Petrologic profile of Apollo 16 regolith at Station 4

The Apollo 16 double drive tube core 64001/2 (total depth about 60 cm) consists of four petrologic units based on the modal abundance of lithic, monomineralic, and other particles in the 20-500 micron size range of samples from 12 levels. Variation in the abundance of particles derived directly from bedrocks is low and the core soils probably represent only one set of source rocks. The chemical signature of an excessively high mare basalt component at about 42 cm correlates with an excess of regolith breccias, which may then be the physical carrier. The core soils as a whole show a systematic size-composition relationship that may be attributed to a large-scale macroscopic reworking and the consequent masking of any or all previous surface process related mixing event. However, on a much smaller scale (about 0.5 cm), individual soil layers seem to have evolved more via mixing than via in situ reworking.