Detrital Zircon Transport Lag in Fluvial Bedload: An Experimental and Numerical Investigation
Abstract
The difference in transport rates and times of different density particles, such as detrital zircons in quartz sand, is critically important to accurately assess sedimentary provenances. Because zircons are typically twice as dense as their surrounding sediment, and because transport rate scales non-linearly with grain density, zircon transport rate as bedload should be one or two orders of magnitude smaller than that of quartz sand (depending on specific grain parameters like size or shape). Moreover, intermittent transport conditions, sediment segregation into floodplains, or abandonment in situ by avulsions until reoccupation can add substantial time lag. We experimentally modeled fluvial bedload containing detrital zircons using a 5 m × 0.6 m domain in a flume. Using magnetite sand as a proxy—it has a similar density as zircons—we developed mature, three-dimensional bedforms with variable scour depths that transported multiple dune lengths (dune length 0.2 m, amplitude 0.1 m). We measured magnetic particle concentration by separating them from hand samples with a magnet, relating change in concentration directly to transport rate. Our experimental results suggest that detrital zircon transport is substantially slower than bulk sediment transport because denser particles segregated to the base of dune lee faces. The ratio of transport rates were then integrated into a meandering river forward model. Factoring in transport intermittency, floodplain segregation, and avulsion, resulted in a distribution of transport times for quartz sand and zircons given a drainage length. These forcings provide constraints on minimum transport lag from source to sink.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP41B2660D
- Keywords:
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- 1810 Debris flow and landslides;
- HYDROLOGYDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGYDE: 3265 Stochastic processes;
- MATHEMATICAL GEOPHYSICS