{"id":4835,"date":"2021-07-08T02:18:31","date_gmt":"2021-07-08T06:18:31","guid":{"rendered":"https:\/\/www.colinmackellar.com\/blog\/?page_id=4835"},"modified":"2026-03-31T09:38:12","modified_gmt":"2026-03-31T13:38:12","slug":"chapter-13-what-did-you-learn","status":"publish","type":"page","link":"https:\/\/www.colinmackellar.com\/blog\/1-apollo-17-diary-of-the-12th-man\/b-chapters-10-18\/h-section-8-the-regolith-of-taurus-littrow\/chapter-13-what-did-you-learn\/","title":{"rendered":"a. Section 1"},"content":{"rendered":"

\u201cSomething Miraculous Happened over 26 Billion Years Ago<\/em>[1]<\/a><\/sup>. We all are living with or studying its wonder, its order, and its consequences.\u201d<\/em><\/strong><\/p>\n

Chapter 13<\/strong><\/p>\n

HISTORY IN THE DUST<\/strong><\/span><\/p>\n

<\/a><\/p>\n

Regolith of Taurus<\/em>–Littrow<\/em>: Ejecta Zones, Source Craters,<\/strong>
\nAges and Implications<\/strong><\/p>\n

\"\"A part of a DTM constructed from four Apollo 17 nadir metric mapping photos from rev. 14 and four from rev. 15 of the Taurus-Littrow<\/em> environs (north is up). The valley extends from the upper middle towards the lower right. The main features are the small Family Mountain<\/em> at the valley entrance at left; the Lee-Lincoln Scarp<\/em> crossing the valley from the South<\/em> to the North Massifs<\/em>; the avalanche from the northeast facing slope of the South Massif<\/em> (horseshoe crab shaped mountain in center); the Crater Cluster<\/em> in the valley center north of Bear Mountain<\/em>; the Sculptured Hills<\/em> mostly in shadow to the right of the North Massif<\/em>; and also the East Massif<\/em> casting a large shadow at the right end of the valley. (Total DTM triangulated from NASA photos AS17-M-0445 through M-0448 and AS17-M-0594 through M-0597 by the editor (Wells, 2021<\/strong><\/span><\/a>: Fig. 3.13c)).<\/span><\/p>\n

<\/a><\/p>\n

Preface<\/strong><\/p>\n

Comparison of the valley of Taurus-Littrow<\/em> on the Moon with the Grand Canyon<\/em> of the Colorado on Earth has been irresistible for over half a century. Since I explored this last site of the Apollo lunar landings, I have used this reference repeatedly.<\/p>\n

Recently, Basil Tikoff and Thomas Shipley wrote in awe of the Grand Canyon<\/em>[2]<\/a><\/sup><\/strong>: \u201cStanding on the rim of the canyon, you viscerally experience the name\u2014it feels big in a way that pictures do not capture. The immensity of absence, which is the Grand Canyon<\/em>, is conveyed across all of the senses. For instance, the soundscape of the rim is not silence; you can hear the wind. Yet the sound quality is unfamiliar; absent are the common echoes from the nearby surfaces. The space of the canyon is so immense that echoes disappear. The Grand Canyon\u2019s<\/em> ubiquity in geology and popular culture reflects in part, the clarity with which stories of time are written in its space.\u201d<\/p>\n

If Tikoff\u2019s and Shipley\u2019s insights about the Grand Canyon<\/em> were applied to Taurus-Littrow<\/em> on the Moon, it might be said: \u201cStanding on the floor of the valley of Taurus-Littrow<\/em>, your brain must assimilate what it knows about size without references to the familiar and without sound other than the life-preserving movement of oxygen in the fragile envelope around you. Brilliant massif walls, illuminated by a morning Sun, silhouetted in reverse against a blacker than black sky, rising above a chasm deeper than the Grand Canyon<\/em>, and watched over by the seemingly stationary blue and white Earth above the highest of the confining walls. The valley\u2019s geological record of time precedes that of even the magnificent strata of the Grand Canyon<\/em>, as far into the past as that natural wonder takes us, but its pages of the history of our solar system are far more subtle, but nonetheless reflect the order imposed by Creation.\u201d<\/p>\n

The presence of an experienced field geologist as Lunar Module Pilot on Apollo 17\u2019s mission to explore the valley of Taurus-Littrow<\/em>, as well as over 53 years of reports on analytical studies from the returned samples and geophysical data, provide an unique opportunity for integrated scientific synthesis. Large scale reviews of the vast stores of observational, photographic, petrographic and analytical data for the areas of Apollo exploration have not occurred over the 40 to 50 years since these data were published, documented in \u201cgray\u201d unpublished volumes and abstracts, or burned into explorers\u2019 memories.<\/p>\n

Beginning in the 1950s, funding for lunar science has almost entirely been the purview of the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF), with earlier contributions by the Geological Survey and various academic institutions. The tendency of scientists to focus on narrow, definable questions as well as on the equally narrow interests and results-oriented biases of federal agencies is understandable. However, these agencies almost never have encouraged proposals to undertake broad integration and correlation of the full range of the resulting vast reservoir of available information. Small exceptions to this existing paradigm of closely bounded research efforts have been NASA\u2019s funding of early \u201cconsortium\u201d studies of specific mission sample suites and the recent Apollo Next Generation Sample Analysis (ANGSA) program. The latter, however, still largely concentrated on one Apollo 17 drive tube core sample.<\/p>\n

Over the last 15 years or so, the author has attempted the synthesis of the observations, imagery and samples related specifically to his Apollo 17 exploration of the valley of Taurus-Littrow<\/em>. Such research is a dynamic and, of course, a continuous process. As the project progressed, new insights required sequential revisions of previous approaches to portions of the synthesis that, in turn, required alternative approaches to be considered. Eventually, an internally consistent picture of the geology and history of the Taurus-Littrow<\/em> valley emerged. The iterative nature of the synthesis of many data sets results in early sections of this work referring to later sections so that the reader is aware of the details that led to various integrated findings that supplanted earlier, more tentative results.<\/p>\n

The ~50 km long Taurus-Littrow<\/em>, fault-bounded valley radially penetrates the outer ring of uplifted and augmented massifs that encircle the 740 km diameter, Serenitatis<\/em> Basin<\/em>. Taurus-Littrow\u2019s<\/em> varied, 1600 to 2200 m high valley walls of impact melt and fragmental breccias constitute ejecta from the Crisium<\/em>, Serenitatis<\/em>, and Imbrium<\/em> basin-forming events. Lithoclastic ash, basaltic lava, pyroclastic ash, and subsequent impact-derived debris that partially fill the valley and covered earlier features provide insights into a variety of eruptive, impact and mass wasting activity. The first of such activity closely followed deposition of ejecta from the Imbrium<\/em> Basin<\/em> and additionally provide insights into the nature and origin of materials in the lunar interior.<\/p>\n

The synthesis of these data has been greatly influenced by early studies that relate to the upper-most 951 million years of a 3.8 billion year accumulation of regolith ejecta that comprise the 294 cm, Apollo 17 deep drill core. Isotopic and maturation data from the core and other samples indicate that the average energy of the solar wind increased about 514 million years ago and then increased again about 200 million years ago, this latter increase by over a factor of ~3.4. A spectrum of impacts, avalanches, debris flows, boulder shadowing, and thrust faults that occurred subsequent to valley volcanism add additional perspectives into recent lunar and solar histories and provide samples from which values for the rates of aging of exposed debris (regolith) have been derived. These rates of aging, in turn, allow estimates for the ages of 10 regolith ejecta source craters located throughout the valley.<\/p>\n

There is great and unique value of a far-ranging synthesis of data related to each Apollo landing site in increasing understanding of the geological history of specific sites as well as the internal, solar and other dynamic factors recorded in that history.<\/p>\n

Harrison H. Schmitt<\/em><\/p>\n

Apollo 17 Lunar Module Pilot and Field Geologist<\/em><\/p>\n

<\/a><\/p>\n

Major Findings:<\/strong><\/p>\n

    \n
  1. \n
      \n
    1. \n
        \n
      1. The Apollo 17, 294 cm long, deep drill core sample of Taurus-Littrow<\/em> regolith (70001\/9<\/strong>; see Fig. 13.1a\u2193\u00ad\u00ad<\/strong><\/span><\/a>, Fig. 13.1b\u2193\u00ad\u00ad<\/strong><\/span><\/a>, Fig. 13.5\u2193<\/strong><\/span><\/a> for location) is comprised of 11 strata or zones of regolith ejecta derived from ten 400-800 m diameter source craters and one 1400 m source crater, the ages of which span 951 million years of lunar history and represent the upper portion of ~11 m of regolith ejecta deposited on ilmenite basalt, the youngest eruption of which was at ~3.795 Ga. (\u00a73.0<\/span><\/a>)<\/li>\n
      2. Increases in exposure-related maturity indices (\u2206Is\/FeO) in the core\u2019s regolith ejecta zones, due to the reduction of structural Fe++<\/sup><\/strong> to Fe\u00ba, is the result of (1) alpha+beta particles from the decay of uranium and thorium (\u2206Is\/FeO \/ Myr = 0.58 per ppm U+<\/strong>Th); and (2) surface exposure to solar protons (\u2206Is\/FeO \/ Myr = 0.11 for young regolith and 0.032 for old regolith). (\u00a76.0<\/span><\/a>)<\/li>\n
      3. Exposure ages and deposition ages for the deep drill core\u2019s regolith ejecta zones can be calculated from the zone’s total half-cm log of \u2206Is\/FeO divided by the zone\u2019s total \u2206Is\/FeO \/ Myr. (\u00a76.0, \u00a77.0<\/span><\/a>)<\/li>\n
      4. Half-cm logging of the deep drill core, comparison of core zone cosmic ray exposure ages with \u2206Is\/FeO-based exposure ages, and Is\/FeO relationships at Shorty<\/em> and Van Serg Craters<\/em> show that impact shock partially resets the \u201cIs\u201d component of maturity indices, ranging from a few percent for small impacts that average one every ~5.8 Myr near the core to over 95% for zone source craters whose impacts that average one every ~<\/strong>95 Myr. (\u00a74.0<\/span><\/a>, \u00a78.0<\/span><\/a>, \u00a79.0<\/span><\/a>, \u00a711.0<\/span><\/a>, \u00a713.0<\/span><\/a>)<\/li>\n
      5. Relationships between the core\u2019s regolith ejecta zones\u2019 \u2206Is\/FeO and \u03b415<\/sup>N\u2030, and ancient regolith \u03b415<\/sup>N\u2030 values <\u2013210\u2030 show: (1) a sharp change in \u03b415<\/sup>N\u2030 from \u2264210\u2030 to about \u2013118\u2030 after ~<\/strong>514 Myr and before 394 Myr; (2) a lunar \u03b415<\/sup>N\u2030 accretionary value of ~+<\/strong>80\u2030; and (3) a factor of \u223c3.4 increase in solar wind energy at ~<\/strong>199 Myr ago, with the increase in solar 15<\/sup>N production at ~514 Myr, within probable error limits, being related to warming associated with the Cambrian Explosion of oceanic life on Earth at ~538 Myr. (\u00a76.0<\/span><\/a>)<\/li>\n
      6. The absence of Is\/FeO values >2 in glassy pyroclastic ash in core 74001\/2, particularly values that would result from alpha+<\/strong>beta particles, and the attenuation of Is\/FeO growth in deep drill core zones as a function of ash content, indicates that, in glass, the separation of Fe++<\/sup><\/strong> from uranium and thorium atoms and from access by solar protons is sufficient to prevent almost all Fe\u00ba formation. (\u00a77.0<\/span><\/a>, \u00a75.0<\/span><\/a>)<\/li>\n
      7. Positive values for \u03b415<\/sup>N\u2030 (+13\u2030) in buried pyroclastic ash of core 74001\/2, versus a current solar wind value of ~<\/strong>118\u2030 indicate a chondritic lower mantle source for the ash magma and its volatiles and suggest a lunar origin by accretion and capture rather than from a giant impact on the Earth. (\u00a710.0<\/span><\/a>)<\/li>\n
      8. The young and old light mantle avalanche deposits are two of at least seven mass wasting deposits from the slopes of the Taurus-Littrow<\/em> South Massif<\/em> and have Is\/FeO-based exposure ages, respectively, somewhere between 27-32 Myr and 10-15 Myr and deposition ages, respectively, somewhere between of 27-32 Myr and 37-47 Myr with a deposition age of 41-51 Myr for the newly identified ancient light mantle. (\u00a717.0<\/span><\/a>)<\/li>\n
      9. Mass wasting activity from the slopes of the South<\/em> and North Massifs<\/em> and from a peak in the Sculptured Hills<\/em> is likely the consequence of repeated thrust faults along the Lee-Lincoln Fault<\/em> caused by continued contraction of the gradually cooling Moon. (\u00a717.0<\/span><\/a>)<\/li>\n
      10. Comparison of North<\/em> and South Massif<\/em> regolith samples from the valley of Taurus-Littrow<\/em> indicate that volatile-rich, lithoclastic volcanic eruptions preceded those that produced the ~3.795 Ga mare basalts. (\u00a725.0<\/span><\/a>)<\/li>\n
      11. Partial coronas in troctolite 76535<\/strong> between plagioclase and olivine, consisting of pressure-release, retrograde symplectitic textures made up of Cr-spinel intergrown with clineoproxene next to plagioclase and with orthopyroxene next to olivine have replaced pressure-stabilized, prograde Cr-rich garnet and indicate this sample and crushed dunite 72415<\/strong> originated below ~<\/strong>400 km and 500 km, respectively, in the fractionally crystallized magma ocean. The movement of these rocks to higher levels where they were accessed by later basin formation was a result of upper mantle overturn triggered by the Procellarum<\/em> basin-forming impact at ~<\/strong>4.35 Ga that also resulted in the partial pressure-release melting of the warm upper mantle to produce Mg-suite plutons in the lower crust and the migration of urKREEP residual magma to the Procellarum region. (\u00a727.0<\/span><\/a>)<\/li>\n
      12. The synthesis of data from Taurus-Littrow<\/em> indicates that the Imbrium Basin<\/em> forming impact occurred between 3.850 and 3.795 Ga. (\u00a722.0<\/span><\/a>)<\/li>\n
      13. The addition of water to the early impact-generated regoliths of Earth and Mars would create smectic clay mineral species (phyllosilicates) whose adaptive silicate sheet crystal structures and compositions could serve as templates for the organization and stabilization of complex, pre-biotic and biotic organic molecules. (Schmitt, 2015<\/span><\/a>, with update to be published subsequently.)<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n

        <\/a><\/p>\n

        1.0 Introduction<\/strong><\/p>\n

        Any discussion of the science of the lunar regolith must acknowledge the foundational observations and interpretations made by Gene Shoemaker (Shoemaker, 1965<\/span><\/a>; Shoemaker et al., 1967<\/span><\/a>), based on his early studies and on the Surveyor III television observations of its landing site in Mare Cognitum<\/em>. Shoemaker\u2019s insights were followed by the seminal work of Larry Taylor that advanced understanding of the lunar regolith sampled by the Apollo astronauts. Taylor\u2019s and his associates\u2019 vast contributions to deciphering the character and formation of lunar regolith are without peer (e.g., Taylor, 1988<\/span><\/a>; Carrier et al., 1991<\/span><\/a>; Taylor et al., 2001a<\/span><\/a>, 2001b<\/span><\/a>; Pieters et al., 2010<\/span><\/a>).<\/p>\n

        Contributing to the studies by Taylor and others, the Apollo 17 mission to the valley of Taurus-Littrow<\/em> (Schmitt and Cernan, 1972a<\/span><\/a>; Schmitt, 1972<\/span><\/a>, 2021<\/span><\/a>; Wolfe et al., 1981<\/span><\/a>; Meyer, 2012<\/span><\/a>) provided a uniquely broad and diverse suite of regolith samples and the massif and volcanic components contained within them. Review, integration and synthesis of the geologic context of this sample suite and published analytical research continue to give special insights into the processes of regolith formation as well as indirect clues related to other important issues of lunar geology and solar and Earth history. Of particular importance to the development of various regolith-related hypotheses have been the maturity indexes (Is\/FeO) conceived of and measured by Richard Morris (1976<\/span><\/a>, 1978<\/span><\/a>), and Morris et al. (1975<\/span><\/a>, 1979<\/span><\/a>, 1989<\/span><\/a>)); the nitrogen isotopic measurements by Mark Thiemens and Robert Clayton (1980<\/span><\/a>), Richard Becker and Clayton (1975<\/span><\/a>, 1977<\/span><\/a>); and John Kerrridge (1975<\/span><\/a>) and Kerridge et al. (1991<\/span><\/a>); cosmic ray exposure ages by Peter Eberhardt et al. (1974<\/span><\/a>), Otto Eugster (1985<\/span><\/a>) and Eugster et al. (1977<\/span><\/a>, 1979<\/span><\/a>, 1981a<\/span><\/a>, 1981b<\/span><\/a>); uranium and thorium analyses by Lee Silver (1974<\/span><\/a>); and, of course, the wonderful Lunar Sample Compendium of Charles Meyer (2012<\/span><\/a>). These pioneers were all assisted by innumerable colleagues of the Apollo lunar science generation.<\/p>\n

        The Lunar Source Book (https:\/\/apollojournals.org\/alsj\/<\/span><\/a>) and the Lunar Sample Compendium (https:\/\/curator.jsc.nasa.gov\/lunar\/lsc\/index.cfm<\/span><\/a>) produced by Grant Heiken, David Vaniman, and Bevan French (1992<\/span><\/a>) and Charles Meyer (2012<\/span><\/a>), respectively, and the Professional Papers on the geology of individual missions published by the Geological Survey are invaluable sources of compiled data and references from a nearly infinite number of sources. Most recently, the Apollo Next Generation Sample Analysis (ANGSA) program has added significant data for integration into studies of avalanche deposits (Shearer et al., 2022<\/span><\/a>, 2024<\/span><\/a>) and Thermoluminescence of shadowed samples (Sehlke and Sears, 2022<\/span><\/a>; Sears et al., 2024<\/span><\/a>).<\/p>\n

        The analytical data are bolstered by the petrographic observations of Grant Heiken and David McKay (1974<\/span><\/a>), Laul et al. (1978<\/span><\/a>, 1979<\/span><\/a>), Jeffrey Taylor and his colleagues (1979<\/span><\/a>, 2001a<\/span><\/a>), and Nagle and Waltz (1979<\/span><\/a>), along with the author\u2019s field observations during the Apollo 17 mission (Chapters 10-12; Schmitt, 2023a<\/span><\/a>, 2024a<\/span><\/a>, b<\/span><\/a>, c<\/span><\/a>). Equally valuable to this synthesis is Eric Jones\u2019s Apollo 17 Apollo Lunar Surface Journal<\/em> with its crew annotated transcripts and referenced Hasselblad camera images (https:\/\/apollojournals.org\/alsj\/a17\/a17.html<\/a>) and Ed Wolfe and his colleagues\u2019 (1981<\/span><\/a>) integration of early Apollo 17 geological interpretations with sample locations and other data.<\/p>\n

        <\/a><\/p>\n

        1.1 General Nature of Lunar Regolith<\/strong><\/p>\n

        Particles that make up the Taurus-Littrow regolith (Shoemaker, 1965<\/span><\/a>; Shoemaker et al., 1967<\/span><\/a>; Heiken and McKay, 1974<\/span><\/a>; Pieters et al., 2010<\/span><\/a>) consist of varying proportions of mineral and rock fragments, regolith breccia fragments, volcanic ash beads and shards, and abundant impact generated, vesicular glassy agglutinates containing some or all these other particles. The mineral and rock fragments and bulk compositions of given regolith areas tend to reflect mixtures of regolith developed on near-by bedrock units. Other than spherical beads of volcanic ash and some transported impact glass, almost all particles are irregular in shape with vesicular glassy agglutinates having largely fractal outlines. Particle sizes range from hand-specimen size and larger to less than a micron with up to fifty percent by weight being less than about 70 microns, and they generally show an approximate bell-shaped size-frequency histogram (Graf, 1993<\/span><\/a>), although variations in histograms’ shape and peak sizes are very useful in some interpretations. Observationally, rock fragments >2 cm in diameter tend to be <5% of the total surface area of inter crater areas (Schmitt, 1972<\/span><\/a>, 2023a<\/span><\/a>, Chapters 10-12; 2024a<\/span><\/a>, b<\/span><\/a>, c<\/span><\/a>; Meyer, 2012<\/span><\/a>, sample 70001\/9; Hasselblad images).<\/p>\n

        Broadly distributed, ancient silicate-dominated surface regolith on Earth and apparently on Mars, likely played a role in the origin of complex organic molecules and their organization into replicating life forms (Schmitt, 2015<\/span><\/a>). Once stable and relatively cool planetary crusts had differentiated from an accretionary magma ocean and stabilized in an impact-dominated and water-rich environment, clay minerals (phyllosilicates), particularly of the smectite group, would have been the dominant mineral species at the Earth\u2019s surface. The characteristic of smectitic clays to incorporate many elements and molecules into their hydrous sheet-like crystal structure offered the potential of organizing organic bases and essential elements into increasingly complex forms.<\/p>\n

        High-energy solar wind ions and micro-meteors impacting the Moon apparently erode plasmas from exposed particle surfaces that re-deposit on local mineral and glass surfaces (Taylor, 1988<\/span><\/a>; Taylor and Meek, 2005<\/span><\/a>; Burgess and Stroud, 2018<\/span><\/a>; Cymes and Burgess, 2022<\/span><\/a>; Cymes et al., 2022<\/span><\/a>; Li et al., 2022<\/span><\/a>). Protons (H+<\/sup>) in the average solar wind have energies of a few Mev and abundances of about (6 ions\/cm3<\/sup>. Protons from solar flares and coronal mass ejections (CMEs), however, arrive at the Moon with Gev energies and abundances of 100s of ions\/cm3<\/sup> (Reames, 2017<\/span><\/a>) and may dominate the plasma-forming process. The resulting re-deposition of plasma material from this so-called \u201csputtering\u201d process, probably with some contribution from micro-meteor impact plasmas, produces a nearly ubiquitous but discontinuous, ~<\/strong>50 \u00b5 thick patina of alumino-silicate glass on regolith particles and rock surfaces. The glass present in the pits formed by micro-meteor impacts on rock surfaces suggests a contribution of impact plasmas to these patinas.<\/p>\n

        Alpha and beta particles from internal uranium and thorium decay, with minor contribution from solar proton radiation, reduces Fe++<\/sup><\/strong> to Fe\u00ba (np\u00baFe) (Morris et al, 1975<\/span><\/a>; Taylor, 1988<\/span><\/a>). Impact gardening gradually exposes new regolith particles to the surface-specific processes and mixes previously exposed particles and U- and Th-bearing minerals throughout the zone. The titanium-bearing mineral ilmenite, FeTiO3<\/sub>, appears to be the preferred host for this concentration of nano-phase iron (Cameron, 1990<\/span><\/a>; Taylor and Meek, 2005<\/span><\/a>). Solar wind volatiles may be concentrated in 5-50 \u00b5 diameter vesicles as well as being present in crystal defects and cracks (see Taylor, 1988<\/span><\/a>; Taylor et al., 2005<\/span><\/a>; Burgess and Stroud, 2018<\/span><\/a>; Cymes and Burgess, 2022<\/span><\/a>; Cymes et al., 2022<\/span><\/a>; Li et al., 2022<\/span><\/a>).<\/p>\n

        Nano-phase iron production occurs throughout a regolith zone due to ionizing alpha particles, and probably by associated beta radiation, that comes from internal uranium and thorium decay. This source of nano-phase iron has been neglected in past maturation studies; however, Bower et al.\u2019s (2016<\/span><\/a>) analysis of pleochroic halos around uranium- and thorium-bearing zircons in biotite found that radiation from uranium and thorium decay also converts structural Fe++<\/sup><\/strong> in biotite to Fe\u00ba. Alpha+<\/strong>beta radiation, therefore, must be taken into account in the interpretation of variations in regolith maturation, as uranium and thorium exist in amounts of 1-4 ppm in Taurus-Littrow<\/em> regolith samples. Extremely fine fragments of minerals and glass containing both elements have been broadly disseminated during long-term impact gardening of lunar regolith. Additionally, earlier in lunar history, the concentrations of these continuously decaying elements were significantly greater than today.<\/p>\n

        <\/a><\/p>\n

        2.0 Error Limits Related to Taurus-Littrow<\/em> Data Synthesis<\/strong><\/p>\n

        Much of the following synthesis of over 55 years of data on the Taurus-Littrow<\/em> regolith involves the integration of different types of measurements (maturity indices, radio-isotopic and cosmic ray ages, petrographic and chemical contents, etc.) each of which have varying estimates of analytical error limits, although many such limits are not reported. Accumulated error limits resulting from various calculations, therefore, can grow to numbers that suggest very large uncertainties. On the other hand, the synthesis itself includes various direct and indirect tests on the reasonableness of the results of calculations, as well as, in some cases, confirmation of those results by independent approaches or by their compatibility with clear constraints imposed by the overall geology of the area, or of the Moon, or of the history of the Earth and Solar System. As a consequence, when available, and unless otherwise noted, the error limits on original published data are quoted, but the accumulated hypothetical error limits inherent in various calculations generally are not considered except in terms of the reasonableness of the results.<\/p>\n

        In this context, the underlying, measurable parameter for initially evaluating the formational history of the lunar regolith consists of the Is\/FeO maturity index for returned regolith samples developed and measured by Richard Morris (1976<\/span><\/a>, 1978<\/span><\/a>) and Morris et al. (1975<\/span><\/a>, 1978<\/span><\/a>, 1979<\/span><\/a>, 1989<\/span><\/a>). This objective, maturity data consists of measuring the intensity of the ferromagnetic resonance (Is<\/sub>) of a sample and then normalizing it for comparison with other samples by dividing by each sample\u2019s FeO content. The author of this current narrative originally considered the Is <\/sub>of a sample basically to reflect the amount of nano-phase iron (np\u00b0Fe) produced by solar wind proton reduction of regolith Fe++<\/sup><\/strong> (Pieters et al., 2010<\/span><\/a>) in proportion to the samples FeO content. It was eventually realized that alpha+beta particle radiation from the decay of uranium and thorium contributes to the formation of np\u00b0Fe (Bower et al., 2016<\/span><\/a>).<\/p>\n

        Morris (1978<\/span><\/a>) states that the precision of the Is <\/sub>measurement used in the Is\/FeO determinations is \u00b15%. As the error limits of FeO determinations used by Morris (usually from R. Warner, unpublished) are not available, measured Is\/FeO values used throughout this paper will be assumed to be accurate to be within 5%, that is, Is\/FeO = 20 would be \u00b1 1 and Is\/FeO = 80 would be \u00b1 4. This assumption implies that inaccuracies in analytical determination of values for FeO are included in the 5% stated by Morris and, nonetheless, would be small enough not to affect the inherent value of Is\/FeO as a synthesis tool. On the other hand, consistency in the results of the following synthesis suggest that the precision of Morris\u2019s combined Is<\/sub> and FeO measurements is significantly better than \u00b15%, possibly about \u00b12% or even better.<\/p>\n

        <\/a><\/p>\n

        3.0 Apollo 17 Deep Drill Core<\/strong><\/p>\n

        <\/a><\/p>\n

        3.1 Introduction<\/strong><\/p>\n

        The Apollo 17, ~<\/strong>3 m deep drill core (70001\/9<\/strong>) (Baldwin, 1973<\/span><\/a>; Meyer, 2012<\/span><\/a>) constitutes the most complete vertical sample of the lunar regolith obtained to date (Meyer, 2012; Heiken, et al., 1992<\/span><\/a>). The deep drill core was obtained during the deployment of the Apollo 17 Apollo Lunar Science Experiment Package (ALSEP) at a location about 180 m west of the landing point of the Lunar Module, Challenger<\/em> (Fig. 13.1a\u2193\u00ad\u00ad<\/strong><\/span><\/a>, Fig. 13.1b\u2193\u00ad\u00ad<\/strong><\/span><\/a><\/strong>). Synthesis of published analytical data provides new insights into the formational, depositional and exposure history of regolith sampled by this core. Of particular importance are the investigations of maturity indices (Morris et al., 1979<\/span><\/a>); petrographic characteristics (Vaniman and Papike, 1977<\/span><\/a>; Vaniman et al., 1979<\/span><\/a>; Taylor et. al., 1979<\/span><\/a>; Heiken et. al., 1992<\/span><\/a>); bulk compositions (Laul et al., 1978<\/span><\/a>, 1979<\/span><\/a>, 1981<\/span><\/a>), volatile element concentrations (Laul and Papike, 1980a<\/span><\/a>, b<\/span><\/a>), nitrogen isotopic measurements (Thiemans and Clayton, 1980<\/span><\/a>), cosmic ray exposure age determinations (Eberhardt et al., 1974<\/span><\/a>), and uranium and thorium concentrations (Silver, 1974<\/span><\/a>; Laul et al., 1978, 1979, 1981; compilations by Meyer, 2012).<\/p>\n

        <\/a><\/p>\n

        \"\"Fig. 13.1a.<\/strong> Apollo 17 landing site with the remaining Challenger <\/em>Lunar Module descent stage located at right; the Apollo Lunar Surface Experiments Package (ALSEP) deployment site; and the deep drill core (DDC; white arrow) site located at left outlined by the light colored box. The ~50 m diameter Rudolph Crater<\/em> is at top left (LROC image).<\/span><\/p>\n

        <\/a><\/p>\n

        \"\"Fig. 13.1b.<\/strong> Enlargement of Fig.<\/strong> 13.1a<\/strong> to show the detail of the ALSEP experiments and the deep drill site locations. Thin parallel tracks were made by the LRV. The heavier, darker tracks were made mostly by my foot traffic. (LROC image).<\/span><\/p>\n

        The in situ<\/em> inter-crater regolith sampled by the Apollo 17 deep drill core is made up of eleven definable zones of regolith ejecta from 400-800 m diameter craters and one 1400 m diameter crater within about 6 km of the core site (Schmitt (2019b<\/span><\/a>, 2021<\/span><\/a>, 2023a<\/span><\/a>)). Such zones superficially resemble each other, but they show significant differences in detailed maturity (Morris et al., 1979<\/span><\/a>), lithology and mineralogy (Taylor et al. (1979<\/span><\/a>)), and bulk chemical compositions (Laul et al. (1978<\/span><\/a>, 1979<\/span><\/a>, 1981<\/span><\/a>); Meyer (2012<\/span><\/a>); Silver (1974<\/span><\/a>)). These differences, in turn, reflect the compositions and, in part, the pre-excavation maturities and cosmic ray exposure ages (Eberhardt et al. (1974<\/span><\/a>)) of the source regoliths.<\/p>\n

        The 11 distinct regolith ejecta zones comprise the ~294 cm of material in the deep drill core and record, directly or indirectly, a significant portion of the cratering, regolith maturation, and volcanic history of Taurus-Littrow<\/em>. These zones also contribute to understanding the distribution of geological units and sequence of impact cratering events that created a corresponding 14 potential source craters, 400-1400 m in diameter, that lie within about 6 km of the core site. The maturity of these regolith ejecta zones due to space weathering and internal alpha+<\/strong>beta particle radiation, as well as associated cosmic ray exposure age data, further allow the approximate dating of these large impact events (\u00a76.0<\/span><\/a>). Certain aspects of the history of the solar wind also are recorded in the core.<\/p>\n

        Much of the following synthesis relies on analyses and observations of portions of the Apollo 17 deep drill core conducted by many researchers; however, the exact length of the returned core, and thus the precise depth of analyses are not absolutely certain within a few centimeters. For example, Morris et al.\u2019s (1979<\/span><\/a>) maturity index data measured at half-cm intervals are available from \u20131.30 to 285.85 cm (Morris, pers. comm.), while Silver\u2019s (1974<\/span><\/a>) uranium, thorium and lead analyses and Eberhardt et al.\u2019s (1974<\/span><\/a>) cosmic ray exposure ages are reported up to 290 cm, and Meyer\u2019s (2012<\/span><\/a>) compilation of element analyses goes to 294 cm. To complicate matters further, Meyer (2012) states that when the core was opened, there was a \u201c10-12 cm void\u201d at the base of the upper pair of returned drill stems, that is, where core sample 70008 is now defined. This \u201cvoid\u201d possibly relates to Astronaut Cernan\u2019s statement, made while the core was still in the ground, that the top, stabilizing \u201cplug\u201d for that section ultimately moved about two-thirds of the length of the compacting rammer. This operation compressed the less compact upper portion of cored regolith. A 10-12 cm thickness of low-density regolith at the surface of inter-crater areas is consistent with direct observations during Apollo 17 EVAs.<\/p>\n

        Top core section, 70009, is listed in Mitchell et al. (1973<\/span><\/a>) as having a length of 25 \u00b1 2 cm, about 15 cm less than the 40 cm of a full section. As the rammer was about 50 cm long, Cernan\u2019s statement probably meant that \u201ctwo-thirds\u201d of the rammer was still showing outside the core section for his statement to match Mitchell et al.\u2019s information. In light of the above, and, as Mitchell et al. measured the total \u201cdrill stem depth\u201d (not core length) at 305 \u00b1 1 cm with 95-97% recovery, the total length of \u201ccore\u201d will be assumed here to be ~294 cm, a length which also matches the Meyer report. Morris (pers. comm.; Morris et al., 1979<\/span><\/a>) records 284.65 cm as the depth of the last Is\/FeO measurement given in Morris et al. (1979<\/span><\/a>), but also says that the first measurement was at a depth of \u201cminus 1.30 cm.\u201d These figures suggest that there is ~7 cm of core at the bottom for which Is\/FeO data was not obtained.<\/p>\n

        The following probably contributed to the \u201c10-12 cm void\u201d reported by Meyer:<\/p>\n

          \n
        1. \n
            \n
          1. It is certain that the loosely consolidated upper 10-15 cm of the regolith compacted upon insertion and \u201cramming\u201d of a plug on top of the core in the first drill stem section before extraction of the drill stem from the regolith.<\/li>\n
          2. During handling and transport to the Lunar Receiving Laboratory in Houston, the core in the first of two drill stem as sections, as well as the top plug, slid away (upward) from the bottom cap.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n

            As will be detailed below (\u00a75.0<\/span><\/a>), the chemical composition of three samples from the upper 20 cm of the compacted core (Laul et al., 1978<\/span><\/a>) and the composition of nearby control sample 70181 are almost identical, indicating that the control sample gives a good representation of the elemental and mineralogical makeup of the top portion of the core.<\/p>\n

            <\/a><\/p>\n

            3.2 Deep Drill Core Maturity Indices and Regolith Ejecta Zones <\/strong><\/p>\n

            Morris et al. (1979<\/span><\/a>) have reported, graphically, the maturity indices (Is\/FeO) for nearly the full length of the Apollo 17 deep drill core (Fig. 13.1c\u2193\u00ad\u00ad<\/strong><\/span><\/a>). These Is\/FeO values reflect the degree of reduction of Fe++<\/sup><\/strong> to Feo <\/sup> by internal alpha+beta and surface solar proton particle radiation. They have been derived from the ferro-magnetic response of nano-phase iron (npo<\/sup>Fe) particles in regolith samples, normalized to reflect the varying FeO content of the measured regolith samples. Morris et al.\u2019s data plotted in Fig. 13.1c\u2193\u00ad\u00ad<\/strong><\/span><\/a>, with a representative example of the raw, detailed, half-cm resolution data set (Morris, pers. comm.) in Fig. 13.1d\u2193\u00ad\u00ad<\/strong><\/span><\/a>, indicates the existence of zones of regolith with significantly different degrees of exposure to the internal and external radiation as well as having distinct petrographic characteristics after comparison with other data. This conclusion is supported less precisely in Fig. 13.2\u2193\u00ad\u00ad<\/strong><\/span><\/a> by agglutinate content (Taylor et al., 1979<\/span><\/a>) and \u201ccosmic ray track maturity\u201d (Goswami and Lal, 1979<\/span><\/a>). Of particular importance, however, are the variations in Is\/FeO measured as a function of depth that provide data on relative age based on superposition.<\/p>\n

            <\/a><\/p>\n


            \n\"\"Fig. 13.1c.<\/span><\/strong> Plot of Is\/FeO maturity indices and FeO content in the Apollo 17 deep drill core (Morris et al.,             1979<\/span><\/a>) with a rough indication of the identified regolith ejecta zones shown in the column on the right.<\/span><\/p>\n

            <\/a><\/p>\n

            \"\"Fig. 13.1d.<\/span><\/strong> Representative portion of the half-cm resolution, raw data set (Morris, pers. comm.) related to the deep drill core\u2019s Is\/FeO values graphically represented in Fig. 13.1c\u2191<\/strong><\/span><\/a>. Column 6 indicates zone decreases and increases of Is\/FeO noted during logging of this data set.<\/span><\/p>\n

            <\/a><\/p>\n

            \"\"Fig. 13.2. <\/span><\/strong>Data on the maturity of the Apollo 17 deep drill core comparing Is\/FeO maturity indices, left column (Morris et al., 1979<\/span><\/a>); cosmic ray track density, center column (Goswami and Lal, 1979<\/span><\/a>); and agglutinate content, right column (Taylor et al., 1979<\/span><\/a>). Figure is after Heiken et al., (1992<\/span><\/a>). Approximate regolith ejecta zones S-Z** are largely based on maturity data shown in Fig. 13.1c\u2191<\/strong><\/span><\/a> as verified by logging of half-cm raw data (Fig. 13.1d\u2191<\/strong><\/span><\/a>).<\/span><\/p>\n

            Table 13.1a\u2193<\/strong><\/span><\/a> provides the depth intervals for defined regolith ejecta zones (Column 1) that are used in the subsequent synthesis of Taurus-Littrow<\/em> geological, petrographical and analytical data. \u201cIs\u201d is a measure of ferromagnetic resonance and thus of the content of nano-phase iron produced through reduction of Fe++<\/sup>, that is, by (1) solar wind weathering, largely by energetic solar protons (Pieters et al. (2010<\/span><\/a>)), and (2) internal alpha+beta particle radiation (Schmitt (2022a<\/span><\/a>)). Micro- and macro-meteor impacts are contributing factors as they continuously garden and mix exposed regolith ejecta as well as produce complementary agglutinates. Sorting out the quantitative effects and implications of these factors is a significant focus of this synthesis.<\/p>\n

            In Table 13.1a\u2193<\/strong><\/span><\/a> and in subsequent discussions, Is\/FeOm <\/sub>and \u2206Is\/FeO refer to the estimated deposition value of Is\/FeO of source regolith, as suggested by the half-cm logging, and the post-deposition accumulation of Is\/FeO, respectively. As will be discussed below, the actual pre-deposition total Is\/FeO of an integrated source regolith is not given by the value of Is\/FeOm <\/sub> in the table, as there is strong evidence that the shock and\/or heat of impact partially resets the ferromagnetic component of the near-impact nano-phase iron on which the \u201cIs\u201d component of Is\/FeO is based. The extent to which impact reset has affected the logged estimated Is\/FeOm<\/sub> given in Column 3 of Table 13.1a will be examined in \u00a78.0<\/span><\/a>.<\/p>\n

            With respect to zone S, it appears that the significantly higher velocity regolith ejecta from the large MOCR Crater<\/em> (\u00a73.4<\/span><\/a>) that constitutes zone S resulted in more mixing with the previously deposited zone T+T* than at other zone boundaries. This mixing zone is about 4 cm thick (22.35 to 18.35 cm) and includes an increase in \u2206Is\/FeO of ~<\/strong>47 points that is not the consequence of maturation after zone S deposition. The logged post-deposition \u2206Is\/FeO of zone S is 46, confirmed by the reported \u2206Is\/FeO = 47 of control sample 70181 (Morris et al., 1978<\/span><\/a>).<\/p>\n

            [In the course of this synthesis, the definitions of the various zones have varied. Initially, those definitions were based purely on broad changes in Is\/FeO shown in Fig. 13.1b\u2191\u00ad\u00ad<\/strong><\/span><\/a>, however, correlations with various other associated data, the half-cm logging of Morris\u2019s detailed data, and improved understanding of source regoliths indicated the need for improvements in these zone definitions. This process first suggested several subzones and then, in some cases, indicated recombination into the original set. This final process is reflected in zones labeled T+T*, V+V*, Y+Y* and Z+Z* in various tables and figures. Subzones W*, X* and Z** proved to be coherent stratigraphic units in their own right, but the asterisk (*) designations have been retained for them.]<\/p>\n

            Table 13.1a footnotes<\/span><\/a>:
            \n            <\/a><\/p>\n

            \"\"<\/a>
            \nLinks to             \u00a78.0<\/span><\/a>, Table 13.1b\u2193<\/strong><\/span><\/a>, Taylor et al. (1979<\/span><\/a>), Nagle and Waltz (1979<\/span><\/a>), Vaniman et al. (1979<\/span><\/a>), Silver (1974<\/span><\/a>), Meyer (2012<\/span><\/a>), and Laul and Papike (1980a<\/span><\/a>).<\/p>\n

            Close examination of the plotted points in Fig. 13.1c\u2191\u00ad\u00ad<\/strong><\/span><\/a> shows that the saw tooth patterns present along the length of the core have Is\/FeO minima that are roughly constant for various sections of the core. The existence of these minima is best shown in the core sections between 115 and 170 cm. These locally constant minima are probably close to the original deposition maturity index (Is\/FeOm<\/sub>). The precise deposition Is\/FeOm<\/sub> values are uncertain within about \u00b1 5 in most cases.<\/p>\n

            In defining stratigraphic zones based on Is\/FeO values in the deep drill core, a large, sharp decease or increase in background Is\/FeOm<\/sub> is interpreted as the boundary between zone depositions. These defined boundaries are generally supported by petrographic and compositional data as will be discussed in \u00a75.0<\/span><\/a>. The sum of the positive magnitudes of the small saw tooth spikes, showing the total increase in Is\/FeO over Is\/FeOm<\/sub> throughout a given zone (\u2206Is\/FeO), is a measure of the post-deposition maturation of the zone before burial by a younger zone.<\/p>\n

            Table 13.1a\u2191<\/strong><\/span><\/a> gives the regolith ejecta zones identified by examination of Fig. 13.1c\u2191\u00ad\u00ad<\/strong><\/span><\/a>, as refined by subsequent analysis that resolved a number of inconsistencies with other data. After preliminary definition, the indicated depths of zones were determined within half a centimeter with reference to the raw Is\/FeO data provided by Richard Morris (pers. comm.).<\/p>\n

            Table 13.1b\u2193<\/strong><\/span><\/a> compares the zone definitions in Table 13.1a<\/strong> with \u201cunit\u201d classifications given by Nagle and Waltz (1979<\/span><\/a>), Vaniman et al. (1979<\/span><\/a>), and Taylor et al. (1979<\/span><\/a>). Although these latter three stratigraphic classifications and their associated descriptions do not line up exactly with the detail in Table 13.1a<\/strong>, they are generally consistent relative to evidence of maturity and source regolith characterization. Nagle and Waltz\u2019s boundaries between zones S and T+T*, V+V* and W, W* X and X* in their sketch of the deep drill core are particularly consistent with the divisions in Table 13.1a<\/strong> Some relevant comparisons are given.<\/p>\n

            Table 13.1b footnotes<\/span><\/a>:
            \n            <\/a>
            \n\"\"<\/p>\n

            Links for Nagle and Waltz (1979<\/span><\/a>), Vaniman et al. (1979<\/span><\/a>), Taylor et al. (1979<\/span><\/a>), Table 13.1a\u2191<\/strong><\/span><\/a>, Silver (1974<\/span><\/a>), Meyer (2012<\/span><\/a>) and Laul et al. (1978<\/span><\/a>, 1979<\/span><\/a>, 1981<\/span><\/a>).
            \n            <\/a>
            \n            <\/a><\/p>\n

            3.2.1 Agglutinate Formation in Relation to Is\/FeO Maturity Index<\/strong><\/p>\n

            Vesicular \u201cagglutinates\u201d composed of mineral and rock particles in a glass matrix accumulate over time at the surface of lunar regolith. These agglutinates are the result of local impact melting and mixing. Their abundance is a rough measure of the relative exposure of a given regolith unit to the geologically steady impact of macro- and micro-meteors. The pattern of abundance of agglutinates (Taylor et al., 1979<\/span><\/a>) in the deep drill core are shown in Fig. 13.3a\u2193\u00ad\u00ad<\/strong><\/span><\/a>.<\/p>\n

            <\/a><\/p>\n

            \"\"Fig. 13.3a.<\/strong> Graph of percentage variations in agglutinates as measured by modal analysis of 171 thin sections from the deep drill core (Taylor et al., 1979<\/span><\/a>).<\/span><\/p>\n

            As deep drill core values of total Is\/FeO (Morris et al., 1979) and total modal-% agglutinates (Taylor et al., 1979<\/span><\/a>) rise with age, a correlation between these two parameters would be expected. Fig. 13.3b\u2193\u00ad\u00ad<\/strong><\/span><\/a> gives a visual comparison of this relationship. The indicated graphical relationships zone by zone are given in Table 13.2a\u2193<\/strong><\/span><\/a> with reference to total Is\/FeO from Table 13.1a\u2191<\/strong><\/span><\/a>; maximum modal-% agglutinate peak; and the ratio of these two parameters. The ratio of total Is\/FeO to maximum agglutinates averages 4.96 \u00b1 ~<\/strong>1.7 (lowest and highest ratios not included), verifying the close and constant relationship between nanophase iron production and agglutinate formation.<\/p>\n

            It would be expected that this relationship would carry over to the ratio between \u2206Is\/FeO and \u2206Agglutinate. Values of \u2206Agglutinate shown in Column 4 of Table 13.2b\u2193<\/strong><\/span><\/a><\/strong> were determined by summing the measured increases with decreasing depth for each zone shown in Fig. 13.3a\u2191\u00ad\u00ad<\/strong><\/span><\/a> Dividing \u2206Is\/FeO values by \u2206Agglutinate values (Table 13.2b<\/strong>) gives a significantly higher \u2206Is\/FeO to \u2206Agglutinate ratio (average of 7.49) than the 4.96 average for total Is\/FeO to maximum agglutinate. This discrepancy is likely due to the low resolution of measurements of changes in modal-% of agglutinates, that is, some increases were missed. This conclusion is supported by the fact that the ratios for total Is\/FeO to total Agglutinate are generally less than those for \u2206Is\/FeO to \u2206Agglutinate. From personal experience, microscopic \u201cpoint counting\u201d to determine modal-% of particles is an art of judgment more than of science.<\/p>\n

            <\/a><\/p>\n

            \"\"Fig. 13.3b.<\/strong> Comparison of total Is\/FeO (Morris et al., 1979<\/span><\/a>) and modal-% agglutinates (Taylor et al., 1979<\/span><\/a>). Red dash lines indicate the zone widths in Table 13.1a\u2191<\/strong><\/span><\/a>.<\/span><\/p>\n

            <\/a>
            \n\"\"Links for             Fig. 13.3a\u2191\u00ad\u00ad<\/strong><\/span><\/a>, Fig. 13.3b\u2191\u00ad\u00ad<\/strong><\/span><\/a>
            \n            <\/a><\/p>\n

            3.3 Regolith Transport after Large Impacts in Lunar Gravity and Vacuum<\/strong><\/p>\n

            Impacts have dominated the evolution of the Moon\u2019s surface for much of its history (Wilhelms, 1987<\/span><\/a>) from primordial accretion, to the creation of the magma ocean, to the creation of the mega-regolith that now constitutes the lunar crust, to the excavation of the large basins, to the evolution of today\u2019s surface regolith since the formation of a region\u2019s last large impact basin. As craters on the floor of the valley of Taurus-Littrow<\/em> are, at least in large part, underlain by ilmenite basalt, regolith ejecta zones identified in the deep drill core have their origins in ejecta from impact craters formed since regolith began to form and accumulate on mare basalt erupted about 3.82 Ga (39-40<\/sup>Ar, Schaeffler et al. (1977<\/span><\/a>)).<\/p>\n

            [Further consideration of the potential closure temperatures for the various isotopic systems suggests that the actual age of the youngest lavas would be close to the 39-40<\/sup>Ar age of rapidly cooled, fine-grained samples. One such sample, 70215<\/strong>, has been dated (using old 40<\/sup>K decay constants) by the 39-40<\/sup>Ar method at 3.82 \u00b1 0.05 Ga. (Schaeffer et al., 1977<\/span><\/a>). In this chapter, this date will be used as representative of the most recent age of the ilmenite basalt lava eruption.<\/p>\n

            As a means to further tighten the chronology of eruptive activity in Taurus-Littrow<\/em>, it would be useful to precisely date by 39-40<\/sup>Ar methods other rapidly cooled ilmenite basalt samples from the Apollo 17 collection (e. g., 70075<\/strong>, 71537<\/strong>, 74235<\/strong>, 78586<\/strong>, and 78587<\/strong>). A close examination of un-numbered basalt fragments in the rake samples from Stations 1, 2, 6, and 8 also may include very fine-grained, rapidly cooled ilmenite basalts suitable for dating.<\/p>\n

            The recently reported revision of the 40<\/sup>K decay constant (Renee et al., 2010<\/span><\/a>); Noumenko-Dezes et al. (2018<\/span><\/a>)); Carter et al. (2020<\/span><\/a>)) would lower previously reported 39-40<\/sup>Ar dates by about 0.025 Ga (Schmitt et al., 2017<\/span><\/a>). However, in order to incorporate as many previously dated samples in this synthesis on a consistent basis, revisions based on the new constant will not be made.]<\/p>\n

            The regolith zones from the Taurus-Littrow<\/em> valley floor that are represented in the deep drill core 70001\/9<\/strong> are distinctive because of the presence of detectable regolith contributions from five diverse geologic units related to the massifs surrounding the valley and volcanic ash deposits that contrast with the low SiO2<\/sub> and low U+Th ilmenite basalt regolith. Those major units are the orange+<\/strong>black low SiO2<\/sub> volcanic ash, Very Low Titanium (VLT) and high SiO2<\/sub> volcanic ash, Sculptured Hills<\/em> Mg-rich suite regolith, North Massif<\/em> medium SiO2<\/sub> and U+Th impact breccias, and South Massif<\/em> high SiO2<\/sub> and high U+Th impact breccias (\u00a75.0<\/span><\/a>). If new insights are to be gained about the source areas of these regolith zones, the geological challenge is to tie specific regolith zones to specific craters in the Taurus-Littrow<\/em> valley.<\/p>\n

            An LROC image-based temporal study of new lunar craters in regolith (Speyerer et al., 2016<\/span><\/a>), indicated that regolith at the sites of recent impacts has been ejected many crater diameters from the impact points and deposited continuously along their trajectory. In contrast, examination of ejecta from fresh craters in lunar basalt of comparable size to the 744 m diameter Camelot Crater<\/em> (Schmitt et al., 2017<\/span><\/a>) indicates that, much as on Earth, ejected bedrock,<\/u> extends only about a crater diameter from the crater rim. Thus, it is very probable that significant amounts of regolith reached the deep drill core location after being ejected within a few micro-seconds of the instant of impact at the sites of large craters in the valley of Taurus-Littrow<\/em>.<\/p>\n

            Support for this conclusion also is found in Oberbeck\u2019s (1975<\/span><\/a>) experiments on \u201chypervelocity impacts against a quartz sand layer resting on an ‘indurated’ quartz sand substrate.\u201d Based on the Oberbeck\u2019s and Speyerer et al.\u2019s (2016<\/span><\/a>) observations, and the numerous regolith zones identified in the Apollo 17 deep drill core, the following inferences about the impacts that created the 400 m diameter and larger craters in Taurus-Littrow<\/em> valley appear to be in order:<\/p>\n