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Evolution of Late Cretaceous-Palaeogene synorogenic basins in the Pieniny Klippen Belt and adjacent zones (Western Carpathians, Slovakia) : tectonic controls over a growing orogenic wedge

Plašienka D., Soták J.

Annales Societatis Geologorum Poloniae

2015

Vol. 85, No. 1

43--76

The Pieniny Klippen Belt and neighbouring zones of the Western Carpathians represent an ancient accretionary wedge that developed during the meso-Alpidic (Coniacian–Eocene) tectonic epoch. After an overview of the extensive literature data, the authors present an interpretation of the synorogenic sedimentary record of these zones as being related to various environments of the foreland basin system consisting of the trench-foredeep and wedge-top depositional areas. The peripheral trench-foredeep depozones migrated from the South Penninic-Vahic oceanic realm towards the Oravic continental fragment in an intra-Penninic position, where the synorogenic deposits were laid down with coarsening- and thickening-upward trends before being overthrust by the propagating orogenic wedge tip. The development of wedge-top, piggyback basins (Gosau Supergroup) was controlled by the dynamics of the underlying wedge, composed of frontal elements of the Fatric and Hronic cover nappe systems of the Central Western Carpathians (Austroalpine units). Several compressional and extensional events are documented in the complex sedimentary and structural rock records within the wedge and related basins. The successive transgressive-regressive depositional cycles and corresponding deformation stages are interpreted in terms of a dynamic accretionary wedge that maintained the critical taper only transiently. The supercritical taper states are reflected in regression, shallowing and erosion in the wedge-top area, while the trench was supplied with large amounts of clastics by various gravity-flow types. On the other hand, the collapse stages tending to subcritical wedge taper are indicated by widespread marine transgressions or ingressions in the wedge-top area and a general deepening of all basins to bathyal conditions. Accordingly, the evolution of the entire trench-foredeep and wedge-top basin systems was principally controlled by the complex interplay of the regional tectonic evolution of the Alpine-Carpathian orogenic system, local wedge dynamics and eustatic sea-level fluctuations.

The Upper Triassic - Middle Jurassic Shemshak Group of Iran: foreland basin or rift basin?

Fürsich F., Wilmsen M., Seyed-Emami K., Majidifard M.

Volumina Jurassica

2006

Vol. 4, no. 1

41-41

The Shemshak Group is a predominantly siliciclastic rock unit occurring over much of the Iran Plate. The group is sandwiched between two unconformities: the lower one resulted from the late Middle Triassic Early Cimmerian Orogeny, which documents the collision of the Iran Plate with Eurasia, the upper one results from the still poorly understood Bajocian Mid-Cimmerian tectonic movements. At the base, the group overlies, with distinct stratigraphic gap documented by karst features and locally extensive bauxite deposits, the platform carbonates of the Shotori and Elikah formations. At the top, the group is overlain by the marls of the Dalichai Formation, part of a widespread carbonate system existing for most of the late Middle-Late Jurassic and locally extending into the Early Cretaceous. The Shemshak Group reaches enormous thicknesses (up to 4000 m) and consists largely of fluvial sediments with common intercalations of coal beds. At the base and at the top, the group is represented by marine sediments which include reef and lagoonal carbonates, deposits of the storm-influenced shelf, deltas, and basinal mudstones. Another characteristic feature are volcanic and volcanoclastic rocks, which are commonly intercalated at or near the base of the group. Conventionally, the Shemshak Formation has been interpreted as the fill of a foreland basin. However, detailed sedimentological and stratigraphic studies over much of the outcrop belt of the group show that such a simple interpretation can no longer be upheld. Instead, the Shemshak Group is thought to reflect the following major tectono-sedimentary settings: during the Late Ladinian - Carnian initial collision of the Iran Plate with Eurasia in northeastern Iran (Koppeh Dagh-Binalud area), the Triassic carbonate platforms of the Iran Plate suffered warping and extensive lateritic weathering. In the Alborz area, a remnant basin of the Palaeotethys persisted, in which basinal sediments were deposited. During the Norian-Raethian, distension of the Iran Plate in connection with the onset of subduction of the Neotethys led to formation of rapidly subsiding marine grabens which were filled with sediments of neighbouring horsts (Nayband Formation). In the Alborz area, the remnant basin of the Palaeotethys became gradually infilled with partly shallow marine and partly fluvial sediments. The major collision between the Iran Plate and Eurasia took place around the Triassic/Jurassic boundary. Concomitant with the rising Cimmerian Mountains, a foreland basin developed, which received a thick conglomeratic fill in the north which southwards graded into a fluvial system with widespread coal swamps. During the Toarcian-Aalenian, this foreland basin changed into a rift basin, which is documented by transgression and a rapid change to basinal deposits, indicative of high rates of subsidence. By the end of the Early Jurassic, the Cimmerian Mountains were more or less eroded. The following Mid-Cimmerian tectonic movements are seen as recording strong distensional tectonics in connection with the opening of the South Caspian Basin in the north.