In the 2019 JGR bedrock mapping paper, we defined "Terra Sabaea" as the cratered highlands between 0E and 60E, and above 45 S (where periglacial modification becomes pervasive). Excluded from this region is an area interior to the Hellas Basin and below +1000 m relative to the Martian datum. Terra Sabaea contains 31 mapped bedrock plains.
Terra Sabaea is among the oldest regions on Mars. It is pockmarked by numerous craters larger than ~16 km in diameter, and surface ages derived from crater counting dating techniques indicate that this region has not seen substantial resurfacing (such as erosion and burial of large craters) for the last 3.7 billion years or more. Much of the evidence for liquid water on the Martian surface comes from this region, as high-standing areas have large, well-developed drainage networks formed via precipitation (e.g. Craddock and Maxwell, 1993). The craters of Terra Sabaea likely hosted intermittent to permanent lakes and fluvial systems (e.g. Irwin et al. 2005, Goudge et al. 2012). Not surprisingly Terra Sabaea hosts many clastic deposits which were likely carried into topographic lows by water, and may have later been altered by prolonged exposure to water. (See Rogers et al. 2018 for a discussion of clastic materials, Irwin et al. 2018 and Cowart et al. 2019 for examples of water-related clastic deposits, and Carter et al. 2012 for a discussion of water alteration.)
In addition to its water-rich history, Terra Sabaea has been profoundly shaped by the influence of the Hellas Basin. Much of the region sits on a gentle regional slope formed by ejecta from the Hellas Basin impact event. This 2300 km wide impact basin (the largest confirmed crater in the Solar System) had a profound effect on the region. In the hundreds of millions of years after the impact, the warm Martian mantle gently flowed back towards the large hole created by the impact, pulling open large canyons (1000s of km long, up to 100 km wide) more than 2500 km away from the point of impact (Wichman and Schultz, 1989). Many of these canyons were subsequently infilled by erosion, sedimentary, and/or volcanic processes.
As a result of these processes, Terra Sabaea hosts a rich record of the early Martian geological system. Many of the bedrock plains mapped by the 2019 JGR paper appear to be clastic in origin. These bedrock plains often contain highly variable surfaces, suggesting a complex history associated with their origin. These plains are prime targets for further exploration.