PALEOECOLOGICAL, PALEOENVIRONMENTAL, AND SEQUENCE STRATIGRAPHIC APPLICATIONS OF SHELL CONCENTRATIONS

The joint consideration of fossil assemblage composition and extractable paleoenvironmental signals may be a valuable tool for the improvement of sequence stratigraphic interpretations. To test this statement, late Quaternary mollusk-rich fossil assemblages from the eastern part of the Po Plain, Italy, were analyzed using multivariate methods. Spanning 150 ky, 8 sampled cores capture two major transgressive-regressive sequences of late Pleistocene and Holocene interglacial intervals and contain fossil assemblages consisting of numerous extant bivalve, gastropod, and scaphopod taxa with known environmental distributions. These cores were densely sampled with 10 cm vertical spacing between samples, and shell material was identified to the species level in each sample. A total of 284 samples have been processed from 8 cores taken at latitudinal and longitudinal transects; and 231 species constituting 120 genera have been identified from a total of nearly 60000 individual specimens. Samples were analyzed via detrended correspondence analysis (DCA), and the resulting DCA scores were calibrated with modern ecological data on extant genera to provide estimates of bathymetry. Depth-related successions of these mollusk associations delineated using DCA were consistent with independent sequence stratigraphic interpretations. The DCA ordination data, calibrated using present-day ecological data, can provide quantitative insights into sequence stratigraphy, including bathymetric and sea-level change estimates, improved interpretation of depositional sequences, and recognition of paleoecological recurrence patterns across comparable systems tracts. Previous analyses were conducted on 3 cores and the patterns are retained reasonably well after data from additional 5 cores have been added. The taxonomic data taken in concordance with sequence stratigraphic information should allow us to develop a regional, 4D reconstruction of the most recent history of this sedimentary basin.