Organic communities and facies development of the Korytnica basin (Middle Miocene; Holy Cross Mountains,•Central Poland)

Abstract

The Korytnica basin that developed during the Middle Miocene (Badenian) transgression onto the southern slopes of the Holy Cross Mountains, Central Poland, comprises a sedimentary sequence composed of the world-famous, much fossiliferous Korytnica Clays, and of overlying marly sands and red-algal (lithothamnian) limestones. The paleogeographic setting and the structure of the basin, being a part of the drowned valley, are discussed with a special attention to the littoral zone of the basin. This zone was featured with rubbles and abrasion surfaces, all of which are densely bored by diverse rock-borers (sponges, polychaetes,. pelecypods, acrothoracican cirripedes). Special littoral facies are exemplified by the oyster shellbed, and sandy clay with brackish gastropods, the latter of which is interpreted as confined to coastal swamps of the mangrove type. The main facies of the basin, the Korytnica Clays, is discussed in regard with its sedimentary conditions, taphonomy of the fossils and their burial conditions. The most important organic communities and their vertical succession are presented, and a conclusion on the seagrass vegetation in the basin is drawn. Discussed are also some biological relationships between the particular species, and results of the activity of hermit crabs upon alive mollusks. The decline of .sedimentation in the basin manifested with the extreme shallow marine facies that correspond to a complete filling of the basin with sediments up to sea level. The climatic conditions that prevailed in the Korytnica basin are characterized as very close to those typical of present-day tropical and/or subtropical zones. Finally, the Indo-Pacific elements within the Korytnica assemblages are indicated, and a discussion on the connections of the Miocene sea of Europe with the lndo-Pacific province is presented.