Paleolakes in the Northwest Hellas Region, Mars: Implications for the Regional Geologic History and Paleoclimate

Hellas basin is one of the largest and oldest impact basins on the Martian surface. Its surrounding highland regions have undergone complicated geologic processes after the formation of Hellas basin. However, the geologic and climatic histories of the highlands surrounding Hellas are still unclear. Paleolakes provide us clues to answer these questions. In this study, we made a detailed investigation of paleolakes in the northwest Hellas region with high-resolution imaging, topographic, and spectral data. A total of 64 paleolakes were identified with diameters larger than 4 km, in which 49 are newly reported. We calculated basic hydrologic parameters of the paleolakes and analyzed the sedimentary landforms, resurfacing processes, and aqueous minerals in the lake basins. Comprehensive analyses of the geomorphology, mineralogy, and age of the paleolakes revealed the geologic and climatic histories of the northwest Hellas region: a climate transition from warm and wet to semi-arid happened in Noachian, and then lakes drained in a cold and dry climate in the early Hesperian, contemporary with or followed by a period of intense volcanic activity peaked around 3.3 Ga, and finally in the Amazonian, an extensive glacial event around 0.9 Ga resurfaced most of the paleolakes in the region south of 25°S. Our study also supports the existence of a “Hellas Ocean” and indicates that the Martian climate could have variations on regional scales and further studies are still needed to clarify the details.