TIETZ, Bethany ('98) (Advisor: Charles McClennen)
Fifty cores taken from salt marsh islands and subtidal mudflats
revealed the lagoonal stratigraphy of the Lagoon of Venice, Italy. Graphic
plots of the cores yielded accurate comparison of features such as grain size,
color, shell abundance, plant fibers/peat and anthropic material distributed at
various depths at each core location. The cores contain similarities which are
dependent upon the depositional sub-environments within the lagoon such as
channel, marsh and mudflat. However distinct differences in stratigraphy are
observed both horizontally and vertically within each specific area. Lagoonal
sediments are dominantly medium gray silts with variations of clay and sand.
Most sediments are shelly with less plant fibers. Artificial fill (sand) is
present at the top of some cores. Thinner sand lenses are evidence of channel
scour and fill events as well as channel migration. Grain size analysis using
the Malvern Mastersizer on selected samples commonly revealed a bimodal
distribution which was dominantly silt to clay, however sand was also present.
The lagoonal sediments commonly show the effects of iron oxide staining from
intertidal and subaerial exposure. Select cores from the Island of San
Francesco del Deserto contain copper enriched clays, stained from previous
industrial activities. The top 1-2 meters of the cores are enriched with
fragments of anthropic material on all island settings. In the longer cores,
a base to the lagoonal stratigraphy was found at depths varying from 4-6 meters.
Pre-lagoonal fluvial sands contain no shells and are locally overlain by anoxic
clays. The general slope from mainland to barrier beach is less than 1:1200
and variations in the depth of the lagoonal base are dependent on locations
within the Lagoon. Cores provide evidence of tidal channel meanders which
have migrated throughout the Lagoon. The rate and depth of channel migration
will be determined by forthcoming AMS-14C dates.
Channel inlet and barrier beach migration are also clearly seen in the cores
from the Lido Barrier Island at San Nicolo which are dominated by buff beach
sands. Variations in the nature of the cored lagoonal sediments provide an
impetus for improved sampling density in future expeditions. This data base
and analysis also has implications for archeological research as well as
coastal and environmental management practices.
