire vertical distribution of the sediments clearly indicates that the source areas did not change during their deposition. A significant change from the texturally and compositionally mature Upper Miocene clastic detritus of alpine origin, to the texturally immature material of the Viviparus beds of local origin is a consequence of compression and inversion of the previously extensional basin resulting in the uplifting and erosion of the mountains within the SW part of the Pannonian Basin System.

Early Cretaceous uplift of the Jiaobei Terrane: Evidence from the detrital zircon and sediment compositions of sandstones in the Jiaodong Peninsula, China

In this study, we conducted sandstone petrography analyses and determined detrital zircon U–Pb ages and Hf isotopes for sandstones collected at different stratigraphic levels of the lowest strata of the Laiyang Group. All results nearly point to an evolutionary trend for the source regions of the strata. The detrital zircon U–Pb results reveal multiple age groups at 140–123 Ma, 810–700 Ma, and 2,500–1,750 Ma, but variable age proportions for two sandstones (19LY‐01Z and ‐05Z) collected at lowermost and middle levels of strata, respectively, but only one unimodal age mode at ca. 1,850 Ma for the uppermost sandstone 19LY‐09Z. Provenance analysis illustrates that the lower strata likely include two source regions, including the Jiaobei Terrane and the Sulu orogen, whereas the upper strata appeared to have one dominant source region (i.e., Jiaobei Terrane). Framework modes of sandstones display that lower samples contain more metamorphic lithic fragments, which corresponds to the recycled orogenic field in the Q‐F‐L diagram, while middle‐upper samples are enriched in feldspars but deficient in lithics and plot in the basement uplift field of the Q‐F‐L diagram. This compositional variation reflects an evolution of the source regions from the Sulu Orogen to the Jiaobei Terrane, completely consistent with the observation of an increase in the amount of detrital zircons sourced from the Jiaobei Terrane, but decreasing detrital zircons from the Sulu Orogen in an upward order. This shift in the provenance of sediments reflects two tectonic events including exhumation of the Sulu Orogen to the surface before sedimentation of the Laiyang Group, and a rapid uplift of the Jiaobei Terrane after ca. 125 Ma following removal of lithospheric mantle.