Lithostratigraphical and biostratigraphical subdivision of Tertiary deposits (Oligocene - Pliocene) in the Winterswijk - Almelo region (eastern part of the Netherlands).

Tertiary sediments (Oligocene - Pliocene) in the Gelderse Achterhoek and Twente (Winterswijk - Almelo region, eastern part of the Netherlands, provinces of Gelderland and Overijssel) are lithologically subdivided in a number of members. In this paper the Ratum Member, the Brinkheurne Member, the Winterswijk Member, the Aalten Member, the Eibergen Member, the Zenderen Member and the Lievelde Member are introduced. The Delden Member, already introduced in 1860, is redefined; this member occurs between the Zenderen Member and the Lievelde Member. The Aalten Member is subdivided in two new beds, the Miste Bed and the Stemerdink Bed respectively. For each of the lithological units a stratotype and some reference sections are designated. In the palaeontological part the fossil content of the lithological units is described. In the Brinkheurne Member two new biozones are introduced: the Cyclocardia kickxi - Astarte kickxi Assemblage Zone and the Serpula septaria - Ancistrosyrinx volgeri Assemblage Zone. In the Aalten Member four new biozones are distinguished: the Hiatella arctica Acme Zone, the Astarte radiata Acme Zone, the Spisula sp. Acme Zone and the Limopsis aurita Acme Zone. Finally, the lithological units described in this paper are correlated with deposits in Belgium, Germany, and Denmark by means of lithological and palaeontological characteristics.