Abstract
Useful information was obtained about the environmental condition of this region such as energy, sediment location, origin, sediment carrying path, pond evolutionary process, and tectonic conditions and origins of sediments by studying physical and geochemical sediment changes processes in place and time, distribution of sediments and elements in lagoon bed, and also identification the effective factors on sediment distribution model. In this regard, 59 sediment samples were taken from Siyah Keshim lagoon and were analyzed chemically and aggregation by XRF and ICP-MS technic. Adaptation of data by Folk diagrams showed that this region is placed in a range of sand, muddy sand, sand with a little gravel, muddy sand with a little gravel, and silty sand. Weak to medium sorting and negative tilting shows sediment in a coastal area. Geochemical evidence shows that SiO2/Al2O3 ratio in these sediments is 2.6-3.7. In addition, Na2O value shows relatively low sediment investigation for sediments of this lagoon. Moreover, determination of the weathering effect in origin place by the chemical index of alteration (CIA) and chemical weathering index (CWI) shows intensive chemical alternation on sediments. Index of combined variety was averagely 1.54 in the studied sediments and show that sediments resulted from the first cycle sediment. Using tectonic separating diagrams based on the primary and secondary oxidants percentage show the sediment in the active continent margin (ACM), continent-island arc (CIA), and oceanic island arc (OIA) and shows that the studied sediments are related to subduction margin.
Highlights
Lagoons have many advantages for having hydrological characteristics
Sediments are considered as data in environmental studies and its conditions are the most important evidence in the previous environmental conditions
Sediments can be examined through various views such as particles size and diameter, ration of the formed particles of a sediment, sorting, particles kurtosis, skewness, rounding, and some other statistical parameters such as mean, mode, standard deviation, etc. each of these cases shows genre, origin, and environmental conditions that formed sediments
Summary
Lagoons have many advantages for having hydrological characteristics. Lagoons supply a part of underground waters, and provide an environment as the best ecosystem to supply many birds and aquatics foods (Nuri, 2009). Anzali lagoon is one of the international protected lagoons that were studied by researchers (Amini Ranjbar, 1998; Riyahi et al, 2005, Sharifi, 2006) This lagoon is an ecosystem of many endangered species and has a more effective role in preventing flood and acts such as sediment traps (Kazanci et al, 2004). Alzali lagoon is one of these coastal back lakes that formed a part of Caspian Sea coastal waters in the past. This lagoon developed a lot in the past but was filled gradually by alluvial-delta sediment of Sefidrud branches and rivers of Rasht, Fuman and Masal region. Changes in Mg/Ca, Sr/ Ca, Mg/Ca ratios along cores show changes in lake conditions chronically (Taghavi et al, 2013)
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