High-energy Currents Research Articles

Evaluating Auroral Forecasts Against Satellite Observations Under Different Levels of Geomagnetic Activity

AbstractThe aurora and associated high energy particles and currents pose a space weather hazard to communication networks and ground‐based infrastructure. Forecasting the location of the auroral oval forms an integral component of daily space weather operations. We evaluate a version of the OVATION‐Prime 2013 auroral forecast model that was implemented for operational use at the UK Met Office Space Weather Operations Cent. Building on our earlier studies, we evaluate the ability of the OVATION‐Prime 2013 model to predict the location of the auroral oval in all latitude and local time sectors under different levels of geomagnetic activity, defined by Kp. We compare the model predictions against auroral boundaries determined from IMAGE FUV data. Our analysis shows that the model performs well at predicting the equatorward extent of the auroral oval, particularly as the equatorward auroral boundary expands to lower latitudes for increasing Kp levels. The model performance is reduced in the high latitude region near the poleward auroral boundary, particularly in the nightside sectors where the model does not accurately capture the expansion and contraction of the polar cap as the open flux content of the magnetosphere changes. For increasing levels of geomagnetic activity (Kp ≥ 3), the performance of the model decreases, with the poleward edge of the auroral oval typically observed at lower latitudes than forecast. As such, the forecast poleward edge of the auroral oval is less reliable during more active and hazardous intervals.

A shallow-water depositional interpretation for the upper Miocene Chagres Formation (Caribbean coast of Panama)

The upper Miocene Chagres Formation, cropping out along the Caribbean coast of Panama, has been previously interpreted as the record of the last deep-water connection between the Caribbean and Pacific oceans based on bodyfossil paleodepth estimates. We test this interpretation by presenting an integrated ichnological and sedimentological analysis on eight coastal localities of the Chagres Formation (Toro Limestone and Chagres Sandstone members). The Toro Limestone Member accumulated under fully marine conditions in a mixed carbonate and siliciclastic marine shelf above storm wave base. Fluctuating high-moderate energy conditions modulated by a combination of tides and high energy currents likely led to the sparse bioturbation of Toro Limestone sediments, corresponding to an archetypal Cruziana ichnofacies assemblage. Bioturbation, dominated by Thalassinoides and Ophiomorpha isp., increases in the overlying Chagres Sandstone Member and corresponds to a proximal expression of the Cruziana ichnofacies. The Chagres Sandstone Member was deposited within the lower shoreface-upper offshore transition zone in a shelf with low sedimentation rates under combined storm, wave, and tidal influence, and includes fossils and sediments of continental origin suggesting proximity to a river mouth. Our results suggest that the Chagres Formation accumulated in shallow waters, contrasting with a previously proposed deep-water accumulation, and are consistent with deposition on a tectonically stable platform of the northern Canal Basin at the apex of the Panama orocline.

Устройства защиты от перенапряжений распределительных электрических систем

Surge protection devices of limiting and combined types used in 0.4 kV electric power distribution networks are described, and results of their experimental studies are presented. The devices have been developed in four earthquake-resistant designs with the use of new-generation nonlinear resistors (varistors) and controlled vacuum arresters. The developed protective devices are intended to limit transient overvoltages, which occur under the influence of man-made, natural and switching electromagnetic pulses, to a safe level, which for the developed design versions of protective devices lies in the range from 1.5 kV to 4.0 kV, and to remove pulses of high-energy currents (up to 500 kJ in a pulse). The article presents the results from studies of the switching characteristics of the developed protective devices in their nominal (multiple) and maximum (single) operation modes, with the measurement of limit voltages at their terminals. The practical effectiveness of using the combined type protective devices is estimated, and the performance characteristics of protection devices from different manufacturers are given.

Observation of nearshore crescentic sandbar formation during storm wave conditions using satellite images and video monitoring data

Crescentic nearshore sandbars (CNSBs) that are observed in the shallow waters (< 10 m) of sandy beaches are important for understanding coastal dynamics because of their strong interaction with nearshore circulation. However, their formation, originating from shore-parallel straight nearshore sandbars (SNSBs), has rarely been observed in the field because their occurrence is typically short (less than a week). In this study, a process in which a nearly SNSB changed into a fully developed CNSB was observed using satellite images, field surveys, and video monitoring data at a sandy beach in South Korea. Freely available Sentinel-2 satellite images and the bathymetry data measured by echosounders were used to find out formation of an SNSB system after attack of Typhoon Tapah in September 2019 and that the SNSB changed to a CNSB in February 2020. The process was narrowed down using video monitoring data and hydrodynamic measurements, observing that two storm waves with maximum wave heights of >3 m developed in the site over a one-month period in January 2020 when the CNSB formed. The first storm wave had a sharp peak wave height that reached ~5 m and lasted ~2 days. The second storm wave had lower wave energy but several peak waves of ~4 m height and a total storm period of ~6 days. During both storm periods, the infragravity wave energy increased and strong (>0.5 m/s) offshore and longshore (northwest) currents developed for ~1 day and ~ 3 days for the first and second storm respectively. The results from video monitoring data show that a nearly developed SNSB system transformed into a weakly developed CNSB system after the first storm when alongshore variability on the nearly SNSB was intensified to become horns and bays of the weak CNSB. During the second storm, the CNSB system fully developed as the horns moved further onshore and the bays further offshore shaping the clear horn and bay pattern. This indicates that positive feedback between the flows and sediments played a key role for the formation of the CNSB and, therefore, the self-organization mechanism might be appropriate to describe the process during the two storm periods. Specifically, the high infragravity wave energy and strong quasi-steady currents were important because they could trigger the development of rip channels during the first storm whereas the channels were further strengthened by the long consistency of currents during the second storm.

Migrated hybrid turbidite-contourite channel-lobe complex of the late Eocene Rovuma Basin, East Africa

Analysis of 3D seismic data and well log data from the Rovuma Basin in East Africa reveals the presence of a late Eocene channel-lobe complex on its slope. The first two channels, denoted as channel-1 and channel-2, are initiated within a topographic low on the slope but come to a premature end when they are blocked by a topographic high in the northwest region of the basin. New channels migrate southeastward from channel-1 to channel-6 due to the region’s sufficient sediment supply and stripping caused by bottom currents. The primary factors controlling the development of the channel complex include its initial paleo-topographic of seafloor, the property of gravity flows, the direction of the bottom current, and the stacking and expansion of its levees. The transition zone from channel to lobe can also be clearly identified from seismic sections by its pond-shaped structure. At a certain point, thest systems record a transiton from erosive features to sedimentary features, and record a transition from a confined environment to an open environment. Channels and lobes can be differentiated by their morphologies: thick slump-debris flows are partly developed under channel sand sheets, whereas these slump-debris flows are not very well developed in lobes. Well log responses also record different characteristics between channels and lobes. The interpreted shale volume throughout the main channel records a box-shaped curve, thereby implying that confined channel complexes record high energy currents and abundant sand supply, whereas the interpreted shale volume throughout the lobe records an upward-fining shape curve, thereby indicating the presence of a reduced-energy current in a relatively open environment. Within the Rovuma Basin of East Africa, the average width of the Rovuma shelf is less than 10 km, the width of the slope is only approximately 40 km, and the slope gradient is 2°–4°. Due to this steep slope gradient, the sand-rich top sheet within the channel also likely contributes to the straight feature of the channel system. It is currently unclear whether the bottom current has any effect on its sinuosity.

Comprehensive assessment of shallow surf zone fish biodiversity requires a combination of sampling methods

Surf zones of sandy beaches are crucial environments for numerous fishes but one of the most challenging habitats when it comes to sampling, due to high-energy currents and waves. In this study, we compared the efficiency of 2 methods currently used to sample the biodiversity of shallow surf zone fish communities: the traditional method of beach seine nets and the more recently introduced surf zone Baited Remote Underwater Video Stations (surf-BRUVS). We applied both sampling strategies at 67 sites along 27 sandy beaches with different environmental characteristics in southeastern Brazil. We compared overall abundance, species richness, and beta (turnover) and functional trait diversity recorded from both methods. Our results showed that seine nets captured a higher species richness, greater abundance, greater functional richness and more functionally singular species than surf-BRUVS, particularly in areas with low wave energy. Beta diversity analyses, however, showed a clear difference in assemblage composition detected by each method regardless of environmental conditions, mainly driven by species turnover and variations in abundance. Only seine nets captured small species (&lt;10 cm total length), while surf-BRUVS were more effective in recording larger species. Our results suggest that shallow surf zone assemblages sampled with surf-BRUVS and beach seine nets are almost totally taxonomically and highly functionally divergent, and the application of both methods provides complementary results. Additionally, the non-extractive nature of surf-BRUVS presents an opportunity for sampling vulnerable areas or species. However, when using a single method, researchers should take into consideration each method’s biases and be aware that biodiversity may be underestimated for certain groups.

Implications for controls on Upper Cambrian microbial build-ups across multiple-scales, Mason County, Central Texas, USA

The morphological architecture and distribution of modern and ancient carbonate systems has been shown to follow spatial-self-organization, however, limited studies describe the morphometrics of microbial carbonates. Upper Cambrian microbial-build-ups outcropping in Central Texas, are exposed laterally (plan view), enabling a study of their morphological architecture and spatial distribution. Drone imagery was acquired to capture the outcrop features and develop a digital terrain model (cm scale resolution) for a bedding plane outcrop (600 × 200 m in size). Four scales of microbial growth (S1- few dm, S2- few m, S3- few tens of m, and S4- few hundreds of m) were identified and mapped. A series of morphometric analysis including Ripley's k, univariate, multivariate, and grouping were conducted and results demonstrate that, the scales S1, S2, and S3 display clustering and the spatial organization of microbial-buildups is naturally organized and not random. Further, as the size of the build-ups increases (from S1–S4), the anisotropy (length/width) increases, their shape becomes oblong, and they become aligned (S2–S4) with the inferred regional winds and tide-associated currents (NE-SW according to the present geography). The S1 scale does not align itself with the regional currents; instead, the build-ups behaved as a baffle during growth, and modified the currents locally, leading to preferential alignment at the edges within S2. As the scales increases in sizes (S2, S3, S4), there is competition for space, and due to regional currents, the larger scales preferentially align parallel to high-energy currents. The trends and spatial relationships identified in this study are particularly relevant and provide a scenario for sub-seismic scale heterogeneities for subsurface microbial hydrocarbon reservoirs.

Beach Nourishment Alternatives for Mitigating Erosion of Ancient Coastal Sites on the Mediterranean Coast of Israel

Since 2011, beach nourishment has become the preferred solution for mitigating coastal erosion along the Mediterranean coast of Israel, as it is considered “soft” and environmentally friendly. However, using fine sand for nourishment in Israel without supporting measures is problematic due to the high wave energy and strong longshore currents in the littoral zone that tend to drift the sand away. This would require ongoing, multiyear, costly, and never-ending maintenance. In the present study, we analyzed sand and pebble alternatives for nourishment of the eroded beach in front of Tel Ashkelon, an important coastal archaeological site in southern Israel that suffers from severe erosion. Based on Pranzini et al. (2018), we analyzed the alternatives, evaluated their cost and efficiency, and assessed their potential environmental impacts. The study concluded that for protecting the southern part of Tel Ashkelon beach, pebble nourishment is the optimal solution, mainly regarding durability and cost. Using this material for nourishment will better absorb the storm wave impact and protect the foot of the archaeological Tel from erosion, and require lower maintenance cost than using finer sand nourishment.

Zoophycos in storm-affected environments: a case study from lower Maastrichtian deposits of the Mateur-Beja area (Northern Tunisia)

The lower Maastrichtian deposits of the Mateur-Beja area in northern Tunisia are mainly composed of fine-grained marl and limestone alternations occasionally interbedded by coarse-grained calcarenites and gravel deposits. In the coarse-grained intervals sedimentary structures are indicative of storm-induced high-energy currents in an outer ramp to slope setting and of local reworking by bottom currents in the basin. In deeper environments, fine-grained sediments accumulated mainly while settling from storm-induced suspensions. The lower Maastrichtian deposits contain abundant Zoophycos exhibiting two main morphotypes, skirt-shaped Zoophycos in deposits around storm-wave base and tongue-shaped Zoophycos in somewhat deeper sediments. The types differ in burrow architecture, morphology of lobes, and size of structural elements. These differences are attributed to different behavioral programs modulated by the availability of benthic food that decreased seaward. Storm-affected environments seem to be a prerequisite for these Zoophycos-producers to choose their habitat.

Mathematical and visual models of asynchronous electric machines energy fields

The research considers the development of topological theory of asynchronous electric machines (AEM). The results of the development of energy aspects of the topological theory are presented in the article. The facts proving the actuality of the research are also given. The central notion giving the topological theory the characteristic of being systematic is the vector space notion. The definition of AEM vector space, its dimension, canonical basis, power and energy field of AEM are presented. Mathematical and visual models of AEM energy fields are analyzed. Energy fields of electric losses and magnetic field dissipation having the spherical symmetry are analyzed in particular. Energy and visual models of the main magnetic field are analyzed using AEM with a short circuited rotor and linear AEM as examples. It is established that this field obtains cylindrical or elliptical symmetry. In general the main magnetic field and the main matrix of winding make AEM vector space fully or partially heterogeneous. Energy efficiency is analyzed and its differences for vector space currents are revealed. The areas of vector spaces with high and low energy currents efficiency are defined. According to this indicator longitudinal and transvers subsets of current having, correspondingly, high and zero energy efficiency are distinguished in the vector space. The description of practical application spheres of AEM topological theory is given.

Influence of climate on the late Pleistocene depositional history of the Gulf of Gemlik (Sea of Marmara)

The late Pleistocene climate-induced water level fluctuations in the Gulf of Gemlik have been first documented in detail by analyses of high-resolution seismic reflection profiles that are tied to radiocarbon-dated sediment cores. In this study, synthetic seismogram for seismic-to-core comparison has enabled a precise correlation between seismic units and core sediments, on which basis it was possible to establish an accurate chronology of the sedimentary successions deposited in the gulf. In the seismic profiles, pre-Holocene depositional units reflect distinctive hydrological and sedimentological processes due to the fluctuating water levels in response to high climate variability. Progressive drop in water level, due to a dry climate phase in the Last Glacial Maximum, is marked by a progradation of a lacustrine delta on the northern shelf of the gulf. Post-glacial warming prior to ca. 18 cal ka BP gave rise to meltwater-driven, high-energy currents on the shelf slopes, producing erosional gullies. The later transgressive freshwater stage of the Gemlik “Lake” began as a result of the meltwater discharge to the gulf basin, which is associated with deposition of the retrograded clinoforms on the shelf margin and infilling the gullies along the slopes. The final post-glacial water level rise in the gulf was mediated by a regressive phase, inferred by seaward-dipping clinoforms and deltaic deposition on the shelf margin. Such a climatic shift to a drier period may coincide with the Heinrich event 1. In the Gulf of Gemlik, transition from the Bolling/Allerod to Younger Dryas periods is recognized by deposition of small clinoform packages on the shelf margin, marking a decrease in water level due to low precipitations on the catchment area. The lake level decrease in the gulf during the YD was modulated by a stillstand, producing a – 65-m erosional terrace and a beach-berm elsewhere along the gulf shelves.

Spatial and temporal distribution of microbial carbonates, skeletal and non-skeletal grains in a Pennsylvanian carbonate platform (Valdorria, Northern Spain)

The Valdorria carbonate platform, in northern Spain, features a well-preserved and continuous outcrop of a Bashkirian platform to basin transect. During the Asatauian (late Bashkirian), the platform growth changed gradually from a progradational to an aggradational mode, recording 10 most likely short-eccentricity-controlled cyclothems. The facies of the platform-top and slope have been mapped, and the architecture of each cyclothem schematically reconstructed. The distribution of microbial carbonates (microbially mediated precipitates), skeletal (grazers/burrowers, corals/filter feeders, algae, foraminifera, Osagia-like oncoids and Thartarella-Terebella worm tubes) and non-skeletal grains (faecal pellets) has been quantified for the transgressive–regressive periods of deposition (transgressive, maximum flooding, early and late regressive intervals) of each cyclothem.This study shows that the distribution of microbial carbonates, skeletal and non-skeletal grains along a carbonate platform transect is variable through time and mainly governed by a set of measurable interconnected factors regulating the local palaeoenvironments: the water depth and the wave energy (facies) along the platform profile (inner, outer, break, slope) during periods of sea-level fluctuations (transgressive to regressive intervals of deposition). Auloporid corals, siliceous sponges, phylloid algae and Osagia-like oncoids are characteristic of a low-energy environment situated from estimated palaeo-water depths of 25 to 80metres below sea level (mbsl onward) that formed in the outer platform during the maximum-flooding intervals. Anthracoporella–Archaeolithoporella boundstone is characteristic of the moderate-energy environments created in the horizontal inner-platform during the transgressive intervals. Microbially mediated precipitates are reliable indicators of the slope and Masloviporidium(?) indicator of low-energy environments of the upper slope. On the platform-top, Ungdarella and Donezella are more abundant during the early regressive intervals than during any other interval. Stacheoids are mainly present in the water depth range of 10 to 60mbsl, tournayellids from 15 to 35mbsl and archaediscids from 15 to 75mbsl, all in low- to moderate-energy conditions. Rugose corals are common in the water depth range of 5 to 35mbsl, either during the transition from the early to the late regressive intervals, as solitary forms or forming boundstone, or during periods of higher sea-level stand, as solitary forms in floatstone. Fenestellids, fistuliporids and trilobites occur mainly in the slope, but are also common in the platform top during the maximum flooding and/or the early regressive intervals. Archaeolithoporella is a reliable indicator of the platform top deposits, but its abundance is closely linked to the presence of adequate substrates. A high abundance in the assemblage of gastropods, endothyrids, palaeotextulariids, bradyinids and fusulinids characterizes the platform top shallow-water coated-grain grainstones formed under high-energy currents during the late regressive intervals. Tetrataxids act as encrusters on microbial precipitates of the slope or on phylloid algae and Archaeolithoporella of the platform top, but are also observed as nuclei of coated grains. Brachiopods are more abundant in low- to moderate-energy and 35 to 55mbsl environments that prevailed during the transgressive intervals. Faecal pellets were commonly observed in low-energy environments, from 50 to 325mbsl, at the platform break and in the slope, and the same applies for Thartarella-Terebella worm tubes that are virtually absent in high-energy deposits. Finally, crinoids, lasiodiscids and tuberitinids are randomly distributed and are not indicative of any specific environment.The here well-constrained distribution patterns of microbial carbonates, skeletal and non-skeletal grains in Valdorria outcrop hold the potential to serve as a reference for interpretation of depositional environments of other platforms using biota associations and depositional texture, particularly in regions where the platform geometry is not preserved or is not fully exposed.

Paleocurrent Analysis of the Sandstone Body in Akpoha and its Enviorns (Lower Benue Trough) South-East Nigeria

Palocurrent analysis study was carried out in Amsiri, Akpoha and its environing in the lower Benue Trough. This study was carried out to determine the direction of ancient flow. Compass/clinometers were used to obtain several measurements from outcrops within the study area. Sedimentary structures were also observed in the study area which includes tabular cross stratification, beddings, herribone structures, asymmetrical ripples and trough cross beds. Asymmetrical ripples and trough cross beds indicates a low energy current. Tabular cross stratifications, herribone structures, where formed by high energy currents. The herribone structures are evidence of different paleocurrent directions as they are formed when current periodically flows in opposite directions. Based on the Rose diagram plot, the paleocurrent direction pointed at two directions; NE direction in location 2 and 3 which are Ameata and Ibii and the NE/SW/NW direction in location 1 which is Akpoha. This however shows that the sediments were derived from two main sources.

Quaternary carbonate deposition and climate variation (Tyrrhenian coast, Calabria, Southern Italy)

A mid-latitude coralgal bioconstruction (Tyrrhenian coast of Calabria, Southern Italy) and associated sedimentary facies record climate and sea-level changes of this coastal area during the Pleistocene. The coralgal bioconstruction, characterized by Cladocora caespitosa bafflestone and red algae bindstone, associated with Spondylus gaederopus sp.-rich boundstone, formed as a result of submergence during Marine Isotope Stage 9 in a moderate shallow-marine environment at a depth of 6 - 20 m. The coast was affected by moderate to high-energy currents and occasional storms; the annual temperature was 12° - 18°C. The lower part of the coralgal body is dominated by Cladocora and the upper part by Lithophylloid algae. The change was likely the result of the occasional influx of coarse clastic material partially buried the C. caespitosa colonies, but provided a suitable substrate for the pioneer encrusting organisms. During a subsequent glacial stage, sea-level fall combined with tectonic uplift induced the partial emergence of the coralgal body, and deposition of an overlying subaerially-deposited breccia. A later resubmergence of the area, likely during the last interglacial period (MIS 5), is recorded as testified by the presence of endolithic microbialites in cavities within the coralgal bioconstruction and the breccia deposit. Microbialite formation took place in a marine environment with cooler water, with respect to the previous submergence phase, possibly during a time of early deglaciation. The low temperature, possibly combined with very shallow depths and an excess of nutrients, could have played a role in preventing further growth of C. caespitosa while favouring the precipitation of microbial carbonate.

Mid-latitude coralgal bioconstruction and endolithic microbialites: environmental significance during Quaternary climate variations

A mid-latitude coralgal bioconstruction (Tyrrhenian coast of Calabria, southern Italy) and associated sedimentary facies record climate and sea-level changes of this coastal area during the Pleistocene. The coralgal bioconstruction, characterized by Cladocora caespitosa bafflestone and red algae bindstone, associated with Spondylus gaederopus sp.-rich boundstone, formed as a result of submergence during Marine Isotope Stage 9 in a moderate shallow-marine environment at a depth of 6–20 m. The coast was affected by moderate to high-energy currents and occasional storms; the annual temperature was 12–18 °C. The lower part of the coralgal body is dominated by Cladocora and the upper part by Lithophylloid algae. The change was likely the result of the occasional influx of coarse clastic material partially buried the C. caespitosa colonies, but provided a suitable substrate for the pioneer encrusting organisms. During a subsequent glacial stage, sea-level fall combined with tectonic uplift induced the partial emergence of the coralgal body, and deposition of an overlying subaerial deposited breccia. A later resubmergence of the area, likely during the last interglacial period (MIS 5), is recorded as testified by the presence of endolithic microbialites in cavities within the coralgal bioconstruction and the breccia deposit. Microbialite formation took place in a marine environment with cooler water, with respect to the previous submergence phase, possibly during a time of early deglaciation. The low temperature, possibly combined with very shallow depths and an excess of nutrients, could have played a role in preventing further growth of C. caespitosa while favoring the precipitation of microbial carbonate.

Regional tectonic control on large size explosive eruptions: Insights into the Green Tuff ignimbrite unit of Pantelleria

Original geological and structural data, which derive from the analysis of the rheomorphic Green Tuff ignimbrite unit of Pantelleria, have offered the opportunity to define its modes of emplacement and the location of the eruptive sources in terms of distribution and geometry. The Green Tuff displays a wide range of rheomorphic structures consisting of preserved penetrative foliations, lineations and folds which, developed at distinct times, have been assigned to three major (D1–D3) deformation events accompanying and following the ignimbrite unit emplacement. The first D1 event produced distinct sets of structures developed along ductile shear zones generated during the emplacement of pyroclastic density currents along current-deposit boundaries. Palaeoflow directions of this event are completely independent from topography and are directly related to high-energy currents generated from the eruption. D2 event is characterized by folding due to down-slope post-emplacement flows related to gravity sliding processes whereas the D3 event was dominated by semi-brittle to brittle structures developed after the complete emplacement of the flow units and their subsequent cooling and compaction. The statistical analysis of these structural data has led to the hypothesis that the Green Tuff eruption developed from fissural sources that are largely superimposed on the NNE-trending dip-slip normal fault zones of the island (the Zinedi and the Montagna Grande faults). Our model also implies that the Green Tuff ignimbrite deposit can be the result of several events within a single eruptive cycle. The orientation of the fissural eruptive systems is evidence that the feeding structures for this large-size explosive event were strongly controlled by the E-W to ESE-WNW directed extension structures that affect the island of Pantelleria and, as a whole, the entire region of the Sicily Channel.

Tectonics of the Strandja Massif, NW Turkey: History of a Long-Lived Arc at the Northern Margin of Palaeo-Tethys

The Strandja Massif, Thrace Peninsula, NW Turkey, forms an important link between the Balkan Zone of Bulgaria, which is usually correlated with Variscan orogen in Central Europe, and the Pontides, where Cimmerian structures are the most prominent. The massif is composed of a Palaeozoic basement and a Triassic metasedimentary cover. The basement is made of various granite gneisses, paragneisses, and schists that are intruded by large plutons of monzonitic metagranites. Detrital zircon studies have revealed Ordovician (433 and 446 Ma) and Carboniferous (305 Ma) ages of the metasedimentary rocks. The isotopic age of the granite gneisses is 308-315 Ma (Carboniferous, Bashkirian-Moscovian) as single zircon evaporation method and conventional U-Pb technique show. The Palaeozoic basement was deformed and metamorphosed before the emplacement of the large monzonitic metagranite plutons yielding zircon ages from 309±24 to 257 Ma (Moscovian-Permian). Geochemical features of the Carboniferous and Permian magmatic rocks indicate a subduction-related tectonic setting similar to coeval rocks exposed in the Balkan zone of Bulgaria. The Triassic metasedimentary cover unconformably overlies the basement with basal conglomerate and arkosic sandstone that pass upward into a thick pile of lithic metasandstones and a metasandstone/pelitic schist alternation. Calcareous metasandstones and black slates appear at the highest structural levels. The Triassic succession reveals obvious orogenic features judged from its great thickness, sedimentary features indicating high-energy currents and the presence of intermediate pillow lavas. Both the basement and the cover units were affected by strong deformation and epidote-amphibolite to greenschist facies metamorphism during the Late Jurassic-Early Cretaceous. This event was terminated by the emplacement of a nappe of unmetamorphosed Jurassic limestones and dolomites occurring at the top of the structural column. Kinematic indicators in mylonites at the base of the nappe suggest its original location in the south. The Strandja Massif shows remarkable similarity to the late Palaeozoic-early Mesozoic Silk Road arc that evolved at the southern margin of Eurasia due to the northward subduction of Palaeo-Tethys (Natal'in & Şengör 2005). The fragments of this arc are exposed in Caucasus, Iran, South Tien Shan, Pamir, and Kunlun. The Precambrian history of the Strandja Massif, as recorded by detrital and inherited zircon ages, reveals many common features with the Baltica-Timanide collage including its fragments distributed in Central Asia. Various sets of data and correlations with surrounding tectonic units show that the Strandja Massif is a fragment of the long-lived, Ordovician to Triassic Silk Road magmatic arc, which evolved on the

Geology and chronology of the continental Pleistocene archeological and paleontological sites of the Orce area (Baza basin, Spain)

The Guadix-Baza Basin hosts a continuous continental record of paleoenvironmental, paleobiological and geological changes from around 8 Ma to 205 ka. A remarkable succession of Pleistocene mammal sites is found in the Lower and Upper members of the Baza Formation in the Orce area. The Upper Member contains the Early Pleistocene paleontological and archeological sites of Barranco León-5 and Fuente Nueva 3. Both sites belong to the early Pleistocene zone defined by Allophaiomys aff. lavocati and a small Mimomys savini. This zone can be correlated with that of central Europe containing Mimomys savini and Microtus praehintoni. These sites are located in the marginal lacustrine deposits of the Baza lake system and originated in expanded phases of the main lake when meteoric surface and shallow groundwater inputs were predominant. The Barranco León-5 site is related to a sudden event of high-energy currents entering a lacustrine - palustrine domain. These currents transported gravels, bones and lithic industries from a short distance (maximum, hundreds of meters). In contrast, the diverse levels in Fuente Nueva 3 do not show evidence of noticeable transport by traction currents. The age of the mammal succession and sites is based on magnetostratigraphy. In the Middle and Upper members of the Baza Formation, only reversed polarities are found (Matuyama epoch). The location of the Olduvai chron is still unclear and could have not been recorded due to the common hiatuses observed in the sedimentary successions. In the Lower Member, normal and reverse polarities (Gauss epoch) are found in the Galera and Vélez-Salar sections. The later contains the site of Fuente Nueva 1, which is pre-Olduvai chron in age according to paleontological data and biostratigraphic correlation.

Large‐scale sediment bodies and superimposed bedforms on the continental shelf close to the Strait of Gibraltar: interplay of complex oceanographic conditions and physiographic constraints

AbstractA previously unknown field of large‐scale sedimentary bodies has been mapped and studied on the continental shelf off the Cape Trafalgar near the Strait of Gibraltar with particular emphasis on the relationship between large‐scale sediment bodies and the superimposed bedforms. This study is based on a grid of 975 km of high‐resolution seismic profiles collected at water depths ranging between 15 and 60 m.High variability of large‐scale sedimentary bodies is attributed to the complex interaction of hydrodynamic agents. The most prominent sedimentary features are sand banks and ridges that indicate long‐term southwest and southward‐directed sediment transport patterns, possibly due to the interplay of two dominant current systems flowing southward and westward. These sediment bodies evolve laterally to distinct external geometries, such as sand shoals in shallow water and sand sheets in the vicinity of larger sand banks that indicate moderate current velocities. In addition, pre‐existing physiography is considered to play a role in the generation of certain sediment bodies, developed over inclined surfaces or confined laterally by elevations.Relationships between superimposed bedforms (mostly very large dunes) and underlying sediment bodies vary across the study area. Most superimposed bedforms occur over the complex mosaic of sediment banks and sheets, suggesting the interaction of several high‐energy currents with different directions, such as tidal and/or wind‐driven currents. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Microbial mat mediated structures in the Ediacaran Sonia Sandstone, Rajasthan, India, and their implications for proterozoic sedimentation

A strong influence of microbial mats on the physics of Neoproterozoic sedimentation is explored within a 60 m-thick stratigraphic interval within the Sonia Sandstone, Jodhpur Group, western India. This marine interval is bounded by two terrestrial units, its base being marked by a transgressive lag and the top by an unconformity. Progradation from upper neritic, above fair-weather wave base to supralittoral settings was later terminated by a transgression; deposits of lower shoreface-upper shoreface transition thus overlie supralittoral aeolian sandstones, the basal contact of the former deposits being marked by another transgressive lag. A wide spectrum and abundant examples of microbial mat or mat-derived structures supports unusual cohesiveness within granular sand deposited in a high-energy marine environment. The cohesiveness is manifested in abundant preservation of several delicate primary structures and also in their replication in overlying beds, even after they were subjected to high-energy currents. A low rate of sedimentation and severely restricted sediment reworking resulted from prolific mat growth, and consequent depletion in the sediment budget was manifested in bedform migration and evolution. These factors could also have influenced the sequence-building pattern in a distinctive way, as is already reported from several Meso- and Neoproterozoic successions. Ubiquitous mat growth thus had the potential to impart significant distinctions to Proterozoic clastic sedimentary successions.