TWO POSSIBLE EPISODES OF KARSTIFICATION IN THE EQUATORIAL LAYERED DEPOSITS (ELDS) WITHIN KOTIDO CRATER, ARABIA TERRA (MARS)

This work describes the karst landforms observed in the evaporite Equatorial Layered Deposits (ELDs) located within Kotido crater in Arabia Terra, a portion of the equatorial region of Mars. We present new data and interpretations of the observed sinkholes, compared to previous studies to better understand the formation and evolution of these features. A detailed morphological and morphometric survey of the ELDs surface morphologies was carried out through an integrated analysis of the available images from the High Resolution Imaging Sci- ence Experiment (HiRISE) instrument on the Mars Reconnaissance Orbiter (MRO). More than 650 karst depressions were analyzed in detail, resulting in the detection of two main groups of depressions, displaying different features: smaller depressions are characterized by continuous scarped margins and limited sediment accumulation on the floors, while larger depressions have more degraded margins and thick sediment accumulations including well-developed dune systems. These differences between larger and smaller depressions do not ap- pear to be related to spatial variations in aeolian erosion and deposi- tion rates. Instead, we suggest that these differences can be explained by erosional variations due to the different ages of the depressions. Larger depressions may be older and may have been exposed to deg- radation and aggradation processes for a longer period of time than the smaller and presumably younger depressions. We propose that the karst landforms observed might represent the result of two possible distinct karstification episodes, related to climatic changes during the Amazonian age.