Une ichtyofaune lacustre dans le Miocène moyen du graben de Kjustendil (Bulgarie occidentale)

La diatomite et l’argillite d’âge probable badenien du graben de Kjustendil (Bulgarie occidentale) renferment de nombreux os isolés de poissons. Parmi eux, les restes de Moronidae sont les plus abondants. Quelques os de Cyprinidae, appartenant au moins en partie au genre Palaeoleuciscus Obrhelová, 1969, ont également été récoltés. Cette association caractérise un environnement lacustre.The diatomite and the argillite of the Kjustendil graben (Western Bulgaria), the age of which is probably Badenian, have yielded numerous fish remains. Among them, the Moronidae remains are the most abundant. Some bones of Cyprinidae which partly belong to the genus Palaeoleuciscus Obrhelová, 1969 were also collected. Such a community is indicative of a lacustrine environment.</p

Une ichtyofaune lacustre dans le Miocène moyen du graben de Kjustendil (Bulgarie occidentale)

Gaudant, Jean, Vatsev, Milorad (2006): Une ichtyofaune lacustre dans le Miocène moyen du graben de Kjustendil (Bulgarie occidentale). Geodiversitas 28 (1): 55-70, DOI: http://doi.org/10.5281/zenodo.537441

Geochemical characteristics of the alteration of volcanic and volcaniclastic rocks in the Feres Basin, Thrace, NE Greece

Summarization: The Tertiary basin of Feres consists of sedimentary rocks, andesitic-rhyolitic volcanic rocks of K-rich calc-alkaline affinities, rocks with calc-alkaline and shoshonitic affinities and volcaniclastic fall and flow deposits. Volcanic and volcaniclastic rocks have variable concentrations of LIL elements (Ba, Sr, Rb, Th) and HFS elements (Zr, V) due to their mode of origin. The pyroclastic flows frequently show more or less intense devitrification, vapour-phase crystallization and, in some cases, evidence of fumarolic activity, as is indicated by the presence of scapolite. The volcanic and volcaniclastic rocks display various types of alteration including formation of zeolites (clinoptilolite, heulandite, mordenite, and laumontite) and smectite, as well as hydrothermal alteration (development of silicic, argillic, sericitic and propylitic zones) associated with polymetallic mineralization. The behaviour of chemical elements during alteration varies. Some are immobile and their distribution is controlled by the conditions prevailing during parent-rock formation and emplacement, but others, such as Ba and Sr, are mobile and selectively fractionate in zeolite extra-framework sites. The formation of zeolite from alteration of volcanic glass is accompanied by an increase in Mg and Al content, and a decrease in Si and Na content, whereas Ca is not affected by alteration. In certain pyroclastic flows, there is a significant difference in K-content between incipient glass and altered rock, due to K-feldspar formation during devitrification and vapour-phase crystallization.Presented on: Clay Mineral