Microfossils from the late Mesoproterozoic – early Neoproterozoic Atar/El Mreïti Group, Taoudeni Basin, Mauritania, northwestern Africa

Beghin, Jérémie; Storme, Jean-Yves; Blanpied, Christian; Gueneli, Nur; Brocks, Jochen J.; Poulton, Simon W.; Javaux, Emmanuelle

doi:10.1016/j.precamres.2017.01.009

Cited by 73 publications

(42 citation statements)

References 81 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…There, the presence of 2,3,4‐ and 2,3,6‐TMAI, in addition to iron speciation, and sulphur isotopes of pyrite and redox‐sensitive trace elements all suggest nearshore PZE conditions (Blumenberg et al., ; Gilleaudeau & Kah, ; Gueneli et al., ; Kah, Bartley, & Teal, ). Moreover, the nitrogen isotopic composition of porphyrins from the El Mreïti Group confirms that primary productivity was dominated by bacteria (Gueneli et al., ), and there is no fossil (Beghin, Guilbaud, et al., ; Beghin, Storme, et al., ) or biomarker evidence for the activity of algae (Blumenberg et al., ; Gueneli et al., ). Thus, the combination of these studies, in addition to trace metal redox work in other locations, suggests environmental heterogeneity in the Mesoproterozoic (e.g., Canfield, ; Lyons, Anbar, Severmann, Scott, & Gill, ).…”

Section: Resultsmentioning

confidence: 94%

Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia

et al. 2019

Self Cite

View full text Add to dashboard Cite

The ca . 1.38 billion years (Ga) old Roper Group of the McArthur Basin, northern Australia, is one of the most extensive Proterozoic hydrocarbon‐bearing units. Organic‐rich black siltstones from the Velkerri Formation were deposited in a deep‐water sequence and were analysed to determine their organic geochemical (biomarker) signatures, which were used to interpret the microbial diversity and palaeoenvironment of the Roper Seaway. The indigenous hydrocarbon biomarker assemblages describe a water column dominated by bacteria with large‐scale heterotrophic reworking of the organic matter in the water column or bottom sediment. Possible evidence for microbial reworking includes a large unresolved complex mixture ( UCM ), high ratios of mid‐chained and terminally branched monomethyl alkanes relative to n ‐alkanes—features characteristic of indigenous Proterozoic bitumen. Steranes, biomarkers for single‐celled and multicellular eukaryotes, were below detection limits in all extracts analysed, despite eukaryotic microfossils having been previously identified in the Roper Group, albeit largely in organically lean shallower water facies. These data suggest that eukaryotes, while present in the Roper Seaway, were ecologically restricted and contributed little to export production. The 2,3,4‐ and 2,3,6‐trimethyl aryl isoprenoids ( TMAI ) were absent or in very low concentration in the Velkerri Formation. The low abundance is primary and not caused by thermal destruction. The combination of increased dibenzothiophene in the Amungee Member of the Velkerri Formation and trace metal redox geochemistry suggests that degradation of carotenoids occurred during intermittent oxygen exposure at the sediment–water interface and/or the water column was rarely euxinic in the photic zone and likely only transiently euxinic at depth. A comparison of this work with recently published biomarker and trace elemental studies from other mid‐Proterozoic basins demonstrates that microbial environments, water column geochemistry and basin redox were heterogeneous.

show abstract

Section: Resultsmentioning

confidence: 94%

Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…Mesoproterozoic eukaryote diversity as gauged from acritarchs (Beghin et al, 2017;Javaux et al, 2004), even from settings interpreted as oxic in the Mesoproterozoic ocean (Sergeev, Knoll, Vorob'eva, & Sergeeva, 2016;Sperling et al, 2014). Furthermore, the apparent disparity between some occurrences of Mesoproterozoic eukaryotic acritarchs yet no detectable record of regular steranes appears to continue till 1.0 Ga in the Malgin Formation of the Siberian Platform (Suslova, Parfenova, Saraev, & Nagovitsyn, 2017), while thermally immature rocks from the 1.1 Ga Atar Group were also shown to be devoid of steroid biomarkers (Blumenberg et al, 2012).…”

Section: Previous Microfossil Studies Indicate Only a Modestmentioning

confidence: 99%

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

et al. 2019

View full text Add to dashboard Cite

By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate–carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and an absence of organic biomarker fingerprints for those organisms, suggesting low diversity and relatively small populations compared to the Neoproterozoic era. Nevertheless, the search for diagnostic biomarkers has not been performed with guidance from paleoenvironmental redox constrains from inorganic geochemistry that should reveal the facies that were most likely hospitable to these organisms. Siltstones and shales obtained from drill core of the ca. 1.3–1.4 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid‐Proterozoic redox landscape. The group is well dated and minimally metamorphosed (of oil window maturity), and previous geochemical data suggest a relatively strong connection to the open ocean compared to other mid‐Proterozoic records. Here, we present one of the first integrated investigations of Mesoproterozoic biomarker records performed in parallel with established inorganic redox proxy indicators. Results reveal a temporally variable paleoredox structure through the Velkerri Formation as gauged from iron mineral speciation and trace‐metal geochemistry, vacillating between oxic and anoxic. Our combined lipid biomarker and inorganic geochemical records indicate at least episodic euxinic conditions sustained predominantly below the photic zone during the deposition of organic‐rich shales found in the middle Velkerri Formation. The most striking result is an absence of eukaryotic steranes (4‐desmethylsteranes) and only traces of gammacerane in some samples—despite our search across oxic, as well as anoxic, facies that should favor eukaryotic habitability and in low maturity rocks that allow the preservation of biomarker alkanes. The dearth of Mesoproterozoic eukaryotic sterane biomarkers, even within the more oxic facies, is somewhat surprising but suggests that controls such as the long‐term nutrient balance and other environmental factors may have throttled the abundances and diversity of early eukaryotic life relative to bacteria within marine microbial communities. Given that molecular clocks predict that sterol synthesis evolved early in eukaryotic history, and (bacterial) fossil steroids have been found previously in 1.64 Ga rocks, then a very low environmental abundance of eukaryotes relative to bacteria is our preferred explanation for the lack of regular steranes and only traces of gammacerane in a few samples. It is also possible that early eukaryotes adapted to Mesoproterozoic marine environments did not make abundant steroid lipids or tetrahymanol in their cell membranes.

show abstract

“…On the other hand, it is similar to many of the latest Mesoproterozoic to early Neoproterozoic organic‐walled microfossil assemblages, such as those from the Atar/El Mreïti Group in Mauritania (Beghin et al . ), Mbuji‐Mayi Supergroup in the Democratic Republic of Congo (Baludikay et al . ), the Gouhou and Liulaobei formations in North China (Tang et al .…”

Section: Discussionmentioning

confidence: 99%

“…; Beghin et al . ). Specimens in our collection are 70–375 μm in vesicle diameter (average = 216 μm; n = 251), and their processes are 1–11 μm in basal width (average = 6 μm; n = 354).…”

Section: Microfossils Of the Lower Madhubani Groupmentioning

confidence: 97%

Late Mesoproterozoic – early Neoproterozoic organic‐walled microfossils from the Madhubani Group of the Ganga Valley, northern India

et al. 2017

View full text Add to dashboard Cite

The age of the sedimentary basement of the Ganga Valley in northern India, which is represented by the entirely subsurface Ganga Supergroup, is key for addressing issues related to the tectonic history of the Himalaya. However, the stratigraphic correlations between the Ganga Supergroup in the Ganga Valley, the Vindhyan Supergroup in cratonic India to the south, and Proterozoic successions in the Lesser Himalaya to the north have long been a matter of controversy. This is largely because of the poor age constraint of the Madhubani Group of the upper Ganga Supergroup, which has been variously interpreted as Proterozoic, lower Palaeozoic, or even Mesozoic. To address this issue, we used a low manipulation maceration technique to extract organic‐walled microfossils from the Ujhani and Tilhar formations of the lower Madhubani Group. Our study recovered a total of 24 taxa, including Devisphaera corallis gen. et sp. nov. The co‐occurrence of Trachyhystrichosphaera aimika, Caudosphaera expansa and Annulusia annulata in the lower Madhubani Group indicates a late Mesoproterozoic to early Neoproterozoic age. Thus, the biostratigraphical data suggest a >300 myr depositional gap between the Madhubani Group and the immediately underlying Bahraich Group, which has been independently constrained to be upper Palaeoproterozoic to lower Mesoproterozoic in age. Therefore, the first‐order stratigraphic architecture, with a Palaeoproterozoic–Mesoproterozoic succession unconformably overlain by a Mesoproterozoic–Neoproterozoic succession, is closely similar throughout the Vindhyan Basin, Ganga Valley and Lesser Himalaya, suggesting a shared sedimentary and tectonic history among them.

show abstract

Microfossils from the late Mesoproterozoic – early Neoproterozoic Atar/El Mreïti Group, Taoudeni Basin, Mauritania, northwestern Africa

Cited by 73 publications

References 81 publications

Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia

Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

Late Mesoproterozoic – early Neoproterozoic organic‐walled microfossils from the Madhubani Group of the Ganga Valley, northern India

Contact Info

Product

Resources

About