Relationships between lobate debris aprons and lineated valley fill on Mars: Evidence for an extensive Amazonian valley glacial landsystem in Mamers Valles

Abstract

We examine the characteristics and relationships of Lineated Valley Fill (LVF) and Lobate Debris Aprons (LDA) in Mamers Valles on Mars, a ∼950 km-long fretted valley at the dichotomy boundary. The relationships and distinctions between these glacial landforms are established by detailed analysis of LDA/LVF morphology, topography, and related features are assessed to understand their origin and modification. We document the transition from unconfined LDA to compressed and folded LVF and vice versa, implying that LDA and LVF are intimately related in morphology and mode of origin. Linear LDA dominate Mamers Valles, originating from alcoves, theater-like remnant crater rims, and tributary valleys, while circumferential LDA are arrayed around isolated mesas. Narrow valley areas display the convergence of lobes originating from either side, forming parallel linear ridges that deform into complex folds and become LVF, typically in a local and regional downvalley direction. In contrast, when LVF flows out of a topographically confined area, the material forms a piedmont-like LDA. Thus, local topography is the primary factor in determining whether a deposit will appear LVF-like, LDA-like, or have characteristics of both. Superimposed crater morphology and ground-penetrating radar data suggest the current presence of subsurface ice protected by ∼15–20 m of sublimation lag deposits, with minimal deformation and flow since superposed crater formation. Regional integration leads to the interpretation that the LDA-LVF exposures and ice entry points into the fretted valleys represent the waning stages of a more widespread regional Amazonian plateau glacial landsystem that occupied fretted terrain valleys formed earlier in the Late Noachian-Early Hesperian.