A Series of Stacked and Entrenched Fan Deltas at Lake General Carrera/Buenos Aires (Chile/Argentina) as Terrestrial Analog to Understand the Entrenchment of Martian Deltas

Friday, 19 December 2014
Gaetano Di Achille, National Institute for Astrophysics (INAF), Astronomical Observatory of Collurania, Teramo, Italy and Francesco Salese, International Research School of Planetary Sciences, Chieti, Italy
The apparent lack of entrenchment on Martian fan deltas has been hitherto uniquely interpreted as evidence for fast disappearance of water and used to support the hypothesis of an abrupt climate change on Mars around 3.7-3.4 Ga. However, hi-res imagery and topography of several martian fan deltas show evidence of erosion and entrenchment in response to decreasing water level settings. Moreover, the boundary conditions for entrenchment have never been investigated from a quantitative point of view. To gain a quantitative understanding on fan delta entrenchment processes, we are studying (using remote sensing, modeling, and fieldwork campaigns) a series of seven stacked fan deltas formed at Lake General Carrera/Buenos Aires (Chile/Argentina). The uppermost deposit is located more than 400 m above the lowest delta presently forming at the current lake water level. The six raised deltas formed during highstands punctuating the overall 15000 yrs long retreat of the lake and are entirely entrenched thus allowing potential sampling over the entire thickness of the sedimentary sequences. These windows to the internal outcrops enable the assessment of water and sediment paleo-discharges (based on the analysis of the grain sizes) and to implement numerical simulations to reproduce the sedimentary deposits using numeric code such as Sedflux 2.0 (Hutton and Syvitski, 2008). The studied sedimentary assemblage offers the unique opportunity to place constraints on the fan deltas entrenchment with strong implications for the modeling of martian entrenched fans and thus for the understanding of the paleoclimate and paleohydrology during their terminal activity. We present the results of remote sensing study from satellite hi-res imagery and topography, numerical modeling, and from a survey field campaign.

E. W. H. Hutton and J. P. M. Syvitski, Sedflux 2.0: An advanced process-response model that generates

three-dimensional stratigraphy, Computers & Geosciences 34 (2008) 1319–1337.