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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.

Organic carbon accumulation events in the mid-Cretaceous rocks of the Pieniny Klippen Belt (Polish Carpathians) : a petrological and geochemical approach

Wójcik-Tabol P.

Geological Quarterly

2006

Vol. 50, No. 4

419-436

New petrological and geochemical data lead to a consistent depositional model of the Corg.-rich sedimentation within the Pieniny Basin during themid-Cretaceous. Considerable terrestrial runoff into the Pieniny Basin occurred during the late Albian. Detritalmacerals accumulated under aerobic conditions on the shelf and continental slope. Fertilization of surface water induced primary productivity; aerobic degradation of organic matter led to the development of an oxygen-minimumzone within mid-water. The oxygen-minimumzone spread over almost all of the Pieniny Basin (Albian/Cenomanian). At the same time, a stagnant pool developed in the Grajcarek Basin. During the mid-Cenomanian the O2 minimum zone retracted and covered only the shelf and upper/middle slope. Stagnant pools might have formed in the depressions. Turbidity currents flowed down the slope and deposited calciturbiditic sequences with organic detritus in the Branisko and Pieniny basins. At the end of the Cenomanian, isolated anoxic or even H2S-bearing basins existed on the shelf. The slope was still occupied by the oxygen-minimum zone. In the deepest part of the sea-floor a stagnant basin formed.