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Sulphur, oxygen and strontium isotope compositions of Middle Miocene (Badenian) calcium sulphates from the Carpathian Foredeep, Poland: palaeoenvironmental implications

Kasprzyk A., Pueyo J.J., Hałas S., Fuenlabrada J.M.

Geological Quarterly

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2007

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Vol. 51, No 3

285-294

EN

Sulphur, oxygen and strontium isotope compositions have been measured in sulphate (gypsum and anhydrite) sam ples from the Badenian evaporite complex in the Carpathian Foredeep Basin (Poland) to determine the origin of brines from which these sulphates were formed. Studied samples display the d values from +22.68 to +24.91‰ CDT for sulphur (ten samples) and from +12.26 to +13.63‰ SMOW for oxygen (ten samples), and 87Sr/86Sr ratios from 0.708915 to 0.716329 (six samples). Most samples show isotopic values (both d34S and 87Sr/86Sr) higher than contem poraneous (Badenian) sea water, and thus suggest that these sulphates were formed (i) from brines with a significant component of non-marine waters, (ii) in a restricted system, where an important role was played by meteoric water inputs as well as by bacterial sulphate reduction. The results of this study show clear differences in the isotopic signatures between sedimen tary (gypsum) and diagenetic (anhydrite) lithofacies. While sedimentary gypsum displays sulphur, oxygen and strontium isotope ratios close to contemporaneous (Badenian) sea water, diagenetic anhydrite values are largely elevated. The higher isotopic values (d34S, d18O and 87Sr/86Sr) for anhydrite when compared to gypsum are interpreted as reflecting different hydrological provenances of sulphate in the Badenian basin. Gypsum was formed from brines marine in origin that were subject to an important in flow of continental waters and a local bacterial sulphate reduction in arestricted, and there fore sulphate-limited basin, which is consistent with earlier interpre tations based on sedimentological and geochemical studies. Our study shows that brines from which anhydrite was formed had a highly-radiogenic non-marine (riverine, ground water) strontium component, which is a new contribution to the knowledge on the Badenian sulphate formation. The results reflect a lateral compositional evolution of parent waters during sulphate deposition and diagenesis in the Carpathian Foredeep Basin.

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Diagenetic alteration of Badenian sulphate deposits in the Carpathian Foredeep Basin, Southern Poland : processes and their succession

Kasprzyk A.

Geological Quarterly

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2005

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Vol. 49, No. 3

305-316

EN

The facies variation of the Badenian sulphate deposits in the Polish Carpathian Foredeep Basin reflects distinct depositional and diagenetic environments. In these environments the primary sulphate (mainly gypsum) was deposited and then underwent different pathways of diagenetic evolution, recognized on the basis of sedimentological, petrographic and geochemical studies. Diagenetic sulphate facies (anhydrite and secondary gypsum) formed in successive stages: syndepositional (the depositional stage), early diagenetic (at the surface and during shallow burial) and late diagenetic (during deeper burial and exhumation). Most anhydrite deposits show sedimentological and petrographic features characteristic of a diagenetic facies formed by replacement (anhydritization) of the precursor gypsum deposits. Four basic genetic models of anhydrite have been proposed: (1) syndepositional interstitial anhydrite growth de novo, (2) syndepositional anhydritization (via nodule formation and pseudomorphous replacement), (3) early diagenetic anhydritization (displacive anhydrite growth), and (4) late diagenetic anhydritization (replacive anhydrite growth). The succession of diagenetic processes and their paragenetic relationships within the Badenian sulphate deposits display a complex diagenetic evolution. Many controlling factors, such as a palaeogeographic setting, tectonic activity, geostructural constraints and physico-chemical changes of the pore fluids, related to sedimentary and diagenetic environments, have been involved in the sulphate diagenesis. The results may be applied to other ancient evaporite basins including the marginal gypsum deposits and anhydrite in the more buried, basinward part.

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Warunki anhydrytyzacji gipsów badeńskich w zapadlisku przedkarpackim

Kasprzyk A.

Biuletyn Państwowego Instytutu Geologicznego

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2005

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nr 417

5-26

PL

Gips jest zastępowany przez anhydryt w temperaturze zależnej od warunków fizykochemicznych środowiska. Większość anhydrytów w badeńskim basenie ewaporatowym zapadliska przedkarpackiego wykazuje cechy sedymentologiczne i petrograficzne facji diagenetycznych, powstałych w wyniku przeobrażeń pierwotnych osadów gipsowych, zarówno selenitowych (autochtonicznych), jak i klastycznych (allochtonicznych). Nieregularne rozmieszczenie anhydrytu w sukcesji gipsowej sugeruje, że anhydrytyzacja gipsów zachodziła preferencyjnie w strefach o zwiększonej mikroporowatości, w ścisłym kontakcie z roztworami porowymi o wysokim zasoleniu. Szereg czynników związanych ze środowiskiem sedymentacyjnym i diagenetycznym (w warunkach pogrzebania) miało wpływ na proces anhydrytyzacji gipsów w badeńskim basenie ewaporatowym. Uwzględniając warunki wgłębne występowania osadów siarczanowych w zapadlisku przedkarpackim, oszacowano hipotetyczną głębokość i czas przejścia gipsu w anhydryt. Uzyskane wartości głębokości wynoszą 630-740 m dla sukcesji basenowej i 610-700 m dla sukcesji brzeżnej. Ponieważ w północnej, peryferyjnej części zapadliska skały gipsowe nigdy nie znajdowały się na tak dużej głębokości, inne czynniki, niezwiązane ze środowiskiem pogrzebania (np. zasolenie wód porowych), prawdopodobnie warunkowały anhydrytyzację gipsów.

EN

The gypsum is replaced by anhydrite in the temperature dependent on the physicochemical environment of gypsum. Most Badenian anhydrite deposits in the Polish Carpathian Foredeep Basin display sedimentary and petrographic features of diagenetic facies formed from the precursor gypsum, both selenitic (autochthonous) and clastic (allochthonous). The irregular distribution of anhydrite within the gypsum succession suggests the replacement occurred preferentially in zones of high microporosity in the contact with highly saline pore fluids. Many controlling factors, related to sedimentary and diagenetic environments, have been involved in anhydrite genesis in the Badenian evaporite basin. The burial environments of sulphate deposits in the Carpathian Foredeep were considered to estimate the predicting depths and time of the gypsum to anhydrite transition. The obtained depths range between 630 and 740 m for the basinal succession and between 610 and 700 m for the marginal succession. Because in the northern part of the Carpathian Foredeep gypsum has never been deeply buried, different factors not related to deep burial conditions (e.g. salinity of pore fluids) must have been involved in anhydritization processes.

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Sedimentology, diagenesis and oil habitat of sulphate-carbonaceous deposits (Middle-Upper Devonian, Predobrogean Depression)

Gnidets V. P., Grigorchuk K. G.

Biuletyn Państwowego Instytutu Geologicznego

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1999

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nr 387

29--30