PERIGLACIAL “ICE” COMPLEXES IN THE HALE CRATER, MARS, AND THE STRATIGRAPHY OF MELT-WATER ACTIVITY AT OR NEAR THE CRATER-RIM SURFACE

The Hale Crater in the southern hemisphere of Mars, immediately northeast of the Argyre impact-crater, is best known for the occurrence of recurring slope lineae and the possibility that the presumed hydrological activity at the central peaks where the RSLs are observed is recent if not episodically ongoing. Here, we report the close spatial and possible cryo-hydrological-association of the following features on the northern rim-(slope) materials of the crater: a) jagged-edged, metre-to decametre-wide blocky masses akin to active-layer detachments; b) scar-like depressions upslope of the blocky masses; c) small-sized (~5-15m in diam.) polygons possibly formed by thermal-contraction cracking; d) rimless, tiered and polygonised depressions consistent with thermokarstic-processes and the loss of near-surface volatiles; and, e) gullies (sometimes polygonised) with sinuous channels and intricately-braided debris-aprons. Similar assemblages are observed on Earth in cold-climate, non-glacial regions such as the Yamal Peninsula in eastern Russia and are referenced as “ice-complexes.” The term designates the current/past presence of meltwater at/near the surface to metres/decametres of depth and identifies freeze-thaw cycling/frost action as key variables in landscape revision.

Stratigraphically, the rim features exhibit a set of complex traits and relationships. For example, the blocky masses and tiered depressions are observed at a lower relative-elevation where a light-toned surface mantle, comprised of talus, ice-dust or a sublimation lag, has eroded or ablated. Similarly, the small-sized polygons are seen only on gully-incised terrain, terrain adjacent to the gullies or within the tiered depressions. On the other hand, nowhere do the polygons overprint gully-channel flows or aprons. Gully-apron morphology is dichotomous. Some aprons are intact; others are truncated by the tiered depressions or by the exposure of bedrock, where the mantle-incised terrain has been removed.

We present a possible geochronology of late (and local) Amazonian Epoch landscape-development at the Hale Crater. It bridges the morphological divide between periglacial, glacial and fluvial processes and suggests that the linking strand is liquid water at/near the surface of the rim materials.