Upper Cretaceous chalk facies and depositional history recorded in the Mona-1 core, Mona Ridge, Danish North Sea

Abstract

The 331 m long core from the Mona-1 well in the Danish North Sea spans almost the entire Upper Cretaceous Chalk Group but only about 10% of Late Cretaceous time is represented. The succession comprises 14 facies representing pelagic deposition, turbidity flow, and mass-transport processes, including mudflow, debris flow, and slumping. Pelagic deposits vary mainly in terms of the concentration of siliciclastic material, the trace-fossil assemblage, and the presence or absence of primary sedimentary structures. Pelagic sedimentation was probably punctuated by the deposition of thin turbidites, and the resultant deposits were thoroughly bioturbated if deposited during normal oxygenation at the sea floor. Periodic benthic dysoxia resulted in the preservation of primary structures, as represented by laminated chalk which consists of thin pelagic laminae alternating with thin turbidites. In addition to the thin turbidites in the laminated chalk, four different turbidite facies are interpreted as representing high- to low-energy flows. Clast-supported chalk conglomerates have previously not been differentiated from other turbidites, but are here interpreted to be directly related to the down-slope evolution of debris flows. Debris flows are represented by matrix-supported conglomerates, which form one of the most common facies in the succession. High-concentration, gravity-driven suspension flows passed into dilute visco-plastic flows during the final stages of deposition and resulted in the deposition of structureless chalks. Limited shear deformation produced distinct quasi-facies from which the precursor facies can be deduced, whereas intense or continued shear deformation produced a shear-banded quasi-facies from which the precursor facies cannot be deduced in all cases. A series of major slump packages (14–18 in total) are interpreted, forming over 40% of the succession; debrites appear to be the most common precursor facies involved in slumping. The vertical succession of facies records an earliest Cenomanian facies shift from dominantly siliciclastic to chalk deposition. The Cenomanian – late Campanian period was dominated by erosion or sediment by-pass with minor associated mass-transport deposits preserved. Basin filling by pelagites and turbidites prevailed in the late Campanian, whereas Maastrichtian pelagic deposition was interrupted by increasingly frequent and voluminous mass-transport events.

Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk

“…However, locally persistent bottom currents at the time of deposition contributed to sediment redistribution, leading to the formation of a variety of sedimentary features such as drifts, valleys, moats, channels and sediment waves, as documented both onshore and offshore north‐west Europe (Quine & Bosence, ; Lykke‐Andersen & Surlyk, ; Anderskouv et al ., ; Esmerode et al ., , ; Surlyk & Lykke‐Andersen, ; Surlyk et al ., ; Esmerode & Surlyk, ; Back et al ., ; Gale et al ., , ; Gennaro & Wonham, ). Episodic redeposition of chalk ooze as a result of downslope movement also occurred in areas experiencing syndepositional tectonic or halokinetic activity, resulting in submarine slides, slumps, debris flows, mud flows, grain flows and turbidites (Watts et al ., ; Hardman, ; Nygaard et al ., ; Bromley & Ekdale, ; Kennedy, ,b; Campbell & Gravdal, ; Bramwell et al ., ; Damholt & Surlyk, ; Anderskouv & Surlyk, ).…”

“…The commonly homogeneous appearance of the chalk due to its fine‐grained texture and generally pervasive bioturbation imposes numerous challenges for the analysis and exploration of this important hydrocarbon reservoir and aquifer rock, and many aspects of the chalk dynamics, including deposition and redeposition, are still poorly understood (e.g. Surlyk et al ., ; Anderskouv & Surlyk, , ). Because the chalk is an important hydrocarbon reservoir in the North Sea, the prediction of the distribution of key reservoir properties (for example, porosity and permeability) within this rock is of particular interest.…”

Geological evolution of the Chalk Group in the northern Dutch North Sea: inversion, sedimentation and redeposition

“…A widespread erosional unconformity was not only recognized in the Dutch North Sea but also in Germany, Denmark, Norway and the United Kingdom. Anderskouv & Surlyk (2011) found evidence of erosion near the Campanian-Maastrichtian boundary in the Danish North Sea and explained it by an inversion pulse or a significant sea-level drop. Vejbӕk & Andersen (2002) stated that continuous inversion took place and identified three different Sub-Hercynian phases of increased intensity: latest Santonian, mid Campanian and late Maastrichtian.…”

“…Especially in the Dutch Central Graben, relatively steep slopes must have been present during the deposition of the Chalk Group due to inversion. Multiple kinds of mass movement were recognized in the chalk in many areas of the North Sea, from both seismic data and drill cores (Kennedy, 1980(Kennedy, , 1987aEvans et al 2003;Lykke-Andersen & Surlyk, 2004;Van der Molen et al 2005;Surlyk, Jensen & Engkilde, 2008;Anderskouv & Surlyk, 2011;Back et al 2011).…”

Controls on upper Campanian–Maastrichtian chalk deposition in the eastern Danish Basin

“…Detailed facies analyses of the chalk are rare (e.g. Voigt, , ; Voigt & Häntzschel, ; Steinich, , ; Kennedy & Garrison, ; Hardman & Kennedy, ; Quine & Bosence, ; Scholle et al ., ; Damholt & Surlyk, ; Anderskouv et al ., ; Lasseur, ; Anderskouv & Surlyk, ; Rasmussen & Surlyk, ) and few attempts have been made to link small‐scale features to seismic‐scale morphologies (e.g. Gale, ; Quine & Bosence, ; Anderskouv et al ., ; Gale et al ., , ).…”