Late Maastrichtian chalk mounds, Stevns Klint, Denmark

TY - CONF

T1 - Late Maastrichtian chalk mounds, Stevns Klint, Denmark

AU - Anderskouv, Kresten

AU - Damholt, Tove

AU - Surlyk, Finn

PY - 2007

Y1 - 2007

N2 - Upper Maastrichtian chalk exposed in the Sigerslev quarry, Stevns Klint, Denmark shows wavy and mound-like bedding geometries outlined by bands of black flint nodules. Bedding geometries are highly variable, but four morphological elements are recognized: 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, and stabilizedthe 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 was not the sole determining factor controlling the depositional thickness variation across a mound and thus mound growth pattern. Relatively long wave-length wavy-bedded chalk shows 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 fall-out of fine-grained pelagic carbonate. 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 mainly by bryozoans. The succession was deposited on the upper part of the flank of a 3 km wide and 35-40 m high depositional ridge formed by contour-parallel bottom currents (Lykke-Andersen and Surlyk, 2004). The mounds may have been deposited by regional bottom currents, or by spill-over currents from the valley south of the large ridge.

AB - Upper Maastrichtian chalk exposed in the Sigerslev quarry, Stevns Klint, Denmark shows wavy and mound-like bedding geometries outlined by bands of black flint nodules. Bedding geometries are highly variable, but four morphological elements are recognized: 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, and stabilizedthe 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 was not the sole determining factor controlling the depositional thickness variation across a mound and thus mound growth pattern. Relatively long wave-length wavy-bedded chalk shows 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 fall-out of fine-grained pelagic carbonate. 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 mainly by bryozoans. The succession was deposited on the upper part of the flank of a 3 km wide and 35-40 m high depositional ridge formed by contour-parallel bottom currents (Lykke-Andersen and Surlyk, 2004). The mounds may have been deposited by regional bottom currents, or by spill-over currents from the valley south of the large ridge.

M3 - Poster

T2 - 13^th Bathurst Meeting of Carbonate Sedimentologists, University of East Anglia,

Y2 - 29 November 2010

ER -