Doctoral Dissertations

Date of Award

8-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Devon M. Burr

Committee Members

Chris Fedo, Jeff Moersch, Liem Tran

Abstract

In this dissertation, I document three multifaceted investigations in which I tested hypotheses regarding the formation of crater-interior features on Mars. The first investigation was global in scope. In it, I tested groups of previously proposed formation mechanisms for central pits – centrally located depressions within certain complex craters – based on observed morphologies that would be expected for each. These groups of mechanisms are (A) explosive volatile release, (B) central peak collapse, and (C) drainage of subsurface melted volatiles. The results of inferential statistical tests do not point to any single group of mechanisms as causative of central pits, although they do support some component of central peak collapse in central pit formation. The results of this study suggest that central pit formation may require some combination between these formation mechanisms and/or other untested process(es).

I next tested the hypothesis that central pits hosted paleolakes. This testing was accomplished by inspecting 96 central pit craters with valleys leading to their central pits, previously identified through a global inspection of CTX images. I used a suite of analyses to identify which central pits had the most evidence in support of a paleolake. Such evidence could include (1) outlet channels, (2) polygonal ground suggestive of desiccation cracks, (3) slope characteristics of valley terminal deposits consistent with deltas, (4) grain sizes and grain size spatial distributions consistent with deltas, and (5) spectral signatures of evaporites or hydrated materials. I found two central pits with two lines of evidence and three central pits with one line of evidence in support of such a paleolake. This number of craters is likely a minimum value due to incomplete data coverage and obscuring erosion and mantling deposits, suggesting that >5% of central pit craters globally had lakes.

Finally, I tested the hypothesis that five craters within the Aeolis Dorsa region, which exhibits extensive paleofluvial and aeolian deposits, once hosted paleolakes. To test this hypothesis, I mapped, characterized, and interpreted intracrater sedimentary deposits. I present possible unit origins and discuss similarities with deposits exterior to the craters. Inferred depositional origins include aeolian, fluvial and (potentially) lacustrine environments.

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