The Moodies Group—a High-Resolution Archive of Archaean Surface Processes and Basin-Forming Mechanisms

Heubeck, Christoph

doi:10.1007/978-3-319-78652-0_6

Cited by 27 publications

(33 citation statements)

References 74 publications

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“…One sample was collected from the Dycedale syncline (sample 14-145: 25 • Figure 1b). It consists of a conglomerate with a coarse sandy matrix (Figure 2c,d), from the lower fluvial to alluvial intercalation of coarse-grained sandstone and conglomerate in the basal Moodies deposits of this location (Unit C in Heubeck et al, 2016) [5,28]. Slightly wavy dark and organic rich laminae (possible fossilized microbial mats) are recognized in the conglo merate.…”

Section: Lithofacies and Sulfide Description Of The Analyzed Rocksmentioning

confidence: 85%

“…The Eureka Syncline exposes Moodies strata of ~3.2 km thickness and has been subdivided in fair detail. The adjacent Dycedale Syncline exposes at least 600 m of Moodies strata [5,28]. The Saddleback Syncline exposes a ~3.5-km-thick complete Moodies section from the basal conglomerates (MdB unit) to the uppermost quartzarenites (MdQ3 unit) and conglomerates (MdQ3cgl unit) [9,28].…”

Section: Geologic Settingmentioning

confidence: 99%

“…The samples for SIMS analyses were chosen based on the content of microscopically visible sulfide. One sample from the Eureka Syncline (sample 12-007-1: 25°42′4.3″ S, 31°04′46.1″ E) is a conglomerate with a sandstone matrix from the base of unit MdQ1 of the Moodies Group (Figures 2a and b) [5,32]. The conglomerate contains common dolomitic clasts that are likely a rip-up clast from reworked carbonate crusts [33].…”

Section: Lithofacies and Sulfide Description Of The Analyzed Rocksmentioning

confidence: 99%

“…The Moodies Group is suggested to be one of the oldest terrestrial-to-shallow marine transitional units in the geological record (e.g., [2,3]). This group is mainly composed of medium-to-coarse-grained sandstone [4,5]. Heubeck et al (2013) estimated that the Moodies Group accumulated rapidly at rates of ca.…”

Section: Introductionmentioning

confidence: 99%

“…0.1 to 1 mm / year within <1 to 14 Ma using zircon U-Pb isochrones [6]. The quartz-rich siliciclastic sands, conglomerates, and silts accumulated on terrestrial to shallow-marine settings, reflecting alluvial, coastal flood plain and intertidal to subtidal depositional environments [5].…”

Section: Introductionmentioning

confidence: 99%

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Multiple Sulfur Isotope Records of the 3.22 Ga Moodies Group, Barberton Greenstone Belt

et al. 2020

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The Moodies Group, the uppermost unit in the Barberton Greenstone Belt (BGB) in South Africa, is a ~3.7-km-thick coarse clastic succession accumulated on terrestrial-to-shallow marine settings at around 3.22 Ga. The multiple sulfur isotopic composition of pyrite of Moodies intervals was newly obtained to examine the influence of these depositional settings on the sulfur isotope record. Conglomerate and sandstone rocks were collected from three synclines north of the Inyoka Fault of the central BGB, namely, the Eureka, Dycedale, and Saddleback synclines. The sulfur isotopic composition of pyrite was analyzed by Secondary Ion Mass Spectrometry (SIMS) for 6 samples from the three synclines and by Isotope Ratio Mass Spectrometry (IR-MS) for 17 samples from a stratigraphic section in the Saddleback Syncline. The present results show a signal of mass-independent fractionation of sulfur isotopes (S-MIF), although t-tests statistically demonstrated that the Moodies S-MIF signals (mostly 0‰ < ∆33S < +0.5‰) are significantly small compared to the signal of the older Paleoarchean (3.6–3.2 Ga) records. These peculiar signatures might be related to initial deposition of detrital pyrite of juvenile origin from the surrounding intrusive (tonalite–trondhjemite–granodiorite; TTG) and felsic volcanic rocks, and/or to secondary addition of hydrothermal sulfur during late metasomatism. Moreover, fast accumulation (~0.1–1 mm/year) of the Moodies sediments might have led to a reduced accumulation of sulfur derived from an atmospheric source during their deposition. As a result, the sulfur isotopic composition of the sediments may have become susceptible to the secondary addition of metasomatic sulfur on a mass balance point of view. The sulfur isotopic composition of Moodies pyrite is similar to the composition of sulfides from nearby gold mines. It suggests that, after the Moodies deposition, metasomatic pyrite formation commonly occurred north of the Inyoka Fault in the central BGB at 3.1–3.0 Ga.

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Section: Lithofacies and Sulfide Description Of The Analyzed Rocksmentioning

confidence: 85%