The structural, stratigraphic, and paleoenvironmental record exposed on the rim and walls of Iazu Crater, Mars

摘要

Iazu is a 6.8 km diameter crater located ~25 km south of Endeavour Crater in Meridiani Planum, Mars. The asymmetrical ejecta deposit and crater shape demonstrate that Iazu was formed by the impact of a projectile moving from west to east at 20 to 30° above the horizontal. The crater rim and walls expose an ~115 m thick section of intact banded bright and dark Burns formation polyhydrated sulfate deposits that overlie a lower section of basaltic crust of unknown thickness that has been slightly altered to Fe~(3+)-Mg~(2+) smectites. The lower section also exhibits several basaltic outcrops that are overlain by banded bright and dark layers similar in appearance to the bright and dark bands evident in the overlying Burns formation. We interpret the lower section as indicative of a transition from regional-scale fluvial activity to accumulation of sulfate-rich deposits, culminating in a thick overlying section of Burns formation strata. Banding in the Burns formation and underlying strata is inferred to be a consequence of periodic variations in sulfate-forming depositional environments.