Age Variations in the Martian Lowlands

Introduction: Studies by Frey et al. [1,2] and Frey [3,4] indicate the northern lowlands of Mars have been in existence for nearly all of martian history, predating even the very large impacts Hellas, Argyre and Isidis. Large populations of “Quasi-Circular Depressions” (QCDs) were observed in the northern lowlands in MOLA data where few impacts were visible in surface imagery. These “non-visible” QCDs have cumulative frequency curves much like those for visible crater populations in the heavily cratered southern highlands, and are most likely buried impact basins [2-4]. Based on large diameter QCDs, the crater retention age for the lowlands is, on average, no younger than Early Noachian [3-5]. A study has begun of the buried and visible crater populations for areas within the lowlands to determine if there are regional age variations that pearlier global study may not have found. This may have implications for when, and therefore possibly how, different parts of the lowlands formed. If QCD density is constant across the lowlands, the lowlands likely formed by one catastrophic process. If there are distinctly different crater retention ages, then multiple events and/or processes may have been involved. Test Regions: Three spatially distinct areas of approximately 3 million square kilometers were selected within the lowlands. These are shown in Figure 1.