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

Jashar Arfai,Dieter Franke,Rüdiger Lutz,Christoph Gaedicke,Jonas Kley

doi:10.1007/s00531-015-1194-y

Abstract

The architecture of intra-chalk deposits in the ‘Entenschnabel’ area of the German North Sea is studied based on 3D seismic data. Adapted from seismic reflection characteristics, four types of mass-transport deposits (MTDs) are distinguished, i.e. slumps, slides, channels and frontal splay deposits. The development of these systems can be linked to inversion tectonics and halotectonic movements of Zechstein salt. Tectonic uplift is interpreted to have caused repeated tilting of the sea floor. This triggered large-scale slump deposition during Turonian–Santonian times. Slump deposits are characterised by chaotic reflection patterns interpreted to result from significant stratal distortion. The south-eastern study area is characterised by a large-scale frontal splay complex. This comprises a network of shallow channel systems arranged in a distributive pattern. Several slide complexes are observed near the Top Chalk in Maastrichtian and Danian sediments. These slides are commonly associated with large incisions into the sediments below. Best reservoir properties with high producible porosities are found in the reworked chalk strata, e.g. Danish North Sea, therefore MTDs detected in the study area are regarded as potential hydrocarbon reservoirs and considered as exploration targets.

Highlights

The Late Cretaceous was a warm temperate to subtropical greenhouse period coinciding with a pronounced eustatic sea-level high stand (Surlyk et al 2003)
Interpretation of 3D seismic reflection data proves that the North Sea Chalk in the Central Graben offshore Germany contains various types of mass-transport deposits (MTDs)
Many of the observed seismic discontinuity features were found in areas affected by Late Cretaceous salt and inversion tectonic activity in the German Central Graben

Summary

Introduction

The Late Cretaceous was a warm temperate to subtropical greenhouse period coinciding with a pronounced eustatic sea-level high stand (Surlyk et al 2003) The latter resulted in a reduced influx of detritus and enabled pelagic sedimentation on the continental shelves, including the North Sea area (Surlyk et al 2003). The chalk sediments were partly redistributed by bottom currents, which locally changed the sea floor morphology, resulting in the development of valleys, ridges, channels, moats, scours and drifts, indicating that the ‘chalk sea’ was a highly dynamic depositional environment (Surlyk et al 2003, 2008; Lykke-Andersen and Surlyk 2004; Surlyk and LykkeAndersen 2007; Esmerode et al 2008). 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)

Methods

Results

Conclusion