Major episodes of geologic history of Isidis Planitia on Mars

► Geologic history of Isidis Planitia consists of four episodes. ► Impact dominated episode (until ∼3.8Ga). ► Volcanically dominated episode (∼3.8–3.5Ga): circum-Isidis volcanic province formed. ► Fluvial/glacial episode (∼3.5–2.8Ga): fluvial and glacial processes dominated. ► Wind-dominated episode (after ∼2.8Ga): minor modification of the surface. We have mapped the area of Isidis Planitia (1–27°N, 75–103°E) in order to assess the geologic history of this region using modern data sets such as MOLA topography and the high-resolution images provided by the HRSC, CTX, and HiRISE cameras. Results of our mapping show that the geologic history of Isidis Planitia consists of three principal episodes. (1) Impact dominated episode (Noachian, until ∼3.8Ga): During this time, the oldest materials in the study area were formed mostly by impact reworking and mass-wasting. Other processes (e.g., volcanism and fluvial/glacial activity) likely operated at this time but played a subordinate role. (2) An episode related to volcanic and fluvial/glacial activities (late Noachian–early Amazonian, ∼3.8–2.8Ga): Volcanism appears as the most important process at the beginning of this episode (∼3.8–3.5Ga) and was responsible for the formation of a large circum-Isidis volcanic province by the early Hesperian epoch. Volcanic materials covered large portions of the Isidis rim, almost completely buried the previous crater record on the floor of the Isidis basin, and probably were the major contributors to the filling of the basin. Fluvial/glacial processes prevailed closer to the end of the episode (early Hesperian–early Amazonian, ∼3.5–2.8Ga) and were responsible for widespread resurfacing in the Isidis Planitia region, mostly at ∼3.1–3.4Ga. Glaciers and/or ice sheets probably resulted in a massive glaciation of the rim and the floor of the Isidis basin. The total volume of material eroded from the Isidis rim by glacial and fluvial activity is estimated to be about 35,000–50,000km3, which is equivalent to a composite layer about 40–60m thick on entire floor of the basin. More important, however, is that the eroded materials were likely saturated with ice/water and could form wet deposits on the floor. (3) Wind-dominated episode (since early Amazonian, ∼2.8Ga): Wind activity dominated the later geologic history of Isidis Planitia but resulted only in minor modification of the surface.