SPATIO-TEMPORAL VARIABILITY IN LATE QUATERNARY MARINE BENTHIC ASSOCIATIONS OF THE PO PLAIN, ITALY

Interpretations of bathymetric gradients through multivariate analyses of fossil associations have been fruitful for understanding paleoecologic and stratigraphic patterns. Moreover, evaluating faunal assemblages in the context of finely-resolved bathymetric gradients can augment interpretations of depositional environments and marine community structure. However, the reconstruction of bathymetric gradients may be hampered by spatio-temporal variation of the fossil record. Namely, the distribution pattern of faunal assemblages is not continuous, but patchy in nature, potentially giving rise to variation in the bathymetric and stratigraphic signal.

Using late Quaternary mollusk-rich assemblages from the Po Plain (Italy), fine-scale spatio-temporal patterns in faunal composition have been explored using quantitative approaches. A total of eight cores were densely sampled at 10 cm intervals yielding 284 samples, 231 species representing 120 genera, and over 60,000 individual specimens. To quantify variation in faunal composition in space and time, detrended correspondence analysis (DCA) was performed individually for each core. The DCA scores were plotted stratigraphically and correlated to explore faunal variation and bathymetry.

Tracking the lateral variation across all eight cores revealed changes in dominant taxa and assemblages. The spatio-temporal stratigraphic deviations revealed greater faunal variation during the highstand systems tracts. Holocene HST assemblages contain distinct faunal associations dominated by Lentidium mediterraneum, whereas late Pleistocene HST assemblages are dominated by Varicorbula gibba. Extensive flooding during the late Pleistocene and possible oversampling from Holocene strata could of caused this shift in assemblages. Analysis of faunal compositions along depositional gradient (along a transect oriented landward from the current Adriatic coastline) demonstrated shifting of communities from faunas indicative of fully marine prodelta to those typical to lagoonal and brackish environments. The onshore-offshore community gradient is remarkably similar when comparing to the late Pleistocene and Holocene sea level cycles.