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Successive stages of calcitization and silicification of Cenomanian spicule-bearing turbidites based on microfacies analysis, Polish Outer Carpathians

Bąk B., Górny Z., Bąk K., Wolska A., Stożek B.

Annales Societatis Geologorum Poloniae

2015

Vol. 85, No. 1

187--203

Mid-Cretaceous turbidites with large proportions of sponge spicules are widely distributed in the Silesian Nappe of the Outer Carpathians, giving rise to diversified types of sediments, from spiculites to spicule-bearing siliciclastics and calcarenites. Part of this succession, Middle–Late Cenomanian in age, was transformed into cherts. A microfacies study showed that these turbidite sediments underwent several stages of calcitization and silicification, which took place during Mid-Cretaceous times in different sedimentary environments, i.e., on a northern shelf bordering the Silesian Basin and on a deep sea floor. The first diagenetic changes were related to changes to the biotic components of the turbidite layers, dominated by siliceous sponge spicules. This process, which took place in the spiculitic carbonate mud on the shelves, was related to the calcitization of sponge spicules. Calcareous clasts and calcified skeletal elements also were corroded by bacteria. After transportation down the slope, the biogenic and siliciclastic particles were deposited below the carbonate compensation depth. Taphonomic processes on the basin floor and alternating phases of carbonate and silica cementations, recrystallization and dissolution occurred in these sediments and were related to the diversification in composition of successive turbidite layers. Silicification was related to the formation of quartz precipitates as fibrous chalcedony or microcrystalline quartz, which were derived from the earlier dissolution of amorphous silica, originating mostly from siliceous sponge spicules and radiolarian skeletons. However, a source of silica from hydrothermal vents was also possible. The initial silica precipitation could have taken place in a slightly acidic environment, where calcite was simultaneously dissolved. A number of silicification stages, visible as different forms of silica precipitate inside moulds after bioclasts, occur in the particular turbidite layers. They were related to changes in various elements of the pore-water profile after descending turbidity-current flows. A very low sedimentation rate during the Middle–Late Cenomanian in the Silesian Basin may have favoured the sequence of initial calcitization and silicification stages of the turbidite sediments.

Famennian, thermally altered chert exotic clasts from the Jędrzychowice/Ludwigsdorf wildflysch (Sudetes)-stratigraphic and tectonic implications

Wajsprych B., Haydukiewicz J., Achramowicz S.

Geological Quarterly

2006

Vol. 50, No. 2

281-288

A wildflysch sequence recently recognized in the Görlitzer Schiefergebirge/western Kaczawskie Mts. boundary zone permits the characterization of the westernmost Kaczawa Unit as a chaotic complex. The cherts,many of which contain numerous radiolarians, occur as exotic clasts within the olistostrome deposits of the wildflysch. They are associated with allochthonous blocks of blueschist, andesite pillow lavas and pyroclastic rocks, flysch facies clastic rocks, mudstones (often of black shale lithology) and carbonates. The conodonts extracted from the grey-greenish radiolarite cherts indicate a mid-Famennian age (Early rhomboidea Zone to Early marginifera Zone). The conodont-bearing radiolarite clasts reveal no trace of a tectonometamorphic fabric. Their 4-4.5 conodont colour alteration index (CAI) indicates that the rock underwent low-temperature (250-285C) thermal alteration. The lack of thermal overprint in the olistostrome matrix allows this alteration to be interpreted as a part of the tectonothermal, post-mid-Famennian evolution of the source area. A number of the exotic blocks of unmetamorphosed volcanic rocks associated with the chert exotics seems to indicate igneous (volcanic) activity as the reason for the chert alteration. The fact that exotic blocks of the Devonian chert have been found as clasts within deposits earlier believed to represent Upper Proterozoic (Cadomian) flysch suggests the need for reassessement of the extent of Cadomian rocks in the westernmost Sudetes.

Badania izotopowe czertów oraz zębów dinozaurów

Durakiewicz T., Sharp Z., Migaszewski Z.

Eksploatacja i Niezawodność

2000

nr 4(7)

38-43

Zastosowania izotopów stabilnych w geologii przedstawiono na dwóch przykładach. Skład izotopowy tlenu w emalii zębowej zdjętej z kopalnych zębów dinozaurów posłużył jako narzędzie do określenia warunków paleoklimatycznych panujących na Ziemi pod koniec okresu kredowego. Zaproponowano nowa metodę określania paleowilgotnośei przy wykorzystaniu zapisu izotopowego w zębach ankylozaurów. Badania izotopów tlenu i wodoru w czortach wskazują na niestabilność procesu ich formowania, charakteryzującą się cyklicznymi zmianami składu izotopowego.

Applications of stable isotopes in geology are illustrated by use of two examples. Isotopic composition of teeth enamel taken from fossil dinosaur's teeth was used as a tool for estimating the palaeoclimatic conditions on Earth at the end of the Upper Cretaceous period. A new method of paleotemperature estimation by use of isotope signature of Ankylosaurid teeth was proposed. Isotope investigations of oxygen and hydrogen in cherts indicate the instability of their formation process, being characterized by cyclic changes of isotopic composition.