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Proquest Dissertations Investigating The Retention Of Bright And Dark Ejecta From Small Rayed Craters On Mars Item Type Thesis Authors Calef, Fred J., Iii Download date 03/10/2021 20:54:46 Link to Item http://hdl.handle.net/11122/9048 INVESTIGATING THE RETENTION OF BRIGHT AND DARK EJECTA FROM SMALL RAYED CRATERS ON MARS By Fred J. Calef III RECOMMENDED: Advisory Committee Chair i Chair, Department of Geology and Geophysics APPROVED: Jean of the Graduate School X 2,0/0 Date INVESTIGATING THE RETENTION OF BRIGHT AND DARK EJECTA FROM SMALL RAYED CRATERS ON MARS A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Fred J. Calef III Fairbanks, Alaska August 2010 UMI Number: 3436654 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI 3436654 Copyright 2010 by ProQuest LLC. All rights reserved. This edition of the work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Abstract Impact cratering is one of the principal geologic processes operating throughout the solar system. On Mars, small rayed impact craters (SRC) form continuously and randomly on the surface. Ejecta retention, the timespan and ability of excavated ejecta to remain in place around a crater rim, records a lineage of recent surface processes. However, the timescales under which small rayed craters are produced and their origin, whether terrestrial or cosmic, plays an important role in further investigating surface processes and possible recent climate variations. By examining thousands of randomly chosen panchromatic images from the Mars Orbiter Camera Narrow Angle (MOCNA) camera, a population of 630 SRC was catalogued across three equatorial and two polar regions on Mars. The survey of MOCNA images also revealed intriguing Enigmatic Linear Features (ELFs) in the northern hemisphere of Mars, which a short side study revealed to be a unique form of dust-devil track. From statistically examining several physical parameters, dust deposition and periglacial erosion were found to be the major factors affecting ejecta retention for the SRC. SRC morphology revealed ejecta retention sequences that followed four stages of ejecta retention from the initial impact to eventual erasure from the surface. By reconstructing the current cratering rate from estimates of atmospheric filtering, it was possible to calculate the ejecta retention age across Mars. In general, SRC ejecta are retained on the surface for <100 ka. Based on ejecta morphology and retention age estimates, a possible shift from depositional to erosional processes just south of the Martian equator is suspected to have occurred within this timeframe. Table of Contents Page Signature Page ............................................................................................................................ i Title Page ....................................................................................................................................ii Abstract......................................................................................................................................iii Table of Contents ......................................................................................................................iv List of Figures ........................................................................................................................... ix List of Tables ..........................................................................................................................xiv Acknowledgements ................................................................................................................ xvi GENERAL INTRODUCTION.................................................................................................1 REFERENCES.......................................................................................................................... 7 CHAPTER 1: Enigmatic Linear Features in the Northern Hemisphere of Mars: Their Formation Process ......................................................................................................................9 ABSTRACT............................................................................................................................... 9 1.1 INTRODUCTION.............................................................................................................10 1.2 STUDY AREA..................................................................................................................11 1.3 METHODOLOGY............................................................................................................12 1.4 RESULTS.......................................................................................................................... 13 1.4.1 General Observations ........................................................................................ 13 1.4.2 Population Statistics .......................................................................................... 15 1.4.3 Orientation Analysis ......................................................................................... 16 1.5 DISCUSSION....................................................................................................................16 V 1.6 CONCLUSION................................................................................................................18 REFERENCES........................................................................................................................ 19 TABLES...................................................................................................................................21 FIGURES..................................................................................................................................24 CHAPTER 2: Geomorphic Analysis of Small Rayed Craters on Mars: Examining Primary versus Secondary Impacts ........................................................................................ 30 ABSTRACT............................................................................................................................. 30 2.1 INTRODUCTION............................................................................................................ 32 2.1.1 SRC Primary and Secondary Populations ....................................................... 35 2.1.2 Geologic Setting .................................................................................................36 2.2 METHODOLOGY........................................................................................................... 38 2.3 OBSERVATIONS............................................................................................................ 43 2.3.1 Primary SRC......................................................................................................43 2.3.2 Secondary SRC ................................................................................................. 46 2.4 RESULTS..........................................................................................................................48 2.4.1 Crater Measurements ........................................................................................49 2.4.2 Ejecta Measurements ........................................................................................50 2.4.3 Directional Analysis ..........................................................................................52 2.5 DISCUSSION....................................................................................................................53 2.5.1 Differences between Primary and Secondary Ejecta Retention ................... 53 2.5.2 Similarity of Primary and Secondary Crater Rims ........................................ 61 2.5.3 Identification of New Primary Cratering Events ........................................... 62 2.5.4 Crossover between Primary and Secondary Cratering Events .................... 63 2.6 Conclusions ......................................................................................................................68 REFERENCES........................................................................................................................69 TABLES...................................................................................................................................79 FIGURES..................................................................................................................................80 CHAPTER 3: Global Distribution of Small Rayed Craters on Mars: Sequences of Ejecta Retention .................................................................................................................................109 ABSTRACT............................................................................................................................109 3.1 INTRODUCTION...........................................................................................................112 3.1.1 Small Impact Craters as Tools for Understanding Current Surficial Processes ...................................................................................................................
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