Abstract
ABSTRACT Quantitative analysis of quartz microtextures by means of scanning electron microscopy (SEM) 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 different 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 nine new samples from active aeolian and glacial environments. Our results demonstrate that PCA can group microtextural samples by transport mode and differentiate between aeolian transport and fluvial and glacial transport across studies. The PCA ordination indicates that aeolian samples are distinct from fluvial and glacial samples, which are in turn difficult to disambiguate from each other. 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.
Highlights
Scanning electron microscopy (SEM) quartz microtextural analysis reveals microscale features that are formed during transport (Krinsley and Takahashi 1962; Krinsley and Doornkamp 1973; Bull 1981)
Quantitative quartz microtextural analysis, which treats microtextural data as a multidimensional statistical problem, is a promising method to quantify the probabilities of occurrence of each microtexture in a specific transport mode (Mahaney et al 2001; Říha et al 2019)
Integrating the microtextural data with field observations from Buldrevågen, Geerabukta (Ny Friesland), and Gimleodden (Nordaustlandet), we show that principal component analysis (PCA) is able to distinguish aeolian, fluvial, and glacial transport modes from each other using microtextural data, but it is able to help elucidate the ambiguous transport histories of ancient sediment grains
Summary
Scanning electron microscopy (SEM) quartz microtextural analysis reveals microscale features (microtextures) that are formed during transport (Krinsley and Takahashi 1962; Krinsley and Doornkamp 1973; Bull 1981). Because different transport modes imprint specific suites of microtextures onto quartz grains, quartz microtextural analysis is a useful technique to understand the transport histories of modern and ancient sedimentary deposits (Krinsley and Doornkamp 1973; Mahaney 2002; Vos et al 2014). We use principal component analysis (PCA) to directly compare quantitative microtextural data from modern and ancient aeolian, fluvial, and glacial sediments across workers. Because experimental studies have shown that certain microtextures form in specific transport settings (Krinsley and Takahashi 1962; Lindé and Mycielska-Dowgiałło 1980; Costa et al 2012; Costa et al 2013; Costa et al 2017), we expect the PCA ordinations to distinguish aeolian, fluvial, and glacial sediments from each other regardless of worker. We hypothesize that the modern and ancient samples will be quantitatively similar to each other in PCA space, and that the depositional histories of ambiguous ancient sedimentary environments can be constrained using this method
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