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Chemical Diversity of Sands Within the Linear and Barchan Dunes of the Bagnold Dunes, Gale Crater, as Revealed by APXS Onboard Curiosity (2018)

O'Connell-Cooper, C. D. ; Thompson, L. M. ; Spray, J. G. ; [et al.]

American Geophysical Union

In: Geophysical Research Letters. 2018; 45(18): 9460-9470. Published 2018 Jul 25. doi: 10.1029/2018gl079026.

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Publication Date: 2018-07-25

Description: Alpha Particle X-ray Spectrometer (APXS) results for Phase 2 of the Bagnold Dunes campaign, focusing on the linear dunes, complement those from Phase 1 (barchan dunes) and add to our understanding of active Martian dune systems. This work highlights both compositional similarities and differences across the dune field. The concentration of elements associated with mafic minerals in coarser grains and along active ripple crests, previously identified in the barchan dunes, highlights differences in Martian and terrestrial weathering, transport, and sorting processes. Concentration of a Cr-Ti mineral phase within the linear sands is identified. The inactive ripple fields are geochemically similar to soil, while active ripple fields are similar to sands. Inferred dust content (S + Cl + Zn concentrations), derived from APXS analyses, provide geochemical confirmation of current and seasonal activity variations, within the barchan and linear dunes, as well as revealing a continuum between inactive soils and active sands. ©2018. American Geophysical Union. All Rights Reserved.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

Published by American Geophysical Union

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A General Model for the Helical Structure of Geophysical Flows in Channel Bends (2017)

Azpiroz-Zabala, M. ; Cartigny, M. J. B. ; Sumner, E. J. ; [et al.]

American Geophysical Union

In: Geophysical Research Letters. 2017; 44(23): 11932-11941. Published 2017 Dec 11. doi: 10.1002/2017gl075721.

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Publication Date: 2017-12-11

Description: Meandering channels formed by geophysical flows (e.g., rivers and seafloor turbidity currents) include the most extensive sediment transport systems on Earth. Previous measurements from rivers show how helical flow at meander bends plays a key role in sediment transport and deposition. Turbidity currents differ from rivers in both density and velocity profiles. These differences, and the lack of field measurements from turbidity currents, have led to multiple models for their helical flow around bends. Here we present the first measurements of helical flow in submarine turbidity currents. These 10 flows lasted for 1–10 days, were up to ~80 m thick, and displayed a consistent helical structure. This structure comprised two vertically stacked cells, with the bottom cell rotating in the opposite direction to helical flow in rivers. Furthermore, we propose a general model that predicts the range of helical flow structures observed in rivers, estuaries, and turbidity currents based on their density stratification. ©2017. The Authors.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics