Sedimentology and Geochemistry of Quaternary Sediments and Determination of Sediment Transport, Tectonic setting in the wetland of Saghalak-Sar Rasht

Wetlands as unique, rich, and fertile ecosystems are among the most vital environments in the world. Quaternary sediments of wetlands are the main components of our environment and an essential source of clastic, organic, and chemical substances that can be caused by natural processes and erosion or created by human intervention. This article broadly deals with the grain size and geochemistry of Quaternary sediments in Saghalak-Sar as one of the wetlands in Guilan province in the north of Iran. The 74 surface and subsurface samples (from 10 core) of the sediments were graded, and sedimentationparameters of the particles (Sorting, Skewness, and Kurtosis) were determined. Also, the frequency of elements oxides and subelements oxides were determined by ICP and XRF, respectively. The sediments were classified into eight sedimentary types including Slightly Gravelly Muddy Sand, Slightly Ggravelly Sandy Mud, Sandy Mud, Gravelly Muddy Sand, Gravelly Mud, Slightly Gravelly Sandy Mud, and Gravelly Sand. On the east of the wetland (core 1 to 8), the percentage of sand is less the mud, and on the south and west of the wetland (core 9 to13), the sand is higher, indicating more energy in the south and west. Sorting of sediments is poorly to moderately sorted and the Skewness in most samples is coarse Skewed. The number of sediment content is 2 to 3, but the sand content is the majority of the samples. According to these data, the sediments are transmitted to sedimentary basins by the river or muddy streams. The comparison of the oxide elements of the above samples with upper continental crust (UCC) indicated the mean value of SiO2 (63.1%) in the wetland sediments is slightly less than the average of this oxide in the upper continental crust (66.6%), the average of CaO (0.8) less than the average of upper continental crust (except the 12 core and surface sediments sw1) and the amount of Na2O (0.8) and K2O (2.1) are less than the upper continental that indicates the destruction of plagioclases as a result of chemical weathering in the source or during the transport process. The comparison of MgO, Fe2O3, TiO2 sediment samples at different depths and upper continental crust shows that the average of MgO (1.2) is lower than the upper continental crust ten but Fe2O3 ( 7.2), TiO2 (1.2) arehigher than the upper continental crust. The decrease of CaO, Na2O, and SiO2 and the increase of Al2O3 and Fe2O3 indicate an increase in weathering during the transport process and the production of clay and aluminum oxide and iron oxide due to the decomposition of complex clays and non-clay minerals. Matching sediment samples on the two-axial diagrams of the main elements oxides, i.e., (Fe2O3+ MgO) versus Al2O3/ SiO2 and TiO2 and log (K2O / Na2O) versus SiO2, as well as the triangular diagrams of the sub-elements Zr, Th, La, and Sc, indicate that the wetland sediments are more inclined towards the range of oceanic arc islands and continental arcs, and are composed of subduction rocks.