Abstract
A study of a late Pleistocene 30 m-thick travertine borecore drilled in the north-western sector of the Acque Albule basin (Tivoli, Rome), type area for these freshwater calcareous deposits, it is here presented. The Tivoli travertines have been traced sideways from the core into wire-cut surfaces well exposed in nearby active quarries. They normally appear well bedded and show erosional-non depositional discontinuities, recurring at a centimetric to metric–decametric scale and show a variable penetration by younger sediments (Ca-carbonates as well as reddish soils), as evidenced by their karstic and/or pedogenetic features. The microstratigraphic and sedimentologic analysis has revealed a number of lithofacies grouped in three associations, suggesting environmental domains spanning from gentle slope to shallow lake. This sedimentary organization and stable isotope (O, C) analyses carried out at cm scale have allowed to recognize a hierarchy of higher to lower frequency cycles. On these bases, it is argued and proposed that the higher frequency cyclicity is due to water table fluctuations, as a consequence of millennial-scale climatic changes that in turn may be linked to the solar perturbations (short-term cycles). The lower frequency, instead, cycles (metres to decametres in thickness) suggest medium-term (sub-Milankovitch) and longer term, precession-driven (Milankovitch) periodicities. These conclusions are supported by the correlation of the hierarchical organization of the travertine cycles with a number of radiometrically dated discontinuity surfaces outcropping along the quarry walls and traceable into the borecore. This correlation allows the cyclostratigraphic analysis to be constrained into late Quaternary geochronology and fits well within the precession and obliquity periodicities, as predicted for this time interval.
Published Version
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