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- Qu, Yuangao, et al.
(author)
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Carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the Ediacaran Doushantuo Formation
- 2017
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In: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 290, s. 184-196
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Journal article (peer-reviewed)abstract
- The Ediacaran Doushantuo Formation (DST) is renowned for exceptionally preserved Precambrian fossils including metazoans. Some of these fossils, particularly microfossils such as multicellular algae and acanthomorphic acritarchs, are preserved in DST chert nodules. To better understand the geomicrobiological processes that contributed to the authigenic formation of DST chert nodules and facilitated exceptional fossil preservation, we analyzed organic matter in these chert nodules and the surrounding matrix (calcareous mudstone) using multiple in-situ techniques: confocal laser Raman spectroscopy, micro-Fourier transform infrared spectroscopy (FTIR), and secondary ion mass spectroscopy (SIMS). We found strong ultrastructural, chemical, and isotopic heterogeneities in the organic matter as indicated by the Raman spectral parameter I-1350/1600 ranging from 0.49 to 0.88, the infrared spectral index R3/2 from 0.12 to 0.90, and an estimated δ13Corg-SIMS range of 44‰ (V-PDB). These micron-scale heterogeneities imply that the organic matter preserved in the DST chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem, including eukaryotic and/or prokaryotic photoautotrophs, as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains. Thus, the microbial ecosystems in Ediacaran ocean waters and sediments were more complex than previously thought, and these microbial processes controlled dynamic micro-environments in DST sediments where chert nodules were formed and fossils were mineralized. The results also show that variations in the relative abundances, activities, and interactions of co-existing microorganisms in DST sediments may have modulated δ13Corg shifts, causing local decoupling between δ13Corg and δ13Ccarb as measured in bulk samples.
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2. |
- Qu, Yuangao, et al.
(author)
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Carbonaceous biosignatures of the earliest putative macroscopic multicellular eukaryotes from 1630 Ma Tuanshanzi Formation, north China
- 2018
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In: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 304, s. 99-109
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Journal article (peer-reviewed)abstract
- The Paleo- and Mesoproterozoic fossil record of multicellular eukaryotes is scarce but extremely important in studying the evolution of life in the Precambrian Era. Typically, fossils heralded as ‘multicellular eukaryotes’ that are older than the Ediacaran are met with controversy. To confront such debates, we investigate the chemical, isotopic, and molecular structural characteristics of organic matter from carbonaceous compressions in the 1630 Ma Tuanshanzi Formation in northern China, some of the earliest putative macroscopic multicellular eukaryote fossils (Zhu and Chen, 1995). The large-size and relative complexity of these fossils and similar remains from the 1.56 Ga Gaoyuzhuang Formation have led to their interpretation as eukaryotes. Raman spectral parameters give an estimated peak-metamorphic temperature TMax in the range of 202–286 °C, confirming the good preservation of the organic remains. Two-dimensional Raman maps of the carbonaceous compressions show ultrastructural variations that suggest diverse subcellular compounds being consistent with multicellular eukaryotes. The organic matter has carbon isotopic composition δ13Corg-SIMS between −45.3 and −32.2‰, and a branching index of carbon chain measured by the micro-FTIR spectral parameter R3/2 between 0.17 and 0.31. Together with their large-size and morphology, the isotopic, geochemical and ultrastructural data supports an interpretation of the Tuanshanzi Formation carbonaceous compressions as derived from phototrophic, multicellular eukaryotic algae. Our data support the early evolution of macroscopic multicellular eukaryotes in the sulfidic and low-oxygen conditions that prevailed in the Paleo- and Mesoproterozoic oceans.
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3. |
- Qu, Yuangao, et al.
(author)
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Evidence for molecular structural variations in the cytoarchitectures of a Jurassic plant
- 2019
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In: Geology. - Boulder, Colorado : Geological Society of America. - 0091-7613 .- 1943-2682. ; 47, s. 325-329
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Journal article (peer-reviewed)abstract
- In this study, we investigate the molecular structural characteristics of organic remains in various cellular organelles from a 180 Ma Jurassic royal fern belonging to the Osmundaceae family of ferns, and compare their carbon isotopic compositions to a now-living species of royal fern (Osmunda regalis). We discovered molecular structural variations indicated by Raman and infrared spectral parameters obtained from various fossilized cellular organelles. The organic remains preserved in the chromosomes and cell nuclei show marked structural heterogeneities compared to the cell walls during different stages of the cell cycle. The fossil and extant fern have similar δ13C values obtained from bulk samples, supporting evolutionary stasis in this plant lineage and an unchanged metabolic pathway of carbon assimilation since the Jurassic. The organic remains in the cellular organelles of the fossil seem to be less heterogeneous than those in the extant fern, likely due to the preferential preservation of certain cellular compounds during fossilization. Taphonomic processes appear to have diminished the subcellular isotopic heterogeneities. Our research sheds light on the functioning of ancient plant cellular organelles during mitosis, provides insights to the taphonomic processes operating at molecular and isotopic levels, and shows the practicability of in situ techniques in studying the evolution and behaviors of ancient cells.
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4. |
- Qu, Yuangao, et al.
(author)
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Sample-scale carbon isotopic variability and diverse biomass in the Paleoproterozoic Zaonega Formation, Russia
- 2018
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In: Precambrian Research. - 0301-9268 .- 1872-7433. ; 315, s. 222-231
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Journal article (peer-reviewed)abstract
- The stratigraphic record of organic matter in the c. 1.97 Ga Zaonega Formation (ZF), Onega Basin, northwestern Russia, exhibits a distinct negative δ13C excursion (δ13Corg from −25 to −40‰ VPDB), which was previously interpreted either to reflect a disturbance in the global carbon cycle after the Great Oxidation Event, or to have been caused by an increase in basinal methanotrophic activity. In order to assess the nature of primary biomass and the effects of post-depositional alteration, we here report the sample-scale carbon isotopic characteristics of organic matter in two drill cores from the ZF, covering 500 m of stratigraphy, by using secondary ion mass spectrometry (SIMS). The results confirm that the organic matter has to a large extent preserved the primary isotopic signatures, whereas secondary effects are limited (<4‰). The sample-scale isotopic heterogeneity, defined as the difference between the maximum and minimum δ13C values obtained by SIMS from every individual sample, increases from typically <5‰ in the lower part of stratigraphy to systematically larger values (up to 11‰) in the upper part, which coincides with the decreasing trend of δ13Corg of bulk samples from −25 to −40‰. Samples with either relatively high (c. −25‰) or low (c. −40‰) δ13Corg values have small sample-scale isotopic heterogeneities, while samples with intermediate δ13Corg values (between −25 and −40‰) have significantly larger heterogeneities. These observations imply the co-existence of photoautotrophic and methanotrophic biomass during deposition of the upper part of the stratigraphy. Our study provides insight into the carbon isotopic characteristics of organic matter and suggests that the negative excursion of δ13Corg in the ZF is induced by a methanotrophic microbial ecosystem sustained by seepage of thermogenic methane during the deposition of the ZF and contemporaneous igneous activities.
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5. |
- Qu, Yuangao, et al.
(author)
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Traces of Ancient Life in Oceanic Basalt Preserved as Iron-Mineralized Ultrastructures: Implications for Detecting Extraterrestrial Biosignatures
- 2023
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In: Astrobiology. - : Mary Ann Liebert. - 1531-1074 .- 1557-8070. ; 23:7, s. 769-785
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Journal article (peer-reviewed)abstract
- Benefiting from their adaptability to extreme environments, subsurface microorganisms have been discovered in sedimentary and igneous rock environments on Earth and have been advocated as candidates in the search for extraterrestrial life. In this article, we study iron-mineralized microstructures in calcite-filled veins within basaltic pillows of the late Ladinian Fernazza group (Middle Triassic, 239 Ma) in Italy. These microstructures represent diverse morphologies, including filaments, globules, nodules, and micro-digitate stromatolites, which are similar to extant iron-oxidizing bacterial communities. In situ analyses including Raman spectroscopy have been used to investigate the morphological, elemental, mineralogical, and bond-vibrational modes of the microstructures. According to the Raman spectral parameters, iron minerals preserve heterogeneous ultrastructures and crystallinities, coinciding with the morphologies and precursor microbial activities. The degree of crystallinity usually represents a microscale gradient decreasing toward previously existing microbial cells, revealing a decline of mineralization due to microbial activities. This study provides an analog of possible rock-dwelling subsurface life on Mars or icy moons and advocates Raman spectroscopy as an efficient tool for in situ analyses. We put forward the concept that ultrastructural characteristics of minerals described by Raman spectral parameters corresponding to microscale morphologies could be employed as carbon-lean biosignatures in future space missions. Key Words: Ultrastructures—Iron minerals—Oceanic basalt—Subsurface biosignatures.
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6. |
- Qu, Yuangao, et al.
(author)
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Ultrastructural heterogeneity of carbonaceous material in ancient cherts: investigating biosignature origin and preservation
- 2015
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In: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 15:10, s. 825-842
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Journal article (peer-reviewed)abstract
- Opaline silica deposits on Mars may be good target sites where organic biosignatures could be preserved. Potential analogues on Earth are provided by ancient cherts containing carbonaceous material (CM) permineralized by silica. In this study, we investigated the ultrastructure and chemical characteristics of CM in the Rhynie chert (c. 410 Ma, UK), Bitter Springs Formation (c. 820 Ma, Australia), and Wumishan Formation (c. 1485 Ma, China). Raman spectroscopy indicates that the CM has experienced advanced diagenesis or lowgrade metamorphism at peak metamorphic temperatures of 150–350C. Raman mapping and micro-Fourier transform infrared (micro-FTIR) spectroscopy were used to document subcellular-scale variation in the CM of fossilized plants, fungi, prokaryotes, and carbonaceous stromatolites.In the Rhynie chert, ultrastructural variation in the CM was found within individual fossils, while in coccoidal and filamentous microfossils of the Bitter Springs and formless CM of the Wumishan stromatolites ultrastructural variation was found between, not within, different microfossils. This heterogeneity cannot be explained by secondary geological processes but supports diverse carbonaceous precursors that experienced differential graphitization. Micro-FTIR analysis found that CM with lower structural order contains more straight carbon chains (has a lower R3/2 branching index) and that the structural order of eukaryotic CM is more heterogeneous than prokaryotic CM.This study demonstrates how Raman spectroscopy combined with micro-FTIR can be used to investigate the origin and preservation of silica-permineralized organics. This approach has good capability for furthering our understanding of CM preserved in Precambrian cherts, and potential biosignatures in siliceous deposits on Mars. Key
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