Late Maastrichtian chalk mounds, Stevns Klint, Denmark: combined physical and biogenic structures

TY - JOUR

T1 - Late Maastrichtian chalk mounds, Stevns Klint, Denmark

T2 - combined physical and biogenic structures

AU - Anderskouv, Kresten

AU - Damholt, Tove

AU - Surlyk, Finn

PY - 2007

Y1 - 2007

N2 - Upper Maastrichtian chalk exposed at the Sigerslev quarry, Stevns Klint, Denmark is characterized by wavy and mound-like bedding geometries outlined by bands of black flint nodules. Four morphological elements are recognized, although bedding geometries are highly variable: southward migrating mounds, eastward migrating mounds, chalk waves and evenly bedded chalk.The mounds are interpreted as having been formed by currents carrying fine-grained suspended sediment which was primarily deposited on the up-current mound flanks. Bryozoans were prolific on the up-current flanks and mound summits, which stabilized the mounds, increased bed roughness and the overall accumulation rate. However, accumulation thicknesses do not correlate consistently with bryozoan density. The bryozoans were therefore important for the formation of the mounds, but the distribution of bryozoans did not solely determine depositional thickness across a mound and thus mound growth pattern. Relatively long wavelength wavy-bedded chalk show gentle convex-up geometries and would probably be described as sediment waves if recognized in seismic sections. The chalk waves were deposited under weaker current velocities than those active during mound formation. The exposed succession is topped by more evenly bedded chalk which was deposited by quiet pelagic fall-out of finegrained material. The whole succession was deposited on the upper part of the northern flank of a large WNW-ESE trending 3 km wide depositional ridge with an amplitude of 35-40 m formed by contour-parallel WNW-ward flowing bottom currents. The mounds may have been deposited by regional bottom currents, or by spill-over currents from the valley south of the large ridge. The succession was deposited during varying bottom current intensities and the depositional architecture indicates a complex and   dynamic environment. The depositional style seems to be controlled by the interplay and relative importance of two end-member processes; those that were purely physical and related to the interaction between available grain sizes and hydrodynamics, and those that were largely biological and associated with benthic growth and sediment trapping of mainly bryozoans. Examples of end-member conditions are known from Haute Normandy, France and the lower Danian of Stevns Klint. The structures described here adds to the considerable complexity of depositional styles in chalk.

AB - Upper Maastrichtian chalk exposed at the Sigerslev quarry, Stevns Klint, Denmark is characterized by wavy and mound-like bedding geometries outlined by bands of black flint nodules. Four morphological elements are recognized, although bedding geometries are highly variable: southward migrating mounds, eastward migrating mounds, chalk waves and evenly bedded chalk.The mounds are interpreted as having been formed by currents carrying fine-grained suspended sediment which was primarily deposited on the up-current mound flanks. Bryozoans were prolific on the up-current flanks and mound summits, which stabilized the mounds, increased bed roughness and the overall accumulation rate. However, accumulation thicknesses do not correlate consistently with bryozoan density. The bryozoans were therefore important for the formation of the mounds, but the distribution of bryozoans did not solely determine depositional thickness across a mound and thus mound growth pattern. Relatively long wavelength wavy-bedded chalk show gentle convex-up geometries and would probably be described as sediment waves if recognized in seismic sections. The chalk waves were deposited under weaker current velocities than those active during mound formation. The exposed succession is topped by more evenly bedded chalk which was deposited by quiet pelagic fall-out of finegrained material. The whole succession was deposited on the upper part of the northern flank of a large WNW-ESE trending 3 km wide depositional ridge with an amplitude of 35-40 m formed by contour-parallel WNW-ward flowing bottom currents. The mounds may have been deposited by regional bottom currents, or by spill-over currents from the valley south of the large ridge. The succession was deposited during varying bottom current intensities and the depositional architecture indicates a complex and   dynamic environment. The depositional style seems to be controlled by the interplay and relative importance of two end-member processes; those that were purely physical and related to the interaction between available grain sizes and hydrodynamics, and those that were largely biological and associated with benthic growth and sediment trapping of mainly bryozoans. Examples of end-member conditions are known from Haute Normandy, France and the lower Danian of Stevns Klint. The structures described here adds to the considerable complexity of depositional styles in chalk.

KW - Faculty of Science

KW - chalk

KW - Upper Cretaceous

KW - bottom currents

KW - mud mounds

KW - bryozoans

KW - Stevns Klint

U2 - 10.1016/j.sedgeo.2007.03.005

DO - 10.1016/j.sedgeo.2007.03.005

M3 - Journal article

SN - 0037-0738

VL - 200

SP - 57

EP - 72

JO - Sedimentary Geology

JF - Sedimentary Geology

ER -