Introduction of the Boxtel Formation and implications for the Quaternary lithostratigraphy of the Netherlands

Abstract

Application of the traditional lithostratigraphic framework to subdivide the Middle- and Upper-Quaternary locally-derived fine-grained depositsin the Netherlands is problematic. Deposits of many formations cannot be distinguished from each other based on lithological characteristics andstratigraphic position alone. To overcome this problem, we present a new, well-defined lithostratigraphy for these deposits, based on detailedresearch in the central part of the Roer Valley Graben. This area contains an up to 35 m-thick sedimentary record of Middle- and Upper-Quaternary sand, loam and peat deposits. These have mainly been formed by aeolian and small-scale fluvial processes and have been preservedas a result of tectonic subsidence. The traditional lithostratigraphic subdivision of these deposits into three formations (Eindhoven Formation,Asten Formation and Twente Formation) was based on a combination of litho-, bio- and chronostratigraphic evidence and the presumed widespreadpresence of a horizon of organic-rich interglacial sediments of Eemian age. To avoid intermingling of criteria regarding lithological characteristics,genesis and age, we now incorporate all fine-grained sediments into the new Boxtel Formation. The implications for the lithostratigraphicframework in other parts of the country are explored and discussed. Eight lithostratigraphic members are introduced that describe the mostcharacteristic parts of the formation. To fully illustrate the sedimentary sequence in the Roer Valley Graben, two new members are defined here.The Best Member incorporates alternating floodloam deposits and sandy aeolian deposits in the lower part of the Boxtel Formation. The LiempdeMember includes reworked aeolian loess and sandy loess deposits ('Brabant loam') that occur in the upper part of the sedimentary sequence.