The gradational history of southern Ismenius Lacus

Abstract

Two epochs of accelerated gradation affected the geomorphic evolution of southern Ismenius Lacus. These periods of enhanced gradational activity were likely related to periods of more clement climate induced by release of either recycled exogenic or juvenile endogenic atmospheric volatiles. Variations in the intensity and duration of gradation during the second epoch are indicated by the variability in the timing of cessation and degree of air fall deposit removal across the study area. Overall intensity of gradation decreased through successive epochs based on: (1) the decreasing diameter at which cumulative statistics from the respective surfaces cease to follow the expected production function; and (2) the decrease in size/increase in density of preserved valley networks incised into surfaces of differing age. A comparable decrease in valley density with time has been noted in the Isidis region