Thickness and volume of mare deposits in Tsiolkovsky, lunar farside

In the 193-km crater Tsiolkovsky on the lunar far side, dark mare deposits overlie a brighter unit presumed to be impact melt. Craters impacting through the mare materials commonly excavate the underlying impact melt and form a high-albedo ejecta deposit. Apollo metric photographs of Tsiolkovsky were divided into 25-sq-km bins, and within each bin a crater was statistically determined to be the minimum size necessary to excavate underlying impact-melt materials. This 'threshold' crater diameter was measured, and the corresponding depth of excavation was determined based on Maxwell's (1973) Z-model calculations. Crater excavation depths were related to mare thicknesses, and an isopach map was derived that shows an average mare thickness of 22.3 m and a maximum thickness of over 70 m. Based on these data, the most probable average thickness is 116 m with a corresponding mare volume of 1182 cu km. Comparing topographic data to those more accurately determined through impact crater excavation indicates that a possible floor resurgence of up to 95 m may have occurred prior to and during mare emplacement.