Interplay Between Tributary Channels and Overbank Splays in the Puchkirchen Channel Belt in the Austrian Molasse Basin

Masalimova, Larisa U.; Lowe, Donald R.; McHargue, Timothy
[email protected]

This study uses 3D seismic-reflection data, core and well logs to address the depositional processes, architecture, and evolution of sediments in the Puchkirchen Formation of the Atzbach, Schwanenstadt and Zell-am-Pettenfirst gas fields in the Tertiary Upper Austrian Molasse Basin. This research provides additional details on depositional setting and documents the spatial variation of main sand bodies and the lithological heterogeneity of these out-of-channel deposits. The evolution of the overbank deposits is documented within the context of the successively migrating and meandering axial channel. The gas-bearing sandstones in these fields were interpreted to be deposited in tributary channels by flows spilling sediments from the axial channel-belt. Tributary channels originated in the Bohemian Massif and had direction of almost perpendicular to the axial channel along the northern slope of the foreland basin. The depth of the channels ranges from approximately 150 to 360 meters and the length is 3 to 5 kilometers. Flows largely bypassed the tributary channels and entered the main channel by eroding through levees, thus the additional space was created in overbank area that remained largely empty. Sediments brought by these flows were dissipated by flows of the main channel-belt. Flows going along the axial channel-belt passively filled the erosional surfaces as can be seen from onlapping and continuous geometries on seismic profiles from channel to overbank areas. The sediments in the overbank area were deposited mostly by low-density turbidity currents, small scale mass-wasting happened along the sides of the tributary channels accompanied by minor erosion. The lithology, thickness of beds and degree of bioturbation are quantitatively described. The research will assist in hydrocarbon exploration in the Molasse Basin and as an analog for overbank deposits in other deep-water systems.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013