Mesozoic Research Articles

Neotectonics and seismicity of the Urals

Introduction. The Ural submeridional mountain belt is an epipaleozoic orogen rejuvenated in the contemporary period (in the Neogene-Quaternary period in the last 20–30 million years). In the pre-Paleozoic era, the Urals developed as a submeridional upland, presumably as a result of the interaction (clash) between the East European and West Siberian plates. In the Mesozoic and Cenozoic eras, the Urals developed as a submeridional upland. As a result, the Ural Paleozoic orogen was largely (almost completely) destroyed by weathering, but in the second half of the Cenozoic time it was rejuvenated and experienced some growth again. The reason for the rejuvenation of the Urals could be the subhorizontal compression of the Urals crust between the East European (EEP) and West Siberian (WSP) plates, which occurred in the contemporary period (in the last 20–30 million years). The epicenters of contemporary Ural sensible earthquakes are localized in the East European Craton bordering the Urals along the boundaries of the Ufa obduction of the EEP. The intensity of Ural earthquakes ranges from 3–4 to 5–6 according to MSK-64 scale, and their magnitude is estimated in the range from 2.0 to 6.0–6.5. Research objective is to assess the seismicity and seismic activity of the Urals in the contemporary period and the relationship between Ural sensible earthquake epicenters and its rejuvenated tectonic structures. Methods of research. The spacing of sensible earthquake epicenters in the Urals relative to tectonic structures of different age was estimated by comparing the corresponding geological and tectonic schemes of the Urals. Results. The analysis showed that the epicenters of sensible earthquakes are located mainly along the periphery of the Ufa obduction of the EEP, which interacts with the Ural orogen. Most of the epicenters are located in the northeastern boundary of the Ufa obduction of the EEP. Earthquake epicenters are located both within the Ural orogen (in the zone of geodynamic influence of the Serov-Mauk regional submeridional fault), and within the eastern edge of the East European Craton, in the trough of the western piedmont of the Ural Mountains and adjacent areas.

Origin of the tropical–polar biodiversity contrast

AbstractAimThe aim was to investigate the evolutionary origins of the striking biodiversity contrast between high‐ and low‐latitude regions in the present day. Is this a relatively recent phenomenon, causally linked in some way to the greenhouse–icehouse transition and onset of global coolingc. 34 Myr ago, or does it have deeper temporal roots and thus other potential causes?LocationEarly Cenozoic fossil assemblages from two tropical and one polar region, and modern counterparts from various tropical localities and Antarctica.Time periodThe Cretaceous–Palaeogene (K/Pg) mass extinction event, Early Cenozoic (Palaeocene–Eocene) and the present day.Major taxa studiedShelf‐depth marine Mollusca; the four richest modern benthic clades: Imparidentia, Pteriomorphia, Neogastropoda and Littorinimorpha.MethodsThe K/Pg mass extinction and subsequent recovery was compared between two tropical and one polar region at four distinct stratigraphic intervals. Taxa were identified to species level and assigned to principal families within the four largest benthic molluscan clades. Taxon counts were compared between the three regions at each level and also compared with standardized tropical and polar modern faunas.ResultsThe mass extinction was followed by a distinct 25 Myr phase of evolutionary radiation, during which the tropical–polar contrast in the taxonomic composition of all four clades was strongly enhanced; as the global molluscan fauna expanded, it differentiated into distinct low‐ and high‐latitude components.Main conclusionsA marked differentiation of tropical and polar molluscan faunas occurred in the immediate aftermath of the K/Pg mass extinction; it is likely that, at least for the two bivalve clades investigated, this differentiation was initiated well within the Mesozoic era. The greater antiquity of the tropical–polar split suggests that it was not the product of any single controlling factor during the Cenozoic.

Discovery of Late Mesozoic volcanic seamounts at the ocean-continent transition zone in the Northeastern margin of South China Sea and its tectonic implication

The Northern South China Sea (SCS) margin experienced the switch from Andean-type active subduction to passive extension during late Mesozoic era. However, the mechanism of cessation of paleo-Pacific subduction in the SCS region is unclear, and the location of suture zone between paleo-Pacific plate and South China block is obscure. In this study, we report new 40Ar/39Ar ages and whole-rock Hf isotopes of basalts from two poorly studied volcanic seamounts (namely, Puyuan and Beipo) at the ocean-continent transition zone in the Northeastern SCS margin, with an emphasis on the existence of exotic, buoyant oceanic plateau and its geodynamic effect on subduction cessation. Results indicate that the OIB-type Puyuan and E-MORB-type Beipo volcanic seamounts were erupted at 154.1 Ma and 93.2 Ma, respectively. Whole-rock trace element, Sr-Nd-Pb-Hf isotopic compositions, and subduction polarity point out that these samples were oceanic intraplate basalts formed within the paleo-Pacific plate, independent of the coeval, Late Mesozoic paleo-Pacific subduction system in the region. The ages and geochemical data of the two volcanic seamounts, combined with geochemical data of Late Mesozoic Pacific oceanic plateaus and seismic data of the Northeastern SCS margin, show that there may exist a Late Mesozoic exotic, buoyant oceanic plateau in the region. The collision between the oceanic plateau and the South China block could lead to the cessation of paleo-Pacific plate subduction, and changes in tectonic regime during the Late Cretaceous era (ca. 100–65 Ma). The pre-existing, Late Mesozoic suture zone has been well constrained by the remnant oceanic plateau and continental arc, and may play a key role in the formation of Cenozoic rifting tectonic units in the region.

Geodynamic Formation Conditions and Age of Granitoids from Small Intrusions in the West of the Yana–Kolyma Gold Belt (Northeast Asia)

Abstract We report results of geological, mineralogical-petrographic, geochemical, isotope-geochemical (Sm–Nd, Rb–Sr), and geochronological (U–Pb, 40Ar/39Ar) studies of acid and intermediate intrusive rocks (granodiorites, leucocratic granites, subalkaline granites, and subalkaline leucocratic granites, diorites, and quartz diorites) of the Bukeschen and Samyr small plutons in the western part of the Yana–Kolyma gold belt (northeast Asia). These rocks are combined with Late Jurassic (151–145 Ma) dikes of basic, intermediate, and acid compositions into a single complex of small intrusions. They intrude the Upper Triassic–Middle Jurassic terrigenous deposits of continental margin blocks in the eastern part of the Verkhoyansk–Kolyma folded area. Our new U–Pb data for zircon (SHRIMP-II) indicate that the Bukeschen and Samyr pluton granitoids formed in the Berriasian, at 144.5 and 143 Ma, respectively. The small-intrusion granitoids have geochemical and isotope (Sm–Nd and Rb–Sr) characteristics similar to those of Late Jurassic dikes of varying composition. Therefore, they can be united into a single complex of small intrusions generated from a mixed source with the participation of mantle (OIB- and E-MORB type), lower crust, and subduction components and with Paleoproterozoic–Mesoproterozoic Sm–Nd model age estimates for the magma sources. Late Jurassic–Early Cretaceous magmatic and postmagmatic events and cooling of the intrusions played an important role in the processes of gold localization in the western part of the Yana–Kolyma gold belt. This is reflected in two tectonothermal stages (accounting for closing temperatures of the U–Pb, 40Ar/39Ar, and Re–Os isotope systems for different minerals) estimated at 151–141 and 138–137 Ma. These results for the small-intrusion complex agree with the tectonic model of the evolution of an active continental margin (northeastern Siberia) in the Mesozoic era, whose final development stage in the Berriasian age saw the formation of mostly small granitoid plutons.

Comparison of vertebrate skin structure at class level: A review.

The skin is a barrier between the internal and external environment of an organism. Depending on the species, it participates in multiple functions. The skin is the organ that holds the body together, covers and protects it, and provides communication with its environment. It is also the body's primary line of defense, especially for anamniotes. All vertebrates have multilayered skin composed of three main layers: the epidermis, the dermis, and the hypodermis. The vital mission of the integument in aquatic vertebrates is mucus secretion. Cornification began in apmhibians, improved in reptilians, and endured in avian and mammalian epidermis. The feather, the most ostentatious and functional structure of avian skin, evolved in the Mesozoic period. After the extinction of the dinosaurs, birds continued to diversify, followed by the enlargement, expansion, and diversification of mammals, which brings us to the most complicated skin organization of mammals with differing glands, cells, physiological pathways, and the evolution of hair. Throughout these radical changes, some features were preserved among classes such as basic dermal structure, pigment cell types, basic coloration genetics, and similar sensory features, which enable us to track the evolutionary path. The structural and physiological properties of the skin in all classes of vertebrates are presented. The purpose of this review is to go all the way back to the agnathans and follow the path step by step up to mammals to provide a comparative large and updated survey about vertebrate skin in terms of morphology, physiology, genetics, ecology, and immunology.

New geochronological and geochemical constraints on the Banke, Dutsen Wai, Guraka, and Zuku alkaline granite complexes from the northcentral Nigerian younger granite province

ABSTRACT An integrated study was carried out on four anorogenic syenite-granite complexes (i.e. Banke, Dutsen Wai, Guraka, and Zuku) from the Nigerian Younger Granite (NaYG) province, in a bid to constrain their magma sources, rare metal mineralization potentials, and tectonic implications. These four complexes primarily consist of quartz syenite, granite porphyry, arfvedsonite aegirine granite, and biotite granite. The studied rocks are chemically characterized by high alkalis, HFSEs, Ga/Al ratios, and zircon saturation temperature (776–1127°C, average = 932°C), typically of A1-type granites. The zircon εHf(t) values of the arfvedsonite aegirine granite (−6.0 to −0.79) are higher than those of the granite porphyry (−9.57 to −7.67) and biotite granite (−9.49 to −5.86) suggesting moderate crustal contamination of mantle-derived melts for the origin of the peralkaline granites. Generation of the biotite granite likely involved inputs of both crustal- and mantle-derived melts and is evidenced by the presence of inherited Pan-African (600–610 Ma) zircons and low whole rock Nb/U and Nb/Ta ratios. Furthermore, input of crustal material likely increased the metal budget of the residual melt and enhanced Nb, Sn, and sulphide mineralization in the Banke granite porphyry and biotite granite and Dutsen Wai biotite granite. Zircon U-Pb dating results constrain the emplacement ages to early Mesozoic era, from the Banke granite porphyry of 180 ± 1 Ma, Dutsen Wai biotite granite of 177 ± 3 Ma, Guraka arfvedsonite aegirine granite of 227 ± 2 Ma and Zuku arfvedsonite granite of 186 ± 2 Ma. These age data indicate a local E-W age migration pattern for the alkaline magma emplacement in northcentral NaYG province. Integrated with other geological evidence, we favour a formation model for the anorogenic NaYG province likely driven by the reactivation of ancient shear zones and structures.

Endophytic insect oviposition traces in deep time

Interactions between the two most abundant groups of organisms on Earth, insects and plants, are especially relevant in evolutionary studies. We review different aspects related to endophytic eggs laid by insects in plants for more than 300 Myrs, from the Carboniferous to the Miocene. This work provides a meta-analysis of endophytic insect oviposition in the fossil record, based on the plant group used as host, the number of oviposition traces on a single leaf, their trace pattern, and the morphometry of the individual egg traces. Our results show that Pinophyta and “pteridosperms” are the host-plant groups most frequently reported up to the Early Cretaceous, and Magnoliophyta (=Angiospermae) from the Cretaceous. The highest number of bibliographic records are from the Permian, while the Mesozoic Era shows the highest richness of trace patterns. No relation was detected between the trace pattern and the host-plant group used for oviposition. Our observations support the proposal that the trace pattern would be insect-specific and does not depend on the host-plant group on which the egg-laying occurs. From the Carboniferous to the Miocene, a gradual increase in the frequency of “Curved” type patterns and a decrease in “Straight” type patterns is observed. Two reduction events of the length of the traces are established, during the Permian, which could be explained by environmental causes, and during the Cretaceous by the emergence and selective predation by birds.

The dawn of the flying reptiles: first Triassic record in the southern hemisphere

AbstractPterosaurs were the first vertebrates to evolve powered flight. The timing of their origin is still debated, and hypotheses range from the end of the Permian Period, to the lower Mesozoic Era, and through to the Middle–Late Triassic epochs. Regardless of when they originated, the oldest records are restricted to the Upper Triassic Norian Stage in the northern hemisphere (Europe, USA and Greenland). We report two new raeticodactylid pterosaurs, Yelaphomte praderioi gen. et sp. nov. and Pachagnathus benitoi gen. et sp. nov. from the upper Norian to Rhaetian Quebrada del Barro Formation in north‐western Argentina. The new specimens (an isolated dentary symphysis, partial rostrum, and distal half of ulna) are the first unequivocal Triassic records of pterosaurs in the southern hemisphere, confirming that the absence of pterosaurs outside north‐western Pangaea during the Late Triassic was the result of poor sampling rather than true absence. These new discoveries provide evidence of a greater diversity of pterosaurs living in terrestrial habitats and a wider global distribution of pterosaurs from the beginning of their evolution on Earth.

Exhumation of plutons controlled by boundary faults: Insights from the kinematics, microfabric, and geochronology of the Taibai shear zone, Qinling Orogen, China

Abstract The Taibai granitic plutons lie between the Taibai ductile shear zone to the north and the Shangdan suture to the south. The deformation mechanism of the ductile shearing is crucial to understanding the exhumation processes of the multiple plutons that formed after the Late Mesozoic period. Geological investigations, microstructures, and kinematic vorticity calculations indicate that the Taibai shear zone deformed in response to pure shear-dominated (54%–65%) transpression and top-to-NW shear sense as a result of NE–SW oblique contractional tectonics. The quartz crystallographic preferred orientations of the prism <a> slip system, the grain boundary migration, and sub-grain rotation dynamic recrystallization of quartz—combined with the plagioclase–hornblende thermometer—constrain the main deformation temperatures to a range of 400–650 °C, which suggests amphibolite to greenschist facies conditions. In addition, it is extremely likely that the mylonites experienced late-stage, lower temperature deformation as demonstrated by the sporadic bulging recrystallization, the quartz basal <a> slip system, and the two-feldspar geothermometer calculation. The samples collected from the weakly deformed mylonitic granite pluton and the undeformed quartz-feldspathic dike that intruded into the mylonites yield zircon U–Pb ages of 129 ± 1 Ma and 115 ± 1 Ma, respectively. This information, with the lower intercept ages of ca. 120 Ma obtained from the mylonite samples, suggests that the ductile shearing probably occurred from ca. 129 Ma to 115 Ma. Combined with the regional geological data, these findings suggest that the Taibai shear zone and the Shangdan suture accommodated the oblique upward extrusion of the Taibai plutons during Early Cretaceous time.

The Mesozoic terminated in boreal spring

The Cretaceous–Palaeogene mass extinction around 66 million years ago was triggered by the Chicxulub asteroid impact on the present-day Yucatán Peninsula1,2. This event caused the highly selective extinction that eliminated about 76% of species3,4, including all non-avian dinosaurs, pterosaurs, ammonites, rudists and most marine reptiles. The timing of the impact and its aftermath have been studied mainly on millennial timescales, leaving the season of the impact unconstrained. Here, by studying fishes that died on the day the Mesozoic era ended, we demonstrate that the impact that caused the Cretaceous–Palaeogene mass extinction took place during boreal spring. Osteohistology together with stable isotope records of exceptionally preserved perichondral and dermal bones in acipenseriform fishes from the Tanis impact-induced seiche deposits5 reveal annual cyclicity across the final years of the Cretaceous period. Annual life cycles, including seasonal timing and duration of reproduction, feeding, hibernation and aestivation, vary strongly across latest Cretaceous biotic clades. We postulate that the timing of the Chicxulub impact in boreal spring and austral autumn was a major influence on selective biotic survival across the Cretaceous–Palaeogene boundary.

Prediction of Suitable Distribution of a Critically Endangered Plant Glyptostrobus pensilis

Glyptostrobus pensilis is a critically endangered living fossil plant species of the Mesozoic era, with high scientific research and economic value. The aim of this study was to assess the impact of climate change on the potential habitat area of G. pensilis in East Asia. The MaxEnt (maximum entropy) model optimized by the ENMeval data package was used to simulate the potential distribution habitats of G. pensilis since the last interglacial period (LIG, 120–140 ka). The results showed that the optimized MaxEnt model has a high prediction accuracy with the area under the receiver operating characteristic curve (AUC) of 0.9843 ± 0.005. The Current highly suitable habitats were found in the Northeast Jiangxi, Eastern Fujian and Eastern Guangdong; the main climatic factors affecting the geographic distribution of G. pensilis are temperature and precipitation, with precipitation as the temperature factor. The minimum temperature of coldest month (Bio6) may be the key factor restricting the northward distribution of G. pensilis; during the LIG, it contracted greatly in the highly suitable habitat area. Mean Diurnal Range (Bio2), Minimum Temperature of Coldest Month (Bio6), Annual Precipitation (Bio12) and Mean Temperature of Driest Quarter (Bio9) may be important climatic factors causing the changes in geographic distribution. In the next four periods, the suitable areas all migrated southward. Except for the RCP2.6-2070s, the highly suitable areas in the other three periods showed varying degrees of shrinkage. The results will provide a theoretical basis for the management and resource protection of G. pensilis.

Enhanced hydrological cycle during Oceanic Anoxic Event 2 at southern high latitudes: New insights from IODP Site U1516

The Oceanic Anoxic Event 2 (OAE 2) represents one of the most profound global environmental disturbances of the Mesozoic Era, which was associated with a positive carbon isotope excursion due to widespread organic carbon burial. However, the character, evolutionary history, and exact driving mechanisms of OAE 2 are still much debated, exacerbated by the lack of records from climate-sensitive southern high latitudes. Here we present a multi-proxy record of a stratigraphically continuous succession spanning the late Cenomanian to early Turonian at the International Ocean Discovery Program Site U1516 in the Mentelle Basin off southwest Australia, which was located at southern high latitudes (~ 60–62°S) during the Late Cretaceous. Sedimentary records at Site U1516 allow the first detailed insights into source-to-sink processes in the Mentelle Basin and associated paleoenvironmental reconstruction in the southern Indian Ocean during OAE 2. Rare earth element abundances and clay-bound neodymium isotopes of the siliciclastic sediment fractions indicate that southwest Australia was the main detrital source of sediment at Site U1516 during OAE 2, with volcanogenic sediments representing only a minor component. A major provenance shift is observed across OAE 2, indicating an increased sediment contribution from distant sources (i.e., Yilgarn Craton and Albany-Fraser Orogen) relative to proximal sources (i.e., Perth Basin and Leeuwin Block) in southwest Australia, interpreted as reflecting a major reorganization of the drainage system due to enhanced fluvial runoff. Based on these findings, we infer that the OAE 2 interval showing the most prominent δ13C excursion was associated with an intensification of the hydrological cycle in the high-latitude southern hemisphere, with potential impacts on regional ocean chemistry and marine productivity. In particular, we suggest that enhanced terrigenous input and riverine nutrient export likely played a key role in controlling siliceous productivity at nearby ocean margins. As a consequence, the intense burial of organic matter (i.e., black shale) at Site U1516, which occurred episodically throughout OAE 2, possibly resulted from the combination of enhanced riverine-driven marine productivity and increased burial efficiency associated with the development of anoxic/euxinic bottom water conditions.

Insect herbivory on Catula gettyi gen. et sp. nov. (Lauraceae) from the Kaiparowits Formation (Late Cretaceous, Utah, USA).

The Upper Cretaceous (Campanian Stage) Kaiparowits Formation of southern Utah, USA, preserves abundant plant, invertebrate, and vertebrate fossil taxa. Taken together, these fossils indicate that the ecosystems preserved in the Kaiparowits Formation were characterized by high biodiversity. Hundreds of vertebrate and invertebrate species and over 80 plant morphotypes are recognized from the formation, but insects and their associations with plants are largely undocumented. Here, we describe a new fossil leaf taxon, Catula gettyi gen et. sp. nov. in the family Lauraceae from the Kaiparowits Formation. Catula gettyi occurs at numerous localities in this deposit that represent ponded and distal floodplain environments. The type locality for C. gettyi has yielded 1,564 fossil leaf specimens of this species, which provides the opportunity to circumscribe this new plant species. By erecting this new genus and species, we are able to describe ecological associations on C. gettyi and place these interactions within a taxonomic context. We describe an extensive archive of feeding damage on C. gettyi caused by herbivorous insects, including more than 800 occurrences of insect damage belonging to five functional feeding groups indicating that insect-mediated damage on this taxon is both rich and abundant. Catula gettyi is one of the best-sampled host plant taxa from the Mesozoic Era, a poorly sampled time interval, and its insect damage is comparable to other Lauraceae taxa from the younger Late Cretaceous Hell Creek Flora of North Dakota, USA.

Middle Triassic to Late Jurassic climate change on the northern margin of the South China Plate: Insights from chemical weathering indices and clay mineralogy

The early Mesozoic greenhouse period was characterized by variable climate conditions. The driving mechanisms of this long-term variability are unclear due to a lack of full-period climate reconstructions. In particular, reconstructions of the terrestrial environment are rare, especially reconstructions representing South China during the early Mesozoic period. We focused on the major, trace and rare earth element compositions and clay mineralogy of 173 mudstones from the northern margin of the South China Plate. These data were used as proxies to evaluate the weathering intensity and reconstruct the climate variability from the Middle Triassic to the Late Jurassic after considering the potential effects of provenance, diagenesis and sedimentary sorting and recycling. From the latest part of the Triassic to the early Middle Jurassic, five well-correlated chemical weathering indices, the chemical index of alteration (CIA), chemical index of weathering (CIW), plagioclase index of alteration (PIA), sodium depletion index (τNa) and weathering index of Parker (WIP), imply an advanced degree of chemical weathering (e.g., CIA corr , the corrected CIA, ranging from 71.1 to 88.0) and a clay mineral assemblage zone with abundant kaolinite. Together, these findings indicate a dominant humid climate. In the pre-Late Triassic and post-Middle Jurassic, the dominant seasonally arid climate was characterized by low and widely variable chemical weathering index values (e.g., CIA corr values of 59.4–85.4) and clay mineral assemblage zones containing chlorite, smectite and mixed-layer illite–smectite but less kaolinite. We suggest that P CO 2 variations, the megamonsoon effect, plate motion and regional topography all contributed to the observed climate changes during the early Mesozoic. • Early Mesozoic terrestrial climate change on the South China Plate was revealed. • A seasonally arid climate prevailed pre-Late Triassic and post- Middle Jurassic. • The humid climate of the Late Triassic–Early Jurassic interrupted this arid climate. • P CO 2 , a megamonsoon, plate motion and topography jointly controlled climate change.

Structural analysis and seismic stratigraphy for delineation of Neoproterozoic-Cambrian petroleum system in central and eastern part of Bikaner–Nagaur basin, India

Bikaner–Nagaur basin is located in the northwestern part of India and lies on the rising flank of Punjab platform of Middle Indus basin in Pakistan. Existence of Neoproterozoic-Cambrian petroleum system was confirmed by the exploration activities in the western periphery of the basin, whereas vast areas of central and eastern parts remain unexplored. Knowledge of petroleum system in this unexplored part of the basin is limited due to non-availability of data. Recently, 2525 line km of regional 2D seismic data acquired for the first time by Government of India under National Seismic Program (NSP) unlocks the opportunity for comprehensive understanding of subsurface geology in unexplored part of the basin. Present work aims to interpret recently acquired 2D seismic data and integrate with available surface (outcrop) data, gravity and well data (drilled in western part of basin) for unfolding the petroleum system elements, structural configurations and stratigraphic features in the hitherto central-eastern part of the basin. Two Neoproterozoic-Cambrian hydrocarbon plays: (1) Jodhpur and (2) overlying Bilara/Hanseran Evaporite Group (HEG) were envisaged. Both the plays depicted distinctive seismic characteristics, structural alignment and distribution of reservoir, source and seal. Fluvio-deltaic sandstone within Jodhpur group and shallow marine fractured dolomites within Bilara/HEG showed potential reservoir characteristics whereas organic rich laminated dolomites, stromatolites and argillaceous litho-units within Bilara/HEG group have been predicted as prospective source. The Halite layers within HEG group were considered as effective regional seals. Fault bounded anticlinal structures associated with Cambrian compression have been identified as the main entrapment for hydrocarbon accumulation. The basin witnessed long tectonostratigraphic history with two major compressional phases Structures formed by Cambrian compression are likely to be charged as the time of source maturity and peak expulsion was later, during early Mesozoic period. Overall, the study indicates new opportunities and potential accumulation of hydrocarbon in the unexplored part of the basin.

Acritarchs of the Mesozoic of Ukraine

Introduction. Acritarchs are one of the orthostratigraphic groups of microfossils that are widely used in Proterozoic and Paleozoic biostratigraphy. In the Mesozoic period there is a decrease in this group, and this is due to certain reasons. Formulation of the problem. Acritarchs are studied by palynologists from samples of Mesozoic sediments in combination with other representatives of organic bone microplankton, primarily with dinocysts. In the practice of Ukrainian micropaleontologists, the role of such a group as acritarchs, which may be unique in paleoecological reconstructions of the environment, is underestimated. History of the study of acritarchs. None of the researchers studied the group of acritarchs in the Mesozoic deposits of Ukraine. In scientific works it was noted only about the presence of these forms in the description of palynological complexes of Jurassic, Cretaceous and other times. Brief description of the group. Acritarchs are unicellular, non-colonial, organic microfossils. Formulation of the purpose of the article. The aim of the study was to focus on such a little-studied group for the Mesozoic as acritars and to prove its role and significance for stratigraphic and paleoecological constructions. Materials and methods. The research material was samples of rocks of the Middle, Upper Jurassic and Cretaceous deposits, selected separately from 93 sections, but from all major tectonic structures of Ukraine: Peninsky zone of the Carpathians, Volyn-Podolsk plate, western and eastern slopes of the Ukrainian Shield, Priazovsky array of the Ukrainian shield, Dnieper-Donetsk basin, Donbas, South Ukrainian monocline (Black Sea basin), Crimea, North-Azov depression and Azov shaft (Ukrainian part of the Sea of Azov). Presentation of the main material of the study. Acritarchs Jurassic and Cretaceous belong to 10 genera, including 11 species. The most common species found in both Jurassic and Cretaceous sediments of Ukraine are acritarchs Micrhystridium fragile and Fromea sp. Jurassic complexes are slightly richer than chalk in terms of percentage and are represented mainly by Micrhystridium spp., Micrhystridium flagile, M. longum, Veryhachium brevitrispinum, Wilsonastrum sp., Baltisphaeridium sp. Cretaceous: Micrhystridium spp., Micrhystridium fragile, M. longum, Baltisphaeridium breviciliatum, B. aff. capillatum, B. annelieae, B. accinctum, Acanthodiacrodium sp., Solisphaeridium inaffectum, Comasphaeridium sp., Comasphaeridium aff. brachyspinosum, Veryhachium spp., Veryhachium singulare, Leiofusa stoumonensis, Fromea sp., Ascostomocystis sp. The article presents photo tables of images of Jurassic and Cretaceous acritarchs. Conclusions. For the first time in Ukraine, acritarchs were found in samples from Jurassic and Cretaceous sediments and attention was focused on such a little-studied group for the Mesozoic. Their certain role and significance for stratigraphic and paleoecological constructions are proved, their species composition and vertical distribution in sections of Mesozoic sediments are studied. The regularities of the distribution of acritarchs in the same age layers are established. Analyzing the Jurassic and Cretaceous microfossils studied from Mesozoic sediments from 93 sections of different regions of Ukraine, we can say that the trend of disappearance of acritarchs during the Mesozoic is weakly observed. Jurassic forms of acritarchs are up to 5% in the complex, Cretaceous - up to 4%. The next stage of work should be the study of acritarch Jurassic and Cretaceous deposits of all regions of Ukraine for the purposes of the overall picture of the reproduction of paleoecological conditions in Ukraine during the Jurassic and Cretaceous period.

First record of the spider family Hersiliidae (Araneae) from the Mesozoic of Europe (Bakony Mts, Hungary)

An adult male Hersiliidae spider is described from amber that originates from the Upper Cretaceous (Santonian) Ajka Coal Formation (Ajka-Csingervölgy, Hungary), the so-called ajkaite. The spider has elongate posterior spinnerets and a short third pair of legs III, both characteristics of the family, but differs from all known Mesozoic (discovered in burmite) and fossil and Recent European representatives of Hersiliidae so that a new genus and species name is proposed for Hungarosilia verdesi gen. et sp. nov. The new taxon is distinguishable by the following unique combination of characters: pro- and opisthosoma nearly circular in dorsal view; posterior spinnerets with a distal article more than three times longer than the basal article; pedipalpal tibia and patella short and stout but pedipalpal femur as long as the cymbium, cymbium egg-shaped and without cymbial apophysis; bulbus of circular shape in ventral view and slightly flattened is lateral view. The fossil represents the first record of Hersiliidae from the Mesozoic of Europe and establishes the second record of this family in the Mesozoic Era. The estimated paleoclimate and paleoflora of the Ajka coal sub-basin correspond well with habitat preferences of Recent relatives that are often arborical and found in association with tree bark. Overall, our findings highlight the importance of a neglected amber type, the ajkaite, for documenting and studying the European arthropod fauna during the Mesozoic.

Geometry and kinematics of the western part of the NE Qaidam Basin: Implications for the growth of the Tibetan Plateau

Based on field geology, seismic reflection profiling data and isopach maps, the structural deformation pattern, timing of deformation, and mechanism of formation of the western part of the NE Qaidam Basin (including the Pingtai Uplift, Lenghu and Eboliang structural belts) during the Mesozoic and Cenozoic eras have been investigated. Several anticlines in the Lenghu and Eboliang structural belts are generally characterized by double fault systems at different structural levels. At shallower crustal levels, a thrust fault system dominates and at lower levels positive flower structures accommodate oblique shortening, and these are mainly separated by weak strata layers in the Upper Xiaganchaigou Formation, of late Eocene age. Left-step en echelon distributed normal faults and trailing extensional imbricate fan structures consistently demonstrate that the Lenghu and Eboliang structural belts are dominated by dextral transpressional deformation. The western part of the NE Qaidam Basin experienced an initial stage of extension in the Jurassic, which was associated with the formation of several NW-striking normal faults. We hypothesize that most of the deep compressional structures and shallow anticlines were formed due to the SW-directed thrusting of the Qilian Shan since the early Eocene, as a far-field effect of the Indo-Asian “hard” collision. The NNE-directed shortening was associated with dextral transpressional deformation within the western part of the NE Qaidam Basin that took place after the deposition of the Shangyoushashan Formation, of middle-late Miocene age. We interpret this phase of deformation to have been an integral part of the pulsed growth of the whole Tibetan Plateau.

<i>Cretopachyderes</i> gen. nov., a new remarkable click beetle (Coleoptera: Elateridae: Agrypninae) from the mid-Cretaceous Burmese amber

Abstract. Although the Mesozoic Era played an important role in the evolution and diversification of Elateridae, the Cretaceous click-beetle fauna remains very poorly known. Here we describe Cretopachyderes burmitinus gen. et sp. nov. based on a single specimen from the mid-Cretaceous Burmese amber. This species is remarkable for its extremely long posterior angles of pronotum, which is a unique character among fossil Elateridae. We discuss the diagnostic characters of Cretopachyderes gen. nov. and tentatively place it to subfamily Agrypninae close to extant genus Pachyderes Guérin-Méneville, 1829.

Mesozoic origin of coleoid cephalopods and their abrupt shifts of diversification patterns

Coleoids are the most diverse group of cephalopod mollusks. While their origin is date during the Mesozoic, the diversification pattern is unknown. However, two hypotheses have been proposed. The first suggests an increasing diversification rate after the Cretaceous–Paleogene extinction event (K–Pg) as consequence of empty habitats left by the ammonites and belemnites. The second hypothesis proposes a mid-Cenozoic increase in diversification rate related to distributional changes during ice ages and biotic interactions. To test these hypotheses, we estimated a lineage through time (LTT) and the gamma-statistic along with model-based diversification rates. These analyses were conducted on a dated molecular phylogeny for coleoids that we reconstructed using five molecular markers (cytochrome b, 16S rRNA, cytochrome oxidase I, rhodopsin, and PAX-6). Our divergence time estimation suggests that coleoids originated in the Mesozoic Era (Middle Triassic) and that both main clades (Decapodiformes and Octopodiformes) diverged in the Cretaceous/Jurassic Period. The LTT, gamma statistic, and diversification rates inferred with the Bayesian Analysis of Macro-evolutionary Mixtures (BAMM), indicate an acceleration in diversification rate over time since the origin of coleoids. Additionally, BAMM allowed us to detect abrupt increases in diversification rate before and after the K-Pg boundary. Our results partially support both hypotheses as all analyses indicate that the coleoid diversification rate was increasing during the Cenozoic. However, our results also indicate increasing diversification rates before the K-Pg boundary. We propose that the radiation of coleoids has been shaped by an acceleration in diversification rate over time, including exceptional episodes of abrupt increases before and after the K-Pg boundary.