On the silica diagenesis processes of the coal debris from Miocene formation from Prahova County

Belonging to the category of gemes, in the same division with amber, silicolitic insertions or agates, silica wood are quasipresent in Oligocene and Miocene age arenitic or coal lithofacies as well as in volcanogenic-sedimentary formations with post-geyser activity, or as remaking in the salt Breccia. The speciality literature mentions frequent occurrences of silica wood in Oligocene and Miocene sand and coal formations, from the Transylvanian basin, Eastern Carpathians, Southern Carpathians and Western Carpathians. In the selective silicification of fossil woods to the context in which they appear silica solutions appeal to the attraction of organic matter. The different porosity, the presence of vacuum cells, the concentration difference of cellar solution, the osmotic predisposition, the humus presence or the subsequent phytotithe within their wood structure would explain the silicification selectivity. We may add to these suppositions the fact that the pH and temperature differences, and therefore silica solubility and subsequently saturation, at the passing of arenitic lithofacies of Kliwa sandstones into the anoxic disodilic lutitic lithofacies, enriched with remanent organic substance favor the silica precipitation. The presence of fossil woods confirms the proximal shelf ambience in which Kliwa arenites were deposited. The impermeable kind of the lutitic context of disodiles facilitated the carbonification allowing the subsequent silicification.