Upper Jurassic bacteria from the Raptawicka Turnia Limestone Formation in the Mały Giewont area (Western Tatra Mountains, Poland)

Abstract

Fossil filamentous and non-filamentous bacteria are reported from the Upper Jurassic limestones of the Raptawicka Turnia Limestone Formation in the Mały Giewont sections of the Western Tatra Mountains (Poland). The filamentous bacteria are subdivided into five groups: thin uniseriate, large multi-cell, large spiral, tapering and branched forms. The thin uniseriate filaments are the main microbial component of the peloids and micro-oncoids from the studied formation, mainly in the Upper Kimmeridgian–Tithonian limestones. The presence of the heterocyte-like terminal cells suggests their interpretation as cyanobacteria similar to the modern order Nostocales and perhaps to the family Nostocaceae. The large multi-cell and tapering filaments are uncommon in the studied limestones. The branched filaments found in the Tithonian limestones, although thinner, probably also may be compared with some modern representatives of the order Nostocales. Non-filamentous fossil bacteria found in the studied limestones consist of rod-shaped bacilli, monotrichous bacilli and spirilla; they belong mainly to the phylum Proteobacteria. Some microborings observed in the microfossils occurring in the micro-oncoids remind the ichnotaxon Scolecia filosa Radtke known to be of wide palaeobathymetric range. The thinnest microborings resemble another group of ichnofossils named “Pygmy form”, probably also of bacterial origin. The Upper Kimmeridgian–Tithonian micro-oncoids were formed mainly by filamentous bacteria (Cyanobacteria) that overgrew successively their nuclei with a few to several laminae. Frequent occurrence of pelagic microfossils as nuclei of micro-oncoids does not match a transport of these coated grains from much shallower sedimentary environments. The fossil filamentous bacteria filling up the peloids and micro-oncoids could be adapted to conditions that existed in the sublittoral zone below the wave base.