International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Assessing provenance of Upper Cretaceous siliciclastics using spectral γ-ray record

Pages: 311 - 329

Authors: DANIEL ŠIMÍČEK, ONDŘEJ BÁBEK

Abstract: The relationship between contents of clay minerals/grain size and spectral γ-ray record (concentrations of K, U and Th) in sediments is used for interpretation of sedimentary facies in wire-line logs. However, this approach is often complicated by the multi-component nature of mineralogically immature siliciclastics. As mineralogy of the source mate- rial and grain-size sorting during transport both contribute to the detrital composition of the final sediment, a joint study of facies and outcrop γ-ray spectra can potentially make the latter an effective tool in provenance studies. This paper provides comparison of outcrop γ-ray data and detailed facies mapping with mineral and chemical composition of the rocks (modal composition; transparent heavy mineral assemblages; WDX SEM chemistry of minerals) and interprets them in terms of provenance changes. We studied the Upper Cretaceous, synorogenic siliciclastic sediments of the Mazák and Godula Formations (Silesian Unit of the Western Carpathians flysch belt). Decreasing mineral maturity of the studied sandstones is consistent with provenance change from craton interior – (Mazák Formation) to transitional continental and recycled orogen sources (Godula Formation). Two major phases of K, U and Th concentration shifts, which occurred close to the Mazák/Godula Formation and Middle/Upper Godula Members boundaries, are consistent with changes in main detrital modes. These trends indicate gradually accelerated influx of material derived from high-grade metamorphic and plutonic rocks during deposition of the Mazák and Godula Formations. These changes are interpreted as reflecting a gradual exhu- mation and erosion of deeper crustal levels of the source area, the Silesian ridge.

Keywords: Western Carpathians, gravity-flow sediments, geochemistry, heavy minerals, γ-ray spectrometry, provenance

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