Paraglacial adjustment of alluvial fans to the last deglaciation in the Snežnik Mountain, Dinaric karst (Slovenia)

Glaciokarst depressions are major glacigenic depocenters in the Dinaric mountain karst areas and often store important information about the timing and nature of glacial processes and paraglacial sediment reworking. This study focuses on Praprotna draga, which is one of the largest glaciokarst depressions in the Sneznik Mountain (Dinaric karst), with an area of similar to 3.4 km(2) and a maximum depth of 140 m. The western slopes of the depression are characterized by undulated moraine morphology and alluvial fans are filling its entire floor. We present the results on the thickness, origin and age of the sediment infill using a complementary geomorphological, sedimentological, geophysical and dating approach. Distribution of moraines point to two glacial advances that were associated with two main alluvial fan aggradation phases recognized using the electrical resistivity tomography measurements. The youngest alluvial deposits were sampled for cosmogenic Cl-36 analysis using amalgamated carbonate pebbles. The depth profile of Cl-36 concentrations suggests an age of 123 +/- 1.7 ka when assuming a likely denudation rate of 20 mm ka(-1). Since the existence of the Younger Dryas glaciers in the study area is climatically difficult to explain, we tentatively propose that the youngest alluvial deposition in Praprotna draga took place after the glacier retreat during the paraglacial period. Our findings suggest that the time window of paraglacial adjustment in the Sneznik Mountain was brief and likely conditioned by quick recolonization with vegetation and inefficient surface runoff on deglaciated karst terrain. (C) 2019 Elsevier B.V. All rights reserved

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Quaternary uplift along a passive continental margin (Oman, Indian Ocean)

Crustal movement along the coastline of the Arabian Sea in Oman is quantified along a 72 km long coastal section characterised by staircases of marine terraces. An extensive topographic, geomorphological and geological survey was conducted on these terraces and an age model based on cosmogenic nuclide (Be-10, Cl-36) and optically stimulated luminescence dating is presented, together with a new approach to extract palaeo-shorelines from a high-resolution digital elevation model. The uplifting crustal block is fault bounded and is composed of obduction related peridotites overlain by shallow marine limestone. Nine distinct terrace levels are identified and the results indicate continuous uplift between Marine Isotope Stage (MIS) 5a and MIS 19. The calculated uplift rates vary along the coastline and a northward tilting of the uplifted coastal block is interpreted as evidence for differential uplift. The geomorphology of the terraces proves that the tilting must have taken place after the last interglacial. Tectonic forcing of the uplift by a crustal forebulge associated with the Makran Subduction Zone is discussed. It is also concluded that the uplift involves processes of serpentinisation of the peridotites in combination with karstification of the overlying limestone formations. As water is essential for both processes, climate change during the Quaternary apparently played a significant role in the uplift process as well as hydro-isostasy. (C) 2019 Elsevier B.V. All rights reserved

Aegean-style extensional deformation in the contractional southern Dinarides: incipient normal fault scarps in Montenegro

We describe two 5-7 km long normal fault scarps (NFSs) 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 NFSs show well-exposed, 6-9 m high, striated, and locally polished fault surfaces, cutting uniformly northeastward-dipping limestone beds at high angles and documenting active faulting. Sharply delimited ribbons on free rock faces show different colors, varying karstification, and lichen growth and suggest stepwise footwall exhumation, which is typical of repeated normal faulting during earthquake events. Displacements, surface rupture lengths, and geometries of the outcropping fault planes imply paleoearthquakes with M-w approximate to 6 +/- 0.5 and slip rates of similar to 0.5-1.5 mm yr(-1) since the Last Glacial Maximum. This is well in line with (more reliable, higher-resolution) slip rates based on cosmogenic Cl-36 data from the scarps for which modeling suggests 1.5 +/- 0.1 mm yr(-1) and 6-15 cm slip every 35-100 years during the last similar to 6 kyr. The total throw on both NFSs - although poorly constrained - is estimated to similar to 200 m and offsets the basal thrust of a regionally important tectonic unit. The NFSs are incipient extensional structures cutting (and postdating emplacement of) the uppermost Dinaric thrust stacks down to an unknown depth. To explain their existence in a region apparently under pure contraction, we consider two possibilities: (i) syn-convergent NFS development or - less likely - (ii) a hitherto undocumented propagation of extensional tectonics from the hinterland. Interestingly, the position of the extensional features documented here agrees with geode- tic data, suggesting that our study area is located broadly 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 southeast, whose effects on the upper plate appear to be migrating along-strike of the Hellenides towards the northwest. In that sense, the newly found NFSs possibly provide evidence for a kinematic change of a thrust belt segment over time. However, with a significantly higher probability, they can be regarded as second-order features accommodating geometrical changes in the underlying first-order thrust faults to which they are tied genetically