HR: 0800h
AN: B41A-0034    [Abstracts]
TI: Submicron-Chemical Speciation of Late Albian, Well-Preserved Fossil Samples from Tlayúa, the Mexican Solenhofen.
AU: * Marcus, M
AF: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
AU: Fakra, S
AF: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
AU: Tamura, N
AF: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
AU: Alvarado-Ortega, J
AF: Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico City, D.F 04510, Mexico
AU: Espinosa-Arruberena, L
AF: Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico City, D.F 04510, Mexico
AU: Banfield, J
AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, United States
AU: Cervini-Silva, J
EM: jcervini@igg.unam.mx
AF: Instituto de Geografia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico City, D.F 04510, Mexico
AB: The Tlayúa slurry quarry constitutes the most important paleontological locality in the American continent, and constitutes the second most important locality in its genre worldwide. The importance of Tlayúa strives inderives from the fact that a great diversity of marine and terrestrial fossils in perfect state of preservation have been found, with ages surpassing 115 million yrs. Paleomagnetic and biostratigraphic determinations conducted in ammonites and belemnites indicate that the formation of the Tlayúa slurry dates back to the late Albian. One of the most accepted hypothesis for explaining Tlayúa's formation relies on the deposition of sediments and fauna on a shallow platform of a tropical sea. A similar geographic place is located in Solenhofen, Germany, where slurries have been exploited for more than 200 yrs with a production of approximately 500 species. Remarkably, in the Tepexi del Rio region alone for the past 20 yrs more than 5,000 fossil specimens representing more than 200 species have been collected alone. An The exceptional specimen preservation found in Tlayúa has been attributed to restricted circulation of water resulting in an anaerobic and/or hypersaline environment, coupled with the general absence of infaunal species. There were periods when the deposition site supported a rich planktontic community. Large quantities of calcareous ooze were produced, resulting in rapid burial of the organisms. The presence of diagnostic terrestrial and freshwater organisms, including arachnids, insects, lizards, and chelonians, along with typical marine fauna, suggests that Tlayúa lagoon had periodic freshwater inflow, in addition to the strong marine, lagoonal, and reefal influence. Some organisms were transported into the lagoon when the barrier was breached, probably during periods of heavy rains and hurricanes, or during high tides. Additionally, some fishes from Tlayua have been found to have affinities with recent families known to inhabit brackish and freshwater environments. In search for reconstructing paleoenvironments in Tlayúa, fish bone samples from a Pachyrhizodontide specimens, from the telesteos incertae sedis group already extinct, were analyzed using XRFmicro X-ray fluorescence,  -X-ray diffraction RD, and -EXAFSnd XANES/EXAFS. Conducting Ca- EXAFS allowed us to resolve Ca-speciation in CaCO3 matrices. Micro Ca-EXAFSDiffraction and Ca K-edge XANES on bone material confirmed the presence of apatite, not hydroxyapatite consistent with highly-weathered environment. High concentrations of As were found in CaCO3) grains, Mn oxides grains as well as Celestine (SrSO4) grains dispersed in the egg core.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0410 Biodiversity
DE: 0419 Biomineralization
DE: 0424 Biosignatures and proxies
SC: Biogeosciences [B]
MN: 2007 Fall Meeting