Ancient River Channels in Arabia Terra, Mars

Mirino, Melissa (2022). Ancient River Channels in Arabia Terra, Mars. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.000148c5

Abstract

‘Inverted channels’ on Mars are sinuous ridges that represent ancient river systems that were buried, preserved, and then exhumed. Many inverted channels occur in Arabia Terra, one of Mars’ oldest regions (about 3.7 Gyr), but precise information about their morphologies, spatial variation, settings, and associated terrain attributes is missing. Since these channels date from a period when Mars’ environment was very different than today’s, understanding how and when they formed can help us interpret Mars’ ancient fluvial and paleo-climatic history.

This thesis presents new results about the morphology, distribution, erosion-styles, and pervasive fracturing of fluvial inverted deposits in Arabia Terra. It reports the results of a regional morphological classification of fluvial ridges and concludes that many were aggradational fluvial systems, formed within the downstream portions of valley networks, or other basins and topographical lows. These locations are analogous to ‘Transfer’ and ‘Depositional’ zones in fluvial systems on Earth. Next, detailed morphostratigraphic mapping (scale 1:2000) of four Mid-Late Noachian martian inverted fluvial systems reveals the presence of long-lived (10⁴ - 10⁶ years) stable fluvial systems, where valley network incision is not preserved.

The volume of alluvial material was estimated for each detailed mapping site and extrapolated to the regional survey database. At least 549-1591 km³ of fluvial-alluvial deposits are still preserved in Arabia Terra. This supports the interpretation that Arabia Terra hosted widespread fluvial activity during parts of the Noachian. Finally, extensive networks of indurated veins and infilled fractures, and “pitted channel” types were found to occur in the study area. I interpret these to have formed by groundwater flows, which demonstrate the influence of groundwater on the landscape, after the development of the inverted channel deposits.

The study favours the existence of a stable hydrological cycle driven by precipitation in a warmer and wetter climate than seen today on Mars.

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