Analysis of modern tides and implications for ancient tidalites

Recently, stacked successions of ancient tidal rhythmites have been found to preserve long records of tidal cycles. These include semidaily, daily, semimonthly, monthly, semiannual, annual and multiyear periods. Though such deposits reveal much about ancient tidal dynamics, the tidal signatures within the rhythmites can be masked or modified by basinal or nontidal effects. This paper discusses the results of an analysis of data from several different modern tidal stations. We show how actual tidal data can be abstracted to a form similar to what might ideally be preserved in the rock record, and then power spectra are calculated to yield estimates of the astronomical periods which can be compared to the current values. In this study, data from four modern tidal stations, ranging from diurnal to semidiurnal, are analyzed as both time- and event-series. A series of tests, which involve selective removal of parts of the tidal signal, are made using the modern tidal-station data. These tests were performed in order to determine to what extent the tidal signal can be degraded and still be recognized. Finally, we discuss some implications of the similarities of the modern and ancient tidal data and suggest how ancient data may be used to constrain basinal paleography and make inferences regarding ancient lunar orbital geometries.