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.