Vltavínyv neogenních a pleistocenních štěrcích z okolíJevišovic na Znojemsku. (Czech)

Moldavites in Neogene-Pleistocene gravels from the vicinity of Jevišovice (Znojmo area, Moravia, Czech Republic). (English)

New sporadic moldavites from the Černín and Vevčice localities in the sandy-gravel sediments along the river Jevišovka in southwest Moravia were found. A high proportion of quartz, black chert, and quartzite pebbles and subordinate portion of surrounding metamorphic rocks resemble moldavite-bearing fluvial sediments of Neogene age known from other places in Southwestern Moravia (e.g. sediments between Stropešín-Dukovany). However, low relative elevation of the sediments above the Jevišovka River (15-40 m), which resemble low-mature gravels of Pleistocene age with numerous pebbles of local rocks (gneiss, granulite, amphibolite) that bear moldavites further to the SE in Oleksovice-Božice-Břežany area is in contrast with this (Fig. 1). The newly discovered moldavites have diversely corroded surface covered with shallow elongated grooves, sometimes with relics of a deep sculpture and are sub-angular and sub-oval in shape (Fig. 2). Their shape and dark green to olive green colours correspond to the Moravian moldavite. These new, but so far only sporadic occurrences along Jevišovka are situated at the junction of the "moldavite strewn field" near Moravské Budějovice and the above mentioned numerous localities of uncommon rounded moldavites located further to the SE in gravels of the Lower- and Middle Pleistocene age (fig. 3). Accepted source of the psephitic clastic material from a wide area of Moravské Budějovice is also supported by heavy mineral assemblage: rare pale violet Mg-spinel, occurring in the source area in dolomite marbles is typical. Other translucent heavy minerals: garnet (2-3 types) + zircon + monazite + sillimanite/kyanite + red acicular rutile + amphibole + tourmaline are of local origin (Tab. 1). The low resistance of moldavites to abrasion in a fluvial environment, however, limits the distance of their transport onto several kilometres only. Probable source of new described moldavites was at that time fully eroded sediments of primary "moldavite strewn field" originally situated to the east of Moravské Budějovice in an area that has the character of a neotectonic elevation, as inferred from a geomorphologic analysis. [ABSTRACT FROM AUTHOR]

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