Coarse Clastic Sediments Research Articles

Late Ordovician Shelf Deposition in Northern Gorny Altai: Lithology, Faunas, and Paleogeography

Abstract ––New and revised previous data based on detailed description of sections have provided better constraints on fauna taxonomy, lithology, and stratigraphy, as well as on biostratigraphic ages of sediments. The lithology and stratigraphy of several key Upper Ordovician sections in the northern Gorny Altai area show that the local units of Sandbian and Katian Savelieva and Bulukhta formations can be used as reference for the regional Ordovician division. It is suggested to include a newly distinguished Bulukhta facies zone, an area of Late Ordovician coarse clastic deposition, into the mapped Ordovician deposits of Gorny Altai. According to paleogeographic reconstructions, the deposition occurred in a large sea gulf surrounded with elevated landmasses exposed to erosion.

Low-amplitude brittle deformations revealed by UAV surveys in alluvial fans along the northwest coast of Lake Baikal: Neotectonic significance and geological hazards

Many large deltas and other areas, underlain by unconsolidated sediments, are heavily populated but impacted by various natural deformational processes. The causes and mechanisms of the deformation are often obscure because of difficulties in the identification of their geological source. We used an unmanned aerial vehicle (UAV) to survey an area of up to several km2 to detect and map surface discontinuities with displacements of a few centimeters, which can indicate the presence of initial geological deformations. We encountered such offsets in the alluvial fans on the northwestern coast of Lake Baikal, overlying the damage zones of several faults. These deformations at the different sites are referred to as primary or secondary co-seismic ruptures, brittle creep, or cryogenic fissures, which have specific origins. They are located a few hundred meters from a principal fault plane, from junctions of faults, and in the peripheral parts of alluvial fans, making these areas potentially hazardous. We analyzed the digital surface models of local segments of one of the delta plains between 2020 and 2021 and established that its periphery has subsided by an average of 5–10 cm. In areas of accumulation of the river sediment, the thickness of coarse clastic deposits has increased by approximately the same amount. Locally and in the coastal zone, the vertical surface changes are larger. In the axial parts of some seismically induced gravitational failures, the subsidence reached 33 cm over a period of 11 months and 19 days. Our results show that sediments of alluvial fans are very susceptible to various tectonic and exogenous deformational processes. The interpretation of the ultra-high resolution UAV's images can help the recognition the low-amplitude brittle deformations at an early stage of their development. Therefore, such UAV surveys are critical in the discernment of neotectonic activity and its related hazards over short observation periods.

Late Paleozoic sedimentary and tectonic evolution of the Linxi basin in the eastern Inner Mongolia, eastern Central Asian Orogenic Belt

The eastern Central Asian Orogenic Belt (CAOB) encompasses a vast region from northeast China to Inner Mongolia, where there were many Late Paleozoic sedimentary basins that can provide key constraints to tectonic evolution of the eastern CAOB. Analysis of sedimentary sequence and environment of eight measured sections from the Linxi basin, Inner Mongolia indicates that there were shallow marine clastic-carbonate sedimentary facies, delta and littoral facies and terrestrial facies during the Early, Middle and Late Permian, respectively, and no oceanic sedimentary facies was found. Sedimentary sequence from the initial clastic-carbonate rocks to marine volcanic rocks reveals a transgression process during 300–270 Ma, while clastic and carbonate rocks with conglomerates and plant fossils represent a regression process during 270–250 Ma. According to the detrital zircon (DZ) age distribution of twenty-two samples (1610 zircons), the northern and southern provenances of the Permian sedimentary strata have been recognized, respectively. These DZ samples express the dispersed polymodal age populations and are attributed to a divergent dominated tectonic setting, implying the Linxi basin is an intracontinental extension basin during the Permian. This is consistent with an extensional process revealed by the syn-depositional deformed structures, coarse clastic sediments and olistostrome successions in the Linxi basin during the Early to Middle Permian and also similar to the speculation that there was an extension setting based on studies of volcanic rocks and intrusions in the Linxi basin. Combined with previous studies on the West Ujimqin basin, the Late Carboniferous to Permian tectonic frame of the eastern Inner Mongolia expresses extensional tectonics characterized by alternating combination of basins and uplifts superimposed on a pre-existing Early-Middle Paleozoic orogenic lithosphere and Precambrian basement, rather than a single ocean basin of Paleo Asian Ocean (PAO), which provides constraints for understanding sedimentary and tectonic evolution of the eastern CAOB during the Late Paleozoic.

TUMBLING EXPERIMENT FOR THE ESTIMATION OF ABRASION AND MASS LOSS OF COASTAL SEDIMENTS FROM AN ARTIFICIAL COARSE-CLASTIC BEACH

In order to assess the accretive or erosive pattern of a stretch of coast, it is essential to estimate its sediment budget, i.e. the quantification of all sources and sinks of sediments. The sediment budget is the basis of a reliable coastal management plan (Ruol et al., 2018). In fact, coastal erosion is usually the result of a negative balance of factors, both natural and anthropogenic, that operate on different scales, none of which may be considered the single cause. Recently, a massive abrasion rate of coarse-clastic sediments was documented in artificial nourished beaches. The mechanism is associated with both mild wave conditions and extreme stormy events, which could also induce chippings. This phenomenon could decrease the durability of nourishments (Bertoni et al., 2012 and 2016) and is usually not considered in the sediment balance. The mass loss due to abrasion can lead to errors in the analysis of erosive and accretive patterns after the nourishment and consequently to erroneous coastal management strategies. Moreover, the sediment grain size in a given beach (naturally present or selected for nourishments) is strictly related to the typical wave energy. The abrasion mechanism and the possible pebble chipping change the sediment grain size, which could become unstable and not adequate for the local wave climate. Based on the large cost of nourishments, which also require strong monitoring in the subsequent years, it is crucial to understand the abrasion and mass loss rates of the filling sediments to extend the life of artificial beaches as long as possible.

Reconstruction of the proto-type basin and tectono-paleogeography of Tarim Block in the Mesozoic

The reconstruction of the proto-type basin and tectono-paleogeography of the Tarim Basin during the Mesozoic is crucial for hydrocarbon exploration, particularly for identifying hydrocarbon source rocks. This study reconstructs the position, thickness, and distribution of the original stratigraphy, the shortening amount by structural deformation, and the distribution of sedimentary facies in each Mesozoic period using paleomagnetic data, residual stratigraphy data, seismic profiles, and lithofacies distribution. During the Triassic period, a syn-collision thrust fault structure formed in the southern Tarim Block due to the successive collision of the Tianshuihai-Bayankara terrane, North Qiangtang terrane, and South Qiangtang terrane with the Tarim Block. The sedimentary strata mainly distributed in the Northern Depression and Kuqa Depression, and their sedimentary centers continuously moved northward. In the Early-Middle Jurassic, faulted basins representing post-collision extensional structures developed on the margins of the Tarim Block. In the Late Jurassic, the Tarim Block was compressed, and the faulted basin transformed into a depressional downwarped basin with red coarse clastic sediments due to the collision of the Amdo-Dongkacuo microcontinent with the Tarim Block. In the late Early Cretaceous, the collision between the Lhasa Block and the Tarim Block caused the entire uplift of the Tarim Block, which stopped accepting deposition except for the deposition of marine facies in the southwestern Tarim Basin influenced by a large-scale transgression event. The complex evolution of the Paleo-Tethys and Neo-Tethys Oceans during the Mesozoic significantly influenced the sediment distribution and structural features of the Tarim Basin.

In search for primary sources of placer diamonds of northeast Siberian craton: Evidence from the U–Pb ages and geochemistry of alluvial zircons

AbstractThe northeastern Siberian craton stores numerous placers of diamonds that differ in morphology and texture, and originate from different types of primary deposits, primarily kimberlites. Analyses of mantle zircons selected from samples of alluvial and coarse clastic sediments in the watersheds of the Olenek and Kyutyungde rivers in the Anabar‐Olenek subprovince of the Yakutian diamond province provide constraints on kimberlite magmatism events in the area. The new U–Pb ages and typical kimberlitic signatures of the Kyutyungde zircons trace‐element patterns reveal three main magmatic events that produced kimberlites: Middle Paleozoic (Late Devonian to Early Carboniferous), Jurassic and Triassic. The Jurassic zircons (177–149 Ma) are mainly related to kimberlites in the proximal Kuoika‐Molodo and Khorbusuon fields. Triassic zircons (240–221 Ma) were probably released during large‐scale erosion of the eastern Anabar shield, however, the presence of such zircons in the Kyutyungde area indicates that kimberlites of the respective magmatic stage may exist within the immediate vicinity of the area. The only Middle Paleozoic zircon sample (358.6 Ma, D3‐C1 boundary) may originate from a proximal kimberlite within the Kyutyungde area. The presence of Middle Paleozoic kimberlitic zircons, along with harzburgite–dunitic pyropes, indicates that the primary deposit of diamonds and related minerals may exist near or within the Kyutyungde area. Late Ediacaran–Early Cambrian (573–473 Ma) mantle zircons found in Early Cambrian conglomerates of the area, along with other mantle minerals including Cr spinel of a diamond assemblage, record another Precambrian event of potentially diamondiferous magmatism in the Kyutyungde basin.

Paleoenvironmental Conditions and Factors Controlling Organic Carbon Accumulation during the Jurassic–Early Cretaceous, Egypt: Organic and Inorganic Geochemical Approach

The Jurassic–Early Cretaceous was a time of variable organic carbon burial associated with fluctuations of marine primary productivity, weathering intensity, and redox conditions in the pore and bottom water at paleo-shelf areas in north Egypt. This time interval characterized the deposition of, from old to young, the Bahrein, Khatatba, Masajid, and Alam El Bueib Formations in the north Western Desert. Although several studies have been devoted to the excellent source rock units, such as the Khatatba and Alam El Bueib Formations, studies on paleoenvironmental changes in redox conditions, paleoproductivity, and continental weathering and their impact on organic carbon exports and their preservation for this interval are lacking. This study presents organic and inorganic geochemical data for the Jurassic–Lower Cretaceous sediments from the Almaz-1 well in the Shushan Basin, north Western Desert. A total of 32 cuttings samples were analyzed for their major and trace elements, carbonates, and total organic carbon (TOC) contents. Data allowed the reconstruction of paleoenvironmental conditions in the southern Tethys Ocean and assessment of the changes in paleo-redox, paleo-weathering, and marine primary productivity, and the role of sediment supply. Additionally, factors that governed the accumulation of organic matter in the sediment were interpreted. Results showed that the Khatatba Formation was deposited during a phase of enhanced marine primary productivity under prevalent anoxia, which triggered enhanced organic matter production and preservation. During the deposition of the Khatatba Formation, significant terrigenous sediment supply and continental weathering were followed by a limited contribution of coarse clastic sediment fluxes due to weak continental weathering and enhanced carbonate production. The Bahrein, Masajid, and Alam El Bueib Formations were deposited during low marine primary productivity and prevalent oxygenation conditions that led to poor organic matter production and preservation, respectively. A strong terrigenous sediment supply and continental weathering predominated during the deposition of the Bahrein Formation and the lower part of the Alam El Bueib Formation compared to the limited coarse clastic supply and continental weathering during the deposition of the carbonate Masajid Formation and the upper part of the Alam El Bueib Formation. Such conditions resulted in the enhanced dilution and decomposition of labile organic matter, and, thus, organic carbon-lean accumulation in these sediments.

The Late Ordovician Tafilalt Biota, Anti-Atlas, Morocco: a high-latitude perspective on the GOBE

Abstract The extensive, predominantly siliciclastic deposits of the Upper Ordovician of the Tafilalt have long been the subject of scientific investigation. In the past 25 years, intensified collecting for commercial purposes has resulted in the discovery of several exceptionally-preserved faunas (Konservat-Lagerstätten) in the Tafilalt region, preserving a range of non-biomineralized and soft-bodied organisms. The preservation of these fossils in the coarse clastic sediments of the Tafilalt is surprising, and in the case of soft-bodied organisms, remarkably similar to the preservational mode of typical Ediacaran biotas. These relatively recent discoveries have increased the scientific significance of the Tafilalt Biota, providing an unparalleled insight into the composition and temporal evolution of the shallow, open-marine ecosystems and their denizens during the later stages of the Great Ordovician Biodiversification Event. At least nine different phyla, in addition to several soft-bodied problematica are represented in the Tafilalt. While the highly diverse and remarkably well-preserved echinoderm and euarthropod faunas are most emblematic for the Tafilalt Biota, further studies have revealed a relatively high diversity of molluscs and brachiopods. Among soft-bodied fossils, the problematic paropsonemid eldonids are iconic for the Tafilalt and stand out both through their abundance, and their wide temporal and geographical range throughout the area.

Lost Norian fluvial tracks: Sedimentology and stratigraphy of the Upper Triassic coarse-grained deposits in Kamienica Śląska (Upper Silesia, southern Poland)

In the Triassic‒Jurassic boundary profiles of the Upper Silesian region, there are locally developed coarse clastic deposits, commonly known as the Połomia Gravels, Połomia Beds or “Połomia Formation’’ (informal name). Due to the lack of reliable stratigraphic tools, the chronostratigraphic position of these deposits remains one of the most controversial aspects of the Triassic‒Jurassic lithostratigraphy in the region. Sparse biostratigraphic data from the overlying and underlying deposits indicate a wide range of ages, from the Late Triassic to Early Jurassic. This paper presents the results of sedimentological, petrographical and palynological analyses of the coarse-grained deposits from the Kamienica Śląska gravel pit, which is currently one of the biggest facilities of this type in Upper Silesia. The outcrop section, with a total thickness of up to 20 m, is dominated by friable, light grey to beige and locally dark grey, large-scale planar to trough cross-stratified conglomerates and coarse-grained sandstones with subordinate thin interbeds of grey and reddish brown mudstones. Three facies associations have been distinguished, representing a main channel belt, secondary channels and floodplains subenvironments. Facies analysis points to a braided river tract with localised floodplain sediments. The grain composition of the Kamienica Śląska gravel/conglomerate is less diversified than that of the polymictic typical Połomia Beds of the Myszków area and resembles oligomictic conglomerates known from the Grabowa Formation of the Norian age and/or conglomerates of the Gorzów Beds of Rhaetian age, which also occur on the studied region. Palynological analysis of mudstone interbeds within the conglomeratic deposits shows the presence of miospores guiding and characteristic for subzone c of the Corollina meyeriana zone of the late Norian‒early Rhaetian age. The appearance of the coarse-grained deposits in late Norian could be associated with the development of a long-reach braided fluvial tract, draining the S and SE part of the Sudetian-Malopolska-Lublin land (S-M-L land) in response to the tectonic rearrangement in the source area and gradual climatic change from semi-arid to humid in the Rhaetian.

Substrate Entrainment, Depositional Relief, and Sediment Capture: Impact of a Submarine Landslide on Flow Process and Sediment Supply

Submarine landslides can generate complicated patterns of seafloor relief that influence subsequent flow behaviour and sediment dispersal patterns. In subsurface studies, the term mass transport deposits (MTDs) is commonly used and covers a range of processes and resultant deposits. While the large-scale morphology of submarine landslide deposits can be resolved in seismic reflection data, the nature of their upper surface and its impact on both facies distributions and stratal architecture of overlying deposits is rarely resolvable. However, field-based studies often allow a more detailed characterisation of the deposit. The early post-rift Middle Jurassic deep-water succession of the Los Molles Formation is exceptionally well-exposed along a dip-orientated WSW-ENE outcrop belt in the Chacay Melehue depocentre, Neuquén Basin, Argentina. We correlate 27 sedimentary logs constrained by marker beds to document the sedimentology and architecture of a >47 m thick and at least 9.6 km long debrite, which contains two different types of megaclasts. The debrite overlies ramps and steps, indicating erosion and substrate entrainment. Two distinct sandstone-dominated units overlie the debrite. The lower sandstone unit is characterised by: 1) abrupt thickness changes, wedging and progressive rotation of laminae in sandstone beds associated with growth strata; and 2) detached sandstone load balls within the underlying debrite. The combination of these features suggests syn-sedimentary foundering processes due to density instabilities at the top of the fluid-saturated mud-rich debrite. The debrite relief controlled the spatial distribution of foundered sandstones. The upper sandstone unit is characterised by thin-bedded deposits, locally overlain by medium-to thick-bedded lobe axis/off-axis deposits. The thin-beds show local thinning and onlapping onto the debrite, where it develops its highest relief. Facies distributions and stacking patterns record the progradation of submarine lobes and their complex interaction with long-lived debrite-related topography. The emplacement of a kilometre-scale debrite in an otherwise mud-rich basinal setting and accumulation of overlying sand-rich deposits suggests a genetic link between the mass-wasting event and transient coarse clastic sediment supply to an otherwise sand-starved part of the basin. Therefore, submarine landslides demonstrably impact the routing and behaviour of subsequent sediment gravity flows, which must be considered when predicting facies distributions and palaeoenvironments above MTDs in subsurface datasets.

Fast exhumation rate during late orogenic extension: The new timing of the Pilat detachment fault (French Massif Central, Variscan belt)

A leucogranite sill in the footwall of the extensional Pilat shear zone (PSZ) Eastern French Massif Central was emplaced and sheared in a short time interval, between 301.8 ± 3.1 and 303.0 ± 1.6 Ma (zircon U–Pb and mica 40Ar/39Ar ages, respectively). Extension ended at 298.5 ± 1.5 Ma (40Ar/39Ar on mica) as shown by a non deformed dike cross cutting the sheared zone. On the hanging wall of the fault, the opening of the St. Etienne Basin filled by coarse clastic sedimentation confirms the existence of a relief south of the PSZ. U-Pb dating of a lithic-rich ignimbrite at the bottom of the basin and of a volcanic layer at the top delivered ages of 310.5 ± 3.4 Ma and 299.3 ± 1.3 Ma, respectively. Close U-Pb and 40Ar/39Ar ages from syn- to post-tectonic granites indicate very fast cooling (∼150 °C/Myr) and exhumation rate (6 mm/yr) corresponding to the emplacement of granites in the middle crust immediately followed by their fast tectonic exhumation and cooling into the upper crust. The development of the Pilat fault in the thermally softened crust is responsible for the rapid exhumation of the Velay dome, a Metamorphic Core Complex localized in the footwall of the sheared zone. Here we propose that its rapid exhumation was due to localized sub crustal lithospheric mantle dripping. These new data show that there was only one extensional phase in the PSZ coeval with the opening of the St. Etienne coal Basin. Finally, the new chronology obtained in this study is challenging previous ages suggesting 20 Ma activity for the Pilat shear zone.

Deep-water reservoir distribution on a salt-influenced slope, Santos Basin, offshore Brazil

Studies of near-seabed datasets show that salt tectonics controls the distribution and architecture of deep-water reservoirs in many salt-influenced basins. It is typically difficult, however, to study the distribution and stratigraphic evolution of depositional systems preserved at deeper, economically significant depths, reflecting poor seismic imaging of steeply dipping strata flanking high-relief salt structures. 3D seismic and borehole data from the Santos Basin, offshore Brazil allow us to identify a range of depositional elements that form the building blocks of three main tectono-stratigraphic phases. During the first phase, channel systems and lobes were confined within updip minibasins and to the hangingwalls of salt-detached faults. During the second phase, channel systems and lobes filled updip minibasins to bypass sediment downslope, with coarse clastic deposition then occurring in downdip minibasins, >100 km from the coeval shelf margin. Syndepositional seafloor relief caused: (i) channel system deflection and diversion around salt-cored highs; (ii) channel system uplift and rotation on the flanks of rising salt structures; (iii) lateral and frontal confinement of channel systems. During the final phase, rising salt walls dissected previously deposited deep-water systems, with MTCs deposition becoming increasingly important. Our results have important implications for post-salt prospectivity in the Santos Basin and other salt-influenced sedimentary basins, with a range of reservoirs and trapping styles present in this underexplored interval. More specifically, we show that large volumes of clastic sediment were not trapped behind the ‘Albian Gap’, a salt-controlled depocenter dominating the north-western basin margin, but were instead delivered further basinward.

Detrital Zircon Age Constraints on the Evolution of Paleo‐Tethys in NE Iran: Implications for Subduction and Collision Tectonics

AbstractThe timings of the onset of oceanic spreading, subduction and collision are crucial in plate reconstructions, but not always straightforward to resolve. The Paleo‐Tethys evolution dominated the Paleozoic‐Early Mesozoic tectonics of West Asia, but the timeline of events is still poorly constrained. We present new detrital zircon ages from the Binalud Mountains of NE Iran, in order to determine the timing of tectonic events in the region, and the wider implications for regional tectonics, paleogeography and climate change. Consistent age patterns in Paleozoic clastic rocks show a dominant provenance from the Neoproterozoic basement of northern Gondwana. We interpret this as deposition on a long‐lasting passive continental margin after the initial spreading of the Paleo‐Tethys Ocean. Central Iran‐Eurasia collision caused coarse clastic deposition of the Mashhad Phyllite in a peripheral foreland basin on the Paleozoic sequence of the northern Central Iran Block. The Mashhad Phyllite yields age clusters at 450–250 Ma and 1,900–1,800 Ma, with a clear provenance from a long‐lived continental arc at the active Eurasian margin since the latest Ordovician. Analysis of the age spectra allows us to constrain the maximum depositional age of the Mashhad Phyllite as no later than 228 Ma. This age provides a tight constraint on the timing of initial collision between Central Iran and Eurasia, which also coincides with the Carnian Pluvial Event (CPE). Our new timing evidence of collision reinforces the previous speculation on the Paleo‐Tethys closure as a causal mechanism for the CPE.

Rock magnetic variability of quaternary deep-sea sediments from the Bering Sea and their environmental implications

IODP Ex. 323 shipboard rock magnetic measurements of Quaternary deep-sea sediments from the Bering Sea identified a dramatic bimodal character to the sediments, alternating between sediments with strong natural magnetic remanence (NRM) and magnetic susceptibility (chi) and those with order-of-magnitude lower values. We now generally associate the high-magnetic-intensity sediments with interglacial/interstadial times and the low-magnetic-intensity intervals are generally associated with glacial/stadial conditions. This pattern can be largely correlated among all seven IODP Ex. 323 sites. We have now completed more detailed rock magnetic measurements on selected u-channeled sediments from these sites. U-channel rock magnetic measurements indicate that the high-intensity sediments contain relatively coarser magnetic grains (sand/silt) associated with coarser siliciclastic sediments while the low-intensity sediments contain finer magnetic grains (silt) associated with finer siliciclastic sediments. We associate the coarser magnetic grains and overall coarser clastic sediments with warmer intervals when more open water conditions permit sediment flux from the continental shelves. The finer magnetic grains and associated finer clastic sediment are largely derived from sediment reworking and redeposition associated with slope processes and deep-sea contour currents when ice cover was more permanent. We have corroborated the grain size variability with magnetic hysteresis measurements and clastic grain size analysis. The clastic grain size distributions of the coarser versus finer grained sediments are significantly different; coarser grained sediments have a broad grain size distribution with 50–60 μm mean grain size, while finer grained sediments have a much more narrow grain size distribution with 15–20 μm mean grain size. The finer grain size distribution is consistent in range and mean grain size to North Atlantic deep-sea sediment deposited as drift deposits by contourite deposition (Heezen and Ruddiman, 1966; Johnson et al., 1988). The dominant magnetic mineral in all sediments is detrital magnetite. Early sediment diagenesis plays a minor role in the overall rock magnetic variability of the Bering Sea deep-sea sediments due to the overall large clastic grain size. The magnetic variability that we see in the Quaternary Bering Sea sediments appears to be comparable to other studies from this region. VanLaningham et al. (2009) attribute deposition of the Meiji drift, directly south of the deep-water exit from the Bering Sea, to sediments derived from the Bering Sea. They see a bimodal distribution in the types of sediments that are deposited with younger arc rocks during interglacials and older continental rocks during glacials. That is consistent with our coarser Interglacial magnetic sediments derived primarily from shelf rocks rich in recent volcanics versus deeper Bering Sea sediments associated with reworking of older Bering Sea sediments during the glacials. We also note the strong similarity in timing of strong versus weak magnetic intensity sediments of Lake Elgygytgyn, about 1000 km to the NW of the Bering Sea, Both seem to be controlled by the degree of intermittent open water conditions, more so in the interglacials and very little in the glacials, but operating on a finer scale than simple glacial/interglacial cycling.

ЛАНДШАФТНАЯ СТРУКТУРА ЗАПАДНОГО ПРИБРЕЖЬЯ ГОРОДА СЕВАСТОПОЛЯ

The information about the landscape structure of the western coast of Sevastopol. Landscape studies (summer 2020) were conducted by detailed study of key sites using landscape profiling. In the landscape structure of the study area identified 8 bottom natural complexes (BCN). The capes at a depth of 0.5-5 m are characterized by underwater slope landscapes with boulder and boulder heaps and bedrock outcrops dominated by Carpodesmia crinita and Treptacantha barbata. Between the capes at these depths, underwater slope landscapes formed by sandy sediments, devoid of benthic vegetation, where individual clumps are also dominated by Carpodesmia crinita and Treptacantha barbata. An underwater coastal slope composed of coarse-clastic sediments dominated by Treptacantha barbata, and with alternating pebble-gravel with battered shell sediments dominated by Phyllophora crispa, was recorded at a depth of 5–10 m. A weakly sloping plain composed of gravel-sandy sediments with broken shells, dominated by Phyllophora crispa, can be traced at a depth of 10–15 m. The formation of its landscape structure is influenced by both the natural features of the coastal zone and economic activities in the adjacent territory.

Adakite-like granitoids of Songkultau: A relic of juvenile Cambrian arc in Kyrgyz Tien Shan

The early Paleozoic Terskey Suture zone, located in the southern part of the Northern Tien Shan domain in Kyrgyzstan, comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deep-marine sediments. In the Lake Songkul area, early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites (SiO2 ​> ​56 ​wt.%, Al2O3 ​> ​15 ​wt.%, Na2O ​> ​3.5 ​wt.% and high Sr/Y and La/Yb ratios). The Songkultau granitoids have positive initial εNd (+3.8 to +6.4) and εHf (+12.3 to +13.5) values indicating derivation from sources with MORB-like isotopic signature. Volcanic formations, surrounding the Songkultau intrusion, have geochemical affinities varying from ocean floor to island arc series. This rock assemblage is interpreted as a relic of an early–middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust. An age of 505 ​Ma, obtained for the Songkultau intrusion, shows that hot subduction under the Northern Tien Shan continued until middle Cambrian. The primitive arc complexes were obducted onto the Northern Tien Shan domain, where the Andean type continental magmatic arc developed in Cambrian and Ordovician. Formation of the Andean type arc was accompanied by uplift, erosion and deposition of coarse clastic sediments. A depositional age of ca. 470 Ma, obtained for the gravellites in the Lake Songkul area, is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan, and corresponds to the main phase of the Andean type magmatism. The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan. On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan, Gorny Altai and Mongolia.

Thermochronological and Geochronological Constraints on Late Cretaceous Unroofing and Proximal Sedimentation in the Sevier Orogenic Belt, Utah

AbstractA source‐to‐sink analysis incorporating geochronometric and thermochronometric data from the Sevier fold‐thrust belt (SFTB) and proximal synorogenic strata of the Canyon Range Conglomerate (CRC) and Indianola Group (IG) provides new insights into orogenic exhumation, erosional unroofing, and the interplay between thrusting and coarse clastic deposition in the Cretaceous Cordilleran foreland basin of western North America. Zircon (U‐Th)/He ages from the Pavant and Nebo thrust sheets record significant Cenomanian cooling indicative of synchronous exhumation and thrusting along a large segment of the SFTB in central and northern Utah. Detrital zircon (U‐Th)/He (DZHe) ages indistinguishable from depositional ages from the Cenomanian Dakota Formation and lower CRC also record rapid unroofing of the SFTB and synchronous deposition. DZHe data from wedge‐top deposits of the CRC record two significant unroofing episodes: Albo‐Cenomanian exhumation of the Pavant thrust and progressive unroofing of the Canyon Range culmination. For the IG, the presence of Paleozoic DZHe ages along with Paleozoic‐Mesozoic DZ U‐Pb ages in the Cenomanian Sanpete Formation suggests derivation from Paleozoic to Jurassic strata exhumed in the frontal Pavant and Nebo thrust sheets. After the Cenomanian episode of rapid exhumation, proximal foredeep strata recorded a widespread DZ provenance shift in the Turonian. Short DZHe lag time values from Campanian CRC and IG deposits reveal rapid exhumation of the SFTB during the Campanian. The synchroneity of major shortening and Campanian and Cenomanian changes in foreland basin architecture and provenance supports models proposing that active shortening in the fold‐thrust belt coincides with coarse clastic influx in foreland basins.

Alluvial sedimentation and tectono-stratigraphic evolution in a narrow extensional zigzag basin margin (northern Teruel Basin, Spain)

The northern part of the eastern margin of the extensional Neogene Teruel Basin (central-eastern Spain) consists of a non-linear, zigzag fault zone made of alternating ca. 2 km long, NNW-SSE trending segments and shorter NNE-SSW ones. Good outcrop conditions made possible a comprehensive integrated stratigraphic and structural study, especially focused on coarse clastic sediments deposited along the basin margin. Well-exposed stratal relationships with boundary faults, allowed the analysis of tectonic influence on sedimentation. Synsedimentary deformation includes growth faulting, rollover anticlines, and monoclines and associated onlap stratal terminations, angular unconformities, and other complex growth strata geometries. One of them is the onlap-over-rollover bed arrangement described here for the first time, which reveals the competition between tectonic subsidence and sedimentary supply. Both, the structural inheritance (dense Mesozoic fracture grid) and the dominant, nearly ‘multidirectional’ (σ1 vertical, σ2 ≈ σ3), Pliocene extensional regime with σ3 close to E-W, are considered to have controlled the margin structure and evolution. Tectono-stratigraphic evolution includes: (i) reactivation of inherited NNW-SSE faults and development of W-SW-directed small alluvial fans (SAF) while NNE-SSW segments acted as gentle relay ramp zones; (ii) progressive activation of NNE-SSW faults and development of NW-directed very small alluvial fans (VSAF); during stages i and ii sediments were trapped close to the margin, avoiding widespread progradation; (iii) linking of NNW-SSE and NNE-SSW structural segments, overall basin sinking and widespread alluvial progradation; (iv) fault activity attenuation and alluvial retrogradation. The particular structure and kinematic evolution of this margin controlled alluvial system patterns. Size of alluvial fans, directly set up at the border faults, was conditioned by the narrowness of the margin, small catchment areas, and proximity between faults, which prevented the development of large alluvial fans. The size of the relay zones, only a few hundred meters wide, acted in the same way, avoiding them to act as large sediment transfer areas and large alluvial fans to be established. These features make the Teruel Basin margin different to widely described extensional margins models.

Ichnological analysis of the Cenomanian–Turonian boundary interval in a collapsing slope setting: A case from the Rio Fardes section, southern Spain

The Cenomanian–Turonian Boundary interval (CTB) at the Rio Fardes section (Betic Cordillera, southern Spain) is characterized by pelagic and hemipelagic deposition mixed with mass-flow conglomerates and sandstones. The Rio Fardes section lends itself to high-resolution ichnological analysis of the late Cenomanian Oceanic Anoxic Event (OAE-2) on a collapsing slope affected by gravity-flow sedimentation. The trace fossils include Alcyonidiopsis isp. A., Alcyonidiopsis isp. B., Chondrites intricatus, C. stellaris, C. targionii, Planolites isp., ?Pilichnus isp., Thalassinoides isp., and Trichichnus isp. This ichnoassemblage differs from most CTB sections given the presence of small Alcyonidiopsis isp., Chondrites stellaris, and ?Pilichnus isp., and the absence of Zoophycos. The particular depositional setting, affected by coarse clastic gravity flow sedimentation, may be responsible for these differences by affecting palaeoenvironmental conditions. The lower part of the Rio Fardes section shows a more or less continuous record of diverse and abundant trace fossils, generally produced under aerobic/low dysaerobic conditions. The middle part is characterized by a diminution in trace fossil diversity and abundance, related to moderately/highly? dysaerobic conditions disrupted by short intervals of anoxia. Both the lower and middle parts represent pre-Bonarelli event conditions. The upper part reflects the most significant change in ichnological characteristics. The absence of discernible trace fossils caused by decreasing oxygenation corresponds to the Bonarelli Level. In comparison with previously studied CTB sections, the lower number and thickness of anoxic layers in the Rio Fardes section point to generally better oxygenation on the sea-floor. A variable influence of factors limiting the macrobenthic trace maker community during the OAE-2 can be related to depositional or palaeogeographic contexts. Oxygenated water in the Rio Fardes section was delivered from shallower areas along with gravity-flow deposits. The usually bioturbated background pelagic or hemipelagic deposits above the coarse gravity-flow deposits suggest rapid re-establishment of the macrobenthic trace maker communities following each mass depositional event.

Sedimentology and petrography of the Svenskøya Formation on Hopen, Svalbard: an analogue to sandstone reservoirs in the Realgrunnen Subgroup

On the island of Hopen, in the Svalbard Archipelago, the Svenskøya Formation is a succession 35 m in thickness, consisting primarily of sandstone beds and forming the youngest strata exposed on the island. We present a sedimentological and petrographic study of the formation and compare the unit with its exposures on Wilhelmøya and in Kong Karls Land, Svalbard. We also compare the onshore characteristics of the Svenskøya Formation with those of the Tubåen Formation, its time-equivalent unit in the Sentralbanken area of the northern Barents Sea. On Hopen, the Svenskøya Formation is interpreted as representing coarse clastic sediments deposited in a fluvial to tidal setting, prior to being overlain by a thin interval composed of tidal channel and marine shale deposits. The unit sits atop the regional “Rhaetian Unconformity” and represents sediments deposited during a regressive system that terminates at a flooding surface representing a local transgression of the palaeo-coastline. Petrographic studies show the formation as being arkosic, both on Hopen and in the Sentralbanken area. The reservoir quality of sandstone samples recovered from Hopen is somewhat lower compared to sandstone reservoirs in the Sentralbanken area. We attribute this to greater effects of diagenesis in the Hopen area, which caused increased compaction, mineral dissolution and extensive precipitation of pore-filling clay minerals.