High-resolution morpho-tectonic profiling across an orogen: tectonic-controlled geomorphology and multiple dating approach in the SE Carpathians

Andriessen, P.A.M. [Promotor]Dinu, C. [Promotor]Matenco, L.C. [Copromotor]Fielitz, W. [Copromotor

Late Pliocene-Quaternary tectonics in the frontal part of the SE Carpathians: Insights from tectonic geomorphology.

The Romanian East Carpathians display large-scale heterogeneities along the mountain belt, unusual foredeep geometries, significant post-collisional and neotectonic activity, and major variations in topography, mostly developed in the aftermath of late Miocene (Sarmatian; ∼11 Ma) subduction/underthrusting and continental collision between the East European/Scythian/Moesian foreland and the inner Carpathians Tisza-Dacia unit. In particular, the SE corner of the arcuate orogenic belt represents the place of still active large-scale differential vertical movements between the uplifting mountain chain and the subsiding Focşani foredeep basin. In this key area, we have analysed the configuration of the present day landforms and the drainage patterns in order to quantify the amplitude, timing and kinematics of these post-collisional late Pliocene-Quaternary vertical movements. A river network is incising in the upstream a high topography consisting of the external Carpathians nappes and the Pliocene-Lower Pleistocene sediments of the foreland. Further eastwards in the downstream, this network is cross-cutting a low topography consisting of the Middle Pleistocene-Holocene sediments of the foreland. Geological observations and well-preserved geomorphic features demonstrate a complex succession of geological structures. The late Pliocene-Holocene tectonic evolution is generally characterised by coeval uplift in the mountain chain and subsidence in the foreland. At a more detailed scale, these vertical movements took place in pulses of accelerated motion, with laterally variable amplitude both in space and in time. After a first late Pliocene uplifting period, subsidence took place during the Earliest Pleistocene resulting in a basal Quaternary unconformity. This was followed by two, quantifiable periods of increased uplift, which affected the studied area at the transition between the Carpathians orogen and the Focşani foreland basin in the late Early Pleistocene and the late Middle to late Pleistocene. Both large-scale deformation events affected the western Focşani basin flank, tilting the entire structure with ∼9° during the late Early Pleistocene and uplifted it as a block during the early Late Pleistocene. The late Early Pleistocene tilting resulted in ∼750 m uplift near the frontal monocline and by extrapolation in a presumed 3000 m uplift near the central parts of the Carpathians. The late Middle to late Pleistocene cumulative uplift reaches ∼250 m and correlates with a contemporaneous progradation of the uplifted areas towards the Focşni Basin. The uplifting events are separated by a second Quaternary unconformity. On the whole, the late Pliocene-Quaternary evolution of the Carpathians orogen/Focşani basin structure indicate large-scale differential uplift during the latest stages of a continuous post-collisional orogenic evolution. © 2005 Elsevier B.V. All rights reserved

Foreland migration of orogenic exhumation during nappe stacking: Inferences from a high-resolution thermochronological profile over the Southeast Carpathians

© 2021 Elsevier B.V.The exhumation mechanism of orogens showing one structural vergence, or single-sided orogens, is still not fully understood due to their common transition from periods of high convergence to slab retreat. The overprinting of inherited nappe stacks by subsequent back-arc extension makes it difficult to assess the low amounts of contractional exhumation observed, which are furthermore difficult to interpret due to long residence times in partial retention zones of typical low-temperature thermochronology markers. This is the case in many orogens worldwide and is often observed in the Mediterranean area as well. One notable exception is the Romanian segment of the Carpathian Mountains, where the back-arc extension took place far from the location where the nappe stack formed. To understand the mechanics of contractional exhumation in this single-sided orogen, we generated a new high-resolution low-temperature (apatite fission-track and U-Th/He) thermochronological transect across the Southeast Carpathian nappe stack and its foreland. This new dataset and its correlation with previous exhumation and kinematic studies demonstrate that the gradual accretion of sediments and crustal material was associated with an exhumation that migrated progressively towards the foreland throughout the entire contractional history. The exhumation style changed when the thin-skinned deformation was interrupted by periods of crustal accretion, associated either with the late Eocene onset of continental collision or with the late Miocene locking of the subduction system. The generally accepted moments of onset and termination of slab retreat are not directly visible in available exhumation data of the Southeast Carpathians. Our results are in agreement with modelling studies, which inferred that the formation of single-sided collisional wedges is primarily controlled by the pre-existing rheology of continental plates and is associated with large amounts of continental subduction

Middel Pleistocene to Holocene fluvial terrace development and uplift-driven valley incision in the SE Carpathians, Romania

This study reveals that in the SE Carpathians terrace development and fluvial incision during the Middle Pleistocene-Holocene are predominantly controlled by tectonic uplift as shown by terrace distributions and uplift amounts and rates. The work focuses on a transect from the internal nappes and Braşov intramontane basin (western domain) to the external nappes and Focşani foredeep basin (eastern domain). New infrared stimulated luminescence ages were obtained and minimum terrace formation ages were determined to derive fluvial incision rates, and thereby, to constrain tectonic uplift. In the eastern domain, non-uniform terrace distributions in adjacent sub-parallel more active Punta and less active Şuşiţa rivers and an eastward migrated fluvial incision from the orogen to the foredeep basin indicate tectonic uplift as dominant control on terrace development. Strath-terraces in the western and eastern domains indicate repeated events of vertical fluvial incision and lateral erosion during the early Middle Pleistocene and late Middle Pleistocene-Holocene, respectively. These events imply successive recurrent disturbances of equilibrium conditions due to pulses of increased tectonic uplift. Fill-terraces in the western domain show that initial aggradation periods were followed by uplift-driven vertical incision during the late Middle-Late Pleistocene. As fill-terraces show a wide-spread development, climatic change and complex response cannot be excluded as contributing factors. Synchronous to terrace development, loess deposition periods during the late Middle-Late Pleistocene and Latest Pleistocene and intercalated episodes of palaeosol formation during the Late Pleistocene imply comparable climatic conditions across the SE Carpathians. Dominant strath-terraces of the eastern domain indicate stronger fluvial incision (~. 240. m) since the late Middle Pleistocene, whereas older strath- and younger dominant fill-terraces of the western domain designate a lower amount (~. 90. m) since the early Middle Pleistocene. Middle Pleistocene-Holocene fluvial incision rates document higher tectonic uplift in the external nappes and lower towards the western intramontane and eastern foredeep basins. © 2013 Elsevier B.V

Landscape response to progressive tectonic and climatic forcing in NW Borneo: Implications for geological and geomorphic controls on flood hazard

(IF 4.12; Q1)International audienceEmpirical models have simulated the consequences of uplift and orographic-precipitation on the evolution of orogens whereas the effects of these forcings on ridgelines and consequent topography of natural landscapes remain equivocal. Here we demonstrate the feedback of a terrestrial landscape in NW Borneo subject to uplift and precipitation gradient owing to orographic effect, and leading to less-predictable flooding and irreversible damages to life and property. Disequilibrium in a large catchment recording the lowest rainfall rates in Borneo, and adjacent drainage basins as determined through χ, a proxy for steady–state channel elevation, is shown to result in dynamic migration of water divide from the windward-side of the orogen towards the leeward-side to attain equilibrium. Loss of drainage area in the leeward-side reduces erosion rates with progressive shortening resulting in an unstable landscape with tectonic uplift, gravity faults and debris flows. 14 C dating of exhumed cut-and-fill terraces reveal a Mid–Pleistocene age, suggesting tectonic events in the trend of exhumation rates (>7 mm a −1) estimated by thermochronology, and confirmed by morphotectonic and sedimentological analyses. Our study suggests that divide migration leads to lowered erosion rates, channel narrowing, and sediment accretion in intermontane basins on the leeward-side ultimately resulting in enhanced flooding. The continued, yet variable rates of interactions between tectonic and climatic forcing result in diversity of landscape evolution. A number of physical and numerical models 1–4 have shown the effects of uplift and orographi-cally enhanced precipitation on the evolution of active mountain ranges. However, in a natural landscape, subject to tectonic uplift and climatic perturbations, the feedback of ridgelines and subsequent rain-shadowed topography remains less-understood. These natural processes, often aggravated by anthropogenic intervention can result in catastrophic geohazards such as flooding, causing irreversible damages. The consequences of floods include loss of human life, crops and livestock, and the spread of water borne diseases 5–7. Economic vulnerability arising from damage to infrastructure such as roads and bridges could have long–term impacts causing disruption to transportation and emergency flood evacuation services. Thus, understanding the consequences of varied landscape evolution under the influences of tectonic and climatic forcing has critical inputs for mitigation of geohazards especially in tectonically dynamic, climatically sensitive and highly populated regions of the World such as Southeast Asia. NW Borneo (Fig. 1) is a typical example where floods have caused community disruptio