TY - JOUR
T1 - Pseudofossils in relict methane seep carbonates resemble endemic microbial consortia
AU - Bailey, Jake V.
AU - Raub, Timothy D.
AU - Meckler, A. Nele
AU - Harrison, Benjamin K.
AU - Raub, Theresa M.D.
AU - Green, Abigail M.
AU - Orphan, Victoria J.
PY - 2010/1/1
Y1 - 2010/1/1
N2 - Pleistocene-age methane seep carbonates from the Eel River Basin, California contain aggregate-like structures composed of tightly-packed hollow spheres that morphologically resemble syntrophic archaeal-bacterial consortia known to catalyze the anaerobic oxidation of methane (AOM). Tetragonal microstructures also present in the carbonates resemble seep-endemic Methanosarcinales cell clusters. Despite morphological similarities to the seep-endemic microbes that likely mediated the authigenesis of Eel River Basin carbonates and sulfides, detailed petrographic, SEM, and magnetic microscopic imaging, remanence rock magnetism, laser Raman, and energy dispersive X-ray spectroscopy, suggest that these microstructures are not microfossils, but rather mineral structures that result from the diagenetic alteration of euhedral Fe-sulfide framboids. Electron microscopy shows that during diagenesis, reaction rims composed of Fe oxide form around framboid microcrystalites. Subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell-like casings (external molds) - a transformation that occurs on timescales of ∼100 kyr or less. Despite their superficial resemblance to morphologically-distinctive extant microbes in local sediments, the presence of acellular precursor grains, as well as of partially-altered transitional forms, complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record.
AB - Pleistocene-age methane seep carbonates from the Eel River Basin, California contain aggregate-like structures composed of tightly-packed hollow spheres that morphologically resemble syntrophic archaeal-bacterial consortia known to catalyze the anaerobic oxidation of methane (AOM). Tetragonal microstructures also present in the carbonates resemble seep-endemic Methanosarcinales cell clusters. Despite morphological similarities to the seep-endemic microbes that likely mediated the authigenesis of Eel River Basin carbonates and sulfides, detailed petrographic, SEM, and magnetic microscopic imaging, remanence rock magnetism, laser Raman, and energy dispersive X-ray spectroscopy, suggest that these microstructures are not microfossils, but rather mineral structures that result from the diagenetic alteration of euhedral Fe-sulfide framboids. Electron microscopy shows that during diagenesis, reaction rims composed of Fe oxide form around framboid microcrystalites. Subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell-like casings (external molds) - a transformation that occurs on timescales of ∼100 kyr or less. Despite their superficial resemblance to morphologically-distinctive extant microbes in local sediments, the presence of acellular precursor grains, as well as of partially-altered transitional forms, complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record.
KW - AOM
KW - Archaea
KW - Framboids
KW - Greigite
KW - Pyrite
KW - Sulfate-reducing bacteria
UR - http://www.scopus.com/inward/record.url?scp=72449149229&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=72449149229&partnerID=8YFLogxK
U2 - 10.1016/j.palaeo.2009.11.002
DO - 10.1016/j.palaeo.2009.11.002
M3 - Article
AN - SCOPUS:72449149229
SN - 0031-0182
VL - 285
SP - 131
EP - 142
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
IS - 1-2
ER -