Westward propagation of thrusts in the external Western Alps (France) reappraised from an updated chronostratigraphy of the Miocene Molasses

<p>The fact that the western Alps Miocene foreland basin succession is poorly dated impacts directly our understanding of the deformation kinematics of that part of the external part of the Alpine belt (France). Here we propose a multidisciplinary approach aiming at building a robust tectono-stratigraphic framework of the Miocene deposits at the basin scale (northern subalpine massifs, southern Jura, Royans, Bas-Dauphiné and La Bresse basins). Sr isotopes stratigraphy combined with magnetostratigraphy and biostratigraphy enable sequence stratigraphy subdivisions S1 to S8 between the Upper Aquitanian (-21 Ma) and the Tortonian (-9 Ma) dated with a precision <0.5 Ma. These results highlight four different palaeogeographical domains during the Miocene: (i) the oriental domain with depositional sequences S1a to S3 (~21.3 to 15Ma), (ii) the median domain, in which sequences S2, S3, S4 and S5 occurred (~17.8 to 14Ma), (iii) the occidental domain with sequences S2 to S8 (~17.8 to ~9.5Ma); and (iv) the Bressan domain, in which sequences S6 to S8 are found (~ 11.5 to ~9.5Ma).</p><p>This revised chronostratigraphy was complemented with a structural and tectono-sedimentary study based on new fieldwork data and a reappraisal of regional seismic profiles, allowing to highlight five major faults zones (FZ). It appears that the oriental, median and occidental paleogeographical domains are delineated by FZ1, FZ2 and FZ3, therefore suggesting a strong interplay between tectonics and sedimentation. Evidences of syntectonic deposits and a westward migration of the depocenters impart the following deformation chronology : a Oligocene compressive phase (P1) corresponding to thrusting above FZ1 rooted east (above) Belledonne, which generated reliefs that limited the early Miocene transgression to the east; an Early- to Middle Miocene W-WNW/E-ESE-directed compressive phase (P2) involving the Belledonne massif basal thrust, which between 18.05 +/- 0.15 Ma and 12Ma successively activated the Salève thrust fault, and the FZ2 to FZ5 from east to west. P2 deeply impacted the Miocene palaeogeographical evolution by a rapid westward migration of depocenters in response to the exhumation of piggy-back basins above the growing fault zones; a last Tortonian phase (P3), less well constrained, apparently implied a significant uplift in the subalpine massifs, combined with the activation of the frontal Jura thrust.</p>

Balance between tectonics and sedimentation during geodynamic evolution of the Adria-Europe convergence zone in central Serbia

<p>The Cretaceous sedimentation along the NE Dinarides margin was associated with subduction and collision of the Neotethys Ocean located between continental units of Adria and Europe (i.e., the Sava subduction system). In this region, we have performed a coupled kinematic and sedimentological study in order to understand the main controlling mechanism of deposition in basins situated above the Sava subduction zone.</p><p>The Cretaceous sedimentation on the upper plate of the Sava subduction system took place in a fore-arc basin developed in frontal parts of the active European continental margin. The sedimentary facies indicate three cycles of deposition during Early Cretaceous–Cenomanian, Turonian–Santonian, and Campanian-Maastrichtian. Lower Cretaceous–Cenomanian deposition was associated with regional contraction and characterized by the clastic-carbonatic cyclic shelf and slope deposits (i.e., the “para-flysch”). The European fore-arc “para-flysch” sequences, deposited during Berriasian–Aptian times, presently outcrop in the Gledićke Mts and Rudnik area in central Serbia. Following the Albian–Cenomanian regression that created regional unconformity across the entire fore-arc domain, Turonian–Santonian extension resulted in subsidence and syn-depositional bimodal magmatism. Fore-arc syn-subductional extension was triggered by retreating and steepening of the subducting Neotethys lithosphere. The final Campanian–Maastrichtian regression was initiated by large-scale shortening during the onset of Adria-Europe collision.</p><p>Unlike the European fore-arc domain, the Cretaceous sedimentation over the passive continental margin of the Dinarides was exclusively controlled by continuous shortening and overall transgression over the subducting Adria plate. Deposition starts with transgressive Albian–Cenomanian coarse-clastics and gradually deepens into the clastic-carbonatic shelf deposits. Rapid subsidence since the late Turonian resulted in deposition of slope carbonates followed by the deep pelagic sedimentation of Coniacian to Campanian–Maastrichtian limestones with cherts (i.e., the Struganik facies). The onset of deposition in the Sava subduction trench, as well as the accelerated subsidence in the entire lower Adria plate domain was coeval with Turonian–Coniacian switch to syn-subductional extension in the European fore-arc basin. The trench sedimentation starts with Turonian distal mudstones overlain by Coniacian–Maastrichtian clastic-carbonatic turbidites, as observed in the Rudnik Formation in Central Serbia. The westward expansion and migration of trench deposition towards the lower Adria plate culminated with Middle Campanian–Late Maastrichtian deposition of siliciclastic trench turbidites observed in the Ljig Formation.</p><p>The onset of the latest Cretaceous–Paleogene Adria-Europe continental collision resulted in large-scale W-wards thrusting that inverted the Cretaceous basins along NE Dinarides margin and emplaced sedimentary infill and basement of the European fore-arc over the Sava trench turbidites. The continued continental collision led to the propagation of thrusting during Eocene, which was characterized by formation of the large offset out-of-sequence thrusts. The eduction that followed break-off of the Neotethys slab beneath the Dinarides triggered Oligocene–Miocene extension which reactivated the inherited thrust contacts as extensional detachments along the entire Dinarides margin. The extension exhumed the lower Adria plate and additionally fragmented and deformed the former Cretaceous basins. The rates of extensional exhumation are decreasing to the NE, from the Dinarides margin towards the Carpathians.</p>

Tectonics and sedimentation of the central sector of the Santo Onofre rift, north Minas Gerais, Brazil

ABSTRACT: The Santo Onofre Group registers the filling of a Tonian, intracontinental paleo-rift that developed along the northern and central Espinhaço regions. This paper examines this unit in the central Espinhaço region with stratigraphic analysis and U-Pb geochronology, reviewing and dividing into the Canatiba and Rio Peixe Bravo Formations, which include the Barrinha Member. The Canatiba Formation mainly comprises carbon-rich mudstones that were deposited through low-density turbidity flows that alternated with sediment settling under anoxic conditions. The Rio Peixe Bravo Formation consists of a succession of sandstones and minor mudstones, which were deposited through low- to high-density turbidity flows. The Barrinha Member mainly consists of conglomerates and is related to channelized debris flows. Detrital zircon grains show maximum depositional ages of 930 ± 33 Ma and around 865 Ma for the Canatiba and Rio Peixe Bravo Formations, respectively. We interpret the Santo Onofre rifting to be relative younger than that for the Sítio Novo Group and to be a precursor stage of the glacial and post-glacial rift-to-passive margin-related sequences of the Macaúbas Group. The lithostratigraphic term “Macaúbas Supergroup” would be of better use to accommodate the unconformity-bounded Tonian sequences that were related to the Rodinia breakup in the Congo-São Francisco paleocontinent.

GEOLOGICAL AND GEOPHYSICAL DATA OF “EPSILON” FIELD IN PRINOS OIL BASIN

The Epsilon field, is located at the centre of Prinos oil basin (N. Aegean, Greece), 11 km NW of the island of Thassos and 4 km NW of the Prinos field, the first productive oil field in the Aegean Sea. The taphrogenetic basin of Prinos has been widely studied, due to its hydrocarbon reservoirs. Extensive geophysical survey, started at early 1970 ‘s, led to a number of drilling jobs, which confirmed the existence of hydrocarbons in the area. The combined geological information, derived from the analysis of lithological, stratigraphic and geochemical data of the basin, suggested a structural and depositional model, strongly related to the Miocene tectonics and sedimentation. The new geophysical and drilling data from Epsilon oil field, are correlated to that already known, completing the model of the basin. Pay zone is found to be below an evaporitic sequence, consisting predominantly of salt, with anhydrite, clay and sandstone intercalations. These upper Miocene aged evaporites extend, varying in thickness, throughout Prinos basin. Reservoir consists mainly of sandstone with intercalations of claystone and trace of siltstone. The geology of the structure and the initial productivity, were positive for further drilling operations in Epsilon field.