COPPER-ENRICHED LAGOONAL SEDIMENT DEPOSITS BURIED AT THE ISLAND OF SAN FRANCESCO NEAR VENICE, ITALY

O'MALLEY, TODD M., and McCLENNEN, Charles E., Dept. of Geology, Colgate University, 13 Oak Drive, Hamilton, NY 13346,
tomalley@center.colgate.edu
cmcclennen@center.colgate.edu

Samples gathered in a pair of 3 to 5 m long hand auger cores on and around the Island of San Francesco del Deserto in the Lagoon of Venice, Italy, display an anomalous layer of firm (overly consolidated) clay rich sediments light blue/grey green in color (1 for GLEY 5/10 Y and 1 for GLEY 5/5 GY) at 2 m depth between normal medium to dark grey lagoonal silts. Testing for the presence of anthropic (?) copper was conducted on both SEM-EDS and XRF for quantitative elemental major and trace abundances. Cu and Zn displayed abundance peaks in the SEM analysis of the target samples. The control samples of typical lagoonal sediments did not show similar peaks. XRF analysis further confirmed the presence of Cu and Zn in significant quantities. Si, Al, and Ca were other prominent elements whose abundances can be attributed to carbonate and quartz-rich sediment deposition in the lagoon. Possible explanations for the copper are: 1) the remnants of ancient cooper industry run-off from the island; 2) insitu, i.e., postdepositional, dissolution of copper/bronze hardware and artifacts in the lagoonal strata; and 3) bioaccumulation in the marine algae, Ulva lactuca, which preferentially incorporate Cu (and to a minor extent, Zn) in the leafy tissue and are subsequently preserved in the buried organic-rich deposits. The overconsolidation of the GLEY colored clay strata may be explained by postdepositional high salinity events and osmotic dewatering. Six additional cores have recently been collected to determine the concentration parameters and the local extent of the copper deposit on and around the island. These samples, presently under XRF analysis, will be correlated for inclusion in this presentation. Similarly, C14 AMS datable plant fibers, bone, seeds, and wood (presently being analyzed) will provide age control on the Cu/Zn enriched lagoonal strata.

http://departments.colgate.edu/geology/ Copyright 1997 © Colgate University.

Geology Home page