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Constraining sediment routing system responses to tectonics and climate

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Both tectonics and climate profoundly influence the erosional-depositional processes that shape the Earth’s surface1,2. Moreover, the magnitude, locus and characteristics of sediment export from catchments to basins play a fundamental role in determining depositional stratigraphy. While progress has been made in understanding the response of erosional-depositional systems to tectonics, the extent to which sediment routing systems are either sensitive, or are buffered, to rapid climate change remains extremely contentious3.

A good way to address this fundamental question is to examine the sedimentary record, because this constitutes the only physical archive we have of mass transport across Earth’s surface as a function of past climate4. Terrestrial sediments have the potential to preserve the erosional record of upland landscape response to high-frequency climate forcing, while advances in exposure-age dating now enable detailed time-series of sediment characteristics, such as grain size, to be compared quantitatively with known palaeo-climate archives. Here, we use exceptionally well-constrained data from the Sierra Nevada, California, to demonstrate that the sediment characteristics and channel widths of alluvial fan deposits capture orbitally-induced climate fluctuations with high fidelity over a complete glacial-interglacial cycle. For examples from Owen’s Valley, we demonstrate that the grain sizes of these sediments scale with Pacific sea surface temperature reconstructions for the last 140 ka, increasing systematically with ocean surface warming. We propose this signal is driven by changes in surface runoff, controlled by the magnitude and intensities of flow-triggering storms. Our results (i) provide new constraints on the sensitivity of sediment routing systems to climate changes of known magnitude; (ii) show that the response time of these systems to climate change can be rapid (≤104 years); and (iii) demonstrate that stratigraphy can be successfully inverted for past environmental changes where transport and deposition rates are high.

References

1Whittaker, A. C., 2012, How do landscapes record tectonics and climate? Lithosphere, 4, 160-164.

2Armitage, J., Duller R. A., Whittaker, A. C., and Allen, P. A., 2011, Transformation of tectonic and climatic signals from source to sedimentary archive, Nature Geoscience, 4, 231-235.

3Armitage, J., Dunkley Jones, T., Whittaker, A.C., , Allen, P.A., 2013, Temporal buffering of climate-driven sediment flux cycles by transient catchment responses, Earth and Planetary Science Letters, 369-370, 200 -210.

4Michael, N. A., Whittaker, A. C., Carter, A., Allen P. A., 2014, Volumetric budget and grain-size fractionation of a geological sediment routing system: Eocene Escanilla Formation, South-Central Pyrenees, GSA Bulletin, 126, 585-599

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