Can Structural Tilt Be Measured From Exhumed Channel Belts on Mars? Numerical Experiments Using Analog Alluvial Strata

Basin-filling strata are Mars's historical record of depositional events, including sedimentation by alluvial rivers, and post-depositional events, including tilting. Measuring stratal tilt on Mars could constrain post-depositional processes, but is difficult to measure where exposures are 3D and lack clear stratal surfaces, as is often the case for martian alluvial deposits. Channel belts exhumed from alluvial strata and exposed as erosional landforms called fluvial ridges have been proposed to have near-horizontal along-ridgetop profiles except where post-depositionally tilted. However, recent work has demonstrated that differential erosion sets ridge topography. Here, we tested the effects of differential erosion and structural tilting on fluvial-ridge longitudinal profiles. We numerically tilted an Earth-analog 3D-seismic-reflectance volume imaging alluvial channel belts to 60 orientations, with dips from 0.5 to 30° toward the cardinal directions. We used a landscape-evolution model to erode each volume, generating fluvial ridges. We fit planes to ridgetop longitudinal profiles to compare plane orientations to the imposed tilt. We found that dips of 1°–4° produce ridgetops with topography that matches structural tilt well when averaged over dozens of ridges across several km². However, volumes tilted only 0.5° produce a similar range of apparent tilts when remote-sensing uncertainty is accounted for. Steeper tilts bias channel-belt preservation toward those oriented along strike, which contain little information about dip, creating a mismatch between imposed tilt and ridge topography even before the preservation bias becomes visually obvious. We emphasize that ridgetops are neither paleochannel beds nor stratal surfaces, but erosional surfaces carved into strata.