The Atlantis basin in the southern highlands likely owes its existence to an asteroid impact that took place in the early history of Mars.

Video: "Flight over Atlantis Chaos" from 2015 [2:59 min]
Copyright: ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)

Atlantis Chaos stands out for its highly disrupted landscape structure consisting of several hundred light-colored small peaks and mesas distributed across a nearly circular lowland plain. These are most likely remnants of outliers. Originally, it may have consisted of sedimentary deposits that were carried into the basin by the wind and subsequently altered by the influence of water. Here on Earth, this kind of sediment layer is referred to as 'loess'. In China, there are loess deposits with thicknesses of up to 400 metres.

Link to press release: Chaos in the Atlantis basin (Aug 03, 2015)  (with option to download the full resolution video)