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Trace elements and mineral assemblage as palaeoenvironmental markers in the Cenomanian/Turonian Magierowa Member (Pieniny Klippen Belt, West Carpathians)

Wójcik-Tabol P.

Studia Geologica Polonica

2008

Vol. 131

247-268

The studied sediments of the Magierowa Member corespond to the Cenomanian/Turonian OAE 2. A better understanding of the genesis and palaeoenvironmental setting of this unit was achieved by means of geochemical indicators integrated with mineral composition. It suggests a strong influence of palaeoproductivity/redox cycles. The black shales are characterised by the enhanced accumulation and preservation of marine-derived organic matter. Lamination and enrich- ment of redox-sensitive elements (e.g., Ag, Cd, Mo, V) imply periodic prevalence of anoxic/euxinic conditions within the sediment (pore water) occasionally extending to the sediment/water interface. The bioturbated claystone intervals record periods of low productivity and development of more normal-marine conditions on the bottom. Furthermore, low Mn-contents, broad pyrite size-distribu- tion and presence of marine-origin organic matter suggest that an oxygen minimum zone (OMZ) must have existed within the water column during accumulation. The mineral assemblage of the Magierowa Mbr includes clay minerals, quartz, feldspar and iron minerals. Mineralogical data comparing with some gechemical ratios: Ti/Al, K/Al, Rb/Al suggest pelagic regime of deposition. Well-crystallised illite corresponding with high kerogen maturation and large iron mineral point to advanced diagenesis.