Calculating lunar retreat rates using tidal rhythmites

Tidal rhythmites are small-scale sedimentary structures that can preserve a hierarchy of astronomically induced tidal periods. They can also preserve a record of periodic nontidal sedimentation. If properly interpreted and un derstood, tidal rhythmites can be an important component of paleoastronomy and can be used to extract information on ancient lunar orbital dynamics in cluding changes in Earth-Moon distance through geologic time, Herein we pre sent techniques that can be used to calculate ancient Earth-Moon distances. Each of these techniques, when used on a modern high-tide data set, result s in calculated estimates of lunar orbital periods and an Earth-Moon distan ce that fall well within 1 percent of the actual values. Comparisons to res ults from modern tidal data indicate that ancient tidal rhythmite data as s hort as 4 months can provide suitable estimates of lunar orbital periods if these tidal records are complete, An understanding of basic tidal theory a llows for the evaluation of completeness of the ancient tidal record as der ived from an analysis of tidal rhythmites, Utilizing the techniques present ed herein, it appears from the rock record that lunar orbital retreat slowe d sometime during the mid-Paleozoic.