Stratigraphic evidence for a Plio-Quaternary uplift developed in the Southern Urals foreland at right angle with the main chain

摘要

The altitudes of the lowest part of the Upper Cretaceous-Paleogene and Plio-Quaternary stratigraphic ensembles known in the Paleo-Volga basin and in the Paleo-Urals have been computed and represented at the same time for comparison. These two surfaces indicate an east-west elongated dome which follows 53° N on the western slope of the Southern Urals. This ridge is superimposed at depth with the remnants of the Sernovodsk-Abdulino Aulacogen and with the Belaya tear fault, which supports the existence of a recent rejuvenation of these deep basement disruptions. The 3D reconstruction shows that the two surfaces display the same type of uplift at around 52.50°N, 56.50°E. The variations in altitude of the two surfaces have been sampled along two sections running at the same longitude. When the two profiles are superimposed, the "post-Cretaceous and Paleogene" curve is higher. This result suggests that the uplift started after the Paleogene and continued until nowadays. Calculation of the local amount of uplift after the Aktschagylian considered the difference between the maximum uplift of the surface and a regional trend corresponding with the almost horizontal surface of the former deposits. In these conditions, the deformation affecting the Aktschagylian-Quaternary ensemble reaches 175 m. Since the measured post Cretaceous-Paleogene uplift incorporates also the Pliocene-Quaternary uplift, before the Pliocene the uplift only reached 23 m in altitude. This result gives an idea of the irregularity of the topography that the Aktschagylian transgression had to face. This result also suggests that the Pliocene-Quaternary amount of uplift was 6 times larger than the former one.