Bathymetric signatures and sequence overprint of mollusk associations from Late Quaternary sequences of the Po Plain (Italy)

Late Quaternary mollusk-dominated sequences of the Po Plain (N. Italy) were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns. Three densely sampled cores (89 samples, 98 genera, >23000 specimens), dominated by extant species with known environmental distributions, were analyzed using Detrended Correspondence Analysis (DCA). The DCA scores, calibrated with ecological data on extant genera, provided outstanding estimates of bathymetry (precision: +/-3m) and related environmental parameters. Depth-related successions of mollusk association delineated using DCA were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques (e.g., quantitative depth estimates for maximum flooding surfaces). The DCA ordination demonstrates the severity of the sequence stratigraphic overprint exerted on the associated fossil record. In all studied successions, samples are highly uniform taxonomically during late TSTs, and highly variable during the following HSTs. This pattern implies that turnover rates and beta diversity should be spuriously exaggerated during HSTs, relative to late TSTs. When data are re-examined across comparable systems tracts, nearly identical species associations repeat during the last and current interglacial cycles, indicating that Po Plain mollusk associations have remained remarkably stable over the last 125ky. The results support the bathymetric interpretation of DC1 postulated previously for the Paleozoic fossil record, demonstrate the strong stratigraphic overprint of paleoecological patterns predicted by computer modeling, and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations.