NASA TECHNICAL MEMORANDUM THE STRATIGRAPHIC SEyllENCE OF VOI-CPNIC AND SEDIMENTARY UNITS IN THE NOR1 rl POLAR REG ION OF WRS (IASA-T!l-78254) THE STR ATTGRRPHTC SEQWENCF NRO- 17004 OF VOLCANIC AND SEDIPIPNTAPY 7YfTS 19 THFZ NORTH POLAR REGION OF PIARS (NASA) 69 p HC AO4/RF A01 CSCL 07E Vncl as G3/91 47039 I. RmtNo 2. Gowrnmont Atcrrtion No. 3. Rsciphnt'r Catalog No. WSA M-WM' I I ud 4. Title P,ubritle 1 L Report Date The St rat igraphic Sequence of Volcanic and Sedimentary Units in the North Polar Region of Mars I 7. Author($) 1 8. PerformingOrprniration Repon No. Michael E. ~otts* I I10. Work Unit No. 1 George C. Marshall Space Flight Center 11. Contract or Grant No. Marshall Space Flight Center, Alabama 35812 . 13. Type of Report and biod Covered Technical Memorandum National Aeronautics and Space Administration Washington, D. C. 20546 14. Sponsoring Agency Coda Prepared by Space Sciences Laboratory, Science and Engintering *universities Space Research Association - 6. Abstract Based on photogeologic mapping of Viking O*;.I~! ter images of Mars, four distinct informal strati- traphic urlits can be defined for the region nort la,,€ 70'~ latitude. liiey are: (a) bulbous plains, b) mantled plains, (c) dune deposits, and (d) LA) red deposits/perel~nial ice. The bulbous plains vnit underlies all other north polar units and represents a sub-unit of the nttled cratered plains. Based on crater slze-frccpency data, bulbous plains is equivalent in age to he relatively old cratered plains unit at Tempu I'l.iteau (9o0w, 30'~). The low albedo of bulbous llains and the appearance of what appears to be a .like suggest that buli~ousplains has a volcanic brigin. Cumulative crater size- frequency distribution functions for bulbvus and mantled plains lispiay two .segment curves with a crater-productior~slope of -2.0 and a cratering-obliteration equilil ium slope of -0.7. This suppoxts the interpretnti~~~rthat mantled plains were formed by dust blanket, .ng of bulbous plains. As calculated from crater SI ,.-frequency distribution functions, the relative 8urface-obliteration rates are le?:88 for bulbous, ~wddratclymantled, and heavily mantled plains, -espectively. The layered deposits probably represent a facies of mantled plail~sin ~hichdust has been leposited onto the perennial ice cap rather than dirrbct ly onto the ground. 'l'hus, the areal extent ~f the layered deposits at the north and south poles ::.~y indicate the maximum extent of the perennial .ce caps as controlled by changes in Martian orbital 1. ~r~imeters. Dune deposits occur in the form of longitudinal, Ilnnsverse, and barchan dunes, and possibly as #beet sand deposits. Actual dunes are generally conf i lied to mantled plains, suggesting that mantling ~rovidesa proper substratum for dune accumulation. Suface winds for the north polar region were dc. 11,ined from dunt orientations to flow pre- lominantly counterclockwise around the polar cap, altht, gh there is evidence for dune modification by iecondary winds spiralling clockwise off of the cap. A gradation from densely spaced transverse dunes i., liiore dispersed barchan and transverse lunes implies a geneid1 thinning of circumpolar dune tlc-p~~~tsdownwind of extensive areas mapped as ~ulbousplains. The author suggests that dune material .. bcing stripped from bulbous plains and is lccu inrlat ing as dunes downwind on mantled plains. '. Kay Weds (Suggested by Authw(sl) 1 18. Distr~butionStatement Mars Aeolian Geology Winds Sand Dunes Crater Counts North Pale 2 I. Security Classif. (of this report! 21. NO. of Pager 22. Rice Unclassified 68 NTIS I I1 I .a IS rl Infurrna~ionService. Springfield, Virginia 22 15 1 ACKNOWLEDGMENTS This research was funded in part by NASA grants NSG-7545 and NSG-7087 from the Planetary Division of The Office of Space Sciences (OSS), NASA Headquarters, to Washington University in St. Louis, Missouri, and was conducted at the NASA Regional Space Imagery Center at Washington University. The results of this research were submitted to Washington University as partial fulfillment of the requirements for the degree of Master of Arts in the Department of Earth and Planetary Sciences. The author is grateful to his thesis advisor, Dr. Raymond E. Arvidson, for his helpful advice and constructive criticism. The final preparation of this report was conducted while the author was engaged in geotechnical research as a Research Associate in the Space Sciences Laboratory, George C. Marshal 1 Space Flight Center, Alabama. The personal interest shown during this tenure by Dr. William W. Vaughan, Chief of the Atmospheric Sciences Division, is acknowledged. Finally, the continued technical and moral support, encouragement, and advice received from Dr. Nicholas C. Cxites, Geotechnical Research Labo- ratory, Space Sciences Laboratory, are greatly appreciated. TABLE OF CONTENTS Page SUWRY ................................ 1 BACKGROUND .............................. 3 Telescopic observations ...................... 3 Mariner mission results ............i .......... 4 Viking mission results (August 1976 .November 1978) ........ 7 DESCRIPTION OF STRATIGRAPHIC UNITS ...................13 Bulbous Plains ........ ; ..................13 Mantled Plains ...........................13 Dune Deposits ...........................14 Layered deposits / Perennial ice ..................14 INTERPRETATION AND DISTRIBUTION OF STRATIGRAPHIC UNITS ........20 Bulbous and mantled plains .....................20 a . Interpretations from visual observations ..........20 b . Cumulative crater size-frequency distributions .......25 Dune deposits ...........................33 Layered deposits ..........................35 Comparisons with previous research .................35 WIND DIRECTIONS ............................39 IMPLICATIONS FOR THE SOURCE OF CIRCUMPOLAR DUNE MATERIAL .......43 CONCLUSION ..............................44 BIBLIOGRAPHY .............................46 APPENDIX A . List of Viking Orbiter imagery used in research .....49 APPENDIX B. Computer programs for crater sire-frequency distributions . 51 Appendix C . Crater size-frequency data ................59 iii LIST OF FIGURES Fiqure Page 1 Mariner 9 mosaic of the north polar region of Mars. .... ...I1 2 Stratigraphic map of the north polar re~ionof Mars ........12 3 Viking Orbiter mosaic of the type area for bulbous plains ....15 4 Viking Orbiter mosaic or the type area for heavily-mantled pldins .I6 5 Viking Orbiter mosaic showing the gradational relationship between bulbous and mantled plains. ..............17 6 Viking Orbiter mosaic showing re1ationshi ps among bulbous plair~s,mantled plains, and dunes ...............18 7 Viking Orbiter mosaic showing the north polar perennial ice cap overlying layered deposits. ..............19 8a Viking Orbiter mosaic shawing a possible dike within lightly- to moderately-mantled bulbous plains .........22 8b Enlargement of a "survivor crater" seen in figure 8a. .......2 3 8c Enlargement of the sqgested dike seen in figure 8a ........24 9a Cumulative size-frcqucrtcy distribution plot for small craters on the type area of bulbous plains seen in figure 3 ......29 9b Cumulative size-frequency distribution plot for small craters on bult~ou:; plains unit seen in figure 6 ....... .30 9c Cumulative size-f requmcy distribution plot for small craters on moder~tely-and heavily-mantled plains .......3 1 9d Composite of cumulative sire-f requency distribution ctirvas wen in fiyres 9a and 9c .........32 10 Viking Orbiter frame 5howing circumpolar dune field typical of area between 130" and 270" W longitude ....37 11 Viking Orbiter frames jt~owingtypical dune field for the circumpolar area between 30' and 130" W longitude ...38 12 Map of dune trends WIthin the north polar region of Mars. .....41 13 Map of near-surface wind directions as inferred from dune orientations in the north polar region of Mars ......42 iv SUMMARY Based on photogeologic mapping of Viking Orbiter images of Mars, four dfstinct informal stratigraphic units can be defined for the region north of 70°N latitude. They are: (a) bulbous plains, (b) mantled plains, (c) dune deposi ts , and (d) 1ayered deposi tslperennial ice. The bul bous plains unit underlies all other north polar uni ts and represents a sub-unit of the mottled cratered plains. Based on crater size- frequency data, bulbous plains is equivalent in age to the relatively old cratered plains unit at Tempe Plateau (90°W, 30°N). The low albedo of bulbous plains and the appearance of what appears to be a dike suggest that bulbous plains has a volcanic origin. Cumulative crater size-frequency distribution functions for bulbous and mantled plains display two-segment curves with a crater-production slope of -2.0 and a crateri ng-cbl iteration equil i brium slope of -0.7. This supports the interpretation that mantled plains were formed by dust blanketing of bulbous plains. As calculated from crater size-frequency distribution functions, the relative surface-obliteration rates are 1:9:88 for bulbous, moderately mantled, and heavily mantled plains, respectively. The layered depsits probably represent a facies of mantled plains in which dust has been deposited onto the perennial ice cap rather than directly onto the ground. Thus, the areal extent of the layered deposits at the north and south poles may indicate the maximum extent of the perennial ice caps as controlled by changes in Martian orbital parameters. Dune deposits occur in the form of longitudinal, transverse, and barchan dunes, and possibly as sheet sand deposits. Actual dunes are