Ironstone clasts in the Cretaceous sandstones near the northern margin of the Bohemian Cretaceous Basin (map sheet 02-223 Mikulášovice)


Jaroslav Valečka

Geoscience Research Reports 35, 2002 (GRR for 2001), pages 78–80
Map sheets: Varnsdorf (02-22)

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Quartzose sandstones of the Cretaceous Jizera Formation (Middle to Upper Turonian) near the northern margin of the Bohemia Cretaceous Basin contain abundant layers of finegrained quartzose conglomerates. Ironstones are common among the clasts in these conglomerates. Their maximum size is 15 cm in the a-axis. Such ironstone clasts have been found neither in the underlying nor in the overlying strata. That is why we usppose that these ironstone clasts are of synsedimentary origin and rapidly forming ferricretes in the adjacent areas could serve as their source material. Conventient climatic conditions (subtropical climate with dry seasons) could have caused formation of such ferricretes during the Turonian.