Description: The Explora Wedge (Hinz and Krause, 1982; Hinz et al., 2004) represents a prominent morphological and structural feature of Earth crust in the north eastern Weddell Sea. Marine geophysical data reveal that it constitutes East Antarctica's volcanic rift margin, with seaward dipping reflectors buried below sediments and floating ice shelves on the continental margin of Dronning Maud Land. Using a vibroseis source on the Antarctic continent for the first time, together with regional aeromagnetic data, these new results show the southward extent of the more than 1000 m thick Explora Wedge (EW) volcanic deposit below the Ekström Ice Shelf (Kristoffersen et al., 2014). While up to now the landward extent of the wedge had been less clearly defined, the new data indicates the top of the wedge outcrop to be about 36 km landward off the shelf edge, or 14 km south of Neumayer III station. One target of the geo-scientific studies will be the top of the EW sequence, which represents the final phase of the initial continent break up and is presumed to be of an Upper Jurassic age. Genesis, magma differentiation, and precise age of the EW volcanics are largely unknown and high-ranking research objectives. The upper boundary of the EW forms a distinct unconformity to the overlaying younger, wedge-shaped sedimentary unit, which reaches about 800 m in thickness close to the Neumayer III station. The age of these sediments is unknown and could be all from Mesozoic to Recent. Considering this largely unexplored Antarctic continental margin, any high latitude palaeo-environmental information about the Mesozoic und lower Cainozoic greenhouse world prior to the start of Antarctic glaciation, the onset of glaciation, and up to the glacial/interglacial variability of the East Antarctic Ice Shield during the Quaternary can best be gathered through drilling at the proposed site. Perhaps we will be able to drill one never reached target of former ODP Leg 113, the Cretaceous black shales that sparsely were dredged from the scarps of the Wegener Canyon close by (Fütterer et al. 1990).

Description: We present implementations of vibroseis system configurations with a snowstreamer for over-ice long-distance seismic traverses (〉100 km). The configurations have been evaluated in Antarctica on ice sheet and ice shelf areas in the period 2010–2014. We discuss results of two different vibroseis sources: Failing Y-1100 on skis with a peak force of 120 kN in the frequency range 10–110 Hz; IVI EnviroVibe with a nominal peak force of 66 kN in the nominal frequency range 10–300 Hz. All measurements used a well-established 60 channel 1.5 km snowstreamer for the recording. Employed forces during sweeps were limited to less than 80% of the peak force. Maximum sweep frequencies, with a typical duration of 10 s, were 100 and 250 Hz for the Failing and EnviroVibe, respectively. Three different concepts for source movement were employed: the Failing vibrator was mounted with wheels on skis and pulled by a Pistenbully snow tractor. The EnviroVibe was operated self-propelled on Mattracks on the Antarctic plateau. This lead to difficulties in soft snow. For later implementations the EnviroVibe with tracks was put on a polyethylene (PE) sled. The sled had a hole in the center to lower the vibrator baseplate directly onto the snow surface. With the latter setup, data production varied between 20 km/day for 6-fold and 40 km/day for single fold for 9 h/day of measurements. The combination of tracks with the PE-sled was especially advantageous on hard and rough surfaces because of the flexibility of each component and the relatively lose mounting. The systems presented here are suitable to obtain data of subglacial and sub-seabed sediment layers and englacial layering in comparable quality as obtained from marine geophysics and land-based explosive surveys. The large offset aperture of the streamer overcomes limitations of radar systems for imaging of steep along-track subglacial topography. With joint international scientific and logistic efforts, large-scale mapping of Antarctica's and Greenland's subglacial geology, ice-shelf cavity geometries and sea-bed strata, as well as englacial structures can be achieved.