3D seismic geomorphology and sedimentology of the Chalk Group, southern Danish North Sea

Abstract

Classically, the North-Sea Chalk is assumed to have deposited under quiet, homogeneous pelagic conditions with local re-deposition in slumps and slides. However, recently the observation of highly discontinuous reflection patterns on 2D and 3D seismic data from the NW European Chalk Group initiated a revision of some general ideas of chalk deposition, assuming that long-lived, contour-parallel bottom currents exert a primary influence on the development of intra-chalk channels, drifts and mounds. In this study, an alternative explanation is suggested for the formation of many of the significant intra-chalk seismic and stratal discontinuities by interpreting these as being caused by gravity-driven processes developing in response to intense syndepositional tectonics. Submarine mass-transport systems identified in the study area include large-scale slumps, slides, debris flows and turbidites. The latter occur in sinuous channel systems flanked by large master overbanks, with the channel fill exhibiting well-developed secondary banks and overbanks on the respective outer bends of the inner channel thalweg. This first documentation of channelised density-flow deposits in the North-Sea Chalk has important consequences for the interpretation and prediction of re-deposited chalk units, emphasising at the same time the strength of vigorous 3D seismic discontinuity detection for subsurface sedimentary-systems analysis.

Mass-transport deposits and reservoir quality of Upper Cretaceous Chalk within the German Central Graben, North Sea

“…The occurrence of significant intra-chalk slump complexes is documented for the first time within the Entenschnabel area (Fig. 7) and fits well to interpretations in the Dutch and Danish North Sea sectors (Van der Molen et al 2005;Back et al 2011). In places, headwall scarps of slope failures are imaged on seismic profiles, but these might be locally often indistinct due to the post-depositional salt tectonics.…”

“…Many different classification schemes and specific nomenclatures in former and recent studies exist for intra-chalk erosional surfaces which are influenced by slope instability in the North Sea (Watts et al 1980;Kennedy 1987;Taylor and Lapré 1987;Surlyk et al 2003; Van der Molen et al 2005;Back et al 2011). In this study, we use the generic term MTDs to describe relocated sediments caused by submarine slope failures.…”

“…Such erosional and sedimentary forms characterise allochthonous sediments, e.g. mass-transport deposits (MTDs), in contrast to autochthonous pelagic chalk that remained in place after deposition (Watts et al 1980;Kennedy 1987;Taylor and Lapré 1987;Van der Molen et al 2005;Esmerode et al 2008;Back et al 2011).…”

“…In the North Sea Chalk, sediment redistribution by mass-transport processes is, e.g., described by slope instabilities leading to the movement of chalk sediment downslope into bathymetric lows of the North Sea Central Graben ( Van der Molen et al 2005;Back et al 2011). Such MTDs can be Abstract The architecture of intra-chalk deposits in the 'Entenschnabel' area of the German North Sea is studied based on 3D seismic data.…”

Seismic expression of depositional elements associated with a strongly progradational shelf margin: northern Santos Basin, southeastern Brazil

“…Despite the indirect character of seismic data and inherent difficulties associated to limited data resolution (see Shanmugam, 2000, for a critical review), reliable genetic interpretations for buried deep-marine deposits have been done based on high-quality seismic data (e.g., Gee et al, 2007;Back et al, 2011;Jiang et al, 2012;Sylvester et al, 2012).…”