QUANTITATIVE PALEOECOLOGICAL PATTERNS ACROSS LATE QUATERNARY TRANSGRESSIVE-REGRESSIVE CYCLES OF PO PLAIN, ITALY

The integration of sequence stratigraphy with paleobiology can enhance our understanding of spatiotemporal biotic patterns recorded in the fossil record. Used in conjunction with a highly-resolved stratigraphic framework, biotic patterns can be assessed in the context of lithology and depositional cycle. The Po basin in Italy has been well studied in terms of sequence stratigraphy, lithology, and facies development. This study focuses on combining the known sequence stratigraphy with the multivariate paleoecology of mollusk associations across systems tracts and through time.

The late Quaternary sequences of the Po Plain include two, well developed transgressive-regressive cycles that record the two most recent interglacial phases. Expanding greatly on our previous work, we have processed 611 bulk samples from 16 cores. These samples yielded 75,103 specimens, representing 334 species from 152 genera of mollusks. All analyses were carried out at the genus level. All rare species (≤2 individuals), all non-marine taxa, and all small samples were removed (≤20 specimens) reducing the dataset to 265 samples, 73,569 specimens, 193 species from 102 genera. Detrended Correspondence Analysis (DCA) was used to perform ordinations on the relative abundance matrix using PAST.

DCA of genera suggests that bathymetry is the primary source of variation in the data. This is confirmed by a strong linear correlation between DC1 scores and the preferred bathymetry of 24 common extant genera. When analyzed across samples, bathymetric interpretations vary depending on the number of depositional environments captured in cores across the study area. Thus, cores with only a few depositional environments display a less robust linear correlation between DC1 scores and bathymetry. DCA-estimated water depths of maximum flooding surfaces indicate that seaward and northern cores record substantial increase in water depth consistent with the northward location of the regional depocenter offshore from the Po River Delta. DCA ordinations calibrated using present-day ecological data provide quantitative sequence stratigraphic insights that allow for the assessment of depositional gradients through time and space based on numerical bathymetric estimates derived from paleobiological patterns.