Formation of a Terraced Fan Deposit in Coprates

Introduction: We have studied a terraced fan deposit centered at 15.0° S, 299.7° E within one of the troughs of Coprates Catena in order to investigate the role that water may have played in its formation. Only a handful of these unique terraced fan deposits have been identified on Mars [1-4], although their small sizes make them difficult to identify with the current data sets. The few fan deposits that do not have terraces and are not classified as alluvial fans in highland craters (e.g., Eberswalde crater, Nili Fossae) have been interpreted as deltas in standing bodies of water [3-7]. The terraced fan in Coprates Catena is unique among the currently known terraced fans because a contributing channel can be seen at the head of the valley that is the apparent source of sediment forming the fan deposit, and a smaller channel and associated valley incise the surface of the terraced fan deposit. Terraced Fan Deposit: The fan deposit (Figure 1) has a maximum width of 7.9 km and length of 8.6 km, and it emanates from a 35 km long sinuous valley that cuts through the plains before terminating in the trough (Figure 2). The fan radius varies from 5.1 km at the eastern edge to 8.6 km at the northern tip. We estimate the area of the deposit to be ~40 km 2