Abstract
Submarine cyclic steps have a significant impact on the evolution of the ocean floor on Earth. These upper-flow regime bedforms should be even more common in Martian reduced-gravity environments. We postulate that, if early Mars had an ocean, cyclic steps would have formed on Martian deltas spreading along the putative ancient shorelines in the northern plains. The main challenge to identifying submarine cyclic steps on Mars is geologic activity, in particular impacts, volcanism, and aeolian erosion, which have erased or modify much of the geomorphic evidence. Even though many Martian deltaic deposits do not bear much resemblance to the original depositional surfaces, we hypothesize that cementation and consolidation of marine sediments had facilitated the preservation of at least some Martian cyclic steps on deltaic deposits. We combine data from several orbital missions at Mars with a literature review and numerical analysis to inspect bedforms near the foreset-bottomset transition of 17 documented deltaic deposits. The most promising piece of evidence for Martian submarine cyclic steps is a linear series of rhythmic long-wavelength bedforms within a channel incised into the upper delta front of the Aeolis Mensae Delta. These bedforms are remarkably similar to their counterparts observed in channels on deltas and deep-water fans on Earth. Moreover, we speculate that two fields of cyclic steps, likely emanating from a crater upstream of the Aeolis Mensae Delta, are a potential example of contemporary cyclic steps and attest to the sporadic presence of flowing water on present-day Mars.
Highlights
Ancient ocean on Mars The paradigm that early Mars could have supported a complex hydrological system and an ancient ocean located in the low-lying northern plains (Fig. 1) is one of the most challenged concepts in Mars research (Baker et al 1991; Parker et al 1989, 1993; Malin and Edgett 1999; Head et al 1999; Ivanov and Head 2001, Fairen et al, 2003; Carr and Head 2003; Ghatan and Zimbelman 2006; McEwen et al 2007)
Hypotheses, and challenges The focused objective of this research is to evaluate whether submarine cyclic steps are present on 17 deltaic deposits documented by Di Achille and Hynek (2010), which spread along the putative shorelines of a primordial northern ocean (Fig. 3)
Aeolis Mensae Delta We examine a deltaic deposit centered at 132.861° E, − 5.149° N near the rim of Robert Sharp Crater, west of Gale Crater
Summary
Ancient ocean on Mars The paradigm that early Mars could have supported a complex hydrological system and an ancient ocean located in the low-lying northern plains (Fig. 1) is one of the most challenged concepts in Mars research (Baker et al 1991; Parker et al 1989, 1993; Malin and Edgett 1999; Head et al 1999; Ivanov and Head 2001, Fairen et al, 2003; Carr and Head 2003; Ghatan and Zimbelman 2006; McEwen et al 2007). The evidence for the northern hemispheric Martian ocean is mounting steadily. Evidence from the surface of Mars today implies that this water at least temporarily pooled to form an ocean in the low-lying northern plains (Fig. 1). The primordial ocean could have held more water than Earth’s Arctic Ocean and covered 19% of the planet’s surface (in contrast to the Atlantic Ocean, which occupies 17% of the Earth’s surface)
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