International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

ROGGENDORF-1 BOREHOLE, A KEY-SECTION FOR LOWER BADENIAN TRANSGRESSIONS AND THE STRATIGRAPHIC POSITION OF THE GRUND FORMATION (MOLASSE BASIN, LOWER AUSTRIA)

Pages: 165 - 178

Authors: STJEPAN CORIC, FRED ROGL

Abstract: Borehole Roggendorf-1 was drilled in the Alpine-Carpathian Foredeep (Molasse Basin) north of the Danube (Lower Austria). Biostratigraphic results and the lithological column revealed until now unrecorded Early Badenian (Middle Miocene) cycles. Calcareous nannoplankton was studied from the upper 800 m of a Neogene sequence and foraminifers were examined from the upper 410 m. The upper 2 m to 255 m fine clastic sediments of the Grund Formation (Lower Badenian, nannoplankton Zone NN5, planktonic foraminiferal Zone Mt6) show a deepening upward, with a maximum depth corresponding to outer shelf. Paleoecological evaluations demonstrate a distinct warming of the surface water. Down-hole, a clastic sequence follows starting with a gravel bed (347–360 m), and ending with a conglomerate bed on top (255–270 m). The latter is probably the transgressive base of the Grund Formation. The boundary of nannoplankton Zones NN 4–NN5 lies within this earlier Badenian cycle, which was deposited on the inner shelf, below 50 m. Limestone and sandstone pebbles originate from the Calcareous Alps and Flysch Unit. The underlying cycle of calcareous silty shales, sands and thin gravel layers belongs to the Laa Formation (Karpatian, nannoplankton Zone NN4; 360–612 m). Deposition occurred, partly under dysoxic bottom conditions on the outer shelf to upper bathyal. Surface waters were distinctly cooler than in the Grund Formation due to strong upwelling with nutrient enrichment. The Karpatian is underlain without a distinct unconformity by the Upper Ottnangian brackish Rzehakia (”Oncophora”) Beds, fine sands and shales, which are barren of fossils (612–678 m). The lower part of the investigated section belongs to the Ottnangian ” Robulus Schlier”. Nannoplankton determinations show that this still belongs to nannoplankton Zone NN4. Nannoplankton Zone NN3/4 is recorded on the basis of the occurrence of Sphenolithus belemnos only in the lowermost samples (790–800 m).

Keywords: Miocene, Alpine-Carpathian Foredeep, Grund Formation, Laa Formation, paleoecology, biostratigraphy, microfossils

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Volume 55 no. 2 / April 2004

Volume 55 no. 2