Present address: DONG Energy E&P, Agern Allé 24-26, DK-2970, Hørsholm, Denmark.
Three-dimensional architecture and development of Danian bryozoan mounds at Limhamn, south-west Sweden, using ground-penetrating radar
Article first published online: 12 AUG 2008
© 2008 The Authors. Journal compilation © 2008 International Association of Sedimentologists
Volume 56, Issue 3, pages 695–708, April 2009
How to Cite
NIELSEN, L., VON BROCKDORFF, A. S., BJERAGER, M. and SURLYK, F. (2009), Three-dimensional architecture and development of Danian bryozoan mounds at Limhamn, south-west Sweden, using ground-penetrating radar. Sedimentology, 56: 695–708. doi: 10.1111/j.1365-3091.2008.00993.x
- Issue published online: 9 MAR 2009
- Article first published online: 12 AUG 2008
- Manuscript received 19 April 2007; revision accepted 5 June 2008
- Danish Basin;
- ground-penetrating radar;
Bryozoan mounds from the middle Danian (Lower Palaeocene) of the Danish Basin represent a possibly new class of non-cemented skeletal mounds. The sedimentology and palaeoecology of the mounds have recently been studied in detail. Three-dimensional images of middle Danian bryozoan mound structures in the Limhamn limestone quarry, south-west Sweden, obtained from combined reflected ground-penetrating radar signals and outcrop analysis provide new information about the architecture and growth development of such mounds. The mounds are composed of bryozoan limestone and dark-grey to black flint bands which outline mound geometries. Ground-penetrating radar data sections are collected over a 120 m by 60 m grid of data lines with trace spacing of 0·25 m, providing a depth penetration of 7 to 12 m and a vertical resolution of ca 0·30 m. The ground-penetrating radar images outline the geometry of the internal layering of the mounds which, typically, have widths and lengths of 30 to 60 m and heights of 5 to 10 m. Mound architecture and growth show great variability in the ground-penetrating radar images. Small-scale mound structures with a palaeorelief of only a few metres may constitute the basis for growth of larger mounds. The outermost beds of the individual mounds are commonly characterized by sub-parallel to parallel reflections which have a circular to slightly oval appearance in map view. The mounds are mainly aggrading and do not show clear signs of pronounced lateral migration during growth, although some mound structures indicate a preferential growth direction towards the south. Growth patterns interpreted from the ground-penetrating radar images suggest that the palaeocurrents in the study area may have shown great variability, even on a small scale. This observation is in contrast to results from studies of extensive, slightly older early Danian mound complexes exposed in coastal cliffs at Stevns Klint and Karlby Klint located 50 and 200 km away from the study area, respectively. At these locations the mounds show a remarkably uniform development and typically are asymmetrical, clearly showing migration directions towards the south. These differences in mound geometry may be the result of differences in the current systems and water depths that existed during formation of the early and middle Danian mounds, respectively. The mounds at Limhamn were located closer to the basin margin in shallower water than those at Stevns Klint and Karlby Klint. In addition, the difference in mound architecture may be due to the occurrence of non-layered, irregular coral mounds intercalated with the bryozoan mounds at Limhamn.