Detrital Rocks Research Articles

Speleothem in Sandstone: Maranhão as a Geo-Speleological Scenario

Background: The municipality of Carolina, located in the southern region of Maranhão, features a terrain composed of hills and plateaus formed from sandstone lithology originating from the Balsas Group formations. This region houses geological features such as caves and speleothems, which pertain to endokarst, primarily formed through erosive processes. Due to its significant speleological potential, the region has been studied by the Conservation Units Research Group (GEUC) of the Maranhão State University (UEMA) since 2013. Objective: The study aims to catalog sandstone caves. In addition to mapping and surveying these caves, a sandstone stalagmite speleothem was recently recorded, supporting studies that defend the legitimacy of karst features in detrital rocks. Theoretical Framework: For a long time, sandstones were considered pseudo-karst. However, recent geological perspectives recognize this rock type as true karst, necessitating a deeper understanding of the intricate formative complex of exokarst and endokarst. Methodology: To obtain research results, after reviewing scientific literature, caves were prospected based on geological, geomorphological, and slope mapping conducted in a geoprocessing environment, followed by surveying existing caves. Specifically, this study aimed to analyze the speleothem and its genesis. Results and Discussion: This study presents a brief discussion on the possible karst formation processes, highlighting the rare occurrence of the sandstone stalagmite found in Carolina-MA and its morphogenetic process. This contributes to the originality of the research, given the scarce literature on this subject. Research Implications: Understanding the detailed characteristics of caves and specifically their ornamentation is important in itself. In this case, studying sandstone caves in a relatively unknown area provides insights necessary for evaluating the local implications of large-scale developments, in addition to supporting geological knowledge regarding these formations. Originality/Value: Two factors contribute to the value of this research. Firstly, it enhances geological understanding of speleothems. Secondly, in the context of the sandstones in the Parnaíba Basin, it provides valuable knowledge about the rare internal formations within these caves.

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.

Coevolving edge rounding and shape of glacial erratics: the case of Shap granite, UK

Abstract. The size distributions and the shapes of detrital rock clasts can shed light on the environmental history of the clast assemblages and the processes responsible for clast comminution. For example, mechanical fracture due to the stresses imposed on a basal rock surface by a body of flowing glacial ice releases initial “parent” shapes of large blocks of rock from an outcrop, which then are modified by the mechanics of abrasion and fracture during subglacial transport. The latter processes produce subsequent generations of shapes, possibly distinct in form from the parent blocks. A complete understanding of both the processes responsible for block shape changes and the trends in shape adjustment with time and distance away from the source outcrop is lacking. Field data on edge rounding and shape changes of Shap granite blocks (dispersed by Devensian ice eastwards from the outcrop) are used herein to explore the systematic changes in block form with distance from the outcrop. The degree of edge rounding for individual blocks increases in a punctuated fashion with the distance from the outcrop as blocks fracture repeatedly to introduce new fresh unrounded edges. In contrast, block shape is conservative, with parent blocks fracturing to produce self-similar “child” shapes with distance. Measured block shapes evolve in accord with two well-known models for block fracture mechanics – (1) stochastic and (2) silver ratio models – towards one or the other of these two attractor states. Progressive reduction in block size, in accord with fracture mechanics, reflects the fact that most blocks were transported at the sole of the ice mass and were subject to the compressive and tensile forces of the ice acting on the stoss surfaces of blocks lying against a bedrock or till surface. The interpretations might apply to a range of homogeneous hard rock lithologies.

About this title - Minor Minerals, Major Implications: Using Key Mineral Phases to Unravel the Formation and Evolution of Earth's Crust

Key minerals, including zircon, apatite, titanite, rutile, monazite, xenotime, allanite and garnet, can retain critical information about petrogenetic and geodynamic processes. This Special Publication showcases snapshots of the latest developments using key minerals in igneous, metamorphic and detrital rocks through current-state reviews, contributions focused on case studies and newly developed techniques.

Mobility, activity ratio significance and risk assessment of radionuclides in sandstone of Magharet El Miah, Southwestern Sinai, Egypt

Sedimentary rocks of Magharet El Miah were radiometrically analyzed for determination of radionuclides 238U, 232Th, 226Ra and 40K activity concentrations. The U-content and Th/U ratio in these rocks illustrated poor weathering and rapid deposition of rock detritus. Preferential dissolution of 234U due to α-decay related processes and its re-adsorption and precipitation are responsible for the observed radioactive disequilibrium in 234U/238U of Magharet El Miah sandstone. 234U mobilization could be related to the effect of surficial or underground water. 226Ra/238U disequilibrium could be revised to the difference in the geochemical characteristics of the two isotopes. 230Th/238U activity ratios were lower than unity in all samples (10 samples) except sample number 1, suggesting selective uranium accumulation in most samples or 230Th leaching by acidified water where the rocks contain high sulpher contents. Many of the 238U/235U activity ratios were shifted from the natural ratio due to the changes in redox conditions that leads to fractionation of higher isotope from lighter one. The plotted value of 234U/238U and 230Th/238U illustrated that the U-accumulation occurred in the period from <6 × 104–105 years. The studied sandstone had higher values for uranium (95.4 ± 7.1 to 130.3 ± 12.3 Bq.kg−1), thorium (65.8 ± 4.2 and 78.4 ± 6.7 Bq.kg−1) and radium (68.2 ± 4.4 and 80.3 ± 9.1 Bq.kg−1) but lower for potassium (38.4 ± 1.2 and 54.2 ± 2.3 Bq.kg−1) in comparison with international permissible levels. All the estimated environmental hazard indices illustrated that most samples lied in the permissible level ranges. Cluster analyses indicated that the main environmental health hazard parameters exist due to the activity concentrations of 238U and 226Ra.

Glacier–rock glacier interactions in the eastern Hindu Kush, Nuristan, Afghanistan [35.92,71.13] in the period 1976–2019

ABSTRACT Landsystem relationships between glaciers and rock debris supply in a mountain landscape domain, (), are described. Decimal latitude-longitude [dLL] geolocations are used to identify features and transects in an information landscape. Geo-located features are coded, enabling transects between a 1976 expedition and 2019 Google Earth imagery to be compared. Rock debris is progressively added to 1-3 km long glaciers which become debris-covered. Cirque glaciers eventually assume rock glacier (RG) forms when supraglacial debris loads are high. Some rock glacier snouts reach main valley floors and still advance over meadows. This behaviour is attributed to high geomorphic activity producing rock detritus and transport to glaciers in the early Little Ice Age. The advances of rock glacier snouts are a consequence of thinning; low-angle glaciers still moving beneath debris-covered glaciers (GLd) covers. Persistent melt pools continue to develop within the surface debris cover of glaciers and rock glaciers and expose glacier ice. All the rock glaciers are below the regional snowline and permafrost can be discounted for rock glacier formation. Scree slope (SS) development may ultimately be sufficient to cover bare glacier ice moving from a glacier (GL) to debris-covered glacier (GLd) to rock glacier (RG). Reverse slopes in the debris at the foot of screes mark the mass continuum of glacier flow below the debris cover, not the ‘rooting zone’ of a permafrost-derived RG. Scree slopes themselves show no evidence of rock glacier-like flow. A simple glacier ice-debris transport continuum model is sufficient and necessary for rock glacier formation and flow.

Стратиграфическая привязка крупнообломочного материала из отложений Южно-Сахалинского грязевого вулкана

One of the crucial tasks in studying the genesis and deep structure of mud volcanoes is to determine the origin of the erupted material and the depth of its original location, the so-called roots. The purpose of this study was to present the first results of stratigraphic control of solid emissions from the Yuzhno-Sakhalinsk Mud Volcano with local stratigraphic units. As a result of field work, a collection of rock material sampled from the mud volcano deposits and natural outcrops of the stratigraphic units typical of the study area has been compiled. According to lithological characteristics, sandstones, siltstones, clay-bearing carbonate, and carbonate rocks have been identified among the large detrital rocks in the solid emissions of the Yuzhno-Sakhalinsk Mud Volcano. The largest group of rock fragments was represented by the sandstone, which was different in its structural and textural characteristics. The first confirmations have been obtained that the mud volcano chamber extends beyond the traditionally accepted boundaries of the Bykov Formation. The preliminary results of stratigraphic control of large detrital rocks indicate the highest lithological similarity with the deposits from the Lower Bykov Subformation and Naiba Formation, suggesting that the main source (mud volcano chamber) of the erupted large detrital rocks lies within the depth range of 2,500 to 3,500 meters. Evidence of Cenozoic rock inclusion in the mud volcano process has also been found

Detrital zircon similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and Meguma

Despite the so-called exotic nature of the South Portuguese Zone relatively to the other major domains of the Iberian Massif of peri-Gondwanan affinity, Devonian detrital rocks of the oldest strata in the Iberian Pyrite Belt have a remarkable resemblance with the Ossa-Morena Zone’s Neoproterozoic-Cambrian rocks and the West Meguma’s Cambrian-Ordovician rocks, presenting the so-called “West African signature”.

Fluid Inclusion, Isotopic, and Elemental Geochemistry Studies of Cave-Filling Calcite in the Lower–Middle Ordovician Yingshan Formation of Tahe Oilfield, NW China: Implication for Karstification in Non-exposed Limestone

Improving the recognition of paleo-fluid circulation history is of great significance to reconstruct pore evolution during carbonate diagenesis. Integrated petrography, fluid inclusion, isotopic and elemental geochemistry (laser ablation inductively coupled plasma mass spectrometry) studies, calcites generated in paleocaves, and fractures were investigated. This study aims to reveal the paleo-fluid origin and karstification event within the nonexposed limestone of the Lower–Middle Ordovician Yingshan Formation in the Tarim Basin. The only generation of blocky calcite growing along the karst paleocave and fracture walls [cave-filling calcite (CFC)] crosscuts burial stylolites. The secondary fluid inclusions obtained from CFC are characterized by the coexistence of liquid-only and liquid-dominated aqueous inclusions with low salinities values (0–2.4 wt%), suggesting that the CFC has experienced a low-temperature environment (&amp;lt;50°C). The depleted δ18O values (−15.32‰ to 12.45‰), seawater-like yttrium and rare earth element patterns, and low ΣREE (&amp;lt;0.65 ppm) have recorded the major episode of meteoric water leaching the Yingshan limestone. This view was further confirmed by the calculated δ18Owater values of parent fluids (−14.3‰ to 2.2‰). The relatively higher 87Sr/86Sr ratios (0.70942–0.70994) are interpreted as the result of meteoric water interacting with the overlying Silurian detrital rock when percolated downward. The geochemical evidence recorded by CFC indicates that the karstification event for Yingshan nonexposed limestone possibly took place in the Early Hercynian period during the late Devonian. Therefore, meteoric water percolating downward along the fractures penetrating insoluble strata and/or migrating laterally along the permeable strata is deemed responsible for the karstification event, although the overlying thick insoluble strata in the coverage area.

Zircon xenocrysts in Late Cretaceous magmatic rocks in the Kermanshah Ophiolite: link to Iran continental crust supports the subduction initiation model

ABSTRACT Geochronological and geochemical data show that Late Cretaceous Zagros ophiolites were generated by forearc seafloor spreading during a subduction initiation event along the southwestern margin of Iran. These ophiolites define a ~ 3000 km long belt passing from Cyprus to Turkey, Syria, Iran, the UAE, and Oman. Ten samples of plagiogranites, amphibole gabbros and diorites of the Kermanshah ophiolite yield U-Pb zircon magmatic ages indicating ophiolite formation at 98 to 96 Ma. Some Kermanshah rocks also contain abundant zircon xenocrysts with age peaks (in order of decreasing size): Triassic (~247 Ma), mid-Paleoproterozoic (~2150 Ma), Late Paleoproterozoic (~1850 Ma), Late Ediacaran (~560 Ma), Early Cretaceous (~140 Ma), and Tonian (~850 Ma). Similar age peaks are seen in magmatic and detrital rocks of Iranian crust to the north. The xenocrysts have εHf(t) values from +6.3 to – 21.6, corresponding to depleted mantle Hf model ages (TDM) of 0.6 to 3.6 Ga. The xenocryst age peaks are similar to those of zircons in Iranian continental crust. The occurrence of zircon xenocrysts in the Kermanshah ophiolite suggests that this formed adjacent to the Iranian continent, as expected for Late Cretaceous subduction initiation.

The Cu-Ag-Pb Polymetallic Mineralization of Agdim-Ait Elfersi Sector, North-Eastern Part of the Saghro Massif, Morocco: Geological Setting, Ore Petrography and Geochemistry

The Cu-Ag-Pb polymetallic mineralization of the Agdim-Ait Elfersi sector is situated in the eastern Anti Atlas Moroccan belt, the northeastern part of the Saghro inlier. The mineralization is hosted in the volcanic rocks of late Neoproterozoic and the detrital sedimentary rocks of the Lower Cambrian. A network of faults has affected this area; it is a brutalizing deformation with NW-SE, NE-SW, E-W, and NNE-SSW directions. NW-SE and NE-SW structures have a metallogenic significance. This tectonic canvas was used as a target of a mineralization vein with Cu, Ag, and Pb in this area. By combining geological, structural, and metallogenic characteristics, it can be assumed that the Cu-Ag-Pb mineralization of the Agdim-Ait Elfersi sector is linked to two major events. A late Pan-African event linked to the extensional tectonics of the late Neoproterozoic, responsible for the establishment of mineralization at the level of the basement, and then a late Hercynian-Atlasic event, which manifests by the remobilization of metals in NE-SW oriented structures. Geochemical analysis shows the polymetallic character of this mineralization. The high contents of silver and mercury observed indicate the presence of similarities of an Ag-Hg epithermal type of mineralization in this area. Geological context, as well as mineralogical and textural characters of the Agdim-Ait Elfersi sector are reminiscent of epithermal-type mineralization as in the Imiter and Zgounder deposit.

Runoff change induced by vegetation recovery and climate change over carbonate and non-carbonate areas in the karst region of South-west China

Karst plant habitats are generally harsh and vulnerable to climate and human interferences. Restoration of karst vegetation and its effect on water resources are affected not only by climate and anthropological interferences but also by different bedrock lithologies. In this study, changes to climatic factors, vegetation indices of the normalized difference vegetation index (NDVI), the leaf area index (LAI) and runoff during 1982–2015 were statistically identified over the Yangchang river basin (YRB) with two contrasting bedrock lithologies (carbonate rock and detrital rock) in southwest China. The Budyko equation and the hydrological model in LPJ (the Lund-Potsdam-Jena Dynamic Global Vegetation Model) were calibrated and improved to separate runoff change that could be attributed to climate and vegetation changes during 1982 ~ 2015. LPJ was used to predict the potential vegetation for natural recovery without human interference and its effect on the hydrological budget in YRB. Results reveal that the execution of the major ecological restoration project (the Grain for Green Project) in YRB since the early 2000 s has significantly increased NDVI and LAI even in the drier period of 2004 ~ 2015. However, the human effort of vegetation restoration only reaches about 25% of the potential capacity in the whole study area. The reforestation in YRB could decrease runoff by about 7.0 to 7.6% in the period from 2004 to 2015, and 11.2% in the future when vegetation shifts from artificial to natural vegetation recovery. Meanwhile, thick soil in the non-carbonate area can store more water to support a large proportion of forest, and raise drought resistance. However, the limited water holding capacity of weathered bedrock in the carbonate area restricts large tree growth, and thus reduces drought resistance. These results point a need for consideration of how bedrock geology influences available water limitations when designing suitable reforestation strategies in southwest China.

Types of river sources of the thin-grained aluminosilicaclastics for the Jurassic and lower cretaceous deposits of the West Siberian megabasin

Background. The lithogeochemical features of fine-grained detrital rocks (mudstones, shales, and fine-grained siltstones) allow, with a certain degree of success, the main parameters of the formation of sedimentary sequences to be reconstructed. These parameters include (primarily in terms of their REE and Th systematics) the types of river systems supplying thin terrigenous suspension in the sedimentation area: the rivers of the 1st category – large rivers with a catchment area of more than 100,000 km2; 2nd category – rivers feeding on the products of erosion of sedimentary deposits; 3rd category – rivers draining mainly igneous and metamorphic rocks; and 4th category – rivers carrying erosion products of volcanic associations.Aim.To reveal, based on the analysis of interrelationships between such parameters as (La/Yb)N, Eu/Eu* and the Th content, the types of river systems that fed the Jurassic and Lower Cretaceous deposits of the Shaim oil and gas region (OGR) (Sherkalinsky, Tyumen, Abalak and Mulymya formations) and the region of the North Pokachevsky field of the Shirotnoe Priobye region (Sherkalinsky, Tyumen and Bazhenov formations, Lower Cretaceous deposits).Materials and methods. The ICP MS data for almost 100 samples of mudstones and fine-grained clayey siltstones were used to analyse the features of distribution of lanthanides and Th in the Jurassic and Lower Cretaceous clayey rocks of the Shaim OGR and the area of the North Pokachevsky deposits. Individual and average composition points for formations, members and layers were plotted on the (La/Yb)N-Eu/Eu*, (La/Yb)N–Th diagrams developed by us with classification areas of the composition of fine suspended material of modern rivers of different categories.Results and conclusion. The results presented in the article showed that during the formation of the deposits of the Shaim OGR in the Early and Middle Jurassic, erosion affected either mainly sedimentary formations or paleo-catchment areas that were very variegated in their rock composition. In the Late Jurassic, the source area was, most likely, a volcanic province, composed mainly of igneous rocks of the basic composition, and located within the Urals. This conclusion suggested that the transfer of clastic material from the Urals to the Urals part of the West Siberian basin “revived” much earlier than the Hauterivian. The Jurassic-Lower Cretaceous section of the vicinity of the North Pokachevsky field was almost entirely composed of thin aluminosilicaclastics formed due to the erosion of volcanic formations. These volcanic formations were located, as followed from the materials of earlier performed paleogeographic reconstructions, probably within the Altai-Sayan region or Northern Kazakhstan. Thus, the supply of detrital material in the considered territories of the West Siberian basin had a number of significant differences in the Jurassic and early Cretaceous.

Detrital rutile tracks the first appearance of subduction zone low T/P paired metamorphism in the Palaeoproterozoic

Earth is unique in the Solar System as the only planet characterised by an active plate tectonic regime. However, there is still no consensus on whether this was fully operational in the Archaean or if it did not develop until the Proterozoic. The metamorphic record offers valuable insight into this debate, since paired, high and low T/P metamorphic conditions are a hallmark of modern plate tectonics. However, much of the metamorphic rock record has either been eroded or overprinted by subsequent tectonothermal events. To address this issue, we examine the detrital rock record and evaluate the potential of rutile, a mineral that forms during subduction and deep-crustal metamorphic processes, as a proxy to track the existence of low T/P and paired metamorphism. At temperatures of 550°C, rutile is mostly stable at pressures higher than ca. 13 kbar. We use this relationship and the Zr-in-rutile thermometer to determine peak metamorphic temperatures of detrital rutile grains to track the temporal distribution of low T/P metamorphism. We have compiled a dataset of detrital metamorphic rutile from Archaean to Permian age to trace the occurrence of low and high T/P metamorphism through time. The earliest evidence of low T/P from detrital rutile is at about 2.1 Ga. This agrees with the earliest evidence of eclogite facies conditions from the rock record and it also implies that these conditions must have been more prevalent than the present rock record seems to indicate. Together, our study confirms that subduction zone low T/P metamorphism has been fully operating since at least the late Palaeoproterozoic.

Mineralization, fluid inclusion and sulfur isotope studies in The Gardane-Shir Pb-Zn deposit ,Ardestan,Isfahan Province

Gardaneshir carbonate-hosted Pb-Zn deposit on the ground of study area located southwest of Ardestan in Isfahan province. Base on lithostratigraphy,the main structure, besides the small outcrops of Jurassic shales, has been made up of carbonate and detrital rock materials depending on Paleozoic,Triassic and Cretaceous time stages. Dolomitic carbonate which is attributed to Shotori Formation , played the major role of host rock in ore-mineralization. Ore-mineral description obtained from the mineralized zone and caused the following ore-paragenesis in ascending order.of:pyrite,chalcopyrite,galena,sphalerite,malachite,cerussite,smithsonite,iron oxides and gangues of barite, quartz and calcite. Physico-chemical information of ore-solutions performed by entrapped fluid inclusion studies in gangue minerals. Liquid-rich two phase(L+V) inclusions as predominant types were recognized. These type of inclusions are homogenized into liquid state with a range of TH and related salinities between; TH :78 to 183 and 216 to 283°C, Salinity:3.5 to 9.7 and 10.2 to 25 wt% NaCl eq. The microthermometric data reflect the nature of two population of fluid inclusions originating from different sources. The source materials could have been provided by basinal brines, derived during compaction of sediments in a shallow sea environment and by movement into sediments, the stratabound Pb-Zn deposit are formed. Furthermore, the negative delta value ranges(δ34S) from -0.6 ‰ to -20.4 ‰ that have been extracted by galena can be an evidence of bacterial sulfate reduction in a subsidence sedimentary basin. In conclusion, based on field, mineralogical, fluid inclusion and sulfur isotope evidence, we propose that Gardaneshir Pb-Zn deposit is a stratabound carbonate hosted of Mississipi Valley Type(MVT).

Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

U–Pb dating and Hf isotopic analyses of detrital zircon grains from Cambrian-Devonian strata in the Moroccan Mesetas were undertaken in order to constrain its Paleozoic paleogeographic evolution. In this work, we analyzed 12 Late Devonian-Late Carboniferous samples of syn-collisional detrital rocks from the Western and Eastern Moroccan Mesetas. All our samples present significant Ediacaran (ca. 620 Ma) and Rhyacian (ca. 2.1 Ga) detrital zircon populations, suggesting that the West African Craton remained the main source of sediments for northern Morocco at least until the Late Carboniferous. Locally, a Stenian-Tonian (ca. 1.0 Ga) detrital zircon population is also present, probably fed from intermittent and distant source areas located in NE Africa (e.g. Sahara Metacraton). The collisional evolution started with the approach of an Avalonian promontory to the northern Gondwana continental margin (latest Devonian - earliest Carboniferous), after the closure of the Rheic Ocean. This process entailed the former subduction of the Rheic oceanic lithosphere underneath the Avalonian continental terrane and the formation of a magmatic arc in the upper plate. In this scenario, the first syn-collisional sediments (Tournaisian; Tiflet and Debdou-Mekkam areas) are characterized by a Devonian detrital zircon population (ca. 370 Ma), presumably derived from the magmatic arc, and an increasing number of Mesoproterozoic dates, putatively also sourced from the continental crust of the Avalonian terrane. After the initial collision, only the Visean samples located in areas close to the exotic terrane (e.g. Ben Slimane area) displayed a minor Avalonian component. Finally, the Late Carboniferous samples from the Jerada area recorded an important Middle Carboniferous (ca. 330 Ma) detrital zircon population, probably sourced from Variscan granitoids emplaced in the Eastern Moroccan Meseta and attesting to crustal thickening and subsequent thermal maturation of the Gondwana continental crust in this area.

MODERN BELIGERATIVE RELIEF (ON THE EXAMPLE OF YAVORIV MILITARY TRAINING GROUND OF LVIV REGION)

The author establishes the types of relief created for military purposes (beligerative) and analyzes its morphology. The territory of the Yavoriv military training ground in the Lviv region, the largest in Ukraine training complex of various types and kinds of troops, was chosen as an example. The military training ground was established in the 30s of the twentieth century. In the past, Polish infantry, German tank divisions, Soviet troops, and nowadays Ukrainian and international ground and air forces trained here. The area of the landfill is 361.5 km2. It occupies an advantageous position in the terrain, as it is located on an elevated part of the Roztochchya Upland, where the Main European watershed passes. Loose sediments are widespread in the territory, which contribute to the creation of deep and elongated forms of beligerative relief. These are mainly quaternary alluvial sands and detritus of native rocks, aeolian and diluvial loess and sandy loams, alluvial sediments. We consider the beligerative relief as an integral part of the field military fortification. The research was performed on the base of interpretation of large-scale space images, aerial photographs and field studies. The modern beligerative relief observed at the Yavoriv military training ground was classified into positive and negative forms depending on the method of military activity. Positive forms include: 1) hills of command posts for control and surveillance, 2) hills of tank or cannon fortifications, 3) micro-hills of protection against small arms, 4) bunkers (wooden-earth defense points), 5) high-altitude targets and firing positions. Negative forms are as follows: 1) trenches of the defense line and the course of connections; 2) open structures for the protection of personnel: individual trenches, pairs, for several infantry, as well as for shooting lying down, kneeling, standing; 3) trenches for the protection of equipment and heavy artillery weapons; 4) closed structures for personnel protection: dugouts, bunkers, cracks, dugouts; 5) excavations from ruptures of artillery shells. There are more negative forms in the modern military relief. Analysis of space images from different times (1980–1990, 2000–2005, 2015–2019) and modern field observations allowed us to trace the dynamics of beligerative relief forms. The formation of new and most widespread forms occurs in the mid-80 of the twentieth century. At the end of the XX and at the beginning of the XXI century, the existing forms decline, steamrolled by exogenous processes, and new ones do not appear. New forms have been appeared since 2015, but only in small local areas. The place they appear are characterized by a significant anthropogenic transformation of the terrain, the development of exogenous processes, such as soil dispersal, desertification, erosion, oozing. Key words: beligerative (military) relief; Yavoriv military training ground (Ukraine); morphological classification.

Palaeoproterozoic turbidite deposition in the Liaodong Penisula, northeastern North China craton – Constraints from the Gaojiayu formation of the Liaohe Group

The Palaeoproterozoic sedimentary environment is difficult to reconstruct because rocks often experience multiple stages of deformation and metamorphism; however, it is critical to understand the Precambrian evolution of sedimentary basin. In this study, we report two un-metamorphosed sections in the Gaojiayu Formation of the North Liaohe Group, central part of the Jiao-Liao-Ji orogenic belt, eastern North China Craton. Rocks consist of shales, carbonaceous slates, calcareous mudstones and sandstones, marlstones, calcarenites, and brecciated limestones in these sections. Detailed field observations indicate that all kinds of original bedding and syn-depositional structure developed in these rocks. Microscope observations suggest that detritus in rocks predominantly contain feldspars, quartz, and calcites, occasionally with volcanic fragments and pyrites. Palaeocurrent study indicates that the provenance of detritus in rock of these two sections was from NW to SE. Detrital heavy minerals mainly consist of pyrite and hematite, occasionally with barite, which are all from the Li'eryu Formation that contains these minerals in sedimentary layers. The increase of percentages of pyrite in a cross-section indicate that the sedimentary environments transformed from an oxidizing to a reducing depositional environment because the depositional setting became deeper. According to the mafic intrusion dated in this study and regional geochronological data such as the age of underlying volcanic rocks, the depositional age of the Gaojiayu Formation is constrained between 2.17 and 2.16 Ga and 2.11 Ga. Archaean basement (2.5 Ga) is recognized as the major provenance providing clastic materials for the Gaojiayu Formation; volcaniclastic rocks in the Li'eryu Formation were also a significant source. Accordingly, in this paper we interpret the Gaojiayu Formation as turbiditic sedimentary rocks that were deposited in an arc-related abyssal and semi-abyssal environment, probably in an extensional back-arc basin setting. Palaeoproterozoic turbidite deposition combined with a 2.17 Ga volcanic arc developed in the study area, we conclude that the modern trench-arc-basin system may had already existed in the early Palaeoproterozoic and deeply affected the tectonic evolution of the Jiao-Liao-Ji orogenic belt, northeastern North China Craton.

Provenance and tectonic implications of the Carboniferous sediments in the Bainaimiao arc belt, northern margin of the North China Craton: evidence from detrital zircon U–Pb–Hf isotopes and trace elements

Sedimentological and zircon U–Pb–Hf isotopic analyses of the Carboniferous strata in the Bainaimiao arc belt (BAB) provide provenance information for the northern margin of the North China Craton (NCC). The late Carboniferous strata in the eastern BAB were dominantly shallow marine carbonate-clastic deposits. Detrital zircon data show that: (1) sandstone from lower Sidaozhangpeng Formation displays two major age peaks of 369 Ma and 2522 Ma, with eHf (t) values of − 25.9 to − 20.4 and 2.2–6.4, respectively; (2) sandstone from upper Sidaozhangpeng Formation shows a significant age peak at 384 Ma, with eHf (t) values of − 25.3 to − 14.5. Determination of detrital zircon parent rock types based on trace element proxies suggests that the protolith rock types consist of felsic (73%) and mafic rocks (22%), with minor alkaline rocks (5%), implying a continental arc setting. The U–Pb–Hf dating of the Carboniferous strata in the western and eastern BAB shows different provenances: the Carboniferous sediments in the western BAB were derived from early Paleozoic magmatic rocks, micro-block (Hunshandake Block) and the NCC basement; the provenances of the Carboniferous strata from the eastern BAB were mainly local Devonian magmatic rocks, with subordinate input of the Neoarchean NCC basement rocks. The early Paleozoic zircon grains recorded by the early Devonian rhyolitic tuff and late Carboniferous sandstone indicate that the early Paleozoic arc magmatic activities also occurred in the eastern BAB.

Reservoirs properties of slump-type sub-lacustrine fans and their main control factors in first member of Paleogene Shahejie Formation in Binhai area, Bohai Bay Basin, China

Abstract High-yielding oil wells were recently found in the first member of Paleogene Shahejie Formation, the Binhai area of Qikou Sag, providing an example of medium- and deep-buried high-quality reservoirs in the central part of a faulted lacustrine basin. By using data of cores, cast thin sections, scanning electron microscope and physical property tests, the sedimentary facies, physical properties and main control factors of the high-quality reservoirs were analyzed. The reservoirs are identified as deposits of slump-type sub-lacustrine fans, which are marked by muddy fragments, slump deformation structure and Bouma sequences in sandstones. They present mostly medium porosity and low permeability, and slightly medium porosity and high permeability. They have primary intergranular pores, intergranular and intragranular dissolution pores in feldspar and detritus grains, and structural microcracks as storage space. The main factors controlling the high quality reservoirs are as follows: (1) Favorable sedimentary microfacies of main and proximal distributary gravity flow channels. The microfacies with coarse sediment were dominated by transportation and deposition of sandy debris flow, and the effect of deposition on reservoir properties decreases with the increase of depth. (2) Medium texture maturity. It is shown by medium-sorted sandstones that were formed by beach bar sediment collapsing and redepositing, and was good for the formation of the primary intergranular pores. (3) High content of intermediate-acid volcanic rock detritus. The reservoir sandstone has high content of detritus of various components, especially intermediate-acid volcanic rock detritus, which is good for the formation of dissolution pores. (4) Organic acid corrosion. It was attributed to hydrocarbon maturity during mesodiagenetic A substage. (5) Early-forming and long lasting overpressure. A large-scale overpressure compartment was caused by under-compaction and hydrocarbon generation pressurization related to thick deep-lacustrine mudstone, and is responsible for the preservation of abundant primary pores. (6) Regional transtensional tectonic action. It resulted in the structural microcracks.