Prolonged Record of Hydroclimatic Changes at Antoniadi Crater, Mars

The first billion years of Martian geologic history consisted of surface environments and landscapes dramatically different from those seen today, with flowing liquid water sculpting river channels and ponding to form bodies of water. However, the hydro-climatic context, the frequency, and the duration under which these systems existed remain uncertain. Addressing these fundamental questions may improve our understanding of early Mars climate. Here, we reconstruct a long-lived archive consisting of an array of fluvial systems inside the Antoniadi crater-one of the largest lake basins on Mars (9.58 x 10(4) km(2)). We found that the fluvial activity occurred throughout four major intermittent active intervals during the Late Noachian to Early Amazonian (similar to 3.7 to >2.4 Ga). This resulted in at least two major lakes, which formed during periods of markedly increased surface runoff production. The record of these four riverine phases is preserved in fluvial ridges, valley networks, back-stepping or down-stepping fan-shaped landforms, and terrace-like formations within an outlet canyon. These morphologies point to lake-controlled base-level fluctuations suggestive of episodic precipitation-fed surface runoff punctuated by intermittent catastrophic floods that were capable of breaching crater-lake rims and incising outlet canyons. Fluvial-deposit thickness, junction angles of channels, and lake morphometry suggest that riverine systems lasted at least 10(3)-10(6) years and episodically occurred under primarily arid and semi-arid climates. These findings place new regional constraints on the fluvial frequency, longevity, and climatic regime of one of the largest Martian lakes, thereby bolstering the hypothesis that episodic warming likely punctuated the planet's early history.