Presentation #515.05 in the session Mars Surface (iPosters).
The north polar layered deposits (NPLD) and Basal Unit make up the plateau of Planum Boreum, and they record deposition and erosion history in stacks of layers. The layers differ in the fractions of ice, dust, and sand, and those variable properties create dielectric contrasts that are observable as radar reflectors. Understanding these layers provides insights into the recent climate processes of Mars. Previous work has found that observed transitions between erosion and accumulation can result in unconformities that are observed at the surface by optical instruments and subsurface by Shallow Radar (SHARAD).
We use a three-dimensional (3D) Shallow Radar data set to understand the stratigraphy of the NPLD. We mapped two radar reflectors called R25 and R29 across most of the NPLD and compared the results with the previous results using 2D SHARAD data to identify whether 3D interpretations agree with the prior interpretations. The 3D data volume has better identification and interpretation of buried deep structures like chasma, outcrops & promontories, and also fine-scale detailing of the reflectors due to changes in the amplitude that are better identified with this data. 2D analysis from 2015 was unable to trace reflectors to the extent that is achieved by 3D data, and interpretations are improved. We identify many features, including the reflector interactions with spiral trough migration, which breaks observe as breaks in continuity. These give us a story about the surface processes at the time when the troughs become established. We observe that R29 is spatially more extensive and continuous than R25, suggesting that R29 was deposited before many of the troughs had fully developed or even began development, giving us a stratigraphic sequence that pinpoints when many of the troughs initiated.
To support radar interpretations, the second part of this study aims to understand how radar mapped reflectors appear when exposed as visible layering in outcrops, at scarps and troughs. We identify at least three locations where the R25 and R29 reach the surface, and from there we are able to interpret more about the surface activity at the time of spiral trough initiation. At these outcrops, we identify scalloped cliff faces in the NPLD layers that belong to layers that appear to always immediately follow a stratigraphic unconformity.