The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

Altermann, Wladyslaw; Lenhardt, Nils

doi:10.1016/j.precamres.2012.02.012

Cited by 37 publications

(6 citation statements)

References 56 publications

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“…The more distal pyroclastic deposits in other regions as described above were likely associated with similar settings at different localities that still need to be found and mapped in detail. Similar processes were discussed for e.g., the Ventersdorp LIP lavas by van der Westhuizen (2006), Altermann and Lenhardt (2012) and Humbert et al (in revision b).…”

Section: The Hekpoort Flood Basalt Formationsupporting

confidence: 61%

Petrology, physical volcanology and geochemistry of a Paleoproterozoic large igneous province: The Hekpoort Formation in the southern Transvaal sub-basin (Kaapvaal craton)

Humbert

Kock

Altermann

et al. 2018

Precambrian Research

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The~2.23 Ga Hekpoort Formation (Transvaal sub-basin) and the~2.43 Ga Ongeluk Formation (Griqualand West sub-basin) represent voluminous Paleoproterozoic igneous events on the Kaapvaal craton of South Africa that predate the emplacement of the~2.055 Ga Bushveld Complex, and probably covered most of the craton at the time of their extrusion. In this contribution, we present a field, petrological and geochemical study of the Hekpoort Formation and compare it with the Ongeluk Formation. The Hekpoort Formation consists of a thick subaerial volcanic sequence in which volcanoclastic rocks occur mainly at the base. Rare, localized hyaloclastites and variolitic rocks record the presence of ponded water, while interbedded sedimentary rocks and paleo-weathered flow tops suggest prolonged time-breaks in volcanic activity. The Hekpoort rocks underwent metamorphism up to greenschist facies but also episodes of metasomatism and silicification. Preserved primary magmatic minerals are clinopyroxene (pigeonite, augite and diopside), and rarely plagioclase (labradorite). Both the variable whole rock Mg# (evolving from 69 to 50) and the change in clinopyroxene composition attest to magmatic fractionation. Lava units of both the Hekpoort and Ongeluk formations are mostly basalts, with silicification responsible for increased SiO2 contents. Lava units of both formations also display remarkably similar trace elements patterns, which is noteworthy for units separated by 200 million years, and unique among the Precambrian mafic magmatic units of the Kaapvaal craton that we evaluated. Similar to other Precambrian mafic magmatic units of the Kaapvaal craton, the Hekpoort Formation shows an arc-like trace element signature, mainly represented by negative Nb-Ta anomalies (in normalized trace element patterns). The Hekpoort (and Ongeluk), together with three other Paleoproterozoic mafic units of the craton older than 2.2 Ga, exhibit relatively high contents of Th and U, which sharply contrasts with Archean units. The data suggest that a subduction process marked the Archean-Proterozoic boundary on the Kaapvaal craton.

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Section: The Hekpoort Flood Basalt Formationsupporting

confidence: 61%

Petrology, physical volcanology and geochemistry of a Paleoproterozoic large igneous province: The Hekpoort Formation in the southern Transvaal sub-basin (Kaapvaal craton)

Humbert

Kock

Altermann

et al. 2018

Precambrian Research

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“…The morphogenetic sequence of millimeter-scale clumps, reticulate ridge and laminated cones, has also been used implicate the ancient presence of O 2 -generating cyanobacteria in the formation of Tumbiana microbialites (36)(37)(38). Similar features exist in the 2.7-Ga Sodium Group, South Africa (39). The presence of microbially induced sedimentary structures (MISS) further supports the notion that FMM that likely hosted cyanobacteria were widespread within Neoarchean alluvial, interfluve, and lacustrine environments (40).…”

Section: Significancementioning

confidence: 74%

Benthic perspective on Earth’s oldest evidence for oxygenic photosynthesis

Lalonde

Konhauser

2015

Proc. Natl. Acad. Sci. U.S.A.

189

147

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The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10−5 times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxygenic photosynthesis in these millimeter-thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. As continental freeboard increased significantly between 3.0 and 2.5 Ga, the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass-balance perspective. These observations help reconcile evidence for pre-GOE oxidative weathering with the history of atmospheric chemistry, and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the GOE.

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“…This conundrum also relates to stromatolites in the Archean Fortescue Group (Australia) with one group of workers arguing the facies reflect a marine setting (Packer, 1990;Thorne and Trendall, 2001;Sakurai et al, 2005) whereas others interpret the same facies as lacustrine (Kriewaldt and Ryan, 1967;Walter, 1984;Buick, 1992;Blake et al, 2004;Walter and Allwood, 2005;Bolhar and Van Kranendonk, 2007;Awramik and Buchheim, 2009). Stromatolites have been recognized in distal shallow lacustrine systems of the Omdraaivlei Formation, Sodium Group of the 2.7 Ga Ventersdorp Supergroup (Kaapvaal craton; Altermann and Lenhardt, 2012).…”

Section: Discussionmentioning

confidence: 98%

Evidence for 2.0Ga continental microbial mats in a paleodesert setting

Simpson

Heness

Bumby

et al. 2013

Precambrian Research

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Early evolved microbial communities characterized the initial biological invasion of Precambrian continental landscapes. In modern arid settings, microbial mats and biological soil crusts are well-developed and stabilize sediment. The Paleoproterozoic Makgabeng Formation in South Africa is one of the oldest and best preserved, dryland systems on Earth. Six types of microbial mat-related structures are now recognized within these depositional systems. This paper presents three newly discovered structures that include tufted microbial mat, biological soil crusts, and gas-escape features, in addition to three previously documented structures that include roll up features, sand cracks, and wrinkled features. These discoveries demonstrate that microbial communities were well-established and inhabited diverse continental settings by 2.0 Ga, approximately 200 million years after the onset of the Great Oxidation Event.

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The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

Cited by 37 publications

References 56 publications

Petrology, physical volcanology and geochemistry of a Paleoproterozoic large igneous province: The Hekpoort Formation in the southern Transvaal sub-basin (Kaapvaal craton)

Petrology, physical volcanology and geochemistry of a Paleoproterozoic large igneous province: The Hekpoort Formation in the southern Transvaal sub-basin (Kaapvaal craton)

Benthic perspective on Earth’s oldest evidence for oxygenic photosynthesis

Evidence for 2.0Ga continental microbial mats in a paleodesert setting

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