The Nullarbor Plain is a ~200,000 km2 planar karst surface in southern Australia, underlain by Cenozoic shallow‐water limestones. During the Miocene the area was uplifted, and although the plain is ...generally considered extremely flat, locally, the geomorphology of the Nullarbor Plain retains evidence of earth surface processes across a long, middle Miocene‐to‐present time span. The accessibility of the recent 0.4 arc‐second TanDEM‐X digital elevation model (DEM) by the German Aerospace Centre motivated the search for other possible fine‐scale landforms that would previously have been unresolvable. The analysis of DEM images revealed an enigmatic annular landform with an outer diameter between 1200 m and 1300 m. It consists of a circular elevated rim and a central dome. Its morphology is distinct from other landforms observed on the plain, and cannot be readily explained as a part of known active or inferred/expected processes on the plain (e.g., fluvial, aeolian, karst, tectonic or extra‐terrestrial impact processes).
More recent karst processes (dayas formation) overprinting the landform indicates the presence of the annular structure prior to dayas formation. A unique microbial boundstone facies sampled from the bed‐rock of the annular structure supports an interpretation of long‐lived, at least partial retention of a primary depositional structure. Differential carbonate deposition, especially bioherm growth, was a likely origin of the annular topographical expression of the present‐day landform and is comparable to biogenic structures in the modern day deeper Great Barrier Reef.
We report an enigmatic annular (ring‐shaped) positive topographic feature on the extensive karst surface of the Nullarbor Plain, southern Australia. Investigation of satellite and drone imagery in conjunction with field sampling suggests that the structure relates to a degraded primary depositional feature analogous to biogenic structures on the modern Great Barrier Reef. This structure confirms slow landscape evolution processes and extends the record of exceptional preservation of environmental features reported from the Nullarbor Plain to the Miocene (∼14 Ma).
Sieve lobes typically appear in gravel‐rich and matrix‐poor alluvial fans. Despite being extensively studied, the sieve‐lobe facies has been defined largely based on qualitative field observations ...without quantitative sedimentological analyses. Additionally, depositional activity of sieve lobes has not been monitored over extended periods (monthly to annually) and not directly associated with specific precipitation triggers. Furthermore, the internal geometry of sieve‐lobe built alluvial fans has not yet been imaged by subsurface methods. We performed a multi‐method analysis of sieve lobes in the Julian Alps (NW Slovenia) on an alpine alluvial fan composed of carbonate gravels. We performed a detailed textural and structural sedimentological analysis of 11 recent sieve lobes differing in size and age. A three‐year aerial survey of the alluvial fan surface with a small unmanned aircraft and photogrammetric modelling was used to detect active sieve‐lobe evolution. Detected sieve‐lobe formation events and volumetric surface changes were paired with triggering precipitation events. Ground‐penetrating radar (GPR) profiling depicted the geometry of the sieve‐lobe built alluvial fan. The sieve‐lobe facies consists of over 80% poorly sorted, open‐framework gravels and less than 2% mud. Lobes exhibit downward coarsening and increase in clast mean size. These textural and structural characteristics are present in all sieve lobes regardless of their age and size. Sieve lobes form with a sub‐annual frequency, usually following 24 h rainfall events exceeding 50 mm. Over 1000 m3 of sediment was deposited during these events. The GPR profiles confirm that the studied alluvial fan is formed predominantly by stacked sieve lobes. Quantitative sedimentary analysis of sieve lobes, monitoring of their recent evolution, and depiction of their subsurface geometry—demonstrated in this study—reinforce the challenged concept that sieve lobes are one of the main building blocks of alluvial fans. This work also demonstrates that, under specific conditions, sieving may become the dominant alluvial fan‐forming process.
We performed a detailed sedimentological analysis of 11 sieve lobes on an active alluvial fan. A three‐year aerial surface survey detected active sieve‐lobe evolution, which was paired with triggering precipitation events. Ground‐penetrating radar depicted the architecture of the sieve‐lobe built alluvial fan. Lobes exhibit downward coarsening and increased clast mean size. They are deposited annually during rainfalls exceeding 50 mm, during which more than 1000 m3 of sediment was deposited. Gravel‐rich and matrix‐poor alluvial fans can be almost entirely sieve‐lobe built.
Debris floods are mass movement events which are usually triggered by intense short duration rainfall events. They often occur on alluvial fans in an alpine environment. Due to their sever geohazard ...potential they pose a serious threat to infrastructure and human life. To minimize their threat understanding of their past magnitude occurrence is crucial. Dendrogeomorphology has proven to be a highly useful method in studies of past slope mass movements. However, establishing magnitudes of past events has so far been based on indirect indicators, such as: spatial distribution of affected trees, characteristics of tree injures and sedimentological records. In this study we present a method that directly estimates the magnitudes of past debris flood events on an alluvial fan using dendrogeomorphological and meteorological data sets. The studied dendrogeomorphological data set is based on tree-ring series from 105 sampled trees (Picea abies, Abies alba and Larix decidua) growing on an active alluvial fan in a typical alpine environment of the Julian Alps in NW Slovenia. Based on sudden growth suppression thirteen debris flood events since 1903 were dated. Meteorological data from a nearby meteorological station was used to determine the exact triggering meteorological event for ten events. Comparing the It index of affected trees and calculated return period of an individual triggering meteorological event established the magnitude of debris flooding. We showed that more trees are affected at high return period/intensity of the triggering meteorological event and therefore higher magnitudes of debris floods. This research presents the first combined use of dendrogeomorphological and meteorological data sets for magnitude estimation of historic debris flood events which could be successfully applied in similar environments.
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•Dating of debris flooding (DFL) events is based on partially buried trees.•DFLs are linked to precipitation records to pinpoint the most likely triggering meteorological event with daily precision.•Return periods of triggering meteorological events relate well with It index of affected trees.•The DFL magnitude is estimated based on relation between It index and return periods of triggering meteorological events.•DFL events triggered by rainfall events of larger return period affect larger number of trees.
We use geophysical and sedimentological data to study the high-resolution acoustic stratigraphy and sedimentology of a Late Quaternary alluvial plain (located in the Gulf of Trieste, northern ...Adriatic) which was transgressed during the post-LGM sea-level rise. With sub-bottom sonar profiling we determined six acoustic facies, of which the top five acoustic facies (A-E) were sampled with a gravity corer. We performed core descriptions, radiocarbon dating and granulometric analysis with a laser particle analyser. The acoustic facies and their corresponding sediments are associated with three general sedimentary environments: Last Glacial to Younger Dryas alluvial (E-B), Early Holocene transgressive (Ab) and Holocene shallow marine (Aa). Acoustic facies E with low-amplitude chaotic reflection geometries is represented by cross-stratified sandy mud deposited by braided or wandering rivers. Acoustic facies D with high-amplitude and high- frequency sub-horizontal reflection geometries is represented by graded deposits (sandy mud and sandy clay grading into clay) of braided or wandering rivers. Acoustic facies C and B with individual low to middle amplitude reflections in an otherwise transparent facies are represented by overbank fine-grained sediments deposited by a meandering river systems. The top surface of AF B presents the Younger Dryas paleosurface in the geophysical record. Acoustic facies Ab with onlapping and concordant middle to low amplitude reflection geometries is represented by bioclastic transgressive sandy mud containing brackish mollusc assemblages. Acoustic facies Aa is acoustically transparent and contains bioclastic sandy mud with shallow marine mollusc assemblages. Our work provides a reference for future studies of the Late Pleistocene-Holocene transition on well-preserved low-gradient mid-to-low latitude continental shelves.
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•We use sub-bottom sonar to determine acoustic facies.•We sample the sediments of acoustic facies with gravity corer.•Correlation of acoustic and Late Quaternary transgressive sedimentary facies•A reference for post-LGM sea-level rise on mid-to-low latitude continental shelves.
The northern slopes of the Vipava Valley are defined by a thrust front of Mesozoic carbonates over Tertiary flysch deposits. These slopes are characterized by a variety of different surface forms, ...among which recent and fossil polygenetic landslides are the most prominent mass movements. We used the height variability method as a morphometric indicator, which proved to be the most useful among the various methods for quantifying and visualizing fossil landslides. Height variability is based on the difference in elevations derived from a high-resolution lidar-derived DEM. Based on geologic field mapping and geomorphometric analysis, we distinguished two main types of movements: structurally induced movement along the fault zone and movements caused by complex Quaternary gravitational slope processes. The most pronounced element is the sliding of the huge rotational carbonate massif, which was displaced partly along older fault structures in the hinterland of fossil rock avalanches and carbonate blocks. In addition to the material properties of the lithology, the level of surface roughness also depends on the depositional processes of the individual sedimentary bodies. These were formed by complex sedimentary events and are intertwined in the geological past. The sedimentary bodies indicate two large fossil rock avalanches, while the smaller gravity blocks indicate translational–rotational slides of carbonate and carbonate breccia.
We present a geomorphological map on a scale of 1:15,000, with detailed sedimentological descriptions, and a general relative spatio-temporal depositional reconstruction of Quaternary sediments in ...the Planica-Tamar Valley (NW Slovenia). After the Last Glacial Maximum, the retreating Quaternary glacier deposited large amounts of glacial sediments. These were followed by Holocene sediments, which differ in their sedimentological characteristics, transport mechanisms, and morphology. These sediments are deposited as sedimentary bodies with complex depositional geometries. They form areas of active, partly active, and inactive sedimentation in response to local/regional climate and bedrock geology. Previous research of the valley was mainly focused on bedrock mapping, while almost completely neglecting Quaternary deposits. This work is the first broader analysis of Quaternary sedimentary deposits in the research area, which offers an insight into the complex geomorphological and sedimentological processes, which shape the current mountainous landscape.
Hypersaline environments are among the most vulnerable coastal ecosystems and are extremely noteworthy for a variety of ecological reasons. Comprehensive assessment of metal(oid) contamination in ...hypersaline sediments from Sečovlje (Northern Adriatic, Slovenia) was addressed by introducing the detrital and diagenetic mineralogy and geochemical properties within the solid sediment material. Close associations between Fe/Mn oxides and oxyhydroxides with As, Cr, Ni, Pb and Zn, and between organic matter with Cu, Pb and Zn were confirmed using X-ray powder diffraction, SEM-EDS and ICP emission spectrometry analysis. Possible incorporation or adsorption on the crystal lattices of clay minerals (As, Cr, Pb, Sn and Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr and Zn) were also detected. All presented correlations were highlighted by various statistical analyses. The enrichment factor (EF) values showed a low degree of anthropogenic burden for As, Bi, Hg and Zn, while Cd, Cr, Cu, Ni, Pb, Sn and Sr originated from the geological background. These results emphasise that a detailed mineralogical and geochemical characterisation of solid (especially detrital and diagenetic) sediment particles is crucial in further understanding the metal(oid) translocation within the hypersaline ecosystems.
The Slovenj Gradec Basin represents one of the marginal western basins of the Neogene Pannonian Basin system. Its sedimentary succession is investigated by combination of field, petrographic and ...geochemical methods. The succession is at least 540m thick and characterised by frequent alternation of conglomerate, sandstone, siltstone and marlstone deposited in terrestrial, brackish and shallow marine environments. Modal composition of the sandstones indicates that they originated from recycled orogen, namely from quartzose sedimentary rocks of the Eastern Alps, and show moderate to absent chemical weathering. The results indicate two different tectonic settings: a collisional, which correlates well with the end-Mesozoic and Cenozoic Alpine collision, resulting in orogeny and thrusting of the Austroalpine nappes, and a passive margin related to the early Neogene lithospheric extension and subsidence as the result of slab retreat in the Carpathian subduction zone, which was responsible for the formation of the Pannonian Basin system.
In this area, where the sediments were subjected to various tectonic events, discriminant function diagrams of Verma and Armstrong Altrin are found to be a good tool for their identification and differentiation.
ABSTRACT
In this study, we focused on the Pliocene–Early Pleistocene fluvial terraces in the Velenje Basin and reconstructed the morphostratigraphy, sedimentary depositional environment, provenance ...and age of the gravel deposits using geomorphological, sedimentological, petrographic and chronological analyses. Geomorphological mapping revealed the presence of two main river‐terrace groups. The terraces in the older terrace group are severely degraded and preserved only as remnants capping high ground, while in contrast the younger group is better preserved. Detailed lithofacies analyses of four selected stratigraphic sections of the older terrace group show that the gravel was deposited in a meandering and wandering environment. The gravel consists of metamorphic, igneous, volcaniclastic, clastic and carbonate lithologies derived from the north, east and west from the Paka River catchments. To determine the timing of deposition, we performed isochron‐burial dating using cosmogenic 26Al and 10Be. Our new age constraints date the deposition of the older terrace group to 2.7 ± 0.3 Ma. Establishing the aggradation and incision model of the Velenje Basin documents pronounced regional tectonic uplift during the Pliocene–Early Pleistocene, which led to incision and the subsequent formation of a terrace staircase.
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