Meta-analysis of Cryogenian through modern quartz microtextures reveals sediment transport histories

Abstract

Quantitative scanning electron microscopy (SEM) quartz microtextural analysis can reveal the transport histories of modern and ancient sediments. However, because workers identify and count microtextures differently, it is difficult to directly compare quantitative microtextural data analyzed by multiple workers. As a result, the defining microtextures of certain transport modes and their probabilities of occurrence are not well constrained. We used principal component analysis (PCA) to directly compare modern and ancient aeolian, fluvial, and glacial samples from the literature with 9 new samples from active aeolian and glacial environments. Our results demonstrate that PCA can group microtextural samples by transport mode and identify the microtextures that differentiate between aeolian and fluvial/glacial transport modes, regardless of study. The PCA ordinations indicate that aeolian samples are distinct from fluvial and glacial samples, which are in turn difficult to disambiguate from each other. The ancient and modern sediments are also shown to have quantitatively similar microtextural relationships. Therefore, PCA may be a useful tool to constrain the ambiguous transport histories of some ancient sediment grains. As a case study, we analyzed two samples with ambiguous transport histories from the Cryogenian Bråvika Member (Svalbard). Integrating PCA with field observations, we find evidence that the Bråvika Member facies investigated here includes aeolian deposition and may be analogous to syn-glacial Marinoan aeolian units including the Bakoye Formation in Mali and the Whyalla Sandstone in South Australia.

Detecting upland glaciation in Earth’s pre-Pleistocene record

“…The probability of high-stress microtextures occurring that reflect microstriae, such as grooves and troughs, is extremely low in eolian systems far removed from modern or Pleistocene glaciation (Reahl et al, 2021). Moreover, samples collected in fluvial systems far removed from a glacial influence yielded very low probabilities of retaining a high-stress signal (Reahl et al, 2021). Thus, while high-stress microtextures have been reported from deposits other than those of glacial origin, most of the reported occurrences are associated with glaciation.…”

“…Percussion microtextures consist of v-shaped cracks and edge rounding, and are common to eolian, coastal, and fluvial systems. High-stress microtextures consist of grooves, troughs, and gouges (Figure 1) resulting from grain-to-grain contact under sustained shear stress and are common in grains recovered from till and proglacial deposits (Mahaney and Kalm, 1996;Hart, 2006;Sweet and Brannan, 2016;Smith et al, 2018;Kalinska et al, 2021;Reahl et al, 2021), but also are reported from structural shear zones and debris flows (Mahaney, 2002). Polygenetic microtextures are the remainder of the mechanically induced microtextures observable on grain surfaces and originate through various processes.…”

“…Since the development of this tripartite suite of microtextures, numerous studies from ancient environments have employed this approach to differentiate between glacial and sub-aqueous or sub-aerial percussion transport (Kirshner and Anderson, 2011;Witus et al, 2014;Keiser et al, 2015;Kalinska-Nartisa et al, 2017;Nartiss and Kalinska-Nartisa, 2017;Kalinska-Nartisa et al, 2018;Kalinska-Nartisa and Galka, 2018). Statistical tests of the tripartite system from modern settings demonstrate that percussion textures prevail in fluvial environments (Smith et al, 2018;Reahl et al, 2021), but Reahl et al (2021) suggested that highstress microtextures carry more ambiguity, as some eolian systems exhibit a higher incidence of high-stress features than glacial systems; for example, upturned plates are a microtexture Undulose surface on quartz grain with grooves >10 µm deep, termed deep troughs (dt). Grain has experienced percussion overprinting due to saltation during fluvial transport as indicated by edge rounding (er) and v-shaped cracks (vc).…”

“…However, all of those high-stress microtexture occurrences are from eolian systems located in proximity to a glacial influence, obfuscating whether the features were created during glacial or eolian transport. The probability of high-stress microtextures occurring that reflect microstriae, such as grooves and troughs, is extremely low in eolian systems far removed from modern or Pleistocene glaciation (Reahl et al, 2021). Moreover, samples collected in fluvial systems far removed from a glacial influence yielded very low probabilities of retaining a high-stress signal (Reahl et al, 2021).…”

“…Near the glacial terminus, fractions of grains exhibiting high-stress values range from ~10% to 30%, whereas polygenetic microtextures are reported on 60%-80% of the grains examined (Sweet and Brannan, 2016;Kalinska et al, 2021). Moreover, Reahl et al (2021) reported that the largest individual source of variance in the data is operator bias. This variance might be resolvable given more studies of modern systems using a double-blind approach and quantitative data analyses, such as used in Smith et al (2018).…”