Publication details
Initial depositional processes on the distal passive margin of the peripheral foreland basin - fluvial deposits of the St.Marein-Freischling
| Authors | |
|---|---|
| Year of publication | 2010 |
| Type | Article in Proceedings |
| Conference | Abstracts Volumen, 18th International Sedimentological Congress (Eds. E. Schwarz, S. Georgieff, E. Piovano) |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | peripheral foreland basin- fluvial deposits |
| Description | Analysis of fluvial systems and its paleodrainage provide crucial data for the reconstruction of ancient landscapes and paleogeography. The fluvial transport is quite important in the determination of the asymmetry of the foreland basin geometry. Fluvial deposits in the distal, cratonic margin of the peripheral foreland basin could often allow the study of paleovalleys preserved along the basal unconformity. The deposits of St.Marein-Freischling Formation (Oligocene – Early Miocene), which cover the crystalline basement of the Bohemian Massif in the area of northwestern Lower Austria, can provide a typical example of such a situation. Studied sandy and gravelly fluvial deposits of the St.Marein-Freischling Formation are reflecting a braiding fluvial style. Eleven lithofacies and four facies associations/architectural elements (gravelly channel dunes and bars, channels, sandy channel dunes and abandoned channels) were recognised. A relatively shallow network of streams with flashflood character can be documented. Ephemeral braided streams or at least fluctuations in the discharge are supposed. The episodic character of transport, erosion and deposition could reflect changes in climatic conditions. Provenance study (pebble petrography, heavy minerals), evaluation of pebble size, shape and roundness, and paleocurrent data suggest two parts of the fluvial system. For the first and main part of the fluvial system a general transport from west to east can be supposed, which finally was diverted towards the south. Transverse tributaries both from north and south were connected to the west-east drained part of the paleovalley. As source deeply weathered crystalline rocks of the South Bohemian Batholith and the Moldanubian zone (Eisgarn granite, Rastenberg granodiorite, Wolfshof syenitic gneiss, Gfohl gneiss, granulites, marbles, eclogites, amphibolites) are supposed. However, local sources strongly influenced the provenance spectra. In a second, probably separate fluvial system in the southeast a general transport from northeast to southwest is evident, where Moravian metamorphic rocks, magmatic rocks of the Thaya Batholith, and probably reworked Mesozoic sediments are the main sources. For the position and orientation of the paleovalley the tectonic influence of the north-ward thrusting Eastern Alps is discussed, causing a back- bulge depression along the passive margin of the foreland basin. These west-east trending paleovalley was tilted to the east, where north-south trending paleovalley was developed along the fault separating different units of the crystalline basement. The tectonic activity within the Eastern Alps is supposed to be responsible for the reactivation of this tectonic contact between the Moldanubian zone and the Moravian zone. Tectonics was the principal ruling factor of the formation of a paleovalleys and paleodrainage system in that position. |
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