CRITERIA FOR THE DETECTION OF LUNAR CRYPTOMARIA

Cryptomaria are mare basalt deposits hidden or obscured by superposed higher albedo material or variations in albedo. They represent a recor d of the earliest mare volcanism, and may be a significant volumetric contribution to the volcanic and magmatic history of the Moon. In orde r to assess their global distribution and significance, criteria for t he identification of cryptomaria are developed and techniques for loca ting them are described. These criteria and techniques include the pre sence of dark halo craters, identification by spectral mixing analysis , identification by geochemical evidence, association with light plain s units, location within basin topography, proximity to known mare, re lation to mascons indicated by gravity anomalies, and identification o f the source of an obscuring agent, such as crater ejecta. On the basi s of these criteria and techniques, several types of cryptomare are re cognized, depending on the nature of ejecta and mare materials. Crypto maria may be formed when maria are obscured by coverings of proximal o r distal basin ejecta, or by crater ejecta dusting, or when ejecta cov ers over basalts which lack a distinctive 1 mu m absorption band. Usin g these concepts we outline three case studies: 1) the Schiller-Schick ard region adjacent to the Orientale basin, classified as a basin-ejec ta cryptomare and grading from distal to proximal, with possible crate r-ejecta covering occurring in the southwestern portion of the region, 2) the Balmer basin, classified as a crater-ejecta-dusting cryptomare , and 3) the Australe basin, in which two types of cryptomare were ide ntified: a) crater-ejecta-dusting on old mare patches and b) possible distal-basin-ejecta covering even older mare material. These case stud ies provide criteria for the further global identification and classif ication of cryptomaria and stress the heed for utilization of multiple criteria and data sets.