CYCLES IN VARVES: ARE THEY OF TIDAL ORIGIN?

CYCLES IN VARVES: ARE THEY OF TIDAL ORIGIN?

A number of cycles in varve thickness have been reported from modern varved sediments. For example, in Santa Barbara Basin off California, a cycle near 12 y, and others near 25, 58 and 100 have been found by spectral analysis (Biondi et al., 1997, Geophys. Res. Letts. 24, 193). Off Pakistan, cycles of period 14, 30, 39, 45, 56, 95, 125 and 250 years have been reported (von Rad et al., 1999, Quat. Res. 51, 39). One possible source of cyclic sedimentation is tidal action, either through periodic sweeping of the shelves by tidal Kelvin waves, or by a tidal influence on climate, or both. Evidence is presented, based on statistical combing of varve spectra, that a portion of the energy contained may be reasonably ascribed to longterm periodicity in tidal forcing.