CONTINENTAL RED BEDS, AND OLD CONCEPT BUT QUESTIONS REMAIN: HOW, WHY, AND WHEN RED, AND WHY SHOULD WE BOTHER?

Ondřej Bábek

Department of Geology

Palacký University of Olomouc

17. listopadu 12
77146 Olomouc, Czechia

Phone: +420 585 634 532
ondrej.babek@upol.cz

geology.upol.cz I petroleum.upol.cz

Abstract

    Continental red beds (CRB) are distinct facies, which have attracted the interest of geologists for about two centuries. They have been traditionally interpreted as time-specific facies, and indicators of arid desert climate especially in the Permian to Triassic periods. In fact, CRBs can develop in various types of depositional environments, not only in arid settings, and they are known from various time periods from the Proterozoic to Recent. But when it comes to a precise definition of CRBs, how red is actually "red" (?), what processes of mineral transformations are involved in the reddening (?), when did these processes occur (?) how are they reflected in chemistry of sedimentary rocks (?), and did they really reflect ancient climates? We will address these questions using rigorous colour quantification by diffuse reflectance spectroscopy, combined with the methods of field facies analysis, gamma-ray spectrometry, sandstone and mudstone petrography, major and trace element geochemistry, in-situ element geochemistry in thin sections, and molybdenum isotopes. We will discuss case studies encompassing the famous Old Red Sandstone (Lower Devonian) of South Wales, Variscan intramontane basins of Bohemian Massif (Permian), Czech Republic, continental sediments of the Colorado Plateau, Utah, USA (Permian to Jurassic), red sediments of the Gercus Formation from the Zagros Foreland, Kurdistan Region of Iraq (Eocene), and Holocene fluvial sediments of the Czech Republic.