REVEALING THE DETAILS OF THE MARTIAN SOUTH POLAR LAYERED DEPOSITS: CREATION OF A USGS 1:2M GEOLOGIC MAP

Mars’ obliquity oscillates quasi-periodically over intervals of hundreds of thousands of years, leading to climate variations over these timescales. In particular, these climate cycles contributed to the formation of icy deposits in the south polar region, including the south polar layered deposits (SPLD) and the south polar residual cap (SPRC) which consist of a combination of mixed layers of H₂O ice, CO₂ ice, and sediment. Seasonal CO₂ frost, in addition to water ice processes, has shaped the surface of these icy deposits resulting in a diversity of landforms like araneiforms and pits. Together these deposits preserve long-term records of climate variation and reflect current climate dynamics, which has spurred an increasing body of research into their formation and evolution. However, that body of research is missing the essential framework of a published geologic map that captures the complexity revealed by the last ~40 years of observation. This motivated us to produce a United States Geological Survey Science Investigation Map of the south polar region of Mars (70°S to 90°S).

Our primary basemap for this mapping effort is the THEMIS daytime IR mosaic (100 m/pixel), while Context Camera (CTX, 5 m/pixel) and MOLA (115 m/pixel) are used as supplemental datasets. We map at a scale of 1:500k to produce a geologic map with a final resolution of 1:2M. We have mapped a diverse set of regions of interest (ROI) within or along the border of the SPLD to identify as many preliminary geologic units as possible before beginning to map the entire map area. This initial mapping effort suggests that the SPLD, overlying SPRC, and underlying basement can be divided into at least 12 geologic units that can broadly be divided into plains materials and crater units. These preliminary geologic units are still in flux. For instance, two units are distinguished only by differences in the slope of their scarps. Currently, we interpret this difference to mean that these two units in the SPLD vary in their susceptibility to erosion. A diversity of surface features have been identified across the ROIs as well, including impact craters and ejecta, dunes, ridges, scarps, and depressions. This map aims to provide an accessible tool for researchers in the Mars community, with a specific focus on the planet's polar and climate history.