No abstract

The southern Rhinegraben represents a key area to unravel the Neogene paleohydrographic history of the northern Alpine foreland. At least, three successive main drainage systems are documented by the youngest sediments of the graben fill. They are respectively pre-, syn-and post-dating the folding of the Jura Mountains (about 10-5 Ma ago).Pliocene to recent uplift and shortening of the Pliocene fluvial gravel ("Sundgauschotter"), which accumulated on a nearly plain surface, and the progressive deflection and capture of rivers resulted from reactivation of preexisting Paleogene faults. The alluvial terraces along the major rivers of the Sundgau area show upward warping near the uplift areas. Furthermore, river beds responded to uplift by lateral shift.During the Pliocene-Pleistocene, fluvial drainage diverted stepwise from the initial, westwards directed course (towards the Bressegraben) to the N (into the Rhinegraben): Firstly, uplift in the south at the boundary between the Rhinegraben and the Jura Mountains induced a northwards directed migration of the middle Pliocene, E-W flowing paleo-drainage system. Successively, a late Pliocene/early Pleistocene lowering of the base level in the Rhinegraben north of Mulhouse resulted in the capture by southwards directed backward erosion of this system into the Rhinegraben, as likewise documented by the reconstitution of the paleo-drainage patterns in the Sundgau area. In addition, a gradually capture moving from NE to SW has been identified for the Sundgau catchment area. ZUSAMMENFASSUNGDie Morphogenese des südlichen Rheingrabens hängt stark mit der hydrographischen Entwicklung des zentralen Alpinen Vorlandes zusammen. In den jüngsten Ablagerungen der Grabenfüllung sind nämlich mindestens drei Hauptentwässerungssysteme dokumentiert. Die fluviatilen Sedimente vom mittleren Miozän bis zum Quartär wurden vor, während und nach der Hauptphase der Jurafaltung abgelagert (ca. 10-5 Ma).Eine Reaktivierung von paläogenen Brüchen während des Plio-Pleistozäns ist sowohl durch die Auffaltung der pliozänen Sundgauschotter als auch durch die fortschreitende Ablenkung und Anzapfung von Flüssen im süd-lichen Elsass (Sundgau) belegt. Alluviale Terrassen entlang der Hauptflüsse im Sundgau wurden in der Nähe von Antiklinalen gehoben und verstellt. Das weist darauf hin, dass die tektonische Aktivität zumindest bis in das Pleistozän anhielt.Die Rekonstruktion des Paläoentwässerungssystems zeigt, dass die Umlenkung des gesamten Flussnetzes im Sundgau, das während des Pliozäns nach Westen in den Bressegraben gerichtet war und sich dann nach Norden in den Rheingraben reorientierte, schrittweise stattfand: Infolge von Hebungen im Süden entlang der Rheingraben/Jura-Grenze migrierte der mittelpliozäne Hauptfluss nordwärts und die Absenkung im Rheingraben nördlich von Mulhouse während des Spätpliozäns und des Pleistozäns führte dann zur allmäh-lichen Anzapfung des Entwässerungssystems von Norden. fluenced the evolution of the adjoining Jura Mountains, when these were folded and thrusted since the Mi...

Although the Neuquén basin in Argentina forms a key transitional domain between the south‐central Andes and the Patagonian Andes, its Cenozoic history is poorly documented. We focus on the sedimentologic and tectonic evolution of the southern part of this basin, at 39–40°30′S, based on study of 14 sedimentary sections. We provide evidence that this basin underwent alternating erosion and deposition of reworked volcaniclastic material in continental and fluvial settings during the Neogene. In particular, basement uplift of the Sañico Massif, due to Late Miocene–Pliocene intensification of tectonic activity, led to sediment partitioning in the basin. During this interval, sedimentation was restricted to the internal domain and the Collon Cura basin evolved towards an endorheic intermontane basin. From stratigraphic interpretation, this basin remained isolated 7–11 Myr. Nevertheless, ephemeral gateways seem to have existed, because we observe a thin succession downstream of the Sañico Massif contemporaneous with the Collon Cura basin‐fill sequence. Comparisons of stratigraphic, paleoenvironmental and tectonic features of the southern Neuquén basin with other foreland basins of South America allow us to classify it as a broken foreland with the development of an intermontane basin from Late Miocene to Late Pliocene. This implies a thick‐skinned structural style for this basin, with reactivation of basement faults responsible for exhumation of the Sañico Massif. Comparison of several broken forelands of South America allows us to propose two categories of intermontane basins according to their structural setting: subsiding or uplifted basins, which has strong implications on their excavation histories.

The southern central Andes foothills are made of imbricate thick‐ and thin‐skinned fold and thrust belts. They were formed during Cretaceous and Miocene compressive periods by successive eastward propagation episodes of the orogenic front. We analyze remnant terraces and alluvial deposits of the Neuquén River and its tributaries to study the Plio‐Quaternary tectonic regime in the southern Neuquén Basin. Topographic profiles of remnant terraces show a crustal‐scale (tens of kilometers) anomaly above the Chihuido South anticline. This anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline. Another anomaly in the terrace profiles, correlated with a knickpoint in the current Neuquén River, is observed farther east, near Añelo. We interpret these anomalies to be the consequence of a Plio‐Quaternary uplift of the Chihuidos and Añelo anticlines. Folding and surface faulting of Plio‐Quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the Miocene orogenic front and of the predominantly thin‐skinned Agrio fold‐and‐thrust belt. From these data we infer that the southern Neuquén Basin is still shortening under a compressive stress regime and that the Andean orogenic front is migrating farther to the east. Extensional features in the study area correspond mainly to thin‐skinned gravitational gliding, resulting from crustal uplift. Thus, we argue that the tectonic compressive regime is preserved in the southern Neuquén Basin throughout the Plio‐Quaternary, though the slab may have steepened during this period.