Pelagic red and gray shales are intercalated within
the lower part of the Mazak Formation of Middle
Cenomanian age in Czech Republic. A detailed geochemical
study of major, trace and rare earth elements
and carbon isotopic compositions of organic carbon
has been conducted on sixteen red and gray shales.
The data suggest that the shales were most likely
accumulated in well-oxygenated bottom waters with
very limited organic matter supply and consisted
of marine organic matter mixed with minor amounts
of terrestrial organic matter. The shales were deposited
below CCD in one of the tectonic troughs developed
along northern margin of the western Tethys. Similar
geochemical covariances of major, trace and rare
earth elements for the shales suggest palaeoceanographic
conditions and provenance during their deposition.
The most probable cause for the variation of redox
bottom conditions in the mid-Cretaceous deep ocean
was periodic changes in the concentration of
dissolved oxygen in bottom waters, due to changes in
deep water circulation and processes driven climate
changes