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M N Müller, A Krabbenhöft, H Vollstaedt, F P Brandini, A Eisenhauer
Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO3 and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ88/86 Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry...
February 12, 2018: Geobiology
C Magnabosco, K R Moore, J M Wolfe, G P Fournier
Phototrophic bacteria are among the most biogeochemically significant organisms on Earth and are physiologically related through the use of reaction centers to collect photons for energy metabolism. However, the major phototrophic lineages are not closely related to one another in bacterial phylogeny, and the origins of their respective photosynthetic machinery remain obscured by time and low sequence similarity. To better understand the co-evolution of Cyanobacteria and other ancient anoxygenic phototrophic lineages with respect to geologic time, we designed and implemented a variety of molecular clocks that use horizontal gene transfer (HGT) as additional, relative constraints...
January 31, 2018: Geobiology
T Sallstedt, S Bengtson, C Broman, P M Crill, D E Canfield
Fossil microbiotas are rare in the early rock record, limiting the type of ecological information extractable from ancient microbialites. In the absence of body fossils, emphasis may instead be given to microbially derived features, such as microbialite growth patterns, microbial mat morphologies, and the presence of fossilized gas bubbles in lithified mats. The metabolic affinity of micro-organisms associated with phosphatization may reveal important clues to the nature and accretion of apatite-rich microbialites...
January 30, 2018: Geobiology
J Marin-Carbonne, L Remusat, M C Sforna, C Thomazo, P Cartigny, P Philippot
Microbial sulfate reduction (MSR) is thought to have operated very early on Earth and is often invoked to explain the occurrence of sedimentary sulfides in the rock record. Sedimentary sulfides can also form from sulfides produced abiotically during late diagenesis or metamorphism. As both biotic and abiotic processes contribute to the bulk of sedimentary sulfides, tracing back the original microbial signature from the earliest Earth record is challenging. We present in situ sulfur isotope data from nanopyrites occurring in carbonaceous remains lining the domical shape of stromatolite knobs of the 2...
January 30, 2018: Geobiology
M B Vrazo, A F Diefendorf, B E Crowley, A D Czaja
The Upper Cretaceous Coon Creek Lagerstätte of Tennessee, USA, is known for its extremely well-preserved mollusks and decapod crustaceans. However, the depositional environment of this unit, particularly its distance to the shoreline, has long been equivocal. To better constrain the coastal proximity of the Coon Creek Formation, we carried out a multiproxy geochemical analysis of fossil decapod (crab, mud shrimp) cuticle and associated sediment from the type section. Elemental analysis and Raman spectroscopy confirmed the presence of kerogenized carbon in the crabs and mud shrimp; carbon isotope (δ13 C) analysis of bulk decapod cuticle yielded similar mean δ13 C values for both taxa (-25...
January 19, 2018: Geobiology
B K Harrison, A Myrbo, B E Flood, J V Bailey
The emplacement of subaqueous gravity-driven sediment flows imposes a significant physical and geochemical impact on underlying sediment and microbial communities. Although previous studies have established lasting mineralogical and biological signatures of turbidite deposition, the response of bacteria and archaea within and beneath debris flows remains poorly constrained. Both bacterial cells associated with the underlying sediment and those attached to allochthonous material must respond to substantially altered environmental conditions and selective pressures...
January 19, 2018: Geobiology
D Wacey, L Urosevic, M Saunders, A D George
Stromatolites are cited as some of the earliest evidence for life on Earth, but problems remain in reconciling the paucity of microfossils in ancient carbonate examples with the abundance of microbes that help construct modern analogues. Here, we trace the mineralisation pathway of filamentous cyanobacteria within stromatolites from Lake Thetis, Western Australia, providing new insights into microfossil preservation in carbonate stromatolites. Lake Thetis cyanobacteria exhibit a spectrum of mineralisation processes that include early precipitation of Mg-silicates, largely controlled by the morphochemical features of the cyanobacteria, followed by aragonite formation that is inferred to be driven by heterotrophic activity...
January 10, 2018: Geobiology
Shinnosuke Aoyama, Yuichiro Ueno
Microbial sulfate reduction is among the most ubiquitous metabolic processes on earth. The oldest evidence of microbial sulfate reduction appears in the ca. 3.5 Ga Dresser Formation in the North Pole area of Pilbara Craton in Western Australia. That evidence was found through analysis of quadruple sulfur isotopes of sulfate and sulfide minerals deposited on the seafloor. However, the activity of microbial sulfate reduction below the Archean seafloor remains poorly understood. Here, we report the quadruple sulfur isotopic compositions of sulfide minerals within hydrothermally altered seafloor basalt and less altered basaltic komatiite collected from the North Pole Dome area...
December 15, 2017: Geobiology
J Sánchez-España, K Wang, C Falagán, I Yusta, W D Burgos
Through the use of scanning transmission electron microscopy (STEM) combined with other complementary techniques (SEM, cryo-TEM, HRTEM, and EELS), we have studied the interaction of microorganisms inhabiting deep anoxic waters of acidic pit lakes with dissolved aluminum, silica, sulfate, and ferrous iron. These elements were close to saturation (Al, SiO2 ) or present at very high concentrations (0.12 m Fe(II), 0.12-0.22 m SO42- ) in the studied systems. The anaerobic conditions of these environments allowed investigation of geomicrobial interactions that are difficult to see in oxidized, Fe(III)-rich environments...
January 2018: Geobiology
N J Butterfield
No abstract text is available yet for this article.
November 11, 2017: Geobiology
L G Tarhan, N J Planavsky, X Wang, E J Bellefroid, M L Droser, J G Gehling
The paleoenvironmental setting in which the Ediacara Biota lived, died, and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of long-standing interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shallow marine to terrestrial. One of the key features invoked by adherents of the terrestrial paleoenvironment hypothesis is the presence of iron oxide coatings, inferred to represent the upper horizons of paleosols, along fossiliferous sandstone beds of the Ediacara Member...
November 6, 2017: Geobiology
L M Ward, A Idei, S Terajima, T Kakegawa, W W Fischer, S E McGlynn
Banded iron formations (BIFs) are rock deposits common in the Archean and Paleoproterozoic (and regionally Neoproterozoic) sedimentary successions. Multiple hypotheses for their deposition exist, principally invoking the precipitation of iron via the metabolic activities of oxygenic, photoferrotrophic, and/or aerobic iron-oxidizing bacteria. Some isolated environments support chemistry and mineralogy analogous to processes involved in BIF deposition, and their study can aid in untangling the factors that lead to iron precipitation...
November 2017: Geobiology
T L Hamilton, P V Welander, H L Albrecht, J M Fulton, I Schaperdoth, L R Bird, R E Summons, K H Freeman, J L Macalady
Little Salt Spring (Sarasota County, FL, USA) is a sinkhole with groundwater vents at ~77 m depth. The entire water column experiences sulfidic (~50 μM) conditions seasonally, resulting in a system poised between oxic and sulfidic conditions. Red pinnacle mats occupy the sediment-water interface in the sunlit upper basin of the sinkhole, and yielded 16S rRNA gene clones affiliated with Cyanobacteria, Chlorobi, and sulfate-reducing clades of Deltaproteobacteria. Nine bacteriochlorophyll e homologues and isorenieratene indicate contributions from Chlorobi, and abundant chlorophyll a and pheophytin a are consistent with the presence of Cyanobacteria...
November 2017: Geobiology
N Cam, K Benzerara, T Georgelin, M Jaber, J-F Lambert, M Poinsot, F Skouri-Panet, D Moreira, P López-García, E Raimbault, L Cordier, D Jézéquel
Cyanobacteria have long been thought to induce the formation of Ca-carbonates as secondary by-products of their metabolic activity, by shifting the chemical composition of their extracellular environment to conditions favoring mineral precipitation. Some cyanobacterial species forming Ca-carbonates intracellularly were recently discovered. However, the environmental conditions under which this intracellular biomineralization process can occur and the impact of cyanobacterial species forming Ca-carbonates intracellularly on extracellular carbonatogenesis are not known...
October 26, 2017: Geobiology
A L Brady, J Goordial, H J Sun, L G Whyte, G F Slater
Cryptoendolithic lichens and cyanobacteria living in porous sandstone in the high-elevation McMurdo Dry Valleys are purported to be among the slowest growing organisms on Earth with cycles of death and regrowth on the order of 10(3) -10(4)  years. Here, organic biomarker and radiocarbon analysis were used to better constrain ages and carbon sources of cryptoendoliths in University Valley (UV; 1,800 m.a.s.l) and neighboring Farnell Valley (FV; 1,700 m.a.s.l). Δ(14) C was measured for membrane component phospholipid fatty acids (PLFA) and glycolipid fatty acids, as well as for total organic carbon (TOC)...
October 26, 2017: Geobiology
M L Gomes, D A Fike, K D Bergmann, C Jones, A H Knoll
In modern microbial mats, hydrogen sulfide shows pronounced sulfur isotope (δ(34) S) variability over small spatial scales (~50‰ over <4 mm), providing information about microbial sulfur cycling within different ecological niches in the mat. In the geological record, the location of pyrite formation, overprinting from mat accretion, and post-depositional alteration also affect both fine-scale δ(34) S patterns and bulk δ(34) Spyrite values. We report μm-scale δ(34) S patterns in Proterozoic samples with well-preserved microbial mat textures...
October 19, 2017: Geobiology
C H Crosby, J V Bailey
Certain phosphatic grains preserved in the rock record are interpreted as microfossils representing a diversity of microorganisms from bacteria to fossil embryos. In addition to bona fide primary biological features, phosphatic microfossils and fossil embryos commonly exhibit features that result from abiotic precipitation or diagenetic alteration. Distinguishing between abiotic and primary biological features can be difficult, and some features thought to represent biological tissue could instead be artifacts that are unrelated to the original morphology of a preserved organism...
October 19, 2017: Geobiology
N R Posth, L A Bristow, R P Cox, K S Habicht, F Danza, M Tonolla, N-U Frigaard, D E Canfield
Anoxygenic phototrophic bacteria utilize ancient metabolic pathways to link sulfur and iron metabolism to the reduction of CO2 . In meromictic Lake Cadagno, Switzerland, both purple sulfur (PSB) and green sulfur anoxygenic phototrophic bacteria (GSB) dominate the chemocline community and drive the sulfur cycle. PSB and GSB fix carbon utilizing different enzymatic pathways and these fractionate C-isotopes to different extents. Here, these differences in C-isotope fractionation are used to constrain the relative input of various anoxygenic phototrophs to the bulk community C-isotope signal in the chemocline...
September 3, 2017: Geobiology
V E McCoy, D Asael, N Planavsky
The most notable trend in the sedimentary iron isotope record is a shift at the end of the Archean from highly variable δ(56) Fe values with large negative excursions to less variable δ(56) Fe values with more limited negative values. The mechanistic explanation behind this trend has been extensively debated, with two main competing hypotheses: (i) a shift in marine redox conditions and the transition to quantitative iron oxidation; and (ii) a decrease in the signature of microbial iron reduction in the sedimentary record because of increased bacterial sulfate reduction (BSR)...
September 2017: Geobiology
R Schinteie, J J Brocks
While numerous studies have examined modern hypersaline ecosystems, their equivalents in the geologic past, particularly in the Precambrian, are poorly understood. In this study, biomarkers from ~820 million year (Ma)-old evaporites from the Gillen Formation of the mid-Neoproterozoic Bitter Springs Group, central Australia, are investigated to elucidate the antiquity and paleoecology of halophiles. The sediments were composed of alternating laminae of dolomitized microbial mats and up to 90% anhydrite. Solvent extraction of these samples yielded thermally well-preserved hydrocarbon biomarkers...
September 2017: Geobiology
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