Geologic Map 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.

An integrated remote sensing, petrology, and field geology analyses for Neoproterozoic basement rocks in some parts of the southern Egyptian-Nubian Shield

The main objective of this study was to use deep learning, and convolutional neural networks (CNN), integrated with field geology to identify distinct lithological units. The Samadia-Tunduba region of the South Eastern Desert of Egypt was mapped geologically for the first time thanks to the use of processed developed CNN algorithms using Landsat 9 OLI-2, which were further enhanced by geological fieldwork, spectral measurements of field samples, and petrographic examination. According to previously published papers, a significant difference was observed in the distribution of rocks and their boundaries, as well as the previously published geological maps that were not accurately compatible with the nature of the area. The many lithologic units in the region are refined using principal component analysis, color ratio composites, and false-color composites. These techniques demonstrated the ability to distinguish between various igneous and metamorphic rock types, especially metavolcanics, metasediments, granodiorite, and biotite monzogranite. The Key structural trends, lithological units, and wadis affecting the area under study are improved by the principal component analysis approach (PC 3, 2, 1), (PC 2, 3, 4), (PC 4, 3, 2), (PC 5, 4, 3), and (PC 6, 5, 4) in RGB, respectively. The best band ratios recorded in the area are recorded the good discrimination (6/5, 4/3, and 2/1), (4/2, 6/7, and 5/6), and (3/2, 5/6, and 4/6) for RGB. The classification map achieved an overall accuracy of 95.27%, and these results from Landsat-9 data were validated by field geology and petrographical studies. The results of this survey can make a significant difference to detailed geological studies. A detailed map of the new district has been prepared through a combination of deep learning and fieldwork.

Leucojum vernum in Intorsurii Mountains (South- Eastern Carpathians)

This study investigates the population structure and ecology of the species Leucojum vernum (spring snowflake) in Întorsurii Mountains, South-Eastern Carpathians, where was supposed to be extinct. The research objectives were: (1) to identify the species in Popii Valley, (2) to estimate its population size, (3) to map the species extent, (4) to delineate the species ecological niche, (5) to identify and describe the vegetation types where the species grows, (6) to identify the co-occurring species as indicators of suitable habitat for L. vernum, and (7) to assess the species conservation status in Popii Valley and in Romania. Identification and description of the species population relied on an intensive survey in the whole watershed of Popii Valley. A detailed vegetation map of the Popii Valley watershed was created. For the description of the species habitat, 27 sampling plots were used. The species ecological preferences were drawn by means of the indicator species analysis, climate and geological maps. Climate suitability was checked by projecting the analyzed population in the bioclimatic envelope of L. vernum in Romania, using principal components analysis (PCA) ordination and classes of aridity index. The assessment of the conservation status followed the principles and methodological standards for monitoring protected species at the European Union and global level. In the studied area L. vernum was found in four forest associations, on moist and nutrient-rich soils. The indicator species of the suitable/unsuitable habitats were identified with the help of the phi coefficient of association between species. The population size and species habitat are in favorable conditions, although signs of bulbs collection for gardening were observed. These findings were discussed in a national and global context. An updated map for species extent in Romania was provided in order to support the assessment of the global and national IUCN category.

Geology and Geochemistry of Aberma and Its Environ Sheet 54se Gusau, Zamfara State, Nigeria

The study area falls within the northwestern part of Nigeria and is underlain by crystalline rocks of the Basement Complex. Field mapping in Aberma and its environs were carried out using topographical map sheet of 54 SE Gusau on a scale 1: 25,000 with an area extends of about 30.8052km2. This field work was carried out using traverse method in conjunction with field equipment such as compass/clinometers, geologic hammer, sample bag and global positioning system. This study however, aims at producing a detail geological map, including the various rock geochemistry and petrography of the study area. The area is underlain by two major lithological rock type which is mica schist and granite gneiss. The granite gneiss is strongly foliated, caused by high temperature and pressure and the minerals observed in plane polarized light include quartz, orthoclase, plagioclase, muscovite, opaque mineral and biotite. The mica schists in the study area are mostly weathered in ditches below the ground surface, the rock is moderately weathered and show schistocyte. The minerals observed in plane polarized light include quartz and muscovite. The dominant structures observed include; joints, Quartz veins, foliation and pegmatite dyke. Structural analysis shows that the rocks have been affected by the Pan African orogeny with the joint’s orientation trending dominantly NNE-SSW and Quartz vein trending in somewhat E-W direction. The microscopic studies revealed that the mineralogical composition of the rocks types of the study area contain varying percentages of quartz, muscovite, plagioclase, orthoclase, opaque mineral and biotite as the major minerals. The geochemical analysis revealed the major and minor elemental distribution of the rock types of the study area. The chemical assay revealed that the granite gneiss and mica schist rock type of the study area are super-saturated with respect to silica, silica (SiO<sub>2</sub>) is the most abundant oxide with an average value of 78.12% in the rock sample. This implies that the rock analyzed is acidic in nature and must have formed from crystallization of an acidic magma because the silica content being greater than 65%.

A 3D bedrock modeling method based on information mining of 2D geological map

A 3D bedrock modeling method based on information mining of 2D geological map

The current state and prospects of geological mapping of the territoryof The Russian Federation: the legal aspect

A brief overview of the purpose, directions, tasks, and current state of regional geological work on solid minerals is given. The results of the work are summarized, the main directions of the regional study of the subsoil for the medium term are considered in order to increase geological knowledge, solve federal and regional tasks for the study, assessment of the state, management of the state fund of the subsoil in terms of solid mineral resources, planning prospecting based on strategic documents. The innovations of the legislation on subsoil, which come into force on September 01, 2024, concerning the regional geological study of the subsoil, are presented.

Mapowanie geologiczne, stratygrafia, paleontologia i mineralizacje paleozoiku wokół kamieniołomu Valério i Muzeum Trylobitów (Geopark Arouca), Canelas, Północna Portugalia

The studied area, a sector in the reverse limb of the Valongo Anticline adjacent to the Museum of Trilobites and to Valério’s Quarry (Canelas, Arouca), is located in the Central-Iberian Zone of the Iberian Massif. The main objective of this study was to obtain a detailed geological map, through the recognition of the lithologies, stratigraphic units, fossils, structures and mineralizations. The Palaeozoic succession from Cambrian to Carboniferous was studied, with the exception of the Devonian, which does not outcrop in the area. Regarding lithologies, a succession of volcano sedimentary layers has been found in Cambrian (Montalto Formation, Middle Cambrian) and in the Lower Ordovician (Santa Justa Formation), either underlying Floian massive quartzites (Tremadocian?) or overlying Floian massive quartzites (Floian). At the top of the Middle Ordovician (Valongo Formation, Dapingian-Darriwilian), near the contact with the Upper Ordovician (Sobrido Formation, Hirnantian), a ferruginous layer with abundant siliceous nodules occurs. In the base of the Sobrido Formation, massive quartzites underlie diamictites. Concerning the fossil record, abundant icnofossils such as Cruziana and Planolites were identified in the quartzites of the Lower Ordovician. Also, different somatofossils occur in the Middle Ordovician slates, namely trilobites (between the largest trilobites in the world) and other arthropods, graptolites, cephalopods, brachiopods, gastropods, bivalves and echinoderms (cystoids and crinoids). In Silurian, besides quartzites (Rhuddanian), light grey slates bearing graptolites, namely Monograptus (Llandovery), are dominant. In Carboniferous (Gzhelian) breccias, sandstones and slates with plant fossils, namely with articulated plants and ferns, occur. Regarding the mineral resources of the area, beyond the slates of Middle Ordovician (Valongo Formation) exploited in Valério’s Quarry, there is a Roman mining work, the Gralheira d'Água mine (Au-As type mineralizations), associated to the Lower Ordovician (Santa Justa Formation) quartzites and volcano sedimentary layers, exploited for gold. Antimony mineralizations (Sb-Au type mineralizations) associated to the volcano-sedimentary succession of the Cambrian-Ordovician transition, were found and studied by Scanning Electron Microscopy (SEM). The final work resulted in a geological map, covering an area of 1200m by 900m, at a scale of 1: 3,400.

DIGITAL INVESTIGATION OF LAMNIFORM SHARK VERTEBRAE FROM THE SIBILLINI MTS. (NORTHERN APENNINES, ITALY)

During the sampling of a stratigraphic section along the shore of the Fiastra Lake (Carg Project - Sheet 313 “Camerino” of the Geological Map of Italy at 1:50 000 scale), a small rock boulder with partially exposed bony material was discovered at the base of a small cliff at the northern termination of the Sibillini Mts. In this area, the classical facies of Umbria-Marche stratigraphic succession are well exposed. The Oligocene-Miocene portion of the succession is represented by the ~200 m-thick Scaglia Cinerea Formation, passing upwards to the ~100 m-thick Bisciaro Formation. The microfossil assemblage has allowed the specimen to be constrained to the lower Burdigalian. The skeletal remains were examined using a CT-SCAN, a non-invasive method that has proven to be highly performing. The analysis revealed some articulated vertebrae, deformed by lithostatic compaction, which are attributed to a shark of the Order Lamniformes. Subsequently, the vertebrae were digitally isolated, extracted from the surrounding matrix, and rendered into three-dimensional prints. Through digital retro-deformation, the body length of the lamniform shark was estimated to be approximately 4 metres. Further considerations on the vertebrae allowed us to infer that the studied shark had similarities to either Isurus oxyrinchus Rafinesque, 1810 or Carcharodon carcharias Linnaeus, 1758. The development of a dead-fall microbial community likely facilitated the preservation of the vertebrae. The studied specimen represents the first occurrence of a lamniform shark in the Lower Miocene of the Umbria-Marche Domain and represents one of the very rare recorded occurrences of lamniforms from the Lower Miocene of Italy.

Reliable Euler deconvolution solutions of gravity data throughout the β-VDR and THGED methods: Application to mineral exploration and geological structural mapping

Reliable Euler deconvolution solutions of gravity data throughout the β-VDR and THGED methods: Application to mineral exploration and geological structural mapping

Seeking sand origins on Mars: Towards testing the volcaniclastic hypothesis globally

Aeolian processes are a dominant cause of Martian surface modification today. Sand is pervasive, even while the contemporary transport of sand at high-threshold wind speeds implies sand breakdown. Thus, detecting the origin(s) of sand on Mars is an important open question in Mars science. One long-standing hypothesis for an origin of Martian sand is as volcaniclastic sediments, either epiclastic (from the breakdown of effusive volcanic rock) or pyroclastic (from explosive sedimentation). Recent analyses identified the most likely pyroclastic unit on Mars, the Medusae Fossae Formation (MFF) – mapped as the Hesperian and Amazonian-Hesperian transitional units (Tanaka et al., 2014) – as an origin of Martian sand, a genesis consistent with inferences from other work. On these bases, we continued in this work to test for a volcaniclastic origin of Martian sand elsewhere on Mars. We inspected the seven units from the global geologic map of Mars interpreted as possibly/partially volcaniclastic and six geographic terrains ascribed as likely volcanogenic in a more recent analysis. Of these units and geographic terrains, potential sand sources (PSSs) were detected only within two locales: 1) the remaining (central and eastern) extent of the MFF, and 2) Arabia Terra. Arabia Terra shows more numerous PSS, commonly characterized as having proximal dune fields. The explosive volcanic history of the region points towards a pyroclastic origin, though the geologic complexity of the region suggests complexity in the provenance of Arabia Terra PSSs. In contrast to PSS identifications in the western MFF, PSSs in the central and eastern MFF were clustered along the contact of the MFF with lava plains, indicating a potential epiclastic sand origin. Thus, these results indicate both pyroclastic and potentially epiclastic origins for sand on Mars. However, these sand origins as detected by this work are confined to limited locales and (for the MFF) in the amount of sand generated. To further evaluate the amount of sand production in these two study regions from volcanogenic processes, spectroscopic analysis of PSSs in comparison with sand deposits would be a means to test first whether the PSSs were indeed generating sand and secondly if that sand were of volcanic origin. Potential sand flux modeling would be a means to establish the source location(s) of the sand. The origin(s) of the pervasive sand on Mars remain(s) to be better understood, for which the work presented here provides a foundation.

Analiza strukturalna i zróżnicowanie pegmatytów w starożytnym twierdzeniu, Giraúl IV, dystrykt pegmatytów Namibe, Angola

Since the early 60´s, in the past XX century, the Giraúl pegmatites have been known for their resources of beryl, mica and feldspars, which were exploited in a regular basis from Giraúl claims I to IV till 1974, during the Portuguese administration of Angolan territory. A broader exploration of this pegmatite field was performed by the ancient Lobito Mining Company (LMC) engaged in detailed geological mapping of the granitic pegmatites and the structural constraints of their location. A structural map of the region was than elaborated, combining the interpretation of aerial photographs with field work performed by the LMC geologists. Recently, a growing economic interest is attributed to these claims, in the region of Bulamucolocai, Pitau and Muvero desert-dry rivers (locally known as “Mulolas”), considering the Li, Cs, and Ta (LCT) metallic specialization of some pegmatite bodies and the occurrence of beryl and tourmaline gemstones, mainly, morganite (Cs-beryl), aquamarine and also elbaite-liddicoatite. Giant crystals of spodumene, up to 6 m in length, define individualized quartz + spodumene units inside some of the more typical LCT pegmatite bodies. Pollucite was identified in the main pegmatites of Giraúl IV claim and not in the adjacent igneous leucocratic breccias. These, in turn, correspond to a complex pegmatite assemblage, very peculiar in what concerns its selective metasomatic effect over some surrounding rocks, with the formation of rims of holmquistite amphibole in contact with gabbro and norite and schorl-dravite tourmaline in contact with gneissic to metapelitic hosts. The breccia-like granitic rock combines clasts of spodumene an K-feldspar with a matrix mainly composed of some quartz, albite and mica including tourmaline, garnet and F-apatite, as accessory minerals. In the same area, huge potassic pegmatites hold giant crystals of microcline and orthoclase and very little quartz, being unusual due to its high content of triplite – zwieselite and triphylite – lithiophilite primary phosphates. The overall composition of these pegmatites is more likely syenitic (low quartz content) than truly granitic. A high-resolution structural analysis of the LCT ensemble (pegmatite plus related lithotypes) is now proposed enhancing the unusual relations between granite breccia plugs, sill-like more typical pegmatites, irregular shaped isodiametric bodies and products of metasomatism. This approach will lead to the understanding of the true dimension, anatomy and inner fraccionation of the different LCT facies and rare-metal deposits with obvious consequences regarding mineral detection and resource – reserve estimation, through the proposal of a more suitable conceptual model to rule its exploration.

Does Soil Acidification Matter? Nutrient Sustainability of Timber Harvesting in Forests on Selected Soils Developed in Sediments of the Early vs. Late Pleistocene

With this study, our aim was to estimate the nutrient fluxes relevant for assessing nutrient sustainability as accurately as possible and to calculate nutrient balances for alternative forest management scenarios. Furthermore, we tested whether mapping units from existing geologic maps can serve as a basis for forest practitioners to estimate nutrient sustainability or whether more detailed data are needed. Positive fluxes include deposition and weathering, while negative fluxes include losses due to leaching and nutrient removal through timber harvesting in the balance. Weathering and leachate losses were modeled with a geochemical model. The SwissStandSim model was used to simulate the biomass growth under different harvesting and silvicultural strategies, allowing for sustainability to be assessed for each nutrient at a given intensity of use. This assessment was made per rotation period based on two criteria: (i) nutrient supply and (ii) total stocking volume. As a result, it can be noted that the accurate estimation of individual fluxes is essential for assessing the sustainability of forestry practices and that it needs detailed site-specific data. Various influencing factors turned out to be important, particularly the assumed depth of the root zone.

Валентин Петрович Твердохлебов (1933–2023)

Dedication to the memory of a colleague, Doctor of Geological and Mineralogical Sciences Valentin P. Tverdokhlebov, a well-known specialist in sedimentology and palaeogeography of the Late Permian and Triassic of the Eastern Russian Plate and Southern Urals, as well as taphonomy of vertebrate localities. Valentin Petrovich is a long-time head of the geological survey party investigating the stratigraphy of continental red-coloured strata, tectonics and placement of minerals in the Orenburg region. He co-authored a number of geological maps of the region. He participated in field work as a member of the joint Soviet-Mongolian palaeontological expedition in the Gobi Desert.

Implications to basin evolution from the interpretation of superficial and buried geological features from remote sensing and magnetic data sets, Lower and Middle Benue Trough, Nigeria

The Lower and Middle Benue Trough is an intra-continental rifted basin with most rocks concealed by thick sediments and vegetation. Geological field mapping is very difficult resulting in high uncertainties. Remote sensing and geophysical techniques can assist in refining lithological boundaries and detecting buried geological features such as intrusive bodies, which can be very useful in interpreting the structural history of a basin. The main aim of our study is to re-process and interpret aeromagnetic and multispectral satellite datasets to understand the evolution of the Benue Trough. We used high-resolution aeromagnetic data and, Landsat 8 and ASTER data sets to interpret surface and near-surface lithologies, particularly igneous bodies, within the Benue Trough, Nigeria, with the aim of better constraining the basin evolution in time and space. A matched bandpass filter was applied to the aeromagnetic data to separate shallow/near-surface (residual) anomalies from deep (regional) anomalies. The result of the residual anomaly was further filtered by derivative-based filters to delineate surface/near-surface igneous bodies. The satellite remote sensing datasets were processed and enhanced, and diagnostic mineral spectral signatures related to geology were interpreted. A spectral angle mapping (SAM) supervised classification was used to map various lithologies and their boundaries. The delineated igneous bodies (volcanic rocks, plugs, dykes, bosses, and sills) are concentrated along the SE margin of the Trough where they intruded along a major NE-SW trend; but changes in the intrusion style are interpreted to relate to specific stages in the basin history. We suggest that the initial magma emplacement was controlled by structures mostly along the SE margin of an asymmetric basin, but the rifting locus later migrated towards the centre of the present basin.

Complex Segment Linkage Along the Sevier Normal Fault, Southwestern Utah

Abstract Major normal fault systems are composed of segments that link as displacement accumulates, with linkage zone characteristics that reveal fault zone evolution. The steeply west-dipping Sevier fault zone in southwestern Utah, displays a complex fault network that developed between two long (>10 km), en echelon segments near the town of Orderville. Geologic map data and cross-sections of the transfer zone between the Mt. Carmel segment in the south and the Spencer Bench segment in the north reveal more than ten normal faults and four relay ramps displaying a range of geometries, including two relay ramps that display ramp-parallel folds. We suggest that transfer zone deformation was initially dominated by faults subparallel to the primary segments with later cross-faults that hard-linked these faults across most of the transfer zone. When the transfer zone was a soft-linked system, a displacement deficit likely existed relative to fault segments to the north and south. This early fault configuration would have reduced the efficiency of slip propagation associated with major earthquakes (>M7.0). In contrast, the present-day transfer zone, with a complex but hard-linked fault network, shows displacements that transition smoothly from the higher displacement (~800 m) southern segment to the lower displacement (~400 m) northern segment. That transition, combined with extensional strain within the zone, suggests that the Orderville fault network would be unlikely to impede propagation associated with future major earthquakes. The kinematic model of fault evolution presented here has implications for those investigating geothermal energy potential, groundwater flow, natural gas and oil reservoirs, mineral deposit formation, or seismic hazards.

Stratigraphic cross-sections, geologic history, and provenance of material at the candidate landing sites of the Artemis missions

From the scientific perspective, Artemis lunar missions focus on the south circumpolar region (SCR) mainly to investigate the existence and abundance of volatiles and to explore and sample ancient lunar deposits. The volatile distribution is primarily related to the cold traps in permanently shadowed regions, while the availability of ancient material is due to the proximity to the early lunar ∼2300 km diameter South Pole-Aitken (SPA) impact basin. One of the critical factors for future missions will be determining the geological structure and provenance (sources) of material at each candidate landing site, which can be predicted utilizing three-dimensional stratigraphic reconstructions of geological map units and crater ejecta deposits. This type of reconstruction permits a better understanding of candidate material that can be collected and analyzed at each site, and a ranking of landing sites can be formulated on this basis. Here, we present reconstructed geological cross-sections at Artemis landing sites using our recent SCR geological map and numerical modelling of crater ejecta thicknesses and their sequence.

Analysis Of The Potential Of Volcanic Aquifers In Supporting The Development Of Groundwater Resources In Bogor District, West Java

This research is crucial for understanding the aquifer potential of volcanic deposits as a sustainable groundwater source, especially in regions experiencing rapid urbanization and agricultural expansion. It aims to analyze the aquifer potential of volcanic deposits in Bogor Regency, focusing on the Bogor Groundwater Basin, the upper Cisadane watershed, the eastern slopes of Mount Salak, and the western slopes of Mount Pangrango. The methods used include secondary data collection from regional geological maps and primary data collection through field surveys, geological mapping, and hydrogeological mapping. The results show that the volcanic rock units in this area, consisting of stony tuff, tuff breccia, lava, and andesite lava, have unique characteristics with significant potential as aquifers. Detailed geomorphological and hydrogeological mapping revealed different types of springs and physical properties of water that support the sustainability of groundwater resources. These findings contribute significantly to the development of better groundwater management policies, effective water infrastructure development, and environmental conservation strategies in Bogor District, ensuring clean water availability for the future.

Deep learning for geological mapping in the overburden area

This paper aims to achieve bedrock geologic mapping in the overburden area using big data, distributed computing, and deep learning techniques. First, the satellite Bouguer gravity anomaly with a resolution of 2′×2′ in the range of E66°-E96°, N40°-N55° and 1:5000000 Asia-European geological map are used to design a dataset for bedrock prediction. Then, starting from the gravity anomaly formula in the spherical coordinate system, we deduce the non-linear functional between rock density ρ and rock mineral composition m, content p, buried depth h, diagenesis time t and other variables. We analyze the feasibility of using deep neural network to approximate the above nonlinear generalization. The problem of solving deep neural network parameters is transformed into a non-convex optimization problem. We give an iterative, gradient descent-based solution algorithm for the non-convex optimization problem. Utilizing neural architecture search (NAS) and human-designed approach, we propose a geological-geophysical mapping network (GGMNet). The dataset for the network consists of both gravity anomaly and a priori geological information. The network has fast convergence speed and stable iteration during the training process. It also has better performance than a single neural network search or human-designed architectures, with the mean pixel accuracy (MAP) = 63.1% and the frequency weighted intersection over union (FWIoU) = 42.88. Finally, the GGMNet is used to predict the rock distribution of the Junggar Basin.

Petrography, U–Pb geochronology and geochemistry of Varcheh intrusions: Insight into younging trend of mid‐Cretaceous subduction in the northern Sanandaj–Sirjan Zone, western Iran

The Neotethyan Sanandaj–Sirjan Zone of western Iran has recorded major magmatic activities due to its continental arc tectonic setting during the Mesozoic. The Varcheh mafic intrusions were less‐studied plutons in the northern Sanandaj–Sirjan Zone (SSZ). Field evidence, petrography, geochemistry and U–Pb geochronological data were used to determine petrographic composition, geochemical nature, crystallization age and also to suggest a conceptual tectonomagmatic model for their emplacement. Small plutonic bodies are dominantly composed of monzogabbro that have intruded into the Cretaceous sedimentary rocks. Based on U–Pb zircon datings, these rocks have crystallized at 125–118 Ma in late Early Cretaceous (Barremian–Aptian), and are older than the supposed ages reported on geological maps. Varcheh rocks are not just typical calc‐alkaline rocks and some show alkaline affinity. Negative anomalies in Nb–Ta–Ti and enrichments in some large‐ion lithophile elements on spider diagrams are consistent with a subduction‐zone setting. Potential deep source for magma generation is partial melting of subcontinental lithospheric mantle wedge above a subducting slab of oceanic lithosphere. The spaces for the Varcheh mafic intrusions are accommodated by dominant dextral strike‐slip movement in a continental arc experiencing extension during late Early Cretaceous subduction. According to the zircon U–Pb geochronology results in this paper and previous U–Pb ages in the northern part of the SSZ, the mid‐Cretaceous magmatism reveals a significant NW‐ward younging trend and migration of the magmatic arc from the Barremian–Aptian in south‐east to the Albian–Cenomanian in the north‐west.

Lithology of surface sediments in the East-Siberian Sea based on geological mapping

New data on the lithology of surface sediments in the coastal areas of the East-Siberian Sea (between Wrangel and Novaya Sibir islands), obtained within the framework of the state geological mapping at the scale of 1:1M, was used to clarify the distribution of granulometric types, mineral composition, and geochemistry of surface seabed sediments in this area. The main sources of sedimentary material and sedimentation patterns of the coastal part of the Western and Eastern sectors of the East-Siberian Sea were considered. An important factor determining sediment redistribution along the seabed, violating the regularities of mechanical differentiation of matter, consists in the plowing of the seabed surface by drifting ice to depths of 50 m.