Loading fractures and Liesegang laminae: new sedimentary structures found in the north‐western North Alpine Foreland Basin (Oligocene–Miocene, south‐west Germany)

Abstract

Spectacular sedimentary structures recently found in the Molasse Basin (Oligocene–Miocene) in southern Germany were produced by soft‐sediment deformation under highly unusual conditions. These large, apparently wedge‐like structures –‘loading fractures’– cut down into beds of marl and are filled with coarse sand and intraclasts of shale. Wrapping the sides of the structures is a thin, continuous bed of layered dark claystone – the ‘DCB’. The upper and lower layers of this bed are an organic‐rich clay; the middle layer is a laminated quartzite. The precursor of the DCB was a lacustrine gyttja rich in diatom frustules. It was supersaturated in silica as it was buried. Subsequent diffusion of oxygen into this gyttja at a burial depth of only a few metres resulted in the formation of Liesegang laminae of quartz. These laminae grew and amalgamated, forming the layer of laminated quartzite. The sediments overlying the DCB were eventually removed by erosion, probably in a high‐energy marine environment. This erosion cut down to the DCB but was unable to penetrate it. The DCB remained exposed on the sea floor until a sudden depositional event occurred – the deposition of a 2·5 metre thick bed of coarse sand with shale intraclasts. Although the DCB had been able to resist the submarine erosion, it could not support the load of this new bed. The quartzite layer in it therefore fractured, transferring that load down onto the underlying, still‐unconsolidated marl. The intraclast‐rich sands were forced down into this marl, carrying ahead of them the partly broken remains of the DCB.

A fourth St. Gallen Formation cycle (?) in the Karpatian Upper Marine Molasse of central Switzerland

“…The Late Ottnangian age for the Kirchberg Formation is supported by biostratigraphic data on mammals and fish otoliths. However, according to Tipper et al (2003), there is no sedimentological or faunal evidence that the erosion that produced the Graupensand channel actually was fluvial. Tipper et al (2003) propose as an alternative explanation for the origin of the "Graupensandrinne" that it was incised by submarine erosion.…”

“…However, according to Tipper et al (2003), there is no sedimentological or faunal evidence that the erosion that produced the Graupensand channel actually was fluvial. Tipper et al (2003) propose as an alternative explanation for the origin of the "Graupensandrinne" that it was incised by submarine erosion. If that is correct, no hiatus need to be present between the top of the Upper Marine Molasse and the bottom of the Brackish Molasse.…”

Vegetation‐induced sedimentary structures from fossil forests in the Pennsylvanian Joggins Formation, Nova Scotia

“…Preliminary reports indicate that VISS are present in Mississippian strata in Atlantic Canada (Gingras, 2002;Melrose & Gibling, 2003), but a search of literature on older plant occurrences has not revealed any detailed descriptions of pre-Pennsylvanian VISS. Although early vascular plants consisted of small, herbaceous forms until the Middle Devonian (Goldring, 1927;Gensel & Andrews, 1984), structures developed around individual calamite stems in the Joggins Formation suggest that stems only a few (Allen, 1982); grooves form disconnected arcs within the circle; some have plant remains at the axis of rotation (Metz, 1991(Metz, , 1999 Spiral burrows of Paraonis fulgens (Bromley, 1990); concentric traces Spirorhaphe and Nereites (Pemberton et al, 1992); circular tool marks (Rigby, 1959) Upturned (Obermeier et al, 1990); poorly preserved stump casts (Mossa and Schumacher, 1993); abandoned channels; cradle knolls; loading fractures (Tipper et al, 2003) Vegetation-induced sedimentary structures 547 centimetres in diameter can interact with flow to generate VISS. Additionally, the development of modern vegetation shadows behind grass tufts shows that even small, delicate plants can interact with transported sediment in certain situations.…”

Self-organized rhythmic patterns in geochemical systems

“…Liesegang bands have also been reported [36] in an Oligocene-Miocene claystone formation from the North Alpine Foreland basin (Germany). Here, a 10 cm thick layer shows symmetric bands of coarse quartz crystals alternating with zones of finer quartz grains.…”