Distal impact-related surface flows associated with the well-preserved Tokmok Crater, Noachis Terra, Mars

Meteorite impact craters on Mars display a diverse range of ejecta morphologies. A number of studies have suggested the presence of impact ejecta deposits beyond the limit of the canonical proximal continuous ejecta blanket, which on Mars is often marked by a topographic high, or “rampart”. It is currently uncertain how such deposits beyond the rampart form, and under what conditions. With the goal of answering such questions, we identified and characterized extensive surface flow deposits beyond the proximal ejecta blanket of Tokmok Crater, a ~ 9 km-diameter well-preserved crater in central Noachis Terra (29.405°S 351.319°E). We refer to these as Distal Flow Deposits (DFDs). We recognize two types: Type 1 flows develop at the base of source crater facing slopes as fan-like accumulations of smooth surfaced material. Type 2 flows form channel-fill like deposits within confining topography that funnel material from flat-lying regions. Through the identification, morphological mapping, and morphometric analysis of various impact units, the DFDs studied here are interpreted to represent the emplacement of outwardly mobilized ground-hugging flows subject to some form of impact-induced fluidization. DFD slope values are consistently below the dynamic angle of repose (Type 1 average = 6°; Type 2 average = 8.4°). DFDs are shown to accumulate where existing target topography captures more extended ejecta than surrounding flat-lying terrains that are resurfaced or obscured by the same deposits. Such deposits are shown to exist well beyond the proximal continuous ejecta blanket, which has important implications for geomorphological studies across Mars. • Cratering on Mars resurfaces the terrain well beyond where canonical models suggest. • Distal impact materials travel via outward travelling fluidized ground flows. • Distal flows accumulate or are redirected in response to existing target topography. • Subtle but continuous extended ejecta occurs on Mars through the mid-latitudes.