Lithologic distribution and geologic history of the Apollo 17 site: The record in soils and small rock particles from the highland massifs

Abstract— Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm–4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm–4 mm fragments provide a bridge between compositions of <1 mm fines, and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm–4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% incompatible-trace-element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm–4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31% agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass-weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their compositions, we conclude the following: (1) North-Massif and South-Massif soil samples differ significantly in types and proportions of ITE-poor highland components and ITE-rich impact-melt-breccia components. These differences reflect crudely layered massifs and known local geology. The greater percentage of impact-melt breccia in the South-Massif light-mantle soil stems from derivation of the light mantle from the top of the massif, which apparently is richer in noritic impact-melt breccia than are lower parts of the massifs. (2) At station 2, the 2 mm–4 mm grain-size fraction is enriched in impact-melt breccias compared to the <1 mm fraction, suggesting that the <1 mm fraction within the light mantle has a greater proportion of lithologies such as granulitic breccias which are more prevalent lower in the massifs and which we infer to be older (pre-basin) highland components. (3) Soil from station 6, North Massif, contains magnesian troctolitic anorthosite, which is a component that is rare in station-2 South-Massif soils. (4) Compositional differences between poikilitic impact-melt breccias from the two massifs suggest broad-scale heterogeneity in impact-melt breccia interpreted by most investigators to be ejecta from the Serenitatis basin. We have found rock types not previously recognized or uncommon at the Apollo 17 site. These include (1) ITE-rich impact-melt breccias that are compositionally distinct from previously recognized “aphanitic” and “poikilitic” groups at Apollo 17; (2) regolith breccias that are free of mare components and poor in impact melt of the types associated with the main melt-breccia groups, and that, if those groups derive from the Serenitatis impact, may represent the pre-Serenitatis surface; (3) several VLT basalts, including an unusual very-high-K basaltic breccia; (4) orange-glass regolith breccias; (5) aphanitic-matrix melt breccias at station 6; (6) fragments of alkali-rich composition, including alkali anorthosite, and monzogabbro; (7) one fragment of 72275-type KREEP basalt from station 3; (8) seven lithic fragments of ferroan-anorthositic-suite rocks; and (9) a fragment of metal, possibly from an L chondrite. Some of these lithologies have been found only as lithic fragments in the soils and not among the large rock samples. In contrast, we have not found among the 2 mm–4 mm lithic fragments individual samples of certain lithologies that have been recognized as clasts in breccias (e.g., dunite and spinel troctolite). The diversity of lithologic information contained in the lithic fragments of these soils nearly equals that found among large rock samples, and most information bearing on petrographic relationships is maintained, even in such small samples. Given a small number of large samples for “petrologic ground truth,” small lithic fragments contained in soil “scoop” samples can provide the basis for interpreting the diversity of rock types and their proportions in remotely sensed geologic units. They should be considered essential targets for future automated sample-analysis and sample-return missions.     

Major and trace element chemistry of Boulder 1 at Station 2, Apollo 17

Twenty-seven samples of matrix and clast materials from Boulder 1 at Station 2, Apollo 17 have been analyzed for major and trace elements as part of the study of this boulder by Consortium Indomitabile. Both unusual and common types of material have been characterized. Gray and black competent breccia (GCBx and BCBx) and anorthositic breccia (AnBx) have compositions which are common at the Apollo 17 site and were common at the site of boulder formation. Light friable breccias (LFBx) have compositions which are not found at the Apollo 17 site other than in the boulder. Pigeonite basalt is a new type of lunar rock and has characteristics that would be expected of a highland volcanic rock. It is associated with LFBx material, and like LFBx material it is exotic to the Apollo 17 site. Coarse norite is an old primitive rock which is no longer (if ever) found as millimeter fragments at the Apollo 17 site. It was, however, present as millimeter fragments associated with GCBx and BCBx materials at the site and time of boulder formation. Therefore the boulder-forming process combined materials from at least two different localities or vertical strata; at least one of these (LFBx) has not been previously sampled and analyzed.     

Geochemical and isotopic evidence for upward flow of saline fluid to the Mississippi River Valley alluvial aquifer,southeastern Arkansas,USA

Hydrogeology Journal - Groundwater from the Quaternary Mississippi River Valley Alluvial (MRVA) aquifer in southeastern Arkansas (SE AR), USA, has higher salinity compared to other MRVA...     

Satellite Remote Sensing as a Reconnaissance Tool for Assessing Nautical Chart Adequacy and Completeness

National hydrographic offices need a better means of assessing the adequacy of existing nautical charts in order to plan and prioritize future hydrographic surveys. The ability to derive bathymetry from multispectral satellite imagery is a topic that has received considerable attention in scientific literature. However, published studies have not addressed the ability of satellite-derived bathymetry to meet specific hydrographic survey requirements. Specifically, the bathymetry needs to be referenced to a chart datum and statistical uncertainty estimates of the bathymetry should be provided. Ideally, the procedure should be based on readily-available, low-cost software, tools, and data. This paper describes the development and testing of a procedure using publicly-available, multispectral satellite imagery to map and portray shallow-water bathymetry in a GIS environment for three study sites: Northeast United States, Nigeria, and Belize. Landsat imagery and published algorithms were used to derive estimates of the bathymetry in shallow waters, and uncertainty of the satellite-derived bathymetry was then assessed using a Monte Carlo method. Results indicate that the practical procedures developed in this study are suitable for use by national hydrographic offices.     

Glacial lake depth and volume estimation based on a large bathymetric dataset from the Cordillera Blanca,Peru

Glacial lakes are most often located in remote places making it difficult to carry out detailed bathymetric surveys. Consequently, lake depths and volumes for unmeasured lakes are often estimated using empirical relationships developed mainly from small bathymetric datasets. In this study, we use the bathymetry dataset of the Cordillera Blanca, Peru comprising 121 detailed lake bathymetries, the most extensive dataset in the world. We assess the performance of the most commonly applied empirical relationships for lake mean depth and volume estimation, but also investigate relationships between different geometric lake variables. We find that lake volume estimation performs better when derived from lake mean depth, which in turn is estimated from lake width. The findings also reveal the extreme variability of lake geometry, which depends on glacio-geomorphological processes that empirical–statistical relationships cannot adequately represent. Such relationships involve characteristic uncertainty ranges of roughly ±50%. We also estimate potential peak discharges of outburst floods from these lakes by applying empirical relationships from the literature, which results in discharges varying by up to one-order of magnitude. Finally, the results are applied to the 860 lakes without bathymetric measurements from the inventory dataset of the Cordillera Blanca to estimate lake mean depth, volume and possible peak discharge for all unmeasured lakes. Estimations show that ca. 70% (610) of the lakes have a mean depth lower than 10 m and very few longer than 40 m. Lake volume of unmeasured lakes represent ca. 32% (5.18 × 10⁸ m³) of the total lake volume (1.15 × 10⁹ m³) in the Cordillera Blanca. Approximately, 50% of the lakes have potential peak discharges > 1000 m³/s in case of lake outburst floods, implying a need for additional studies for risk assessment. © 2020 John Wiley & Sons, Ltd.