Figure 12. Natural log ratios of APXS data for the Fleurac experiment relative to the nearby rock target, Limeyrat_offset. The data for Fleurac are most like the rock target, followed by the Fleurac_offset, consistent with the visual appearance of rock fragment abundances shown in the MAHLI image (Figure 11). Ratharsair is an APXS target within a ripple trough the edge of the Sands of Forvie and is least like the rock target.
Specifically, the compositions change from more bedrock-like for the Fleurac measurement to less for the Fleurac_offset measurement, consistent with bedrock areal abundances as seen in the MAHLI image (Figure 11). Further, the trend toward more basaltic sand is consistent with the composition of the Ratharsair sand trough measurement obtained during the stop at the northern margin of SoF (see: Weitz et al., 2022).
To further illustrate the contributions of local bedrock, all APXS bedrock and sand measurements in the immediate vicinity of the MDI and SoF sampling locations were analyzed via correspondence analysis (CA) to evaluate relationships between compositional trends and target types (e.g., bedrock or sand). The analysis employed log ratio data to avoid known complications that can arise from normalized data sets (Aitchison, 1994) like APXS compositional data. The data used in the CA analysis for the MDI area were acquired between sols 1596 and 1677. For the SoF area the sol range was 2989‑2994 and 3022‑3047. We note that the sol 1606 Pogy measurement was not included because it is a compositional outlier, and initial analyses suggest the sample is a float rock. Two other measurements, Ash_Island (sol 1638) and Halftide_Ledge (sol 1647) were also excluded as compositional outliers. A CA bivariate plot of the first two most important eigenvector directions captures 84% of the variance in the APXS data set, with locations of targets and oxides shown in Figure 13.