Was there ever a Terminal Lunar Cataclysm?: With lunar viscosity arguments

About 30 years ago there was a suggestion by several able scientists at the California Institute of Technology that the Moon had undergone a Terminal Lunar Cataclysm. This meant that most of the early impact cratering had been concentrated strongly at about the time of formation of the Imbrium basin. This solution was discussed in many papers and the idea of a cataclysm gradually faded away. In about 1990 it was again revived by several scientists. The idea of a Terminal Lunar Cataclysm at about the time the Imbrium basin was formed was advanced albeit in a somewhat different manner. The present paper has been written to analyze the various observations and interpretations that have been advanced to permit a cataclysm. It is concluded that the three main proposals, which, if correct, would have permitted a cataclysm to have occurred, are each faulty and not consistent with such a cataclysm. To demonstrate this conclusion it was necessary to determine absolute ages of various lunar features. This meant, in part, determinations of the existence and nature of lunar crustal viscosity consistent with times of formation of six lunar basins. The results of such studies yielded an internally consistent model which requires a long period from the original formation of the Moon at about 4.5 byr to a time slightly earlier than that of the formation of the Imbrium basin at about 3.84 byr. On this model there is no indication of a clustering of events and it is concluded that a Terminal Lunar Cataclysm never occurred.