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 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 9 new samples from
active aeolian and glacial environments. Our results demonstrate that
PCA can group microtextural samples by transport mode and differentiate
between aeolian and fluvial/glacial transport modes 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.