Facies architecture of a Late Jurassic carbonate ramp: the Korallenoolith of the Lower Saxony Basin

Abstract

The sedimentary succession of a Late Jurassic (Oxfordian to basal Kimmeridgian) carbonate ramp is described and interpreted. The study area is located in the central part of the Lower Saxony Basin in NW Germany, which forms part of the Central European Basin. Eight well-exposed and undeformed sections of the study area (Suntel area, Wesergebirge and eastern part of the Wiehengebirge) provide detailed information about lithofacies and lateral thickness variations. Biostratigraphically, the age of these sediments is poorly constrained. Twenty microfacies types are recognized that can be grouped into seven facies associations: (a) strongly bioturbated marlstones deposited near storm wave base (SWB), (b) foraminifera-rich wackestones, (c) wackestones and floatstones with biostromes and (d) bioclastic limestones deposited between SWB and fair-weather wave base (FWWB), (e) oolitic and iron-oolitic limestones and (f) siliciclastic sediments deposited above FWWB, and (g) lagoonal deposits. These facies associations characterize a storm dominated shallow mixed carbonate-siliciclastic ramp. Based on facies changes, quartz content, and gamma ray logs, the Korallenoolith Formation can be subdivided into a lower carbonate-dominated and an upper siliciclastic-dominated part, build up by different scales of small- to large-scale deepening- and shallowing-upward cycles. A preliminary correlation of measured outcrops of this formation is presented.