CLIMATE-CONTROLLED FAULT-VALVE CYCLES REVEALED BY 3D STRATIGRAPHY AND U-SERIES GEOCHRONOLOGY OF THE LAPIS TIBURTINUS TRAVERTINE, TIVOLI, CENTRAL ITALY

The depositional and erosional history of the upper Pleistocene Lapis Tiburtinus travertine located 25 km in the east of Rome, Italy, near the Colli Albani quiescent volcano is analyzed by three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures within active quarries and of 114 drilled cores from industrial databases (kindly provided by Centro Valorizzazione Travertino Romano, www.centrotravertinoromano.it) reveal that the travertine body is approximately 20 km2 wide and averagely 60 m thick. The travertine thickens to about 90 m toward its western, N-S-elongated side, where thermal springs occur aligned over a seismically-active, N-striking, shallow fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 120 and 30 ka, respectively. The travertine succession is interrupted by five main erosional surfaces associated with paleosoils, conglomerates, and karstic features. Ages of erosional events match cold and dry climate periods occurred during late Pleistocene time. We interpret the aggradational growth of the travertine body as connected with warm and humid climate periods. The increase of the water table height in the travertine basin and in the surrounding carbonate massifs increased fluid pressures and discharge, and forced fault slip and related dilational deformations, thus keeping open the fluid pathways along the fault underlying the travertine. A hypothetical correlation is hence established between climate cycles and fault-valve activity. Results may be tested in sites where recent travertines and seismically-active faults occur (e.g. California, Greece, Nevada, and Turkey) to assess fault slip recurrence intervals and improve seismic hazard estimates.