Quantifying the latitudinal distribution of climate-related landforms on Mars' southern hemisphere

Abstract

The focus of this work is to contribute information about possible climate-related environments on Mars from a geomorphological perspective. In order to understand the latitudinal distribution of current and former climatic environments on Mars, we applied the so-called grid-mapping approach in order to quantify the geography of 17 climate-related landforms that each indicates a particular morphoclimate at the time of their evolution. Grid-mapping combines small-scale mapping with large-scale analyses; thus, it is possible to reveal relations that are only visible from a wider perspective. While the northern mid-latitudes of Mars have already been analysed by using this method, there was no adequate equivalent for the southern hemisphere. We therefore mapped three study areas representative of the southern cratered highlands. These study areas were in Noachis Terra, Terra Cimmeria, and Terra Sirenum respectively. As the basement of the southern highlands has been formed during the Noachian, we considered all latitudes (from the equator to the pole) and climate-related landforms of all Martian eras (Amazonian, Hesperian, Noachian), in order to determine any possible morphoclimatic belts. Unlike on Earth, we could not simply transfer existing geomorphologic classes to Mars. Instead, we reclassified the landforms into H2O– and CO2-based morphologies, as both constituents have different physical properties. As a result, we detected three cumulative morphoclimatic environments, formed under the same or very similar conditions during the late Amazonian: an aeolian zone (0°-~30°S), an H2O zone (~30°-70°S), as well as a CO2 zone (≥70°S). The aeolian and H2O zones could be further subdivided into two subdivisions: an active (0°-10°S) and inactive (10°-~30°S) aeolian zone as well as a volatile/unstable (~30°S-~60°S) and permanent/stable (60°-~70°S) H2O zone. Our observations are consistent with recent models of the distribution of water-ice on the Martian surface during the Amazonian. Although we detected landforms pre-dating the Amazonian, we could not detect clear evidence for Noachian or Hesperian morphoclimatic environments, as more recent landforms cover most of the mid to high latitudes. Grid-mapping also enabled the finding of a widely undescribed crater morphology on Mars, which we term multi-annular craterlets. They are characterised by small diameters (<1 km), a multi-ring facies, and a widely flat topography (the former crater depression is entirely filled with multi-layered deposits). We suggest that they were formed during deposition and erosion of multiple layers of the latitude-dependent mantle.