An analysis of cyclic tidal deposits: Statistical time series properties, extraction of Earth-Moon parameters, and observed intertidal sedimentation.

摘要

Tidal rhythmites/bundles are facies that can encode process-related depositional information and luni-solar periodicities. These deposits have been widely recognized in the stratigraphic record. Detailed empirical studies of deposition in the modern regime, and more precise analyses of the frequency content of tidalite signals, can facilitate more detailed sedimentological interpretations and extraction of paleotidal parameters. In this study, rhythmic sedimentation at two unique fluvio-estuarine transitions in a macrotidal estuary is discussed. Further work on general rhythmite signals addresses time series properties and describes a method to extract primary tidal constituents. A formulation is then provided to calculate past day length and Earth-Moon distance from sub-yearly data.;Turnagain Arm, Alaska possesses a number of glacial meltwater streams that drain transversely into the ord/estuary, forming unique fluvio-estuarine depositional systems. Two such systems, one located within a small embayment in a broad alluvial valley and the other where a stream debouches into mudflats directly from mountain slopes, were studied and compared. The embayed site exhibited slower deposition rates, finer-grained sediments with pronounced mud drapes, and slower evolution than the open-flat transition. Position in the tidal frame was a sensitive parameter determining deposition, with lower regions more subject to fluvial erosion (seasonal-scale), and higher regions only exhibiting spring-cycle deposition. Deposition is well-approximated by a linear flow model. Grain size statistics were gathered and revealed laminae thicknesses correlated to median grain diameter.;Time series properties of sub-yearly tidalite records were investigated and numerical experiments were performed utilizing maximum entropy and periodogram spectral analysis methods. Analyzing precision as a function of record length and missing deposits reveals approximately 90-95% precision can be obtained for records of 6-7 neap-spring cycles missing few deposits. Amplitude modulation properties of tidalite signals facilitate extraction of M2 and S2 frequencies and, thus, relative lengths of the lunar and solar days. Employing these analytical methods and fundamental physical relations, the past sidereal period and day length can be calculated in consistent temporal units, along with Earth-Moon distance. A calculation using Carboniferous tidalites reveals an average lunar recession rate of 0.740 +/- 0.069 cm/year and day length of 23.572 +/- 0.379 hours.