Paper No. 257-8
Presentation Time: 3:00 PM
STRATIGRAPHIC PALEOBIOLOGY AND HISTORICAL ECOLOGY OF THE QUATERNARY DEPOSYSTEM OF PO PLAIN
The Po Basin contains a thick succession of Quaternary sediments and represents one of the best understood active sedimentary systems owing to numerous stratigraphic, geochronological, and paleobiological studies. This progress report is based on quantitative sampling of a network of 16 cores and a newly established time-series of 249 mollusk specimens dated using radiocarbon-calibrated amino-acid racemization (AAR) methods. The analyses conducted so far produced five tentative conclusions. First, paleobiological patterns carry a predictable sequence stratigraphic overprint. TST (Transgressive Systems Tract) samples display a significantly higher alpha diversity than HST (Highstand Systems Tract) samples, whereas beta diversity is higher within HST relative to TST. Second, mollusk samples yield bathymetric estimates consistent with independent stratigraphic interpretations and the resulting depth proxies yield insights inaccessible via routine stratigraphic techniques. Third, AAR dating demonstrates that time averaging varies over multiple orders of magnitude across the sequence stratigraphic cycles. The late TST and Condensed Section display multi-millennial time averaging, whereas the early TST and HST successions are characterized by sub-millennial levels of temporal mixing. Fourth, the results substantiate the key predictions of the Sequence Stratigraphic Model. The frequency of depositional events, net-accumulation rates, and the temporal resolution of the fossil record all decrease upward through TST. The reverse trend is observed in the overlying HST. Fifth, marine communities reemerged unchanged following the most recent glaciation. The Late Pleistocene and Holocene interglacial ecosystems are both dominated by the same species, extinction and origination rates match predictions of simulations mimicking a homogenous system, and comparable bathymetric trends in beta turnover, alpha diversity, dominance, and specimen abundance are observed. The resilience of Po communities to natural climate oscillations contrasts with volatile responses of ecosystems affected by anthropogenic changes. These results support the utility of the stratigraphic paleobiology approach for investigating long-term ecological trends and basin-scale depositional processes.