On estimating contributions of basin ejecta to regolith deposits at lunar sites

Abstract

On estimating contributions of basin ejecta to regolith deposits at lunar sites Oberbeck 1975), and takes into account the size distribution of the individual fragments ejected from the primary crater. Using the model, we can estimate, for an area centered at the chosen location of interest, the average distribution of thicknesses of basin ejecta deposits within the area and the fraction of primary ejecta contained within the deposits. Model estimates of ejecta deposit thicknesses are calibrated using those of the Orientale Basin (Moore, Hodges, and Scott 1974) and of the Ries Basin (Hörz, Ostertag, and Rainey 1983). Observed densities of secondary craters surrounding the Imbrium and Orientale Basins are much lower than the modeled densities. Similarly, crater counts for part of the northern half of the Copernicus secondary cratering field are much lower than the model predicts, and variation in crater densities with distance from Copernicus is less than expected. These results suggest that mutual obliteration erases essentially all secondary craters associated with the debris surge that arises from the impacting primary fragments during ballistic sedimentation; if so, a process other than ballistic sedimentation is needed to produce observable secondary craters. Regardless, our ejecta deposit model can be useful for suggesting provenances of sampled lunar materials, providing information complementary to photogeological and remote sensing interpretations, and as a tool for planning rover traverses (e.g., Haskin et al. 1995Haskin et al. , 2002.

The lunar‐wide effects of basin ejecta distribution on the early megaregolith

“…The analysis by Oberbeck and Morrison (1976) and later by Haskin et al (2003b) highlighted the importance of two Table 1. Identified basins in order of formation as identified by Wilhelms (1987) with the center latitude and longitude, and Main Topographic Ring Diameter from Spudis (1993).…”

“…Petro and Pieters utilized the ejecta scaling equations of Pike (1974) and Housen et al (1983) and the concept of an ejecta mixing ratio from Oberbeck et al (1975). Although similar in concept to the detailed model of Haskin et al (2003aHaskin et al ( , 2003b, the Petro and Pieters approach readily allows global scale issues to be addressed. Several permutations of the Oberbeck mixing ratio were evaluated to determine how adjustments to the mixing ratio altered the results of the model.…”

“…Craters with diameters larger than 300 km, collectively known as basins, are thought to have formed only during the first ∼700 Myr of lunar history (Hartmann and Wood 1971;Wilhelms 1987;Spudis 1993;Ryder 2002). Given the size, distribution, and the early formation of these large impact structures, they are thought to have played an important part of the geologic evolution of the lunar crust (e.g., Moore et al 1974;Wilhelms 1987;Wieczorek and Phillips 1999;Jolliff et al 2000;Haskin et al 2003b). Because of their large sizes, each basin excavated and distributed a large amount of material across the entire Moon (Short and Foreman 1972;McGetchin et al 1973;Pike 1974;Arvidson et al 1975;Head et al 1975;Haskin 1998;Wieczorek and Phillips 1999).…”

Thickness of proximal ejecta from the Orientale Basin from Lunar Orbiter Laser Altimeter (LOLA) data: Implications for multi-ring basin formation

“…If, however, the transient crater was well within the Cordillera ring, as discussed below, the thickness at the rim of the transient cavity implied by this equation is potentially consistent with our results. Petro and Pieters [2006] applied the Housen et al [1983] scaling [see also Haskin et al, 2003] to suggest T TR = 0.0078R TR, which would imply a thickness of 3600 m if the Cordillera rim is the appropriate radius for the transient crater.…”

Mars Sedimentary Geology: Key Concepts and Outstanding Questions

“…Finally, there is one very important process for sediment generation on Mars that has been well appreciated on the Moon: impact shattering of bedrock (Haskin et al, 2003;Petro and Pieters, 2008). This also was likely a very important process on Mars, particularly early on in its history showing stratigraphic change from clay-rich strata to overlying sulfate-rich strata.…”