TESTING AND REFINING STRATIGRAPHIC APPLICATIONS OF QUANTITATIVE PALEOBIOLOGY USING QUATERNARY SUCCESSIONS OF THE PO PLAIN (ITALY).

Over the last decade multiple studies focused on quantitative integration of paleontological and sequence stratigraphic patterns. This new approach (Stratigraphic Paleobiology), showed that rigorously collected paleontologic data may archive high-resolution environmental signatures that can be quantified by applying multivariate methods and then used to augment stratigraphic interpretations. In this study, mollusk associations found in two cores were used to test the informative power of quantitative paleoecological patterns derived from well-understood marine sedimentary successions. Specifically, using empirical data from the Holocene sedimentary, glacioeustatic depositional cycle of the Po Plain (Italy) bathymetric patterns are examined at different cyclicity scale. Two cores (205-S9 and 205-S14) were densely sampled with maximum vertical spacing of 1m. The resulting database (i.e., more than 10000 specimens, ~ 100 genera and 110 samples), dominated by extant mollusk taxa with known environmental distribution, was treated with multiple ordination techniques (such us DCA) proved very useful in linking stratigraphic and paleoecological data. To minimize the distorting impact of very abundant genera the values were log-transformed. A comparison of multiple ordination outputs of data matrices derived using various filtering parameters allowed us to separate the analytically robust patterns, which persist regardless of the analytical technique and data filters applied, from the analytically volatile (and thus suspect) outcomes, which vary depending on data filters applied. By examining samples with ordination techniques a depth-related pattern seems displayed along the first ordination axis. Hence, the DCA axis 1 outcome has been confronted with an ecological (bathymetric) dataset compiled for extant genera from the Italian Mollusk Census Database (ENEA-CRAM). A bathymetric interpretation of the first DCA axis is confirmed directly by a strong and statistically significant correlation between DCA genera values (plotted along DCA axis 1) and the preferred bathymetry of the same extant mollusk genera recorded in the ENEA-CRAM database. The resulting outputs indicate that: 1) Late Quaternary fossil assemblages can be used to calibrate quantitatively bathymetric gradients in the shallow marine sedimentary successions; 2) Fossils association clearly track long time-scale cyclicity (here, 4th order). Moreover, our incipient data (that require more extensive testing) suggest that the approach may be applicable to even higher-frequency cycles (103yr); 3) Quantitative Paleobiology represents a useful sequence-stratigraphic tool by enhancing sedimentary basin analysis with numerical bathymetric estimates.