Petrology and Petrography of Neogene Sandstone Reservoirs of the East Slovakian Basin, Czechoslovakia

Abstract

The Neogene East Slovakian basin forms the northwest depocenter of the Transcarpathian depression. It is a back-arc transtensional basin, approximately 100 km long with up to 7 km of sedimentary fill consisting of shallow-marine to continental clastics and locally abundant volcanities, volcaniclastics, and tuffs. Volcanism was most active during the Miocene (late Badenian to early Sarmatian), with subsidence and sedimentation rates reaching their peak during this period. The sandstones within the basin are primarily immature lithic arenites, commonly up to 8 m thick, derived from the Inner West Carpathians, from local volcanics, and from earlier flysch and molasse sediments. Sandstones are typically composed of very fine- to fine-grained subangular quartz, lithic fragments, and feldspars with accessory micas, chert, pyrite, clays, heavy minerals, and calcite cement. Carbonaceous material is present in many of the sandstones. Porosity has been severely reduced in many of the sandstones by carbonate cementation and alteration of unstable grains. Authigenic clay minerals and zeolites further reduce porosity. A complete paragenetic model has yet to be defined; however, the complexity of the diagenetic/paragenetic relationships suggests multiple episodes of alteration.