Evolution of the Navua Valles region: Implications for Mars' paleoclimatic history

Abstract

The Navua Valles are comprised of a system of channels and valleys on the inner Northeastern rim of Hellas Basin, which is a 1500-km-long sloping terrain. Drainage systems and regional geology in this unique setting were not previously mapped in detail. We mapped this region using CTX (6 m/px) as the base map and assessed surface unit ages resulting from our crater counting. We found that the timing of the deposit-forming episodes in this region during the Hesperian and Early to Middle Amazonian largely correlated to active phases of the Hadriacus Mons volcanic center. We found evidence for several episodes of fluvial activity Hesperian to the Amazonian with declining intensity, and transitioning to ice-dominated processes. The channels in the Navua Valles region erode into deposits dating from the Noachian to Early Amazonian, including the Noachian highlands, Noachian to early Amazonian crater ejecta, and likely volcanic plains formed from the Hesperian to the Hesperian–Amazonian transition. Channels directly originating from Hadriacus Mons are younger, while precipitation-fed channels at larger distance from the volcanic center are older, indicating different triggers for fluvial activity. Crater counting results indicate that almost all channel floors were at least partially resurfaced during the Amazonian and that several channel deposits formed during the last 0.5 Gyr. Water pathways likely included surface channels, lakes, and subsurface flow. The Navua Valles channel system is discontinuous, and the number of terminal deposits (sink locations) is almost as high as the number of channel sources, which is unusual for valley networks elsewhere on Mars. Interior channels formed only in the major Navua channels, they are even more fragmented than their parent channels, but occur along their entire length. Channels and valley systems within the Navua Valles are potential targets for in situ astrobiological studies, as they could have provided potential habitats at least periodically, from the Late Hesperian to the Late Amazonian.