New insights into Middle Devonian chitinozoans from Bolivia

CAMINA, SONIA C.; GARCÍA MURO, VICTORIA J.; CLAUDIA VIVIANA RUBINSTEIN

Oxford

Congreso; The Palaeontological Association 64th Annual Meeting Virtual meeting; 2020

Oxford University Museum of Natural History

The TCB X-1001 ? Tacobo borehole, located at the Foothills in Bolivia, eastern sub-Andean ranges,was palynologically analyzed. Itcomprises the Middle Devonian shallow marine sedimentary succession of the LosMonos Formation. A late Eifelian? to middle Givetian age was already interpreted,based on organic-walled phytoplankton and miospores of the same cuttingsamples. Sixhundred and sixty-nine chitinozoan specimens were examined under SEM. A moderatelywell preserved chitinozoan assemblage was recognized from the middle levels ofthe formation, allowing the identification of 5 genera and 33 species. Thelower and upper levels produced scarce and poorly preserved specimens. The formationyielded a typical late Eifelian to early Givetian chitinozoan fauna of westernGondwana. The assemblage is dominated by the genus Ancyrochitina, whichconstitutes the 43%, with representatives of Ancyrochitina biconstricta andAncyrochitina multibrachiata amongothers. It reveals strong similarities to assemblages previouslyrecorded from the Middle Devonian of Bolivia. The presence of Ramochitinastiphrospinata, which is the index species of the eponymous early Givetian chitinozoanzone of western Gondwana, supports the age assignment basedon other palynomorph groups. Other early Givetian characteristic species are Ancyrochitinaflexuosa, Ancyrochitina frankeli, Ancyrochitinamorzadeci and Ramochitina boliviensis, the latter very abundant inthe studied assemblage.