Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

Brian M. Hynek

Second Advisor

Philip J. Armitage

Third Advisor

David A. Brain

Abstract

The presence of valley networks across much of the ancient surface of Mars, together with the locations and morphologies of the ancient Martian deltas and paleolakes, provides strong evidence that the Martian surface environment was once capable of sustaining liquid water at the surface. Many of the largest valley networks have characteristics consistent with their formation primarily by precipitation and surface runoff. However, the timing and duration of clement conditions on Mars has remained unclear. Ten of the largest valley networks on Mars were mapped, crater-age dated, and analyzed to understand changes in fluvial erosion during early Martian history. Crater-age dating of individual valley networks revealed ages that cluster in the Late Noachian and Early Hesperian, consistent with their formation during a period of enhanced fluvial erosion and incision on Mars. Formation timescales of the valley networks were investigated through the use of three different sediment transport models, the Darcy-Weisbach flow velocity equation, and a variety of parameters to encompass a range of possible formation conditions. With runoff rates similar to intense storms in arid regions on Earth, the minimum formation timescales of these Martian valley networks range from 10^5 to 10^7 years. Shorter formation timescales require hurricane-scale flows that, if minimized with assumptions of continuous formation unlike even terrestrial rates, could complete large valley network formation in as little as 200 to 5000 years, though this is not the preferred interpretation. Investigating the effects of changing hydrologic and sedimentary conditions on Martian delta formation with 3-D modeling indicates that significant off shore sedimentation is common, particularly with high river discharge scenarios. These results have important implications for the formation timescales of the deltas and the lack of identifiable deltas on Mars today. While the results of this thesis do not support impact-induced climate change as the mechanism for creating precipitation sufficient to incise the large valley networks, neither do they extend the amount of time required to form the features beyond their range in age, consistent with hypotheses that precipitation was constrained to a relatively short period of Martian history near the Noachian-Hesperian boundary, approximately 3.6 to 3.8 Ga.

Share

COinS