<p>This paper aims to inform researchers and practitioners in radioglaciology about current and future trends in mapping the englacial stratigraphy of ice sheets. Radio-echo sounding (RES) is a useful technique for measuring the subsurface properties of ice sheets and glaciers. One of the most important and unique outcomes is the mapping of ice sheets' englacial layer stratigraphy, mainly consisting of isochronous reflection horizons. Mapping those is still a labor-intensive task. This review provides an overview of state-of-the-art (semi-)automated methods for identifying ice surface, basal, and internal reflection horizons from radargrams in radioglaciology. Methods for segmenting (and detecting) different regions of radargrams are also included due to their data and methodological similarity to methods tracing internal reflection horizons. We discuss a variety of methods which have been developed or applied to RES data over the last few decades, including image processing, statistical techniques, and deep learning approaches. For each approach, we briefly summarize their procedures, challenges, and potential applications. Despite major advances, we conclude that gaps remain in effectively mapping internal reflection horizons in an automated way but with deep learning representing a potential advancement.</p>
<p>This study employs numerical simulations based on the limit analysis (LA) method to calculate the stress distribution in a model that includes a basal detachment, featuring the lateral termination of a generic fault under compression. We conduct 2500 2D and 500 3D simulations with varying basement and fault friction angles to analyze and classify the results into clusters representing similar failure patterns to understand the stress fields. Automatic fault detection methods are employed to identify the number and positions of fault lines in 2D and fault surfaces in 3D. Clustering approaches are utilized to group the models based on the detected failure patterns. For the 2D models, the analysis reveals three primary clusters and five transitional ones, qualitatively consistent with the critical Coulomb wedge theory and the influence of inherited structural and geometric aspects over rupture localization. In the 3D models, four different clusters portray the lateral prolongation of the inherited fault. High stress magnitudes are detected between the compressive boundary and the activated or created faults and at the root of the inherited active fault. Tension zones appear near the outcropping surface relief, while stress decreases with depth at the footwall of the created back thrusts. A statistical cluster-based stress field analysis indicates that for a given cluster, the stress field mainly conserves the same orientations, while the magnitude varies with changes in friction angles and compressive field intensity, except in failure zones where variations are sparse. Small parametric variations could lead to significantly different stress fields, while larger deviations might result in similar configurations. The comparison between 2D and 3D models shows the importance of lateral stresses and their influence on rupture patterns, distinguishing between 3D analysis and 2D cross-sections. Lastly, despite using small-scale models, stress field variations over a span of a couple of kilometers are quite large.</p>
The Rönneholm-Ageröd peatland complex, situated in central Scania, contains numerous archaeological sites discovered since the 19th century. Two sediment sequences were obtained at the Ageröd peatland to compare the sediment stratigraphy with a previous sequence obtained in 1960 to detect any modern-day changes and to establish the Holocene environmental development in the area. To clarify the timing of ceased peat-cutting activities, dendrochronological analysis was performed on trees growing on the peatland. The results indicate that the lake transitioned into first a fen stage and later a raised bog stage, at about 7300 cal BP and 6500 cal BP, respectively. Furthermore, the dendrochronological analysis indicates that peat cutting ceased at least before 1960 in the sampled areas. Depending on e.g. hydrological conditions and human impact, the potential for preservation of organic remains varies greatly within the Rönneholm-Ageröd peatland complex. After peat-cutting activities ceased at the Ageröd peatland, the area was abandoned, without being restored to its original state and the drainage systems were left open but without maintenance. Our results show that these drainage ditches are still effective at the Ageröd peatland, which contributes to an active loss of peat at the top of the stratigraphic sequence. This causes the youngest formed peat layers to degrade, in turn, exposing older layers and reducing the buffer zone above the preserved organic cultural heritage from the lake-phase of the wetland with their destruction. To increase the understanding of modern-day processes affecting the preservation of organic remains in peatlands, continued monitoring and measuring of the peatland preservation status is needed in areas with archaeological deposits. We predict that if we fail to take action and establish a routine for finding and mitigating ongoing wetland degradation, the organic cultural and environmental heritage in them will, in the not-too-distant future, collapse and irrevocably deteriorate.
Twenty-four diagnostic Paleocene benthic foraminiferal species of Anan, which related to eighteen genera were erected from five widely separated countries in the Southern and Northern Tethys, its proposed evolutionary trends of them, and the taxonomic revision of these taxa, which will greatly aid paleontologists and biostratigraphers to helpfully understanding. Thirteen species of them were erected from Egypt ((Siphogaudryina strougoi, Pseudoclavulina hewaidyi, P. youssefi, Annulofrondicularia bignoti, Tristix aubertae, Lenticuzonaria misrensis, Percultazonaria alii, P. ameeri, Palmula berggreni, P. salimi, Vaginulinopsis boukharyi, Citharina plummerae, Gyroidinoides luterbacheri), five species from UAE (Repmanina mazeni, Psammolingulina bahri, Laevidentalina hudae, Hemirobulina olae, Ramulina futyani), three species from Pakistan (Textularia haquei, Spiroloculina haquei, S. pakistanica), two species from Jordan: (Pseudoclavulina futyani, Lenticuzonaria hodae), and one species of them is recorded from Tunisia (Leroyia tunisica). The paleogeographic distribution of these taxa are recorded in some other countries in the Southern and Northern Tethys than the original type locality, e.g. Iran, Czech, Bulgaria and Argentina. Some of these species are used to introduce an evolutionary trend marked by changes in the morphology and other characters of these benthic foraminiferal test. The Southern Tethys assemblage indicates an open marine environment, which represents middle-outer neritic environment and shows an affinity with Midway-Type Fauna (MTF).
A microtremor survey based on ground surface data acquisition was used to identify and characterize the karst area of Cerme Cave, Yogyakarta, Indonesia, from the entrance to the exit of the cave. The entrance and exit of the cave are used as tie-in points because the characteristics of the two locations can be directly observed. Parameters used in this study include ground vibration amplification, shear wave velocity, and Poisson’s ratio. The presence of cavities can be characterized by a relatively strong contrast between these physical parameters and their surroundings. The exit of the cave, which can be considered as a sinkhole, has a dominant frequency of 3.2 to 4.6 Hz, which is relatively higher than that of the surrounding area. At the entrance of Cerme Cave, which has a large cavity, a small ground vibration amplification was detected, less than 0.1. The entrance and exit of the cave also exhibit a low shear wave propagation velocity of less than 350 m/s. The presence of a subsurface fluvial channel in Cerme Cave can be characterized by a high Poisson’s ratio of 0.4–0.5, a gain value of less than 0.1, and a shear wave velocity of less than 350 m/s.
Pierre Sabatier, Jasper Moernaut, Sebastien Bertrand
et al.
Event deposits in lake sediments provide invaluable chronicles of geodynamic and climatic natural hazards on multi-millennial timescales. Sediment archives are particularly useful for reconstructing high-impact, low-frequency events, which are rarely observed in instrumental or historical data. However, attributing a trigger mechanism to event deposits observed in lake sediments can be particularly challenging as different types of events can produce deposits with very similar lithological characteristics, such as turbidites. In this review paper, we summarize the state of the art on event deposits in paleolimnology. We start by describing the sedimentary facies typical of floods, glacial lake outburst floods, avalanches, hurricanes, earthquakes, tsunamis, volcanic eruptions, and spontaneous delta collapses. We then describe the most indicative methods that can be applied at the scale of lake basins (geophysical survey, multiple coring) and on sediment cores (sedimentology, inorganic and organic geochemistry, biotic approach). Finally, we provide recommendations on how to obtain accurate chronologies on sediment cores containing event deposits, and ultimately date the events. Accurately identifying and dating event deposits has the potential to improve hazard assessments, particularly in terms of the return periods, recurrence patterns, and maximum magnitudes, which is one of the main geological challenges for sustainable worldwide development.
shamsallah Asgari, Hamidreza peravan, samad Shadfar
et al.
In some areas, it is surprisingly possible to see a dense cover of rangeland species that has sustained soils and controlled the sedimentation rate of marl lands. It seems that some of the physical and chemical properties of marl are the main reasons for such a cover in the areas covered by Marlene formations. This research was carried out with the aim of thorough and systematic examination of plant species and determining the need for habitat and their protective role in the eastern, southern and western regions of Ilam. For this purpose, 48 specimens of Marne deposit were harvested from three areas and 33 physical and chemical tests were carried out. Botanical investigations were carried out using recurrent field observations and plots at 180 points, and plant specimens were identified after transfer to the plant museum According to the results of experiments on marl samples in these three regions, according to the stratigraphy of marl formations Gurpi, Pabdeh, Gachsaran and Aghajari, the sediments of these three areas were evaluated for the salinity (EC), bulk density (BD), sodium (Na +) and Soil saturation percentage (SP) and some physical parameters such as sand, sand and silt particles have significant differences. This difference can be one of the factors affecting the diversity and diversity of vegetation grown in three areas. The most important point is that in both eastern and western regions of Ilam, the species of Quercus brantii is abundant and dominant, and it can undoubtedly be considered as the most adapted plant species in the areas covered by Marlene formations of Gurpi and Pabdeh in these zones. . The second dominant species is No mu, Ha sa and Zi nu, which is compatible with the southern marl zone of the city of Ilam.
D. G. A. M. Aerden, D. G. A. M. Aerden, A. Ruiz-Fuentes
et al.
<p>The small island of Groix in southern Brittany, France, is well known for
exceptionally well-preserved outcrops of Variscan blueschists, eclogites, and
garnetiferous mica schists that mark a Late Devonian suture between Gondwana
and Armorica. The kinematics of polyphase deformation in these rocks is
reconstructed based on 3D microstructural analysis of inclusion trails
within garnet and pseudomorphed lawsonite porphyroblasts using differently
oriented thin sections and X-ray tomography. Three sets of inclusion trails
striking NE–SW, NNW–SSE, and WNW–ESE are recognized and interpreted to
witness a succession of different crustal shortening directions orthogonal
to these strikes. The curvature sense of sigmoidal and spiral-shaped
inclusion trails of the youngest set is shown to be consistent with
northwest and northward subduction of Gondwana under Armorica, provided
that these microstructures developed by overgrowth of actively forming
crenulations without much porphyroblast rotation. Strongly non-cylindrical
folds locally found on the island are reinterpreted as fold-interference
structures instead of having formed by progressive shearing and fold-axis
reorientation. Six samples of a lower-grade footwall unit of the Groix
ophiolitic nappe (Pouldu schists) were also studied. Inclusion trails in
these rocks strike E–W, similar to the youngest set recognized on Groix
island. They record Carboniferous N–S shortening during continental
collision. These new microstructural data from southern Brittany bear a
strong resemblance to earlier measured in inclusion-trail orientations in the
northwestern Iberia Massif. A best fit between both regions suggests not more than about
15<span class="inline-formula"><sup>∘</sup></span> anticlockwise rotation of Iberia during the Cretaceous opening of
the Gulf of Biscay.</p>
The Harz Mountains in Germany are a south-tilting block of variscan-folded Devonian and Carboniferous rocks thrust over Mesozoic sediment along its northern border. Along the South Harz the overlying, unfolded upper-most Carboniferous, Permian and Buntsandstein (lower Triassic) series are exposed in a wide belt. They include a thick series of Upper Permian (“Zechstein”) evaporitic rocks, dipping with about 10° S to SW, representing a nearly continuous sulfate and carbonate karst area about 90 km long, covering 338 km². In his dissertation, the first author compiled a new geological map for the Zechstein at a scale of 1:10,000 and deduced a tectonic model to advance our understanding of the karstic features. Karstification determines the morphology of the South Harz including over 180 registered caves, thousands of sinkholes, uvalas, sinking creeks and large karstic springs. Specifically, lines of sinkholes appear to follow faults. By detailed mapping of the three lowermost Zechstein cycles, a dense matrix of faults is revealed. 85° to 125° striking faults reoccur every few 500 m, formed during the Harz-lifting compressional phase during the Upper Cretaceous. Many of these faults are reverse with a Nward thrust. This leads to repetitive exposure of the strata, causing the broadening of the Zechstein outcrop beyond what would be caused by the dip of the series alone. In other areas, horstand graben-structures are present, resulting in kilometer-long Lower Buntsandstein ridges. Below ground, the groundwater flowing southward along the dip is diverted into the direction of diachronicalthe strike, thus causing strike-parallel depressions, valleys and sinkhole rows. In the final extension phase, faults striking 150° to 180° have caused graben-structures, allowing groundwater and surface rivers to flow southward, breaking through the escarpment of the overlying Lower Buntsandstein. Therefore, the tectonic structure of the South Harz determines its hydrology and the karst features apparent at the surface. The tectonic situation of the three largest karstic springs, the Salza Spring at Förste, the Rhume Spring, and the Salza Spring at Nordhausen is discussed along with more shallow karstic settings of the Hainholz/Beierstein, the Trogstein and the area of Hainrode.
Mouloud Benammi, Elina Aidona, Gildas Merceron
et al.
This paper aims to contribute to the stratigraphic and geochronological evaluation of the primate bearing Dafnero fossil site of Northern Greece by means of lithostratigraphic, paleomagnetic and paleontological analyses. The 60 m thick fossiliferous deposits of fluviatile origin are recognized as representing a typical braided-river sequence unconformably overlying molassic sediments. Rock magnetic investigations indicate the presence of both medium and low coercivity minerals. Paleomagnetic sampling of the Dafnero sediments yielded a stable magnetic remanence, and the characteristic remanent magnetization directions pass reversal test with dual polarity. Based on calibration from mammal fossils, the normal polarity magnetozone N1 located in the upper third of the studied section could correlate with chron C2n (the Olduvai subchron), suggesting that the fossil horizon is within C2r with an extrapolated age of 2.4–2.3 Ma and rather closer to the upper age limit. The results allow the re-calibration of several middle Villafranchian assemblages of S. Balkans and the correlation of the corresponding mammal fauna with the environmental shifts of Praetiglian, as it is recorded in climatostratigraphic data from the Black Sea.
The many years of history of the studies of Bolgar ceramics have resulted in the need for its division into subgroups in accordance with certain visually identified signs: design technology, color and relative plasticity of clay, presence of impurities in the dough, and firing degree. Over ten subgroups of common Bolgar group of ceramics were identified based on the materials from the excavations at Bolgar fortified settlement. Of particular interest is the ceramic material from layers VI (late 10th – first half of 11th centuries) and V (second half of 11th – early 13th centuries) in terms of the general stratigraphy of Bolgar fortified settlement, as it reflects the development of pottery in this area since the beginning of the establishment of the Volgar Bolgaria state. It should be noted that in the early layers a rather large portion of all group I ceramics is represented by subgroups with the signs of elongation of the hollow body on a circle. A total of 3 subgroups are distinguished in terms of quantity in the materials of VI, and 6 subgroups in layer V. The variety of the subgroups reflects the different approaches of Bolgar pottery craftsmen to the selection and preparation of clay raw materials, vessel construction techniques, surface treatment of the products, and firing modes. A small percentage of common Bolgar ceramics is composed of fragments of ware with signs of firing in a regenerative medium. The author suggests that this was home-crafted ceramics not intended for market distribution.
<p>Image correlation techniques have provided new ways to analyse the distribution of deformation in analogue models of tectonics in space and time. Here, we demonstrate, using a new version of our software package (TecPIV), how the correlation of successive time-lapse images of a deforming model allows not only to evaluate the components of the strain-rate tensor at any time in the model but also to calculate the finite displacements and finite strain tensor. We illustrate with synthetic images how the algorithm produces maps of the velocity gradients, small-strain tensor components, incremental or instantaneous principal strains and maximum shear. The incremental displacements can then be summed up with Eulerian or Lagrangian summation, and the components of the 2-D finite strain tensor can be calculated together with the finite principal strain and maximum finite shear. We benchmark the measures of finite displacements using specific synthetic tests for each summation mode. The deformation gradient tensor is calculated from the deformed state and decomposed into the finite rigid-body rotation and left or right finite-stretch tensors, allowing the deformation ellipsoids to be drawn. The finite strain has long been the only quantified measure of strain in analogue models. The presented software package allows producing these finite strain measures while also accessing incremental measures of strain. The more complete characterisation of the deformation of tectonic analogue models will facilitate the comparison with numerical simulations and geological data and help produce conceptual mechanical models.</p>
<p>I present in this work the GHOST (Geoscientific
Hollow Sphere Tessellation) software which
allows for the fast generation of computational meshes in hollow sphere
geometries counting up to 100 million cells. Each mesh is composed
of concentric spherical shells which are built out of quadrilaterals or
triangles. I focus here on three commonly used meshes used in
geodynamics/geophysics and demonstrate the accuracy of shell surfaces and
mesh volume measurements as a function of resolution. I further benchmark the
built-in gravity and gravitational potential procedures in the simple case of
a constant density geometry and finally show how the produced meshes can be
used to visualise the S40RTS mantle tomography model. The code is open source
and is available on the GitHub sharing platform.</p>
V času med eocenom in pliocenom so bile s temena krednega apnenčevega antiklinorija v osrednjem in zahodnem delu planote Kras in s kozinsko-podgrajske antiklinale erodirane flišne plasti, zaradi česar se je ob splošnem zniževanju okoliške ravnine ob pogojih zajezenega krasa razširjal in zniževal ravnik na razkritih apnencih. Največji del planote Krasa predstavlja najstarejši del kraškega ravnika. Na Krasu so se v pliocenu in kvartarju pasovi ravnika hitreje zniževali v smeri proti SZ, vmesno zastajajoče ali dvigujoče se površje pa je s tem dobilo obliko vzpetin na severozahodnem robu planote. Zaradi hitrejšega grezanja vipavske sinklinale so vodni tokovi prenehali teči preko planote Krasa še preden je bil fliš, ki jim je preprečeval pot proti jugu, odstranjen zaradi grezanja severnega dela Tržaškega zaliva. Zaradi tega na Krasu ni slepih dolin ali polj. Pač pa je veliko vrtač, površje je kamnito, zaradi česar je iz Krasa nastal splošni pojem kras. Obe značilnosti sta tipični za submediteranske dinarske kraške ravnike, gosto naseljene in obdelane ter zaradi tega brez gozdov
Between Eocene and Pliocene, erosion of flysch strata on the top of Cretaceous limestone anticlinorium in the central and western part of the Kras plateau and the Kozina-Podgrad anticline uncovered and widened – and simultanously lowered - the karst plain in the conditions of dammed karst. The largest portion of Kras plateau is covered with karst plain, its oldest part. In Pliocene, the karst plain was fractured and subsided towards the NW regardless of older folded structure; during this process, several zones of elevations were formed through slower subsiding or uplifting. Due to faster lowering of the Vipava syncline, water streams stopped running over the Kras plateau before the flysch, damming the waters from the Kras plateau to the south was removed due to the subsiding in the northern Gulf of Trieste. Thus, no fossil blind valleys or poljes are found on the Kras plateau. However, there is considerable density of dolines and the surface is stony, giving the karst its original name. Both phenomena are typical of deforrested, densely populated and cultivated Submediterranean Dinaric karst plains.