A combination of a dense reflection seismic grid and up to 50‐m‐long records from sediment cores and cone penetration tests was used to study the geometry and infill lithology of an E–W‐trending buried tunnel valley in the south‐eastern North Sea. In relation to previously known primarily N–S‐trending tunnel valleys in this area, the geometry and infill of this 38‐km‐long and up to 3‐km‐wide valley is comparable, but its E–W orientation is exceptional. The vertical cross‐section geometry may result from subglacial sediment erosion of advancing ice streams and secondary incision by large episodic meltwater discharges with high flow rates. The infill is composed of meltwater sands and reworked till remnants on the valley flanks that are overlain by late Elsterian rhythmic, laminated, lacustrine fine‐grained sediments towards the centre of the valley. A depression in the valley centre is filled with sediments most likely from the Holsteinian transgression and a subsequent post‐Holsteinian lacustrine quiet‐water setting. The exceptional axis orientation of this tunnel valley points to a regional N–S‐oriented ice front during the late Elsterian. Copyright © 2012 John Wiley & Sons, Ltd.

As part of the German R/V Meteor M67/2 expedition in 2006 to the southern Gulf of Mexico, a set of 2D high resolution seismic profiles was acquired across the Chapopote knoll to study seafloor asphalt occurrences. On the basis of regional seismostratigraphic studies and DSDP drilling, a more highly reflective, coarse‐grained sediment unit of late Miocene age is identified as a potential shallow hydrocarbon reservoir. Although a unit of that age would typically be buried by Pliocene and Pleistocene sediment cover, at Chapopote, local salt tectonism has highly elevated the structure since the late Miocene, and the Miocene reservoir is locally above present‐day regional datum. The elevation resulted in a thin (100–200 m), fine grained sediment cover on the crest of the knoll above the reservoir. Because oil and gas production can be expected at depth in Jurassic, Cretaceous and Tertiary source rocks, the presence of high‐amplitude reflector packages within the reservoir unit is interpreted as an evidence of hydrocarbons. This is variously supported by observations of crosscutting reflectors, polarity reversal, and drops in instantaneous frequency. The thin seal above the reservoir unit facilitates leakage of trapped hydrocarbons. Hydrocarbons apparently invaded into the seal sediments in the wider vicinity around the crest of the knoll, even extending beyond the area where seafloor asphalt is known. The asphalt site thus may be a currently active spot, while the rest of the crest may be temporarily sealed by solid phase hydrocarbons. We propose that a shallow, large reservoir with deeply sourced, relatively heavy petroleum is principally responsible for the formation of asphalts on the seafloor.

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Shallow free gas is investigated in seismoacoustic data in 10 frequency bands covering a frequency range between 0.2 and 43 kHz. At the edge of a gassy patch in the Bornholm Basin (Baltic Sea), compressional wave attenuation caused by free gas is estimated from reflection amplitudes beneath the gassy sediment layer. Imaging of shallow free gas is considerably influenced by gas bubble resonance, because in the resonance frequency range attenuation is significantly increased. At the resonance frequency of the largest bubbles between 3 and 5 kHz, high scattering causes complete acoustic blanking beneath the top of the gassy sediment layer. In the wider resonance frequency range between 3 and 15 kHz, the effect of smaller bubbles becomes dominant and the attenuation slightly decreases. This allows acoustic waves to be transmitted and reflections can be observed beneath the gassy sediment layer for higher frequencies. Above resonance beginning at ∼19 kHz, attenuation is low and the presence of free gas can be inferred from the decreased reflection amplitudes beneath the gassy layer. Below the resonance frequency range (<1 kHz), attenuation is generally very low and not dependent on frequency. Using the geoacoustic model of Anderson and Hampton, the observed frequency boundaries suggest gas bubble sizes between 1 and 4–6 mm, and gas volume fractions up to 0.02% in a ∼2 m thick sediment layer, whose upper boundary is the gas front. With the multifrequency acoustic approach and the Anderson and Hampton model, quantification of free gas in shallow marine environments is possible if the measurement frequency range allows the identification of the resonance frequency peak. The method presented is limited to places with only moderate attenuation, where the amplitudes of a reflection can be analyzed beneath the gassy sediment layer.

The inundated Doggerland in the North Sea Basin has been a coveted research target for many years due to its key location with respect to geological evolution since the last glaciation and its archaeological potential related to prehistoric hunter-gatherer populations. Still, many uncertainties related to glacial and sea level forcing on erosion and deposition remain, and the first discovery of submerged settlements is yet to be reported. In this study, we present a range of seismic morphologies and facies characteristic for the late glacial and Holocene succession near a major drainage system at the eastern Dogger Bank. Five of these facies are dominant in the area while two facies can be associated with a terrestrial-fluvial landscape buried 0-22 m below the seafloor. We detect various erosion levels of the terrestrial-fluvial landscape greatest towards the south where sediment has been removed likely due to a combined terrestrial-fluvial and marine erosion. We find that five subareas show geo-archaeological potential in terms of 1) preservation degree of terrestrial strata based on erosion estimates, 2) accessibility of terrestrial strata based on burial depths and 3) paleolandscape configuration based on spatial setting in relation to the drainage system and the paleo-coastlines. We further document a geological evolution of the study area, which is comparable to the evolution at the western Dogger Bank. However, we find more evidence for an extended flooding period because of the vicinity to the major drainage system and the Elbe Paleo Valley. We propose that our approach can be used as a workflow for marine investigations that focus on submerged hunter-gatherer heritage.