Textural Maturity Research Articles

ANÁLISE DO COMPORTAMENTO EROSIVO E CARACTERIZAÇÃO SEDIMENTOLÓGICA DA BARRA ARENOSA NA FOZ DO RIO ITABAPOANA, PRESIDENTE KENNEDY-ES

The state of Espírito Santo, despite being the smallest in the Southeast region, presents a significant diversity in the variations between the effects of retrogradation and coastal progradation. This dynamic is influenced by a complex interplay of variable factors, such as coastal geomorphology, hydrodynamics, and geology, which directly affect coastal cities and their development. The objectives of this study are to understand the phenomenon of coastal erosion and to analyze the morphological behavior of the sandy bar at the mouth of the Itabapoana River and at Praia das Neves, generating relevant information for the preservation of the coastal environment and minimizing material losses in urban areas adjacent to the sea. This work used tools such as the Ground Penetrating Radar (GPR) for the interpretation of radarfacies, as well as remote sensing and satellite image geoprocessing methodologies, combined with sedimentological characterization studies applied to Environmental Geology. The integration of GPR data revealed a complex sedimentary dynamic, with reflectors that indicate the progradation of beach deposits, as well as eolian, fluvial and marine influences, observing the presence of filled paleochannels and fluvial deposits. The analysis of satellite images allowed us to identify variations in the morphology of the beach and the location of the sandy bar at the mouth of the Itabapoana River, which shows migration patterns in a north-south direction. The compilation of the results suggests that coastal erosion in the region is cyclical, alternating between moments of progradation and retrogradation throughout the analyzed period, reflecting a complex coastal environment that involves climatic factors and marine and fluvial dynamics. The sediments analyzed were well selected, ranging from fine to medium fraction, with heavy fine sediments from the Araçuaí-Ribeira Orogen, showing low textural maturity.

Fluid–Melt–Rock Interaction during the Transition from Magmatism to HT-UHT-Granulite- and Amphibolite-Facies Metamorphism in the Ediacaran Adrar–Suttuf Metamafic Complex, NW Margin of the West African Craton (Southern Morocco)

Abstract Underplated mafic intrusions ponded at the base of the lower continental crust in extensional settings can experience ultra-high-temperature (UHT) granulite-facies metamorphism during tens of My due to slow cooling rates. These intrusions are also the source of heat and carbonic fluids for regional high-temperature (HT) granulite-facies metamorphism in the continental crust. This work analyses the fluid–melt–rock interaction processes that occurred during the magmatic to HT-UHT-granulite- and amphibolite-facies metamorphic evolution of high-grade mafic rocks from the Eastern Ediacaran Adrar–Suttuf Metamafic Complex (EASMC) of the Oulad Dlim Massif (West African Craton Margin, Southern Morocco). P–T conditions were determined using Ti-in-amphibole thermometry, two-pyroxene and amphibole–plagioclase thermobarometry, and phase diagram calculations. The thermobarometric study reveals the presence of tectonically juxtaposed lower- and mid-crustal blocks in EASMC that experienced decompression-cooling paths from, respectively, UHT and HT granulite-facies conditions at ca. 1.2 ± 0.28 GPa and 975 ± 50°C, and ca. 0.82 ± 0.15 GPa and 894 ± 50°C, to amphibole-facies conditions at ca. 0.28 ± 0.28 GPa and 787 ± 45°C (precision reported for the calibrations at 1 s level). An age for the magmatic to UHT granulite-facies metamorphic transition of 604 Ma was constrained from published SHRIMP Th–U–Pb zircon ages of the igneous protoliths. An amphibole 40Ar–39Ar cooling age of 499 ± 8 Ma (precision at 2 s level) was obtained for the lower-crustal blocks. Amphibole 40Ar–39Ar closure temperatures of 520–555°C were obtained for an age range of 604–499 Ma and an average constant cooling rate of 4.2°C/My, suggesting that the lower-crustal blocks cooled down to the greenschist–amphibolite facies transition in ca. 100 My. During the high-temperature stage, interstitial hydrous melts assisted textural maturation of the rock matrix and caused incongruent dissolution melting of olivine and pyroxenes, and, probably, development of An-rich spikes at the grain rims of plagioclase, and local segregation of pargasite into veins. Subsequent infiltration of reactive hydrous metamorphic fluids along mineral grain boundaries during cooling down to amphibolite-facies conditions promoted mineral replacements by coupled dissolution-precipitation mechanisms and metasomatism. Ubiquitous dolomite grains, with, in some cases, evidence for significant textural maturation, appear in the granoblastic aggregates of the high-grade mafic rocks. However, calculated phase relationships reveal that dolomite could not coexist with H2O–CO2 fluids at HT-UHT granulite- and low-medium P amphibolite-facies conditions. Therefore, it is proposed that it may have been generated from another CO2-bearing phase, such as an immiscible carbonatitic melt exsolved from the parental mafic magma, and preserved during cooling due to the prevalence of fluid-absent conditions in the granoblastic matrix containing dolomite. The lower-crustal mafic intrusions from EASMC can represent an example of a source of heat for granulitisation of the mid crust, but a sink for carbon due to the apparent stability of dolomite under fluid-absent conditions.

Tectonostratigraphy of the Upper Jurassic-Lower Cretaceous siliciclastic (Shurijeh Formation) in the eastern Kopeh Dagh fold and thrust belt, Iran

During the Late Jurassic-Early Cretaceous, a significant gas-bearing siliciclastic succession was deposited in the Kopeh Dagh fold-thrust belt in northeastern Iran. Study of the regional evolution of depositional system and geodynamic setting of the red beds continental strata can help in a better understanding of the development of an intracontinental extension in this part of the Eurasia Plate. However, this evolution is driven by faulting events that are not fully understood. Facies analysis in wells and outcrops of the Upper Jurassic-Lower Cretaceous Mozduran and Shurijeh formations in the Saleh Abad area, the easternmost part of the Kopeh Dagh Basin, led to the identification of two fluvial braided river systems in the Shurijeh Formation. Provenance and sedimentological studies indicate that siliciclastic sediments were supplied from the south into the north during the Late Jurassic-Early Cretaceous in the Kopeh Dagh Basin. The higher compositional and textural maturity in the upper part of the Shurijeh Formation relative to the lower part indicate more recycling and more extensive transport of the sediments. Two stages of normal faulting can be identified based on the tectonostratigraphic evolution in this interval: The first phase was initiated with polymictic conglomerates during the Late Jurassic in the lower part of the Shurijeh Formation, while the basin-controlling fault was a buried structure. The second phase started with an influx of quartz conglomerates when the basin-controlling fault reached the surface in the middle part of the Shurijeh Formation. This study integrates new field observations and interpretations to enhance understanding of a complex history of multiphase deformation controlled facies patterns, structural geometries of the Late Jurassic-Early Cretaceous. Renewed Cretaceous extension generated accommodation space for the transgressive Shurijeh Formation.

Variations of sedimentary environment under cyclical aridification and impacts on eodiagenesis of tight sandstones from the late Middle Jurassic Shaximiao Formation in Central Sichuan Basin

Understanding eodiagenesis is essential to decoding the diagenetic pathways of tight sandstones that act as excellent unconventional oil & gas reservoirs. Great paleoclimate change is capable of influencing eodiagenetic processes of tight sandstones through variations of sedimentary environment. However, it is less noted how climate gradients between the greenhouse and the hothouse conditions impact the eodiagenesis of tight sandstones. We examined eodiagenetic processes that has been operated in the Shaximiao Formation sandstones using petrographic observation, scanning electron microscopy, geochemistry, and XRD analysis to reveal impacts of the transitional climate changes on the differential eodiagenesis and implications for the diagenesis-porosity evolution. Based on sequence stratigraphy, the Shaximiao Formation is divided into four sub-members SXM1, SXM2, SXM3, and SXM4, respectively. Dark sandstones and mudstones mainly occurred in the SXM1 and the SXM2. Grey-green clastic rocks are dominant in the SXM3, whereas red mudstones frequently appear in the SXM4. Paleoclimate indices denote that a cyclical aridification from the warm-humid to hot-semiarid conditions took place from the SXM1 to the SXM4. It could have been caused by the megamonsoon effect and the paleogeographic shift along with the breakup of the Pangaea supercontinent. Combined with the migration of depocenters, the paleoclimate change resulted in transformation of sediment provenances from mafic igneous rocks to quartzose sedimentary rock along with the decreasing textural maturity. Therefore, sedimentary environments varied from the high-saline to low-saline and from low-oxygen to high-oxygen conditions respectively, which had a crucial impact on eodiagenetic cements which were formed in the Shaximiao Formation. Chlorite and laumontite cement precipitation was promoted by high-saline alkaline fluids. Chlorite proportions show an arched trend from the SXM1 to the SXM4, compatible with those of primary and secondary porosities. In contrast, laumontite proportions exhibit a decreasing variation from the SXM1 to the SXM4. High percentages of early cements are favorable to improving resistance to the compaction and preservation of primary pores. However, high chlorite (>5%) and laumontite (>10%) proportions are destructive for the reservoir quality. Large quantities of laumontite cements occupy primary pores and impede diagenetic fluids flowing and are not favorable to the dissolution. By contrast, an excess of chlorite cements can be dissolved to produce secondary pores during the organic acid release. Thus, the SXM2 is potential as a reservoir for oil & gas. Therefore, those eodiagenetic cements can control the late diagenetic evolution and the reservoir quality. Observations made here have implications for understanding tight sandstone reservoirs elsewhere in the world.

Petrographical and Geochemical Studies of the Upper Cretaceous Sandstones in Wadi Feiran, West-Central Sinai, Egypt: Implications for Depositional Environment and Diagenesis

The main focus of this paper is on the sandstones from the Upper Cretaceous period found in the Wadi Feiran area. The study aims to investigate various aspects of the sandstones, including their petrographic characteristics such as textural maturity and mineralogical classification, as well as their paleoenvironment, diagenesis, and chemical composition. The results show that the sandstones are sub-mature and were formed in relatively shallow neritic environments. Based on their mineralogical composition, they are classified as quartz arenite. The paleoenvironmental analysis suggests that the sediments were deposited in an area of mild tectonic stability. During diagenesis, the sandstones underwent various physical and chemical stages. Analysis of their chemical composition indicates that they were deposited under relatively warm and slightly alkaline conditions in a relatively shallow and restricted medium, with major and trace components including Al2O3, SiO2, Fe2O3, CaO, MgO, K2O, Na2O, P2O5, Cl, SO3, Ti, Mn, Cu, Ni, and Sr.

A Study on the Dissolution Behavior of Typical Minerals in Continental Deposited Reservoirs during CO2 Geological Storage

CO2 sequestration in saline aquifers is one of the most potential sequestration modes, and saline aquifers are ideal sites for CO2 geological sequestration. After CO2 is injected into a saline aquifer, it will have a long-term complex geochemical reaction with the formation of minerals and water, and the minerals will undergo multiple reactions such as dissolution and reprecipitation. Therefore, an in-depth study of the geochemical reaction mechanisms between CO2 and formation minerals is of great significance to the accurate calculation and prediction of CO2 storage volume and the safety evaluation of long-term CO2 sequestration. In China, continental saline aquifers are widely distributed, whose mineral compositions and texture maturity are markedly different from those of the marine sedimentary basins in North America, and their stratigraphic environments are more complicated. The studies on the CO2–water–rock (mineral) still have many research gaps or insufficiencies, and there is no report on the dissolution mechanisms of individual minerals in the reaction. Taking one certain block of Daqing Oilfield, which is a typical continental deposit in China, as an example, we analyze the dissolution laws and four types of typical continental deposited minerals under the effect of CO2 and the change features of ionic compositions and pH of the formation water in the process of geochemical reaction. The research results indicate that CO2 has different dissolution degrees for the four types of minerals, among which, feldspar, as the main mineral in continental sedimentary formations, has the lowest dissolution rate. Furthermore, in terms of the water type (Na+-enriched NaHCO3) of the saline aquifer in the deep part of the continental deposit, feldspar can precipitate into the secondary minerals represented by dawsonite in the later stage, which can act as the potential minerals of carbon fixation to increase the CO2 mineralization storage volume in continental deposited saline aquifers.

Detrital zircon and tourmaline unravel polycyclic provenance of sedimentary infill of the Cretaceous Tupanciretã formation, southern Brazil

The recognition and evaluation of polycyclic processes in sedimentary units are critical for proper provenance analysis and sedimentary system interpretation. The chemical composition and textural maturity of detrital tourmalines and zircons allow identification of sediment source areas, transport, and deposition. This study investigates the origin and history of post-Gondwanan sediments of the Tupanciretã Formation in southern Brazil, which lacks provenance studies. The Tupanciretã Formation is in a similar setting of the Bauru Supersequence at the uppermost portion of the Paraná Basin. Detrital zircon ages indicate sediment provenance from the Transamazonian, Grenvillian, and Brasiliano orogenic cycles of the Rio Grande do Sul Shield and younger grains (280-128 Ma) record contribution from the Choiyoi and Serra Geral igneous events, with a maximum deposition age of 127 Ma. Detrital tourmaline chemical analyses points to the Sul-riograndense Shield as the ultimate source, with metapelitic, metapsamitic and granitic origins. The predominant degrees of roundness are well rounded to rounded suggest evidence of sediment recycling from sedimentary units of the Paraná Basin, with important aeolian reworking involved. Zircon U–Pb signatures are compatible with the eastern sector of the Botucatu Formation in Rio Grande do Sul as the immediate source and the northeastern Sul-riograndense Shield as the ultimate source. Intermediate sources between the Sul-riograndense Shield and the Tupanciretã Formation were Gondwanan sedimentary units of the Paraná Basin, with possible participation from the Camaquã Basin.

Analysis of size, shape and textural maturity of sands from the Kaligandaki River

The Gandaki River System is one of the major river basin of the Himalaya originating from China and flows through Nepal and eventually mixes with the Ganga River in India. The study aims at analyzing the textural properties (size and shape) and maturity of the Kaligandaki River sands, and their downstream variation. Sand samples were collected along the river from the Tethys Himalayan region up to the Indo-Gangetic Plain of Nepal. The sands are classified as slightly muddy sand, in which mean and median sizes and sorting increase with respect to the distance downstream from the provenance. The results indicate that coarsely skewed and platy to mesokurtic sands become nearly symmetrical to finely skewed and leptokurtic suggesting increase in fine-grained sands and enhancement of sorting downstream. The percent of fines (mud) ranges from 0 to 5% and shows no distinct downstream variation trend. Mean roundness of quartz is generally sub-angular (2 to 3 p), and downstream variation does not reflect change in roundness category. However, there occurs slight diminish of roundness with distance downstream. Inclusive graphic standard deviation (Cj) varies from 0.30 to 1.38j. After 100 km downstream, Gj decreases reflecting improvement of sorting. Sediments are immature to mature, and are sub-mature in upstream and midstream segments except for few sites where they are immature not due to flux, but probably due to local contribution of fines. Due to increased downstream distance, sediments tend to be more mature owing to enhancement of sorting

Effect of undercooling on clinopyroxene crystallization in a high K basalt: Implications for magma dynamics at Stromboli volcano

We present undercooling (∆T) experiments aimed at investigating the effect of growth kinetics on the textural and compositional evolution of clinopyroxene crystals growing from a high-K basalt erupted during the 2003 paroxysm of Stromboli volcano (Italy). The experiments were performed at P = 350 MPa, T = 1050–1210 °C, H2Omelt = 0–3 wt%, and fO2 = Ni-NiO + 1.5 buffer. An initial stage of supersaturation was imposed to the melt under nominally anhydrous (∆Tanh = 10–150 °C) and hydrous (∆Thyd = 25–125 °C) conditions. Afterwards, this supersaturation state was mitigated by melt relaxation phenomena over an annealing time of 24 h. Results show that plagioclase is the liquidus mineral phase of the high-K basalt at ∆Tanh = 10 °C and dominates the phase assemblage as the degree of undercooling increases. Conversely, clinopyroxene and spinel co-saturate the melt at ∆Thyd = 25 °C, followed by the subordinate formation of plagioclase. At ∆Tanh/hyd ≤ 50 °C, the textural maturation of clinopyroxene produces polyhedral crystals with {−111} (hourglass) and {hk0} (prism) sectors typical of a layer-by-layer growth mechanism governed by an interface-controlled crystallization regime. At ∆Tanh/hyd ≥ 75 °C, the attainment of dendritic and skeletal morphologies testifies to the establishment of diffusion-limited reactions at the crystal-melt interface. 3D reconstructions of synchrotron radiation X-ray microtomographic data reveal a composite growth history for clinopyroxene crystals obtained at ∆Tanh/hyd ≥ 95 °C. The early stage of melt supersaturation produces rosette-like structures composed of dendritic branches of clinopyroxene radiating from a common spinel grain, which acts as surface for heterogeneous nucleation. As diffusive relaxation phenomena progress over the annealing time, the elongate dendrites that constitute the inner crystal domain are partially infilled by the melt and develop skeletal overgrowths in the outer domain. With the increasing degree of undercooling, TAl and M1Ti cations are progressively incorporated in the lattice site of clinopyroxene at the expense of TSi and M1Mg cations. Because of the effect of H2Omelt on the liquidus depression and melt depolymerization, crystals obtained at ∆Thyd are also more enriched in TAl and M1Ti and depleted in TSi and M1Mg than those growing at ∆Tanh. The emerging picture is that the morphological and geochemical evolution of clinopyroxene is mutually controlled by the combined effects of melt supersaturation and relaxation phenomena. A new empirical relationship based on the cation exchange reactions in the lattice site of clinopyroxene is finally proposed to estimate the degree of undercooling governing the crystallization of augitic phenocrysts erupted during normal and violent explosions at Stromboli.

DEM multi‐scale insights on the pre‐failure behavior of mature structured sands: Influence of bond type, amount, breakage pattern and heterogeneity

AbstractA new approach in the calibration process of DEM samples of structured sand is presented. Micromechanical‐based experimental data are interpreted to develop a failure model and a range of input parameters in the DEM analyses are incorporated considering strong and a weak bonds in the simulated samples. Subsequently, the numerical samples correspond to analog mature structured soil/sandstone in terms of both compositional and textural maturity, and the study focused on the small‐to‐medium strain shear modulus and on providing multi‐scale insights of the simulated materials. The heterogeneity of the structured sand is incorporated based on Gaussian and Weibull distributions of the contact properties and four major parameters are examined including bonding amount/content, bonding strength, heterogeneity, and confining pressure. The numerical results showed, at the macroscopic level, agreement with respect to a number of element‐size experiments on sandstones which were re‐analyzed in the present work, in terms of stiffness—pressure relationship, stiffness reduction, and occurrence of the yield point associated with the initiation of bond breakage. It was shown that even though the bond strength and amount of bonds are important influencing factors on the macroscopic behavior of the structured sand, the incorporation of heterogeneity can significantly alter the interpretations of the microscopic involved mechanisms. This unveils that the implementation of “average” input parameters cannot capture well the contributing mechanisms which influence the deformation characteristics of structured soils and sandstones.

Morphosedimentary characteristics and formation mechanisms of new beaches generated after the Tajogaite volcano eruption of 2021 (La Palma, Spain)

Only in very special circumstances can new beaches develop due to natural processes in areas where they did not exist before. One such circumstance is related to volcanic eruptions, when a lava flow reaches the ocean. The sudden formation of new beaches is examined in this paper. Following the Tajogaite volcano eruption in September 2021, two lava deltas formed after the arrival of several lava flows to the coast. Attached to the flanks and front of these lava deltas, thirteen gravel beaches formed in just a few months. Detailed topographic and sedimentologic information was collected both on the beaches and adjacent submarine areas. The volume of sediments accumulated on these beaches was obtained after comparison of the actual topography with a previous one, yielding a total net accumulation of about 79,000 m3 of volcanoclastic pebbles and cobbles. This material comes from two major source areas: extensive offshore deposits of volcanic clasts within the depth of closure which are moved onshore by low steepness swell waves, and rock fragments derived from erosion of the lava delta front by high energy waves. Two types of beaches were identified. Beaches that already existed prior to the eruption showed significant increases in cross-shore length and height, with a net accumulation of 67,000 m3. In contrast, the dismantling of the lava delta front led to the formation of totally new beaches in certain locations, accounting for about 12,000 m3 of sediments. Several features, such as a steep foreshore slope, a well-developed storm berm and the presence of wood debris in many of these beaches at several meters height and tens of meters inland, are examined conjointly with the sediment characteristics, showing how textural maturity can change in response to the forcing agents acting in the different parts of the beach profile. The future evolution of these beaches is also considered. This study can enrich the knowledge regarding how new gravel beaches can form in volcanic settings.

Petrography and geochemistry of successions from northwest Bolivia

A complete section of Paleozoic sedimentary rocks has been sampled in northwest Bolivia to investigate compositional changes based on petrographic but mainly geochemical data. Studies of Paleozoic succession in southern Peru, northern Chile and northwest Argentina allowed to decipher the paleotectonic history of the region for the Paleozoic (e.g. compilations in Bahlburg et al., 2009). However, a few is only known about the area geographically in between. We focus here on an area in the vicinity of the capital La Paz, where the Paleozoic belongs paleogeographically to the so-called ‘altiplano’ and the ‘Cordillera Oriental del Norte’ and tectonically to the ‘Faja de Huarina del Norte’. The objective of the study is, hence, to establish a first complete stratigraphic insight of the Paleozoic to enable further studies on key formations or horizons. While the abovementioned areas to the north and south do reflect in the sedimentary record the emergence of a continental arc during the Ordovician, followed by a significant tectonic quiescence during the late Silurian and Devonian and succeeded by the evolution of a second active margin with a continental arc during the late Paleozoic, these events are not visible in the Bolivian samples which is sandwiched between the westerly Arequipa Massif and the eastern Sunsas belt, both composed of mainly metamorphic rocks.The Paleozoic section in northwest Bolivia shows highly recycled quartz-arenites of Ordovician age followed by Silurian and Devonian successions mainly composed of subangular to surrounded detritus, moderately sorted, devoid of significant typical metamorphic detritus. During the late Paleozoic, the rocks tend to a larger variability, partly even poorly sorted, higher amount of angular grains and the occurrence of volcaniclastic debris. Geochemically the same trend can be observed, with strongly recycled successions during the Ordovician (Zr/Sc 20–200) followed by moderately recycled rocks (mainly Zr/Sc 10–20100) with typical trace element composition for unrecycled upper continental crust (UCC). During the Permian, sediments which are less weathered and slightly less fractionated in their overall geochemical composition, have been deposited. The geochemistry may point to the evolution of late Paleozoic volcanism, recorded in overlying, but however, Triassic rocks. Significant increase or even typical UCC values of compatible elements or ratios are absent besides Cr and Ni increase in Ordovician rocks. The absence of any significant input of arc related detritus can be explained by not effective sediment dispersal system to transport arc related detritus into the depositional area. The low compositional and low to moderate textural maturity throughout the entire post-Ordovician stratigraphy implies relatively proximal sources and insignificant intra-basinal recycling. This together with the absence of metamorphic detritus, allows in proposing thick homogeneous sedimentary successions with low or no metamorphic overprint as major sources. Those covered possibly the today exposed metamorphic successions of the aforementioned basin surroundings. Sedimentary or any other lithologies older than the Ordovician and younger than Mesoproterozoic are nearly unknown in the region, besides one exception (Chilla beds; Bahlburg et al., 2020). Those hypothetical deposits would be at this stage of knowledge the best explanation.

Geochemistry and zircon geochronology of the Late Triassic volcanic–sedimentary successions in northern Tibet: Implications for the provenance and tectonic evolution of the Mesozoic Qiangtang Basin

The Late Triassic volcanic–sedimentary successions deposited in the Qiangtang Basin are linked with the initiation of the Mesozoic Qiangtang Basin. However, the nature of this basin is hotly debated. Here, we synthesize petrographic, mineralogical, geochemical, and detrital zircon U–Pb age data of these volcanic–sedimentary successions to constrain their chemical weathering history, provenance, and tectonic setting and to reconstruct the tectonic evolution of the Mesozoic Qiangtang Basin. The chemical weathering indices, especially the chemical index of alteration (CIA), are controlled by grain size and hydraulic sorting rather than sediment recycling. Low compositional and textural maturities, high index of compositional variation (ICV) values, and low CIA and plagioclase index of alteration (PIA) values in most samples suggest that the sediments from the Fanghu and north Woruoshan sections are predominantly from low-maturity sources that may have experienced a weak chemical weathering history. Based on provenance-sensitive geochemical indices (La/Th versus Hf, La/Sc versus Co/Th, and Sc/Th versus Cr/Th) and petrographic features, the detrital contributions to the Nadi Kangri Formation siliciclastic rocks are predominantly proximal felsic rocks. Detrital zircon age spectra suggest that the Nadi Kangri Formation siliciclastic rocks exhibit a provenance change from the Fanghu to the well QK-1 area, although all of the rocks were derived from the Qiangtang terrane itself. The Fanghu section was primarily sourced from synchronous magmatic rocks and pre-Triassic strata from the North Qiangtang and Central uplift belt, while well QK-1 was primarily sourced from recycled sediments from the South Qiangtang and Central uplift belt. Therefore, we propose that the Nadi Kangri Formation volcanic–sedimentary successions were deposited in a rift basin and that its evolution was likely related to the interaction of the rapid expansion of the Meso-Tethys Oceanic crust, collapse of the collisional orogen, and rollback of the Jinsha Paleo-Tethys subducting slab during the Late Triassic.

Establishing Provenance from Highly Impoverished Heavy Mineral Suites: Detrital Apatite and Zircon Geochronology of Central North Sea Triassic Sandstones

A study of Triassic sandstones in the central North Sea, UK, has shown that combined detrital zircon and apatite geochronology and apatite trace element analysis is a powerful tool for reconstructing provenance for sandstones with diagenetically impoverished heavy mineral suites. Sandstones in the earlier part of the succession (Bunter Sandstone Member and Judy Sandstone Member) have characteristics that indicate derivation from Moinian–Dalradian metasediments affected by Caledonian tectonothermal events, in conjunction with a Palaeoproterozoic-Archaean source unaffected by Caledonian metamorphism. Palaeogeographic reconstructions indicate that the sediment cannot have been input directly from either of these cratonic areas. This, in conjunction with the presence of common rounded apatite, indicates that recycling is the most likely possibility. The zircon-apatite association in the younger Joanne Sandstone Member sandstones indicates derivation from lithologies with mid-Proterozoic zircons (either crystalline basement or metasediments in the Caledonian Nappes), subjected to Caledonian metamorphism to generate early Palaeozoic apatites. This combination is compatible with a source region in southern and western Norway. The low degree of textural maturity associated with the detrital apatite, together with the unimodal Caledonian age grouping, indicates the Joanne sandstones have a strong first-cycle component.

Sedimentary Characteristics and Their Controlling Factors of Lower Cretaceous Fan Deltas in Saidong Sub-Sag of Saihantala Sag, Erlian Basin, Northeastern China

Fan deltas of the Lower Cretaceous area in Saihantala sag, Erlian Basin have been identified as major petroleum exploration opportunities. The sedimentary evolution is, however, still debatable, which hinders insights into its controlling factors. This research employed new core observations, thin section observations, and grain size analyses of 28 wells in the Saidong sub-sag, together with numerous borehole and seismic data points, to explore lithofacies types, subfacies, and microfacies characteristics, thus leading to a further investigation of the sedimentary facies evolution of the sag and its controlling factors. The findings showed there are 3 categories, 12 sub-categories, and 20 fine lithofacies types in the Saidong sub-sag. Additionally, various sand-conglomerate lithofacies were characterized by lower composition and texture maturity. With dentate-shaped, box-bell-shaped, and other morphological well-logging responses, fan deltas were mostly developed in the A’ershan Formation and the Tengge’er Formation, which could be subdivided into three subfacies and eight microfacies. Given the sedimentary features and lithofacies characteristics of each microfacies, it can be determined that three main stages occurred in formations from the A’ershan to the Tengge’er: the water transgression, the water oscillation, and the water regression. Moreover, fan delta deposits were regulated primarily by semi-arid hygrothermal and semi-arid paleoclimate and paleotectonic factors.

Linking South China Plate to Arabian margin of Gondwana: Significance for Cambrian global plate reconstruction

Large-scale plate convergence processes led to the assembly of the Gondwana supercontinent during the Ediacaran–Cambrian. Herein, we present the results from petrological and geochemical studies on fine-grained sedimentary rocks belonging to the Lower Cambrian strata from the western part of South China Plate (SCP) in the Yangtze terrane, to reveal the location of SCP in the Gondwana supercontinent. Our results show that these rocks are of high compositional and textural maturity and belong to the same tectono-sedimentary cycle. The rare earth element (REE) distribution curve standardized by Post-Archean Australian Shale is similar to that for typical post-Archean shale. Characteristics of major and trace elements indicate that these fine-grained sedimentary rocks might mainly be derived from moderately felsic magmatic provenance with only a minor supply from mafic–ultramafic sources. Trace element ternary discriminant plots reveal the geotectonic setting as a continental island arc, although some passive margin sediments might have also been involved; R-type cluster analysis based on trace elements and REEs also shows that the tectonic setting of the sample provenance area is most likely to be that of continental island arcs and active continental margins. Combined with the published detrital zircon geochronological data of SCP and global tectonic-magmatic activity during the Cambrian, we propose that the Lower Cambrian clastic sediments in SCP were mainly supplied by the Cadomian island arc along the northern margin of Gondwana during the Ediacaran–Early Cambrian. Based on the above analysis, we believe that SCP might have been located closer to Arabian Plate than to Australian Plate.

Geochemical, mineralogical and textural nature of beach placers, north-east Sri Lanka: Implications for provenance and potential resource

The Pulmoddai placer sands in Sri Lanka (9°3′23.65″–8°51′38.83″N and 80°55′22.91″–81°3′32.65″E) is considered to be one of the major rare earth element (REE) prospects world-wide. This deposit has a global significance in terms of strategic economic resources and can provide valuable insight for resource estimation and for its economic use. A detailed study of the geochemical, mineralogical, and textural properties of the heavy minerals of this region is undertaken applying the scanning electron microscopy–electron dispersive X-ray spectroscopy (SEM–EDS), inductively coupled plasma–optical emission spectroscopy (ICP–OES), X-Ray diffraction (XRD), and X-Ray fluorescence (XRF) techniques. The results from these analyses are modeled to delineate the source(s) which contribute to the formation of the mineral deposits and their subsequent enrichment. The beach sediment from this region, exhibited elevated concentrations of major elements like silicon (Si) and manganese (Mn) and high abundance of minor and trace elements like yttrium (Y), strontium (Sr), lanthanum (La), barium (Ba), which indicates that the provenance is similar to calcium-silicate rocks. The highest (total) concentration of Y, La, scandium (Sc) and cerium (Ce) are mainly associated to fine grained sediment, signifying that their occurrences are governed by the grain size distribution and ambient hydrodynamic conditions primarily from lagoonal input. Monazite, zircon, ilmenite, rutile, and xenotime are more abundant than garnet in the study area, as is evident from the higher abundance of thorium (Th) and uranium (U) and the enrichment of zirconium (Zr), Ce, vanadium (V), chromium (Cr), and Y. Textural analysis of sediment shows sediment particles are poorly sorted and have more angular grain boundaries, indicating their lower textural maturity. This suggests that the sediment is fluvially derived from a close source rock of charnockite specific to the hinterland lithology. The sediment transported by perennial rivers and the hydrodynamic conditions of the Kokkilai Lagoon estuary, are the two primary sources of heavy mineral enrichment in the study area, which is quite unique in terms of the placer formation. Subsequently, these sediment particles formed the beach placer deposits enriched in REE–Th rich heavy minerals, which are of immense strategic importance.

Sediment provenance of the Lulehe Formation in the Qaidam basin: Insight to initial Cenozoic deposition and deformation in northern Tibetan plateau

AbstractUnravelling early Cenozoic basin development in northern Tibetan Plateau remains crucial to understanding continental deformation mechanisms and to assessing models of plateau growth. We target coarse‐grained red beds from the Cenozoic basal Lulehe Formation in the Qaidam basin by combining conglomerate clast compositions, paleocurrent determinations, sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology to characterize sediment provenance and the relationship between deformation and deposition. The red beds are dominated by matrix‐supported, poorly sorted clastic rocks, implying low compositional and textural maturity and short transport distances. Although most sandstones have high (meta)sedimentary lithic fragment contents and abundant heavy minerals of metamorphic origin (e.g., garnet, epidote and chlorite), spatiotemporal differences in detrital compositions are evident. Detrital zircon grains mainly have Phanerozoic ages (210–280 Ma and 390–480 Ma), but Proterozoic ages (750–1000 Ma, 1700–2000 Ma and 2300–2500 Ma) are also prominent in some samples. Analysed strata display dissimilar (including south‐, north‐ and west‐directed) paleocurrent orientations. These results demonstrate that the Cenozoic basal deposits were derived from localized, spatially diverse sources with small drainage networks. We advocate that initial sedimentary filling in the northern Qaidam basin was fed by parent‐rocks from the North Qaidam‐South Qilian belts and the pre‐Cenozoic basement within the Qaidam terrane interior, rather than southern distant Eastern Kunlun regions. Seismic and drilling well stratigraphic data indicate the presence of paleohighs and syn‐sedimentary reverse faults and noteworthy diversity in sediment thickness of the Lulehe Formation, revealing that the Qaidam terrane exhibited as several isolated depocenters, rather than a coherent basin, in the early stage of the Cenozoic deposition. We suggest the Cenozoic Qaidam basin to have developed in a contractional deformation regime, which supports models with synchronous deformation throughout most of Tibet shortly after the India‐Eurasia collision.

The Evolution of Permian Source-to-Sink Systems and Tectonics Implications in the NW Junggar Basin, China: Evidence from Detrital Zircon Geochronology

The basin type of the Junggar Basin changed during the Permian, but the time constraint of the tectonic evolution remains unclear. Besides, the fan deltas developed in the Permian in the Mahu Sag in the northwestern of the oil-rich basin. However, the provenances of the sedimentary systems remain unclear. Based on petrology and detrital zircon U-Pb ages, this study investigates the source-to-sink systems evolution and tectonics implications. Abundant lithic clasts in sandstones with low compositional and textural maturity imply proximal sources. The dating results showed a dominant peak (310–330 Ma) and a secondary peak (400–440 Ma) in the northern Mahu Sag, only one peak at 295–325 Ma in the central Mahu Sag, several peaks at 270–350 Ma in the southern Mahu Sag, and multiple peaks at 370–450 Ma in the Zhongguai Uplift. Thus, the north-western Junggar Basin was divided into four major source-to-sink systems, with adjacent central West Junggar as the main provenance and northern and southern West Junggar as the secondary provenance. The proportion of sediment supply from the southern and northern West Junggar is higher during the Middle-Late Permian. It suggests that the source-to-sink systems show inheritance and evolve from a single provenance into a complex provenance, indicating the uplift of West Junggar. The tectonic inversion may occur early in the Middle Permian and the response to tectonic activity is stronger in the southern West Junggar than in the northern West Junggar.

The Tight Sand Reservoir Characteristics and Gas Source in Coal Measures: A Case Study of Typical Areas in China

Interbedded sandstones, shales, and coal seams were formed in marine-continental transitional environments of coal measures, and the gas source of its tight sand gas has been uncertain, which hinders the progress of natural gas exploration. This article uses the Longtan tight sand gas in west Guizhou as an example to investigate the reservoir features, gas charging history, and main source rock of tight sand gas by examining thin sections, scanning electron microscopy images, X-ray diffraction results, and the fluid inclusions with burial and thermal histories and noble gas analysis. The Longtan sandstones in this study are classified as litharenites which are characterized by low compositional and textural maturities, and high clay contents, and are distinguished petrographically from conventional sandstones by the extensive existence of micropores and microfractures. The results of the homogenization temperatures of the fluid inclusions show that the Longtan tight sand gas is a single-stage accumulation which occurred during the Late Triassic. Furthermore, through the analysis of the helium and argon isotopes of noble gases, a calculation model was established for determining the shale and coal contributions to the tight sand gas. The research results show that the Longtan tight sand gas mainly belongs to the crust-derived gas, mostly from the Longtan shale-derived contribution and to a lesser extent from the Longtan coal-derived contribution. The measured 40Ar/36Ar values of the Longtan shales and coals are consistent with the forecasted 40Ar/36Ar values from the calculation model, demonstrating that the model is viable to calculate the source rock contribution to the tight sand gas. Therefore, the Longtan shales as main source rocks can generate hydrocarbons to charge neighboring tight sandstones to form tight gas accumulation in the Longtan Formation, which provides an opportunity for tight gas development in west Guizhou.