Diagenesis of Luxembourg Sandstone

Research has been conducted into the diagenesis of the Luxembourg Sandstone. Literature studies were followed by a visit to the outcrop, after which thin sections were studied. The Luxembourg Sandstone Formation has been deposited in the Hettangian and Sinemurian, both lower Jurassic ages. A sea strait connecting the Northern German Basin and the Paris Basin was located in present day Luxembourg. A tidal dominated delta deposited the weathering products form a part of the Rhenohercynian Zone, the Ardennes, into the transgressive sea strait to create sandstone deposits. The outcrop near the village of Echternach is characterised by two rock types visible as horizontal beds and lenses: one well cemented and a less cemented sandstone. The less cemented zones tend to be better resistant to weathering and this causes the less cemented rock to overhang the cemented rock. The cemented zones have been cemented with calcite crystals and minor amounts of quartz cement. The sandstone consist of fine grained, moderately sorted, angular quartz grains with minor amounts of feldspars, opaque minerals, muscovite and zircon crystals. Detrital mudstone grains and ferroan cement were also present. The cemented rocks are classified as Lithic Arenites whilst the less cemented zones are classified as Sublithic Arenite, both have a recycled orogenic provenance. Three parameters have influenced the cementation. Firstly permeability differences caused by deposition of clay and deposition of coarser material. Paths of permeability have formed through the sediments and this favoured cementation. Secondly, heterogeneous deposition of carbonate holding content provided extra nucleation sites, again encouraging cementation. Lastly, carbonate redistribution took place in later stages causing carbonates to move from less cemented zones to cemented zones, causing even more cement to precipitate. Since calcite crystals dissolve more easily than quartz in the meteoric realm, the cemented rocks have been dissolved more, creating the appearance of the formation.