From the Pleistocene incision of a palaeo-valley until the Holocene formation of sandbanks: the Quaternary evolution of a shelf with low accommodation potential (Belgian Continental Shelf, southern North Sea)
Mathys, M.; Baeteman, C.; De Batist, M. (2007). From the Pleistocene incision of a palaeo-valley until the Holocene formation of sandbanks: the Quaternary evolution of a shelf with low accommodation potential (Belgian Continental Shelf, southern North Sea). Quaternary International 167-168(Suppl. 1): pp. 273 In: Quaternary International. Elsevier: Oxford. ISSN 1040-6182; e-ISSN 1873-4553, more |  |
| Abstract | With respect to the Quaternary deposits, the Belgian Continental Shelf (BCS) was one of the last unmapped and unknown areas of Belgium. Because of the absence of a distinct shelf break and the virtually complete lack of subsidence, the BCS has very little accumulation space to accommodate and preserve Quaternary sediments. The Quaternary on the BCS is very patchy and discontinuous, and has a maximum thickness of only 45 m. From this fragmented record it was very difficult to produce a coherent reconstruction of the Quaternary evolution, in times when only analogue data were available. At present, > 16.000 km of analogue high-resolution seismic profiles have been scanned, converted into digital ‘segy’ format, and integrated with almost 500 core descriptions, enabling us to develop a genetic model for the Quaternary evolution of the BCS. The seismic data show seven seismic-stratigraphic units, in agreement with previous studies on one of the sandbanks of the BCS. Two basal units fill in the deepest parts of a large incised valley (the Ostend Valley), and have possibly been deposited in an estuarine or fluvial environment. The third and fourth unit, separated by an erosional surface, completely fill up the incised valley, and even extend beyond it. They are assumed to have been deposited in an estuarine and tidal flat setting, respectively. The fifth and sixth unit are interpreted as nearshore and coastal sandbank deposits, and the seventh unit represents recent tidal sandbank and swale deposits. Thanks to the integration of all the available sedimentological core data with the seismic stratigraphy, it became evident that this 7-unit seismic-stratigraphic sub-division of the Quaternary cover has indeed a regional validity. Based on seismic-stratigraphic evidence, it is assumed that for instance unit three and four were initially deposited across a large area of the BCS and were subsequently affected by erosion and the formation of sandbanks. Probably, the formation and infill of the Ostend Valley is the result of a combination of erosive phases during successive glacial sea-level lowstands, and tidal scouring and infilling during the last interglacial highstand and early Holocene. The younger units are deposited in a straightforward vertical facies succession reflecting an overall transgressive context: first a tidal environment was established, followed by the formation of coastal, wave-dominated sandbanks, after which offshore tidal sandbanks formed under the current macro-tidal regime, and the continuing –but slowing- rise of the sea level. |
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