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Jezero crater is a similar to 45-km impact crater on the margin of Isidis basin on Mars. Jezero is the landing site for NASA's Mars 2020 rover mission. The crater hosts a paleolake, and fluvio-lacustrine deposits formed in this lake remain accessible to exploration. A dark-toned deposit on the crater floor overlies light-toned carbonate-bearing deposits and has been interpreted as a lava flow. We determined the average thickness of this deposit at the margins to be similar to 13.00.8 m. We analyzed the statistics of impact craters superposed on this deposit and estimated its model age as 2.60.5Ga in the Hartmann system, placing it most likely in the Early Amazonian. The error estimate here includes an estimate of the uncertainty associated with the crater counts. Acquisition, caching, and eventual return of a sample from this unit could provide an important calibration point for Mars crater chronology.

Plain Language Summary Jezero crater is a large impact crater on Mars with a diameter of about 45 km. In the Martian deep past this crater hosted a long-lived lake. On 19 November NASA announced that Jezero crater will be the landing site for the coming Mars 2020 mission. On top of sediments on the central crater floor is a distinctive deposit of dark rocks that possibly originated as a lava flow after the lake had dried out. We studied the statistics of small impact craters on this dark deposit. Such impact crater statistic is widely used as a tool for dating Martian terrains. We report a derived model age of 2.60.2 Ga for these rocks. One central goal of the Mars 2020 mission is to select and store a cache of rock samples that will be returned to Earth by a later mission for study in terrestrial laboratories. If this dark deposit is indeed lava, a sample could be dated in terrestrial laboratories. Together with our crater statistics reported here, this could provide a crucial tie-point for recalibration of the crater count dating system for Mars, which now relies on extrapolation from samples collected on the Moon.