The post-flysch (Oligocene–Miocene) palaeogeographic evolution of the entire North Alpine Foreland Basin (NAFB) between Savoy (France) and Lower Austria is presented in eight sketch maps. The ...compilation considers the palinspastic evolution of the Alps. It includes intramontane deposits, which represent a continuous marginal facies of the NAFB during Rupelian to Early Burdigalian times.
The facies distribution in the NAFB was driven by two major types of processes, which are related to the tectonic evolution of the Alpine orogen. The first type, representing tectonic processes at the thrust front of the Alps, directly influenced the facies distribution of the narrowing NAFB. The second type represents an indirect impact of Alpine uplift and tectonics to the NAFB, transformed by varying sediment discharge.
A strong increase in sediment discharge due to uplift of the Alps is the major reason for the generally regressive coarsening- and shallowing-upward cycle from the Lower Marine to the Lower Freshwater Molasse (UMM, USM) between 33 and 21 Ma. The development of the “Burdigalian Seaway” at ∼20 Ma was coeval with a reduction of thrust advance rates in the western and central part of the NAFB. Shallow marine conditions (Upper Marine Molasse, OMM) prevailed for ∼3 million years. In the Eastern Alps, reduction of relief due to lateral (east–west-oriented) extension caused a strong reduction in sediment discharge. Closure of the “Burdigalian Seaway” around 17 Ma occurred during a phase of tectonic reorganisation in the Alpine orogen and is coeval with a short-term increase in sediment discharge. Between 17 and 12 Ma, the NAFB was constantly overfilled (Upper Freshwater Molasse, OSM), despite strongly decreasing sediment discharge. Termination of sedimentation in the (unfolded) NAFB occurred diachronously in an undramatic process. It started in the western NAFB in the course of uplift of the Swiss Jura Mountains after 11 Ma and reached Lower Austria around 6–5 Ma. Strong uplift of the Alps and the NAFB started at around 6 Ma in the Swiss and Western Alps and at 4–3 Ma in the Eastern Alps. The uplift was followed by reworking and erosion of more than 2 km of Molasse sediments in the western NAFB.
Deckenschotter (‘Cover Gravels’) are proximal glaciofluvial gravels located in the northern Alpine Foreland mainly beyond the extent of the Last Glacial Maximum. They cover Tertiary Molasse or ...Mesozoic bedrock with an erosional unconformity. In Switzerland, Deckenschotter are referred to as Höhere (Higher) and Tiefere (Lower) Deckenschotter based on their topographical positions with a significant phase of incision that separates these two units. For this study, we performed sedimentological analyses to identify the provenance, transport mechanisms and depositional environment of these gravels. In addition, we established the chronology of the Höhere Deckenschotter gravels at Stadlerberg using cosmogenic 10Be depth-profile dating technique. The inherited 10Be concentration then allowed estimation of a catchment-wide palaeo-denudation rate. The results from clast fabric investigations indicate that braided rivers within a glaciofluvial environment transported these sediments to the study site mainly as bedload. In addition, the petrographic composition of the deposits shows that a large portion of the gravels was derived through erosional recycling of Miocene Molasse conglomerates. Some material was additionally sourced in the northern Central Alps. We then conclude that gravel accumulation in the Swiss Alpine Foreland was completed at 1.9±0.2Ma. This age, however, represents a minimum age and the oldest 10Be depth-profile age ever obtained for a geological unit. Furthermore, a palaeo-denudation rate of c. 0.3–0.4mm/a was estimated for the catchment of Stadlerberg gravels. Finally, elevation differences between the bedrock underlying the Höhere Deckenschotter and the modern base level imply a long-term regional incision rate of c. 0.12mm/a.
•1.9±0.2Ma 10Be depth-profile age for gravels in the northern Alpine Foreland•Provenance from the northern Central Alps and reworked from Miocene Molasse•Transport mainly as bedload in braided rivers in a glaciofluvial system•0.12mm/a long-term bedrock incision rate•0.3–0.4mm/a palaeo-denudation rate estimation for the palaeocatchment
The age of high-elevation planation surfaces in Corsica is constrained using new apatite (U-Th)/He data, field observations, and published work (zircon fission track, apatite fission track AFT data ...and landform/stratigraphical analysis). Thermal modeling results based on AFT and (U-Th)/He data, and the Eocene sediments uncomformably overlapping the Variscan crystalline basement indicate that present-day elevated planation surfaces in Corsica are the remnants of an erosion surface formed on the basement between ∼120 and ∼60 Ma. During the Alpine collision in the Paleocene-Eocene, the Variscan crystalline basement was buried beneath a westward-thinning wedge of flysch, and the eastern portion was overridden by the Alpine nappes. Resetting of the apatite fission track thermochronometer suggests an overburden thickness of >4 km covering Variscan Corsica. Protected by soft sediment, the planation surface was preserved. In the latest Oligocene to Miocene times, the surface was re-exposed and offset by reactivated faults, with individual basement blocks differentially uplifted in several phases to elevations of, in some cases, >2 km. Currently the planation surface remnants occur at different altitudes and with variable tilt. This Corsican example demonstrates that under favorable conditions, paleolandforms typical of tectonically inactive areas can survive in tectonically active settings such as at collisional plate margins. The results of some samples also reveal some discrepancies in thermal histories modeled from combined AFT and (U-Th)/He data. In some cases, models could not find a cooling path that fit both data sets, while in other instances, the modeled cooling paths suggest isothermal holding at temperature levels just below the apatite partial annealing zone followed by final late Neogene cooling. This result appears to be an artifact of the modeling algorithm as it is in conflict with independent geological constraints. Caution should be used when cross-validating the AFT and (U-Th)/He systems both in the case extremely old terrains and in the case of rocks with a relatively simple, young cooling history.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Mesozoic and Cenozoic exhumation and cooling history of Corsica is reconstructed by fission track (FT) data on basement and sedimentary rocks. Apatite ages are 105–16 Ma; zircon ages are 160–145 ...Ma. The Jurassic and Cretaceous ages show that parts of the Variscan basement escaped Alpine influence. The basement was thermally affected by rifting prior to Jurassic opening of the Ligurian‐Piedmont Ocean; then it cooled to near‐surface temperatures. In Paleocene‐Eocene times, subduction buried parts of the basement and overlying flysch to greater depth. In the Oligocene, both collapse of the nappe stack and rifting prior to opening of the Ligurian‐Provençal Basin affected the apatite FT system of the basement in different, partly overlapping areas causing a complex age pattern. The study shows that thorough analysis of FT data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern.
The Swiss Deckenschotter (“cover gravels”) is the oldest Quaternary units in the northern Swiss Alpine Foreland. They are a succession of glaciofluvial gravel layers intercalated with glacial and/or ...overbank deposits. This lithostratigraphic sequence is called Deckenschotter because it “covers” Molasse or Mesozoic bedrock and forms mesa-type hill-tops. Deckenschotter occurs both within and beyond the extent of the Last Glacial Maximum glaciers. The Swiss Deckenschotter consist of two sub-units: Höhere (Higher) and Tiefere (Lower) Deckenschotter. Although the Höhere Deckenschotter sub-unit (HDS) is topographically higher than the Tiefere Deckenschotter, it is older. The only available age for the Swiss Deckenschotter is 2.5–1.8 Ma based on mammal remains found in HDS at the Irchel site. In this study, we present an exposure age for the topographically lowest HDS, calculated from a cosmogenic
10
Be depth-profile. Our results show that the first phase of the Deckenschotter glaciations in the Swiss Alps terminated at least 1,020
-
120
+
80
ka ago, which is indicated by a significant fluvial incision. This line of evidence seems to be close to synchronous with the beginning of the Mid-Pleistocene Revolution, when the frequency of the glacial-interglacial cyclicity changed from 41 to 100 ka and the amplitude from low to high, between marine isotope stages 23 and 22.
The Mediterranean is regarded as a region of intense climate change. To better understand future climate change, this area has been the target of several palaeoclimate studies which also studied ...stable isotope proxies that are directly linked to the stable isotope composition of water, such as tree rings, tooth enamel or speleothems. For such work, it is also essential to establish an isotope hydrology framework of the region of interest. Surface waters from streams and lakes as well as groundwater from springs on the island of Corsica were sampled between 2003 and 2009 for their oxygen and hydrogen isotope compositions. Isotope values from lake waters were enriched in heavier isotopes and define a local evaporation line (LEL). On the other hand, stream and spring waters reflect the isotope composition of local precipitation in the catchment. The intersection of the LEL and the linear fit of the spring and stream waters reflect the mean isotope composition of the annual precipitation (δ P) with values of−8.6(±0.2) ‰ for δ ¹⁸O and−58(±2) ‰ for δ ²H. This value is also a good indicator of the average isotope composition of the local groundwater in the island. Surface water samples reflect the altitude isotope effect with a value of−0.17(±0.02) ‰ per 100 m elevation for oxygen isotopes. At Vizzavona Pass in central Corsica, water samples from two catchments within a lateral distance of only a few hundred metres showed unexpected but systematic differences in their stable isotope composition. At this specific location, the direction of exposure seems to be an important factor. The differences were likely caused by isotopic enrichment during recharge in warm weather conditions in south-exposed valley flanks compared to the opposite, north-exposed valley flanks.
In this study, we use contrasting zircon fission track age signatures of Alpine detritus and detritus derived from the Variscan realm to trace sediment pathways in Central Europe. Our data show that ...the Molasse Basin was connected with the Rhine Graben Sea during the Mid-Oligocene, thus joining the North Sea to the Paratethys. Within the Rhine Graben Sea, fairly strong south-north directed currents existed, transporting sand-sized Alpine detritus nearly 300 km towards the north. A connection between the Rhône-Bresse Graben and the Rhine Graben and/or the French Molasse Basin and the Swiss Molasse Basin, by contrast, is not supported by the fission track data. This may be explained by the existence of submarine rises that hampered the transport of sand-sized sediment towards the north/northeast.PUBLICATION ABSTRACT
The Alps are representing the most prominent topographic feature of central Europe in the last 30 Million years. Integration of sediment budget and thermochronological data show that crustal blocks ...within the Swiss and Eastern Alps experienced differential erosion and uplift, with eastward decreasing rates. Since 30Ma, in the course of collision and slab breakoff, the Swiss and western Eastern Alps were uplifted and formed a mountain range. Moderate erosion rates stabilized ∼2Myr later after adaption to the new base level. Between 28Ma and 5Ma, erosion rates shifted above and below different regional mean levels. These shifts of erosion rates were governed by changes of the tectonic setting. Moderate temporary drops of erosion rates and lowering of topography occurred at ∼21Ma and ∼15Ma in the course of lateral extension. Temporary rises occurred between 24 and 22Ma during thrust loading and between 18 and 16Ma during axial updoming of core complexes. By 5Ma, a sustainable strong increase of erosion rates occurred in the Swiss and Western Alps. A much weaker increase is detected in the Eastern Alps somewhat later, which makes a tectonic trigger, probably a 2nd slab breakoff, more reasonable than a climatic trigger. However, this controversial 5-Ma event is superimposed by accelerated erosion after 2.7Ma, governed by the onset of cyclic glaciations. Effective valley incision and sediment evacuation by glacial erosion caused isostatic compensation and pronounced young uplift of the Alps.
The post-Eocene paleotopographic evolution of key areas is indirectly assessed on the base of erosion rates. Spatial change of paleotopography of the Alps and central Europe is estimated and illustrated in 3 paleogeographic maps.
The Tertiary reactivation of the Paleozoic basement in NE Sardinia is shown to reflect transtensional back‐arc tectonics, related to the western Mediterranean subduction rollback. During the ...Algéro‐Provençal basin opening, the left‐lateral Nuoro Fault, which is the prevailing structure in central Sardinia, operated as radial transfer between the west Sardinian rift and northern Tyrrhenian basin. Subsequently, it contributed to a tension gash‐like opening of the southern Tyrrhenian basin as conjugate fault to a right‐lateral fault set in SE Sardinia. Resulting antithetic rotations with respect to the arc are revealed by reoriented dikes in the basement. The tension gash‐like opening of the southern Tyrrhenian basin determined the gulf shape of the east Sardinian margin and the arc shape of its Calabrian counterpart. This structural control on the southern Tyrrhenian rollback scenario suggests that tension gash‐like opening of back‐arc basins represents an intrinsic aspect of subduction rollback.
A new multi-thermochronological dataset from Corsica–Sardinia is here employed to constrain the Meso–Cenozoic evolution of the Western Mediterranean area and the problematic transition in space and ...time between the opposite-dipping Alpine (European) and Apenninic (Adriatic) subductions.
The dataset, including zircon and apatite fission track and apatite (U–Th)/He data, covers the whole Meso–Cenozoic time interval, and fits the theoretical age pattern that is expected in distal passive margins after continental break-up. This demonstrates that Corsica–Sardinia represents a fragment of the northern Tethyan margin still preserving the thermochronological fingerprint acquired during Middle Jurassic rifting. Mesozoic apatite (U–Th)/He ages from crustal sections located close to the Tethyan rift axis (i.e., central and eastern Sardinia) show that no European continental subduction took place south of Corsica since the Mesozoic. Along the Sardinia transect, post-Jurassic Adria–Europe convergence was possibly accommodated by Adriatic subduction, consistent with the onset of orogenic magmatism. In middle Eocene–Oligocene times, the northward translation of the Adriatic slab beneath the former Tethyan margin induced a coeval northward migration of erosional pulses at the surface, constrained by a trend of progressively decreasing fission track ages from southern Sardinia to NW Corsica. The Adriatic slab reached the Alpine wedge of Corsica by the end of the Oligocene without any breakoff of the European slab, and started retreating in Neogene times triggering the long-recognized basin opening in the backarc region.
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•First full spatial coverage of Sardinia by three low-T thermochronometers•A reconstruction of the northern Tethyan margin by low-T thermochronometry•Thermochronological evidence of Adria slab translation beneath Sardinia and Corsica
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