Early diagenesis and clay mineral adsorption as driving factors of metal pollution in sediments: the case of Aveiro Lagoon (Portugal)

This work aims to define the factors driving the accumulation of metals in the sediment of the lagoon of Aveiro (Portugal). The role of initial diagenetic processes in controlling trace metal retention in surface sediment is traced by mineralogy, magnetic susceptibility and geochemical analyses. Although several studies have focused on the metal distribution in this polihaline and anthropized coastal lagoon, most of them have been solely focused on the total metal concentrations. This study instead represents the first attempt to evaluate in a vast area of the Aveiro Lagoon the role of biogeochemical processes in metal availability and distribution in three extracted phases: exchangeable cations adsorbed by clay and elements co-precipitated with carbonates (S1),organic matter (S2) and amorphous Mn hydroxides (S3). According to the sediment guideline values, the sediment is polluted by, for instance, As and Hg in the inner area of theMurtosa Channel, Pb in the Espinheiro Channel, Aveiro City canals and Aveiro Harbour, and Zn in the northern area of the Ovar Channel. These sites are located near the source areas of pollutants and have the highest total available concentrations in each extracted phase. The total available concentrations of all toxic metals are however associated, firstly, with the production of amorphous Mn hydroxides in most of the areas and, secondly, with adsorption by organic compounds. The interplay of the different processes implies that not all of the sites near pollution sources have polluted surface sediment. The accumulation of metals depends on not only the pollution source but also the changing in the redox state of the sediments that may cause alterations in the sediment retention or releasing of redox-sensitive metals. Results of this work sugsuggest that the biogeochemical processes may play a significant role in the increase of the pollutants in the sediment of the Aveiro Lagoon

Petrographic study and geochemical investigation of the evaporites associated with the Germik Formation (Siirt Basin, Turkey)

Evaporites of the Oligocene Germik Formation are represented by massive, laminated, laminated-banded, banded, nodular and/or brecciated nodular and nodular-banded lithofacies in the Siirt-Kurtalan area. Observations of massive and laminated-banded gypsums with undulated-shaped stromatolitic algal mats, corrugated folded structures and clay-carbonate and interlayered marl in laminated gypsum levels are very important in terms of their mechanisms of occurrences. Petrographic and mineralogic examinations of secondary gypsums in the Germik Formation generally display alabastrine and porphyroblastic textures with corroded anhydrite. Structures as satin-spar, chickenwire, enterolithic and minerals as dolomite, calcite and celestite are also observed. Geochemical evaluations of gypsum and anhydrite samples belong to the lithofacies have provided an approach of their original formation and understandings the environmental impacts (such as pH, paleotemperature, paleosalinity, surface-groundwater activity and bacterial activity). Therefore, a number of analyses were conducted on the different samples for major and trace elements and the gypsum-anhydrite samples were analyzed for isotope compositions. Trace elements of these evaporites were found to be in the range of the geochemical values of the depositional environment of shallow marine evaporites. These values show also occasional influx of terrestrial waters to the environment. Moreover, the differences in the isotopic values of the lithofacies identified by the stable isotopic studies indicate the effects of temperature, salinity, biogenic activity and diagenetic processes for the formation of evaporites, under the influence of climate. Geochemical evolution of gypsum and anhydrite lithofacies of the Germik Formation leads up to muddy evaporites indicating that they were deposited in the coastal sabkha or shallow marine environments within effectively developed paleoclimatic conditions, tectonic activities, diagenetic processes and depositional system