Age determination for valley networks on Mars using tectonic-fluvial interaction.

Two areas on Mars in the old Thaumasia region were analysed, where interaction between fluvial and tectonic landforms provided conditions to improve age estimation for valley network formation. An Earth analog terrain was also involved in this work at Villány Hills (Hungary) for reference and to see the relations in tectonic-fluvial interaction. On Mars such interaction was observed by morphology (parallel curvatures of neighbour valleys) and by the comparison of statistical analyses of the fluvial and tectonic lineaments' azimuthal orientation. While in the case of Mars the fluvial network elements' distribution closely follows that of the tectonic elements' distribution, in the case of the Earth the connection is weaker. The comparison gives an interesting example for tectonic landforms controlling fluvial valley orientations, occasionally producing resembling features in valley tracks, influencing the sediment transport and the locations of deposits. Because the tectonic faults crossed a much larger area than the fluvial valleys they influenced, crater size frequency distribution based ages could be better measured with them. Using this approach, we found the minimal age of the fluvial network formation to be around 3.7 Ga (or up to 3.9 Ga). This result demonstrates that the small, scattered, and poorly integrated valleys might also have formed at the same period as the larger, branching systems with well determined ages: around the Noachian/Hesperian transition. Thus valley network formation even in the case of small, non-integrated systems might not necessarily extend into the early or middle Noachian ages and might have happened at a potential climatic optimum around 3.7 Ga ago. However the most difficult task remains the exact dating of old and small valleys at other locations on Mars, to confirm this possibility. • Fluvial-tectonic interaction was analysed on Mars and Earth. • Characteristic lineament orientation distribution was found at both sample sites. • Interaction between tectonic faults and fluvial channels were identified on Mars. • Channels followed more accurately the preformed tectonic directions on Mars. • Calculated age for fluvial activity was 3.7 Ga. [ABSTRACT FROM AUTHOR]