NATURE, RANK AND ORIGIN OF PHANEROZOIC SE DIMENTARY CYCLES

The sedimentary record can be described as the surimposition of severa l orders of relative sea-level variations, the sum of tectonics and eu static changes. Three types of relative sea-level variation signals ha ve been identified: (1) cyclic, periodic, high-frequency signals (14,0 00 to 400,000 years), mainly of eustatic origin, (2) cyclic, non perio dic, middle-frequency signals (0.6 to 15 Ma), of mixed origin and (3) non cyclic, low-frequency signals (10 to 40 Ma), mainly of tectonic or igin. Differential preservation of sedimentary environments occurs dur ing a high-frequency relative sea-level variation: marine environments are preserved during progradation (regression) and continental domain s during retrogradation (transgression). The surimposition of several orders of relative sea-level changes produces a modification (or a dis torsion) of the stratigraphic response of the high-frequency sequences .