Stratigraphic Horizons Research Articles

Revision of Salvinia pseudoformosa Type Specimen Ages

Salvinia pseudoformosa has been established as a Miocene species based mainly on specimens collected from the Sasakizawa River, Numata, Hokkaido, Japan. However, both Eocene and Miocene sediments are distributed within this area. In this study, we conducted geological surveys along the Sasakizawa River to identify the stratigraphic horizon bearing S. pseudoformosa and found that S. pseudoformosa occurs from the middle Eocene Itarakaomappu Formation of the Uryu Group. We also reexamined syntypes of this species and concluded that only those from the Sasakizawa River can be identified as S. pseudoformosa with certainty. Therefore, we designated a syntype from the Sasakizawa River as the lectotype. Although we could not specify the exact localities of the lectotype and remaining syntypes from the Sasakizawa River, lithological characters of the slabs containing these specimens indicate their occurrence from the Uryu Group. Salvinia pseudoformosa has been recorded from the middle Miocene in Japan and Korea, but the venation patterns of these specimens differ from those of S. pseudoformosa.

Holocene palaeoenvironmental conditions in NE Bulgaria uncovered by mineral magnetic and paleomagnetic records of an alluvial soil

Retrieving well-dated terrestrial archives of Holocene climate change is fundamentally important for building robust climate models and predictions. In this study we obtained records of paleomagnetic direction and relative paleointensity of the Earth's magnetic field from an alluvial soil situated on a flood river terrace close to the well-dated and stratigraphically confined Chalcolithic mound near the village of Koprivetz in NE Bulgaria. Anisotropy of magnetic susceptibility data revealed a coherent imbricated magnetic fabric reflecting the effects of water flow in the lower alluvial clays and the direction of delluvial sedimentation from the slope in the upper soil horizons. Variations of declination, inclination and relative paleointensity along depth of the soil profile were correlated to the archaeomagnetic secular variation curves for Bulgaria, using the age of the earliest archaeological stratigraphic horizon as the main tie point. Based on this correlation, an age model was constructed and temporal variations of environmental magnetic parameters were examined for their suitability as paleoclimate proxies. The ratio of frequency dependent susceptibility to anhysteretic susceptibility (χfd/χARM) is a reasonable proxy for paleoprecipitation due to its close resemblance to paleo-flood records from the Northern and Southern Alps. Events of increased flood intensities during the late Holocene (post – 4700 y BP) are registered through χfd/χARM and reveal good correspondence to the flood records of rivers in Southern Alps and Carpathians. The ratio of isothermal remanent magnetization after 20 mT alternating field demagnetization (IRM20mT) normalized to the full IRM showed good consistency with the GISP2 ice record of temperature variations in Greenland during the Holocene. Six major cold incidents during the last 7000 y BP with the major one at 4500 y BP are evidenced. The obtained results suggest that climate at mid-latitude SE Europe is sensitive to the changes in North Atlantic circulation.

The Proto- and Palaeo-Tethys tectonic evolution in Southeastern Tibetan Plateau: Constraints from detrital zircon dating of metasedimentary rocks from the Diancang Shan complex

ABSTRACT Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete ‘Wilson Cycle’ from early Palaeozoic to the Late Triassic.

Aftershock distributions, moment tensors and stress evolution of the 2016 Iniskin and 2018 Anchorage Mw 7.1 Alaskan intraslab earthquakes

SUMMARY We present a detailed study of two Mw 7.1 intraslab earthquakes that occurred in southern Alaska: the Iniskin earthquake of 24 January 2016, and the Anchorage earthquake of 30 November 2018. We have relocated and recovered moment tensors for hundreds of aftershocks following both events, and inverted for stress histories. The aftershock distribution of the Iniskin earthquake suggests that the rupture propagated updip along a fault dipping steeply into the Pacific Plate and terminated at a stratigraphic horizon, inferred to be either the interface or Moho of the subducting slab. In addition, four earthquakes ruptured the main fault in the preceding two years and had similar moment tensors to the mainshock. This evidence suggests that the mainshock likely reactivated a pre-existing, outer-rise fault. The Anchorage earthquake sequence is complex due to its location near the boundary of the subducting Yakutat and Pacific plates, as evidenced by the aftershock distribution. Aftershock hypocentres form two main clusters that appear to correspond to orthogonal, conjugate faults, consistent with the two nodal planes of the dominant focal mechanisms. Both geographic groups display many focal mechanisms similar to the mainshock, which could indicate simultaneous rupture on conjugate planes. The time dependence in stress ratio for the Iniskin sequence can be interpreted in terms of pore-pressure evolution within the mainshock fault zone. In particular, our observations are consistent with a dehydration-assisted transfer mechanism where fluids are produced during rupture through antigorite dehydration and raised to high pore pressures through matrix collapse and/or thermal pressurization. The Anchorage sequence exhibits a more complex stress ratio evolution that may be associated with stress adjustments within a distributed fault network, or reflect a strongly heterogeneous stress field.

Isotopic analysis of radium geochemistry at discrete intervals in the Midwestern Cambrian-Ordovician aquifer system

Radium (Ra) is a geogenic radioactive contaminant that frequently occurs at elevated levels in the Midwestern Cambrian-Ordovician aquifer system (MCOAS). Geochemical indicators (e.g., redox conditions or total dissolved solids) can broadly characterize conditions associated with elevated Ra levels in groundwater, but do not consistently correlate to elevated Ra within specific stratigraphic horizons. A coupled geochemical and isotopic study of groundwater and aquifer solids for major and trace elements, Ra, and uranium (U) at discrete intervals in the MCOAS was used to elucidate processes that may be responsible for this disconnect, via analysis of groundwater as well as extracted and digested solid aquifer samples. We find that the potential for Ra mobilization varies by stratigraphic unit, as observed by whole-rock 226Ra/238U (dis)equilibrium. Overall, the examined aqueous geochemical characteristics (e.g., redox conditions, total dissolved solids) do not explain Ra concentrations within the system, suggesting that alternative factors, like solid-phase associations or the extent of alpha recoil damage, may be more important. A relation between aqueous 87Sr/86Sr and 226Ra suggests that minerals with radiogenic 87Sr/86Sr are more likely to release 226Ra to the aqueous system. Overall, the release of U and Ra due to water-rock interaction varies with discrete stratigraphy, depending on aqueous geochemistry and available mineral associations. Due to complex Ra-rock interactions and the heterogeneous geology of the MCOAS, aqueous geochemistry does not fully predict the mobilization and concentration of Ra in groundwater. As sources and sinks of Ra within the MCOAS vary across stratigraphy, knowledge of aqueous geochemistry, available solid-phase associations, and nuclide leachability all are important to consider for understanding elevated Ra occurrence in aquifer systems.

Holocene Faulting and Earthquake Recurrence along the Northern Agua Tibia–Earthquake Valley Fault Zone and Implications for Slip Distribution in Southern California

ABSTRACTSlip rates determined along the Elsinore and San Jacinto faults indicate that south of 33.5° N, the slip rate along the Elsinore fault decreases by ∼2.5 mm/yr, whereas the slip rate along the San Jacinto fault increases by nearly 6 mm/yr. A transfer of slip from the Elsinore to the San Jacinto faults is the likely explanation, but a fault with Holocene activity had yet to be identified to support this hypothesis. We report the results of new mapping and paleoseismic work along the Earthquake Valley fault, the eastern strand of the Elsinore fault, in Warner basin. Our paleoseismic investigation at Big Lake documents three stratigraphic horizons at which there is evidence of coeval shattering and displacements. The uppermost interpreted event breaks up to within 20 cm of a historical horizon and suggests a very young surface rupture. We attribute this event (E1) to either the 1890 or 1892 earthquakes. The ages of the two previous earthquakes are constrained to be between 486 C.E. and 1125 C.E., and between 158 B.C.E. and 235 C.E. These data suggest individual interevent recurrence intervals of 1106 ± 340 yr (E1–E2) and 760 ± 406 yr (E2–E3), respectively. The minimum slip rate of 1.95 ± 0.4 mm/yr is estimated for the Earthquake Valley fault from the offset of two main drainages that cut into the sedimentary fill of Warner basin, which contains the Bishop tuff. We propose that with its geomorphological expression, late Holocene earthquake record, and slip rate estimate, the Earthquake Valley fault is the main structure responsible for transferring slip from the northern Elsinore fault to the southern San Jacinto fault. Given the recency of a surface rupture and our recurrence interval calculations, however, a large earthquake along the Earthquake Valley fault in the near future is unlikely, if time dependence is considered.

New data on the stratigraphy of the Middle Jurassic siliciclastic rocks from the West Balkan Mountains (West Bulgaria)

The present study is a contribution to the lithostratigraphy of Middle Jurassic strata in the area of the Zimevitsa Plateau (West Balkan Mts, West Bulgaria). Based on its lithological and regional properties, the Dobravitsa Member is distinguished from the surrounding rocks of the Etropole Formation. The new member consists of alternating shales, siltstones and fine-grained sandstones. It also contains abundant siderite and calcite concretions, which are distributed in discrete stratigraphic horizons in both the mudrocks and coarser lithologies. Fossils are extremely rare. Poorly preserved ammonites and belemnites are found only. Based on several ammonite finds, the Dobravitsa Member of the Etropole Formation is assigned to a narrow stratigraphic interval of the lower Bajocian (unlimited, probably lower part of the Witchellia laeviuscula Zone). Although it has restricted lateral distribution, which is exclusively confined to its type-area, the Dobravitsa Member has a proper place in the formal Bulgarian Jurassic lithostratigraphic scheme, as it represents a discernible atypical development of the Etropole Formation in the West Balkan Mts region. Another emphasis of this study is laid on concretions from the Etropole Formation. Besides siderite and calcite concretions, a few examples of iron oxyhydroxide concretions, from localities outside the Zimevitsa Plateau area, are also described. The latter are also an atypical component of the Etropole Formation, which deserves a further special study and systematization, as it implies unknown history of this lithofacies, in both depositional and diagenetic terms.

Insights into the Metallogenesis of the Felsic Volcanic Hosted Mundiyawas-Khera Cu Deposit, Alwar Basin, Western India

Copper and associated gold mineralization in the Mundiyawas-Khera area of western India is hosted by the Proterozoic felsic volcanic rocks of rhyo-dacite composition. Signatures of hydrothermal alteration represented by sericite, epidote, scapolite and carbonates are well observed around the ore mineralization zone. The felsic volcanic rocks with gently to flat sloping REE pattern, variable negative Eu anomaly, intermediate abundances of HFSE and moderate to low Zr/Y anomalies are suggested to be FII, FIIIa and FIV type rhyolite. The felsic volcanic host rock for copper mineralization has a depleted and flat HREE pattern and indicates the crustal source, which is garnet free. Negative Eu anomaly in the rock is probably because of the intracrustal partial melting formed in a rift related environment. The high temperature magmatic activities are probably evolved due to the partial melting of crust at shallow to moderate depths, suggesting an evolved continental crust. The δ13C values of the mineralized carbonate veins range between −10.4‰ and −0.9 ‰ (min = −10.6‰, n = 27), whereas the δ18O values show a range of 16.35‰ to 25.23‰ (min = 21.49‰, n = 27), ideally suggesting a mixed source for the ore bearing fluid. Geological, geochemical and stable isotope data of the Mundiyawas-Khera copper deposit suggest it to be a VMS/VHMS setup and these insights will lead to finding new deposits in the nearby areas, having same stratigraphic horizons and similar lithogeochemical assemblages.

Paleo Isobaths in 3D Seismic Exploration Data Uncover Submerged Shorelines From Glacial Lowstands: A Case Study From the Levant Basin

Modern petroleum exploration extracts 3D volumes of seismic data where certain curves can be drawn delimiting stratigraphic horizons. Such curves hold a promise as piercings for identifying tectonic offsets in 3D. Pinchout points on vertical sections connect with adjacent sections to form contours in 3D. Such a contour, showing quasi-uniform depth, may be considered a paleo-isobath. Here we focus on pinchout paleo-isobaths in the western shores of the Levant that might record ∼120 m drop in sea level at the peak of late Quaternary glacials. We identified a pinchout isobath, ∼15 km offshore, ∼140 m below sea level. Water depth averages ∼90 m, and sediment cover averages ∼45 m. Allowing for isostatic adjustment, this is compatible with eustatic levels of the last two glacial maxima. We hypothesize that the contour mapped is closely related to the shoreline of one of the last glacial maxima. The pinchout pattern is continuous for ∼25 km in the southern reaches of the survey area, at depths of 137 ± 2.5 m, an isobath within the observational uncertainty. The isobath is lost for ∼10 km in the central portion of the survey, north of which a slightly deeper isobath reappears for 7 km, until it disappears approaching a bathymetric trough. The deeper pinchout isobath reappears in the northernmost section of the survey, where it deepens by an average of 5–6 m relative to the southern part (from 137 m to 142 m). The deepening of the pinchout contour is consistent with massive sliding underlying the trough. Sliding here has been attributed to sediment load or salt tectonics, and has been recently associated with a local tsunami dating 9.6 ± 0.3 ka. Recent work relocated the deepest earthquakes on the Levant southern shelf (depths circa 30 km) to the trough, with epicenters coinciding with the boundary faults. This may indicate an active deep-seated tectonic feature. Expressions of the contour outside the survey area will offer tests to our paleo-shoreline hypothesis. Additional pinchout isobaths and pinchout contours associated with earlier lowstands will help constrain tectonic rates as well as glacial eustatic levels and hydro-isostatic effects, with potential regional and global applications.

New thyreophoran dinosaur material from the Early Jurassic of northeastern Germany

Thyreophora is a clade of globally distributed herbivorous ornithischian dinosaurs. The earliest forms are known from the Early Jurassic, and their latest surviving representatives witnessed the end-Cretaceous mass extinction. Throughout their evolutionary history, these ‘shield bearers’ became lumbering quadrupeds, evolved a wide array of bony armor, plates and spikes, as well as sweeping tail weapons in the form of tail clubs and thagomizers. An isolated new thyreophoran osteoderm from a Lower Jurassic Konservatlagerstätte near Grimmen is described and, with the aid of micro-CT data, compared to an osteoderm of the early diverging thyreophoran Emausaurus ernsti from a different stratigraphic horizon at the same locality.

PERMIAN NON-MARINE BIVALVES FROM THE COLLIO AND GUNCINA FORMATIONS (SOUTHERN ALPS, ITALY): REVISED BIOSTRATIGRAPHY AND PALAEOBIOGEOGRAPHY

Non-marine bivalves are key fossils in Permian continental stratigraphy and palaeogeography. Although known since the end of 19th century, the occurrences from the continental basins of the Southern Alps have never been extensively studied. The non-marine bivalves from the Lower Permian Collio Formation (Brescian pre-Alps) are herein revised, and those from the Guncina Formation (Athesian District) are described for the first time. These two units yielded non-marine bivalves belonging to the genus Palaeomutela sensu lato, which is widespread in the Permian continental successions of eastern Euramerica. Three Palaeomutela morphotypes have been herein described: oval-subtriangular, subtrapezoidal and elongated. The latter includes several specimens herein assigned to Palaeomutela (Palaeanodonta) berrutii sp. nov. and dominates the Collio Formation association. The Guncina Formation yielded also the genus Redikorella, for the first time co-occurring on the same stratigraphic horizon of Palaeomutela, herein assigned to Palaeomutela (Palaeanodonta) guncinaensis sp. nov. To-date, it was generally accepted that the first members of the genera Palaeomutela and Redikorella occurred during the Ufimian (late Kungurian of the global scale) in the non-marine basins of the Cis-Ural Foredeep and of Angara, respectively. Such new finds in the early-middle Kungurian of southwestern Europe, well constrained by radioisotopic dating, suggest new global first appearance (First Appearance Datum) and a possible new center of origin of these genera. This fact raises new questions on biostratigraphy, palaeobiogeography and palaeoecology, which will require further research. If we assume that the genera Palaeomutela and Redikorella had only one center of origin, we need to hypothesise possible migration routes from SW Europe to the continental basins of Eastern Europe and Angara. Apparently, such migration could be better supported by a Pangaea B palaeogeographic configuration.

The debate concerning the origin of the Whin Sill of NE England during the early and mid-nineteenth century

The term sill nowadays employed for a broadly concordant igneous intrusion is widely believed to have been derived from the local term for persistent hard beds in the Carboniferous sequence of NE England, in particular the Whin Sill. Despite the intrusive origin of the Whin having been demonstrated in Teesdale by Adam Sedgwick in 1827, for much of the nineteenth century the alternative extrusive hypothesis, of which John Phillips (1836) was the principal proponent, was widely favoured. There were three principal reasons why the intrusive origin was not more widely held, unquestioning acceptance of the erroneous belief of local miners that the Whin Sill was always at the same stratigraphical horizon, a perception that the Teesdale outcrops were not necessarily typical of the rest of the region and a reluctance to accept that the intrusion of such large volumes of magma over such a great area was physically possible. In the 1870s, first the work of Tate and then the detailed six-inch to one-mile mapping of the Geological Survey finally dispelled any notion that the sill was at a consistent stratigraphical level. Curiously, though the correct determination of the intrusive origin of the Whin Sill was one of Sedgwick's earliest and greatest achievements in Northern England, it was not deemed of sufficient importance to merit mention by his biographers.

Images of Fishes on the Glazed Ware from Sougdaia from the Second Half of Thirteenth and Fourteenth Centuries

The article supplies the information on the glazed pottery showing the images of fishes obtained during all the years of excavations at mediaeval Sougdaia and collected for the first time. According to the scholars who have analysed the zoomorphic scenes on the glazed pottery from Sougdaia dating to the Byzantine and Golden Horde Periods, there was almost complete predominance of images of birds, with a minimum number of those of animals. The images of fishes are more than four times less common than birds. In total, the collection of pottery originating from the excavations at the ancient town of Sougdaia comprises ten specimens, four of which were imported from Byzantium and the rest were locally made. This is one of the most representative collections of the kind in the Crimean Peninsula. It does not include the plates depicting fishes and belonging to the Italian group graffita arcaica tirennica from Savona, which were uncovered by the underwater researches in the bay of the modern settlement of Novyi Svet. So far, this type of plates does not occur in the ancient town of Sougdaia. In the collection in question, there is one fragment combining the images of a bird and a fish. Archaeological contexts of finds in questions vary from closed assemblages from the second half of the twelfth century to closed assemblages and stratigraphical horizons from the second half of the fourteenth century. Among the local ware, there are three groups showing specific scenes. The origins of the images of fishes on them are most likely associated with the Byzantine pottery group Fine Sgraffito Ware produced by pottery workshops of Halkis.

Interpretation of Construction Procedure and Physicochemical Characteristics for Soil Layers from Sowangneung (Small Royal Tomb) of Ssangneung (Twin Tombs) in Iksan, Korea

The Iksan Ssangneung (twin tombs), a pair of tombs comprising the Daewangneung (large royal tomb) and the Sowangneung (small royal tomb), were constructed in the typical style of stone tunnel and chamber tombs in the Baekje Kingdom during the Sabi period (538 to 660 AD) of ancient Korea. Soil layers exposed during excavation of Sowangneung in a trench east of the tomb are: the bottommost layer, the ground level layer, the Panchuk (rammed earth) layer of the Baekje, the layer created by a grave robbery, and soil recovered during the Japanese colonial period. Soil samples were obtained by segmenting an easy stratigraphic horizon into sub categorized soil layers, and their material properties were analyzed; they are composed mainly of sandy loam based on the particle size distributions. In the site foundation, loamy sand is packed in the bottommost layer, and sandy loam with high sand and silty sand fills most of the overlying layer. The central and topmost portion of the Baekje layer is composed of loam with high clay content. All soil layers show geochemical behaviors similar to those of the bottommost layer. X-ray diffraction analysis verified kaolinite in all layers, also observed in soil layers displaying high crystallinity. Kaolinite and halloysite were identified by scanning electron microscopy. Thus, we conclude that the Baekje layer of the Sowangneung is composed of sandy loam containing kaolin procured from near the site. An impermeable middle to upper layer was created using viscous loam. The top of the tomb was closed tightly.

PALEOPEDOLOGICAL INVESTIGATION OF LATE CENOZOIC DEPOSITS ON THE ARCHEOLOGICAL LOCATIONS GOLOVCHYNCY-1 IN KHMELNITSKAYA DISTRICT

It is represented paleopedological investigation of the new archeological section on the watershed inside of the territory of granite quarry near v. Golovchyncy with detail morphological description of deposits and scale field drawing with sticks of natural material; 10 samples with undisturbed structure are selected on micromorphological analysis. It is analysised 10 thin sections with undisturbed structure from site Golovchyncy-1 deposits under polarizate microscope are looked through, peculiarities of micromorphological building are interpretated. According to the results of the obtained new paleopedological data, three stratigraphic horizons have been singled out in the archeological section, located above the granite weathering crust – Illichiv, Shyrokyno and Holocene. Illichiv horizon is represented by yellowish-light-gray sands with a large number of fragments of stony material. The Shyrokyno horizon is represented by dark brown sandy-clay leached soil-pedosidiment (sh3), a layer of crumbly sand (sh2) and orange-rusty-brown in color, brown forest (southern facies) soil-pedosidiment (sh3). The modern Holocene horizon is represented by brown forest leached soil. The obtained paleopedological (morpho- and micromorphological) data allowed to reproduce the natural conditions during certain paleogeographic stages of the Pleistocene and to reconstruct the living conditions of ancient man in the Lower Paleolithic. In particular, Shyrokyno soils with artifacts, formed in temperate climate. Their ancient age is confirmed by the high position on the modern watershed, the presence of a strong weathering crust grants and a primitive culture of processing the artifacts found. The upper Shyrokyno soil (sh3) reflects the conditions of the warm-temperate, warmer temperate-humid climate of the zone shifted to the north compared to the modern temperate. The lower (sh1) was formed in a warm-temperate, warmer than modern climate with a sufficiently precipitation regime, when the zones were shifted further north, compared to sh3 soil. Key words: paleopedology; Pleistocene; soils; morphology; micromorphology.

Post-Oligocene evolution of Indo-Burma wedge: Insights from deformation structures of Tripura Mizoram fold belt

The Tripura Mizoram fold belt (TMFB) belongs to the widest segment of the outer wedge of Indo-Burma Wedge (IBW). The structure of the outer wedge is characterized by a series of north-south trending anticlines-and-synclines of varying tightness, which progressively decreases towards the foreland direction. To explain their development, earlier workers proposed the model of fault-related folding, assuming that crustal shortening between India and Burma occurred dominantly by brittle deformation. However, our field investigations in TMFB reveal imprints of unequivocal ductile deformation, including interference of folds. Based on new structural map coupled with outcrop-scale structures, we recognize the existence of multi-ordered folds in the Neogene sequence of TMFB. However, the complexity of folding increases toward the hinterland part of wedge. We substantiate the spatial variations of penetrative ductile structures of TMFB with laboratory experiments under oblique convergence. Model results show consistency with the existence of along-strike variations of deformation intensity in the outer wedge of IBW, which gradually increases southward with narrowing the width of the wedge. Combining our field observations and laboratory experiments with earthquake focal depth distributions around TMFB, we propose that stratigraphic horizons of the entire outer wedge are mechanically weak to have deformed dominantly by brittle faulting.

Features of the Hydrocarbon Distribution in the Bottom Sediments of the Norwegian and Barents Seas

The results of the study of hydrocarbons (HCs): aliphatic (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in bottom sediments (2019 and 2020, cruises 75 and 80 of the R/V Akademik Mstislav Keldysh) in the Norwegian-Barents Sea basin: Mohns Ridge, shelf Svalbard archipelago, Sturfiord, Medvezhinsky trench, central part of the Barents Sea, Novaya Zemlya shelf, Franz Victoria trough are presented. It has been established that the organo-geochemical background of the Holocene sediments was formed due to the flow of sedimentary material in the coastal regions of the Barents Sea on shipping routes. The anthropogenic input of HCs into bottom sediments leads to an increase in their content in the composition of Corg (in the sandy sediments of the Kaninsky Bank at an AHC concentration up to 64 μg/g, when its proportion in the composition of Corg reaches 11.7%). The endogenous influence on the of the Svalbard archipelago shelf in Sturfiord and in the Medvezhinsky Trench determines the specificity of local anomalies in the content and composition of HCs. This is reflected in the absence of a correlation between HCs and the grain size composition of sediments and Corg content, as well as a change in hydrocarbon molecular markers. At the same time, the sedimentary section is enriched in light alkanes and naphthalene’s that may be due to emission during point discharge of gas fluid from sedimentary rocks of the lower stratigraphic horizons and/or sipping migration.

Mineral paragenesis and stratigraphic setting of the Neoproterozoic volcano-sedimentary succession of Samran Group, Jabal Farasan Area, West central Arabian Shield, Saudi Arabia

Jabal Farasan is located in the west central part of the Arabian Shield. The present study aims to reveal the stratigraphic setting and mineral paragenesis of the exposed volcano-sedimentary succession of the Samran Group in Jabal Farasan area. The succession of Samran Group is composed of three successive facies: the lower interbedded andesitic tuffs and tuffaceous andesites and trachyte’s (F1), the middle-altered quartz diorite/andesite (F2) and, an upper interbedded andesitic tuff, tuffaceous andesites and trachytes (F3). The vertical variations in the petrographic lithotypes depend mainly on the position of the depositional sites relative to the volcanic centers (proximal and distal). Both the volcanic rocks and the associated units are subjected to syn-and post-depositional diagenetic/metamorphic processes. These processes include the formation of the Fe2+-silicates: (i.e., chlorite instead of the volcanic ashes and the formation of plagioclase minerals). Post diagenetic recrystallization of the tuffaceous mudstones and the formation of microcrystalline quartz. The diagenetic oxidation of the Fe2+-silicates led to the formation of volcaniclastic red beds in certain stratigraphic horizons.

The syn‐rift tectono‐stratigraphic record of rifted margins (Part II): A new model to break through the proximal/distal interpretation frontier

AbstractOne fundamental lesson from the last decade's research into rifted margins is that stratigraphic horizons cannot be simply correlated from the proximal into distal domain, which makes the interpretation of poorly calibrated and largely inaccessible distal margins difficult. In this contribution, we propose a new tectono‐stratigraphic model to help break through the proximal/distal interpretation frontier. After reviewing the scientific advances on rifted margins achieved during the last century, we describe the primary spatio‐temporal evolution of active deformation during rifting. We show that different rift domains are associated with specific (1) periods of active deformation; (2) tectonic structures and related stratigraphic architecture; (3) amounts of accommodation creation owing to specific ranges of horizontal widening and vertical deepening and (4) depositional environments. We demonstrate that the sequential localization of extension during rifting results in a younging of the base of passive infill (i.e. sediment deposited in a non‐tectonic setting) oceanward. We propose a panel of few to few tens of My time intervals related to specific tectonic events—our Tectonic Sequences—that may be correlated more or less easily and continuously across rifted margins. This study underlines the value of an iterative approach between fieldwork on fossil rifted margins and offshore geophysical studies, where field studies offer easy‐to‐access and high‐resolution calibration of dismembered rifted margin remnants, while geophysical studies provide comparatively low‐resolution imaging of entire, intact but largely inaccessible, rifted margins. It also highlights the necessity of jettisoning outdated dogma on rifted margins and changing our routines when interpreting seismic sections and outcrops.

Synsedimentary deformation structures within the Paleoproterozoic Espanola Formation, Huronian Supergroup, Canada: Implications for basin tectonism and paleodepositional conditions

The Espanola Formation represents part of the lower Huronian Supergroup (2.45–2.2 Ga), which is interpreted to have been deposited in a restricted, fault-bound, intracontinental rift basin during Early Proterozoic episodes of crustal stretching and contemporaneous faulting along the southern margin of the Archean Superior Province. Field examination of Espanola Formation outcrops exposed north of Elliot Lake, Ontario, Canada, revealed widespread synsedimentary deformation structures, which can be broadly grouped into three main categories: (1) forceful-injection structures, (2) slump structures, and (3) soft-sediment deformation structures. Examples of these structures include clastic dykes, large-scale slump structures, intraformational conglomerate, load casts, ball-and-pillow structures, convolute laminae, and dish-and-pillar structures. Most of the reported deformation structures are restricted to discrete stratigraphic horizons, are laterally continuous on an outcrop scale, are abundant and widespread across the studied region and are confined between undisturbed strata of similar lithology. These characteristics strongly indicate an origin by liquefaction and fluidization mechanisms that were triggered by syndepositional rift-related seismic activity, inferred to have been induced by movement along bounding normal faults during subsidence of the lower Huronian basin. Autogenic triggers such as overloading by rapid sedimentation, slump emplacement, inverse density gradient, gravity-driven sediment transport and mobilization, and storm waves may have also locally contributed to the development of the reported soft-sediment deformation structures.