Limestone Clasts Research Articles

Rock Mass Quality Type Analysis On The New Kretek Girijati Road Construction Site Based On Reconnaissance Survey

Abstract The research activity was carried out at the location of the national road construction plan for The Kretek-Girijati Road Section. The National Kretek-Girijati Section is in the Nglanggran Formation, which consists of volcanic breccias, agglomerates, tuffs, andesitic-basalt and andesitic lava flows, and the Wonosari Formation, which is dominated by carbonate rocks consisting of layered limestone and massive limestone. This investigation aims to obtain a typical analogy of excavation slopes at road construction sites, making recommendations for additional drilling locations and geophysical surveys for appropriate data by making an engineering geological map. Based on the geological engineering description, the location plan for the construction of The Kretek-Girijati Road Section is dominated by limestone and andesite. The types of limestone rock mass quality consist of Massive limestone (very hard) with good to very good rock mass quality with a GSI value of >80 and Clastic limestone with poor to medium rock quality with a GSI value of 30 – 60. The types of andesite rock mass quality consist of massive andesite (weakly jointed) with good – excellent rock mass quality with an RMR value of 70-80 and moderately fractured andesite with moderate rock mass quality (good 50 – 70).

Signs of crustal extension in Lower Jurassic carbonates from central Slovenia

The Lower Jurassic Podbukovje Formation represents a succession of shallow marine carbonate rocks deposited on the former Southern Tethyan Megaplatform and one of its successors, the Adriatic Carbonate Platform. Several outcrops of the Podbukovje Formation from central Slovenia (southern margin of the Ljubljana Moor) are presented, bearing possible evidence of Early Jurassic extensional tectonics. Peritidal facies of the lowermost, Hettangian – Sinemurian, part of the Podbukovje Formation locally interfingers with bodies of matrix supported pervasively dolomitized polymictic breccia, several metres to tens of metres thick and is locally cut by neptunian dykes some few decimetres to metres wide. The same or slightly younger part of the formation locally contains grabens/half-grabens metres to tens of metres deep and filled with poorly sorted pervasively dolomitized matrix supported polymictic breccia. Small miliolid foraminifera are present within the clasts and in the matrix. Finally, partly dolomitized blocky breccia tens of metres thick locally overlies the Pliensbachian – lowermost Toarcian limestone with lithiotid bivalves. Besides completely and partly dolomitized clasts, the breccia contains a variety of limestone clasts and preserves common radial ooids and some bioclasts within the partially dolomitized matrix. The Hettangian-Sinemurian breccias and dykes are presumably related to the early, diffused rifting stage of the Penninic (Alpine Tethys) Ocean, whereas Toarcian breccias relate to the main, focused rifting stage. Together with evolving biota and changing paleo-oceanographic conditions, the extensional tectonics may have been an important factor behind the facies changes observed within the Podbukovje Formation.

Lower Permian Košna conglomerates of the Velebit Mt. (Croatia): modal composition, provenance and depositional environment

The multicoloured ‘Košna’ conglomerates are investigated in the area of the Košna Voda spring, in the Brušane area of Velebit Mt., Croatia. The studied conglomerates consist of red-coloured matrix and clasts of various lithologies (sandstones, limestones, chert and quartz pebbles) and sizes, suggesting provenance from different areas. Average clast size and their percentage was determined by the Udden-Wentworth classification with estimation of the matrix content. Clasts and matrix lithological and mineralogical characteristics were determined using petrographic, ore microscopy, and X-ray diffraction analysis. Sandstone clasts in the studied conglomerates are classified as lithic arenites, subarkoses and arkoses. Limestone clasts are mostly wackestones to packstones with foraminifera, ostracods, echinoid and bryozoan fragments that derive from late Carboniferous/early Permian shallow-marine limestones. Calcispheres and incipient growth forms of Microcodium are also present, suggesting different sediment sources and resedimentation processes. Fragments of fusulinid foraminifera were identified in the matrix of the ‘Košna’ conglomerates. Based on the analyses performed, and field observations, the ‘Košna’ conglomerates are described as early Permian (Cisuralian) polymictic clast-supported to matrix-supported conglomerates and breccia-conglomerates that share structural and textural similarities with conglomerates from other areas in the Dinarides, as well as in the Eastern and Southern Alps. The ‘Košna’ conglomerates are younger than the Sakmarian and are comparable with the Trogkofel limestones of the Carnic Alps and the Karavanke Mts. in Slovenia. We suggest that the studied deposits originated from the uplifted Variscan Mountains during the Variscan and Saalian orogenic movements, and were finally deposited from tractive flows and occasional debris flows in a shallow marine environment of the Palaeo-Tethys, possibly in fan deltas.

Assessment of Hydrochemical Facies on Groundwater Quality in Daenaa Village and its Surroundings, West Limboto District

The study is required to evaluate the groundwater condition, such as finding the relationship with the lithology, determining the facies of groundwater, and providing an overview of the present groundwater conditions, genetics, and groundwater quality. This study aims to explain the relationship between lithology and groundwater chemistry, groundwater quality, and the determination of the chemical facies of groundwater to determine the genetic type of groundwater. This study uses field survey methods and random sampling techniques, measurements of groundwater physical properties, trilinear piper diagrams, and laboratory analysis in the form of rock geochemical analysis (XRF) at the PSDMBP Laboratory and chemical analysis of groundwater at the PT Global Quality Analytical Laboratory. The results show that the lithology in the study area consists of clastic limestone, sandstone, breccia, and dacite. Lithology in the study area primarily plays an essential role in chemical ion enrichment in groundwater. Determination of groundwater quality is based on Permenkes, Permen ESDM, and ISDW, which obtained eleven well points in the good quality category, five well points in the poor quality category, and four other well points categorized as poor quality. Based on the analysis results in the trilinear piper diagram, there is one type of groundwater chemical facies (not varied), namely the Ca-Cl type facies. The presence of the Ca-Cl facies type is interpreted as a seawater intrusion phase.

Contribution to the Ostracoda (crustacea) Fauna of the karstic region of Texas with the description of a new species

Iron oxide deposits in the form of crusts are examined in the field and in the laboratory with scanning electron microscopy. Samples came from two caves developed in different geological settings but assumed by previous studies to be of hydrothermal-hypogene origin. The relation of iron oxide crusts to cave wall and ceiling morphology created by the cave’s primary dissolution (speleogenesis), as well as to the formation of other speleothems, is investigated. Scanning electron microscope (SEM) elemental analysis showed a high iron content (20–78 % by weight) consistent with iron oxide minerals such as goethite, hematite, magnetite, etc. Three distinct types of iron oxide crusts were identified from the four samples that were analyzed: (1) high iron content crusts with some porosity formed on the host rock surface and discontinuities, (2) high iron content (but lower than type 1) crusts, including limestone clasts and pores originating from dissolved clasts, and (3) high iron content, significantly-porous crusts that are formed by a network of filaments that indicate microbial activity. The formation of these deposits in relation to other speleothems and to dissolution events is discussed.

Late Paleozoic and Early Mesozoic radiolarians from chert conglomerates embedded in the Kaeng Raboet Formation (Upper Mesozoic continental red-bed), Kanchanaburi Province, western Thailand

Continental clastic red-beds including red and fine- to medium-grained sandstone, pebbly sandstone, and conglomerates are distributed in the Sai Yok area of western Thailand. This rock sequence is known as the Jurassic Kaeng Raboet Formation by Thai geologists. A similar clastic rock succession, approximately 150 m thick, outcropping at Wat Phu Toey, near Ban Tha Sao, was investigated for paleontological analysis. The lithostratigraphy of the sequence in this section consists of Units 1-3 in ascending order. Unit 1 is characterized by pebble-sized chert conglomerates, Unit 2 by medium-grained massive sandstone, and Unit 3 by fine-grained red sandstone and shale with ripple marks and cross-laminations. Several thin layers of chert conglomerate are intercalated in the lower parts of Units 2 and 3. We collected six chert conglomerate samples from this section and distinguished Tournaisian (Lower Carboniferous) to middle Norian (Upper Triassic) radiolarian-bearing chert clasts that have not been not separated as single clasts but treated as one sample. Although the preservation of radiolarians is generally poor, we identified 40 species belonging to 26 genera with one radiolarian gen. et sp. indet. The exact age of the Kaeng Raboet Formation is still equivocal; however, we assigned the age of the red-bed to the Late Jurassic to Early Cretaceous based on the presence of Middle Jurassic foraminifer-bearing limestone clasts in the limestone conglomerate embedded in equivalent formations. The present chert conglomerate, including radiolarian-bearing chert clasts is interpreted to have been derived from the grained siliceous rock bodies of the Mae Sariang Zone and deposited in an alluvial depositional basin and braided river system during the Late Jurassic to Early Cretaceous.

Mid‐Cretaceous Exhumation of the Central Qiangtang Mountain Range Metamorphic Rocks as Evidenced by the Abushan Continental Redbeds

AbstractMetamorphic rocks and surrounding Paleozoic strata in central Tibet compose the core of an anticlinorium associated with the Central Qiangtang Mountain Range. The analysis of Mesozoic strata flanking the anticlinorium provides insights into the geological and landscape evolution of the range, which is important in determining the Mesozoic evolution of central Tibet and the paleo‐elevation of the Tibetan Plateau. Here we present a detailed stratigraphic study of the Shuanghu Conglomerate and over 1‐km‐thick mid‐Cretaceous continental redbeds of the Abushan Formation, which non‐conformably overlie the Qiangtang metamorphic belt. Pollen assemblages and detrital zircon ages along with published magnetostratigraphic results indicate a mid‐Cretaceous depositional age for the Abushan Formation. The Shuanghu Conglomerate is undated but may have been coeval with the Abushan Formation as suggested by foraminiferal assemblages contained within limestone clasts. The Abushan Formation shows a fining‐ and deepening‐upward megasequence, changing from braided river delta‐plain conglomerate and sandstone to lacustrine delta‐plain and delta‐front sandstone, siltstone and carbonate rocks. Both the Abushan Formation and Shuanghu Conglomerate received metamorphic detritus, indicating that the exhumation of the Qiangtang metamorphic belt to the surface took place at or before mid‐Cretaceous time. The lower member of the Abushan Formation contains dominant limestone clasts, whereas quartz, metamorphic, and volcanic clasts increase in percentage up‐section reflecting an unroofing sequence. The stratigraphic, sedimentologic, and provenance evolution suggests that exhumation of the Central Qiangtang Mountain Range metamorphic rocks may have occurred primarily by tectonic extension after the end of a long period of late Mesozoic Lhasa‐Qiangtang convergence.

Potential Geotourism Attractions on Nusa Penida Island, Klungkung Regency, Bali

Nusa Penida Island is one of the leading tourist destinations in Bali Province. Tourist destinations on the Island consist of various types of beaches, hills, caves to unique landscapes formed due to the karstification process. Nusa Penida Island is geologically composed of limestones (the Selatan Formation) with various types such as clastic limestones and coral limestones(Hadiwidjojo et al, 1998). In addition to the unique geology of Nusa Penida Island, it also has archaeological uniqueness. The Gede Cave shows that Nusa Penida was once inhabited by prehistoric humans (Abdillah, 2011). During the COVID-19 pandemic, tourism seems to be forced to accelerate and requires new tourist attraction innovations that support sustainable tourism. This research discusses geotourism-based tourist attractions that can be developed and explored in Nusa Penida. The approach used is geological diversity inventory method (Geological Agency, 2017). Primary data was obtained through survey activities. From the research carried out, it can be concluded that 10 geological site locations in the Nusa Penida area have the potential to be developed as areas with geotourism attractions, which offer unique geology, especially regarding karts landscape processes and one of the key geological history on the island of Bali. In addition, Nusa Penida Island has the potential to be developed as a geopark as an effort to develop sustainable tourism in Klungkung Regency.

Provenance and statistical analysis of the Lower Oligocene gravelly deposits in central Pindos foreland basin, western Greece: Implications for orogenic build‐up and unroofing

This study integrates provenance and statistical data, along with published sedimentological results, applied on the Lower Oligocene submarine‐fan deposits in Pindos foreland basin. Twelve outcrops were analysed using conglomerate clast composition, petrographic and statistical analysis and this integration suggests that the studied deposits were sourced by the Pindos Orogen. Conglomerate clast composition analysis suggests that the studied deposits contain mainly limestone clasts, followed by sandstone and chert clasts. This conclusion is further supported by the petrographic and cathodoluminescence analyses that have been conducted on the conglomerate matrix and, additionally, suggest the influence of a low‐grade metamorphic source. Potential source rock candidates in the Pindos Orogen that provided the detritus in the succession are represented by the Mesozoic carbonates (limestone and chert), the Cenozoic transitional (mixed carbonate and siliciclastic) and the Cenozoic clastic submarine‐fan deposits (sandstone). The rock units of Pelagonian zone likely represent the low‐grade metamorphic source rock. The principal component and cluster analysis of clast lithologies suggest the existence of three compositional clusters, with the first one being controlled by black chert clasts, the second one by sandstone clasts and the third one by limestone and red chert clasts. The upward increase of chert and lithic fragment abundances is ascribed to the progressive unroofing of the Pindos orogenic source regions. This study utilizes the Pindos foreland basin as an example to unravel the contribution of orogenic processes on sedimentary provenance of the adjacent pro‐foreland basins. Furthermore, this study highlights the advantage of implementing a multi‐faceted approach, including statistical treatment in sedimentary provenance.

Source Rock Potential of Nampol Formation Sumbermanjing Area, Malang, East Java, Indonesia Based on Geochemistry Analysis of the Selected Sample

Nampol Formation of the Southern Mountains of eastern Java (Indonesia) has a distribution from its type location in Pacitan to the South Malang area. In the research area, this formation consists of clastic limestone with black shale inserts, claystone, siltstone, carbonate sandstone and claystone which are interpreted to be deposited in a restricted platform interior environment with closed water circulation. A total of three samples were analyzed to evaluate the organic matter content, kerogen type, thermal maturity, and hydrocarbon generating potential. Samples were taken from clastic carbonate deposits of the Nampol Formation. Based on the results of geochemical analysis, the three samples from the Nampol Formation have a TOC content of 3.48 - 26.18 wt% and possess good to excellent hydrocarbon generating potential. Hydrogen Index (HI) values for the studied samples ranged from 43 to 86 mg HC/g TOC and S1+S2 results ranged from 1.52 to 19.55 mg HC/g rock, indicating that the sample has the potential to produce gas. All three samples were dominated by Type III kerogen and were thus considered gas prone based on the HI vs. Tmax diagrams. The three samples were categorized as thermally immature based on Tmax pyrolysis analysis and Vitrinite Refl ectance (VR) values in the range of 0.44 to 0.46 % Ro. Based on the results obtained, the black shale and coal in the Nampol Formation has the capability to generate hydrocarbon but are considered as an immature source rock that can be predicted to produce gas at its peak maturity.

Depositional Environment of Nampol Formation and Its Implications as Potential Source Rocks in the Sumbermanjing Area, South Malang

The decline in oil and gas production inevitably forces explorationists to be more creative in finding new potential reserves. Nampol Formation is expected to have the potential to become hydrocarbon source rocks due to their organic matter content. However, the depositional environment of Nampol Formation has not been thoroughly researched. The focus of this research is to reveal the depositional environment of Nampol Formation that may lead to a suitable condition for the deposition of potential source rocks layers. Detailed geological mapping in several selected traverses and micropaleontological analysis was carried out to determine lithological characteristics and depositional environment of Nampol Formation. The microfacies approach was also used to determine the carbonate facies zone of this unit. Source rock samples taken from outcrops on the surface then were analysed to evaluate organic matter content, type of kerogen thermal maturity, and its potential to produce hydrocarbons. The Nampol clastic limestone unit in the study area is composed of clastic limestone with intercalation of black shale, claystone, siltstone, sandstone and calcareous claystone. The microfacies approach shows that the wackestone and mudstone belong to the SMF 15-M (Ooid wackestone) and SMF 23 (Non-fossiliferous mudstone) which can be interpreted belong to Facies Zone (FZ) 8 in the Flügel carbonate facies model (2004). This zone is located in the Restricted interior platform or platform environment with closed water circulation which is situated behind the barrier reef (back reef). Based on the results of geochemical analysis, source rock samples from Nampol Formation can be considered as a gas prone source rock, with type III kerogen, total organic content ranging from 3.48 – 26.18 wt%, po-sess the potential to produce

High-resolution geophysical imaging of reptile burrows (San Salvador rock iguana, the Bahamas): implications for ichnology and conservation ecology

Abstract Neoichnological research of terrestrial tracemakers in coastal settings provides important palaeoenvironmental information about their context within the subaerial facies. Here we present the first geophysical dataset of reptile burrows in a carbonate substrate and use it to help visualize parts of the burrows of the Bahamian (San Salvador) rock iguana ( Cyclura rileyi ). High-resolution 800 MHz ground-penetrating radar (GPR) images within an enclosure on San Salvador Island were employed to discriminate between the electromagnetic signal response from subsurface anomalies related to air-dominated voids or live animals within burrows. The dielectric contrast between the carbonate substrate and open burrows was sufficient to identify the majority of the 15–20 cm-wide subsurface extensions of the inclined tunnels in the upper 30–40 cm. Whereas limestone clasts induced some interference, it is possible to differentiate their high-amplitude diffractions from those produced by the iguana burrows. Our research indicates that GPR imaging is a viable, rapid, non-invasive method of visualizing animal burrows, with implications for neoichnology, palaeoichnology, and conservation ecology of semi-fossorial species. Furthermore, the critically endangered status of Bahamian land iguanas, as well as ongoing threats from natural and introduced pressures, highlights the need for research into their ichnological record.

A Study on Geotechnical Properties of Weak Rocks in Sudan

Weak rocks are available in different areas in Sudan. These include sandstone, mudstone, siltstone usually referred to as Nubian Formations (N.F.). Clastic limestones are present in other areas of Sudan. Organic limestones in the form of coralline deposits are present in eastern Sudan, mainly on the Red Sea coast. Weak rocks constitute an important geological feature on which the foundations of most of the important structures are resting. The sandstone is also used as a primary buildingmaterial or as a facing stone over other construction. The geotechnical properties of these formations were investigated bydifferent insitu and laboratory testing methods. This paper summarizes the origin, distribution of Nubian formation and limestone. The paper also presents most of available data on the geotechnical properties of these formations. It is concluded that the Nubian formation and limestone coral deposit are weak rocks with poor quality of core samples; hence feld testingmay give better geocharacterization result for such deposit.

An Oligocene olistostrome with exotic clasts in the Silesian Nappe (Outer Ukrainian Carpathians, Uzh River Basin)

In the Ukrainian part of the Silesian Nappe (Outer Carpathians, Uzh River Basin) the exotic clast-bearing Uzhok Olistostrome (up to 60 m thick) occurs within the Oligocene Krosno Formation and underlies the Pikui Sandstone (Otryt Sandstone in Poland). The Uzhok Olistostrome consists of debris/grain/mud flow deposits with clasts of schist and bioclastic limestone. These deposits contain redeposited pelagic sediments with planktonic foraminifers including Parogloborotalia pseudocontinuosa (Jenkins), Ciperoella ciperoensis (Bolli), Globoturborotalita woodi (Jenkins), Chiloguembelina adriatica Premec Fucek, Hernitz Kucenjak and Huber. The age of the Uzhok Olistostrome based on planktonic foraminifers correlates with the middle Oligocene within the middle O2–O5 zones. The source area for the Uzhok Olistostrome and Pikui Sandstone was a mid-Oligocene intrabasinal palaeouplift (the Pikui Ridge) interpreted as the fore-bulge located in the Silesian Sub-basin ahead the emerging Outer Carpathian accretionary prism (including the Dukla Nappe and other West Carpathian inner flysch nappes).

Multiproxy provenance analysis of Lower to Upper Cretaceous synorogenic deposits in the Southern Andes (34–35°S): Evidence of coeval volcanism during the onset of the Andean orogeny

The combination of detrital low-temperature thermochronology with previous U–Pb geochronology, petrological and sedimentological analyses, has proven to be a valuable approach to constrain the provenance of non-marine Lower to Upper Cretaceous synorogenic deposits in the northern Neuquén Basin. This work focuses on the study of the Diamante Formation, a fluvial succession that represents the first synorogenic products of the Andean foreland basin at 34–35°S. The results indicate that the deposition of the Diamante Formation occurred simultaneously with the existence of an active western volcanic arc during the onset of the foreland basin. The facies associations evidence the transition between the backarc and the foreland basin stages as well as the inception of fluvial sedimentation in the foredeep. Petrographic analyses, together with changes in the paleocurrents and the record of limestone clasts suggest a regional detrital source shift. Apatite fission-track analyses (AFT) of a sample collected from the lower part of the Diamante Formation indicate an Albian central cooling age. This sample also evidences a remarkable presence of angular apatite and zircon crystals with subordinated rounded and subangular grains. Zircon fission-track analyses (ZFT) of a sample from the upper part of the Diamante Formation yield two discrete populations of cooling ages, both reflecting source-cooling during the Late Jurassic (∼161 Ma) and the Permian (∼265 Ma). Finally, a comparison between the AFT and the U–Pb maximum depositional zircon-age reveals a short lag time (ca. 3 ma), likely related to the rapid magmatic cooling of a coeval volcanic source at ∼110 Ma (Albian).

Micropore Structures and Percolation Characteristics of Carboniferous Carbonate Reservoirs in the Zanarol Area.

Proven oil and gas reserves in carbonate rocks comprise a high proportion of oil and gas fields, but these reservoirs have high heterogeneity. It is of great importance to study the micropore structures and percolation characteristics of carbonate rocks for the development of oilfields. In this paper, reservoirs are studied by means of casting sections, high-pressure mercury injection, and water and gas flooding oil phase permeability experiments. Reservoirs are classified into three categories, I, II, and III, by the k-means cluster analysis method. The results show that class I reservoirs are mainly composed of biolimestone with strong dissolution, displacement pressure of 0.016 MPa, median pressure of 0.135 MPa, mercury removal efficiency of 17.15%, well-developed pore throats, and good connectivity. They have the highest reservoir quality index and strong percolation ability. Class II reservoirs are mainly biogenic limestone and granular limestone with intergranular pores, a displacement pressure of 0.098 MPa, a median pressure of 6.026 MPa, and a mercury removal efficiency of 25.82%. The pore throat class is complex, and the sorting is poor. Class III reservoirs are mainly clastic limestone with residual intergranular pores, poor connectivity, displacement pressure of 0.403 MPa, median pressure of 3.77 MPa, mercury removal efficiency of 14.01%, small median radii, and good sorting performance. Relative permeability experiments show that water drive permeability at the isopermeability point is (0.049 10–3 μm2) higher than that of gas drive (0.041 10–3 μm2). The permeability of oil and water phases in class I reservoirs is obviously higher than those of class II and III reservoirs. When gas flooding is used, the phase permeability characteristics of class I and II reservoirs are no different than when water flooding is used. The permeability of gas flooding is slightly lower than that of water flooding. Because of the high proportion of micropores in class III reservoirs, gas can easily enter the pores, so the relative permeability of the gas phase increases rapidly. With increases in injection volume, the ultimate oil displacement efficiency of class I reservoirs can reach 53.2%, while those of class II and III reservoirs are 50.7 and 46.1%, respectively. This study provides important guidance for formulating oilfield development plans.

New insights into the depositional environment and stratigraphic position of the Gugu Breccia (Pădurea Craiului Mountains, Romania)

The study of the carbonate clasts and matrix of a problematic sedimentary formation (the Gugu Breccia) from the Pădurea Craiului Mountains reveals new information concerning its depositional environment and stratigraphic position. The identified microfacies and micropaleontological assemblages demonstrate that all the sampled limestone clasts from the Gugu Breccia represent remnants of a fragmented Urgonian-type carbonate platform. The Barremian age of the clasts suggests that the stratigraphic position of the Gugu Breccia at its type locality could be uppermost Barremian-lowermost Aptian, a fact demonstrated also by the absence of elements from Lower Cretaceous carbonate platforms higher in the stratigraphic column (e.g., Aptian or Albian) of the Bihor Unit. The sedimentological observations together with the matrix mineralogy bring new arguments for the recognition of terrigenous input during the formation of the Gugu Breccia.

Limestones of the Uk Formation (Upper Riphean, the Southern Urals): Effect of contamination and diagenetic fluids on the distribution of rare-earth elements and yttrium

Research subject. A study was conducted into the geochemical features of various lithotypes of carbonate rocks (granular and clastic limestones, limestones with planar, planar-columnar and columnar stromatolites) from the upper subformation of the Uk Formation. This formation crowns the Upper Riphean Karatau Group on the Western slope of the Southern Urals (Bashkir meganticlinorium). Material and methods. The research material was two collections of carbonate rocks (11 and 32 samples), the general geochemical features of which were previously considered in publications in 2019. The main research method was the analysis of the correlation relationships of the main rock-forming components, trace elements and their indicator relationships. Research results. It was established that all lithotypes are characterized by a significant content of both the main rock-forming components and the trace elements that make up the insoluble residue/fine-grained terrigenous admixture. This suggests that the area of accumulation of carbonate sediments was located near the continent, which served as a source of a significant amount of fine-grained/clay suspension. Conclusions. A strong positive correlation was observed between K2O and REE in the carbonate rocks of the Upper Uk Subformation, and a strong negative correlation was observed between REE and CaO. This suggests that the REE content in carbonate rocks is controlled mainly by terrigenous/clay admixture. A positive correlation is also observed between REE and Th, Zr, and Al2O3. All this shows that REE in carbonate rocks are mainly present in clay admixtures. The correlation coefficient between Ce/Ce* and (Dy/Sm)N is 0.20, while this coefficient for Eu/Eu* and (Pr/Sm)N equals 0.12. Thus, a definite conclusion about the effect of diagenetic fluids on the distribution of REE cannot be made. The data obtained show that the distribution of REE and Y in our collection of carbonate rocks of the Upper subformation of the Uk Formation of the Southern Urals is controlled mainly by clay admixtures.

The Upper Jurassic Garedu Red Bed Formation of the northern Tabas Block: elucidating Late Cimmerian tectonics in east-Central Iran

The Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine limestones of the Esfandiar Subgroup (Callovian–Oxfordian) and is assigned to the Kimmeridgian–Tithonian. In the lower part, it consists of pebble- to boulder-sized conglomerates/breccias composed of limestone clasts intercalated with calcareous sandstones, litho-/bioclastic rudstones and lacustrine carbonates. Up-section, sharp-based pebbly sandstones and red silt-/fine-grained sandstones of braided river origin predominate. Palaeocurrent data suggest a principal sediment transport from west to east and a lateral interfingering of the GRBF with marine greenish marls of the Korond Formation at the eastern margin of the Tabas Block. Westwards, the GRBF grades into the playa deposits of the Magu Gypsum Formation. Red colours and common calcretes suggest arid to semi-arid climatic conditions. The onset of Garedu Red Bed deposition indicates a major geodynamic change with the onset of compressive tectonics of the Late Cimmerian Tectonic Event (LCTE), being strongest at the eastern margin of the northern Tabas Block. When traced southwards, the same tectonic event is expressed by extension, indicating a shift in tectonic style along the boundary fault between the Tabas and Lut blocks. The complex Upper Jurassic facies distribution as well as the spatio-temporal changes in tectonic regime along the block-bounding faults are explained by the onset of counterclockwise vertical-axis rotation of the CEIM in the Kimmeridgian. The block boundaries accommodated the rotation by right-lateral strike slip, transpressional in today’s northern and transtensional in today’s southern segments of the block-bounding faults. Rotation occurred within bracketing transcurrent faults and continued into the Early Cretaceous, finally resulting in the opening of narrow oceanic basins encircling the CEIM. Palaeogeographically, the GRBF is part of a suite of red bed formations not only present on the CEIM, but also along the Sanandaj-Sirjan Zone (NW Iran), in northeastern Iran and beyond, indicating inter-regional tectonic instability, uplift and erosion under (semi-)arid climatic conditions across the Jurassic–Cretaceous boundary. Thus, even if our geodynamic model successfully explains Late Jurassic tectonic rotations, fault motions and facies distribution for the CEIM, the basic cause of the LCTE still remains enigmatic.

The Devonian–Carboniferous boundary in Belgium and surrounding areas

The Devonian–Carboniferous boundary is associated with a major extinction event of the Phanerozoic. It was also a time marked by a rapid but short-lasting change in deposition called Hangenberg Event. In the Namur–Dinant Basin the uppermost Devonian (‘Strunian’) deposits recorded a third-order transgression that produced a progressive switch from coastal siliciclastic to proximal mixed deposits with an increase of the carbonate production on the ramp. Hence, the Comblain-au-Pont and lower Hastiere formations are considered as the transgressive system tract, whereas the middle member of the Hastiere Formation is interpreted as the highstand system tract, capped by an erosion surface corresponding to the third-order sequence boundary. Superimposed on these third-order sequences are well-marked orbitally forced precession cycles (wet–dry climate alternations) of c. 18.6 ka, appearing as irregular c. 30–80-cm-thick couplets of limestone and calcareous shale beds. The Hangenberg Black Shale Event is locally present as dark shales that likely spread over the shelf, marking the maximum flooding surface of the sequence. Before and after this event, carbonate facies rich in benthic macrofauna and microfauna continued to develop. The Hangenberg Sandstone Event, appearing as a sandstone bed in pelagic sections, is variously recorded at the base of the Hastiere Formation, either as a sandy siltstone bed in proximal sections or as a horizon with limestone clasts and reworked fossils in more distal settings. The Hangenberg Sandstone Event beds occur sharply in the stratigraphic record and do not correspond to the long sea level fall of a third-order sequence boundary, but most probably to a short out-of-sequence event. The revision of the stratigraphic distribution of major fossil groups pleads for a continuous biostratigraphic succession with no obvious hiatus. The variable development of some micropalaeontological zones at the end of the Devonian is the result of complex eco-biostratigraphic interactions with the environment rather than the reflection of true hiatuses. It is marked by extinctions of Devonian taxa, concomitantly with the end of the reworking produced by the Hangenberg Sandstone Event, most probably immediately below the entry of the conodont Protognathodus kockeli. It is also coincident with the boundary between the foraminiferal zones DFZ7–MFZ1, rugose coral zones RC0–RC1 and between the palynozones LE–VI. After the short-lasting regressive phase of the Hangenberg Sandstone Event, normal depositional settings returned with the deposition of the Hastiere Formation. Hence, the end of the Hangenberg Sandstone Event is proposed as the most natural proxy to pinpoint the Devonian–Carboniferous boundary.