Clastic Research Articles

Analysis of sedimentary and geochemical characteristics of sedimentary clastic rock samples from Alpha-Mendeleev Rice (underwater sampling)

The paper presents new data from a comparative analysis of sedimentary rocks from the Mendeleev Rise (seamount Shamshura), presumably of Triassic age, with sandstones of Aptian age, obtained during underwater sampling of the Alpha-Mendeleev Rise during expeditions in 2012, 2014 and 2016. The geochemical characteristics of the rocks are very similar, and, as a rule, data from samples of different ages form common fields on different diagrams. The petrographic investigations have established that the sandstones of presumably Late Triassic age, as well as the sandstones of Chukotka and Wrangel Island, are dominated by fragments of shale and acid effusives. The Aptian samples are dominated by fragments of mafic rocks. Also, sharp differences are observed in the nature of the age spectra of detrital zircon populations, indicating fundamentally different feeding provinces for the Triassic and Cretaceous sandstones of the Alpha-Mendeleev Rise. Samples from the Shamshura seamount are characterized by populations similar to populations from Triassic rocks of Chukotka and Wrangel Island, indicating the presence of Triassic rocks in this part of the Mendeleev Rise.

Strontium isotopic composition of the Mesozoic sedimentary formations of the southern Central Andes (33°–34°S) and its paleogeographic implications

Strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr) in sedimentary and igneous rocks may provide valuable interpretations that allow constraining the geologic evolution of sedimentary basins. We present a new ⁸⁷Sr/⁸⁶Sr dataset from sedimentary units in the southern Central Andes (33°–34°S)—coupled to available isotopic information of igneous rocks—to examine the paleogeographic evolution of the Andes at the western margin of South America during the Mesozoic. These new data was obtained from shales, limestones and fine-grained sandstones from Mesozoic formations in the Coastal Cordillera and the Principal Cordillera of the main Andes. The new Sr-isotopic data on the Mesozoic sedimentary rocks can be grouped by both rock type and location: a) Continental red sandstones: 0.7038–0.7124; b) Calcareous rocks of the main Andes (Principal Cordillera): 0.7070–0.7081; and c) Calcareous rocks of the Coastal Cordillera: 0.7041–0.7067. The ⁸⁷Sr/⁸⁶Sr signatures in most of the clastic units in both Cordilleras are related to an evolved or enriched magmatic source for clasts and matrix indicating different sources. On the other hand, the Sr-isotopic composition of calcareous rocks differs between the units in the Andean and the Coastal mountain belts: shales and limestones in the Principal Cordillera of the Andes display ⁸⁷Sr/⁸⁶Sr ratios corresponding to the contemporary ocean in the Late Jurassic and Early Cretaceous; whereas the carbonatic units in the Coastal Cordillera do not show a relation with any oceanic signatures. The Sr-isotopic compositions of the Andean carbonatic units in the Principal Cordillera support the interpretation of their marine depositional environment in the paleo Pacific Ocean. In contrast, carbonate rock samples from the formations in the Coastal Cordillera suggest that they formed in brackish-water depositional basins made by topographic highs partially disconnected from the ocean. In the case of clastic rocks, their Sr-isotopic compositions provide insights into the contributions derived from the magmatic arc to the clastic units. Therefore, the Sr-isotopic composition of the sedimentary rocks provides a new dataset which can improve our understanding of the geological evolution of the southern Central Andes.

Diverse Behaviors of Feldspar Grains during Sandstone Diagenesis: Example from the Xujiahe Formation in the Western Sichuan Basin, China

Feldspar alteration is among the most important processes in clastic rocks during diagenesis, but uncertainty remains about the factors that control feldspar diagenesis under subsurface conditions. Hence, the Upper Triassic Xujiahe formation of the Western Sichuan Basin were examined by an integrated petrographic, mineralogical and geochemical approach to unravel the causes and effects of feldspar diagenesis, with implication for mass transfer and openness of the geochemical system. The sandstones at various depths demonstrate three distinct, separate diagenetic behaviors of detrital feldspar within a single formation including (1) the complete dissolution of both plagioclase and K-feldspar in the upper member; (2) conservation of abundant detrital feldspar grains with minor albitization or overgrowths within the lower member of depths greater than 5 km; and (3) complete disappearance of K-feldspar within the uppermost horizons of the lower member, while plagioclase have survived in significant amounts. The exceptional disappearance of K-feldspar is the result of selective dissolution of K-feldspar during burial, accompanied by illite cementation and substantial K transfer at a scale of tens of meters. It is apparent that the clay diagenesis in the overlying mudstones, rather than porewater chemistry, is the major control of the reactivity of K-feldspar in adjacent deeply buried sandstones.

Petrology dataset of Pliocene-Pleistocene sediments in northeastern Slovenia

This is a dataset of petrological analysis of Pliocene-Pleistocene fluvial sediments from 14 gravely samples from the Slovenj Gradec, Nazarje, Celje and Drava-Ptuj Basin (northeastern Slovenia), collected for clast lithological analysis. The petrological analysis includes description of 155 thin sections of metamorphic, volcanic, volcaniclastic, clastic and carbonate rocks. This dataset provides grounds for determining the provenance of these gravel deposits, revealing possible resedimentation processes, and serves as a tool for drainage network interpretation in the Pliocene-Pleistocene.

Hydrogeomorphology and recharge mechanism of a coastal aquifer in tectonic-controlled watersheds: A multi-proxy approach based on remote sensing and environmental isotopes

Coastal aquifers worldwide can be considered an essential water source required for preservation of the coastal ecosystems. However, these aquifers are vulnerable to seawater intrusions and over-pumping due to their proximity to the sea and human activities, respectively. Therefore, the investigation of recharge mechanism has special importance in the regions of tectonic rift activities where they exhibit complex geological structures and hydrogeological characteristics. In the current research, an integrated approach of remote sensing and environmental isotopes together with field investigation and subsurface datasets (aeromagnetic, gravity and well logs) are employed to identify the nature and factors affecting groundwater recharge of the Miocene coastal aquifer along the Red Sea-Gulf of Suez western margin (continental rift basin). The research findings reveal that: (1) The coastal Miocene aquifer consists of both clastic (sandstone, sand and gravels) and carbonate rocks (limestone and dolomite) with subsurface thickness ranges between 100 and 200 m. (2) Its groundwater shows contrast salinity values (expressed by total dissolved solids, TDS) between 2755 and 10,996 mg/l, due to the variation in recharge rates and the lithologic dissimilarity of the water bearing formations. (3) The environmental isotopes indicate that the Miocene groundwater has a mixed isotopic signature between modern meteoric (rainfall) and fossil waters. (4) The isotopic data of the Miocene aquifer and the enriched Gulf of Suez verifies that no seawater intrusions are affecting this aquifer with existing hydraulic barriers (clogged/sealed faults or impermeable massive blocks). (5) The hydrogeomorphological investigations, aeromagnetic and gravity data reveal an existence of two morphotectonic depressions (water collectors) which have paleo and recent recharge opportunities for the subsurface sedimentary layers (2–4 km thick). From the applied viewpoint, these two depressions have potential prospects for future groundwater exploration, which has significant impact on food security and land reclamation.

Distribution of magmatic intrusions and key petroleum system elements in the Pliocene–Holocene Pangani Rift Basin, Northeastern Tanzania

The sedimentary fills in the Pangani rift basin (PRB) of northeastern Tanzania have not yet been studied in detail and their petroleum potential is poorly understood. This study aims at assessing distribution of magmatic intrusions and key petroleum system elements in the PRB based on 2D seismic, remote sensing, and aeromagnetic data interpretations. Results show that evolution of the basin fill was influenced by sediment supply, magmatism, and tectonics. The PRB contains Pliocene–Holocene clastic, magmatic, and volcaniclastic deposits. The clastic sediment was sourced from the north-northeast and east-southeast of the PRB. The magmatic and volcaniclastic rocks were formed during Pleistocene–Holocene and are increasing in frequency toward the north and northeast of the basin. Tectonics and faulting created depocenters and magma conduits; magmatic intrusions and fault systems form potential petroleum traps. Seismic interpretation has shown that PRB contains potential reservoir and seal rocks for possible petroleum accumulations. Fault systems dissecting the PRB provided petroleum migration pathways from deep buried source rocks to potential reservoirs. For the first time, this study has shown that the PRB contains key petroleum system elements for petroleum accumulations to occur. Our results will be of interest to researchers working in different East African Rift basins.

The Proterozoic–Cambrian salt detachment zone at Lakhar Kuh, Iran: a seismic-scale analogue for salt stringers, detachment folding and multiphase structural development

Abstract In the Middle East, significant evaporite units formed in the latest Precambrian–Cambrian, Triassic, Jurassic, Cretaceous and Cenozoic. The Precambrian–Cambrian period gave rise to the Ara Salt carbonate stringer plays, southern Oman and the giant Zagros anticline traps (Hormuz Formation). While outcrops of salt diapirs are common, basal detachment exposures are extremely rare. The Lakar Kuh area of Central Iran reveals the Precambrian–Cambrian basal salt detachment, on satellite images, in natural cross-section view through the entire Phanerozoic sedimentary section east of Ravar. This view illustrates how older diapiric structures (pillows and normal faults) were the focus of later contractional folds, particularly in the Jurassic and Cenozoic. The salt detachment zone contains many floating blocks (stringers) of clastic, carbonate and igneous rocks. Some blocks were stoped from the overlying beds, while most were layers originally interbedded with the evaporites. Block size, distribution and orientation is highly variable, and folding is infrequent. Lakar Kuh encompasses several key themes generally pertinent to structural geology and salt system research: the presence of sedimentary stringers within evaporites, multiple detachment levels within a thick (>5 km) stratigraphic section, detachment folding, multiphase salt activity, reactivation of older structures by newer ones and multi-stage development of salt bodies.

Geochemical Characteristics of Soil Rare Earth Elements within Spontaneous Combustion Coalfields of Rujigou Coal Mine

(1) Background: The spontaneous combustion of coal (SCC) not only consumes huge amounts of coal resources but also causes environmental degradation. Rare earth elements (REE) can be taken as an effective indicator to evaluate the environmental effects of SCC. Coal in the Rujigou Mine has been spontaneously combusting for hundreds of years. (2) Methods: The geochemical properties of REE and major elements in the soil of the Rujigou coal mine are methodically examined to reveal the environmental effects of SCC. (3) Results: Soil REE concentration in the Rujigou mine is 216.09 mg/kg, and there is an enrichment of light rare earth elements (LREE) and a depletion of heavy rare earth elements (HREE), LREE/HREE in Rujigou mine was 5.52. The spontaneous combustion of coal could change the vertical distribution of REE, which is conducive to the enrichment of LREE. According to the Eu anomaly and δCe/δEu, the source of material in this mine may be derived from the terrigenous clastic rock controlled by weak reduction. Aluminum and titanium have similar geochemical behavior to REE, especially LREE. The concentration of sulfur is negatively correlated with REE, especially HREE. Calcium, sodium, and magnesium all had a negative correlation with LREE. (4) Conclusions: The spontaneous combustion of coal can lead to the fractionation of light and heavy rare earth elements, resulting in the enrichment of LREE and depletion of HREE.

Microbial mat-induced microfacies in clastic deposits – An overview

Abstract This contribution reviews microbial microfacies recognisable in vertical sections through modern or fossil mat-overgrown sediment. Microfacies are products of endobenthic or epibenthic microbial mats interacting with sediment dynamics. Laminae of such mats form during sediment dynamic quiescence by organisation of filaments to an interwoven mat fabrics (binding), and biomass enrichment (growth) by cell replication and the production of extracellular polymeric substances (EPS). Vertical sections through mat-covered sediment may show buried stacks of subrecent mat laminae (biolaminites) that rose from alternating periods of mat development and sediment deposition. Mat laminae that drape ripple marks are visible as sinoidal structures in sediment core or sections. If the sediment-stabilising properties of a microbial mat is overcome by currents or waves of high strengths, cm-size mat fragments (mat chips and roll-ups) are ripped off and redeposited. Intrasedimenary gases, trapped beneath mat layers, may cause a high secondary porosity (sponge pore sand) in the sandy substrates. The internal build-up (microfabrics) of mat laminae is investigated under high magnification. Endobenthic microbial mat fabrics include filamentous and coccoid cells forming a network, EPS, and sedimentary grains. The grains derived from interaction of the endobenthic mats with bed load. Epibenthic microbial mat fabrics may include also silt-size particles syndepositionally enriched by baffling and trapping of suspension load. The fabrics of these mats commonly also include oriented sedimentary grains. These grains (now aligned bedding parallel) were dragged upward from the substrate during the development and growth of the mat. Overall, microbial microfacies provide insight into the sedimentation pattern of the (paleo-)environment and into the types of the substrate-colonising microbial mats.

Configuration of Carbonatite Constrained in Preintrusion Transpositional Foliation in the Bayan Obo Giant Rare Earth Element Deposit, China

Abstract The Bayan Obo ore deposit is the largest rare earth element (REE) deposit in the world and has been assumed to be hosted in dolomite that was folded in a syncline. This has been challenged by results from drill holes and low-resistivity, controlled-source audio-frequency magnetotellurics (CSAMT) survey. In this paper, we present structural analysis of clastic sedimentary rocks from around the deposit, their relationship with carbonatite, and the orientations of the carbonatite bodies and dikes to constrain the possible configuration of carbonatite. Clastic sedimentary rocks underwent mylonitic deformation to slate, metasandstone, and metaconglomerate, displaying dramatic changes of thickness along strike. Slates locally preserve intrafolial folds and hook folds bounded by foliations; metasandstones have parallel layers of recrystallized and preferred-orientated quartz aggregations; metaconglomerates contain flattened pebbles with Flinn k values of 0.01 to 0.05 and 0. The above structures and foliations were crosscut and intruded by carbonatite and associated fenite, demonstrating preintrusion transposition of original bedding to steep foliation. Preintrusion foliation provides zones of weakness that were exploited by upwelling of carbonatite magma. Northeast-SW–striking left-stepping en echelon carbonatite dikes and E-W–striking carbonatite bodies indicate that the carbonatite was emplaced in a sinistral transtensional zone. The northern and southern segments of the carbonatite bodies are parallel to the steep foliation at shallow depths and merge together at depth, constraining a Y-shaped configuration, consistent with the low resistivity result of the CSAMT survey. The newly recognized Y-shaped morphology indicates that the carbonatite extends deeper than 1,775.4 m, more than twice the previously inferred maximum depth of the syncline model, and contributes to a significant >1.78 times increase in global potential RE2O3 resources than previously estimated in 2021.

Genetic mechanism and main controlling factors of high-quality clastic rock reservoirs in deep and ultradeep layers: A case study of Oligocene Linhe Formation in Linhe Depression, Hetao Basin, NW China

Based on new data from cores, drilling and logging, combined with extensive rock and mineral testing analysis, a systematic analysis is conducted on the characteristics, diagenesis types, genesis and controlling factors of deep to ultra-deep abnormally high porosity clastic rock reservoirs in the Oligocene Linhe Formation in the Hetao Basin. The reservoir space of the deep to ultra-deep clastic rock reservoirs in the Linhe Formation is mainly primary pores, and the coupling of three favorable diagenetic elements, namely the rock fabric with strong compaction resistance, weak thermal compaction diagenetic dynamic field, and diagenetic environment with weak fluid compaction-weak cementation, is conducive to the preservation of primary pores. The Linhe Formation clastic rocks have a superior preexisting material composition, with an average total content of 90% for quartz, feldspar, and rigid rock fragments, and strong resistance to compaction. The geothermal gradient in Linhe Depression in the range of (2.0–2.6) °C/100 m is low, and together with the burial history of long-term shallow burial and late rapid deep burial, it forms a weak thermal compaction diagenetic dynamic field environment. The diagenetic environment of the saline lake basin is characterized by weak fluid compaction. At the same time, the paleosalinity has zoning characteristics, and weak cementation in low salinity areas is conducive to the preservation of primary pores. The hydrodynamic conditions of sedimentation, salinity differentiation of ancient water in saline lake basins, and sand body thickness jointly control the distribution of high-quality reservoirs in the Linhe Formation.

Retrieving meaningful information from detrital zircon in Palaeoproterozoic sedimentary rocks: Provenance, timing of deposition, metamorphism and alteration of zircon in sandstones of the Pretoria Group in the Transvaal Basin, South Africa

Abstract The Palaeoproterozoic sandstones and quartzites of the Pretoria Group (Transvaal Supergroup) in the Transvaal Basin of South Africa are important markers for regional correlations and dating of events of global importance (e.g., the Great Oxidation Event). The succession has few independent age markers, and much of the discussion about the time of deposition and the source of material of these rocks has been based on data from detrital zircon suites. The clastic sedimentary rocks of the Pretoria Group contain detrital zircon grains ranging from the Mesoarchaean to ages that are near-contemporaneous to, and even younger than the overlying and crosscutting igneous rocks of the Bushveld Complex. We show that the U-Pb age and Lu-Hf isotope distributions of the detrital zircon population in the Pretoria Group are the result of three different types of processes, acting successively: (1) Crystallisation in the igneous or metamorphic protosource rock (i.e., the rock where the zircon originally crystallised), (2) Metamorphic and hydrothermal resetting of the U-Pb chronometer induced by emplacement and crystallisation of the 2 055 Ma Bushveld Complex, and (3) Late, low-temperature processes (e.g., weathering). Critical age markers of maximum ages of deposition obtained after excluding effects of (2) and (3) are the 2 200 Ma Magaliesberg Formation (outside of the Bushveld aureole) and the 2 080 to 2 100 Ma Lakenvalei Formation. The Leeuwpoort Formation is a worst-case example, containing both young (<2 200 Ma) unmodified detrital zircon and hydrothermally altered zircon in the same age range. The two can only be distinguished from trace element analyses. Age distributions of Archaean and early Palaeoproterozoic zircon age fractions overlap with detrital zircon age suites in lower (i.e., pre-Timeball Hill Formation) parts of the Transvaal Supergroup, suggesting recycling within the basin or from the basin margin. Overlaps in 2 200 to 2 350 Ma zircon ages with those of volcanogenic zircon in the Timeball Hill Formation again suggest recycling. The origin of 2 080 to 2 150 Ma zircon is uncertain, but neither poorly constrained sources in the Kaapvaal Craton (e.g., Okwa Basement Complex) nor recycling of volcanogenic material from post-Magaliesberg formations can be ruled out.

Apatite Fission‐Track Thermochronology in the Tamusu Area, Bayingobi Basin, NW China, and its Geological Significance

AbstractThe Bayingobi basin is located in the middle of Central Asia Orogenic Belt, at the intersection of Paleo‐Asian Ocean and Tethys Ocean, as well as the junction of multiple tectonic plates. This unique tectonic setting underpins the basin's intricate history of tectonic activity. To unravel the multifaceted tectono‐thermal evolution within the southwestern region of the basin and to elucidate the implications of sandstone‐hosted uranium mineralization, granitic and clastic rock samples were collected from the Zongnai Mts. uplift and Yingejing depression, and apatite fission track (AFT) dating and thermal history simulation analysis were performed. AFT dating findings reveal that the apparent ages of all samples fall within the range of 244 Ma to 112 Ma. In particular, the bedrock of the Zongnai Mts. and Jurassic detrital apatite fission tracks have undergone complete annealing, capturing the uplift‐cooling age. Meanwhile, the AFT ages of Cretaceous detrital rocks are either equivalent to or notably exceed the age of sedimentary strata, signifying the cooling age of the provenance. A comprehensive examination of AFT ages and palaeocurrent direction analyses suggests that the Cretaceous source in the Tamusu area predominantly originated from the central and southern sectors of the Zongnai Mts. uplift. However, at a certain juncture during the Late Early Cretaceous, the Cretaceous provenance expanded to include the northern part of the Zongnai Mts. uplift. Based on the results of thermal history simulations and previous studies, it is considered that the Tamusu area has undergone four distinct tectonic uplift events since the Late Paleozoic. The first is the Late Permian to Early Triassic (260–240 Ma), which is associated with the closure of the Paleo‐Asian Ocean and the accretionary orogeny within the Alxa region. The second uplift event took place in the Early Jurassic (190–175 Ma) and corresponded to intraplate orogeny following the closure of the Paleo‐Asian Ocean. The third uplift event is the Late Jurassic to Early Cretaceous (160–120 Ma), which is linked to the East Asia's position as the convergence center of multiple tectonic plates during this period. The fourth uplift event is linked to the Late Early Cretaceous (112–100 Ma), driven either by the westward subduction of the eastern Pacific plate or the mantle upwelling resulting from the Bangong–Nujiang oceanic lithosphere subduction and slab break‐off. The primary stress orientation for the first three tectonic uplift phases approximated a nearly SN direction, while the fourth stage featured a principal stress direction of NW. The fourth tectonic uplift event of the Late Early Cretaceous and basaltic eruption thermal event during this period likely exerted a significant influence on the formation of the Tamusu sandstone‐hosted uranium deposit.

Initial sedimentation after the closure of the Sumdo Paleo-Tethys Ocean: Implications for early Mesozoic tectonics in the East Tethys domain

The closure of the Paleo-Tethys Ocean and subsequent collisional orogenesis in the early Mesozoic played an important role in the formation of the Qinghai–Tibetan Plateau. However, the final closure of the southernmost Paleo-Tethys branching ocean basin in the Qinghai–Tibetan Plateau—known as Sumdo Paleo-Tethys Ocean—and collision between Central and Southern Lhasa terranes remain controversial. In particular, the tectonic significance of early Mesozoic volcanism and sedimentation in the Lhasa terrane is unknown, but crucial for understanding the final stages of ocean closure. Here, we investigate the depositional ages and provenance of detrital zircon in clastic sedimentary rocks, as well as the petrogenesis of the interbedded andesite from the volcano-sedimentary sequence of the Late Triassic to Early Jurassic Xionglai Formation in the Tangjia-Sumdo area. Detrital zircon dates from the Xionglai Formation define five age peaks at 180–200 Ma, 230–340 Ma, 500–620 Ma, 1000–1240 Ma, and 1600–1800 Ma. Detrital zircon trace elements and Hf isotopic characteristics are interpreted to represent derivation from an accretionary wedge and later magmatism related to oceanic slab break-off as well as a minor component from coeval magmatic rocks in the Nyainrong-Nang area in northern Lhasa terrane. Interbedded andesite has a magnesian andesite signature and yields ages of 192–184 Ma with zircon εHf(t) values that range from −3 to +1. We interpret these data as the andesite being sourced from sediment-derived melts that interacted with the overlying mantle wedge in a post-collision extensional setting. Our study suggests that the closure of the Sumdo Paleo-Tethys Ocean and subsequent collision between Central Lhasa and Southern Lhasa terrane may have happened in Late Triassic-Early Jurassic. The final closure of the multi-Paleo-Tethys Ocean and subsequent collision in the Qinghai–Tibetan Plateau may have induced initial subduction of the Meso-/Neo-Tethys Ocean, representing the tectonic transition from collision/post-collision to subduction/accretion in the Qinghai–Tibetan Plateau during the Late Triassic to Early Jurassic.

Soil-forming accumulation of heavy metals in geological high background areas: Constraints of structure, lithology, and overlying soil geochemistry

Heavy metals (HMs) are often abnormally enriched in soils in geologically high background areas, posing a serious threat to the ecosystem and human health. However, the material origin of HMs in overlying soils is unclear. In this paper, we studied the accumulation control and formation process of HMs (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in soils overlying bedrock from different geological periods in a typical anticline structure area in southwest of Guizhou province. The results revealed that the content of HMs in the bedrock were ranked as Carboniferous carbonate rocks < Permian carbonate rocks < Triassic clastic rocks, while the opposite trend was observed for the HMs content in the overlying soil. The slopes of the EF-Q values of HMs in the soils overlying the Carboniferous, Permian, and Triassic rocks were 0.003, 0.007, and 0.83, respectively, which suggests that HMs enrichment or leaching was more complicated in the process of carbonate weathering soil-forming, whereas it was mainly in situ weathering during the process of clastic weathering soil-forming. The soils overlying the bedrock of the three geological periods experienced similar weathering processes and had the same source of soil-forming matrices, as it was observed that their Fe2O3-Al2O3, Hf-Zr, Nb-Ta, Th/Sc-Zr/Sc and Y/Ho-Y contents were significantly correlated (with R2 values of 0.80, 0.94, 0.72, 0.60, and 0.76, respectively) with very similar REE assignment patterns. The results corroborated the causes of the high background geological heterogeneity of HMs in the overlying soils in karst areas and supported the theory of the source of weathering soil-forming materials from carbonate rocks in karst areas.

Late Carboniferous–Early Permian sedimentary–tectonic evolution in the eastern Qaidam Basin, Western China: Insight into the zircon U–Pb geochronology of ash-fall tuffs and sandstones

The Late Carboniferous–Early Permian period is a significant transitional phase within the late Paleozoic ice age and to investigate the sedimentary–tectonic evolution of the Qaidam Basin in this period is crucial for comprehensively understanding the tectonic history of the northeastern Paleo-Tethys Ocean and the related response to energy and mineral resources. This paper focuses on the Carboniferous–Permian strata of the Wanggaxiu-Dongdagou outcrop that was taken to represent the southern Oulongbruk terrane in the eastern Qaidam Basin. We determined the ages of tuff interbeds within the Zhabusagaxiu Formation originally identified as the upper Carboniferous and obtained the crystallization age spectra of detrital zircon grains from Carboniferous to lower Permian sandstones using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) isotope geochemical techniques. The origin of the volcanic ash and the sedimentary–tectonic evolution in this period were analyzed. The results indicate that the original Zhabusagaxiu Formation can be divided into two chronostratigraphic units: the upper Carboniferous Zhabusagaxiu Formation and the lower Permian. The earliest age obtained from tuffaceous layers within the dark shale interval is 297.8 ± 3.0 Ma (mean square weighted deviation (MSWD) = 0.87), which suggests a stratigraphic boundary between the Carboniferous and Permian periods. Detrital zircons from Carboniferous–Permian samples in the southern Oulongbruk terrane predominantly originated from the Qaidam block-North Qaidam ultrahigh-pressure belt continental island arc to the south. The ultrahigh-pressure belt had a significantly increased contribution to the detrital source supply system from the Late Carboniferous to Early Permian, while the Qaidam block experienced frequent volcanic eruptions from 298 to 293 Ma, dispersing volcanic ash only northward to the Oulongbruk back-arc basin and the Zongwulong Trough. The upper Carboniferous Zhabusagaxiu Formation was marked by siliceous clastic rock–carbonate rock interbedding in an epicontinental sea, while the lower Permian was characterized by shallow to bathyal marine shelf to subaqueous sedimentation. The Early Permian transgression potentially represents the largest transgression during the late Paleozoic ice age, indicating an enriched hydrocarbon-generating interval.

Exploration potential of Papua New Guinea – latest multiclient 3D provides new insight into the underexplored Papuan Basin over the Papuan and Eastern Plateaus

The Gulf of Papua, part of the regional Papuan Basin, is characterised by extensional to passive margin tectonics from the Triassic to Late Oligocene and collisional tectonics from the Late Oligocene until the present day. The basin has experienced rapid clastic deposition in the late Neogene which covers an underlying extensive Miocene carbonate shelf with local bioherms and associated carbonate facies. Underlying the carbonates, an array of deformed and complex rift basins are present, with potential petroleum plays in undifferentiated Mesozoic sediments which onlap basement highs. The Miocene carbonates are the primary exploration targets, along with Pliocene clastic turbidite sediments in the Fly River Delta, Western Gulf of Papua. It is postulated that these were charged by Mesozoic marine–deltaic/terrestrial source rocks that were deposited during the opening of the Coral Sea. The offshore Papuan Basin is underexplored and the Gulf of Papua play types seen in the onshore Aure Fold Belt and offshore Fly River Platform could potentially extend offshore into the Coral Sea area. New broadband Pre‐Stack Depth Migration seismic data covering a part of the Eastern and Papuan Plateaus reveals new insights into the structural development of the region, rift basin geometries, configuration, and association of rift clastics and post-rift carbonates. Internal carbonate features can be observed on the new seismic data set, and new plays in the yet undifferentiated rift sediments of Mesozoic age are proposed in this study.

The influence of topography and transport history on the composition of clastic deposits from the Jurassic Tlaxiaco basin, southern Mexico: limitations on the use of mineral and chemical indices as proxies for paleoclimate

ABSTRACT The mineral and chemical composition of clastic deposits is commonly used as a proxy for reconstructing the climatic history of the Earth. A mineralogical and chemical study of clastic deposits from the Jurassic Tlaxiaco basin of southern Mexico illustrates that the entire sedimentary system in which detritus is generated, subaerially transported, and deposited exerts a major control on the composition of sedimentary rocks, placing some constraints on the use of mineral and chemical indices as paleoclimatic proxies. Since clastic deposits of the Tlaxiaco basin were formed under similar humid climatic conditions, but in sedimentary systems with different topography and transport histories, they represent a natural laboratory for testing the control that these parameters exert on the composition of clastic rocks. Our petrographic and chemical results show that, in sedimentary systems associated with low relief and in which detritus had the possibility of being temporarily stored in floodplains and meandering bars, parent rocks and the derivative detritus interacted with weathering fluids over a long time, producing clastic deposits with composition that is representative of the weathering conditions and climate of the region. On the other hand, in environments associated with steep and tectonically active relief, the rates of sediment transport and burial exceed the rate at which weathering can generate detritus, producing sedimentary deposits with composition that largely underestimates potential weathering and provide unreliable information on climate. Mineral and chemical indices should be considered as reliable paleoclimate proxies only when sedimentological data indicate that the sedimentary system allowed sediment interaction with weathering fluids over a long time.

Lithology-driven soil properties control of N2O production by ammonia oxidizers in subtropical forest soils

Lithology can strongly influence soil's physical and chemical properties, significantly affecting soil nitrogen (N) transformation rates. Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and complete ammonia oxidizers (comammox Nitrospira) constitute the major producers of soil nitrous oxide (N2O), but the importance of different lithology on their relative contributions still poorly understood, especially in terms of newly discovered and widespread comammox. To address this knowledge gap, three nitrification inhibitors, acetylene (ammonia oxidizers inhibitor), 1-octyne (AOB inhibitor) and 3,4-dimethylpyrazole phosphate (DMPP) (both AOB and comammox inhibitor), were used to selectively inhibit the activity of different ammonia oxidation groups in order to discriminate their respective roles in N2O production in forest soils developed on different lithologies (limestone and clastic rock). The results showed that AOB dominated N2O production (63.5 ± 3.3 %) in limestone soils with ammonium amendment, followed by AOA (34.5 ± 7.6 %), while comammox contributed 1 % of total N2O production with N2O yield of 0.03 ± 0.04 %. Higher N2O production by AOB in limestone soils is associated with higher soil pH, exchangeable calcium/magnesium and lower short-range order iron/aluminum minerals. However, the N2O yield by comammox (0.12 ± 0.12 %) in clastic rock soils was comparable to that by AOA (0.15 ± 0.14 %) and AOB (0.20 ± 0.13 %). Based on the results of the correlation analysis, comammox in the clastic rock soils produce greater amounts of N2O is closely related to the higher soil organic carbon and available phosphorus. The present study provided evidence that the lithology-driven soil properties markedly affect the N2O production from different ammonia oxidizers.

Effects of soil aggregates and minerals on microbial necromass carbon are regulated by parent materials

Microbial necromass carbon (MNC) is a key soil organic carbon (SOC) pool. Soil aggregates and minerals play pivotal roles in controlling soil carbon storage. Although soil minerals and aggregates are tightly linked to parent materials, it is uncertain whether the relative importance of aggregates and minerals in governing MNC varies depending on soil parent materials. In this study, we determined the MNC content in forest soils originating from two contrasting soil parent materials, namely karst (carbonate rocks) and non-karst soils (clastic rocks) across a climatic gradient in southwest China. The MNC contents (24.5 ± 0.8 mg g−1 in karst and 24.1 ± 1.8 mg g−1 in non-karst soils) and their respective contribution to SOC (43.7 ± 1.3 % in karst and 41.1 ± 1.4 % in non-karst soils) were similar between the two parent materials. In karst soils, MNC was influenced by aggregates rather than minerals, whereas the opposite was true in non-karst soils. A higher proportion of microaggregates directly increased the MNC content in karst soils, whereas greater mineral contents indirectly increased the MNC through their effects on microbial biomass carbon. The divergent effects of aggregates and minerals on MNC were predominantly attributed to the formation of secondary carbonate crystals in calcium-rich karst soils as well as to the differences in pH between karst and non-karst soils. Additionally, climate (mean annual temperature and precipitation) and vegetation properties (aboveground biomass or richness) indirectly affected the MNC through their effects on aggregates or minerals in karst and non-karst soils. Consequently, the influence of soil aggregates and minerals on microbially derived carbon is mediated by the parent material. Our findings emphasize the importance of considering lithology-dependent drivers in predicting soil carbon accumulation, particularly in relation to the stability of microbial-derived carbon.