Abstract
On Mars, the presence of extensive networks of sinuous valleys and large channels provides evidence for a wetter and warmer environment where liquid water was more abundant than it is at present. We undertook an analysis of all major channel systems on Mars and detected sharp changes in elevation along the river long profiles associated with steep headwall theatre-like valleys and terraces left downstream by channel incision. These breaks in channel longitudinal slope, headwalls and terraces exhibit a striking resemblance with terrestrial fluvial features, commonly termed ‘knickpoints’. On Earth, such knickpoints can be formed by more resistant bedrock or where changes in channel base-level have initiated erosion that migrates upstream (such as tectonic uplift or sea level change). We observed common elevations of Martian knickpoints in eleven separate channel systems draining into the Martian Northern lowlands. Numerical modeling showed that the common elevations of some of these knickpoints were not random. As the knickpoints are spread across the planet, we suggest that these Martian knickpoints were formed in response to a common base level or ocean level rather than local lithology. Thus, they potentially represent a record of past ocean levels and channel activity on Mars.
Highlights
On Mars, the presence of extensive networks of sinuous valleys and large channels provides evidence for a wetter and warmer environment where liquid water was more abundant than it is at present
We have analyzed the major channel systems spread across Mars using a systematic and automated procedure to identify channel knickpoints likely formed by base-level changes
Each knickpoint was visually checked for features frequently found on terrestrial base-level change knickpoints – e.g. those formed by the movement of a tectonic fault or a drop in relative sea level – and ranked according to how many of these identifiers were present
Summary
On Mars, the presence of extensive networks of sinuous valleys and large channels provides evidence for a wetter and warmer environment where liquid water was more abundant than it is at present. Beginning in the Southern highlands and extending down to the Northern lowlands, some channels exceed a thousand kilometers in length and drop several kilometers in elevation[21,22] These channel systems have few tributaries but contain theatre-shaped head walls and major knickpoints – sometimes referred to as ‘cataracts’ or ‘inner channel headcuts’, – which previous research has suggested to be caused by episodes of bedrock erosion by high-discharge flows[22,23]. We have analyzed the major channel systems spread across Mars using a systematic and automated procedure to identify channel knickpoints likely formed by base-level changes These knickpoints are geographically widespread and fall into four common elevation zones with tests showing the lower two have a likelihood of being formed by random processes of less than 5% (see Supplementary Material). This suggests that the lower two knickpoint elevation zones were formed either under periods of two stable ocean levels or during two or more phases of fluvial activity coupled with changing Northern ocean levels
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