Set Of Wedges Research Articles

On the acoustic wedge absorber design in underwater and its interior pressure computation in a chamber

This study presents a design of wedged shape absorber used in underwater in range of high frequency. The analysis of a set of periodical wedges, where each wedge is oriented 90 deg with other wedges. The set of periodical wedges is analyzed using finite element methods as a 3-D virtual impedance tube. The incident wave is on the normal direction of the tube. This 3-D model is able to simplify to a simple 2-D model and a two-point transfer function method is employed to compute reflection coefficient. The ation of frequencies higher than the cut-off plane wave frequency is addressed of that higher duct acoustic modes are excited by the wedge. These higher modes are recognized as stationary non-propagating waves, not contributing reflected waves away from the wedge. An impedance value associated with the reflection coefficient is identified based on plane wave condition. The impedance value is applied to surfaces of a closed space to computed interior pressures.

Foot kinematics as a function of ground orientation and weightbearing.

The foot is responsible for the bodyweight transfer to the ground, while adapting to different terrains and activities. Despite this fundamental role, the knowledge about the foot bone intrinsic kinematics is still limited. The aim of the study is to provide a quantitative and systematic description of the kinematics of all bones in the foot, considering the full range of dorsi/plantar flexion and pronation/supination of the foot, both in weightbearing and nonweightbearing conditions. Bone kinematics was accurately reconstructed for three specimens from a series of computed tomography scans taken in weightbearing configuration. The ground inclination was imposed through a set of wedges, varying the foot orientation both in the sagittal and coronal planes; the donor body-weight was applied or removed by a cable-rig. A total of 32 scans for each foot were acquired and segmented. Bone kinematics was expressed in terms of anatomical reference systems optimized for the foot kinematic description. Results agree with previous literature where available. However, our analysis reveals that bones such as calcaneus, navicular, intermediate cuneiform, fourth and fifth metatarsal move more during foot pronation than flexion. Weightbearing significantly increase the range of motion of almost all the bone. Cuneiform and metatarsal move more due to weightbearing than in response to ground inclination, showing their role in the load-acceptance phase. The data here reported represent a step toward a deeper understanding of the foot behavior, that may help in the definition of better treatment and medical devices, as well as new biomechanical model of the foot.

Improving Hospital-Acquired Pressure Injury Outcomes by Overcoming Barriers to Implementing Patient Positioning Devices.

Improving Hospital-Acquired Pressure Injury Outcomes by Overcoming Barriers to Implementing Patient Positioning Devices.

In situ areal mass measurement of laser shock-loaded aluminum using point-projection x-ray backlighting.

X-ray backlighting is been widely used today in dynamic phenomena observation. By applying proper synchronizing techniques, the in-situ data of the intensity distribution of the fragments in laser-driven shock-loaded aluminum were obtained for a particular moment using x-ray backlighting imaging. The image resolution was better than 40 µm in this context by introducing a pinhole. In order to obtain the areal mass of the fragments, a set of reference Al step wedges with certain thicknesses was employed. Furthermore, a novel, to the best of our knowledge, calibration method is introduced to calibrate the x-ray intensity distribution. It was effective to decrease the non-uniformity influence of the x-ray intensity with this calibration method by simulating a light field. After calibration, the standard deviation of 30 regions of interest reduced to 4.17%. In consequence, the areal mass distribution of the fragments is well quantified. It should be noted that the uncertainty in the areal mass conversion mainly comes from the non-uniformity of the x-ray intensity distribution with about 5% and the measurement uncertainty of the step thicknesses with less than 10%.

Fixed Point Sets of Digital Curves and Digital Surfaces

Given a digital image (or digital object) (X,k), we address some unsolved problems related to the study of fixed point sets of k-continuous self-maps of (X,k) from the viewpoints of digital curve and digital surface theory. Consider two simple closed k-curves with li elements in Zn, i∈{1,2},l1⪈l2≥4. After initially formulating an alignment of fixed point sets of a digital wedge of these curves, we prove that perfectness of it depends on the numbers li,i∈{1,2}, instead of the k-adjacency. Furthermore, given digital k-surfaces, we also study an alignment of fixed point sets of digital k-surfaces and digital wedges of them. Finally, given a digital image which is not perfect, we explore a certain condition that makes it perfect. In this paper, each digital image (X,k) is assumed to be k-connected and X♯≥2 unless stated otherwise.

Laser shadowgraphy and Mach-Zehnder interferometric imaging of convection, concentration and growth kinetics during unidirectional solution growth of benzophenone crystal

Fluid convection and concentration during unidirectional growth of benzophenone crystal were imaged in an online and in-situ manner using optical techniques of laser shadowgraphy and Mach-Zehnder (MZ) interferometry. The fluid dynamic behavior of the plumes, the frequency of their appearance and the number of plumes provide information about the crystal growth mechanism and also growth rates as a function of supersaturation. Comparing the images captured using above techniques, it was found that shadowgraphy was most appropriate to visualize the convective field. It was used to image the life cycle of convection plume starting from its birth at the crystal surface to its diffusion in to the bulk of the solution. Comparative analysis of the images grabbed using different type of imaging techniques reveal that MZ infinite fringe technique is best suitable for visualizing the concentration gradient. This is followed by MZ horizontal wedge setting and then MZ vertical wedge setting fringes. The shadowgraph technique is not able to discern the concentration gradient as clearly as seen in the MZ images. The solutal boundary layer (SBL) was better visualized using shadowgraphy as compared to Mach-Zehnder interferometry. The thickness of SBL was an indicator of the relative growth kinetics. It is demonstrated that by choosing appropriate optical technique, one can monitor as well as control the growth process to achieve the desired results.

Provenance of upper Permian-lowermost Triassic sandstones, Wutonggou low-order cycle, Bogda Mountains, NW China: implications on the unroofing history of the Eastern North Tianshan Suture

This study investigates the provenance of sedimentary rocks in Bogda Mountains, NW China, and reconstructs the lithology and unroofing history of the Eastern North Tianshan Suture. Petrographic point counting data of sandstones and compositions of conglomerates of upper Permian-lowermost Triassic Wutonggou low-order cycle from Zhaobishan, North Tarlong, Taodonggou, and Dalongkou sections in the southern and northern foothills of Bogda Mountains were used to interpret the temporal and spatial variations of lithology of the Eastern North Tianshan Suture, which is the sediment source area. Three compositional trends were identified. A trend of upward-increasing quartz content and granitic pebbles in Zhaobishan section suggests a change from the undissected volcanic arc, accretionary wedge and trench setting to predominantly transitional volcanic arc and subordinate accretionary wedge and trench, in the eastern part of the Eastern North Tianshan Suture. In North Tarlong and Taodonggou sections, however, the lithic content decreases and the contents of quartz and granitic pebbles increase up sections. These trends indicate that the western part of the Eastern North Tianshan Suture changed from an undissected volcanic arc to the transitional volcanic arc, accretionary wedge and trench. No clear trend in the lithic-rich sandstones of the Dalongkou section indicates that sediments were derived from the undissected volcanic arc in the Eastern North Tianshan Suture and local rift shoulders. Compositional variations of studied rocks suggest that the Eastern North Tianshan Suture was an amalgamated complex with great spatial and temporal heterogeneities in lithology and experienced persistent unroofing during late Permian-earliest Triassic. This study reconstructs a key element of the Chinese Tianshan Suture and serves as an example to understand the unroofing processes of ancient sutures.

Petrology of a Neoproterozoic mantle peridotite–chromitite association from Abu Dahr area, Eastern Desert, Egypt: Infiltration of a boninitic melt in highly depleted harzburgite

Peridotites of Abu Dahr represent the main litho–unit of a Neoproterozoic dismembered ophiolite sequence and are among the best–preserved and well–exposed mantle rocks in South Eastern Desert of Egypt. Here, we present new geochemical and mineral chemical data for peridotites and associated pyroxenites and for chromitites and their platinum–group minerals to constrain their petrogenesis and geotectonic setting. The Abu Dahr ophiolite mantle section consists mainly of harzburgites, cut by pyroxenite dykes and containing dunite–chromitite lenses. The harzburgites are composed of olivine, orthopyroxene, spinel and minor clinopyroxene (˂1.0 vol %) and amphibole. Olivine from harzburgites is highly magnesian (Fo 91–93) and Cr–spinel shows a wide–range of Cr2O3 and Al2O3 contents. The enstatite component of orthopyroxene decreases from harzburgite (En = 90–91) to orthopyroxenite (En = 84–87). Amphiboles are represented by magnesiohornblende and tschermakite. The chromitites are massive to disseminated and composed of magnesiochromite with high Cr# (83–93) and Mg# (66–79), and low TiO2 (<0.1 wt%) content. Solid inclusions in chromite include olivine, orthopyroxene and hornblende. Laurite (RuS2) is the most common PGM detected in the investigated chromitite samples and forms micrometer–size inclusions in fresh chromite. Various Ni–sulfides are found both in fresh chromite and along serpentine veinlets. Harzburgites have a refractory composition with a very low Al2O3 (0.4–0.8 wt%) and CaO (0.2–1.6 wt%) contents and high bulk–rock Mg# (89–92). Geochemical data suggest that the Abu Dahr peridotites are highly depleted SSZ peridotites formed in a forearc mantle wedge setting by high degrees of hydrous partial melting and emplaced as a result of the collision of the intra–oceanic arc with the Beitan gneisses. The podiform chromitites and orthopyroxenites were formed due to impregnation of mantle wedge harzburgites by boninitic melt. The highly depleted nature of the harzburgite is responsible for the small reserves of chromite ore at Abu Dahr and in the South Eastern Desert in general.

Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area, South Eastern Desert, Egypt: constraints from their mineralogical and geochemical characteristics

Petrological and geochemical studies of Neoproterozoic metagabbros were carried out in the Muiswirab area, South Eastern Desert of Egypt. The Muiswirab area comprises of ophiolitic metagabbroic rocks (MOM), which are tectonically thrusted over a thick pile of metavolcanic rocks and intruded by syn- and post-tectonic granitoid rocks. The whole-rock geochemical variations coupled with chemical compositions of mineral constituents are used to attain the genesis and tectonic evolution of the studied metagabbros. The geothermobarometric investigation of the analyzed amphiboles from (MOM) revealed that these metagabbros underwent regional metamorphism under lower to upper greenschist facies (biotite zone) conditions (at a temperature of 450 to 500 °C and pressure of 1–3 kbar). Geochemically, the metagabbros (MOM) show tholeiitic affinity and exhibiting both arc- and MORB- like characters as evidenced by their clinopyroxene compositions and the Ti/V ratios (11.84–31.65), which considered as prominent features of forearc tectonic regime. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The parental magma of the investigated MOM rocks seems to be developed in a sub-arc mantle wedge setting due to the enrichments of LILE (e.g., Rb, Ba, Sr, Pb) over HFSE (e.g., Ti, Nb, Y, Zr, Hf, Ta). The studied MOM rocks have lower values of Nb/U relative to MORB and OIB indicating that their geochemical variation produced due to the enrichment of a lithosphere mantle by OIB-like components. The ratios of Zn/Fet, La/Sm, Sm/Yb, Th/Yb and Nb/Yb indicate that the MOM rocks represent a fragment of oceanic crust originated at a supra-subduction zone environment and their parental magma developed by 5–30 % partial melting of a spinel lherzolite mantle rather than pyroxenite in an island arc setting and conformable with most of the Egyptian ophiolitic metagabbros.

Experimental study on water entry of twin wedges

This article presents an experimental study on the water entry of twin wedges commonly used as sections of catamaran craft. A twin wedge is a combination of two single asymmetry wedges connected by so-called wet-deck. The single asymmetry wedge has a vertical side and a non-vertical side with a range of deadrise angles. This study is carried out on a set of twin wedges of 7°, 15° and 20° deadrise angles. For calibrating the experimental equipment, the twin wedges symmetric quality, tank depth effect, three-dimensional effect, repeatability and sampling rate effects are examined. The water entry experiments are conducted through a drop test method. Time histories of impact pressure are recorded for different deadrise angles, drop heights and space between two single wedges. The results show that the effect of space on the peak pressure is negligible. In water entry experiment, the pressure on the non-vertical side of an asymmetry wedge is considerably lower than that on the equivalent symmetry wedge. The vertical side of an asymmetry wedge is under the effect of air entrapment. It has much less pressure than the non-vertical side.

Neoproterozoic magmatism in the northern margin of the Yangtze Block, China: Implications for slab rollback in a subduction-related setting

The South Qinling Belt was located in the northern part of the Yangtze Block during the Neoproterozoic. Here we investigate two major magmatic intrusions in the northern and southern part of the belt, the Douling plutons (DLP) and the Fenghuangshan plutons (FHSP), to gain insights into the Neoproterozoic tectonic processes along the northern segment of the Yangtze Block. Zircon grains in the DLP yield weighted mean 206Pb/238U ages of 750–709 Ma, whereas those from the FHSP show ages of 749–728 Ma. The new results, together with the published data, reveal that these plutons were emplaced at ca. 759–685 Ma and ca. 802–704 Ma, respectively. Geochemically, the intermediate-felsic rocks from the DLP and FHSP show enrichment of light rare earth elements (LREE) and large-ion lithophile elements (LILE) (Rb, Ba and K), depletion of high field strength elements (HFSE) (Nb, Ta, P and Ti), and low Sr/Y and (La/Yb)N values, which are typical features of arc magmatic rocks. The gabbros from the FHSP have high Mg#, and display LREE and LILE (Rb, Ba, K, and Sr) enrichment and depletion of HFSE (Th, U, Nb, Ta, and Ti), suggesting that they were probably formed in a mantle wedge setting. Both DLP and FHSP show arc-related geochemistry modified by slab-derived fluids, and were formed at relatively high-temperature and low-pressure conditions. However, they display distinct Sr-Nd-Hf isotopic compositions. Zircon grains of two samples from the DLP respectively show mean εHf(t) values of −2.6 ± 0.3 and 0.9 ± 0.3, whereas zircon grains of four samples from the FHSP show mean εHf(t) values ranging from 7.5 ± 0.5 to 8.7 ± 0.4. The DLP shows dominantly negative εNd(t) values and inconsistent initial 87Sr/86Sr ratios, whereas FHSP shows relatively constant and positive εNd(t) values (3.69–3.74) but variable initial 87Sr/86Sr ratios. The Sr-Nd-Hf isotopic and geochemical features suggest that the enriched mantle and crustal materials were involved in the magma evolution of the DLP, whereas the FHSP is characterized by significant juvenile components with a rising asthenospheric mantle source playing a key role. We propose a subduction-related setting for these intrusions, and envisage slab rollback during the Neoproterozoic.

Late Carboniferous (Kasimovian) closure of the South Tianshan Ocean: No Triassic subduction

The proposed Triassic age of oceanic subduction and high-pressure/low-temperature (HP-LT) metamorphism in the South Tianshan orogen (STS) of the southwestern Central Asian Orogenic Belt needs to be re-examined on the basis of field relationship and precise age dating. Our biostratigraphic study in the Atbashi Range of southern Kyrgyzstan indicates that sedimentary strata unconformably overlie the HP-LT metamorphic rocks within the Turkestan suture zone and have a late Kasimovian (ca. 305 Ma) age. This constrains the minimum age of eclogite metamorphism in the HP-LT metamorphic complex. A Late Pennsylvanian to early Permian (Asselian) hinterland basin overlaps the margins of the Middle and South Tianshan and the ophiolitic suture between them, thus leaving no space for an oceanic basin in the northern STS in the late Permian or Triassic. In the south, overlap assemblages stitching the STS with the Tarim Craton consist of late Asselian to early Sakmarian limestones and early Permian rhyolites. Early Permian (ca. 295–265 Ma) post-collisional A-type granites and sub-alkaline plutons are widespread in the STS and are not affected by thrust deformation. These facts indicate that thrust packages of the STS were stacked together and welded to the margin of the Tarim Craton by the early Permian. The widespread occurrence of early Permian sub-alkaline granites is also not compatible with an oceanic accretionary wedge setting in the STS during the Permian or Triassic.Permian and Triassic zircon ages for subduction-related HP-LT metamorphic rocks and ophiolitic gabbro from the Atbashi and Djandjir ranges reported in two recent papers contradict geological relationships. A review of reported analytical data shows that anomalously young ages in all studied samples are based on geologically meaningless single zircon analyses and/or discordant data, which cannot be used for age calculation. The suggestion that an oceanic basin in the STS remained open and subduction continued until the Middle Triassic is erroneous because of insufficient consideration of basic regional geological relationships and incorrect interpretations of analytical results.

Shale-related minibasins atop a massive olistostrome in an active accretionary wedge setting: Two-dimensional numerical modeling applied to the Iranian Makran

Financial support was provided by the Swiss National Science Foundation (grants 2-77644-09 and 2-77297-15).

Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau

The Bayan Har Orogen comprises a major part of the “Qingzang-Dianxi fold region” in western China. It preserves important information of the tectono-thermal evolution covering the time span from the closure of the Paleo-Tethys Ocean up to the formation of the Himalayas. Low temperature metamorphic indicators, such as mineral assemblages, illite “crystallinity” (IC), chlorite “crystallinity” (CC), illite polytype, b-cell dimension of K-white micas, geothermometry of selected minerals were analyzed. The values of Kübler index (KI) of the Triassic flysch in the Bayan Har Orogen range from 0.23–1.63°Δ2θ while Árkai index (ÁI) in a range of 0.21–0.60°Δ2θ. Iso-thermal zones mapped with KI describe a pair of anchizones and an anchiregion within the Bayan Har Orogen: the “Giant Yushu Anchizone” in the southwest (extending >750km long and 100km wide), the “Zaling-Eling-Lakes Anchizone” in the center (about 150km long and 40km wide) and the “Xing-Tong-Zhe Anchiregion” in the northeast (covering an area of roughly 60,000km2). They are separated by diagenetic zones. Peak metamorphic conditions are estimated around 280–330°C and a low to intermediate (N. New Hampshire) pressure type. A slight change with increasing then decreasing pressure was observed from SW to NE. The relationship between anchimetamorphic pattern of Triassic flysch and large-scale folds and faults indicates syn- to post structural metamorphism. Compression at the end of the Triassic, induced by the interaction of the Tarim, North China and Indian blocks caused the closure of the Paleo-Tethys Ocean and led to the folding of the Triassic flysch within the Paleo-Tethys Ocean basin. Anchimetamorphism may have been caused by crustal thickening of >10km due to an accretionary wedge setting and a temperature increase in those rocks due to burial. Such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic-palaeogeograph and the evolutionary history of Tibetan plateau.

Abyssal and hydrated mantle wedge serpentinised peridotites: a comparison of the 15$$^\circ$$20$$'$$N fracture zone and New Caledonia serpentinites

Subduction of serpentinised mantle transfers oxidised and hydrated mantle lithosphere into the Earth, with consequences for the oxidation state of sub-arc mantle and the genesis of arc-related ore deposits. The role of subducted serpentinised mantle lithosphere in earth system processes is uncertain because subduction fluxes are poorly constrained. Most subducted serpentinised mantle is serpentinised on the ocean floor settings. Yet this material is poorly represented in the literature because it is difficult to access. Large volumes of accessible serpentinite are available in ophiolite complexes, and most interpretations of subduction fluxes associated with ultramafic rocks are based on ophiolite studies. Seafloor and ophiolite serpentinisation can occur under different conditions, so it is necessary to assess if ophiolite serpentinites are a good proxy for seafloor serpentinites. Serpentinites sampled during ODP cruise 209 were compared with serpentinites from New Caledonia. The ODP209 serpentinites were serpentinised by modified seawater in a shallow hydrothermal seafloor setting. The New Caledonia serpentinites were serpentinised in a mantle wedge setting by slab-derived fluids, with possible contributions from oceanic serpentinisation and post-obduction serpentinisation. Petrological, whole rock and mineralogical analyses were combined to compare the two sample sets. Petrologically, the evolution of serpentinisation was close to identical in the two environments. However, more oxidised iron, Cl, S and C is present in serpentine from the ODP209 serpentinites relative to the New Caledonia serpentinites. Given these observations, the use of serpentinites from different geodynamic settings as a proxy for abyssal serpentinites from spreading settings must be undertaken with caution.

IDENTIFICATION OF FRICTION CONDITIONS IN HUMAN JOINTS

The purpose of the paper is to explain the friction conditions and the lubrication mechanism in healthy joints, based on rheological tests of synovial fluid and the identification of structures and the shape of articular surfaces. The tests were performed on cadaver preparations of large lower limp joints: hip, knee, and ankle joints. The analysis included combined experimental activities with the use of modern research and test techniques in the area of viscosity and microscopy as well as diagnostic imaging, image analysis, modelling, and FEM simulation. The tests performed allowed for the analysis of lubrication process which can be described as bioelastohydrodynamic lubrication (BEHL). The most important are viscoelasticity properties of the synovial fluid and the process whereby the external load is taken over by the pressure generated by a set of oil wedges of synovial fluid formed by naturally wavy articular surface. The multi-layer structure of the joints is characterised by variable wavy shape of cartilaginous surfaces and of bone tissue and by the variable wavy thickness of the cartilage.

WITHDRAWN: Submarine depositional terraces in the Tyrrhenian Sea as a proxy for paleo-sea level reconstruction: Problems and perspective

Abstract In the last decade great effort was put in the study of relative sea-level changes on Mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo-shorelines. In this paper, we show potential and limitations of using additional marine geomorphic/sedimentary markers for earlier and lower sea levels. These markers are submarine depositional terraces (SDTs), i.e., deposits formed by a set of small prograding sedimentary wedges, having a terraced shape and found at variable shallow-water depths (mainly the first −150 m) on continental and insular shelves in the Tyrrhenian Sea. The shallowest terraces (near-shore) have their edges at depths between −10 m and −30 m, approximating the modern, local storm-wave base level. Their formation is thought to be associated with the modern sea-level highstand and thus, can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf. Mid-shelf terraces have their edges at variable depths between −40 m and −90 m and probably formed during the last sea-level rise. They show a patchy spatial distribution and a large variability in their internal structure, so that they are not suitable for correlation on a regional scale. Shelf-edge terraces have their edges at depths between −120 m and −170 m, which is close or deeper than the Last Glacial Maximum (LGM) sea-level stand. They show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and, thus, represent a proxy for the sea-level position at around 20 ka. However, the position of SDTs' edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors, such as the base of the storm wave and its variation in response to coastal physiography, as well as the occurrence of subsequent erosional or depositional processes. Depending on the geophysical and mapping methods used to determine their depth, the associated error range can also differ. Based on the analysis of these complexities and a wide range of physiographic settings of the Tyrrhenian Sea, we discuss these error ranges in order to assess potential and limitation of the SDT for analyses of vertical mobility of an area.

Calculation model of technological process of soil crumbling by means of tillage working organs

Working organs being used currently for subsurface tillage do not comply with agrotechnical requirements. In particular, the crumbling of soil layer is unequal across the width of cutting plane of working organ. The scientific hypothesis is that variable cutting angle along the length of blade improves the crumbling of soil layer. The mathematical model of interaction between the soil and a wedge is proposed. As the result, the theoretical dependencies of resistance force of soil to destruction and of thickness of shear layer on the setting angle of tillage tool are obtained. A set of dihedral wedges with different angles of inclination has been used in experimental studies. The tests have been performed in media with a wide range of physical and mechanical properties (ordinary humus, sand, clay). It is determined experimentally that all media interacting with the wedge have some common characteristics depending on the parameters of wedge, in spite of differences of physical and mechanical properties and the appearance of layer formation. The experimental dependence of equivalent stresses on cutting angle of the wedge is obtained. Experimental and theoretical results agree well with each other. On the basis of these studies, the working organs with variable cutting angle are developed. It is revealed that the blade with variable cutting angle creates more tension in the soil layer than a blade with constant cutting angle. It is experimentally confirmed that the working organs with variable cutting angle along the length of the coulter crumble the layer by 20-50% better than serial working organs. The economic effect of the introduction of working organs with variable cutting angle is 200-1300 rubles per hectare of cultivated area.

Submarine depositional terraces in the Tyrrhenian Sea as a proxy for paleo-sea level reconstruction: Problems and perspective

In the last decade great effort was put in the study of relative sea-level changes on Mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo-shorelines. In this paper, we show potential and limitations of using additional marine geomorphic/sedimentary markers for earlier and lower sea levels. These markers are submarine depositional terraces (SDTs), i.e., deposits formed by a set of small prograding sedimentary wedges, having a terraced shape and found at variable shallow-water depths (mainly the first −150 m) on continental and insular shelves in the Tyrrhenian Sea. The shallowest terraces (near-shore) have their edges at depths between −10 m and −30 m, approximating the modern, local storm-wave base level. Their formation is thought to be associated with the modern sea-level highstand and thus, can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf. Mid-shelf terraces have their edges at variable depths between −40 m and −90 m and probably formed during the last sea-level rise. They show a patchy spatial distribution and a large variability in their internal structure, so that they are not suitable for correlation on a regional scale. Shelf-edge terraces have their edges at depths between −120 m and −170 m, which is close or deeper than the Last Glacial Maximum (LGM) sea-level stand. They show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and, thus, represent a proxy for the sea-level position at around 20 ka. However, the position of SDTs' edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors, such as the base of the storm wave and its variation in response to coastal physiography, as well as the occurrence of subsequent erosional or depositional processes. Depending on the geophysical and mapping methods used to determine their depth, the associated error range can also differ. Based on the analysis of these complexities and a wide range of physiographic settings of the Tyrrhenian Sea, we discuss these error ranges in order to assess potential and limitation of the SDT for analyses of vertical mobility of an area.

Earth's oldest mantle fabrics indicate Eoarchaean subduction.

The extension of subduction processes into the Eoarchaean era (4.0–3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern Earth such fabrics are associated with deformation of mantle rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a mantle origin and a supra-subduction mantle wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics.