Ridge and valley systems in the Upper Cretaceous chalk of the Danish Basin: Contourites in an epeiric sea
E. V. Esmerode, H. Lykke-Andersen, F. Surlyk, 2007. "Ridge and valley systems in the Upper Cretaceous chalk of the Danish Basin: Contourites in an epeiric sea", Economic and Palaeoceanographic Significance of Contourite Deposits, A. R. Viana, M. Rebesco
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Extensive low-lying parts of the NW European craton were flooded during the Late Cretaceous transgression, creating a relatively deep epeiric sea with reduced supply of siliciclastic material and insignificant coastal upwelling. The chalk, essentially an oceanic sediment type, was deposited as a pelagic rain of mainly coccolith debris and with local redeposition along structural highs. The study area is located in the eastern part of the Danish Basin, where the bordering Ringkøbing–Fyn High and the inverted Sorgenfrei–Tornquist Zone converge. Multichannel seismic reflection lines show the Chalk Group to be far from the expected flat-lying pelagic succession. A multitude of features of considerable relief, comprising an extensive unconformity, sediment waves, drifts and moats, are recognized. At least two episodes of widespread drift deposition are identified, one in the Santonian–Late Campanian and one in the Maastrichtian, separated by a Top Campanian Unconformity. The structures were formed by strong bottom currents flowing northwestward through the basin parallel to bathymetric contours. A lateral northeastward change, from more depositional to more erosional architecture, indicates a positive current velocity gradient towards the inversion zone, probably as a result of the Coriolis force. The strong similarity between the chalk drifts and modern contourite deposits supports the proposal that the oceanographic conditions linked to continental margins were extended into the Late Cretaceous epeiric sea of NW Europe.
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There has lately been a growth in the number and level of studies of contourite deposits. Most recent studies of contourites have two major lines of interest. One, propelled by the oil industry's continuous move into increasingly deep waters, concerns their economic significance. The other involves the stratigraphic/palaeoceanographic record of ocean circulation changes imprinted on contourite deposits that can be a key to understanding better the climate-ocean connection. The application of many different theoretical, experimental and empirical resources provided by geophysics, sedimentology, geochemistry, petrology, scale modeling and field geology are used in the 16 papers of this volume, proposing answers to those two main aspects. The papers are subdivided into two major categories (economic interest and stratigraphic/palaeoceanographic significance), with case studies ranging from well-documented drifts to new examples of modern and fossil series, involving a large diversity of geographic and physiographic scenarios worldwide.