Stealth quasi-circular depressions (sQCDs) in the northern lowlands of Mars

While QCDs are quasi-circular depressions revealed in the Mars Orbiter Laser Altimeter (MOLA) gridded data set, "stealth QCDs" (sQCDs) are those QCDs that have no obvious structural representation in visible images of Mars. It has been suggested that sQCDs are surface representations of buried impact craters, and on the basis of this assumption, size-frequency distributions of all QCDs in the northern lowlands have been constructed to date the buried lowland floor. Expanding upon previous studies of stealth QCDs around the Utopia Basin, 446 sQCDs with diameters ranging from 7 to 115 km have been identified in the northern lowlands of Mars. The direct relationship of sQCD surface relief to diameter indicates that stealth QCDs form due to differential compaction of a cover material over buried impact craters. A comparison of sQCD location to the geologic map of the northern lowlands reveals that stealth QCDs are only located in geologic units predicted to be capable of differential compaction, consistent with models of their formation. The slope of the trend of the sQCDs surface relief versus diameter has a coefficient of determination (R2) approaching 1, when sQCDs are evaluated by geologic unit and by regions of inferred comparable cover thickness. Trend-slope analysis also indicates that the lowland cover material is thickest in the Scandia region and the center of the Borealis and Utopia basins and thinnest in Isidis Planitia and north of Arabia Terra.