MINERALOGY OF A CEMENTED INVERTED CHANNEL, ATACAMA, CHILE: CLUES TO ITS FORMATION THE FORMATION OF A MARS-ANALOG LANDFORM

Understanding the armoring and preservation mechanisms of inverted channels on Earth may allow us to better understand the environment on Mars. The WIN ridge in the Pampa del Tamarugal Region of the Atacama Desert, Chile, is the inverted form of a channel that incised into Pleistocene playa deposits. It is located near the distal end of fluvial deposits sourcing from the Andes Mountains to the east and is flanked by yardangs consisting of friable material. In contrast to other inverted channels in the area, the WIN ridge is not armored by gravel, but instead exhibits resistant Ca-sulfate cements both at the surface and throughout its volume. In this work, we provide compositional information acquired with XRD and VNIR (0.35-2.5 µm) spectroscopy of a vertical transect of the WIN channel. We find anhydrite to be pervasive throughout the transect, exhibiting average abundances of almost 70 wt%. Quartz, plagioclase, and mica (likely felsic detritus sourced from the Andes to the east), extend from the base of the ridge at 330 cm depth up to 55 cm depth, and account for almost 20 wt%. Between 55 cm depth and the surface, plagioclase and mica become absent, and quartz diminishes in abundance from 10-30 wt% to 2-4 wt%. The remaining material, consisting of glauberite, gypsum, halite, and jarosite, is distributed in overlapping horizons: a halite + glauberite horizon extends from the surface to about 29 cm depth where it transitions into a jarosite horizon that in turn extends to 95 cm depth. Finally, a thin halite horizon occurs at about 95 cm depth. Gypsum appears on the exposed surface of the top layer only, and is likely derived from the interaction of anhydrite with atmospheric water vapor. Additionally, a cm-thick layer of anhydrite-rich cement is draped along the escarpments of the ridge, occurring a few cm below the talus. The abundance of anhydrite within the WIN section exceeds the amount expected from pore-filling cement and likely records a slowly aggrading evaporite sequence associated with ephemeral flows within the channel. The gradational nature of the transitions in salt mineralogy, and the draping cement suggest a subsequent groundwater story.