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Provenance of Upper Cretaceous quartz-rich sandstones from the North Sudetic Synclinorium, SW Poland: constraints from detrital tourmaline

Biernacka J.

Geological Quarterly

2012

Vol. 56, No 2

333-344

Upper Cretaceous quartz arenites that fill the North Sudetic Synclinorium on the northern periphery of the Variscan Bohemian Massif show high compositional but low textural maturity. They have been interpreted for years as derived largely from nearby granite plutons, i.e. as first-cycle sediments. A different provenance was revealed on the basis of a combined light and heavy mineral analysis, and particularly a detrital tourmaline study, given that tourmaline is a sensitive indicator of granitic/metamorphic/sedimentary (multi-recycling) origin. Cenomanian, Turonian, Coniacian and Santonian sandstones contain abundant angular tourmaline grains, together with zircon and rutile, and subordinately staurolite, garnet, anatase, kyanite, sillimanite and monazite. The successive – Cenomanian to Santonian – tourmaline populations are similar with regard to shape, colour and chemical composition. The latter points unambiguously to various metamorphic rocks with a predominant group of Al-rich metapelites (Al-rich, F-poor dravite). It is concluded that, in the Late Cretaceous, large Sudetic granite plutons such as the Karkonosze and Strzegom–Sobótka massifs were not exposed but were buried under a thick siliciclastic cover. These results coupled with published apatite fission-track data from the granitic Karkonosze Pluton and the gneissic/migmatitic Góry Sowie Massif reveal that Late Cretaceous quartz arenites of the North Sudetic Synclinorium reflect gradual exhumation of the surrounding massifs, but do not record the final exposure of crystalline rocks. Since the latest Turonian, this exhumation corresponded to the Late Cretaceous inversion episode in Central Europe. The textural immaturity of Upper Cretaceous sandstones is misleading in terms of their recycled origin, and it is inherited from immature clastic source rocks.