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Solid earth : SE 12(10), 2211-2234 (2021). doi:10.5194/se-12-2211-2021, Published by Copernicus Publ., Göttingen

In tectonically active mountain ranges, the landscape is shaped by the interplay of erosion/sedimentation and tectonically driven crustal deformation. Characteristic landforms such as moraines, wind gaps, fault scarps, and river terraces can be used to decipher the landscape evolution. However, the available data often allow for different interpretations. Here we study the Pradol (Pradolino) Valley in Western Slovenia, a deeply incised canyon whose floor rests several hundreds of metres above the surrounding valleys. We use high-resolution digital elevation models, geomorphic indices and field observations to unravel the evolution of this peculiar landform. We present a six-stage evolution model of the canyon that includes the blockage of valleys by advancing glaciers, river diversion, and rapid incision due to a high discharge of post-glacial meltwater. The formation of the Pradol Valley was most likely facilitated by an underlying fault that serves as an easily erodible weakness zone in the Mesozoic limestones. Our model indicates that the formation of the canyon could have occurred during the last glaciation, which results in incision rates of several cm/yr. With the proposed model we can explain all remote and field observations available. Our study shows that a complex interplay of different landscape-shaping processes is needed to explain the occurrence of the Pradol dry valley and that rapid changes in the morphology occurred after the last glacial maximum.

The Klagenfurt Basin in the southern Austrian region of Carinthia was glaciated during the Last Glacial Maximum (LGM). Next to numerous lakes, the present-day landscape predominantly exhibits landforms such as moraines and large river terraces systems. These landforms can be seen as markers for post-LGM tectonics: If they are deformed, the basin has taken up a share of the ~N-S shortening prevailing due to the ongoing collision of Adria and Europe. If the landforms are undeformed, this deformation is accommodated elsewhere, most likely further south along the Periadriatic and Sava Fault system or by a NW-SE-trending strike-slip fault system at the junction between Southern Alps and Dinarides in Slovenia. Our study is motivated by the recent discovery of earthquake-triggered mass movements in Carinthian lakes and new data on Late Pleistocene-Holocene speleothem damage in the Karawanken mountains, illustrating that the area is seismically active. We used newly available high-resolution digital elevation models to scan the area for post-glacial deformation but found no conclusive evidence for tectonic activity since the Würm glaciation. We then analysed several outcrops of Late Pleistocene sediments throughout the Klagenfurt Basin to check for soft-sediment deformation features that could be linked to strong seismic shaking. These outcrops were documented as 3D virtual models. Deformed silty-sandy layers were encountered in several places, and one outcrop showed spectacularly folded fluvial gravels. However, we do not need to invoke tectonics as the causative mechanism. Instead, we interpret these structures as evidence for a late glacial advance. Luminescence dating is underway to put constraints on the timing of this event. Our study implies that although there are records for recent strong earthquakes around the Klagenfurt Basin, the rates of deformation are so low that they can not be detected in the post-LGM landscape.

The Periadriatic Fault System (PAF) is among the most important post-collisional structures of the Alps; it accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 until 15 Ma. The scarcity of instrumental and historical seismicity on the easternmost segment of the fault is intriguing, especially when compared to nearby structures in the adjacent Southern Alps. Through this project, we aim to show which segments accommodated seismotectonic deformation during the Quaternary by applying Electron spin resonance (ESR) dating to fault gouges produced by the fault system. The method is especially useful for dating shear heating during earthquake activity at near-surface conditions due to its dating range (~104 ~106 years) ) and low closing temperature (< 100°C). During our field campaigns, we acquired structural data and collected 19 fault gouge samples from 15 localities along the PAF, the Labot/Lavanttal Fault, and the Šoštanj Fault. We measured the ESR signals from the Ti and Al centers following the additive and regenerative protocols on 60 mg aliquots of quartz, and compared the measurements between different grain size fractions. Here, we present our preliminary results from select localities, suggesting Quaternary earthquake activity along the fault system.

Due to the collision of the European and Adriatic plates, about 3 mm/yr of N-S convergence are accommodated in the Eastern and Southern Alps. This shortening is mainly taken up by c. E-W-trending reverse faults along the South Alpine Front and on NW-SE-trending dextral strike-slip faults in western Slovenia. Strong historical earthquakes and instrumental seismicity, however, show that some deformation also occurs in the interior of the Southern Alps. Little is known about which faults are active here. In this study we present results from a regional-scale remote sensing analysis focusing on the Bellunese and Friulian sectors of the Southern Alps in northeastern Italy. Our aim was to identify areas with relatively increased tectonic activity based on landscape features. We made use of high-resolution digital elevation models from aerial laser scanning campaigns. We downsampled the data to 5 m resolution and calculated the most widely used geomorphic indices that might indicate active tectonics: normalised steepness index, the Chi­ value, terrain ruggedness index, and stream knickpoints. The results were checked with geological data, mapped faults, and seismicity. We also conducted extensive field work to verify the results on the ground. Our results show that the application of large-scale tectonic geomorphology in this particular Alpine region is complicated by numerous factors. Small-scale variations in lithologies with variable erodibility strongly influence the analysis. The same holds true for variations in dip direction and dip angles of bedding planes; occasionally, vertical strata erroneously suggest linearly trending faults. In addition, we found that glacial features and alluvial deposits have locally overprinted the traces of known faults. Despite of these challenges, we found hints for active deformation in the landscape, in particular in the epicentral area of the 1976 Friuli earthquakes. We highlight potential pitfalls of the applied methods and discuss ways to overcome some of the problems we encountered.

The Dinarides fold and thrust belt resulted from the collision of the Adriatic Microplate with Eurasia and shows an overall SW-vergent and in-sequence structural architecture. In the Paleocene the ophiolite-bearing internal Dinarides were exclusively affected by crustal shortening. The outward SW propagation of the deformation front reached the eastern Adriatic passive continental margin mainly composed of Mesozoic carbonate platform rocks in Mid-Eocene times. This led to high crustal Mid Eocene to Oligocene shortening and the formation of the external Dinarides. Two balanced cross-sections across the external Dinarides show an along-strike contrasting deformation styles observed in two orogenic segments separated by the 250 km long dextrally transpressive Split-Karlovac Fault: the southern segment dominated by SW-vergent forethrusts, and the northern segment dominated by NE-vergent backthrusts, located to the SE and NW from the Split-Karlovac Fault, respectively. So far, it is not known why the regionally rather uniform Mesozoic Adriatic carbonate platform sequence had undergone such contrasting along-strike deformation. To improve the understanding of the initiation of the NE-vergent backthrusts and to assess the amount of crustal shortening in the NW segment, a 2D kinematic forward model across the central Velebit Mt. was set up. The Velebit Mt. extends for about 130 km along the eastern Adriatic coast and form a SW-dipping monocline with topographic elevations reaching close to 1800 m. This fault-related monocline is formed in the hanging wall of a NE-vergent backthrust system. The 2D kinematic forward model approach applied to a pre-deformed lithostratigraphic template scaled to reported stratigraphic thicknesses enabled us to test various geometries and temporal successions of fault activity not only for the Mid Eocene – Oligocene contraction, but also for the Mesozoic passive margin extension. Through an iterative trial-and-error method, we were able to reproduce the present-day deformed reference section across the Velebit Mt. and the Lika Plateau in its northeastern hinterland. Our best-fit balanced kinematic model suggests that the reactivation of Middle Triassic and Upper Jurassic basement-rooted half grabens played a key role in the initiation of the backthrusts. These half grabens were mainly reactivated by hanging wall shortcuts. This inversion of normal faults led to predetermination of the thin-skinned NE-vergent back thrusts, forming the upper part of a complex 68 km wide triangle structure. The structurally lower part comprised of a SW-vergent antiformal stack involving Paleozoic basement. We assessed a crustal shortening for the triangle structure of 47 km and a shortening of 98 km for the entire cross-section. Our results show that the differences in both the lithostratigraphic and Mesozoic half grabens along the eastern Adriatic passive margin played a crucial role in the Mid Eocene – Oligocene deformation of the external part of the Dinarides fold and thrust belt, which led to the contrasting along strike deformation styles to the NW and SE of the Split-Karlovac Fault.

The Sava suture zone of the internal Dinarides contains Maastrichtian trench-fill sediments, termed “Sava flysch” that record the closure of the northern branch of the Neotethys. Subsequent collision between Adria-derived thrust sheets and blocks of European affinity in Latest Cretaceous to Paleogene times culminated in the formation of the Dinarides fold-and-thrust belt. The suture zone hosts numerous Oligocene plutons of I-type granitic composition. Many of these intrusions are located in the center of metamorphic core complexes (MCCs) that were exhumed in early Miocene times. This phase of post-collisional extension was concomitant with the opening of the northerly adjacent Pannonian Basin and associated with granitic S-type magmatism. Both the processes responsible for extensional deformation and magmatic activity in the internal Dinarides are still a matter of debate. Our Study contributes spatio-temporal constraints to better understand the tectono-magmatic processes of this area. We present field-kinematic, geochronological, and thermobarometric data from two MCCs at the transition between the internal Dinarides and the Pannonian Basin. Both MCCs are characterized by plutonic rocks in the center, surrounded by up to amphibolite-grade mylonites of exhuming shear zones. Heterogeneous extensional reactivation of formerly contractional structures that gave rise to these core complexes as low-angle detachments in the early Miocene is indicated by a variation in deformation ages of 3 Ma, obtained by Ar-Ar in-situ dating of white mica from deformed rocks of the respective shear zones. While Motajica MCC was exhumed from within the Sava zone during E-W extension at approximately 20 Ma, Cer MCC was exhumed as part of the underlying Adriatic basement during N-S extension between 17-16 Ma. For the Cer MCC, a concordia age of 17.6±0.1 Ma (2σ) obtained by U-Pb LA-ICP-MS on zircons from an S-type granite in combination with an Ar-Ar inverse isochron age of 16.6±0.2 Ma (2σ) obtained on white mica from the same sample, indicate a cooling rate of approximately 400°C/Ma. Our results contribute to the idea of rapid exhumation of mid-crustal material in the form of MCCs in response to the opening of the Pannonian Basin. This is further corroborated by results of Raman spectroscopy on carbonaceous material, as the temperature profile across the shear zone implies extremely condensed isotherms of 250°C/km. Additionally, U-Pb analyses show that zircons of the I-type intrusion contain inherited cores with age maxima at 270 Ma and 516 Ma and newly formed rims with an age maximum at 31.7 Ma, indicating the timing of intrusion. The S-type granite of Cer in parts reworks the I-type intrusion, as inherited cores include ages of 31-32 Ma, while the rims show an age of 17-18 Ma, suggesting a syn-extensional emplacement. Our data further shows that zircons of the I-type intrusion contain a significant amount of inherited cores with an age spectrum that resembles the detrital age spectrum from sediments of the Sava zone. This challenges the idea that these I-type melts were solely generated from igneous protoliths, and rather suggests a formation from melting of Paleozoic to Mesozoic successions constituting tectonically buried nappes of the internal Dinarides.

The Periadriatic Fault System (PAF) is one of the most important tectonic and geomorphological features in the Alps. It has accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 Ma until 15 Ma. However, for such a large-scale feature, the eastern PAF reveals relatively little instrumental and historical seismic activity, especially when compared to nearby structures in the adjacent Southern Alps. With this project, we aim to show which fault segments of the eastern PAF system accommodated seismotectonic deformation in the Quaternary by applying trapped charge dating methods to fault gouges produced by its activity. We use optically stimulated luminescence (OSL) and electron spin resonance (ESR). The principle for both is the accumulation of unpaired electrons in lattice defects of quartz and feldspar, due to natural radiation product of the decay of radiogenic nuclides, which are then released during an earthquake due to shear heating allowing the system to reset (Fukuchi 1992, Aitken 1998, Tsukamoto et al., in Tanner 2019). Due to their dating range (a few decades to ~1Ma) and low closing temperature, trapped charge methods provide a unique opportunity to date earthquake activity during the Quaternary at near-surface conditions. During our field campaigns, we collected 19 fault gouge samples from 15 localities along the PAF, the Labot/Lavanttal fault, and the Šoštanj fault. From each locality, we controlled the structures found in the field, which allowed us to relate the observed deformation features in outcrop scale to the activity along each fault. Aside from the fault gouge in the cores of the large-scale structures at the sampled localities, we additionally found gouge and cataclasites formed within the host rocks in small-scale faults presenting the orientation of the respective regional fault, providing supplementary evidence of activity.

Solid earth 13(6), 957-974 (2022). doi:10.5194/se-13-957-2022, Published by Copernicus Publ., Göttingen

A significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold‐Thrust Belt. However, the spatial and temporal distribution of active shortening within the belt, especially in its NW part, is not yet well constrained. We determined depositional ages of uplifted river terraces crossing the belt along the Greater Zab River using luminescence dating. Kinematic modeling of the fault‐related fold belt was then used to calculate long‐term slip rates during the Late Pleistocene to Holocene. Our results provide new insight into the rates of active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 1.46 ± 0.60 mm a−1 of slip, while a more external basement fault further to the SW accommodates less than 0.41 ± 0.16 mm a−1. Horizontal slip rates related to detachment folding of two anticlines within the Zagros Foothills are 0.40 ± 0.10 and 1.24 ± 0.36 mm a−1. Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and in the distribution of uplifted terraces. In the southwestern part, the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment. In the NE, deformation is associated with slip on basement thrusts. Our study sheds light on the distribution of shortening in the Zagros Mountains and helps to understand the regional tectonic system. Our results may be the foundation for a better seismic hazard assessment of the entire area., Plain Language Summary: In active mountain belts, river terraces found above the present‐day river level can be indicative of differences in uplift rates due to the thickening, faulting, and folding processes in the Earth's crust. These processes, driven by the motion of tectonic plates, are responsible for the formation of mountain belts. Here, we took sediment samples from uplifted river terraces along the Greater Zab River that crosses the Zagros Mountains in the Kurdistan Region of Iraq. We determined their deposition age using luminescence dating. From their age and elevation, we calculated uplift rates. We built a geometrical model of the fault zones in the area and determined how fast the slip occurs on these faults based on the uplift rates. Our results indicate that there were less than two millimeter per year of slip on these faults on average during the last 60 thousand years. This motion is a result of the convergence between the Arabian and Eurasian plates. With studies like this we can measure how fast fault blocks move, even if they were not associated with large earthquakes in the recent past. This approach helps to better assess the potential earthquake hazard in the area under investigation., Key Points: We estimated fault slip rates in the NW Zagros Mountains by luminescence dating of river terraces and structural modeling. There is c. 1.46 mm a−1 slip on the Mountain Front Fault and c. 1.64 mm a−1 slip from detachment folding in the NE part of the Foothill Zone. Crustal thickening and basement thrusting occur in the NE parts of the Foothill Zone and only cover deformation occur in the SW parts., German Academic Exchange Service (DAAD) http://dx.doi.org/10.13039/501100001655, German Research Foundation (DFG) http://dx.doi.org/10.13039/501100001659

We describe two previously unreported, 5–7 km long normal fault scarps (NFS) occurring atop fault-related anticlines in the coastal ranges of the Dinarides fold-and-thrust belt in southern Montenegro, a region under predominant contraction. Both NFS show well-exposed, 6–9 m high, striated and locally polished fault surfaces in limestones, documenting active faulting during the Holocene. Sharply delimited ribbons on free rock faces show different color, varying karstification and lichen growth and suggest stepwise footwall exhumation, typical of repeated normal faulting earthquake events. Displacements, surface rupture lengths and geometries of the outcropping fault planes imply paleoearthquakes with Mw ≈ 6 ± 0.5 and slip rates of c. 0.3–0.5 mm/yr since the Last Glacial Maximum. Slip rates based on cosmogenic 36Cl data from the scarps are significantly higher: modeling suggests 1.5 ± 0.1 mm/yr and 6–15 cm slip every c. 35–100 yrs, commencing c. 6 kyr ago. The total throw on both NFS – although poorly constrained – is estimated to max. 200 m, and offsets the basal thrust of a regionally important tectonic unit. Both NFS are incipient extensional structures that postdate growth of the fault-related anticlines on top of which they occur. Interestingly, the position of the extensional features agrees with recent geodetic data, suggesting that our study area is located exactly at the transition from NE-SW-directed shortening in the northwest to NE-SW-directed extension to the southeast. While the contraction reflects ongoing Adria-Europe convergence taken up along the frontal portions of the Dinarides, the incipient extensional structures might be induced by rollback of the Hellenic slab in the SE, whose effects on the upper plate appear to be migrating along-strike the Hellenides towards the northwest. The newly found NFS provide evidence for a kinematic change of a thrust belt segment over time. Alternatively, the NFS might be regarded as second-order features accommodating changes in dip of the underlying first-order thrust faults to which they are tied genetically.

Young and recent tectonic activity can be discerned from instrumentally recorded seismic data as well as numerous geomorphological phenomena in the transition between the Dinarides and Hellenides fold-and-thrust belts. We introduce a multiparametric approach using field, remote sensing, and seismic data from the region SW of Shkodra Lake between the towns of Bar (Montenegro) and Lezha (Albania), an area that offers unique opportunities of relating landscape development with tectonic deformation. Particularly, we focus on windgap development on anticlines bound by Pliocene-Quaternary active faults that allow statements on relative timing and rates of tectonic movement during the Quaternary. We propose an overall orogen-perpendicular (NE-SW) gradient from enhanced uplift and high tectonic activity in the hinterland to lower activity in the foreland. An orogen-parallel (NW-SE) gradient is added by the (far field) effects of Shkodra-Peja Transverse Fault Zone (SPFZ). These overall tendencies are valid despite a complex small-scale mosaic of local differential uplift and subsidence. Recent GPS studies and plate movement reconstructions are sparse, providing rough estimates of 4–5 mm/y horizontal and ca. 1 mm/y vertical movement. Geomorphological and paleoseismological studies are crucial to particularize recent and to estimate long-term relative and absolute ground movement rates for this area.

The Dinarides fold and thrust belt on the Balkan Peninsula is the result of the long-lasting convergence between the Adriatic and Eurasian plates since the Mid-Jurassic. Late Jurassic obduction of ophiolites, Early Cretaceous composite nappe stacking, and subsequent continent-continent collision in the latest Cretaceous resulted in folding and thrusting that in the most external part of the Dinarides took place during the Middle Eocene – Oligocene. This extensive last phase of substantial crustal shortening and thickening was associated with flexural foreland basin deposition, resulting in Eo- to early Oligocene syntectonic units. These rocks and older Mesozoic carbonate platform units now form the mountain chain of the external Dinarides. So far, the driving mechanism behind the rock uplift was unknown and it was not clear when the present-day topography formed. Here we show that horizontal marine terraces preserved at elevations of up to 600 m in the external Dinarides are crucial to answer these questions.We extracted horizontal surfaces, river incision profiles, and the Adriatic and Black Sea catchments from a digital elevation model (DEM). The extracted horizontal surfaces are interpreted as marine terraces because they are degradational, locally preserved in a staircase morphology, neither bedding- nor fault-related, and located close to the present-day Adriatic shoreline. The marine terraces stretch c. 600 km along-strike the entire Dinaric coastal region. Their spatial correlation agrees with the position of a reported positive P-wave tomography anomaly beneath the Dinarides. This up to 180 km deep anomaly correlates also with the thinnest part of the Adriatic lithosphere and the Adriatic-Black Sea drainage divide. The orogen-perpendicular river incisions profiles reveal a symmetric river incision pattern on both sides of the drainage divide. The mean amount of the river incision is equivalent to the mean elevation of the documented marine terraces. All results point to an orogen-wide surface uplift of the Dinarides.Based on the geological record this post-collisional uplift event can be relatively dated to Oligocene-Miocene (28-17 Ma) and seems to be broadly contemporaneous with the emplacement of igneous rocks with mantle affinity (33-22 Ma) in the internal Dinarides. Previously published geophysical and petrological, as well as the new geomorphological data presented here suggest that the post-collisional reorganization of the Dinarides is attributed to an Oligocene-Miocene mantle delamination event, which results in uplift event affecting the entire Dinarides. We also show that no significant, orogen-scale deformation affected the uplifted Dinarides after the Early Miocene.

Extension across the southern Pannonian Basin and the internal Dinarides is characterized by the occurrence of a chain of Oligo-Miocene metamorphic core complexes (MCCs) exhumed along mylonitic low-angle extensional shear zones which in part represent former suturing thrusts. Cer MCC at the transition between the internal Dinarides and the Pannonian Basin occupies a structural position within the distal-most Adriatic thrust sheet and originates from two different tectonic processes: Late Cretaceous-Paleogene nappe-stacking during continent-continent collision between Adria and fragments of European lithosphere with Adria residing in a lower plate position, followed by Miocene exhumation. Structural data and a balanced cross section through the Cer massif show that the exhuming shear zone links to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact between the two distal-most Adriatic thrust sheets. At Cer MCC, Paleozoic greenschist- to amphibolite-grade lithologies surround a polyphase intrusion composed of I- and S-type granites. These lithologies were exhumed along the shear zone by top-N transport. Thermobarometric analyses indicate an intrusion depth of 7-8 km of the Oligocene I-type granite; cooling below ~500°C occurred at 25.4±0.6 Ma (1σ) yielded by 40Ar/39Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield 40Ar/39Ar ages of 17-18 Ma independent of the used techniques (in-situ laser ablation, single-grain total fusion, single-grain step heating, and multi-grain step heating). White mica from the S-type granite yield an 40Ar/39Ar age of 16.7±0.1 Ma (1σ). Associated dikes intruding the shear zone were also affected by N-S extension, indicating that deformation was still ongoing at that time. Our data suggests that exhumation of the MCC was related to the opening of the Pannonian back-arc basin in response to the Carpathian slab-rollback and triggered extensional reactivation of thrusts in the internal Dinarides.

The Dinaric Fault System in western Slovenia, consisting of NW-SE trending, right-lateral strike-slip faults, accommodates the northward motion of Adria with respect to Eurasia. These active faults show a clear imprint in the morphology and some of them hosted moderate instrumental earthquakes. However, it is largely unknown if the faults also had strong earthquakes in the Late Quaternary. This hampers our understanding of the regional tectonics and the seismic hazard. Geological evidence of co-seismic surface ruptures only exists for one historical event, the 1511 Idrija Earthquake with a magnitude of ~M6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to show that two of these faults, the Predjama Fault and the Idrija Fault ruptured in strong earthquakes in the Holocene. In a paleoseismological trench across the Predjama Fault we found at least one earthquake with a minimum magnitude of MW6.1 that occurred between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake with a magnitude of at least MW6.1 happened in the last ~2.1 ka. This event could correspond to the 1511 Idrija earthquake. Our results show that the faults rupture in rare, but strong earthquakes, which dominate the seismic moment release. We show that instrumental and historical seismicity data do not capture the strongest events in this area. The fact that many of the NW-SE trending, parallel faults are active implies that the deformation in western Slovenia is distributed, rather than focussed on one major structure.

The Cenozoic foreland fold and thrust belt of the external Dinarides along the eastern shore of the Adriatic Sea shows an overall NW-SE structural strike that changes to E-W in its central part, between Zadar and Mostar. This change is associated with a dextrally transpressive zone, named Split-Karlovac Fault. Segments of this fault straddle the Eo-Oligocene flexural foreland basin system of the external Dinarides. Two balanced cross-sections across the northern and southern segments of this transverse fault zone document highly contrasting styles of deformation and amount of shortening. The northern segment across Velebit Mountain is characterized by a triangle structure with a minimum shortening of 44 km. This triangle structure is formed by a set of thick-skinned top-SW thrust duplexes, topped by a thin-skinned passive top-NE roof backthrust. By contrast, the southern segment, traversing north of Split, shows a thin-skinned top-SW to top-S directed nappe stack, associated with a minimum shortening of 127 km and rooting into a basal detachment in the Paleozoic basement. To better understand parameters controlling these contrasting styles of deformation, we modelled the flexural response of the foreland lithosphere that provided the accommodation space for the Eocene to Oligocene syn-orogenic Promina Beds, a prevailingly carbonate-clastic and conglomerate-bearing sequence making a part of the foreland basin fill. Tectonic load exerted by the hinterland nappe stack was estimated using the two balanced cross-sections. Estimates of tectonic load allowed modelling the amount of flexural response that yielded depth and shape of the basin containing the Promina Beds. The best fitting modelling results provided additional confidence in the validity of the balanced cross-sections. It is shown that shortening in the two structurally contrasting segments of the thick-skinned thrust belt were contemporaneous with dextral strike-slip along the thick-skinned Split-Karlovac Fault and coeval with sedimentation of the Promina Beds. We propose that the Velebit triangle structure acted as a back-stop that prevented the propagation of the deformation front towards the SW. Instead shortening was transferred along the Split-Karlovac Fault into the southern transect, where deformation propagated towards the foreland along a successively shallowing stepped detachment. The contrasting style of Eo-Oligocene deformation probably resulted from the interplay of Permo-Triassic evaporites with the reactivation of inherited Middle Triassic normal faults to both sides of the transpressive zone.

Ar/Ar-in-situ geochronology by laser ablation NGMS (noble gas mass spectrometry) provides a powerful tool to determine inter- and intra-granular age variations of potassium-bearing minerals while maintaining the structural integrity of a sample. This makes it an excellent method in targeting the understanding of the post-collisional evolution of an orogen by dating different mica generations. In order to investigate the timing of exhumation related to extensional deformation in the Internal Dinarides, we sampled paragneisses from the upper greenschist- to amphibolite-grade mylonitic detachment zones of two metamorphic core complexes (MCC’s). The MCC’s are located at the distal Adriatic passive margin (Cer MCC, central western Serbia) and within the Late Cretaceous suturing accretionary wedge complex (Motajica MCC, northern Bosnia and Herzegovina) that separates Adria-derived units from blocks of European affinity.Mica grains were assigned to either pre-kinematic or syn-kinematic growth, according to their structural context, texture and grainsize. Pre-kinematic growth is characterized by large, deformed minerals of up to 3.5 mm in size, while rather fine-grained, recrystallized mineral aggregates that usually formed in the strain shadow of larger clasts represent syn-kinematic growth.The ages of pre-kinematic white mica from paragneisses of the Motajica detachment range from approx. 80 to 25 Ma. They partly show a large intra-granular age spread characterized by significantly older core ages becoming progressively younger towards the rim. This pattern likely suggests diffusive loss of radiogenic Ar. Ages between 80-55 Ma in the central parts of the grains, associated with a top-W transport direction, are interpreted as the time interval of mineral growth and subsequent deformation in an accretionary wedge during E-ward subduction of the Adriatic passive margin underneath European units.Syn-kinematic white mica from Motajica yielded ages between 22 and 16 Ma, which are interpreted as the time of peak activity of extension. This also corresponds with the time of crustal extension in the Pannonian Basin to the north. At Cer MCC, located roughly 150 km ENE of Motajica MCC and structurally below the accretionary wedge complex, ages of deformed white mica indicate exhumation between 19 and 15 Ma with a top-N directed transport. Our results suggest that the opening of the Pannonian Basin in response to slab-retreat underneath the Carpathian orogen resulted in the extensional reactivation of suturing thrusts that separated Adriatic from European units, leading to exhumation of parts of the accretionary wedge (Motajica MCC). This event was followed by the progressive exhumation of the passive Adriatic margin (Cer MCC) that occupied a structural position below the suturing accretionary wedge.

Assessing the extent of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Liguro-Piemont (LP) Ocean (or Alpine Tethys) in Mesozoic time using plate kinematic reconstructions of the Western Mediterranean-Alpine area.Our kinematic model is based on a compilation of geological-geophysical data and published reconstructions of the opening of the Atlantic for the motion of Europe, Africa and Iberia, and of the Cenozoic deformation along fold-and-thrust belts (Alps, Apennines, Dinarides, Provence) and extensional basins (Liguro-Provencal Basin and Sicily Channel Rift Zone) for the motion of the Adriatic plate (Adria) and Sardinia-Corsica. For Jurassic and Cretaceous times, our main assumption is to avoid significant convergence or divergence between Adria and Africa and between Iberia and Sardinia-Corsica, as there is no geological evidence for such deformation. This implies in return strike-slip motion between southern France and Iberia-Sardinia-Corsica and within the Adriatic plate.Our model shows that the LP basin opened in three phases: (1) first a slow extensional phase of c. 4 mm/yr (full rate) in Lower-Middle Jurassic between 200-165 Ma, followed by (2) a faster (up to 1.5 cm/yr) oblique extension in Middle-Upper Jurassic between 165-154 Ma, which coincides with emplacement ages of gabbros and pillow-lavas, and (3) a final main extensional phase in Upper Jurassic between 154 and 145 Ma, with rates up to 2.3 cm/yr. At 145 Ma, Iberia starts to move relative to Europe and thus extension in the LP domain decreases rapidly till it ceases completely at about 130 Ma. We interpret the first phase as rifting of the proximal part of the continental margins (200-165 Ma) followed by hyper-extension and formation of the ocean-continent transition zone (165-154 Ma), and break-up and ultra-slow oceanic spreading during the final third phase (mainly 154-145 Ma). Along a NW-SE transect between Corsica and northern Adria, we estimate the width of the LP Ocean to a maximum of ~ 240 km (oceanic domain) and the extent of the whole rifted margins to ~ 500 km, subdivided into ~380 km for the proximal and necking zones, and ~120 km for the hyper-extended and ocean-continent transition zones. Our results are supported by high-resolution thermo-mechanical modelling of the rifting phase that, using our kinematic constraints, reproduces very well the geometry of the Adriatic margin, as obtained by published geological reconstructions of the Southern Alps.We test other kinematic scenarios for the motion of Sardinia-Corsica and for the opening of the Ionian Basin which would increase the obliquity of rifting and reduce even more the width of the extended domain. Therefore, our calculated extent of the LP Ocean constitutes a maximum estimate providing crucial constraints for geodynamic modelling and a better understanding of subduction processes during the Alpine Orogeny.

Within the NW segment of the Zagros belt in the Kurdistan Region of Iraq, the Zagros Mountain Front Flexure separates the High Folded Zone from the Foothill Zone and forms a pronounced topographic and structural step. Due to the lack of outcrops and subsurface data, balanced and kinematic valid geometrical interpretations for the subsurface deformation associated with this step are not well constrained yet. To solve this, we estimated the structural relief across seven regional transects crossing the Mountain Front Flexure and we constrained the geometry of deformation from deformed-state and forward-modeled balanced cross-sections. The calculated structural relief for six out of seven transects ranges from 2 to 3 km. By using forward modeling, we show that predominantly thick-skinned deformation is needed to explain this amount of relief across the Mountain Front Flexure. Our best-fitting result suggests c. 6.5 km of displacement along a basement thrust fault that dips c. 25° at the top of the basement and that is shallowing downwards. About 4.2 km of this displacement on the basement fault were accommodated up-section by thrust-related and detachment folding of the Triassic and younger units within two prominent anticlines. About 2.3 km of displacement was transferred to the Foothill Zone, forming detachment folds above the Triassic detachment level. Inclined river terraces on the flank of anticlines within the Foothill Zone indicate ongoing displacement on this basement fault. The amount of shortening within the low topographic part of the belt from the deformation front to the limit of seismogenic thrusting within the Imbricated Zone, implies that the Late Miocene to Quaternary shortening rates there were much lower than the present-day geodetically derived convergence rates for this part of belt. These results shed new light on the geometry of the Zagros and its structural evolution.

On 26th of November 2019 an Mw 6.4 earthquake ruptured near the port town of Durrës, only 25 km from Tirana, the capital of Albania. It caused major damage and killed 51 people, making it the deadliest earthquake in 2019 worldwide.The earthquake occurred on the eastern Adriatic margin, where the Adriatic micro-plate collides with Eurasia causing widespread distributed deformation and crustal shortening that built the peri-Adriatic orogenic belts. Convergence is accommodated in the external Dinarides/Albanides by thrust faulting, mostlyalong E-dipping low-angle detachments with subordinate W-dipping back-thrusts in the most external thrust belt segment. The deformation front, particularly along the southeastern Adriatic coast, is seismically highly active, manifested not only by this most recent event, but also, e.g., by one of the largest instrumentally recorded earthquakes in Europe, the 1979 M7.1 Montenegro event slightly further north and a number of disastrous historic earthquakes.The 2019 Durrës mainshock was apparently relatively deep (~25 km) and of thrust type. It was preceded by significant foreshock activity starting in September 2019 with two Mw 5.6 and 5.1 earthquakes a few kilometres south of the mainshock that also had a thrust mechanism, however with nodal planes differing from the mainshock, indicating that these occurred on a different fault.Approximately two weeks after the mainshock, we installed a 30-station short-period seismic network to densely cover the epicentral area. We will present a preliminary analysis of the mainshock and its aftershock sequencehopefully elucidating the fault network responsible for the earthquake sequence.

The Taiwan orogen formed as a consequence of the oblique subduction of the Eurasian continental margin below the Luzon volcanic arc of the Philippine Sea Plate since the late Miocene. The Yuli Belt of the eastern Taiwan Central Range, exposed in the retro-wedge of the fold-and-thrust belt, hosts slivers of a heterogeneous unit of blueschist-facies rocks that are among the youngest blueschist units worldwide. However, the palaeogeographic provenance of this unit is still debated. This is due to the fact that numerous structural aspects, including the kinematics of the Yuli Belt’s tectonic contacts with adjacent units, are improperly understood.Our studies form part of an ongoing reinvestigation of the tectonic evolution of the Yuli Belt. A revised geological map of the Yuli Belt was generated, incorporating own structural data from several river transects. Fieldwork and microstructural analyses suggest that the Yuli Belt was polyphasely deformed. Based on newly constructed cross sections we suspect that the blueschist-facies units were tectonically emplaced along thrusts on top of a mostly greenschist-facies metasedimentary unit that locally exhibits characteristics of a mélange. Later, both blueschist-facies and metasedimentary units were tightly folded, likely during the emplacement of the Yuli Belt onto the westerly adjacent Eurasia-derived Tailuko Belt along the so-called Shoufeng Fault. Lithological and fabric transitions across this fault are gradual, suggesting that the juxtaposition of Yuli and Tailuko Belts occurred during an early W-directed transport direction before becoming refolded during later E-vergent backfolding. Peak metamorphic temperatures in the greenschist-facies metasediments, estimated by Raman spectroscopic analyses of carbonaceous material (RSCM), reveal systematic spatial variations across the Yuli belt, supporting the idea of an allochthonous nature of the blueschist units on top of the lower grade metasedimentary unit.The incorporation of published geochronological and whole-rock geochemical data and their combination with own paleogeographic reconstructions led us to fundamentally reinterpret the structural position of the Yuli Belt. We suggest that the blueschist-facies unit most likely represents a mid-Miocene fragment of oceanic crust and mantle issued in the South China Sea before having been subducted, exhumed and ‘sandwiched’ between the (Eurasia-derived) Tailuko Belt and the easterly adjacent Coastal Ranges derived from the Philippine Sea plate. The Yuli Belt should hence be considered to contain the suture between the Eurasian and the Philippine Sea plates.

s & presentations : EGU General Assembly 2020 EGU General Assembly 2020, EGU2020, online, 4 May 2020 - 8 May 2020; Göttingen : Copernicus Gesellschaft mbH EGU2020-10254, 1 Seite (2020). doi:10.5194/egusphere-egu2020-10254, Published by Copernicus Gesellschaft mbH, Göttingen

Understanding the kinematics of pre-existing fractures under the present-day stress field is an indispensable prerequisite for hydraulically increasing fracture-induced rock permeability, i.e. through hydraulic stimulation, which forms the basis of economically viable exploitation of resources such as natural gas and geothermal energy. Predicting the likelihood of reactivating pre-existing fractures in a target reservoir at particular fluid injection pressures requires detailed knowledge of the orientations and magnitudes of the prevailing stresses as well as pore fluid pressures. In the absence of actual in-situ stress measurements, e.g. derived from boreholes, as is mostly the case in previously underexplored “frontier areas”, such predictions are often difficult. In this study, the potential of reactivating pre-existing fractures in a likely exploration region of the southern Karoo of South Africa is investigated. The orientations of the present-day in-situ stresses were assessed from surrounding earthquake focal mechanisms, implying c. NW-SE oriented maximum horizontal stress and a stress regime changing between strike-slip and normal faulting. A comparison with paleo-stress axes derived from inverted fault-slip data suggests that the stress field very likely did not experience any significant reorientation since Cretaceous times. Maximum possible in-situ stress magnitudes are estimated by assuming that these are limited by frictional strength on pre-existing planes and subsequently, slip and dilation tendency calculations were performed, assuming hydrostatic pore fluid pressures of c. 32 MPa at targeted reservoir depth. The results suggest that prevalent E-W and NW-SE oriented sub-vertical fractures are likely to be reactivated at wellhead pressures exceeding hydrostatic pore fluid pressures by as little as 2–5 MPa, while less prevalent sub-horizontal and moderately inclined fractures require higher wellhead pressures that are still technically feasible. Importantly, actual in-situ stress measurements are essential to test these theoretical considerations and to guide the design of safe and effective exploration linked to fracture manipulation, such as shale gas recovery.

The structural evolution of Central Europe reflects contrasting tectonic regimes after the Variscan orogeny during Mesozoic – Cenozoic time. The brittle deformation related to each tectonic regime is localized mainly along major fault zones, creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events. By contrast, fracture patterns in less deformed domains often provide a pristine structural inventory. We investigate the brittle deformation of a relatively stable, wide area of the central German platform using fault-slip data to identify the regional stress fields required to satisfy the data. In a non-classical approach, and in order to avoid local stress variations and misinterpretations, the fault-slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks. Direct stress tensor inversion was performed through an iterative refining process, and the computed stress tensors were verified using field-based observations. Criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events, which begins with a post-Triassic normal faulting regime with σ3 axis trending NE-SW. The deformation then follows by strike-slip and thrust faulting regimes with a change of σ1 axis from N-S to NE-SW, supposedly in the Late Cretaceous. Two younger events are characterized by Cenozoic normal and oblique thrust faulting regimes with NW-SE-trending σ3 and σ1 axes, respectively. The fracture patterns of both the cover and basement rocks appear to record the same states of stress.

The NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq forms a prominent topographic and structural step separating the High Folded and Foothill zones. Due to scarcity of subsurface data, the geometry of faults underlying this flexure and the degree of basement involvement are poorly constrained. To overcome this, we estimated the structural relief along seven transects across the belt and reconstructed deformed geometries using balanced cross-sections. The average structural relief for six transects is around 2.6 km. Iterative kinematic forward modeling along one of these transects suggests that a multi-stage evolution involving both thin- and thick-skinned deformation can explain the observed structural relief. Our preferred model shows that early detachment folds in the Mesozoic to Neogene succession were overprinted by a NE-dipping basement-rooted thrust system with a cumulative displacement of 6.5 km. Up-dip, the basement thrust bifurcates into two splay thrusts. While the structurally higher splay accommodated 4.2 km of slip and amplified frontal anticlines to form the Mountain Front Flexure, the lower and younger splay took up 2.3 km of slip, which was mainly transferred into the Triassic basal detachment of the Foothill Zone. The shortening across the NW Zagros is calculated at c. 24.8 km. The shortening amount within the topographically low part of the belt implies that the Late Miocene to Quaternary shortening rate was much lower than the geodetically derived convergence rate.

The NW-SE trending Udine-Buttrio Thrust is a partly blind fault that affects the Friulian plain southeast of Udine in NE Italy. It is part of a wider fault system that accommodates the northward motion of the Adriatic plate. Although seismic reflection data and morphological evidence show that the fault was active during the Quaternary, comparably little is known about its tectonic activity. We used high-resolution digital elevation models to investigate the surface expression of the fault. Measured vertical surface offsets show significant changes along strike with uplift rates varying between 0 and 0.5 mm/yr. We then analyze a topographic scarp near the village of Manzano in more detail. Field mapping and geophysical prospections (Georadar and Electrical Resistivity Tomography) were used to image the subsurface geometry of the fault. We found vertical offsets of 1&ndash, 3 m in Natisone River terraces younger than 20 ka. The geophysical data allowed the identification of deformation of the fluvial sediments, supporting the idea that the topographic scarp is a tectonic feature and that the terraces have been uplifted systematically over time. Our findings fit the long-term behaviour of the Udine-Buttrio Thrust. We estimate a post-glacial vertical uplift rate of 0.08&ndash, 0.17 mm/yr recorded by the offset terraces. Our results shed light on the Late Quaternary behaviour of this thrust fault in the complicated regional tectonic setting and inform about its hitherto overlooked possible seismic hazard.

Eocene to Early Oligocene syn-rift deposits of the southern Upper Rhine Graben (URG) accumulated in restricted environments. Sedimentation was controlled by local clastic supply from the graben flanks, as well as by strong intra-basinal variations in accommodation space due to differential tectonic subsidence, that in turn led to pronounced lateral variations in depositional environment. Three large-scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions. They form three major base level cycles that can be traced throughout the basin, each of them representing a stratigraphic sub-unit. A relatively constant amount of horizontal extension (ΔL) in the range of 4–5 km has been estimated for the URG from numerous cross-sections. The width of the rift (Lf), however, varies between 35 and more than 60 km, resulting in a variable crustal stretching factor between the bounding masterfaults. Apart from block tilting, tectonic subsidence was, therefore, largely controlled by changes in the initial rift width (L0). The along-strike variations of the graben width are responsible for the development of a deep, trough-like evaporite basin (Potash Basin) in the narrowest part of the southern URG, adjacent to shallow areas in the wider parts of the rift such as the Colmar Swell in the north and the Rhine Bresse Transfer Zone that delimits the URG to the south. Under a constant amount of extension, the along-strike variation in rift width is the principal factor controlling depo-centre development in extensional basins.

Blueschist facies rocks in the Yuli Belt of Taiwan’s Central Range record ongoing subduction of the Eurasian plate. We present a prograde Lu–Hf garnet–whole-rock age of 5.1 � 1.7 Ma from a retrogressed blueschist in the Yuli Belt. This age is considerably younger than the previously assumed age of 14–8 Ma for high-pressure metamorphism in the Yuli Belt and represents the youngest Lu–Hf garnet age ever recorded for blueschist facies metamorphism. The age sheds new light on the palaeogeographic origin and exhumation scenario of the Yuli Belt. We propose that the Yuli Belt originated from the ocean–continent boundary of the Chinese passive margin. It was subducted eastward during collision with the Luzon island arc and rapidly exhumed when the forearc lithosphere was removed from above the continental slab by discrete subduction (extraction). This process reduces the pressure above the continental slab and may prompt the ascent of subducted crust into the opening gap. Thus, it can control the exhumation of high-pressure rocks.

In order to better understand the mode of subduction polarity reversal in the Taiwan–Luzon arc-continent collision zone, we mapped its crust–mantle boundaries using local earthquake tomography. By contouring surfaces of constant Vp = 7.5 km s− 1, we identified three Moho discontinuities and the plate interface that juxtaposes Eurasian lower crust against mantle lithosphere of the Philippine Sea plate. The plate interface dips to the east under southeastern Taiwan and steepens progressively towards north until it becomes vertical at 23.7°N. From there it continues northward in a vertical orientation, until the limit of the tomographic model inhibited further mapping. For the Moho, additional depth constraints were derived from 1D models using P-wave arrivals of local earthquakes. The Mohos of the Eurasian and Philippine Sea plates are disconnected across the plate interface. Beneath southern Taiwan, the Eurasian Moho dips to the east at 50–60°, following the orientation of the plate boundary and continuous with the Benioff zone. Towards north, the Eurasian Moho steepens into subvertical, again together with the plate boundary. The Philippine Sea plate Moho exhibits a synform-like crustal root, interpreted as the base of the magmatic Luzon arc. Towards the north, this root deepens from 30 to 70 km underneath the Ryukyu trench. In northernmost Taiwan, the hinge of the vertically subducting Eurasian slab steps westward out of the thrust belt, leaving the deformation front to the east inactive and giving way to the north-dipping Philippine Sea plate. A subhorizontal Moho at 30–35 km depth overlies the north-dipping Philippine Sea slab and is interpreted as a newly formed Moho, established after westward rollback and delamination of the subducting Eurasian slab. In combination, these data support a model of progressive subduction polarity reversal, in which a tear within the Eurasian lithosphere propagated southwestward, deactivating the deformation front.

The Motajica Massif in Bosnia, situated in the Sava Zone between the Tisza Unit and the Dinarides, hosts a Late Cretaceous flysch series, which is partly preserved in an anchimetamorphic state, partly affected by amphibolite-facies overprint. Samples from both parts contain abundant accessory monazite, which was investigated by means of the electron microprobe with reference to age and composition. In the amphibolite-facies samples new metamorphic monazite has formed. Chemical Th–U–Pb monazite ages indicate that the regional metamorphic event happened in the Late Cretaceous or the Early Palaeogene. In addition, inherited detrital monazite of Permian age has been identified. Based on various observations it is argued that the detrital monazite was not the direct precursor to the metamorphic monazite. The latter may rather have grown from other, more reactive REE carrier minerals, either detrital ones (e.g. detrital allanite) or such that formed during diagenesis and low-grade metamorphism. A later greenschist-facies event that occurred in connection with a ca. 27 Ma old granodiorite intrusion led in some samples to the formation of late fluorapatite–allanite coronas around both detrital and newly formed monazites. The anchimetamorphic samples contain exclusively detrital monazite. These are partly of Permian as well as Jurassic to Early Cretaceous age. Based on their compositional and textural features, the Jurassic to Early Cretaceous monazite relics are considered to be mainly derived from metamorphic rocks. The Permian monazite displays high yttrium content up to ca. 3.5 wt.% Y 2 O 3 , indicating a high formation temperature (> 650 °C) and therefore probably a magmatic origin. Apart from almost ubiquitous Permian high-Y monazite, the Motajica flysch also contains large Permian xenotime with magmatic zoning patterns, fluorapatite with parasitic monazite inclusions (formerly REE-rich fluorapatite), and zircon with A-type granite morphology. This accessory mineral spectrum implies that, among others, rift-related REE-rich Permian A-type granites or rhyolites should be considered as a source for the Sava Zone flysch.

Situés dans la partie la plus distale du bassin molassique suisse et dans le prolongement sud du fossé rhénan, les dépôts conglomératiques appartenant au groupe stratigraphique des Gompholithes & Conglomérats ont fait l’objet d’une étude sédimentologique et paléontologique détaillée. La multitude des affleurements réalisés lors des travaux de construction de l’autoroute Transjurane dans la région de Porrentruy (Jura), permet d’appréhender ces paléoenvironnements rupéliens (Oligocène inférieur). Les études sédimentologiques et paléontologiques révèlent l’existence d’environnements côtiers avec des falaises de calcaires mésozoïques entaillées par des canyons où se trouvent des rivières au régime torrentiel. Ces rivières qui érodent les couches du Mésozoïque créent des galets qui sont déposés sous la forme de deltas marins progradant vers le nord. A l’abri des exutoires des canyons se développent quelques environnements lacustres. Ces dépôts conglomératiques sont fortement liés à l’activité tectonique rupélienne. La distension rhénane et l’activité de la faille transformante située entre le fossé rhénan et le bassin de la Bresse subdivisent les différents blocs mésozoïques en horsts et grabens, permettant ainsi l’érosion des sédiments dans les parties hautes (horst) et leur transport dans les zones basses (graben). La découverte de rares galets de roches endogènes et effusives dans les dépôts conglomératiques montre un transport du socle des Vosges vers le sud dans la région de Porrentruy par l’intermédiaire sans doute d’une dérive littorale. Bien que la surrection des Vosges et de la Forêt-Noire et leur mise à l’érosion soient connues dès la base du Miocène, la présence de ces galets atteste l’existence de failles dès le début du Rupélien qui mettent à l’érosion le socle du massif des Vosges. Located in the distal part of the Swiss Molasse Basin and in the southern extension of the Rhine Graben, the conglomeratic deposits belonging to the Gompholithes & Conglomérats stratigraphic group have been the object of detailed sedimentological and paleontological studies. The great number of outcrops that came into sight during the building works of the Transjurane highway in the vicinity of Porrentruy (Swiss Jura) lead to a better understanding of Rupelian paleoenvironments (Early Oligocene). The sedimentological and paleontological studies reveal the existence of coastal environments with Mesozoic limestone cliffs notched by canyons with torrential rivers. Those rivers eroding the Mesozoic series create pebbles deposits forming marine deltas prograding towards North. In protected areas, some lacustrine environments can develop. These conglomeratic deposits are strongly bound to the Rupelian tectonic activity. The rhenish distension and the activity of the transform faults located between the Rhine Graben and the Bresse basin divide the Mesozoic blocks in horst and graben structures, thus allowing the erosion of sediments in higher regions (horst) and their transport in lower zones (graben). The discovery of rare pebbles made of endogene and effusive rocks in those conglomeratic deposits shows a transport coming from the Vosges massifs towards south to the Porrentruy region, probably with the support of a littoral drift. Although the surrection of the Vosges and Schwarzwald massifs (and the beginning of their erosion) is normally attributed to the base of the Miocene, the presence of those pebbles attests the existence of faults putting the basement of the Vosges massif to erosion since the base of Rupelian. Im distalsten Teil des schweizerischen Molasse-Beckens und in der Südverlängerung des Rheingrabens befinden sich die Konglomeratablagerungen der stratigraphischen Gruppe Gompholithes & Conglomérats, die hier einer sedimentologischen und paläontologischen detaillierten Studie unterzogen werden. Die zahlreichen Aufschlüsse, die beim Bau der Autobahn Transjurane in der Region von Porrentruy (Jura) zu Tage getreten sind, erlauben, diese rupelische (fruhes Oligozän) Paläoumgebung besser zu verstehen. Die sedimentologischen und paläontologischen Studien deuten auf die Existenz einer Küste aus mesozoischen Kalkklippen hin, die von Cañons eingeschnitten wurde. Sintflutartige Flüsse, die das Mesozoikum erodierten, Gerölle sedimentierten, die in einem nach Norden progradierenden Delta in das Meer geschüttet wurden. Lokal entwickelte sich eine lakustrine Umgebung mit kontinentalen Kalksedimenten. Diese Konglomeratablagerungen entstanden im Zusammenhang mit der tektonischen Aktivität im Rupelium. Die Rheingrabendehnung und die Aktivität der Blattverschiebungen zwischen dem Rheingraben und dem Bresse-Becken führten zur Zergliederung der mesozoischen Blöcke in Horste und Gräben. Es resultierte die Erosion der Sedimente in den gehobenen Teilen (Horste) und ihr Transport respektive Ablagerung in die niedrigen Zonen (Gräben). Die Nachweis von Geröllen endogener und effusiver Gesteine in den Konglomeratablagerungen weist auf einen Transport aus dem Vogesen durch Küstenströmungen in Richtung Süden hin in die Region von Porrentruy und auf die Herkunft der Gerölle aus dem Vogesen Massiv. Die Anhebung der Vogesen und des Schwarzwaldes und der Beginn ihrer Erosion wurde bislang mit Unter-Miozäns datierte. Unsere Untersuchungen belegen die Existenz von Brüchen, und den Beginn der Erosion schon an der Basis des Rupelium.