Post by G. de Villiers, Faculty of Geoscience, Utrecht University.
Fan-shaped deposits have been identified on the surface of Mars (Image 1). These sediment bodies often occur within impact craters and, specifically in the cases of fan deltas, suggests that these craters were once lakes early in Martian history. Fan delta morphologies are indicative of upstream (e.g. flow discharge and sediment properties) and downstream (e.g. basin characteristics) parameters, from which the hydrological conditions at the time of formation can be inferred (e.g. Kleinhans et al. 2010).
Image 1: Examples of fan delta deposits on Mars, formed in enclosed impact crater or rift basins. A) Single-scarped, branched prograding delta (PSP_006954); B) Single-scarped, smooth prograding delta (I10805012); and C) Multiple-scarped, stepped retrograding delta (V17040003). White line is approximately 5 km.
We experimentally created deltas in crater-shaped basins (in the Eurotank facility at Utrecht University) by feeding a range of constant flow discharges over a feeder channel of various sand textures. We constructed crater-shaped basins carved in sand, with diameters of 2 m and 4 m and shapes comparable to those of a complex impact crater of 40 km diameter without a central mound (Image. 2).
Image 2: Example DEM of a retrograding, stepped, delta deposit in the large crater (4 m diameter).
We reproduced three categorically different types of deltas including most of the types that have been identified on Mars (Image. 3). We found that water level behaviour, itself a unique function of flow discharge, basin size and hypsometry, and basin floor permeability, can explain most delta morphologies observed on Mars. Stepped, retrograding deltas formed during water level rise, prograding deltas formed in constant water level, and during water level fall deltas were partially destroyed by channel incision. On Mars numerous retrograding and prograding deltas were preserved, most of them without indications of channel incisions or other fluvial modification. Furthermore the formative durations were modelled using flow reconstructions based on feeder channel dimensions and sediment transport predictors as performed earlier for full-scale martian deltas (Kleinhans et al. 2010).
Image 3: Example photographs of delta deposits in the small crater (2 m diameter). A) Retrograding, stepped delta (run F) and B) Prograding delta (run G). White line is approximately 50 cm.
Our observation that the main difference between a single-foreset prograding delta and a multiple-foreset retrograding delta is the behaviour of the water level in the basin. This leads us to conclude that these simple delta morphologies cannot be reconciled with long-duration hydrological activity, because that would imply complex morphologies due to inherent complex water level histories along with complex sediment delivery histories. Our experiments and numerical verifications demonstrate that such deltas preferentially form during one aqueous event, which parsimoniously argues for short-duration hydrological activity.
Further Reading:
de Villiers, G., M.G. Kleinhans, G. Postma, Experimental delta formation in crater lakes and implications for interpretation of Martian deltas, J. Geophys. Res. Planets 118, 1-20, doi: 10.1002/jgre.20069, 2013. [Abstract]
Di Achille, G., and B. Hynek, Ancient ocean on Mars supported by global distribution of deltas and valleys, Nature Geoscience, 3 (7), 459–463, doi: 10.1038/ngeo891, 2010. [Abstract]
Hauber, E., K. Gwinner, M.G. Kleinhans, D. Reiss, G. Di Achille, G. Ori, F. Scholten, L. Marinangeli, R. Jaumann, and G. Neukum., Sedimentary deposits in Xanthe Terra: Implications for the ancient climate on Mars, Planetary and Space Science, 57 (8-9), 944–957, doi: 10.1016/j.pss.2008.06.009, 2009. [Abstract]
Irwin, R.I., A. Howard, R. Craddock, and J. Moore, An intense terminal epoch of widespread fluvial activity on early Mars: 2. increased runoff and paleolake development, J. Geophys. Res., 110, E12S15, doi: 10.1029/2005JE002460 2005. [Abstract]
Kleinhans, M.G., H. van de Kasteele, and E. Hauber, Palaeoflow reconstruction from fan delta morphology on Mars, Earth and Planetary Science Letters, 294 (3-4), 378–392, doi:10.1016/j.epsl.2009.11.025, 2010. [Abstract]
Kraal, E., M. van Dijk, G. Postma, and M.G. Kleinhans, Martian stepped-delta formation by rapid water release, Nature, 451 (7181), 973–976, doi:10.1038/nature06615, 2008. [Abstract]
Postma, G., M.G. Kleinhans, P. Meijer, and J. Eggenhuisen, Sediment transport in analogue flume models compared with real-world sedimentary systems: A new look at scaling evolution of sedimentary systems in a flume, Sedimfsentology, 55 (6), 1541–1557, doi: 10.1111/j.1365-3091.2008.00956.x, 2008. [Abstract]
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