DEPOSITIONAL AND DIAGENETIC HISTORY OF TRAVERTINE DEPOSITED WITHIN THE ANIO NOVUS AQUEDUCT OF ANCIENT ROME

Travertine deposits preserved within ancient aqueduct channels record information about the hydrology, temperature, and chemistry of the flowing water from which they precipitated. However, travertine is also chemically reactive and susceptible to freshwater diagenesis, which can alter its original composition and impact reconstructions of aqueduct operation, maintenance, and climate. Hydraulic reconstructions in combination with a suite of high-resolution optical, laser, electron, and x-ray microscopy analyses, have been used to determine the original crystalline structure and diagenetic alteration of travertine deposited in the Anio Novus aqueduct built in AD 38-52 at Roma Vecchia. Age-equivalent travertine deposits, precipitated directly on the mortar-covered floor at upstream and downstream sites along a 140 m-long continuous section of the Anio Novus channel, exhibit consistent crystalline textures and stratigraphic layering. This includes aggrading, prograding and retrograding sets of linguoid, sinuous and hummocky ripple mark bedforms, as well as sand lags with coated siliciclastic grains deposited on the lee slope of travertine ripple crests. The original aqueduct travertine, which is similar to travertine formed in analogous natural environments, is composed of shrub-like dendritically branching aggregates of 1-3 mm-diameter euhedral calcite crystals. Dark brown organic matter-rich laminae, formed by microbial biofilms and plant debris, create stratigraphic sequences of high-frequency dark-light layering. This hydraulic and petrographic evidence suggests that large radiaxial calcites diagenetically replaced the original aqueduct travertine crystalline shrubs, forming upward branching fabric destructive and mimetic replacement crystals that crosscut the biofilm laminae. These approaches create the type of depositional and diagenetic framework required for future chemostratigraphic analyses of travertine deposited in the Anio Novus and other ancient water conveyance and storage systems around the world, from which ancient human activity and climate change can be more accurately reconstructed.