Publication details
Fluvial deposits of the St. Marein Freischling Formation insights into initial depositional processes on the distal external margin of the Alpine Carpathian Foredeep in Lower Austria
| Authors | |
|---|---|
| Year of publication | 2011 |
| Type | Article in Periodical |
| Magazine / Source | Austrian Journal of Earth Sciences |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | St. Marein-Freischling Formation - fluvial deposits - braided river - Oligocene Lower Miocene - Molasse zone - external margin - Austria |
| Description | In the SE Bohemian Massif of Lower Austria sandy and gravelly fluvial deposits of the St. Marein Freischling Formation (Oligocene Early Miocene) are reflecting a braided channel system. Eleven lithofacies and four facies associations/architectural elements (gravelly channel dunes and bars, channels, sandy channel dunes and abandoned channels) were recognised. A network of relatively shallow streams with seasonal fluctuations in the discharge are supposed. The episodic character of transport, erosion and deposition could reflect changes in climatic conditions. Provenance studies (pebble petrography, heavy minerals), evaluation of pebble size, shape and roundness, and paleocurrent data point at two parts of the fluvial system. For the main fluvial system a general transport from west to east can be supposed, which finally turned against the south in the surroundings of Horn. Tributaries both from north and south ended in the west-east reach of the main river. Deeply weathered crystalline rocks of the South Bohemian Batholith and the Moldanubian zone (Eisgarn granite, Rastenberg granodiorite, Wolfshof syenitic gneiss, Gföhl gneiss, granulites, marbles, eclogites, amphibolites) are supposed as source rocks. 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 external margin of the foreland basin. Additionally, in the lower reach of the fluvial system (Horn Basin), the position of the paleovalley at the tectonic contact between the Moldanubian and Moravian zones and the reactivation of the fault-system seems to be evident. Moreover, fluvial style and discharge of the St. Marein-Freischling Formation deposits were affected by climatic processes. |
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