[B-BG01] Earth and Planetary Science Frontiers for Life and Global Environment

[BBG01-P10] Geomicrobiological conditions required for stromatolite formation in travertines at a sulfide-rich hot spring

*Tomoyo Okumura¹, Chizuru Takashima², Katsunori Yanagawa³, Agung Harijoko⁴, Akihiro Kano⁵ (1.Kochi University, 2.Saga University, 3.The University of Kitakyushu, 4.Gadjah Mada University, 5.The University of Tokyo)

Keywords:travertine, stromatolite, photoheterotroph

Travertine, a carbonate precipitates from calcareous hot spring water, shows sub-mm order laminations that appear similar to ancient stromatolites. Herein, we investigated the travertine in a calcareous and sulfidic hot spring at Sipoholon, Northern Sumatra, Indonesia. The travertine deposits were associated with microbial mats of different colors that change from yellow, pink, and green, lowering water temperature and H₂S concentration along the water passages. A phylotype analysis of the Prokaryotic 16S rRNA gene revealed that chemolithoautotrophic sulfur and hydrogen oxidizing bacteria were abundant in the yellow sediment around vent sites. While a linage of Anaerolineae dominated the pink to green sediment at mid- to downstream. Stromatolite textures are developed within pink and green-colored sediments. Monitoring water chemistry and sediment texture for an Anaerolineae-dominated sample collected from a midstream site revealed that daily lamination was formed due to the daytime biofilm formation under the stable chemical composition of water conditions except for dissolved oxygen concentration. Daily laminations were also formed in other samples by microbial communities with lower Anaerolineae abundance. Further, the results showed that if mineral precipitation and microbial growth rates are appropriately balanced, cyanobacteria were not essential for the lamination development. This indicates that such a geomicrobiological system could occur in early-time stromatolites even before the evolution of cyanobacteria.