Cenozoic Deposits Research Articles

Diagenetic evolution of continental to shallow marine Mesozoic–Cenozoic deposits, Eastern Dahomey Basin, Nigeria: Implications for reservoir quality

Diagenetic evolution of continental to shallow marine Mesozoic–Cenozoic deposits, Eastern Dahomey Basin, Nigeria: Implications for reservoir quality

A new pachyrukhine (Notoungulata: Typotheria) from the late Early Miocene of south-central Chile

ABSTRACT Here, we studied several Pachyrukhinae (Mammalia: Notoungulata: Typotheria: Hegetotheriidae) fossils recovered from the late Early Miocene (Santacrucian SALMA) beds of the Cura-Mallín Formation at the Laguna del Laja (Biobío Region, Chile). The specimens are referred to a new species of the genus Pachyrukhos Ameghino, 1885, P. ngenwinkul sp. nov. The holotype of this taxon is a relatively well-preserved articulated skull and mandibles, which was investigated using 3D X-ray Microscopy. The new taxon is distinguished from other Pachyrukhos species by having a p2 smaller than p3, M3 mesiodistally shorter (around 30%) than M1, and upper premolars of a rather subtriangular contour. Pachyrukhos ngenwinkul is the most common mammal and the smallest-sized (with ~2 kg of body mass) notoungulate found in the Santacrucian assemblage at the Laguna del Laja. The discovery of this new taxon improves our understanding of the Neogene pachyrukhine diversity in southern South America and highlights the potential of the Chilean Andean Cenozoic deposits in revealing a hidden diversity of extinct continental mammals. https://zoobank.org:pub:9B23EF16-2085-49E8-AE8E-7EBEBB9261ED

Sources of Late Cenozoic Deposits from the Aeolian “Sands” Massif in the Chara Basin of the Baikal Rift Zone: First Results of U–Th–Pb (LA-ICP-MS)-Geochronological Study of Detrital Zircon

Sources of Late Cenozoic Deposits from the Aeolian “Sands” Massif in the Chara Basin of the Baikal Rift Zone: First Results of U–Th–Pb (LA-ICP-MS)-Geochronological Study of Detrital Zircon

SOURCES OF THE LATE CENOZOIC DEPOSITS FROM THE AEOLIAN “SANDS” MASSIF IN THE CHARA BASIN OF THE BAIKAL RIFT ZONE: FIRST RESULTS OF U–TH–PB (LA-ICP-MS) GEOCHRONOLOGICAL STUDY OF DETRITAL ZIRCON

The results of U–Th–Pb (LA-ICP-MS) geochronological studies of detrital zircon (fraction more than 50 µm) from the Late Cenozoic deposits of the large aeolian “Sands” massif of the Chara Basin of the eastern flank of the Baikal Rift Zone show that they are dominated by detrital zircon with ages of 263–265 and 1861–1864 Ma. Archean ages have been obtained only for individual zircon grains. Quite possibly, this is due to the fact that zircon of this age is present in “small” fractions, the study of which is not possible due to the technological features of the method of geochronological studies used. Based on the geological situation, only granites of the Kodar complex can be considered as the only source of detrital zircon of the Early Proterozoic age. The source of detrital zircon with an age of 263–265 Ma remains a mystery. Granitoids of this age are not known on the territory of the Aldan Shield. They are widespread in its western frame.

Using clay mineralogy and micropalaeontological observations to unravel Neogene climate variations in Northern Arabia

The Zagros Mountain belt in Iran comprises an extensive record of Mesozoic and Cenozoic deposits uplifted by collision of the Arabian and Iranian continental plates. This area has been shown to provide important information to decipher the climatic history of Western Asia, especially regarding the evolution of deserts in Mesopotamia and Northern Arabia. In a high-resolution geological record of 84 samples, we combine clay mineralogy and micropalaeontological observations to refine the late Neogene climate record in Northern Arabia. We investigated a 2.6-km-thick sedimentary profile from the Simply Folded Zagros Mountain belt spanning ca. 10.2 myrs from the late Middle Miocene (Serravallian) to earliest Pleistocene (Gelasian) comprising floodplain sediments and saline mudstones with a strong aeolian contribution. The clay fraction < 2 µm reveals palygorskite, smectite, illite, chlorite and the zeolite mineral erionite. Using clay mineralogy, arid conditions during the Serravallian and early Tortonian in Northern Arabia are identified, followed by semi-arid conditions during the late Tortonian. Clay mineralogy suggests a transition to sustained arid conditions during the early Messinian and provides a more complex picture on a previously proposed period of hyperaridity (NADX) in Northern Arabia penecontemporaneous with the apex of the Messinian salinity crisis.

OSL and radiocarbon dating and evidence of palaeo-wildfires in Quaternary deposits of the Tacutu basin, northwestern Brazil

This work presents data on charcoal fragments found in Cenozoic deposits of the Boa Vista Formation and the first absolute dating for this unit. The methodology consisted of the definition of sedimentary facies, as well as the establishment of depositional age using optically stimulated luminescence (OSL) in quartz grains. Analysis was carried on charcoal samples with the help of Scanning Electron Microscopy (SEM), AMS 14C dating, and organic petrography. The facies analysis identified four distinct facies: lateritic massive gravel facies (Gcm1), ferruginous massive gravel facies (Gcm2), massive sand facies (Sm) and fossiliferous massive sand (Smf). The ages of the deposits ranged between 105,2 and 3,2 thousand years before present, indicating that this unit is positioned in the Upper Pleistocene-Upper Holocene transition. The anatomical structures observed in SEM are well preserved and the studied charcoal samples have angiospermic affinity. Two episodes of fires were identified with range ages between 5663 and 3377 cal years BP, with burning temperature varying from 340 °C to 400 °C.

The Relationship between Lineament Patterns and Mass Movements in the Municipality of Vitória (Espírito Santo, Southeast Brazil)

The main objective of this research is to analyze and relate lineament patterns to the occurrence of mass movements in the municipality of Vitória (Espírito Santo, Brazil). The methodology used consists of cabinet and field analyses. In a cabinet, Lineament Maps were made from the manual extraction technique, using ArcGIS 10.5 tools, on a Digital Elevation Model (DEM) with different artificial lighting (scale 1:110000) and Digital Orthophotos (scale 1:25000) and orientation rosettes generated. In the field, the geological structures were identified and analyzed from the lineaments identified in the cabinet, and their orientations were measured (Brunton compass). These data were integrated and analyzed from the Municipal Civil Defense mass movements records, referring to the period between 2006 and 2020. It was possible to verify the orientation patterns of dominant geological structures in the area (NNW-SSE and NW-SE, followed by NE-SW), including all measured fractures. At the regional scale, more mass movements occurred near NNW-SSE, NW-SE, and NE-SW orientation lineaments. At the local scale, these processes occurred more frequently in the vicinity of NNW-SSE, NNE-SSW, and NE-SW orientation lineaments. Data analysis demonstrates the important relationship between lineaments and occurrences of mass movements with regional geological structures and neotectonic events of the Espírito Santo in altered rocks of the Precambrian basement and Cenozoic deposits. The data revealed an association between the density of geological structures and the occurrence of mass movements since the increase in density is directly proportional to these processes, except for the Very High -density class, which presented little area representation.

The Lithological-Geochemical and Paleogeographic Characteristics Mesozoic–Cenozoic Deposits of the Yenisei-Khatanga Trough

The Lithological-Geochemical and Paleogeographic Characteristics Mesozoic–Cenozoic Deposits of the Yenisei-Khatanga Trough

(?)REPTILE COPROLITES FROM THE CAMPANIAN AND MAASTRICHTIAN (LATE CRETACEOUS) OF THE LUHANSK REGION

Problem Statement and Purpose. Vertebrate coprolites have important paleobiological and paleogeographical significance. They are quite common trace fossils, but have almost never attracted the attention of researchers, despite the fact that in the literature there are numerous references to the findings of vertebrate coprolites in the Mesozoic and Cenozoic deposits of Ukraine. The aims of this study are to describe the morphology of coprolites, compare them with morphologically similar vertebrate coprolites, and identify their potential producers. Data &amp; Methods. Two well-preserved specimens of the vertebrate coprolites(Morphotype A and Morphotype B) were found in sediments of the late Campanian Sydorove Formation and early Maastrichtian Konoplyanivka Formation of the northern part of the Donets Basin. Results. Chondrichthyes fishes are excluded from the list of potential producers of coprolites due to the absence of spiral grooves on the surface of a more wellpreserved coprolite and the spiral pattern on its transverse section. These coprolites differ from coprolites of crocodiles in shape, but are close to them in size. One of the coprolites (Morphotype A) probably belongs to a marine reptile of the family Mosasauridae. Mosasaurids were large marine reptiles that appeared and flourishedin the Late Cretaceous (Turonian-Maastrichtian). The morphology of mosasaurids confirms their adaptation to active swimming. They fed mainly on fish, mollusks and other marine reptiles. It was not possible to identify the systematic position of the coprolite producer of Morphotype B. Skeletal remains of mosasaurids are known in the Campanian and Maastrichtian sediments of the Donets Basin. The study results showed that coprolites are important for paleoecological studies, so they deserve a detailed study.

POLYCHRONIC-POLYGENIC PARAGENETIC-SPATIAL TITANIUM ORE SYSTEM OF THE SEDIMENTARY COVER OF THE SOUTH-WESTERN PART OF THE KORSUN-NOVOMYRHOROD PLUTON

Information is provided on the titanium-zirconium ore content of the weathered crust and continental and coastal Mesozoic- Cenozoic deposits within the Byrzulivska, Valuivska, Likarivska, Andriivska, Novomyrgorodska, Vytiazivska areas, which are located in the southwestern part of the Korsun-Novomyrhorod pluton within the Novomyrgorod massif. On the basis of the coordinates, description and results of testing wells for the specified areas, a target database was created on the basis of which cartographic constructions were made. The results of studies of the spatial distribution of the thickness of the weathering crust, sands and redeposited kaolins of the Lower Cretaceous within the Byrzulivska, Valuivska, Likarivska, Andriivska areas are presented; sands and redeposited kaolins of the lower-middle Eocene within the boundaries of the Novomyrhorodska area; Quaternary sands within the Vytiazivska area. It was found that the lateral distribution of the thickness of the weathering crust is due to the relief of the surface of the crystalline rocks of the foundation and the partial erosion of the eluvium during the geological development of the territory. Instead, the uneven distribution of the thickness of Mesozoic-Cenozoic sediments is caused by the amount of terrigenous material entering the sedimentation basin, facies conditions of formation, and erosion and redeposition of sediments to higher stratigraphic levels. The lateral distribution of the average content of ilmenite, rutile, and zircon and the correlations between these minerals in the weathering crust, redeposited kaolins, and sands of the specified areas were studied. It was found that the ore bearing of the weathered crust and the Mesozoic-Cenozoic continental and coastal marine sediments is paragenetically and spatially related to each other and is determined by the ore bearing of the crystalline rocks of the foundation. The average content of ilmenite, rutile and zircon in the weathering crust is determined by their average content in the parent rocks of the crystalline basement, in the continental and coastal formations of the Mesozoic and Cenozoic — by the content of minerals in the weathering crust and intermediate reservoirs (for deposits that do not lie on the weathering crust), facial conditions of formation. As a rule, aureoles of increased mineral content do not coincide spatially, and correlations between their average content are mostly very weak or absent. The obtained results confirm and complement the results of previous studies on ore bearing capacity and prospects for increasing the mineral-raw material base of critical raw materials within the Novomyrhorod massif. Research results can serve as an information base for forecasting, prospecting and mining operations within the investigated areas.

Fossil fruits of Trapa L. from the late Miocene of southeastern Qaidam Basin (Qinghai, China)

ABSTRACT Trapa L. (Lythraceae J. ST.-HIL) is a genus of annual free-floating plant, widely distributed in the Northern Hemisphere. The Qaidam Basin is regarded as an ideal region to understand the Cenozoic palaeoclimatic and palaeobiological evolution of the northern Tibetan Plateau. A few records of Trapa have been previously mentioned from the Cenozoic deposits of the Qaidam Basin, northern Tibetan Plateau. Here, we describe some fossil fruits of Trapa from the late Miocene Shangyoushashan Formation of southeastern Qaidam Basin (Tuosu Lake area), which were identified as Trapa qaidamensis sp. nov. based on their morphology. Extant species of Trapa usually live in the environments with mean temperature of warmest quarter (MTWQ) ranging from 14.9°C to 30.9°C, as well as mean temperature of warmest month (MTWM) ranging from 19.6°C to 37.3°C in the living areas of Trapa. Compared with MTWQ 16.5°C and MTWM 17.5°C in current fossil locality, the present fossil site was warmer during the Miocene than in the present day. urn:lsid:zoobank.org:act:9F7DAD1B-DA2D-4734-BE27-99276F57DD2A

Cenozoic deposits of western Kotel’nyi Island (New Siberian Islands): key insights into the tectonic evolution of the Laptev Sea

ABSTRACT The Arctic sedimentary basins are still poorly studied in comparison with other regions. The lack of deep wells across the eastern Russian Arctic has resulted in numerous contrasting geodynamic models for the geological evolution and age of sedimentary successions within this frontier region, where a modern mid-ocean ridge breaks through the continental crust in the Laptev Sea. The only onshore evidence of rifting processes is a number of small graben-like depressions exposed on the New Siberian Islands and along the Laptev Sea coast. We present U-Pb detrital zircon provenance and palynology study results of the Cenozoic sedimentary rocks filling graben-like depressions across western Kotel’nyi Island. Palynological data indicate that these sedimentary rocks are Early Eocene to Pleistocene in age. Based on U-Pb detrital zircon dating, Early Eocene and Late Oligocene clastic sediments were sourced from underlying deformed Palaeozoic rocks as well as by reworking of Upper Mesozoic rocks outcropping elsewhere on Kotel’nyi Island, which bear Siberian signature. Plio-Pleistocene clastic sediments were not derived from the erosion of deformed Palaeozoic rocks, suggesting the cessation of active uplift by this time and the development of a regional peneplain. Therefore, by extrapolating our onshore observations to the neighbouring offshore, we propose that graben structures imaged by seismic profiles along the eastern flank of the Laptev Rift System are likely to host Eocene and Oligocene sediments. Thus, it implies the Cenozoic extension led to formation of grabens on- and offshore in the eastern portion of Laptev Sea as early as Eocene. Further studies are necessary to evaluate the age of graben-related basins in the central and western part of the Laptev Sea.

Reconstruction of a Ross lost CambrianSeries 2mixed siliciclastic–carbonate platform from carbonate clasts of the Shackleton Range, Antarctica

ABSTRACTThe presence of archaeocyath-bearing clasts from Cenozoic tills and Cambrian Mount Wegener Formation reveal erosion of a hidden Cambrian carbonate platform in Shackleton Range, Antarctica. We provide microfacies, paleontological, diagenetic and tectonically induced fabric data from carbonate clasts which, in addition to available geochemical and geochronological data from Shackleton Range, allow the paleoenvironmental reconstruction of a lost CambrianSeries 2mixed siliciclastic–carbonate platform that was developed and eroded during the Ross orogeny. Carbonate production was dominated by non-skeletal grains in possibly restricted platform-interior and oolitic shoal complex settings, while open subtidal sub-environments (calcimicrobe carpets, calcimicrobe–archaeocyath patch reefs, muddy bottoms) were dominated by a diverse calcimicrobe assemblage and/or by secondary to accessory heterozoan assemblage (archaeocyaths and other sponges, chancelloriids, hyoliths, coralomorphs, trilobites, echinoderms). We describe a Botoman assemblage with 34 archaeocyathan species among 12 existing archaeocyathan genera. A new archaeocyath family Shackletoncyathidae is proposed. New species (Rotundocyathus glaciussp. nov.,Buggischicyathus microporusgen. et sp. nov.,Paragnaltacyathus hoeflei,Shackletoncyathus buggischigen. et. sp. nov.,Santelmocyathus santelmoigen. et sp. nov.,Wegenercyathus sexangulaegen. et sp. nov.) andTabulaconus kordaecoralomorph are reported from Antarctica for the first time. Archaeocyathan fauna share few species with contemporary fauna of South Australia (9) and even fewer with the Antarctic platforms of the Shackleton Limestone (2) or the Schneider Hills limestone (1). Similarity is greater with Antarctic allochthonous assemblages of Permo-Carboniferous tillites from Ellsworth Mountains (2), Cenozoic deposits from King George Island (4) or Weddell Sea (1). The Shackleton Range lost/hidden platform shows a distinct entity related with its tectonosedimentary evolution, in a possible back-arc basin on the Mozambique seaway during the E and W Gondwana amalgamation, which distinguishes it from those developed on the palaeo-Pacific margin of the E Antarctic craton.

Alpine tectonic movements and salt tectonics of Eastern Ukraine

Within Eastern Ukraine, in the course of previous studies, neotectonic movements were established, caused by both salt tectonics and Attic (post-Miocene - pre-Pliocene) thrust dislocations of northeastern vergence. They are partially displayed in modern relief. The aim of the study was to reveal the structural results of the interaction of post-Pliocene fold-thrust deformations and modern salt tectonics of Eastern Ukraine. Research methodology. The base of the Cenozoic deposits of Eastern Ukraine was chosen as an indicator surface reflecting both those and other movements. Its initial orientation is horizontal. Deviations from the horizontal reflect the direction and amplitude of deformations. The morphology of this surface was depicted by isolines with a vertical step of 20 m. To build a map of the supporting surface, state geological maps and data from more than 2,100 wells drilled in this area were used. Research results. A map of the shape of the Cenozoic base in tectonic blocks between the Attic thrusts and beyond their development has been constructed. Uplifts of this surface, which are not associated with thrust movements, have been revealed. The dimensions of such uplifts are 8÷30 × 6÷15 km with vertical amplitude of 40 - 100 m or more. The uplifts are usually contoured by ring or arc compensation troughs a few kilometers wide and 20-100 m deep. Some of these uplifts are associated with the known salt domes of the area. Other uplifts do not contain such domes. It is possible that they formed over salt "pillows", which did not have enough salt reserves to form salt diapirs. The area of distribution of such uplifts approximately corresponds to the area of distribution of Devonian salt deposits at a depth of 5-10 km or more. Scientific novelty. Neotectonic uplifts were discovered, similar in shape and size to those caused by salt tectonics, but located outside the areas of distribution of known salt-bearing strata. It is hypothesized that this is related to the older Hercynian overthrusts. The uplifts are located above the hanging blocks of the Hercynian overthrusts in the north and south of the study area. These thrusts were formed on the northern and southern sides of the former Dnieper-Donetsk depression during its destruction by the Hercynian folding. It is possible that the nappes over thrusts the Devonian salt-bearing deposits with metamorphic rocks of the crystalline basement. The decrease in the level of the World Ocean in the Quaternary period further increased the lithostatic load on the salt-bearing strata. This activated the isostatic upwelling of salt and the formation of gently sloping neotectonic uplifts. Practical significance. These results clarify the geological structure of the territory and make it possible to expand the area of hydrocarbon prospecting.

Multi-attribute geomorphological characterization of the Cenozoic deep-water strata in the Exmouth Plateau, Northern Carnarvon Basin: a contribution to the understanding of deep-water mixed carbonate–siliciclastic environments

Abstract The stratigraphic architecture and relationships to the expression of deep-water architectural elements geomorphology are explored for Cenozoic deposits in the Exmouth Plateau Sub-basin in Northern Carnarvon Basin. We used a high-quality 3D seismic survey and an integrated seismic attribute analysis to provide a guide for seismic interpretation of the mixed carbonate–siliciclastic depositional systems focused on four aspects: morphology, lithology, strata thickness and reflector distortion. Three depositional elements are classified into several categories: mass transport deposits (MTDs), channel systems (channel–levee and braided-like) and lobes, whose deposition is closely related to eustatic changes, and can be explained in a sequence stratigraphic framework. The falling stage system tract is characterized by the initial development of MTDs deposited on the basin floor and small erosive channels on the upper slope. Lobes are deposited in lowstand system tracts while highstand system tracts are characterized by the deposition of MTDs and progradational segments. This mixed carbonate–siliciclastic example proved to be sensitive to other variables such as climate (Middle Miocene Climate Optimum) and plate tectonics (northward Australian Plate drift), which affect geomorphological aspects such as the dimensions and preservation of internal characteristics.

Major structural unconformities across Malaysia: geodynamics and basin development of Lawin, Perak

The first deposits overlying an unconformity may give important insights on the tectonic vertical motions and erosion processes that erased previous records. The Early Cenozoic Deposits in Peninsular Malaysia are reported to be isolated and lie unconformably on Paleozoic basement rocks. Denudation pulses from the Late Cretaceous to Eocene left the Cenozoic deposits in scarce. Stratigraphic and sedimentology studies were restricted to the availability of the resources. This study aims at providing information on the development of the early deposits from a structural perspective with the emphasis on source to sink dynamics. We interpreted the structural settings of Lawin using Digital Elevation Model (DEM) data and satellite images. Structural interpretations were cross-checked with published studies. Field observations were conducted and have been assessed through chemical and petrographic analyses. Evidence of compression and shearing are found to support interpretation. We learned that Lawin had experienced a compression and stages of extensions in its history and developed during extension. Lawin is associated to a major fault that reactivated several times, and from XRD analysis, we have illite-mica which has a close-relationship to a frequent tectonic activities and kaolinite is due to weathering. Petrography analysis were performed from SEM images and thin sections to support minerals found. Evidence of mineral fragments, iron-rich sedimentation and clay fillings were common with few kaolinite pouches. Sedimentology studies were modelled as alluvial fans. Based on DEM analysis, two different lobes are observed and on outcrop, two different angles of tilted bedding between the two lobes were measured, thus we modelled them as incised alluvial fans where the recent fan we see on DEM has extended further from abandoned lobe. Due to its tilting towards the west, we modelled them following an extensional regime.

Fault Rock Property Prediction on Jurassic Clastics of the Barents Sea, Norway

Summary We analyzed the fault rocks of a compartmentalized field in the Barents Sea, in an area with several tectonic elements, which formed at different tectonic events. Standard fault seal analysis (FSA) was conducted to predict the shale content of the fault rock (shale gouge ratio, SGR). A static cellular model based on well data, seismic data, and geological concepts served as input. The fault rock calibration workflow required various data acquired by different methods. We analyzed the Middle Triassic to Upper Jurassic clastic deposits to reconstruct the tectonic history. Apatite fission track (AFT) and (U-Th)/He thermochronology were used to determine the maximum burial depths and exhumation history. The results of high-resolution shale ductility analysis, a compaction trend study, kinematic analysis, and structural modeling (section balancing) served as additional input constraints for fault rock calibration. The interpretation of the results helped to reconstruct the following tectonic evolution. The orthogonal faults developed shortly after deposition, during Late Triassic to Early Jurassic times at relatively shallow depth, below 1000 m. Ongoing subsidence created accommodation space for Upper Jurassic to Cenozoic deposits with a maximum burial depth of 2000 m for the Middle Jurassic rocks. Exhumation of the area started around 10 Ma and continued through to Quaternary times. The predicted across-fault-flow values for fault rock permeability show a wide range when using poorly constrained input for fault rock calibration: 9.9E−15 to 9.9E−13 m² for SGR values around 0.08 at reservoir/reservoir juxtaposition. Fault rock calibration using elaborated results reduced the uncertainty of fault rock permeability estimates, and ultimately, for transmissibility multipliers (TMs). The reason for the sensitivity of the fault rock calibration is a combination of following factors: highly permeable reservoir sandstone, shallow depth of initial faulting, maximum burial depth and low shale content at the upper, main reservoir level. The study shows that an accurate reconstruction of the geohistory provides essential parameters for fault rock calibration and fault rock permeability prediction. The range of values can widely scatter if boundary conditions are not acknowledged. Well-constrained fault rock calibration reduces the uncertainty on possible flow scenarios, increases the reliability on production forecasts and helps determine the most efficient drainage strategy.

Morphometric analyses of the vertebrae of Ambystoma (Tschudi, 1838) and the implications for identification of fossil salamanders.

Ambystoma (Tschudi, 1838) represents a speciose clade of salamanders that are found across much of North America. Fossils referred to Ambystoma are reported from early Cenozoic deposits and are common in Quaternary fossil deposits. Most fossils identified as Ambystoma are isolated vertebrae. Both quantitative and qualitative characters were reported as being useful for identifying fossilized vertebrae of Ambystoma below the genus level. However, there is limited information on intraspecific variation in those characters and previous studies noted intracolumnar variation which affects the utility of those characters for fossil identification. A lack of understanding of variation in modern species of Ambystoma casts uncertainty on our ability to identify fossil vertebrae confidently. We aimed to document intraspecific and intracolumnar variation in vertebral morphology among species of Ambystoma and examine the implications for fossil identification. We assembled one of the largest skeletal data sets for Ambystoma and took linear measurements on 15 species. We used 2D geometric morphometric analyses to characterize atlantal shape variation in Ambystoma. We apply those morphometric data in a case study where we identify fossil vertebrae from Hall's Cave, a Quaternary fossil locality in central Texas. We found patterns of intraspecific and intracolumnar variation that have substantial implications for fossil identification. Classification accuracies for species and clades within Ambystoma varied considerably. Overall classification accuracies based on size-adjusted measurements and 2D geometric morphometric landmarks were lower compared with classifications from non-size adjusted linear measurements. We identified fossil vertebrae from our case study as likely belonging to the tiger salamander clade within Ambystoma, but found that some fossils with lower classification probabilities are of uncertain identity. We discuss biogeographic implications for our fossil identifications and comment on challenges and next steps for advancing our understanding of morphological variation in Ambystoma.

Geoelectric studies of the Kozloduy nuclear power plant region, Bulgaria

The task of the work was geoelectrical studies using variations of the magnetotelluric (MT) field of the Kozloduy nuclear power plant (KNPP) region and the integration of its results with other geological and geophysical knowledge. This paper presents the determined interpretation parameters of the MT field. The KNPP is located on the right bank of the Danube River in close proximity to the river. This fact, together with the location of electrified railways determined the unique network of locations of observation points for MT field variations. Based on the analysis of Earthquake Catalogs of Bulgaria and international seismicity databases, a map of the seismicity of nuclear power plant areas was built. Over the past 50 years, about 750 earthquakes (mainly south of KNPP) have been recorded at a distance of 40—80 km from the KNPP. Two magnetotelluric stations GEOMAG-02 were used at measurement sites, but equipment for recording electrical channels was available only for one station (due to the lack of another set of non-polarizable electrodes). The MT field variations were observed at 21 points, which are located on the territory with sides approximately 30—35 km from east to west and 40—50 km from north to south. For all observation points on the profile, only the parameters of the vertical magnetic transfer function (VMPF) were determined, in the form of the real (Cu) and imaginary (Cv) parts of the induction vector. The steadily induction vector was defined for periods from 10—20 to 4900—10 800 s. For most points it was possible to estimate the values Cu, Cv with an error of 0.02—0.04 and AzCu, AzCv 3—5°. The analysis showed the presence of anomalous behavior of Cu, Cv in different intervals of periods at some points. In the shortest (about 20 s) and longest periods (600 to 1000 s), the Cu directions completely coincide and indicate the presence of anomalous conductivity of the quasi-longitudinal strike to the west of the study area. This behavior of the Cu vector is in good agreement with power isohypsum strike of the Cenozoic deposits. At intermediate periods of 50—200 s, the behavior of Cu is more complex. Approaching the zone of high seismicity, the direction of the Cu differs from the previous ones by almost 90°. On the Geoelectrical sections, obtained as a result of 1D inversions of MTS curves at 4 points located in the southern part of the region, anomalous layers are identified (ρ about 10 ohm · m, the depth of the center of the object is 15—20 km). It can be assumed that well-conducting objects in the Earth’s crust of the region, apparently, prevent the propagation of seismic waves from nearby earthquakes to the north towards the KNPP.

ГЕОТЕМПЕРАТУРНЫЕ 2D-МОДЕЛИ КАЙНОЗОЙСКИХ ОЧАГОВ ГЕНЕРАЦИИ УГЛЕВОДОРОДОВ САНЬЦЗЯН-СРЕДНЕАМУРСКОГО БАССЕЙНА

The oil and gas potential of the Cenozoic deposits of the Sanjiang-Middle Amur sedimentary basin was assessed on the basis of two-dimensional spacial-temporal digital models. The obtained results show that favorable conditions for gas formation are in the southwestern part of the Pereyaslav graben, while both oil and gas formation is characteristic of its northeastern part. The Birofeldsky and Chernorechensky centers in the Cenozoic complex of the Pereyaslavsky graben are the main sources of hydrocarbons. Cenozoic deposits within the Nongjiang graben currently also generate hydrocarbons.