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K R Moore, T Bosak, F A Macdonald, D J G Lahr, S Newman, C Settens, S B Pruss
Cryogenian cap carbonates that overlie Sturtian glacial deposits were formed during a post-glacial transgression. Here, we describe microfossils from the Kakontwe Formation of Zambia and the Taishir Formation of Mongolia-both Cryogenian age, post-Sturtian cap carbonates-and investigate processes involved in their formation and preservation. We compare microfossils from these two localities to an assemblage of well-documented microfossils previously described in the post-Sturtian Rasthof Formation of Namibia...
January 6, 2017: Geobiology
W Wang, C Guan, C Zhou, Y Peng, L M Pratt, X Chen, L Chen, Z Chen, X Yuan, S Xiao
The Ediacaran Doushantuo Formation in South China is a prime target for geobiological investigation because it offers opportunities to integrate chemostratigraphic and paleobiological data. Previous studies were mostly focused on successions in shallow-water shelf facies, but data from deep-water successions are needed to fully understand basinal redox structures. Here, we report δ(13) Ccarb , δ(13) Corg , δ(34) Spyr , δ(34) SCAS , and δ(15) Nsed data from a drill core of the fossiliferous Lantian Formation, which is a deep-water equivalent of the Doushantuo Formation...
January 6, 2017: Geobiology
C E Rosenfeld, J A Kenyon, B R James, C M Santelli
Microbial processes are known to mediate selenium (Se) oxidation-reduction reactions, strongly influencing Se speciation, bioavailability, and transport throughout the environment. While these processes have commonly been studied in anaerobic bacteria, the role that aerobic fungi play in Se redox reactions could be important for Se-rich soil systems, dominated by microbial activity. We quantified fungal growth, aerobic Se(IV, VI) reduction, and Se immobilization and volatilization in the presence of six, metal-tolerant Ascomycete fungi...
January 2, 2017: Geobiology
T Tang, W Mohr, S R Sattin, D R Rogers, P R Girguis, A Pearson
Anoxygenic, photosynthetic bacteria are common at redox boundaries. They are of interest in microbial ecology and geosciences through their role in linking the carbon, sulfur, and iron cycles, yet much remains unknown about how their flexible carbon metabolism-permitting either autotrophic or heterotrophic growth-is recorded in the bulk sedimentary and lipid biomarker records. Here, we investigated patterns of carbon isotope fractionation in a model photosynthetic sulfur-oxidizing bacterium, Allochromatium vinosum DSM180(T) ...
January 1, 2017: Geobiology
T W Dahl, A Chappaz, J Hoek, C J McKenzie, S Svane, D E Canfield
The geochemical behavior of molybdenum (Mo) in the oceans is closely linked to the presence of sulfide species in anoxic environments, where Fe availability may play a key role in the Mo scavenging. Here, we show that Mo(VI) is reduced in the presence of particulate organic matter (represented by sulfate-reducing bacteria). Molybdenum was immobilized at the surface of both living cells and dead/lysed cells, but not in cell-free control experiments. Experiments were carried out at four different Mo concentrations (0...
December 20, 2016: Geobiology
C Li, D S Hardisty, G Luo, J Huang, T J Algeo, M Cheng, W Shi, Z An, J Tong, S Xie, N Jiao, T W Lyons
Records of the Ediacaran carbon cycle (635-541 million years ago) include the Shuram excursion (SE), the largest negative carbonate carbon isotope excursion in Earth history (down to -12‰). The nature of this excursion remains enigmatic given the difficulties of interpreting a perceived extreme global decrease in the δ(13) C of seawater dissolved inorganic carbon. Here, we present carbonate and organic carbon isotope (δ(13) Ccarb and δ(13) Corg ) records from the Ediacaran Doushantuo Formation along a proximal-to-distal transect across the Yangtze Platform of South China as a test of the spatial variation of the SE...
December 20, 2016: Geobiology
M C Sforna, M Daye, P Philippot, A Somogyi, M A van Zuilen, K Medjoubi, E Gérard, F Jamme, C Dupraz, O Braissant, C Glunk, P T Visscher
The use of metals as biosignatures in the fossil stromatolite record requires understanding of the processes controlling the initial metal(loid) incorporation and diagenetic preservation in living microbialites. Here, we report the distribution of metals and the organic fraction within the lithifying microbialite of the hypersaline Big Pond Lake (Bahamas). Using synchrotron-based X-ray microfluorescence, confocal, and biphoton microscopies at different scales (cm-μm) in combination with traditional geochemical analyses, we show that the initial cation sorption at the surface of an active microbialite is governed by passive binding to the organic matrix, resulting in a homogeneous metal distribution...
December 9, 2016: Geobiology
T L Hamilton, J Havig
The majority of geomicrobiological research conducted on glacial systems to date has focused on glaciers that override primarily carbonate or granitic bedrock types, with little known of the processes that support microbial life in glacial systems overriding volcanic terrains (e.g., basalt or andesite). To better constrain the role of the supraglacial ecosystems in the carbon and nitrogen cycles, to gain insight into microbiome composition and function in alpine glacial systems overriding volcanic terrains, and to constrain potential elemental sequestration or release through weathering processes associated with snow algae communities, we examined the microbial community structure and primary productivity of snow algae communities on stratovolcanoes in the Cascade Range of the Pacific Northwest...
December 5, 2016: Geobiology
R M Klaebe, M J Kennedy, A J M Jarrett, J J Brocks
Large magnitude (>10‰) carbon-isotope (δ(13) C) excursions recorded in carbonate-bearing sediments are increasingly used to monitor environmental change and constrain the chronology of the critical interval in the Neoproterozoic stratigraphic record that is timed with the first appearance and radiation of metazoan life. The ~10‰ Bitter Springs Anomaly preserved in Tonian-aged (1000-720 Ma) carbonate rocks in the Amadeus Basin of central Australia has been offered as one of the best preserved examples of a primary marine δ(13) C excursion because it is regionally reproducible and δ(13) C values covary in organic and carbonate carbon arguing against diagenetic exchange...
January 2017: Geobiology
S K Lengger, J Fromont, K Grice
Over 8600 species are currently recorded in the phylum Porifera (sponges). They produce a large diversity of biochemical compounds including sterols, with more than 250 different sterols identified. Some of these sterols are of great interest, due to their use for fingerprinting in ecological and biomarker (molecular fossil) studies. As a large number of identified extant species from biodiversity surveys are housed in museum collections, preserved in ethanol, these present a potentially rich source of identified specimens for comparative lipid analyses...
January 2017: Geobiology
A M Penny, R A Wood, A Yu Zhuravlev, A Curtis, F Bowyer, R Tostevin
Namacalathus hermanastes is one of the oldest known skeletal metazoans, found in carbonate settings of the terminal Ediacaran (~550-541 million years ago [Ma]). The palaeoecology of this widespread, goblet-shaped, benthic organism is poorly constrained yet critical for understanding the dynamics of the earliest metazoan communities. Analysis of in situ assemblages from the Nama Group, Namibia (~548-541 Ma), shows that Namacalathus exhibited size variation in response to differing water depths, hydrodynamic conditions and substrate types...
January 2017: Geobiology
J N Ricci, R Morton, G Kulkarni, M L Summers, D K Newman
Hopanes are abundant in ancient sedimentary rocks at discrete intervals in Earth history, yet interpreting their significance in the geologic record is complicated by our incomplete knowledge of what their progenitors, hopanoids, do in modern cells. To date, few studies have addressed the breadth of diversity of physiological functions of these lipids and whether those functions are conserved across the hopanoid-producing bacterial phyla. Here, we generated mutants in the filamentous cyanobacterium, Nostoc punctiforme, that are unable to make all hopanoids (shc) or 2-methylhopanoids (hpnP)...
January 2017: Geobiology
D R Monteverde, L Gómez-Consarnau, C Suffridge, S A Sañudo-Wilhelmy
Coenzymes are essential across all domains of life. B vitamins (B1 -thiamin, B2 -riboflavin, B3 -niacin, B5 -pantothenate, B6 -pyridoxine, B7 -biotin, and B12 -cobalamin) represent the largest class of coenzymes, which participate in a diverse set of reactions including C1 -rearrangements, DNA repair, electron transfer, and fatty acid synthesis. B vitamin structures range from simple to complex heterocycles, yet, despite this complexity, multiple lines of evidence exist for their ancient origins including abiotic synthesis under putative early Earth conditions and/or meteorite transport...
January 2017: Geobiology
B Stackhouse, M C Y Lau, T Vishnivetskaya, N Burton, R Wang, A Southworth, L Whyte, T C Onstott
The response of methanotrophic bacteria capable of oxidizing atmospheric CH4 to climate warming is poorly understood, especially for those present in Arctic mineral cryosols. The atmospheric CH4 oxidation rates were measured in microcosms incubated at 4 °C and 10 °C along a 1-m depth profile and over a range of water saturation conditions for mineral cryosols containing type I and type II methanotrophs from Axel Heiberg Island (AHI), Nunavut, Canada. The cryosols exhibited net consumption of ~2 ppmv CH4 under all conditions, including during anaerobic incubations...
January 2017: Geobiology
M G Babechuk, I C Kleinhanns, R Schoenberg
Fractionation of stable Cr isotopes has been measured in Archaean paleosols and marine sedimentary rocks and interpreted to record the terrestrial oxidation of Cr(III) to Cr(VI), providing possible indirect evidence for the emergence of oxygenic photosynthesis. However, these fractionations occur amidst evidence from other geochemical proxies for a pervasively anoxic atmosphere. This study examined the Cr geochemistry of the ca. 1.85 Ga Flin Flon paleosol, which developed under an atmosphere unambiguously oxidising enough to quantitatively convert Fe(II) to Fe(III) during pedogenesis...
January 2017: Geobiology
M R Lindsay, C Anderson, N Fox, G Scofield, J Allen, E Anderson, L Bueter, S Poudel, K Sutherland, J H Munson-McGee, J D Van Nostrand, J Zhou, J R Spear, B K Baxter, D R Lageson, E S Boyd
A railroad causeway across Great Salt Lake, Utah (GSL), has restricted water flow since its construction in 1959, resulting in a more saline North Arm (NA; 24%-31% salinity) and a less saline South Arm (SA; 11%-14% salinity). Here, we characterized microbial carbonates collected from the SA and the NA to evaluate the effect of increased salinity on community composition and abundance and to determine whether the communities present in the NA are still actively precipitating carbonate or if they are remnant features from prior to causeway construction...
January 2017: Geobiology
E R Estes, P F Andeer, D Nordlund, S D Wankel, C M Hansel
Manganese (Mn) oxides participate in a range of interactions with organic carbon (OC) that can lead to either carbon degradation or preservation. Here, we examine the abundance and composition of OC associated with biogenic and environmental Mn oxides to elucidate the role of Mn oxides as a reservoir for carbon and their potential for selective partitioning of particular carbon species. Mn oxides precipitated in natural brackish waters and by Mn(II)-oxidizing marine bacteria and terrestrial fungi harbor considerable levels of organic carbon (4...
January 2017: Geobiology
P M Shih, J Hemp, L M Ward, N J Matzke, W W Fischer
The rise of oxygen ca. 2.3 billion years ago (Ga) is the most distinct environmental transition in Earth history. This event was enabled by the evolution of oxygenic photosynthesis in the ancestors of Cyanobacteria. However, long-standing questions concern the evolutionary timing of this metabolism, with conflicting answers spanning more than one billion years. Recently, knowledge of the Cyanobacteria phylum has expanded with the discovery of non-photosynthetic members, including a closely related sister group termed Melainabacteria, with the known oxygenic phototrophs restricted to a clade recently designated Oxyphotobacteria...
January 2017: Geobiology
X L Wang, N J Planavsky, P M Hull, A E Tripati, H J Zou, L Elder, M Henehan
The chromium isotope system ((53) Cr/(52) Cr expressed as δ(53) Cr relative to NIST SRM 979) is potentially a powerful proxy for the redox state of the ocean-atmosphere system, but a lack of temporally continuous, well-calibrated archives has limited its application to date. Marine carbonates could potentially serve as a common and continuous Cr isotope archive. Here, we present the first evaluation of planktonic foraminiferal calcite as an archive of seawater δ(53) Cr. We show that single foraminiferal species from globally distributed core tops yielded variable δ(53) Cr, ranging from 0...
January 2017: Geobiology
S J Loyd
Concretions are preferentially cemented zones within sediments and sedimentary rocks. Cementation can result from relatively early diagenetic processes that include degradation of sedimentary organic compounds or methane as indicated by significantly (13) C-depleted or enriched carbon isotope compositions. As minerals fill pore space, reduced permeability may promote preservation of sediment components from degradation during subsequent diagenesis, burial heating and outcrop weathering. Discrete and macroscopic organic remains, macro and microfossils, magnetic grains, and sedimentary structures can be preferentially preserved within concretions...
January 2017: Geobiology
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