AR-40 AR-39 GEOCHRONOLOGY OF ROMAN VOLCANIC PROVINCE TEPHRA IN THE TIBER RIVER VALLEY - AGE CALIBRATION OF MIDDLE PLEISTOCENE SEA-LEVEL CHANGES/

The close proximity of the Roman volcanic province to the Tyrrhenian S ea coastline provides a unique opportunity to combine clastic stratigr aphy with Ar-40/Ar-39 geochronology to constrain the timing of Pleisto cene sea-level oscillations. The main eruptions from the Monti Sabatin i volcanic district occurred during the interval 568-280 ka, and the A lban Hills volcanic district mails eruptions span 560-350 ka. The inte rfingering of volcanics from these two centers with fluvial and shallo w-marine sediments of the Tiber River and delta provides a datable rel ative sea-level record for this portion of middle Pleistocene time. We calculate the timing of glacial terminations using analytical errors only, then assess age uncertainties that include analytical plus syste matic errors; the latter is required to compare Ar-40/Ar-39 ages with those from other dating methods. Terminations III, V, and VI occur at 278 (261, 285) ha (95% confidence interval), 430 (422, 442) ka, and 53 4 (520, 541) ka, respectively, when only analytical uncertainties are used to calculate the ages of bracketing volcanic horizons. The confid ence interval expands significantly when full external errors are cons idered, with predicted ages of 276 (258, 289) ka, 430 (416, 448) ka, a nd 533 (512, 548) ka for the terminations. The resultant Ar-40/Ar-39 c hronology is generally consistent with the deep-sea delta(18)O record of sea-level change tuned to Earth's obliquity cycle for glacial termi nations VI, V, and III. In addition, the Ar-40/Ar-39 constrained Tiber River delta sea-level record has the added benefit of identifying whe n coastal sections respond to complex (multistep) terminations.