Lineated Valley Fill Surface Textures, Nilosyrtis Mensae, Mars: Comparison with Analagous Glacier Surface Textures in the Antarctic

Introduction: Understanding the formation processes of deformation features originating in association with viscous flow on Mars, including lineated valley fill (LVF), is a key component in the estimation of climate conditions on Mars during its recent history [1-3]. Previous work has focused on estimating temperature conditions from temperature-dependent flow laws [e.g., 1-2]. In order to extract climate data from such features, however, we must first determine which features are structurally controlled (i.e., by flow due to internal deformation) and which are climate controlled (i.e., modification of surfaces by sublimation, aeolian processes, etc.). Previous Work: Mangold [4] considered the evolution of surface textures of lineated valley fill, providing extensive descriptions and interpretations of LVF in Deuteronilus Mensae and interpreting the pit-and-butte texture (10 m tall, flat-topped mounds, 10s of meters wide) as sublimation residue from an ice-rich-dust mantle overlying LVF LDAs. Cracks in the underlying LVF and LDA created by viscous deformation are expressed in the mantling unit as the buried fractures lead to enhanced sublimation in the mantling layer [4]. Nilosyrtis Mensae Observations: We build on the findings of [4] and test them using observations of LDA/LVF units in Nilosyrtis Mensae (33.5°N, 68.5°E) [5]. A prominent lobate structure in the Nilosyrtis Mensae LVF (Fig. 1) is located in the center of a ~5 km wide, N-S trending valley and points down-valley towards the north. The lobe is dominated by a pit-and-butte texture similar to that described by [4]. Along the lobe margin, the pit-and-butte texture appears oriented approximately orthogonally to the margin; however, toward the lobe interior, the texture appears non-oriented (Fig. 1). As observed in [4], buttes are 10s of meters wide with troughs ~10 m wide between each butte; however, high-sun angles and short spaces between buttes prevent accurate heights to be determined by sun-angle measurements. South (up-valley) of the lobe front (Fig, 3), the lobate LVF feature can be traced back to a confluence of four valleys. Pit-and-butte textures are observed in this area, and appear oriented in a lobate fashion along the axis of the main lobe. Along the west margin, the lobate feature transitions from pit-and-butte texture to a smooth texture. The smooth region of LVF is in a topographic low. Down-valley (north) of the lobe-front (Figure 4), the valley 5 LVF abuts valley 6 LVF [5]. The valley 6 LVF is more extensively pitted and with fewer, larger buttes than that observed in the …