Chemistry of Hematite-Illite and Chamosite Ooids From the Silurian Red Mountain Formation (Alabama); A Solution to the Ooidal Ironstone Enigma

Chowns, Timothy M.; Ashley, Aaron

doi:10.1130/abs/2016am-283415

Cited by 2 publications

(3 citation statements)

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“…The mineralogical transition from iron (Fe 3+ ) oxide in the matrix to the Fe 2+ -bearing chamosite inside the calcified cyanobacteria (Fig. 8) is likely an indication that the cyanobacterial microbial mat created a redox buffer near the water-sediment interface that facilitated the chamosite authigenesis (Fischer & Knoll, 2009;Chowns & Ashley, 2018).…”

Section: Microbial Role In Modifying Seawater Chemistry For Chamosite...mentioning

confidence: 99%

“…This factor could have promoted the seawater precipitation of iron oxide-microquartz aggregates into the matrix (Figs 7F, 7G and 8A). On the other hand, the respiration of cyanobacteria during low light intensity and decomposition of organic matter produced by microbial mats have been suggested as capable of maintaining benthic, reducing conditions (Chowns & Ashley, 2018;Dodd et al, 2018;Todd et al, 2019). In such a reducing setting, earlier precipitated iron oxide and microquartz are prone to dissolution (Harder, 1989).…”

Section: Microbial Role In Modifying Seawater Chemistry For Chamosite...mentioning

confidence: 99%

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Microbe‐mediated, marine authigenic formation of ooidal chamosite: Insights from upper Ordovician carbonates of the South‐Western Yangtze platform (China)

et al. 2023

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Chamosite is a common marine authigenic mineral and microbial involvement has been often assumed during its formation. However, the fossil record of such microbial activity is ambiguous. Chamosite oolitic ironstones widely occur in the Upper Ordovician of the Yangtze Platform, but their origin remains unclear. In this study, detailed sedimentological and mineralogical investigations on ironstones from the Haima section (south-western Yangtze Platform) helped unravel the critical role of cyanobacterial activity during marine chamosite authigenesis. Stratigraphically, deposition of the Haima oolitic ironstones corresponded with an early Katian transgression, temporally equivalent to many other early Palaeozoic counterparts worldwide. Petrographic observations revealed that different chamosite forms (ooids, peloids and matrix) all developed in close association with calcified cyanobacteria, suggesting that cyanobacteria-involved chamosite formation existed across a wide range of hydrodynamic conditions from above fairweather wave base to below storm wave base. Further mineralogical characterization (backscatter imaging and electron-microprobe analyses) at singlegrain scale revealed clear mineral zonation from the matrix (dispersed iron oxide and microquartz) through the calcified cyanobacterial sheaths (dispersed chamosite) to the ooid (chamosite). This zonation is best explained by cyanobacterial microbial mats that created benthic reducing and high-pH conditions. These conditions drove near-seafloor, dispersed iron oxide and microquartz (primary precipitates formed in oxic seawater) to form chamosite. The authigenic chamosite, originally dispersed within and surrounding the microbial mats, could be reworked to develop other chamositic grains. It is proposed here that the early Katian transgression was responsible for the chamosite-oolitic-ironstone development. The marine transgression submerged earlier-exposed lands and likely supplied Fe-Al-rich colloidal materials to an open marine setting for the chamosite authigenesis. Moreover, transgression likely triggered upwelling, delivered ferruginous deeper water as an extra Fe source and provided nutrients for the cyanobacterial microbial-mat development, which was essential for the widespread chamosite authigenesis across the south-western Yangtze Platform.

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Section: Microbial Role In Modifying Seawater Chemistry For Chamosite...mentioning

confidence: 99%

Section: Microbial Role In Modifying Seawater Chemistry For Chamosite...mentioning

confidence: 99%

Microbe‐mediated, marine authigenic formation of ooidal chamosite: Insights from upper Ordovician carbonates of the South‐Western Yangtze platform (China)

et al. 2023

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“…The Red Mountain Formation is an unconformity-bounded unit, locally underlain by the Sequatchie Fomation (Upper Ordovician) and overlain by the Chattanooga Shale (Devonian), with the type section at Birmingham, Alabama (Chowns, 2006). The formation is presently divided into six members, but only the three lowest members are present around Chattanooga, higher strata having been truncated beneath the Chattanooga Shale.…”

Section: Geologic and Stratigraphic Settingsmentioning

confidence: 99%

Platymerella—a cool-water virgianid brachiopod fauna in southern Laurentia during the earliest Silurian

Jin

Santamaría²,

Mikulic³

et al. 2022

J. Paleontol.

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Platymerella from the lower Red Mountain Formation in Georgia and Tennessee, the Bowling Green Dolomite of west-central Illinois, and the Elwood Dolomite of northeastern Illinois represents a paleosubtropical, cool-water occurrence of virgianid brachiopods in Laurentia during the early Silurian (middle–late Rhuddanian). These occurrences were located in the southern Appalachian foreland basin and the distal end of the Sebree Trough, likely subjected to frequent cool-water current and upwelling from Gondwana. Compared with broadly coeval species of Virgiana from lower paleotropical to equatorial latitudes, Platymerella has significantly smaller, dorsoventrally flattened shells, with subequal ventral and dorsal umbones and beaks that extend only slightly above the hinge line. Relative to its shell size, however, Platymerella has more prominent thickening of the shell wall, median septum, spondylium, and hinge plates than Virgiana, resembling more closely the extravagant shell thickening of Tcherskidium and Proconchidium from the Late Ordovician (late Katian) equatorial regions. The thickening of hinge plates resulted in the formation of a pseudocruralium, which separates Platymerella from Virgiana. In latest Ordovician–earliest Silurian virgianids, there was a general morphological gradient toward a smaller shell, reduction in the ventral-valve convexity, and reduction in the size and height of the ventral umbo from paleoequatorial to southern subtropical regions, with Platymerella representing the most southerly forms.

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Chemistry of Hematite-Illite and Chamosite Ooids From the Silurian Red Mountain Formation (Alabama); A Solution to the Ooidal Ironstone Enigma

Cited by 2 publications

References 0 publications

Microbe‐mediated, marine authigenic formation of ooidal chamosite: Insights from upper Ordovician carbonates of the South‐Western Yangtze platform (China)

Microbe‐mediated, marine authigenic formation of ooidal chamosite: Insights from upper Ordovician carbonates of the South‐Western Yangtze platform (China)

Platymerella—a cool-water virgianid brachiopod fauna in southern Laurentia during the earliest Silurian

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