Ismenius Cavus, Mars: A deep paleolake with phyllosilicate deposits

Ismenius Cavus is a basin where several fluvial valleys converge. Three depositional fan deltas are observed at the valleys outlets at similar elevations. These fans suggest long-term fluvial activity accompanied by a lake inside the basin. The elevational difference between the delta plains and the deepest part of the basin floor implies that this lake was 600 m deep. Iron–magnesium phyllosilicates, which are mapped from near-infrared spectral data, are associated with layered sediments >300 m thick at the base of one of the fans. Stratigraphic relationships with the surrounding plateau show that the valleys are hesperian in age (3.0–3.7 ga), thus dating the lake activity to this period. The coexistence of a deep lake and phyllosilicates demonstrates that persistent bodies of liquid water were present during the hesperian period.