Mesozoic Stage Research Articles

Formation mechanisms and resource potential of carbonate geothermal reservoirs in the Beijing-Tianjin-Hebei plain

Investigating the formation mechanisms of carbonate geothermal reservoirs is of theoretical and practical significance for summarizing the formation pattern of geothermal resources and further guiding their effective exploitation. The Beijing-Tianjin-Hebei Plain (BTHP), predominantly located within the Jizhong Depression and Cangxian Uplift in the Bohai Bay Basin, serves as the primary region for geothermal exploitation and utilization in China. More than 1500 geothermal wells have been drilled therein, with water temperature at the wellhead ranging from 55 to 110 °C, single-well flow rate ranging between 80 and 120 m3/h, and cumulative heating area exceeding 100 × 106 m3. However, the exploration and research in the region remain limited overall. As per the previous geothermal and petroleum exploration results and the latest geothermal drilling data, this study comprehensively evaluated the geothermal resources of karst geothermal reservoirs. The results show that two suites of carbonate karst reservoirs, namely the Jxw Formation and the Ordovician strata, have primarily developed in the BTHP, and their formation and evolution can be divided into four stages: the Mesoproterozoic-Early Paleozoic stage with carbonate sedimentation and the development of interlayer karst, the Late Paleozoic stage with the development of direct sedimentary cover, the Mesozoic stage with compressional uplifting and development of buried hill karst, and the Cenozoic stage with regional cover deposition and the modification and finalization of karst geothermal reservoirs. Accordingly, the porosity evolution history of the geothermal reservoirs is composed of three stages, namely a significant decrease followed by a minor increase, a gradual decline, and then a small fluctuation from increase to decrease before slowly rising again. The karstification in geothermal reservoirs can be summarized into quasi-syngenetic karstification, epigenetic karstification, and burial karstification, which can be subdivided into seven subcategories. The carbonate geothermal reservoirs in the study area boast total geothermal resources of 53.821 × 109 GJ, or 184.155 × 109 t of standard coal equivalent (tce), and the annual exploitable geothermal resources in the urban area can heat an area of (400‒500) × 106 m3, indicating great potential of geothermal exploitation.

Tectonic structure and stages of geological development of the Sterlitamak shikhans

The article considers the features of the tectonic structure and geological development of the Lower Permian single mountains – shikhans on the left bank of the Belaya River near the city of Sterlitamak (Republic of Bashkortostan). The analysis of published and archival materials, field research, the study of core material, lithological and structural observations allowed us to get an idea of the tectonics of single mountains (shikhans). The Shikhans are part of a single chain of carbonate massifs composed of reef facies and located submeridionally (from south to north) in the western side of the Pre-Uralian Foredeep. In the area of Sterlitamak four massivеs are brought to the surface of the Earth as part of a single Shikhan block. The tectonic structure of the territory is determined by paleotectonic (the period from 3600 to 23 million years) and neotectonic (23 – 5 million years).years and up to the present) events that are combined into periods and are divided into stages. The formation of reef complexes composing the shikhans was controlled by paleotectonic events of the collision stage of development, which led to the formation of the continental shelf margin with conditions favorable for the formation of reef communities on the border of the Pre-Uralian Foredeep during the Asselian and Sakmarian epochs (for 15 million years). Subsequent geological events – in the Artinskian and Kungur time, in the Late Permian-Early Mesozoic stage and in the Middle Jurassic-Miocene platform stage caused the destruction and leveling of the Early Permian relief, erosion of sediments and their overlap with younger sediments. The tectonic impact of the last Pliocene-Quaternary neo-orogenic stage (5 – 0 million years) is most intensively manifested in the rocks of Shikhans. It is expressed in intense fracturing and fragmentation of rocks, their recrystallization with loss of primary structural and textural features. The neotectonic movements of the blocks of the Earth's crust contributed to the removal to the surface of individual sections of the reef complexes distribution zone. The isolation of reef shikhans was a result of presence of an evaporites оver them, which were easily eroded. The tectonic effect on the carbonate rocks of reef nature contributed to the formation of zones of increased fracturing observed in the rocks of the Sterlitamak shikhans and penetration of oil-containing solutions and fluids, which formed areas of rocks with increased reservoir properties. Leaching and karst zones with residual bitumen are observed on almost all shikhans.

Model of Formation of Gold-Bearing Placers in Platform Areas (East of the Siberian Platform)

A model of the formation of gold-bearing placers for platform areas is proposed for the first time. Placers on the platforms are formed mainly due to the Precambrian ore sources spatially confined to the basement outcrops, and, locally, Mesozoic, formed when tectonic-magmatic activation occurs in the zones of paleorifts and deep faults. Placers formed due to the Precambrian sources are characterized by the presence of fine and thin gold with a size of 0.1‒0.25 mm and, as a rule, are not of commercial interest. They bar alluvial and coastal-marine allochtonous placers and are considered as complex, with associated mining of titanium, zirconium and other useful components. Placers formed due to the sources of the Mesozoic stage of ore formation belong to the class of small and medium reserves, the size of gold in them ranges from dust-like to 0.2‒0.25 mm or more and they are usually mined by prospectors' team. Placers on the platforms do not form sheet deposits, since they are formed mainly due to sources of non-placer-generating formations. The presence of such placers indicates the proximity of the ore occurrence, which the type and location can be determined based on the study of the mineralogical and geochemical features of the placer gold itself.

Structure and interpretation of the anomalous magnetic field of the South Turgay petroleum region

Purpose. Study on the deep structure of the South Turgay petroleum region to assess the influence of magnetic causative masses on the processes of generation, migration, accumulation and conservation of hydrocarbon (HC) accumulations, taking into account the evolution of rift development modes of the same sedimentary basin. Methodology. The combination of regional magnetometry data is applied with deep drilling data using a priori data on historical-geological, structural-formation, reservoir qualities and other factors. With the complex spatial anisotropy of the geomagnetic field and the distribution of magnetization of rocks in the Earth’s crust, the physical prerequisites of magnetic survey data provide quite correct geological interpretation of the results obtained. Findings. Classification and zoning of geomagnetic field anomalies by their morphology, intensity values, gradient and size was conducted, which made it possible to perform identification and geological forecast of magnetically causative bodies and determine their qualitative (structural) features.Various degrees of magnetization of different-age rocks of the South Torgay Petroleum region, as well as their relative location, structure, and depths of occurrence were established. It was revealed that the sedimentary cover and the upper part of the basement here are composed of low-magnetic and non-magnetic formations, and the upper edges of the magnetically disturbing masses lie at different depths in the consolidated crust, but, in general, deeper than the intervals of the section penetrated by deep drilling. Originality. The genetic, historical, geological, and tectonic-magmatic features of the South Torgay basin differ sharply from those of the adjacent Lower Syrdariya arch and Shu-Sarysu Depression. At the present stage of evolution, South Torgay sedimentary basin has a significant endogenous warming of the lithosphere in contrast to the adjacent Lower Syrdariya arch and Shu-Sarysu depression. To some extent, it indicates the inheritance in the regime of development of the South Turgay sedimentary basin from the Paleozoic and Mesozoic stages of rifting. Practical value. The depth of occurrence of magnetically causative objects significantly expand the stratigraphic interval of sediments that can be involved in the exploration process. The inherited mode of rift evolution of the basin suggests a favorable combination for the formation of a wide range of hydrocarbon traps, oil and gas source rocks, migration pathways, accumulation and preservation of HC accumulations.

АНТИКАВКАЗСЬКА СКЛАДЧАТІСТЬ КУРИНСЬКО-ПІВДЕННОКАСПІЙСЬКОЇ ЗАПАДИНИ (НА ПРИКЛАДІ ПІВДЕННОКАСПІЙСЬКОГО БАСЕЙНУ І ПЕРЕДМАЛОКАВКАЗСЬКОГО ПРОГИНУ)

The South Caspian Basin (SCB) is the deepest submerged sedimentary basin in the World and occupies the entire southern deep-water part of the Caspian Sea and the Kura and West Turkmenian lowlands adjacent to it from the west and east. The SCB has the thinnest (6...8 km) consolidated oceanic-type crust and the thickest sedimentary cover (25...30 km). The thickness of the Pliocene-Quaternary deposits is 10...12 km. The thickness of the main oil and gas complex – Productive-Red-Colored Strata of the Lower Pliocene is 7 ... 8 km. More than 6 km of volcanic-sedimentary deposits accumulated within the Lesser Caucasian trough at the Mesozoic stage of development. However, in the western part of the trough the translucent pre-Jurassic basement which has a northeastern orientation formed a similar orientation of the overlying deposits. All of the above mentioned events took place under conditions of compression in the north of SCB which were realized at the level of the consolidated crust by subduction, and at the level of the sedimentary cover by structure forming processes. Primary migration passes into the lateral from the submerged zones to the uplifted ones. Deep faults that have formed transverse folding can also serve as migration routes. The submerged predominantly gas-bearing depositional zone of the Productive Strata is represented by folding of both Caucasian and anti-Caucasian strike. Despite the fact that the Kura-South-Caspian depression at the present stage covers the territory from the Dziruly massif in the west to the West Turkmenian depression in the east inclusive as a single negative structural element, in the Mesozoic time as follows from the above it represented two independent areas of subsidence and sediments accumulation in the Transcaucasian microcontinent (western part) and the Greater Caucasian-South Caspian rift basin (eastern part). Therefore, the anti-Caucasian folding of the Kura-South Caspian depression has a different genesis and naturally a different oil and gas potential.

СЕРЕБРЯНАЯ МИНЕРАЛИЗАЦИЯ В ГЛУБИННЫХ МАГМАТОГЕННЫХ СИСТЕМАХ ДРЕВНИХ ОСТРОВНЫХ ДУГ: ИЛЬДЕУССКИЙ УЛЬТРАОСНОВНОЙ МАССИВ, СТАНОВОЙ МОБИЛЬНЫЙ ПОЯС (ДАЛЬНИЙ ВОСТОК РОССИИ)

The Triassic (232–233 Ma) Ildeus mafic-ultrabasic massif is a fragment of a large mineralized magmatogenic system formed within the Stanovoy mobile belt at the Mesozoic stage of its evolution. Ultrabasic rocks are represented by cumulative plagioclase- and amphibole-bearing dunites, peridotites, websterites, and pyroxenites; basic rocks are gabbro-anorthosites, norites, and two-pyroxene gabbro. Most intrusive rocks of the Ildeus magmatogenic system experienced ultramafic (serpentine, chlorite, talc, carbonates) and acidic (quartz, biotite, potassium feldspar, secondary micas) metasomatism. Geochemical characteristics (calc-alkaline differentiation trend, negative anomalies of highly charged incoherent elements) indicate the subduction nature of the primary magma in the Ildeus system. The ultrabasic rocks are intruded by intermediate-acid intrusions with geochemical characteristics of adakite. Magmatic-stage silver mineralization is represented by microinclusions of cuprous silver, alloys of silver, copper, gold and zinc, acanthite and silver halides in association with pentlandite, chalcopyrite, bornite, and pyrrhotite. These rocks are characterized by microinclusions of native platinum, gold, tungsten, bismuth, lead, PGE alloys, W-Co-Ti, Sb-Pb, Cu-Zn-Sn, minerals of Ag-Cu-Sb-Se-S and Zn-Ni systems -Co-Fe-S, barite, chlorapatite and Bi-Sn-Pb chlorides. At the metasomatic stage, native silver, Au-Ag alloys, silver and copper chlorides, acanthite, silver and lead tellurides coexist with digenite, heathlewoodite, pyrite, sphalerite, galena, native nickel and gold, Cu-Zn alloys, sulfides of the Pb-As- Cu-Fe-S and bismuth chloride. At the magmatic stage, silver minerals crystallized under reducing conditions in the presence of high-temperature aqueous fluids enriched in sulfide sulfur, halogens, and volatile siderophile (W, Pt) and chalcophile (Ag, Bi, Sn, Sb, Pb) metals that entered the primary melt from serpentinites, metamorphosed gabbroids, and metal-bearing pelagic sediments of the subducting oceanic plate. Metasomatic parageneses of silver minerals were formed under oxidized near-surface conditions with the participation of low-temperature water-salt solutions with elevated concentrations of sulfate sulfur, arsenic, and tellurium. A two-stage model is proposed for the formation of silver mineralization in island arc magmatic systems, in which the high-temperature magmatic stage of formation in deep crustal parts is replaced by low-temperature hydrothermal ore formation processes in near-surface conditions.

Internal Structures of Placer Gold as an Indicator of Endogenous and Exogenous Processes

The study of the internal structures of placer gold on the territory of the east of the Siberian platform, overlain by a thick cover of Mz-Kz deposits, where traditional methods of searching for gold deposits are not effective, allowed us to determine, for the first time, the stages of ore formation and conditions of its occurrence. The identified indicators of the internal structures of placer gold (structures of primary recrystallization, secondary recrystallization, thick high-grade shells) indicate that placer gold content is formed mainly due to the supply and repeated redeposition of native gold from ancient gold-bearing deposits of the Precambrian stage of ore formation to younger ones. The discovered coarse-, medium-grained, mono-grained, unclear-zonal, granulation and disintegration structures suggest a supply of gold from nearby ore sources of the Mesozoic stage of ore formation. In the weathering crust, a high-grade shell is formed. In the hydrodynamic environment, the internal structures of gold practically do not change and fully correspond to the internal structures of endogenous gold. In aeolian conditions, the internal structures are transformed. In ancient gold-bearing conglomerates, under the impact of lithostatic pressure, as well as in metamorphogenic conditions, when the PT conditions change, the internal structure changes. Thus, for the first time, on a huge factual material, it is proved that the internal structures contain extensive information both about the endogenous origin of gold (the stages of ore formation—Precambrian and Mesozoic) and about its transformation in various exogenous conditions. The identified indicator of the internal structures of placer gold for certain types of sources contribute to a more correct selection of methods for searching for ore and placer gold deposits in closed territories and assessing their prospects. The use of this method makes it possible to develop criteria for forecasting different sources and types of gold deposits based on internal structures.

Mineralogical and Geochemical Features of Native Gold From Placers of the Evota Gold-Bearing Region (Russia, Aldan Shield)

Evota gold-bearing region is located in south of Republic Sakha (Yakutia) within the Nimnyr terrane of Aldan shield. A large numbers of gold-bearing placers are known on studied territory, but the primary sources for them have not been established. In this work, based on the study of the mineralogical and geochemical features of gold from alluvial deposits of the Evota gold-bearing region, possible genetic types of primary sources are considered. Obtained data showed that native gold in the studied objects has a very high, high and medium fineness. The roundness of gold is different. Almost ore crystals with sharp edges and well-rounded individuals with polished faces were found. The fineness of the studied gold grains was determined by microprobe analyzer Cameca Camebax-micro and varies in the range from 812 to 1000 %⁰. A thin (up to 20 μm) high-grade rim was found in two grains (cr. Zolotoy). The central part of one of them has a fineness of 865 %o, and in the edge part it reaches 1000 %⁰, which indicates that this gold was in the hypergenesis zone. Admixture elements determined as traces and are presented Cu, Pd, Fe, Ni. Minerals-microinclusions - quartz, potassium feldspar, pyroxene, staurolite, maldonite, bismuthite revealed in gold grains. In some watercourses, for example, in the creek Sukhoi, only very high fineness gold (993-1000 %⁰) was found. The presence of high-grade gold (cr. Sukhoi), intergrowths of gold with bismuthite (cr. Zolotoy), as well as inclusions of maldonite (cr. Yagodny) gives opportunity for assuming that primary sources could be basic ores such presented in the P. Pinigin deposit. At the sites (cr. Elovyi, r. Evota), both medium-grade and very high-grade gold were found, the fineness range varied from 827 to 998 %⁰. The presence of gold with medium fineness and good roundness in studied watercourses probably indicates an additional supply of gold from primary sources formed as a result of the alkaline magmatism development of the Mesozoic age. Thus, for gold with high and very high fineness by admixture-elements, chemical composition and microinclusions, a genetic relationship with primary sources similar to the P. Pinigin deposit was found; for gold grains with medium fineness, formation in gold-ore mineralization characterized for the Mesozoic stage ore development such in deposits of Central-Aldan ore region is assumed.

Становление структуры западной части Алтае-Саянской складчатой области (мезозойский этап)

Рассматриваются вопросы становления структуры западной части Алтае-Саянской складчатой области. Современная структура герригoрии рассмотрена как коллаж террейнов, сформированных в мезозойское (триас, юра, мел) время. Определяющим для формирования структуры региона стал юрский период. Возраст тектонической активизации устанавливается по возрасту самых молодых пластин в основании террейнов. Последним проявлением мезозойского тектогенеза в регионе следует считать смещение в юго-восточном нанравлении герригoрии Западно-Сибирской плиты с фрагментом Томь-Колыванской складчатой зоны, фиксируемое формированием раннемеловой Неня-Чумышской впадины.

Tectonic Conditions for the Formation of Structures of the Sakandzha Ore District (Selennyakh Ridge, NE Asia)

The Sakandzha gold-ore district occurs in the north-western margin of the Selennyakh allochthonous block of the Omulevka terrane forming part of the Kolyma-Omolon micricontinent (Verkhoyansk-Chersky orogenic belt, NE Asia). Tectonic structures of the Sakandzha ore district were formed in two stages of the Late Mesozoic deformation: thrust and strike-slip fault ones. Formation of the fold-and-thrust structures of the early Late Mesozoic deformation stage within the Selennyakh block and its thrusting, in the form of a thrust sheet, over the fold structures of the Tuostakh-Polousnyi zone in Neocomian time were almost synchronous with the intrusion of large granite plutons (Sakhanya and Syachan) into the fold-and-thrust structures in the northern part of the Verkhoyansk-Chersky orogenic belt. By the end of the Neocomian or in pre-Aptian time, strike-slip deformations of the second Late Mesozoic stage were superposed on the early thrust structures. At that time, the Selennyakh block was divided into smaller blocks by strike-slip faults, among them the Kalychan one. Two ore-bearing segments of different structure, Pologiy and Arbat, are distinguished within the Kalychan dextral strike-slip fault zone. As a result of strike-slip motions, the sedimentary rocks of these segments became steeply inclined, strongly deformed, and were pierced by a network of variably oriented fractures and cracks, which made them highly permeable for the circulating hydrothermal and ore solutions. The major Kalychan, Upper Kalychan and Arbat strike-slip faults are interpreted as the ore-feeding faults. The feathering subsidiary faults as well as strongly fractured zones are considered as ore-controlling and ore-bearing structures. The end of the Neocomian was marked by completion of the collision, and the Aptian-Albian period saw the inception of the Dzhakhtardakh volcanogenic belt of Early to Late Cretaceous age. Its formation is considered to be related to the crustal extension processes preceding the opening of the Eurasian ocean basin.

Starogroznensky oil and gas field: historical background and current status

The paper is devoted to one of the largest deposits of the North Caucasus, i.e. Starogroznenskoye field. There are identified the main development stages of this field, i.e. well production, development of the Miocene and Mesozoic deposits, and the current stage. Well production continued almost until the end of the 19th century. At the Miocene stage, the production was carried out from thrust and subthrust sand formations of Karagan and Chokrak. The paper also mentions the experimental adit on Mamakayevskaya gill. Which was headed by mining engineers A.A. Klushin and A.E. Yeronin. The beginning of the Mesozoic stage dates to the end of the 1940s. The main production was associated with the Upper Cretaceous sediments. At the end, an assessment of the current state of the structure of proven reserves is given. In conclusion, an assessment of the opportunities aimed at further development of the field associated with the additional exploration and additional development of the Miocene and Lower Cretaceous deposits is given.

О возможности формирования крупных золоторудных месторождений мезозойского этапа рудообразования (восток Сибирской платформы)

О возможности формирования крупных золоторудных месторождений мезозойского этапа рудообразования (восток Сибирской платформы)

Kinematic analysis of Jurassic grabens of soulthern Turgai and the role of the Mesozoic stage in the evolution of the Karatau–Talas–Ferghana strike-slip fault, Southern Kazakhstan and Tian Shan

The Karatau–Talas–Ferghana Fault (KTF) extending for 1500 km from Turgai to western Tarim is one of the world’s largest intracontinental strike-slip faults. This paper overviews the evolution of the KTF, providing insight into its relatively poorly studied northern segment in the Karatau Range and Turgai, known as the Main Karatau Fault (MKF). The right-lateral strike-slip along the KTF developed during three stages in the late Permian–Triassic, Early–Middle Jurassic, and late Cenozoic. The total strike-slip decreases northward from 200 km in the Ferghana Range to 100 km in the Karatau Range and decreases to zero in southern Turgai. Kinematic analysis of Jurassic grabens compensating the strike-slip in southern Turgai shows that strike slip along the KTF in the Jurassic, previously regarded as insignificant, actually measures tens of kilometers and 50% of the total strike slip in the northern segment of this fault.

Late Mesozoic rifting at the flanks of the Dzhagda segment of the Mongolia-Okhotsk collisional orogen: global and regional aspects

The role of rifting in the formation of the recent structure of the Mongolia-Okhotsk orogen is extremely high, but it is still underestimated with regard to flanks of the Dzhagda segment of this orogen. Current researches refer to a combination of physical and chemical processes in the depth of the lithosphere, as well as interactions between the Izanagi, Eurasian and Pacific plates as explanations of repeated rifting events in East Asia. Upwelling of the asthenosphere due to significant differences in the lithosphere thickness (150–200 km under cratons, and only 100 km under orogenic belts) was viewed as a cause of rifting. It was assumed that rifting was controlled by mantle plumes, volcanism and heat regime. Structures bordering the Mongolia-Okhotsk orogen from north and south were considered as superimposed or marginal troughs. Recent studies have revealed numerous riftogenic Late Mesozoic structures in the Central Asian orogenic belt, which resulted from the collision of the Siberian and North Chinese cratons. New geological survey and geochemical data on volcanites confirmed the riftogenic origin of the Zeya-Uda (or Uda) and Nora-Selemdzha troughs bordering the Mongolia-Okhotsk orogen from north and south, respectively (Fig. 1, and 2). Geology and geophysics of those troughs has been described. It is noted that riftogenic volcanites formed later in the east than those in the west. The Late Mesozoic rifting is widely manifested in North Eastern Asia across the area exceeding two million square kilometers, from Lake Baikal to the Sikhote-Alin region (west to east) and from the Southern Yakutia basins to North China (north to south). It is evidenced by intra-continental rifts of various trends, volcanic provinces and extension structures along large strike-slip faults [ Ren et al., 2002 ]. The Uda and Nora-Selemdzha marginal troughs located along the Dzhagda segment of the Mongolia-Okhotsk orogen give evidence that compression was replaced by extension in the study area. Rifting structures may be due to physical and chemical processes, the development of plumes [ Yarmolyuk et al., 2000 ], as well as the interaction between the Pacific and Eurasian lithospheric plates. Volcanic activity took place earlier in the west and then propagated to the east due to the shifting of the subduction zone in this direction. This paper analyzes regional and global geological events on the basis of new drilling data and the geochronological dating of volcanites. It describes the Late Mesozoic stage of rifting at the flanks of the Dzhagda segment of the Mongolia-Okhotsk collisional orogen.

Mesozoic age of the last episode of high-temperature metamorphism of the Sutam block of the Stanovoi suture

The U–Pb (zircon) age of 250 ± 1 Ma was determined for differentiated gabbro–monzonite intrusions, which were formed prior to metamorphism of high-temperature amphibolite facies of high pressures in the southeastern part of the Sutam block of the Stanovoi suture. These data indicate that this episode of metamorphism belongs to the Mesozoic stage of evolution of the Stanovoi suture rather than to the Early Precambrian, as was suggested before. It most likely corresponds to the age of the last episode of the high-temperature metamorphism of amphibolite facies (140 Ma), which is manifested within the Dzhugdzhur–Stanovoi superterrane of the Central Asian foldbelt adjacent from the south to the Stanovoi suture and is caused by collision of the Dzhugdzhur–Stanovoi superterrane and the epi-Paleozoic Amur microcontinent during the closure of the Mongol–Okhotsk oceanic basin.

The fossil record and taphonomy of butterflies and moths (Insecta, Lepidoptera): implications for evolutionary diversity and divergence-time estimates.

BackgroundIt is conventionally accepted that the lepidopteran fossil record is significantly incomplete when compared to the fossil records of other, very diverse, extant insect orders. Such an assumption, however, has been based on cumulative diversity data rather than using alternative statistical approaches from actual specimen counts.ResultsWe reviewed documented specimens of the lepidopteran fossil record, currently consisting of 4,593 known specimens that are comprised of 4,262 body fossils and 331 trace fossils. The temporal distribution of the lepidopteran fossil record shows significant bias towards the late Paleocene to middle Eocene time interval. Lepidopteran fossils also record major shifts in preservational style and number of represented localities at the Mesozoic stage and Cenozoic epoch level of temporal resolution. Only 985 of the total known fossil specimens (21.4%) were assigned to 23 of the 40 extant lepidopteran superfamilies. Absolute numbers and proportions of preservation types for identified fossils varied significantly across superfamilies. The secular increase of lepidopteran family-level diversity through geologic time significantly deviates from the general pattern of other hyperdiverse, ordinal-level lineages.ConclusionOur statistical analyses of the lepidopteran fossil record show extreme biases in preservation type, age, and taxonomic composition. We highlight the scarcity of identified lepidopteran fossils and provide a correspondence between the latest lepidopteran divergence-time estimates and relevant fossil occurrences at the superfamily level. These findings provide caution in interpreting the lepidopteran fossil record through the modeling of evolutionary diversification and in determination of divergence time estimates.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0290-8) contains supplementary material, which is available to authorized users.

Метаморфогенные плагиоклазиты зоны ГУР как результат мезозойского этапа формирования Уральского орогена

Метаморфогенные плагиоклазиты зоны ГУР как результат мезозойского этапа формирования Уральского орогена

Gold resource potential of the eastern Siberian Platform: Placers and their feeding sources

The data on typomorphism of placer gold and its localization in the eastern Siberian Platform have been integrated for the first time. The alluvial, pseudolode, and eolian morphology of gold determines the origin of placers, which is explained not only by hydrodynamic but also by eolian processes. The recent and older alluvial (Au-bearing reservoir rocks in the second case), as well as eolian (unconventional type), genetic types of placers are recognized in the given territory. Precambrian and Mesozoic stages of ore formation are distinguished by the set of typomorphic attributes of placer gold (chemical composition, microinclusions, internal structure, etc.). On the basis of distinguishing features of placer gold, Precambrian lode deposits of great depth spatially related to outcrops of the basement have been forecasted for the first time and classified into low-sulfide gold-quartz, Au-bearing banded iron formation, Au-Cu porphyry, and Au-PGE types. The inferred shallow-seated gold-silver and gold-sulfide-quartz disseminated deposits occur locally and are related to the Mesozoic tectonomagmatic reactivation. The elaborated methods and approaches to the study of placer gold typomorphism in the eastern Siberian Platform also could be helpful in providing insights into placer origin, and forecasting and prospecting gold deposits on the East European Platform, which is close to the Siberian Platform in geological evolution.

Structural stages and evolution of the Urals

Five main structural and historical stages are established in the territory of the Urals: 1) Archean-Paleoproterozoic, a time of formation of the Volgo-Uralia subcontinent and its amalgamation with the other blocks of the craton of Baltica; 2) Riphean-Vendian (Meso- and Neoproterozoic), а stage that was finished with formation of Timanides; 3) Paleozoic-Early Mesozoic stage, corresponding to the development of the Uralides; 4) Mid-Jurassic-to Miocene platform stage; 5) Pliocene-Quaternary neo-orogenic stage. In this paper stratigraphic data are discussed, schemes of the structural zonation are presented, and the problems of the structural geology and geodynamics of sedimentary and magmatic complexes are discussed in a chronological order. Ideologically, the paper is based on plate and plume tectonics, in their modern versions.

An Extraordinary Early Jurassic Planthopper from Hunan (China) Representing a New Family Qiyangiricaniidae fam. nov. (Hemiptera: Fulgoromorpha: Fulgoroidea)

Abstract:A new family of planthoppers Fulgoromorpha from the Lower Jurassic of southern China is described to comprise Qiyangiricania cesta Lin, 1986. The new family differs in venation pattern from the other Jurassic representatives of Fulgoroidea, presenting particular model of tegmen venation, not found among extinct and recent planthoppers. The Mesozoic stage of Fulgoroidea evolution is discussed. The extinct taxon Ricaniites fulgens (Brodie, 1845) from the Purbeck of United Kingdom is excluded from the Hemiptera.