The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of ...siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.
The aquifers of alpine karst and high karst plateaus are abundant water resources. They are difficult to characterise due to their complex, partly glaciokarstic, evolution in active tectonic ...environments, and an unsaturated zone up to two kilometres thick. We present and discuss the results of a tracing test in the alpine karst of the Julian Alps (Slovenia), more precisely in the Migovec System, the longest cave system in Slovenia (length = 43 km, depth = 972 m). The cave extends below a mountain ridge that separates the Soča and Sava Valleys, thus forming a topographic divide between the Adriatic and Black Sea basins, which gives the test greater regional significance. In early September 2019, three kilograms of uranine were injected into a perched lake in a remote part of the system, approximately 900 metres below the plateau and 100 metres above the low water table. All known springs in the valleys on either side of the mountain were monitored by manual or instrumental sampling and a field fluorometer. Due to the unexpectedly dry season, no tracer was detected at any site for two months until a heavy rainfall event in early November. Subsequently, about 60-65 % of the tracer mass appeared within 60 hours in the Tolminka River. No tracer was detected at other sites, either becauseit was not present or because it was highly diluted. The study suggests that the lake containing the tracer is bypassed by the vadose flow and that the tracer was only mobilised during large events when the lake became part of the epihreatic flow. The linear peak flow velocity from the injection site to the Tolminka Spring was only about 1.7 m/h. However, assuming that the tracer was only mobilised by the large rain event, the velocity would be 70 m/h. The study highlights the challenges and pitfalls of water tracing in alpine karst systems and suggests ways to avoid them.
Large glaciers and ice caps formed in the Mediterranean mountains during the cold stages of the Pleistocene and some small glaciers remain today. Here we review 157 outputs that include radiometric ...dates on glacial deposits or outwash in the Mediterranean published between 1975 and 2020. The last decade has seen a striking increase in the use of terrestrial cosmogenic nuclide (TCN) dating and this has revolutionised our understanding of the Late Pleistocene glacial record. Our meta-analysis of 1663 radiometric ages highlights much greater complexity in the timing of Pleistocene glaciation across the region than hitherto recognised. Evidence from multiple dating methods, in a range of depositional settings, confirms that the Mediterranean glacial record extends through all of the Late Pleistocene and deep into the Middle Pleistocene. Evidence of Early Pleistocene glacial activity has been recognised from outwash deposits in the Julian Alps of Slovenia. The most extensive glaciations occurred during the Middle Pleistocene: their ages have been established primarily by using 40Ar/39Ar in the Italian Apennines and U-series dating in the glaciokarst of the Balkans. The Late Pleistocene glacial geochronologies are based on optically stimulated luminescence (OSL), radiocarbon and TCN dating. TCN dating is now the dominant method for dating Late Pleistocene glacial landforms. It is now clear that glaciers were present throughout the Late Pleistocene and, in most parts of the Mediterranean, they were at or near their maximum extent before the global last glacier maximum (27.5–23.3 ka). The outwash record in river valleys downstream of the glaciated terrains confirms that glaciers were important agents of landscape change throughout this period. Deglaciation in the Mediterranean mountains was punctuated by glacier stabilisations as well as some readvances towards the very end of the Pleistocene. The deglacial trend has continued throughout the Holocene with rapid change in recent decades due to rising global temperatures. Some small glaciers remain today due to the influence of locally favourable topoclimatic factors. For much of the Quaternary Period conditions in the Mediterranean mountains involved much more extensive glaciation than recorded at any time in the Holocene.
We investigated complex tectonic structures within a km-scale shear zone (Cima Lunga unit), which is traditionally interpreted as generated by multiple, distinct deformation phases, despite showing ...unique schistosity and lineation. Based on structural analyses we discovered sheath folds developed in relatively weak gneissic/schistose rocks, enveloping inclusions of stronger ultramafics. The internal layering of inclusions experienced superimposed folding, boudinage and folding, attesting to layer-parallel shortening followed by stretching and further again shortening. Using 3D numerical modelling, we explored the structure evolution within and around deformable viscous inclusions under far-field simple shear. The numerical results showed that the internal deformation of ellipsoidal inclusions and the fold development around the inclusions are both dependent on the viscosity ratio, shear strain and the inclusion aspect ratio. The Cima Lunga structural patterns were reproduced for finite strains exceeding 7.5 and viscosity ratio between 2.8 and 9. Inclusions are characterized by persistent rotation of the internal layering, resulting in super-simple shear regime, with kinematic vorticity number >1. An important corollary is that ultramafics and host rocks experienced coupled deformation since the prograde metamorphic evolution. Finally, we emphasise that progressive deformation in shear zones may offer sufficient explanation for complex structural patterns, without invoking unjustified polyphase deformation.
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•We study 3D deformation pattern within and around deformable inclusion in simple shear.•Sheath folds can develop around deformable inclusions.•Super-simple shear deformation develop within deformable inclusions.•Cima Lunga structures are likely formed during single, progressive deformation phase.•Backward modelling supplies constraints on the rock rheology and shear strain.
Deciphering deformation mechanisms within Quaternary sediments in a highly dynamic environment such as the southeast European Alps is often a challenging task that requires the use of a variety of ...methods. Due to the geohazards involved, the interpretation of deformation mechanisms can have a major impact on society and may enable the preparation of appropriate engineering solutions. We present an example of how deformation structures can be studied by integrating geomorphological, sedimentological and structural geological mapping using photogrammetric and leveling surveys, paleoseismological techniques, optically stimulated luminescence dating and ground penetrating radar surveys. Quaternary deposits on the slopes of the formerly glaciated Soča Valley near Most na Soči are tilted and dissected along numerous faults within the deformation zone of the Idrija Fault, a large, active, dextral strike-slip fault. Reconstruction of deformation history indicates that at least five deformation events occurred during deposition of the glaciofluvial succession interbedded with glaciolacustrine deposits, dated to Penultimate Glaciation. Ground penetrating radar profiles and outcrop observations reveal NE – SW striking faults, which are approximately perpendicular to the primary Idrija Fault. Based on the local geologic setting, we considered glaciotectonics, gravitational faulting due to ice-decay collapse or slope instability, and tectonic faulting as possible deformation mechanisms. Based on detailed documentation and analysis of the geometry and kinematics of the deformations, we interpret the observed deformations as secondary structures that result from paleoseismic activity of the Idrija Fault, and some structures resulting from glaciotectonics and gravitational faulting. The transtensional type of deformations at the studied site shows the local character of the main fault, which occurs here due to geometrical and kinematical changes of the Idrija Fault causing local transtension in the Most na Soči area. The complexity of the fault and the first paleoseismic evidence dating back to Penultimate Glaciation provide valuable new data for understanding the seismic hazard in the region.
•Origin of deformations within Quaternary sediments in a highly dynamic environment unraveled.•Glaciofluvial and glaciolacustrine deposits record recurrent faulting and non-tectonic deformations.•First paleoseismological evidence on the major Idrija Fault extending back to Penultimate Glaciation.•Local scale fault complexities reflect fault geometric and kinematic changes.
Mountain landscapes are the areas characteristic for a great spatial variability of precipitation amounts. On the windward sides of orographic barriers there is intense rising of air, and on the lee ...sides air descends. The intensity of the two processes is manifested in great differences in precipitation amounts at short distances. Although the network of precipitation stations is the densest in the Alps of all mountain regions in the world, precipitation regime at the micro level continues to be poorly known at many a place. Precipitation stations in mountainous landscapes are the most numerous in lower-lying and settled areas, whereas they are rather few in the high-lying areas. Also the accuracy of measurements is problematic in the mountains. As a result, the information on precipitation regime is inadequate right in the areas with the largest precipitation amounts. This means that the estimation of water balance is inadequate, and it is difficult to forecast the precipitation-related processes, such as torrential floods, landslides, avalanches, and the like. The present paper deals with horizontal precipitation gradients in the Alpine valleys of Planica, Krnica and the stream Beli potok which are all situated in the north-western part of the Slovenian section of the Julian Alps.
We investigated olivine minette dykes from the Rio Colan Valley of the Julian Alps (NE Italy) to provide new constraints on the mantle geochemistry underneath this extreme sector of the Italian ...Southern Alps. Petrographic observations, high Mg#s, high Cr and Ni contents, low Dy/YbCN ratios and flat heavy rare earth element (REE) profiles imply these are primary magmas derived from a depleted peridotite with olivine and garnet as possible residual phases. However, high K2O and incompatible trace element contents, coupled with superchondritic Nb/Ta ratios, suggest that the source was modified into a rutile–phlogopite-bearing carbonated peridotite by multiple metasomatic events such as recycling of crustal material and carbonatitic metasomatism related to an old orogenic event and rutile-rich metasomatism linked to the Pangaea break-up. Laser ablation – multi-collector – inductively coupled plasma – mass spectrometer (LA-MC-ICP-MS) U–Pb geochronology of apatites from two dykes yielded differences between unforced and forced discordia ages up to ∼45 Ma, likely due to the initial 207Pb/206Pb correction adopted. Nonetheless, because forced discordia and 206Pb/238U weighted mean ages are overall similar within the uncertainty, our preferred interpretation is that olivine minettes intruded and crystallized at ∼67 Ma. The age and anorogenic signature of these magmas are consistent with the regional extensional tectonics in the Julian Alps due to the advance of the external Dinaric front following Adria plate eastward subduction. Eventually, we show also that Rio Colan magmas are geochemically hybrid products between lamprophyres and lamproites compared with similar Italian and Western Mediterranean volcanics.
It has been argued that the beginning of significant pelagic calcification could have been linked to the Carnian Pluvial Episode (CPE), a climate change in the Late Triassic (~234–232 Ma) that was ...marked by C-cycle disruption and global warming. Nevertheless, abundant calcareous nannofossils have been described so far only in post-CPE rocks, and therefore no conclusive hypotheses can be drawn on possible causal links with it. Here we show that in deep-water successions of the Western Tethys, Orthopithonella calcispheres interpreted as calcareous dinocysts became an important component of carbonate sedimentation from the onset of the CPE, and could constitute up to 8% of hemipelagic limestones. Before the CPE, in similar depositional environments, calcispheres are rare or absent, and never constitute a significant part of the sediment. This change in the deep-water carbonate sedimentation, is mirrored in the shallow water environments by the rise of the reefs built by Scleractinia corals. These important innovations in Earth's carbonate systems may indicate a deep modification in the ocean biogeochemistry during the CPE.
•Calcispheres were studied in successions across the Carnian Pluvial Episode (CPE).•In Western Tethys Calcispheres are abundant from the onset of the CPE.•They belong to the genus Orthopithonella.•They were a significant component of CPE hemipelagic–pelagic limestones.
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