Isotopic composition of Pongola Supergroup limestones from the Buffalo River gorge, South Africa: constraints on their regional depositional setting

Eglington, B. M.; Talma, A.S.; Marais, Stephen; Matthews, P.E.; Dixon, John

doi:10.2113/1060001

Cited by 21 publications

(9 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Among the oldest large‐scale still‐carbonate stromatolite reefs extant in the geological record are those at Steep Rock NW Ontario, Canada (Wilks & Nisbet, 1985, 1988; Nisbet & Wilks, 1989) (Fig. 3), at Mushandike, Zimbabwe (Abell et al ., 1985b), and in strata of similar age in the Pongola belt, South Africa (von Brunn & Hobday, 1976; Gutzmer et al ., 1999; Eglington et al ., 2003). The Steep Rock and Mushandike stromatolites were sampled in this study but the Pongola material was not analysed in this work.…”

Section: The Geological Evidencementioning

confidence: 99%

“…These rocks have been subject to some postdepositional decarbonation, shifting C isotopic ratios. In five samples studied by Eglington et al . (2003) δ 13 C carb ranges from +1.2 to +2.1‰.…”

Section: The Geological Evidencementioning

confidence: 99%

“…In the three successions, results show that δ 13 C reduced is around –25‰, and δ 13 C carb around +1.5‰. In all three, the carbonates may have been subject to a slight postdepositional metamorphic resetting (Abell et al ., 1985b; Eglington et al ., 2003) shifting δ 13 C by a few ‰. As with the younger Ngezi Group samples, the results, together with the characteristic difference, 27‰, between δ 13 C in organic matter and carbonate suggest, though do not prove, that processes controlling carbon isotopic partitioning were oxygenic.…”

Section: Interpretation Of the Geological Evidence: Dating The Originmentioning

confidence: 99%

“…δ 13 C carb was likely slightly shifted in this event, as in the Mushandike rocks, and original δ 13 C carb values may have been close to 0‰. Pongola succession Eglington et al (2003) and Veizer et al (1990) both report carbon isotopes on carbonate samples (aragonite, calcite, ankerite, and dolomite) from the Pongola Supergroup, which is >2.84 Ga old (Gutzmer et al, 1999). These rocks have been subject to some postdepositional decarbonation, shifting C isotopic ratios.…”

Section: Steep Rock Successionmentioning

confidence: 99%

See 3 more Smart Citations

The age of Rubisco: the evolution of oxygenic photosynthesis

et al. 2007

View full text Add to dashboard Cite

The evolutionary history of oxygenesis is controversial. Form I of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in oxygen‐tolerant organisms both enables them to carry out oxygenic extraction of carbon from air and enables the competitive process of photorespiration. Carbon isotopic evidence is presented from ~2.9 Ga stromatolites from Steep Rock, Ontario, Canada, ~2.9 Ga stromatolites from Mushandike, Zimbabwe, and ~2.7 Ga stromatolites in the Belingwe belt, Zimbabwe. The data imply that in all three localities the reef‐building autotrophs included organisms using Form I Rubisco. This inference, though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesizers first appeared ~2.9 Ga ago, and were abundant 2.7–2.65 Ga ago. Rubisco specificity (its preference for CO2 over O2) and compensation constraints (the limits on carbon fixation) may explain the paradox that despite the inferred evolution of oxygenesis 2.9 Ga ago, the Late Archaean air was anoxic. The atmospheric CO2:O2 ratio, and hence greenhouse warming, may reflect Form I Rubisco's specificity for CO2 over O2. The system may be bistable under the warming Sun, with liquid oceans occurring in either anoxic (H2O with abundant CH4 plus CO2) or oxic (H2O with more abundant CO2, but little CH4) greenhouse states. Transition between the two states would involve catastrophic remaking of the biosphere. Build‐up of a very high atmospheric inventory of CO2 in the 2.3 Ga glaciation may have allowed the atmosphere to move up the CO2 compensation line to reach stability in an oxygen‐rich system. Since then, Form I Rubisco specificity and consequent compensation limits may have maintained the long‐term atmospheric disproportion between O2 and CO2, which is now close to both CO2 and O2 compensation barriers.

show abstract

Section: The Geological Evidencementioning

confidence: 99%

Section: The Geological Evidencementioning

confidence: 99%

Section: Interpretation Of the Geological Evidence: Dating The Originmentioning

confidence: 99%

Section: Steep Rock Successionmentioning

confidence: 99%

See 2 more Smart Citations

The age of Rubisco: the evolution of oxygenic photosynthesis

et al. 2007

View full text Add to dashboard Cite

show abstract

“…These were large microbial carbonate reefs, not greatly different from modern examples extant today in places like Shark Bay, Australia. They occur as "stromatolites" (sedimentary structures built by microbial consortia) at Steep Rock in Canada (Figure 2), where the reef is kilometres long [26], in the Pongola Belt in South Africa [27], and at Mushandike in Zimbabwe [28]. All three sequences are, coincidentally, dated as over 2.83 Ga old: the rounding of ~2.9 Ga, approximating the likely age, is used here for convenience.…”

Section: Late Archean Life: Oxygenesismentioning

confidence: 99%

The evolution of the atmosphere in the Archaean and early Proterozoic

Nisbet

Fowler

2011

Chin. Sci. Bull.

View full text Add to dashboard Cite

Key steps in atmospheric evolution occurred in the Archaean. The Hadean atmosphere was created by the inorganic processes of volatile accretion from space and degassing from the interior, and then modified by chemical and photochemical processes. The air was probably initially anoxic, though there may have been a supply of oxidation power as a consequence of hydrodynamic escape to space of hydrogen from water. Early subduction may have removed CO 2 and the Hadean planet may have been icy. In the Archaean, as anoxygenic and then oxygenic photosynthesis evolved, biological activity remade the atmosphere. Sedimentological evidence implies there were liquid oceans despite the faint young Sun. These oceans may have been sustained by the greenhouse warming effect of biologically-made methane. Oxygenesis in the late Archaean would have released free O 2 into the water. This would have created oxic surface waters, challenging the methane greenhouse. After the Great Oxidation Event around 2.3 to 2.4 billion years ago, the atmosphere itself became oxic, perhaps triggering a glacial crisis by cutting methane-caused greenhouse warming. By the early Proterozoic, all the key biochemical processes that maintain the modern atmosphere were probably present in the microbial community.

show abstract

Micro‐Raman spectroscopic investigations of mineral assemblages in parallel to bedding laminae in 2.9 Ga sandstones of the Pongola Supergroup, South Africa

Bower

2011

J Raman Spectroscopy

View full text Add to dashboard Cite

Laminated sandstones from the 2.9 Ga Pongola Supergroup, South Africa, were characterized using micro-Raman spectral imaging to elucidate the origin of the mineral components. These sandstones were formed in a paleoenvironment conducive to sustaining life and contain compelling features reminiscent of ancient microbial mat remains. Most sedimentary rocks of this age have been altered over time through metamorphism and weathering, obscuring any original biologic or mineralogic signatures. Therefore, determination of the exact formation mechanism for biologically associated features is often precluded, resulting in large gaps in our understanding of early life and Earth's early habitable environments. The results of the Raman analyses show that the parallel to bedding laminations in these rocks consist of elongated muscovite grains that are intimately associated with anatase, rutile, goethite, and graphitic carbon. The morphology, orientation, and intimate associations of the component mineral assemblage in the laminations suggest that physiochemical events, such as weathering, low-grade metamorphism, or hydrothermal fluids, were also key in their formation and influenced their geochemical makeup. Given the complicated histories of ancient sedimentary rocks, the use of techniques such as micro-Raman spectroscopy is crucial in determining the origins of sedimentary structures that might otherwise be misinterpreted.

show abstract

Isotopic composition of Pongola Supergroup limestones from the Buffalo River gorge, South Africa: constraints on their regional depositional setting

Abstract: Carbonate samples from exposures of the Pongola Supergroup in the Buffalo River gorge, South Africa, preserve high Sr contents and relatively low Mn concentrations. Some of the Buffalo River gorge samples have substantially higher Sr, lower Mn, lower 87 Sr/ 86 Sr and similar ␦ 13

Cited by 21 publications

References 21 publications

The age of Rubisco: the evolution of oxygenic photosynthesis

The age of Rubisco: the evolution of oxygenic photosynthesis

The evolution of the atmosphere in the Archaean and early Proterozoic

Micro‐Raman spectroscopic investigations of mineral assemblages in parallel to bedding laminae in 2.9 Ga sandstones of the Pongola Supergroup, South Africa

Contact Info

Product

Resources

About