HR: 0800h
AN: B21A-1006    [Abstracts]
TI: Preservation and Significance of Vestimentiferan Tube Worms in Paleocene Cold Seep Carbonates, Panoche-Tumey Hills, California
AU: * Schwartz, H
EM: hschwartz@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Sciences Dept., Santa Cruz, CA 96064 United States
AU: Hull, I
EM: ihull@ucsc.edu
AF: University of California, Santa Cruz, Earth Sciences Dept., Santa Cruz, CA 96064 United States
AB: Vestimentiferan tube worms are the dominant chemosynthetic macroinvertebrates at many active cold seeps, but their remains are surprisingly rare in paleoseeps. A 20 km-long paleoseep system in the Panoche-Tumey Hills (PTH), northwestern San Joaquin Valley, is an exception. At this Paleocene site methane-derived carbonate masses (δ¹³C-depleted to -54 per mil) within the siliciclastic Moreno Formation contain abundant evidence of chemosynthetic communities, including ubiquitous microbialites and scattered remains of infaunal lucinid and nuculanid bivalves. Abundant tube structures also occur in the carbonates and though most are nondescript, a few well-preserved specimens suggest that many or all of these structures represent replaced vestimentiferan tube worm exoskeletons. Modern Vestimentifera secrete thin-walled, multi-layered tubes made of β-chitin and protein complexes which have high potential for chelation and microbe-mediated carbonate precipitation. The best-preserved PTH tubes are circular to oval in cross section, 7-10mm in diameter and multi-layered. The inner and outer layers consist of thin brownish sheaths, 0.1 to 0.5mm in diameter. The middle layer consists of isopachous radiaxial and microspar calcite cement (~2mm thick), with opposing crystal growth directions. The exterior surfaces of the outer sheaths have distinctive banding reminiscent of incremental growth lines. Less well-preserved tubes have progressively thicker and more complex cement rims and progressively less distinctive sheaths. Variable preservation may reflect degree of exposure to seep fluids, as poorly-preserved tubes are generally infilled with fluid-derived blocky calcite while well-preserved tubes are infilled with silty micrite matrix. Low δ¹³C values (to -20 per mil) indicate that some of the carbon and all tube-replacing cements was derived from seep fluids. In contrast to tube worm remains, suspect abiotic fluid conduits in the PTH are irregularly shaped, variable in size and sheath free. Tube worms thus seem to represent the dominant fauna in the PTH paleoseep ecosystem, and though it is not possible to positively identify the tubes they bear a striking resemblance to the modern seep tube worm Lamellibrachia barhami, which is widely distributed in the eastern Pacific.
DE: 0456 Life in extreme environments
DE: 3035 Midocean ridge processes
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
SC: Biogeosciences [B]
MN: Fall Meeting 2005