Ammonite Taphocycles in Carbonate Epicontinental Platforms

Abstract

Variations of preservational features of the successive recorded associations of ammonites in carbonate epicontinental platforms enable distinction of taphonomic cycles induced by relative sea-level changes. A taphocycle comprises two or more successive recorded-associations showing cyclical variations in their taphonomic characters, resulting from an environmental cycle. Shallowing-upwards sequences in carbonate outer platforms, and positive taphosequences, were formed during phases of increasing water turbulence and decreasing rate of sedimentation. Positive and negative taphosequences, (or taphosequences of increasing and decreasing turbulence), enable identification of shallowing-upwards sequences and infilling sequences of fifth-order respectively. Condensed sections show different characters in shallow and proximal environments in relation to deep and distal environments of the carbonate epicontinental platforms. The degree of taphonomic condensation in preserved ammonite associations reaches the highest values in shallow and proximal environments of the platform, not in deep and distal environments, though the degree of taphonomic heritage (i.e., the ratio of reelaborated (reworked) elements to total recorded elements) can, in both cases, reach 100%. These taphonomic data are of stratigraphic interest since they provide an independent test of the cycles distinguished in sequence stratigraphy.