Friday, October 21, 2016

Carbonate deposits from the ancient aqueduct of Béziers, France as Evidence of Local Environment During Roman Empire


Passchier et al


Carbonate deposits from a Roman aqueduct in Béziers, southern France, record environmental conditions during the late first century C.E. These deposits formed in a steep section of the aqueduct with a high flow velocity, which caused rapid deposition of up to 11 mm of calcite per year over a period of 22–24 years. The microstructure, trace element and stable isotope composition show that regular deposition was interrupted by high-discharge events, probably in response to heavy rainfall during autumn and winter, transporting colloidally- and particle-bound elements and depositing calcite with elevated δ18O values. Individual autumn high-discharge events coincide with abrupt decreases in δ13C from − 8 to − 12‰ giving rise to a saw-tooth profile. In some years, several high flow events persisted throughout the winter, suppressing this profile. Event horizons of micrite capping sparite growth surfaces, enriched in Mg, may represent anomalously low water levels or periods when the channel fell dry. In comparison to carbonate deposits from Roman aqueducts in the Eastern Mediterranean, visible layering is less regular and pronounced in Béziers, reflecting a more complex precipitation pattern.

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