GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 225-11
Presentation Time: 3:50 PM


FRIESENBICHLER, Evelyn, Institute of Earth Sciences, Graz University, Heinrichstraße 26, Graz, 8010, Austria, BAUD, Aymon, BGC, Parc de la Rouvraie 28, Lausanne, CH-1018, Switzerland, KRYSTYN, Leopold, Institute of Palaeontology, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria, SAHAKYAN, Lilit, Institute of Geological Sciences, National Academy of Sciences of Armenia, 24a Baghramian Avenue, Yerevan, 375019, Armenia and RICHOZ, Sylvain, Institute of Earth Sciences, University of Graz, Heinrichstraße 26, Graz, 8010, Austria,

The Transcaucasia area (central Armenia) offers the opportunity to study a distinctive sponge-microbial community development in the aftermath of the end-Permian mass extinction (Permian-Triassic Boundary sponge-microbialites PTBSM): isolated communities started to built vertical edifices up to 12 m high during Griesbachian times (Induan, Lower Triassic), and show two growth phases within a pelagic carbonate ramp. The first sponge-microbial build-ups, which are rich in sponge spicules, co-occur with impressive calcium carbonate crystal fans (CCFs) that vary in thickness between 5 cm to 2 m. A comparison between the δ13C values from the PTBSM that formed during the first growth phase and the surrounding sediment revealed a remarkable differences: the δ13Cmicrobialite values are up to 2.3‰ more positive than the corresponding δ13Csediment values.

During the second sponge-microbial growth phase, numerous thrombolitic domes with specific internal structures were formed. The highest growth reaches a total height of up to 12 m with an 8 m top head diameter. Its asymmetry indicates a steady bottom current condition, which also contributes to the concomitant deposition of thin bedded bioclastic lime-wackestone containing ostracods, foraminifers, gastropods, bivalves as well as ammonoids, and to the embedding of the PTBSM. Within these buildups the δ13Cmicrobialite and δ13Csediment values are nearly the same, which is a remarkable contrast to the sponge-microbial build-ups that formed during the first microbial growth phase.

Regarding the growth phase duration, instead of a Lower Griesbachian microbialite short existence found in South China as in South Turkey, the Armenian PTBSM growth extends all over the Griesbachian from parvus to krystyni conodont zones, which is at least twice as long.