Cool-water
Carbonate Contourites – Not Reefs – Examples from the Great
Australian Bight and the North Sea Basin
Huuse, Mads1, Finn Surlyk2,
Holger Lykke-Andersen3 (1) University of Aberdeen, Aberdeen, United
Kingdom (2) University of Copenhagen, Copenhagen, Denmark (3) University of
Aarhus, Aarhus, Denmark
Thick successions of cool-water
carbonates occur in the Upper Cenozoic of the Great Australian Bight and in the Upper
Cretaceous – Danian of the North Sea Basin, including on- and
offshore Denmark. Traditionally these
deposits have been considered largely pelagic or hemipelagic, locally
resedimented along structural highs or with biogenic mounds, causing local
bathymetric relief. However, data from recent offshore seismic investigations,
seabed mapping and sampling suggest that contourites formed by long-lived
bottom current systems are important elements in these deposits. In the Great Australian Bight, contourites are linked
with palaeo-bathymetric variations at the shelf/slope break and the eastward flowing
arm of the Leeuwin Current. The elongate contour-parallel contourite drifts
form nucleation sites for bryozoan colonies and are thus best interpreted as
‘bryozoan-rich contourites' rather than ‘bryozoan reef mounds' as they have
previously been described. In the Danish offshore chalk contourite drifts,
moats and channels were formed along the Sorgenfrei-Tornquist Zone (STZ), which
experienced significant tectonic inversion in the latest Cretaceous – Danian.
The contourite system extends for more than 100 km along the STZ demonstrating
how the bottom currents were focused along the inversion zone and exerted an
important control on carbonate deposition in the area. These discoveries
highlight that erosion, transport and redeposition of carbonate oozes by bottom
currents are important processes in the formation of cool-water carbonates with
immediate implications for basin reconstruction, stratigraphic architecture and
reservoir properties of cool-water carbonate deposits.