Het Tertiair rond Winterswijk – Resultaten van het onderzoek verricht in de jaren 1968 en 1969

The fieldwork on the Tertiary of Winterswijk (Netherlands, prov. of Gelderland) has heen continued based on the ideas published in 1967• The lithostratigraphical succession has been extended by e.g. the provenance of the Miocene deposits near Miste (Van den Bosch, 1968) and of the sandy facies of the Rupelien (Oligocene) met with in several borings. The Miocene of Miste consists of a black glauconitic sand extremely rich in Mollusca, resembling the fauna of the “Hemmoor-Stufe”, and is overlain by the “Laag van Ticheloven”. The thickness of the sand is 2-3 metres. A division of the Oligocene into three lithostratigraphical units can be applied with certainty, viz.: 8 – 12 m moderate fine sand, overlain by ± 40 m very heavy clay, with septaria, and 40 – 50 m sandy clay, intercalated with clayey sands. The Upper-Oligocene has not been found near Winterswijk uptill now. Much more information has broadened the idea about the structure of the area. Strong tectonic activity has been known from the Eocene while from the Upper Oligocene and Lower Miocene a moderate and from the Pliocene a very important activity has been established. Salt-dome rising has had its influence during the Pleistocene-Holocene period. This research-project is to be continued.