Geologica Belgica

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Etienne STEURBAUT & Chris KING

The composite Kortrijk section (W Belgium): a key reference for mid-Ypresian (Early Eocene) stratigraphy in the southern North Sea Basin

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Abstract

The upper part of the Kortrijk Clay Formation (the Roubaix Clay and Aalbeke Clay Members of mid-Ypresian age) has been exposed in road and canal cuttings and clay quarries in the Kortrijk area (western Belgium), and penetrated by several cored boreholes. It is overlain disconformably by the Mont-Panisel Sand Member of the Hyon Sand Formation (upper middle Ypresian). The Roubaix Clay Member contains diverse and well-preserved calcareous nannofossils, dinoflagellate cysts, foraminifera, ostracods and other calcitic microfossils, and less well-preserved mollusc assemblages, while the Aalbeke Clay Member is secondarily decalcified. The calcareous nannofossil subdivision of upper NP11 and lower NP12 has been recognised in the Kortrijk area, and calibrated with the NW European mid-Ypresian dinoflagellate cyst, ostracod and planktonic foraminiferal zones and datums (e.g. Subbotina influx). Several medium-scale depositional sequences, with an estimated duration of 400 kyr or less, have been recorded. Their respective boundaries coincide with the resistivity maxima identified on the majority of the wireline log profiles of the Belgian Ypresian. Integrated biostratigraphic, magnetostratigraphic and sequence stratigraphic analysis enables correlation with other areas in Belgium, with the London Clay Formation of southern England, and with the standard chronostratigraphic scale. A marine erosion surface has been identified at the base of Unit 20 in the Kortrijk area (mid-Ypresian, early Biochron NP12, middle C24n.1n, ~52.8 Ma), corresponding to the first occurrence of estuarine channel-fill units in southern England. This indicates a brief but profound sea-level fall, either eustatically or tectonically controlled. The composite Kortrijk section is proposed as a reference section for the middle Ypresian in the southern North Sea Basin, and for similar settings in mid- to high-latitudes of the Northern Hemisphere (e.g. Kazakhstan and Crimea).

Keywords : integrated stratigraphy, microfossils, mid-Ypresian, key reference, southern North Sea Basin

To cite this article

Etienne STEURBAUT & Chris KING, «The composite Kortrijk section (W Belgium): a key reference for mid-Ypresian (Early Eocene) stratigraphy in the southern North Sea Basin», Geologica Belgica [En ligne], Volume 20 (2017), number 3-4, 125-159 URL : http://popups.ulg.ac.be/1374-8505/index.php?id=5779.

About: Etienne STEURBAUT

Royal Belgian Institute of Natural Sciences, Operational Directory Earth and History of Life, Vautierstraat 29, B-1000 Brussels and KU Leuven, Belgium; etienne.steurbaut@naturalsciences.be.

About: Chris KING

Chris King sadly passed away while this paper was in its final stage. It is dedicated to his memory, in recognition of his lifetime achievements in stratigraphy and biostratigraphy and to his great love and fascination for the Ypresian strata of Belgium.