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Grain size and transport biases in an Ediacaran detrital zircon record
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  • Marjorie D. Cantine,
  • Jacob B Setera,
  • Jill A VanTongeren,
  • Chiza Mwinde,
  • Kristin D Bergmann
Marjorie D. Cantine
Massachusetts Institute of Technology

Corresponding Author:[email protected]

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Jacob B Setera
Rutgers University
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Jill A VanTongeren
Rutgers University
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Chiza Mwinde
University of Chicago
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Kristin D Bergmann
Massachusetts Institute of Technology
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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.