Geological and hydrological histories of the Argyre province, Mars

The geologic history of the multi-ringed Argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative-age dating of rock materials and structures. The impact formed a primary basin, rim materials, and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin, as well as structurally-controlled local basins. Since its formation, the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice, debris flows, and groundwater through and over its basement structures. The basin is interpreted to have been occupied by lakes, including a possible Mediterranean-sized sea that formed in the aftermath of the Argyre impact event The hypothesized lakes froze and diminished through time, though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time. At its deepest, the main Argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the Sun, but with impact-induced hydrothermal heat, geothermal heat flow due to long-lived radioactivities in early martian history, and concentration of solutes in sub-ice brine, liquid water may have persisted beneath thick ice for many millions of years. Existence of an ice-covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions. The Argyre rock materials, diverse in origin and emplacement mechanisms, have been modified by impact, magmatic, eolian, fluvial, lacustrine, glacial, periglacial, alluvial, colluvial, and tectonic processes. Post-impact adjustment of part of the impact-generated basement structural fabric such as concentric faults is apparent. Distinct basin-stratigraphic units are interpreted to be linked to large-scale geologic activity far from the basin, including growth of the Tharsis magmatic-tectonic complex and the growth into southern middle latitudes of south polar ice sheets. Along with the migration of surface and sub-surface volatiles towards the central part of the primaiy basin, the substantial difference in elevation with respect to the surrounding highlands and Tharsis and the Thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation, even today. In addition, the impact event caused long-term (millions of years) hydrothermal activity, as well as deep-seated basement structures that have tapped the internal heat of Mars, as conduits, for far greater time, possibly even today. This possibility is raised by the observation of putative open-system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures. Long-term water and heat energy enrichment, complemented by the interaction of the nutrient-enriched primordial crustal and mantle materials favorable to life excavated to the surface and near-surface environs through the Argyre impact event, has not only resulted in distinct geomorphology, but also makes the Argyre basin a potential site of exceptional astrobiological significance. (C) 2015 Elsevier Inc. All rights reserved.

Overdeepened glacial basins as archives for the Quaternary landscape evolution of the Alps

The Alps and the Alpine foreland have been shaped by repeated glaciations during Quaternary glacial-interglacial cycles. Extent, timing and impact on landscape evolution of these glaciations are, however, poorly constrained due to the fragmentary character of terrestrial archives. In this context, the sedimentary infills of subglacially eroded, ‘overdeepened’, basins may serve as important archives to complement the Quaternary stratigraphy over several glacial-interglacial cycles. In this thesis, the infills of deep subglacial basins in the Lower Glatt valley (N Switzerland) are explored to better constrain the Middle- to Late Pleistocene environmental change. Five drill cores gave direct insight into to the up to ~200 m thick valley fill at the study site and allowed for detailed analysis of sedimentary facies, age and architecture of the basin fills. A first focus is set on the sedimentology of coarse-grained diamicts with sorted interbeds overlying bedrock in the trough center, which mark the onset of deposition in many glacial bedrock troughs. Evidence from macro- and microsedimentology suggests that these sediments are emplaced subglacially and reflect deposition, reworking and deformation in response to repeated coupling and decoupling of the ice-bed interface promoted by high basal water pressures. Overlying these subglacial sediments, large volumes of sandy glacio-deltaic, fine-grained glacio-lacustrine and lacustrine sediments document sedimentation during glacier retreat from the basins. On these thick valley fill sequences the applicability and reliability of luminescence dating is investigated in a second step on the basis of experiments with several different luminescence signals, protocols and experiments to assess the signal stability. The valley fill of the Lower Glatt valley is then grouped into nine depositional cycles (Formations A-I), which are related to the Birrfeld Glaciation (~MIS2), the Beringen Glaciation (~MIS6), and up to three earlier Middle Pleistocene glaciations, tentatively correlated to the Hagenholz, Habsburg, and Möhlin Glaciations, according to the regional glaciation history. The complex bedrock geometry and valley fill architecture are shown to be the result of multiple erosion and infilling cycles and reflect the interplay of subglacial erosion, glacial to lacustrine infilling of overdeepened basins, and fluvial down-cutting and aggradation in the non-overdeepened valley fill. Evidence suggests that in the study area deep bedrock incision, and/or partial re-excavation, occurred mainly during the Beringen and Hagenholz Glaciation, while older structures may have existed. Together with the observation of minor, ‘inlaid’ glacial basins, dynamic changes in the magnitude and focus of subglacial erosion over time are documented.