Abstract
We present four new 40Ar/39Ar ages of tephra layers from an aggradational succession (Valle Giulia Formation) near the mouth of the Tiber Valley in Rome that was deposited in response to sea-level rise during Marine Isotopic Stage (MIS) 13. These new ages, integrated with seven previously determined ages, provide the only extant independent, radioisotopic age constraint on glacial termination VI and on the duration of MIS 13 sea-level rise. The new geochronologic constraints suggest a long duration for the period of sea-level rise (533 ± 2 through 498 ± 2 ka) encompassing two consecutive positive peaks of the δ18O curve (substages 13.3 and 13.1). Consistently, the litho-stratigraphic features of the sedimentary record account for two aggradational phases separated by an intervening erosional phase. Moreover, the ages obtained for this study give us the opportunity to compare the timing of the sea-level fluctuations inferred from the stratigraphic record and that provided by the astrochronologic calibration of the Oxygen isotopic curves, and to assess the calibrations of 40Ar/39Ar standards. Results of this comparison indicate that the best match is for an age of 1.186 Ma for the Alder Creek Rhyolite sanidine and 28.201 Ma for the Fish Canyon Tuff sanidine.
Highlights
Assessing ages of sedimentary successions deposited in near-coastal environments in response to sea-level fluctuations is a straightforward mean to investigate the timing of glacio-eustatic cycles and provide insights on their forcing mechanisms
When interpreted in the light of the sedimentary model by, these stratigraphic features substantiate the use of the Tufo del Palatino (TP) age to date glacial termination VI at the onset of Marine Isotopic Stage (MIS) 13.3
New geochronologic and sedimentary data presented here show that the stratigraphic record of the Valle Giulia Formation (VGF) represents among the best records of glacial termination VI and the associated sea-level fluctuations during MIS 13
Summary
Assessing ages of sedimentary successions deposited in near-coastal environments in response to sea-level fluctuations is a straightforward mean to investigate the timing of glacio-eustatic cycles and provide insights on their forcing mechanisms In this light, the coastal plain of the Tiber River near Rome (Fig. 1) is a natural laboratory for investigating the timing of the Pleistocene glacial terminations, thanks to the presence of two active volcanic districts, yielding continuous intercalation of tephra layers within the fluvial and coastal sediments. 8) used the ages of the gravel-clay transitions in the older aggradational successions of the Paleo-Tiber River, determined through 40Ar/39Ar dating of intercalated tephra layers, as a proxy of the last four glacial terminations II through V These ages were compared to the astrochronologically calibrated ages (e.g. 12) and those provided by the independently dated Relative Sea-Level (RSL) curve[13]. Note that the uncertainties on the 40Ar/39Ar ages used include the analytical and systematic (i.e., decay constant) uncertainties when being compared to ages of an orbitally tuned timescale
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