Jezero crater fluvio-deltaic system: insights on its geological evolution through a sedimentary mass balance modelling
Authors: Silva David C. A. , Vaz David , Le Deit Laetitia , Di Achille Gaetano 
Published: July 2024

Introduction and objectives: Despite currently being an arid planet, Mars is believed to once have had a milder climate, with a dense atmosphere capable of supporting a hydrological cycle. The sedimentary deposits putatively of deltaic origins found across all Martian surface, are good indicators of water distribution and can provide valid information to this climatic evolution [1, 10].The Mars 2020 Perseverance rover has collected samples from the sedimentary deposit and has moved on to the Neretva Vallis. In this same area, sediments containing hydrated silica were previously identified [2]. There are also stratigraphic and morphological evidences that allow defining different phases of progradation and transgression, as well as a phase of erosion subsequent to the deposition of the sedimentary body [3]. This set of evidence suggests that this deposit was formed by fluvio-deltaic processes [4] at the end of the Noachian and beginning of the Hesperian [5].With this work, we seek to better understand the different evolutionary phases of this fluvio-deltaic system, proceeding with a mass balance analysis to evaluate deposition and exhumation processes [6]. These phases can provide key insights into better understanding the possibility of the existence of a large body of water in the northern hemisphere [7], particularly through a comparison with the knickpoints proposed by Duran et al. (2019) [8].Data and methods: In order to cover the entire area under study, 21 digital terrain models and their respective orthoimages were created. These data were produced using images from the Context Camera (CTX), processed using ISIS (Integrated Software for Imagers and Spectrometers) and NASA Ames Stereo Pipeline.Vaz et al. (2020) [10] identified the existence of two different groups of fan-shaped deposits on the Martian surface. To do so, a mass balance analysis was conducted between the material removed from the valley and the material deposited at its mouth. Volumes were estimated from digital terrain models, using the methodologies described in Vaz et al. (2020) [10].Preliminary results: After mapping the valley, deposits, and crater (basin) (Fig. 1), volume calculations were performed, and several discontinuities on the valley longitudinal profile were identified. We associate these discontinuities with different phases of valley incision.Figure 1 - Mapped valley (blue), thalweg line (light blue), deposits (yellow) and crater (red)Initially, only two possible scenarios were considered: a) the entire valley (Neretva Vallis) and the visible deposited material of the western deposit; and b) only the portion of the valley closest to the crater and the deposit inside the crater (Fig. 2). Considering a deposit porosity of 0.3, a valley porosity of 0.25 [9], and an erosion rate of 2.7 nm/year, we obtain: scenario a) the volume of material removed from the valley is about ten times greater than the volume of deposited material; scenario b) the material removed from the section of the valley closest to the crater is not sufficient to fill the adjacent deposit.Figure 2 - above) Color grading of the deposit&#8217;s depth (from blue to red). Below) Color grading of the first valley section depth (from blue to yellow).Discussion and work to be done: Currently, from the preliminary results, the mass deficit calculated for the maximum extent of the valley stands out. The material deposited in the fan only corresponds to approximately 8% of the material that was eroded to form the valley. To further evaluate these values, different parameters will be tested, namely porosities and erosion rates. The original extent of the deposit, which goes beyond the initially mapped area in this work (e.g., Kodiac Butte), will also be studied. Subsequently, information on the different known knickpoints [8] will be incorporated to try to explain the different valley sections. One other objective is to try to correlate these sections with the different depositional phases captured by the Perseverance rover in situ [11].Acknowledgments: CITEUC (UID/Multi/00611/2021&amp;POCI-01-0145-FEDER-006922), FCT (2021.05116.BD &amp; CEECIND/02981/2017) and the Laboratory of advanced computation of the University of Coimbra for the computing resources.References:[1] Di Achille, G., &amp; Hynek, B. M. (2010a). Deltas and valley networks on Mars: Implications for a global hydrosphere. In Lakes on Mars (pp. 223&#8211;248). Elsevier.[2] Pan, L., Carter, J., Quantin-Nataf, C., Pineau, M., Chauvir&#233;, B., Mangold, N., Le Deit, L., ... (2021). Voluminous silica precipitated from martian waters during late-stage aqueous alteration. Planetary Science Journal, 2(2).[3 Goudge, T. A., Mohrig, D., Cardenas, B. T., Hughes, C. M., &amp; Fassett, C. I. (2018). Stratigraphy and paleohydrology of delta channel deposits, Jezero crater, Mars. Icarus, 301, 58&#8211;75.[4 Fassett, C. I., &amp; Head, J. W. (2005). Fluvial sedimentary deposits on Mars: Ancient deltas in a crater lake in the Nili Fossae region. Geophysical Research Letters, 32(14), 1&#8211;5.[5] Mangold N., &amp; Quantin-Nataf C. (2021). Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars. Science.[6] Quantin-Nataf, C., Holm-Alwmark, S., Lasue, J., Calef, F. J., &#8230; (2021). The Complex Exhumation History of Jezero Crater Floor Unit. 52nd Lunar and Planetary Science Conference.[7] Di Achille, G., &amp; Hynek, B. M. (2010b). Ancient ocean on Mars supported by global distribution of deltas and valleys. Nature Geoscience, 3(7), 459&#8211;463.[8] Duran, S., Coulthard, J., &amp; Baynes, E. R. C. (2019). Knickpoints in Martian channels indicate past ocean levels. Scientific Reports, 9(1).[9] Macke, R.J., Kiefer, W.S., Britt, D.T., Irving, A.J., Consolmagno, G.J., 2011. Densities, porosities and magnetic susceptibilities of meteoritic lunar samples: early re- sults. In: 42nd Lunar and Planetary Science Conference, LPI Contribution No. 1608. The Woodlands, Texas, p. 1986.[10] Vaz, D. A., Di Achille, G., Hynek, B. M., Nelson, W., &amp; Williams, R. M. E. (2020). Martian fan deposits: Insights on depositional processes and origin from mass balance survey. Earth and Planetary Science Letters, 533.[11] Mangold, N., Caravaca, G., Gupta, S., Williams, R. M., Dromart, G., Gasnault, O., ... &amp; Wiens, R. C. (2024). Architecture of Fluvial and Deltaic Deposits Exposed Along the Eastern Edge of the Western Fan of Jezero Crater, Mars. Journal of Geophysical Research: Planets, 129(3), e2023JE008204.