Cryogenic powderization of Triassic dolostones in

Authors: Zsófia Poros Hans G Machel Andrea Mindszenty Ferenc Molnár

Publish Date: 2013/03/20

Volume: 102, Issue: 5, Pages: 1513-1539

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Abstract

Disintegration of dolostones to dolomite powder powderization was a widespread phenomenon in Triassic dolostones of the Buda Hills where the areal extent of powdered dolostones is large compared to similar occurrences elsewhere in the world In the Buda Hills dolostone disintegration proceeded in four stages that correspond to a gradual decrease in particle size that is from the parent dolostone to 1 crackle breccia via 2 mosaic breccia diameter 2 cm via 3 mosaic breccia blocks ‘floating’ in dolomite powder to 4 dolomite powder diameter 100–300 μm Stable isotope ratios and trace element compositions of dolomite remained constant throughout these stages and there are no indications of dissolution in most locations suggesting that disintegration was predominantly a mechanical process Combining these findings with the geological history of the region and supported by a simple freezing/thawing experiment and pertinent experimental studies on weathering of building stones it appears that powderization in the Buda Hills was caused by repeated freeze–thaw cycles during and/or after the Pleistocene glaciations Subaerial exposure under cold climate conditions involves multiple freeze–thaw cycles that create mechanical stresses in the rock framework related to the opposing thermal expansion of rock and water that freezes and of ice that liquefies This process is herewith called ‘cryogenic powderization’ Our data further suggest that the synergy of four factors promoted dolostone powderization in the Buda Hills 1 tectonics which created a pervasive fracture network 2 intercrystalline porosity of the dolostone 3 relatively high water saturation and 4 subaerial exposure under cold climate conditionsThe project was initiated as part of a cooperation between Eötvös Loránd University Budapest Hungary and ENI SpA Milano Italy Principal financial support for the research was provided by ENI SpA The authors are grateful to Paola Ronchi ENI SpA for initiating and coordinating this cooperation We also appreciate that she called our attention to the powderization of dolostones outside of Hungary and for sharing her experience related to dedolomitization Additional financial contribution was provided by the Hungarian Scientific Research Fund OTKA project numbers K 72590 and K 81296 and also by the Natural Sciences and Engineering Research Council of Canada NSERC to H Machel We are thankful to Gergely Surányi for the UTh measurements The assistance of Orsolya Győri Benedek Gál and Róbert Part especially in the field work and the help of Péter Pekker and Zsolt Bendő during XRD and SEM analyses are appreciated The authors are grateful to János Haas and Kinga Hips for thoughtprovoking discussions Siegfried Siegesmund opened our eyes to the prolific literature on natural and experimental weathering of carbonate rocks The authors are grateful to Qilong Fu and Bob Loucks for their thorough reviews

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