Age determination of linear surface features using the Buffered Crater Counting approach – Case studies of the Sirenum and Fortuna Fossae graben systems on Mars

Buffered Crater Counting (BCC) offers a possibility to determine ages of linear/curvilinear surface features that provide no or only very limited surface areas for the conventional crater counting approach. In this study we applied the BCC analysis to two tectonic fault systems, Fortuna Fossae and a subsection of Sirenum Fossae. We compared BCC results with age estimates derived from conventional crater counting on the surrounding geologic units and investigated to what extent crater ejecta blankets can be used for determining the stratigraphic placement of craters pre- or post-dating the formation of linear features. Furthermore, we introduce a new functionality of the CraterTools software for ArcGIS which allows for a user-friendly semi-automatic application of the otherwise time-consuming procedure of BCC analysis. The software provides the resulting crater size-frequency data in a standard format, which can be read and analyzed in the CraterStats analysis software. se studies showed that the BCC approach provides equivalent or even more precise age results compared to the conventional stratigraphic approach. Here, we found that the investigated section of Sirenum Fossae is younger than previously thought. The derived formation age from the BCC analysis is 3.44 - 0.25 + 0.1 Ga which corresponds to Late instead of Early Hesperian. Fortuna Fossae formed shortly after the emplacement of its now-fractured geologic host unit (Late Hesperian). Ages derived from BCC analysis vary between 3.53 - 0.11 + 0.06 Ga and 3.50 - 0.11 + 0.07 Ga . Furthermore, we recommend the use of crater ejecta blankets to position them in the stratigraphic sequence in order to improve crater statistics. However, the accuracy of the results depends on the extent and preservation state of the continuous ejecta blankets in the region of interest. Thus, the applied buffer width has to be chosen carefully according to investigated crater sizes and local observations.