Martian Paleolake Outlet Canyons - Evidence for Controls on Valley Network Formation

Abstract

Martian valley networks (VNs) have been viewed as one of the most compelling pieces of evidence for ancient fluvial activity during the Late Noachian and Early Hesperian periods (3.7–3.5 Ga), likely as a result of precipitation (snowfall/rainfall). During this period, paleolakes also formed, predominantly due to water accumulation within impact crater interiors. Some of these paleolakes breached the rim of their basins (e.g., crater rim) which caused outburst flooding and incision of a paleolake outlet canyon over a short period of time (weeks to years). After the Late Hesperian, valley formation vastly decreased indicating a waning water cycle. There have been inferences that paleolake outlet canyons may have controlled the trajectories of adjacent valley networks that formed after them, yet no direct evidence has been observed. In this study, we map and apply paleohydraulic, morphometric, and morphological calculations to two hydrological systems located west of the Tharsis Rise, where hydrological systems are defined as a combination of a paleolake outlet canyon and adjoining VNs. We aim to determine whether the paleolake outlet canyons show evidence of control on the trajectory of adjacent VNs and the impact this has on their development. We find that the paleolake outlet canyons do place control on the trajectories of adjacent VNs, causing them to detour from the regional slope direction and causing the basin to deviate from the natural fractal geometry formed by precipitation-fed fluvial incision. Additionally, the paleolake outlet canyons display a decrease in the cross-sectional area down their profile, indicating they experienced water loss as they were active. The examined paleolake outlet canyons have altered the evolution and interconnectivity of the adjoining VNs, leading to water loss, likely to the subsurface. Finally, given the proximity of these hydrological systems to the Tharsis Rise, we note that they display a complex history of fluvial and tectonic activity, indicating that fluvial activity both preceded and post-dates Tharsis-induced tectonic activity.