Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Suchý

The "white beds" - A fossil caliche of the Barrandian area: Its origin and paleoenvironmental significance

Journal of the Czech Geological Society, volume 47 (2002), issue 1-2, 45 - 54

So-called "white beds"- a snowy white to rusty yellow, sandy to chalky weathered carbonate alteration horizons locally developed over the lower Paleozoic limestones-are interpreted in terms of fossil carbonate soil (caliche, calcrete). A typical caliche sequence affects as much as 6-8 meters of the limestone host and develops gradually from a transitional zone exhibiting largely dissolution phenomena. These altered limestones grade upwards into a chalky zone of completely disintegrated carbonate that, in turn, gives way to a zone of coalescing carbonate nodules commonly developed below the recent soil cover. Microscopic phenomena observed in the carbonates closely match those known from both recent and ancient caliche elsewhere, and include calcite nodules, circum-granular cracking, rhizoliths, Microcodium, alveolar septal structures, tangencial needle-fiber calcite cements and floating calcite rhombs. Following the paleosoil formation, some of the caliche deposits were subject to redeposition and/or collapse into the paleorelief depressions and introduction of alluvial gravels and fine siliciclastic material into the caliche matrix. The age of the caliche is not known. Assuming that the formation of caliche paleosoil requires the conditions of long-lasting geomorphologic stability and arid to semi-arid climatic setting with low annual rainfall, the alteration can be tentatively attributed to a protracted period of peneplenization and reduced deposition that occurred in the Bohemian Massif during the Mesozoic-Tertiary era. Alternatively, the caliche facies may have also developed in response to Pliocene-Pleistocene climatic fluctuations.