Weathering by dolomite dissolution responsible for the formation of an important palaeontological locality in the Prague Synform

0496386 - ÚSMH 2019 RIV CZ eng J - Journal Article
Rowberry, Matthew David - Dubois, C. - Kaufmann, O. - Baele, J.-M. - Blahůt, Jan
Weathering by dolomite dissolution responsible for the formation of an important palaeontological locality in the Prague Synform.
Acta geodynamica et geomaterialia. Roč. 15, č. 3 (2018), s. 297-309. ISSN 1214-9705. E-ISSN 2336-4351
Institutional support: RVO:67985891
Keywords : carbonate rock weathering index * polarising light microscopy * cathodoluminescence microscopy * calcite dissolution * dolomite dissolution * Lower Devonian * Slivenec Limestone * Prague Synform
OECD category: Geology
Impact factor: 1.062, year: 2018
https://www.irsm.cas.cz/materialy/acta_content/2018_doi/Rowberry_AGG_2018_0022.pdf

Karst landforms can result from a single stage process in which chemical dissolution and mechanical erosion proceed simultaneously or from a two stage process in which chemical dissolution recedes mechanical erosion. During the second of these processes, chemical dissolution leads to the creation of karst features hosting a residual weathering product, here referred to as alterite. An example of one such feature is the enclosed mass of altered rock at Červený Quarry near Klukovice which represents one of the richest localities for exceptionally preserved echinoderm ossicles in the Prague Synform. In this study the processes responsible for the formation of this feature have been investigated. Nineteen samples were obtained from the bioclastic Slivenec Limestone and from these it has been possible to calculate the carbonate volume content, which defines the weathering intensity, and the carbonate rock weathering index, which defines the weathering state. The results demonstrate that carbonate dissolution has not been accompanied by gravitational compaction or the incorporation of mineral inputs. Thin sections analysed under polarised light and under cathodoluminescence emphasise heterogeneous dolomitisation of the limestone. As the weathering grade intensifies, empty rhomboidal pores become increasingly common until, ultimately, the rhomboidal forms are lost due to corrosion and enlargement. In contrast it is rare to find evidence of calcite dissolution and, therefore, the altered mass still hosts almost all of its post dolomitisation micrite, sparite, and bioclasts. Negligible calcite dissolution helps to explain the exceptional nature of the fossil preservation at the site while the dolomite dissolution accounts for the ease with which it is possible to extract the fossils. Further research should focus on better understanding the role of dolomite dissolution in the formation of other important palaeontological localities in the Prague Synform.
Permanent Link: http://hdl.handle.net/11104/0289187