Spatial and temporal distribution of sinuous ridges in southeastern Terra Sabaea and the northern region of Hellas Planitia, Mars☆

Abstract

Sinuous ridges are an important yet understudied component of Mars' hydrologic history. We have produced a map of sinuous ridges, valleys and channels, and tectonic ridges across southeastern Terra Sabaea and into northern Hellas Planitia (10°-45° S, 35°-80° E) using a CTX mosaic. Although we mapped different types of ridges and negative relief features, the focus of this paper are the sinuous ridges. We present here a new dataset of sinuous ridges that includes basic morphometry (e.g., length, width, sinuosity), morphology, and the types of terrains they are located on. We chose our region of interest because it includes surface ages spanning Mars' geologic history, with emphasis on Noachian and Hesperian terrains. The shift from either a warm and wet or a cold and icy environment to our modern cold and dry climate occurred towards the end of the Noachian and into the Hesperian, a critical temporal window to characterize fluvial landforms. Our CTX-based mapping significantly improved the documentation of fluvial landforms within the study region, with over an order of magnitude increase in the number of valley networks and channels, and nearly 1700 sinuous ridges. Sinuous ridges are found in concentrated settings, with the majority (∼80%) located within impact craters and relatively few (∼20%) on the intercrater plains. Fluvial features are prevalent on Early and Middle Noachian-aged terrain but are relatively rare in the Late Noachian, signifying a shift in fluvial activity that likely led to a decrease in channel incision and subsequent inversion of relief. A subset of sinuous ridges—radial ridges in high-elevation, degraded craters— are possible records of ancient proglacial lakes. The youngest sinuous ridges are associated with intracrater alluvial fans in a narrow zone (∼12°S to 30°S and ∼ 62°E to 77°E). These formed in the Late Hesperian into the Amazonian, reflecting a later epoch of punctuated fluvial events driven by pre-existing topography and solar insolation.