The architecture of the Kattendijk Formation and the implications on the early Pliocene depositional evolution of the southern margin of the North Sea Basin

1. Introduction During the early Pliocene, the glauconite-bearing sands of the Kattendijk Formation were deposited in a shallow marine environment in the southern part of the North Sea Basin (Fig. 1). Its presence was established in the subsurface of the city of Antwerp and its harbor during excavation works (see Cogels, 1874; Gaemers, 1975; De Meuter et al., 1976; Louwye et al., 2004; De Schepper et al., 2009) and by means of boreholes in the Waasland (Laga, 1971) and Campine areas (Louwye & Laga, 1998; for location see Fig. 2). At these observation points, the Kattendijk Formation overlies units from different ages, ranging from the upper Miocene Diest Formation in the Campine area and northeast of the city of Antwerp (De Meuter et al., 1976; Louwye & Laga, 1998;) to the lower to middle Miocene Berchem Formation in the northern part of the city of Antwerp (Cogels, 1874; De Meuter et al., 1976) and even the lower Oligocene Boom Formation in the Waasland area (Laga, 1971; Gaemers, 1975; Fig. 2). The base of the Kattendijk Formation forms an important regional unconformity. Little detail is known about the geometry of the unconformity, only a few regional insights are known from schematic cross-sections (Laga, 1983) and the regional geological models (Jacobs et al., 2010; Matthijs et al., 2013; Deckers et al., 2019). This is mainly due to the poor distinction between the Kattendijk Formation and over- and underlying glauconite-bearing sands in low quality borehole descriptions