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Project Progress

Microbial Fossilization Processes in Extreme Environments (dm)

The goal of this project is to understand the taphonomic processes that govern the fossilization and long-term preservation of biosignatures in extreme sedimentary environments dominated by microbial life. Progress was made on several fronts in the past year. Results of work reported last year to determine the taphonomic controls on preservation in Yellowstone hot-springs is now in draft ms form, and a completed manuscript is anticipated by the end of the summer.

The past year we began new studies in conjunction with EcoGenomics Focus Group.

1) We completed previous work on determine the origin of laminated fabrics on submerged cyanobacterial mats in saltern environments at Guerrero Negro, Baja Sur, an mat system that accretes at a rate of about 1 cm/yr.

2) As a part of the Guerrero Negro study, we have also begun to assess the role of meiofaunal grazers in the overall mat economy. To advance this project, samples were collected in conjunction with a group diel experiment conducted by the EGFG. The goal was to determine whether there is vertical migration of the meiofauna during diel excursions of oxygen-sulfide in the surface mat environment. Samples were fixed in the field and returned to the lab where they were dehydrated and embedded in low viscosity resin.Using standard methods, 20-micrometer-thick petrographic sections (of both stained and unstained materials) were prepared for light microscopy. In addition, fixed samples were critical point dried for observation by FESEM. Detailed light microscopy and FESEM are presently underway.

3) In addition to studies of submerged mat systems found in salterns at Guerrero Negro, we also began a new study of microbial mats in natural lagoon supratidal and tidal channels environments. During field work in June, we deployed permanent temperature data recorders at several sites to monitor the frequency and duration of tidal submergence for these mats over the next 6 months. We also collected mat-sediment samples to determine whether mats show grain size selectivity during the trapping and binding of detrital sediments brought in during tidal cycles. (This has implications for the recognition of mat-mediated detrital sediments in the ancient record). Upon returning to the lab, mat samples were oxidized to remove all organic matter, and the size frequency distribution of mat-associated detrital grain was determined by mechanical sieving. (Data are presently being analyzed by statistical methods to quantify grain size differences between different mat types). In addition, mat-sediment samples were prepared for light microscopy using the procedures described under 2) above.