Constraining the formation of paleolake inlet valleys across crater rims

Abstract

Impact crater lakes with an inlet valley were common on Mars during past epochs. However, it has not been established exactly how impact craters with initially high-standing rims were breached by an inlet. We investigated four potential mechanisms for inlet valley breach formation: (1) rim erosion, (2) depositional rim burial, (3) drainage head erosion, and (4) overflow. We used remote sensing measurements to assess the relative likelihood of these mechanisms for 39 crater paleolake inlet systems, keeping in mind that either a single mechanism or multiple mechanisms may have occurred. Our findings indicate that crater degradation associated with (1) rim erosion and/or (2) depositional rim burial played an important role in establishing connections between exterior fluvial systems and crater interiors, especially during the late Noachian - early Hesperian valley network era. Isolated fluvial valleys, interpreted to post-date the main valley network era, breached craters in a wider range of degradation states compared to valley network-fed craters. Interestingly, in many cases, these younger systems accomplished a comparable magnitude of fluvial erosion via drainage head erosion and across crater rims as the valley network inlets, despite differences in broader landscape dissection. This finding suggests fluvial activity was able to accomplish comparable geomorphic work during later periods of Mars' history, at least locally. Our catalog of analyzed paleolakes includes Jezero crater, and so our work provides broader context for in situ rover analyses at this site.