High-resolution seismic reflection data acquisition and interpretation, Lake Neusiedl, Austria, northwest Pannonian Basin

A combined 400+ km of single- and multichannel seismic reflection data were acquired on Lake Neusiedl in northeast Austria in May 2013. This geophysical campaign was a multinational academic effort among the Universities of Vienna, Budapest, Bremen, and Southampton. Lake Neusiedl is an exceptionally shallow lake, with an average water depth of only approximately 1.4 m. Although high-resolution single-channel seismic reflection data have been collected before on this lake, the multichannel seismic acquisition, towing a 60 m cable and an air gun behind a retrofitted ferry boat, was a completely new approach in this area. The quality of the multichannel data turned out to be exceptionally good; i.e., the high-frequency data illuminated the subsurface of the lake for the first time, down to the pre-Cenozoic basement at approximately 600 m depth. The most prominent findings of the new data include (1) a consistent southeasterly dip of erosionally truncated Late Miocene (Pannonian) sediments beneath a very thin Holocene mud layer, (2) the presence of major throughgoing fault systems (including a positive flower structure), (3) at least one Pannonian progradational sequence defined by seismic clinoforms indicating a paleowater depth of approximately 40–80 m, (4) flat spots in several locations of the study area corresponding to possibly biogenic gas in a few hundred meters depth beneath the lake, (5) vertical data wipeouts, which are interpreted as gas chimneys reaching the lake bottom, and (6) definition of the pre-Cenozoic basement. Interestingly, the gas chimneys are interpreted to correspond to the well-known gas seeps (“Kochbrunnen”) in Lake Neusiedl, which were originally described as subaqueous water springs on the lake floor responsible for ice-free areas in the lake ice cover during winter.