Sequence stratigraphy and the resolution of the fossil record

Sequence stratigraphy, a major theoretical achievement of earth sciences, integrates facies associations and stratal architecture within a chronological framework of the geological record. The sequence stratigraphic model implies that sediment supply to the basin, preservation potential of individual horizons, and the resolution of paleontological data co-vary with base-level fluctuations, especially for siliciclastic depositional systems. Using Holocene transgressive-regressive successions of the Po Plain (Italy), we assessed the model's hypotheses by analyzing 249 marine mollusk shells dated individually using C-14-calibrated amino acid racemization methods. As postulated by the model, the temporal resolution of the fossil record, frequency of depositional events, and net accumulation rates decreased upward concomitantly through the transgressive systems tract reaching minima in the condensed section (maximum flooding zone). The reverse trend, with increasingly frequent, thicker, and less time-averaged beds, was observed throughout the overlying highstand systems tract. The results quantify the postulated sequence stratigraphic asymmetry in temporal resolution of the fossil and sedimentary records.