Revealing sediment transport histories with quartz microtextural analysis and principal component analysis (PCA)

Analysis of quartz microtextures using 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 more than one worker. We use principal component analysis (PCA) to directly compare 89 modern aeolian, fluvial, and glacial samples from the literature with 9 new samples from active aeolian, fluvial, and glacial environments. Our results show that PCA can group microtextural samples by transport mode and identify key microtextures that differentiate between aeolian, fluvial, and glacial transport modes, across SEM operators. We use a PCA ordination built with modern samples to analyze 22 previously published ancient samples from well-constrained depositional environments. Our results demonstrate that ancient sediments and modern sediments have quantitatively similar microtextural relationships and shows that PCA may be a useful tool to elucidate the ambiguous transport histories of some ancient sediment grains. As a case study, we analyze 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.