•; LIBRARY. .1. Summary of Lunar Stratigraphy- 1 Telescopic Observations --.· By DON E. W~LHELMS ., CONTRIBUTIONS TO ASTROGEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 599-F Prepared on behalf of the National Aeronautics and Space A dminz"stration \ UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretar:v Y;'I GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 77-608123 For sale by the Superintendent of Documents, U.S. Government Printing . , .. ~Office, .Washington, D.C.. 20402- Price 60 cents (paper cover) ). CONTENTS Page Page F1 ~bstract ----------------------------------------- Lunar stratigraphic column-Continued Introduction -------------------------------------­ 2 Imbrian System-Continued Previous work-------------------------------- 3 Terra units of the Theophilus quadrangle F29 ~cknowledgments ----------------------------- 6 nfare material (formerly Procellarum Group) 29 ~pplication of stratigraphic principles to the moon __ 6 Nomenclature -----------------------­ 30 Properties and sequence of lunar material units-­ 6 nfare materials with topographic relief _ 32 Lunar time-stratigraphic and geologic-time units _ 9 ~penninian and ~rchimedian Series -------- 32 Separation of observation and interpretation ___ _ 9 Imbrian or Eratosthenian Systems -----------­ 33 Types of geologic units -------------------­ 11 Dark terra-mantling units ---------------­ 33 nfap conventions ------------------------- 11 . Units with intrinsic relief ---------------- 33 Lunar stratigraphic column ---------------------- 12 Eratosthenian and Copernican Systems -------­ 36 13 General observations -------------------------­ Crater materials ------------------------­ 36 15 Pre-Imbrian units ---------------------------­ nfantling materials ---------------------­ 37 Pre-Imbrian and (or) Imbrian units ---------- 22 Plains-forming materials -----------------­ 37 ..,.. 23 Imbrian System ------------------------------ Units with intrinsic relief ---------------- 37 Definition and general features -----------­ 23 39 Fra nfauro Formation -------------------­ 23 Slope material --------------------------- 39 Definition ---------------------------- 25 nfiscellaneous units --------------------------­ 39 nfembers ----------------------------- 25 ~bandoned names ---------------------------­ 40 Interpretation ------------------------ 27 Crater material subunits ---------------------- Cayley and ~pennine Bench ~ormations ___ _ 27 Summary and-· conclusions ..,..,., __ _,,__,..; __ ..:...:_~...;.:. __ .:... __ .:.. __ _ 42 45 ··( Crater materials ------------------------­ 28 References cited ---------------------------------­ Materials near the Orientale basin --------- 28 Preliminary lunar geologic maps ------------------ 47 ILLUSTRATIONS Page FIGURE 1. Index map showing status of mapping at the 1:1,000,000 scale as of late 1967-------------------------- F2 2. Photomosaic of part of the lunar near-side showing areas covered by illustrations in this report_ _______ _ 4 3. Photograph of the craters Copernicus and Eratosthenes and vicinity under low-sun illumination _________ _ 8 4. Photograph and geologic sketch map of the vicinity of the crater ~rchimedes ___________ _: _____________ _ 10 5. Rectified photograph of nfare Imbrium and its multiringed basin _____________________________________ _ 14 6. Photograph of nfare IIumorum ______________________ ~---------------------------------------------- 19 7. Lunar ~stronautical Chart of IIyginus rille-------------------------------------------------------- 20 8-14. Photographs of: 8. Central part of moon showing "Imbrian sculpture" -------~------------------------------------ 21 9. The ~pennine nfountains and terra peninsula extending southward _____________________________ _ 24 10. The type area of. the Fra Mauro Formation __________________________________________________ _ 26 11. Flow lobes in Mare Imbrium----------------------------------------------------------------- 31 12. The craters Copernicus and Eratosthenes and vicinity under near-full-moon illumination__________ _ 34 13. The ~ristarchus plateau and IIarbinger Mountains ------------------------------------------- 35 14. Part of the crater Theophilus and the Theophilus Formation ---------------------------------- 38 15. Example of map explanation box for crater material subunits --------------------------------------- 41 TABLES Page TABLE 1. Composite lunar stratigraphic columnar section showing most units discussed in text ---------------- F16 2. Formally defined lunar stratigraphic names ---------------------------------------------------------- 39 3. Stratigraphic names that have appeared in Geological Survey publications but have not been defined formally 40 iii CONTRIBUTIONS TO ASTROGEOLOGY SUMMARY OF LUNAR STRATIGRAPHY-TELESCOPIC OBSERVATIONS By DON E. WILHELMS ABSTRACT pre-Imbrian basins, but greater degradation hinders their The geology of much of the moon has been mapped from recognition. the earth by means of telescopic photographs and observa­ Sufficient time elapsed between the formation of each mar~ tions. This mapping is based on the premise that the lunar basin and the completion of its flooding by the dark smooth crust is composed of material units that can be defined by material called mare material for extensive units to form. physical properties and ranked in order of relative age by Those units in or near the Imbrium and Orientale basins are application of the principles of stratigraphy. Units are of Imbrian age, whereas those in the pre-Imbrian basins may ranked locally by their superposition and transection relations be either pre-Imbrian or Imbrian in age. The most common and both locally and regionally by subordinate criteria such units are crater materials and light plains-forming materials. as density of superposed craters and degree of topographic Crater materials include those of Archimedes in the Imbrium y.· freshness. basin and of Gassendi in the Humorum basin. Light plains­ A moonwide stratigraphic column of material units has forming materials of Imbrian age include the Apennine been divided into approximate and tentative time-strati­ Bench Formation on the shelf south of Archimedes and the graphic ·units, whose type areas are near the craters Coper­ Cayley Formation in troughs surrounding the Imbrium basin. nicus, Eratosthenes, and Archimedes. The oldest time-strati­ Most light plains-forming materials are confined to depres­ graphic unit is the pre-lmbrian (not a formal system), sions or low plateaus. Other light materials of probable followed by the lmbrian, Eratosthenian, and Copernican Imbrian age form undulating or rolling topography and Systems. elevated plateaus. Pre-Imbrian materials have a subdued topography and are The top of the mare material between the craters Eratos­ highly cratered. Most are associated with craters and circular thenes and Archimedes has been used to define the top of the multiringed mare basins. Many pre-Imbrian craters originally Imbrian System. Most mare material is Imbrian in age but may have resembled the young crater Copernicus but are now some is post-Imbrian. The youngest mare materials ar~ the modified. The formation of each multiringed mare basin was darkest and least cratered; the oldest are almost as light and a major event which obliterated the earlier geologic record as heavily cratered as the light plains-forming materials. over a large area and started a new stratigraphic sequence. Indeed, mare and light plains materials may be composition­ On the basis of density of superposed craters and general ally similar, though different in age. Mare materials were freshness of appearance, the sequence of formation of some once called the Procellarian System and when this name was pre-Imbrian multiringed basins is believed to be, from oldest dropped, the Procellarum Group. The latter name as well as to youngest: Fecunditatis, Serenitatis, Nectaris, Humorum, the two series of the Imbrian System, the Apenninian and Crisium (or Crisium-Humorum). Other less distinct basins Archimedian, should be dropped. are also pre-Imbrian in age. Materials whose age relative to Imbrian mare material is Deposits called the Fra Mauro Formation that partly doubtful have been designated "Imbrian or Eratosthenian." surround another fresher appearing mare basin, the Imbrium They include crater materials, dark terra-mantling materials, basin, are used to define the base of the Imbrian System. The and materials that form domes, cones, sinuous rilles, and Fra Mauro apparently forms a blanket that grades in texture prominent stringy ridges. The dark mantling units occur and thickness away from the basin, and otherwise resembles mainly at the margins of maria and may be partly inter­ the ejecta of craters such as Copernicus that are believed to bedded with mare materials. have been produced by impact. Accordingly the Fra Mauro The two youngest lunar time-stratigraphic systems the Eratosthenian and Copernican, have been defined on the basis is believed to be ejecta from the impact that formed the of the physical properties of crater materials. Materials of Imbrium basin. Structures radial to and concentric with the rayless craters that are superposed on Imbrian mare material basin also apparently were formed at the same time as the are assigned an Eratosthenian age; some superposed on terra basin. The Fra Mauro and the structures divide the materials are also doubtless Eratosthenian but are not telescopically