FACIES ARCHITECTURE AND SEDIMENTOLOGY OF A MEANDERING FLUVIAL SYSTEM - A PALEOGENE EXAMPLE FROM THE WEISSELSTER BASIN, GERMANY

The Schleenhain open pit coal mine, located 30 km south of Leipzig, Ge rmany, exposes Upper Eocene and Oligocene non-marine strata representi ng fluvial deposition in the centre of the Weisselster Basin. Active m ining and successive cuts provided the rare opportunity to obtain a th ree-dimensional perspective of laterally extensive surface outcrops. T hese were used to construct a detailed fence diagram, which provided t he basis for recognition of key architectural elements in the weakly c onsolidated meandering stream deposits. In addition to the eight basic architectural elements of Miall (1985), the element SL (shallow lake deposits) was newly defined and the element CH (channel) was subdivide d into CHg (palaeo-river system) and CHk (small channel). The pro file s contain parts of two fining-upward cycles, which are separated by an unconformity spanning the Early Oligocene. Deposits of the first cycl e begin with transverse sand bars (downstream accretion deposits-DA) a nd point bars (lateral accretion deposits-LA). The upper part of the c ycle is represented by overbank fines (OF) and the element SL, which c onsists of laterally discontinuous lenses of dark, plant-bearing, kaol inite-rich clays, that were deposited in shallow lakes adjacent to the active channel. Coal seams interlayered with palaeosols are the main constituents of element OF. Sheetlike bodies of medium to fine gravels (gravel bars and bedforms-GB) on an erosive coal surface mark the beg inning of the second cycle. Dissolution of underlying Permian salts an d. sulphates prior to, during, and after the deposition of the Palaeog ene strata caused the development of two synclines within the outcrop. Coal seams and clay horizons which thicken and dip towards the centre of the synclines, provide evidence for their chronological developmen t.