CONSTRAINING CEMENT VOLUME RESPONSIBLE FOR PRESERVATION OF LITHIFIED BEDFORMS ON MARS

Thermal inertia (TI) is an essential tool for understanding the physical nature of planetary surfaces. Ancient lithified bedforms, or paleobedforms, reveal such detail through their TI. These features appear similar to modern dunes, but share characteristics found in lithified rock, such as sharp erosional scarps and retention of meteorite impacts. Many paleobedforms on Mars were likely similar to modern dunes prior to their lithification (Chojnacki et al., 2020). This permits estimation of a paleobedform’s original thermal inertia and grain size (using modern dunes; Edwards et al., 2018). Therefore, paleobedforms present an opportunity to study the change between pre- and post-lithification TI which can be used as a quantitative lithification value.

Complications associated with TI investigations, specifically surface mixtures (e.g., vertical layering), is considered following the methods of Ahern et al., (2021). Little to no heterogeneity most likely exists in a surface when modeled TI from different observations is constant over the day. This ensures the modeled TI, and grain size derived from it, applies to the paleobedform feature and not loose, post-lithification material. Heterogeneity at the surface is handled using a mixture model to identify vertical layering scenarios between paleobedforms and overlaying material.

We have modeled TI for 52 paleobedform sites across Mars using KRC (Kieffer 2013). Low range TI sites (TI<200) are likely representative of some degree of modern dust mantling which might be too thick to ascertain any useful information. Certain sites within intermediate (200>TI>350) and high (TI>350) ranges indicate little to no heterogeneity. The TI of those sites is also greater when compared to modern dunes (e.g., ~180). Taking the evidence these features started out similarly to modern dunes together with lithification traits, we attribute their raised TI to cement agents filling pore space, rather than larger grains. Since our CRISM investigations do not reveal any alteration products within paleobedforms – but we are confident of their presence – the amount of cement is likely under the detection limit of CRISM (5-10%). Constraining the cement volume responsible for paleobedform preservation is the first step in understanding the formation history of these enigmatic features.