Post contributed by Francesco Salese from IRSPS/Dipartimento INGEO, Università D’Annunzio, Pescara, Italy.
Mars, is one of the planetary bodies where water flowed and where it may transiently flow today under certain conditions. Many martian paleodrainage systems and well-preserved fluvial and lacustrine deposits have been recognized and studied in the last two decades (see further reading). Widespread dendritic valley networks and the presence of extensive fluvial features on ancient martian terrains suggest that a relatively “warm and wet” climate was prevalent early in the planet’s history (about 3.7 Ga). This is in stark contrast with the hyper-arid, extremely cold climate that is thought to have persisted from 3 Ga until the present (Amazonian Era). The subject of this post is Moa Valles [Salese et al., 2016], which is a 2 billion year old paleodrainage system (Figure 1) that is nearly 300 km long and is carved into ancient highland terrains of Tempe Terra in the northern hemisphere of Mars. Understanding the origin and evolution of this type of complex and interconnected paleo-fluvio-lacustrine system is critical for understanding the early martian climate.
The Moa Vallis paleofluvial system consists of a series of dam-breach paleolakes with associated fan-shaped sedimentary deposits. The paleolakes are interconnected and drain eastward into Liberta crater, where there is a complex and multilobate deltaic deposit with a well-developed channelized distributary pattern with evidence of avulsion on the delta plain (Figure 2).
A breach area, consisting of three spillover channels, is present in the eastern part of the crater rim. These channels connect the Liberta crater to the eastward portion of the valley system, continuing towards the main trunk of Moa Valles which has a complex pattern of anabranching channels (Figure 3) stretching over 180 km.
Based on hydrological calculations of infilling and spillover discharges of the Liberta crater lake, the formation of the whole fluvial system is consistent with short to medium (<1000 year) timescales, conversely from comparison with terrestrial analogs, the length and morphology of the observed fluvial-lacustrine features suggest long-term periods of activity (Figure 4). The relatively recent activity of the Moa Valles fluvio-lacustrine system was likely sustained by relatively short fluvial events (<100 years), thereby supporting the hypotheses that water-related erosion might have been active on Mars (at least locally) during the last 3 Ga, despite this epoch being commonly considered as having a cold and dry climate. The water source for the system could have been shallow ice melting triggered by impact.
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