Original paper

The Late Aalenian Polyplocussandstein Formation in SE Lower Saxony, Germany: Meandering distributary and crevasse splay sedimentation on a lower deltaic plain

Zimmermann, Jens; Franz, Matthias; Wolfgramm, Markus


The Late Aalenian (earliest Middle Jurassic) Polyplocussandstein Formation in the vicinity of Wolfsburg (SE Lower Saxony, Germany) was deposited on the progradational lower delta plain of a large fluvial-dominated delta system. Detailed lithofacies analyses on several outcrops point to five associations of eight lithofacies types: i) point bar sheets, ii) chute channels, iii) natural levees, iv) crevasse splay sheet sandstones and v) interdistributary bays and, combined with published well data, enable a more detailed palaeogeographic reconstruction than previously available. Palaeohydraulic analysis on lateral shifting point bar sheets of a subsidiary distributary channel enable the reconstruction of an up to 45 m wide and 4 m deep meandering channel of high sinuosity (P 1.8) and mean transport direction towards 298°. The meander belt was at maximum 350 m wide (Wm ) and characterised by an annual discharge of up to 17 m³/s (Qm ) and mean flood discharge of up to 210 m³/s (Qma ). Discharge varied only slightly between stages of bankfull and low depth but resulted locally in crevassing of natural levees and formation of crevasse splays. Crevasse splays were transported towards northwestern and northeastern direction and are characterised by tabular sand sheets of aggradational architecture. Their propagation is indicated by downstream accreting cross-bedded bedforms and their termination by down-current directed thinning and rapid facies transitions to clayey lithologies of interdistributary bays. However, dark clays of interdistributary bays are slightly enriched in organic carbon but redox indices (Ni/Co, U/Th) indicate deposition under oxic conditions.


central european basinchute channelfacies analysislate aalenianlower delta plainmeandering distributary channelpoint bar reactivationpoint bar sheetpolyplocussandstein formationsheet sandstone