Abstract
Detrital zircon records of provenance are used to reconstruct
paleogeography, sediment sources, and tectonic configuration.
Recognition of the biases in detrital zircon records that result from
hydraulic sorting of sediment and the initial characteristics of zircons
in source regions (e.g., size and abundance) has added new complexity
and caution in the interpretation of these records. In this study, we
examine the role of transport process and sediment sorting in these
records. We begin our analysis by investigating the influence of grain
size and transport process in biasing detrital zircon provenance records
in an idealized sedimentary system. Our modeling results show that
settling and selective entrainment can leave distinct, process-dependent
fingerprints in detrital zircon spectra if initial size variation
between source zircon populations exists. We then consider a case study:
a detrital zircon record from Ediacaran to Terreneuvian Death Valley. We
focus on the Rainstorm Member, which is geochemically, mineralogically,
and sedimentologically unusual. In addition to Earth’s largest negative
carbon isotope excursion (the Shuram excursion), the Rainstorm Member
also contains anachronistic carbonate structures and a detrital mineral
suite enriched in heavy minerals. We evaluate the detrital zircon
provenance record of the Rainstorm Member, and find that, despite its
unusual character, the provenance of the unit is similar to other units
in the succession, with substantial input from Yavapai-Matzatzal
provinces. Size and density measurements of heavy and light density
components of the deposit suggest that its enriched heavy mineral suite
is best explained through concentration by selective entrainment and
winnowing. We find that our detrital zircon dataset is susceptible to
hydrodynamic fractionation, so that grain size exerts influence on its
provenance record, in particular for large Grenville-aged (1.0-1.2 Ga)
grains.