SEDIMENTARY SOURCES AND TRANSPORT SYSTEMS IN THE LATE NOACHIAN OF MARS: TESTING COMPETING CLIMATE SCENARIOS

Abundant evidence exists for extensive fluvial, lacustrine and eolian sedimentary environments and sediment transport and deposition systems during the Late Noachian period of early Mars history, suggesting a warm and wet climate, unlike today. Recent global climate models with a faint young Sun, however, have been unable to reproduce warm and wet conditions. Instead they predict extremely cold temperatures (~225 K); with atmospheric pressure above a few tens of millibars, atmospheric-surface thermal coupling is induced and adiabatic effects cause water vapor to be deposited in the highlands, leading to the “Late Noachian Icy Highlands” (LNIH) climate model. How to distinguish between these two end-member models? We utilize the conceptual framework of sedimentary sources and transport systems in order to test these models. We use the extremely cold and dry climate of the McMurdo Dry Valleys (MDV) and adjacent cold-based glaciers as a process analog for the “Cold and Icy” model, and explore the predictions of this model for sediment sources, rates of erosion, transport pathways and sediment sinks. Key aspects of the predictions of the MDV based “Cold and Icy” scenario (1) include: 1) top-down cold-based glacial melting and runoff during punctuated heating scenarios (e.g., volcanism, impact); 2) localized sources of meltwater dictated by glacial equilibrium line altitude and local ice accumulations and topography; 3) fluvial erosion style altered by the presence of a shallow permafrost ice table underlying loose soil (stream vertical incision followed by lateral migration along top of ice table); 4) stream and lake waters dominated by a high flux of glacial meltwater rather than leached stream substrate chemistry; 5) a simplified hydrological cycle/system dictated by extreme climate and topography stability; 6) reuse of existing channels during repeated ice-melting episodes; 7) eolian modification, transport and deposition related to katabatic winds from the ice deposits. We then compare these predictions to a “Warm and Wet” climate scenario using a range of arid-semiarid to temperate climate process analogs.

(1) J. Head & D. Marchant (2014) The climate history of early Mars: Insights from the Antarctic McMurdo Dry Valleys hydrologic system, Antarctic Science, 26, 774-800, doi: 10.1017/S0954102014000686.