2D grain size data of sandstones from the 3.2 Ga old Moodies Group, Barberton Greenstone Belt (South Africa)

Cite as:

Reimann, Sebastian; Zametzer, Andreas; Heubeck, Christoph (2023): 2D grain size data of sandstones from the 3.2 Ga old Moodies Group, Barberton Greenstone Belt (South Africa). GFZ Data Services. https://doi.org/10.5880/fidgeo.2022.023

Status

I N R E V I E W : Reimann, Sebastian; Zametzer, Andreas; Heubeck, Christoph (2023): 2D grain size data of sandstones from the 3.2 Ga old Moodies Group, Barberton Greenstone Belt (South Africa). GFZ Data Services. https://doi.org/10.5880/fidgeo.2022.023

Abstract

The Moodies Group (ca. 3.22-3.21 Ga) of the Barberton Greenstone Belt (BGB), South Africa, is the uppermost and youngest unit of the BGB, the largest and best-preserved Greenstone belt in the basement of the Kaapvaal Craton. It consists predominantly of fine- to coarse-grained, composi-tionally immature to mature, quartzose sandstones up to 3.6 km thick, with significant units of con-glomerates and siltstones and minor volcanic rocks and ferruginous sediments. The quartz-dominated Moodies sandstones mark long-term, large-scale access of surface systems to crust-stabilizing, high-level granitoid igneous rocks.

47 petrographic thin sections of sandstones from these sandstone units were analyzed for 2D grain size analyses. At least 500 measurements of long axes per thin were taken, using a Keyence VHX-6000 digital microscope. Samples which show significant grain boundary migration and subgrain rotation were excluded from this analysis (Passchier and Trouw, 2005). The data are presented as single ASCII file (tab-delimited text). The file 2022-023_Reimann-et-al_2D-grain-size-data.txt contains measurements of grains long axes from thin sections.

Methods

47 petrographic thin sections of sandstones from these sandstone units were analyzed for 2D grain size analyses. At least 500 measurements of long axes per thin were taken, using a Keyence VHX-6000 digital microscope. Samples which show significant grain boundary migration and subgrain rotation were excluded from this analysis (Passchier and Trouw, 2005).

The determination of grain size from 2D sections is widely discussed in literature (e.g., Gundersen and Jensen, 1985; Kellerhals et al., 1975; Rosenfeld et al., 1953) and requires correction. We used the approach described by Harrell and Eriksson (1979) who provide thin-section-to-sieve correla-tion equations for the correction of textural parameters and the correction of cumulative percen-tiles. Both approaches generate similar values which changes their classification rarely (Folk, 1974). The data is then compared to recent eolian sands and further discussed in Reimann et al. (2023) and Zametzer et al. (2023) to which these data are supplementary material.

Authors

Reimann, Sebastian;Friedrich-Schiller-Universität Jena, Jena, Germany
Zametzer, Andreas;Friedrich-Schiller-Universität Jena, Jena, Germany;Timescales of Mineral Systems Group, The Institute for Geoscience Research (TIGeR), Curtin University, Perth, Australia
Heubeck, Christoph;Friedrich-Schiller-Universität Jena, Jena, Germany