Abstract
Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6–3.0 Ga. Despite widespread geomorphic evidence, few analyses of Mars’ alluvial sedimentary-stratigraphic record exist, with detailed studies of alluvium largely limited to smaller sand-bodies amenable to study in-situ by rovers. These typically metre-scale outcrop dimensions have prevented interpretation of larger scale channel-morphology and long-term basin evolution, vital for understanding the past Martian climate. Here we give an interpretation of a large sedimentary succession at Izola mensa within the NW Hellas Basin rim. The succession comprises channel and barform packages which together demonstrate that river deposition was already well established >3.7 Ga. The deposits mirror terrestrial analogues subject to low-peak discharge variation, implying that river deposition at Izola was subject to sustained, potentially perennial, fluvial flow. Such conditions would require an environment capable of maintaining large volumes of water for extensive time-periods, necessitating a precipitation-driven hydrological cycle.
Highlights
Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6–3.0 Ga
While the present-day Martian surface is generally dry and cold, its geomorphic record contains compelling evidence for the former presence of liquid water[1,2,3,4,5,6,7]. In addition to this rich geomorphic archive, Mars’ increasingly accessible sedimentary rock record provides a repository of information from which to study how planet-wide patterns in deposition have changed over time
Unequivocal sedimentarystratigraphic evidence of alluvium has only been identified in-situ by rover-led studies[14], and whilst rovers provide unprecedented direct access to extraterrestrial strata[15], methodologies are typically limited by accessible outcrop dimensions
Summary
Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6–3.0 Ga. The channel forms and associated sedimentary packages are interpreted as the product of an actively depositing fluvial system, with the final sedimentary architecture suggesting that these Noachian-aged rivers were not typified by high-energy episodic floods, but rather perennial or semi-perennial fluvial flow. Areas containing clusters of channels are bottomed and topped by laterally extensive (up to 640 m), low relief, fifth-order surfaces, which suggest a change in the type or location of the dominant depositional process.
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