Stratified ejecta boulders as indicators of layered plutons on the Moon

• High resolution images show boulders with alternating low and high albedo layering.
• These boulders exhibit features such as cross-bedding and tapered layering.
• Measurements and observations used to test four hypotheses of their origin.
• Layer features are consistent with having formed in a layered igneous intrusion.

High resolution images of stratified ejecta boulders on the lunar nearside reveal layers of alternating low and high albedo material. We measured the thickness and albedo of each alternating light and dark layer from 29 stratified boulders located in Aristarchus Crater and Mare Undarum. The results were used to test hypotheses to explain the origin of the observed strata in these impact ejected boulders. Morphologically, these boulders demonstrate cross-bedding, trough-shaped layering, tapered layering and cumulate enclaves. We interpret these characteristics to be evidence that these layers result from periodic disruption by convection or density currents within a cooling layered igneous intrusion. We demonstrate that the layering observed in these boulders cannot be the result of known processes occurring on the surface, but instead suggests a history of complex intrusive igneous processes within the lunar crust.