The Evolution Of East Candor Chasma Valles Marineris Mars Proposed Structural Collapse And Sedimentation

Abstract

Valles Marineris (VM), Mars has a long history of sedimentary deposition. East Candor Chasma is located on the eastern flank of Valles Marineris. Previous studies of the chasma suggests a complex geological history of collapse and basin infill. Interior Layer Deposits (ILDs) in East Candor Chasma span over 475 km long, 145 km wide and range in elevation from -5.5 km to 3.5 km at datum. The ILDs can be separated into six different unit varieties-massive, thick layer unit, thin layer unit, steeply inclined unit, deformed layer unit, and thin mesa unit. The massive unit contains no visible layering and a distinct erosional style. Thick layer units are found overlying the massive unit and tend to thin upwards within the mound. The thin layer unit overlies the thick layer unit and can be observed truncating thick layering. A steeply dipping unit is anomalous and found only in one mound within the chasma. A Deformed layer unit is commonly observed along the walls of the chasma indicating post erosional slumping. A thin mesa unit is thought to be a late ash cover which conformably drapes all pre-existing geology. Unconformities are observed throughout the chasma, three occur at an elevation of ~1000 m within the thick layer unit. This indicates the chasma likely underwent multiple periods of erosion and deposition. Attitude measurements taken within the layered units of the central mounds reveal a possible secondary collapse along the north wall of the chasma. The lower stratigraphic section along the north face of the central mounds reveals dips of ~20˚, indicating that the massive unit was likely eroded prior to thick layer unit deposition. These observations can be used to interpret the geological history of East Candor Chasma. We suggest that a secondary collapse occurred along the north wall of the chasma after the massive unit was emplaced. Sedimentation and erosion continued after chasma collapse allowing for the emplacement of layer and thin mesa units. Two models for the history of East Candor Chasma are presented.