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 sedimentation parameters 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) are higher 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.

Ключові слова: водно-болотні угіддя, осад, Сагалак-Сар, тектонічне середовище, геохімія Introduction. Wetlands ecosystems have many benefits and values, including water supply, storage of food from floodplains, wood production, storing river sediments, water storage, flood control, etc. (Kazanci et al., 2017;Bruland et al., 2004). Sediments are a reservoir of pollutants in aqueous media and therefore, it is used in most studies to determine the pollution load of aquatic environments (Salomons, 1984;Sobczyński, 2001;Eggleton, 2004;Ying Wang[, 2011). Also, wetlands play an important role in trapping river sediments and nutrients and reducing their transmission to seas (Bruland et al., 2006). These sedimentary environments play an effective role in sediment trapping and flood prevention. (Kazanci et al., 2004). The composition of siliciclastic sediments such as sand and mud in relation to tectonic position, origin and proximity has been studied by many researchers (Armstrong and Verma, 2005;Osae et al., 2006;Jafarzadeh;Al-Juboury et al, 2009;Adabi, 2011;Etemad Saeed and Barzi, 2009;Bite Gol and Barzi, 2011). The composition of these sediments is affected by transport factors such as aerodynamic rates, feature of origin rock, climate, tectonic activities and diagenetic effects (Whitmore et al, 2004;Von Eynatten, 2004). Also geochemical studies can complete lithological studies. The Caspian marginal wetlands were formed by longitudinal coastal sediment transport, the increase of Caspian Sea level, and or anticline syncline structures (Leontiev et al., 1977) and the third process forms the considered wetland. According to Leontief, the sediments of the Iranian coastal shores from the borders of Azerbaijan to Turkmenistan originate from the Alborz slopes. Therefore, studies of surface sediments and in-vestigating their state in terms of sediment type and distribution of these wetlands can be a suitable basis for subsequent studies. Saghalak-Sar wetland is one of the Caspian marginal wetlands that formed by the anticline-syncline process. The origin of the Quaternary sediments of this wetland is Alborz Mountains, and it provides a large amount of the water used by the surrounding countryside for agriculture and animal husbandry, and so on. With regard to the increasing trend of drought, the decrease of groundwater, wetland maintenance and solving its environmental problems (sediment volume control, the potential for accumulation of human and natural contaminations in sediments, etc.) are particularly significant. This study was performed to investigate the sedimentary and geochemical characteristics of Quaternary sediments in this wetland. Also, using geochemical analysis results were identified source rock, tectonic setting, accumulation of different elements in wetland sediments and climatic conditions. Methodology. At first, the sampling location was determined by GIS software (Coakley, 1991) and satellite imagery then 70 surface samples and 12 subsurface (From 10 core) samples were taken (Fig. 1). In each core, the samples were selected according to the apparent variation in grain size, color, and sediment composition. The samples were graded in the laboratory according to dry sieving and using a shaker and Anderson method (Anderson, 2004). Then, the statistical and sedimentation parameters of the particles (Sorting, Skewness, and Kurtosis) were determined. Also, percentage of sediment particles was plotted on (Folk, 1957) charts using the Gradistats software. The suspension content and the mutation and deflection of sediments and their turning point were recognized by using the accumulation diagram (Visher, 1969). Then, using the above data, based on the Folk method (1954), the sediment type was determined, and the lithology columns were drawn in 13 cores by Rockwork software.
Chemical analysis was performed by X-ray fluorescence (XRF) method on 66 samples of fine sediments (less than 62 microns) to determine the percentage of 13 oxide of elements. Also, 12 samples of fine-grained sediments were tested by the spectrophotometer radiation (ICP-OES, MS), and the percentage of 54 elements was detected. Finally, the sedimentary environment and the tectonic location of the source area was determined using Batia, Roser and Korsch diagrams Korsch, 1988 and. Geographic location and sampling points. Saghalak-Sar Lake is 15 km off the south of Rasht, in the village of Lakan in Gilan province, in the geographical location of 37°,09´,23˝N and 49°,31´,30˝E (Fig. 1). The elevation of wetland is 64 meters above the sea level, with about 600 meters length, 500 meters wide, and calculated are of 15 hectares. According to the Karimkhani (Karimkhani, 2016), the studied area is located on the Delta of the Sefid Roud River. Geology of the region. The studied area is in the southwest of Rasht and in the northwest of the Alborz structural zone (Stoklin, 1968). Tectonically, it is in Gorgan-Rasht zone and south of Alborz fault (Nabavy, 2005). According to the classification by Eftekharnejad (1980), this zone is the Caspian Sea subsidence, and the time of the emergence of this zone is Precambrian according to the transformed Schists of the southern Gorgan (Nabavy, 1976). The presence of alkaline tensile lava in Jurassic sedimentary, volcanic units up to Cretaceous indicates the development of the Caspian Basin (Darvishzadeh, 1991). The oldest rocks in this area are Slate-Phyllite deposits of Carboniferous (Hercynian) age, and the youngest units are the river, delta, and coastal deposits. The lithology of the rocks around the study area includes: Schists and Phyllites of the southern Lahijan (CSP), Argelite and Sublitarnite deposits of Shemshak (Rjsh), Biomicrite Limstone and Silty Limestone (k 1 1), Volcanic horizons of the Andesite to Basaltic-Andesite (k 1 v), the flood-river facies (Q 1 da), and Silty-Clay alluvial facies (Q 1 al) (Fig. 2). Discussion. Study of the characteristics of sediments (facies and texture and structure, color, mineral type) transported to the wetland is important for geological assessment of the area (such as origin of sediments, the ancient tectonics, the processes during transmission) (Das [28] et al., 2006). This research has been done in two different directions including sedimentology and geochemical studies.

Sedimentary facies in subsurface deposits.
After being sieved, determining the percentage of each category of particle size by weighting them, the particle size dispersion charts have been plotted. Also statistical parameters have been obtained.
Since the prevalence of coarse grains in sediments, even to a slight level, is valuable for interpreting the environmental energy and the type of environment (Harami, 2004). Sedimentary facieses were determined by triangular Folk diagrams (Fig3). Facieses in the sediments of subsurface (core) was identified as follows: Slightly Gravelly Muddy Sand, Slightly Gravelly Sandy Mud, Sandy Mud, Muddy Sand, Gravelly Muddy Sand, Gravelly Mud, Slightly Gravelly Sandy, and Gravelly Sand).
Nearly in the majority of the sediments, the sand is the main component of the sediment name and forms the most abundant grain (Fig. 3). Two types of sediment are observed more at a depth of about 20-40 cm. (Fig. 2). 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 (Fig. 3). The above data indicated the transport energy in the east of the wetland was lower than in the south and west.
The bell-shaped curve of particle is leptokurtic in a number of samples (in the core 4, 8, 3, 6, 2) and show that sand grains is well sorted but the rest of the samples have a mesokurtic to platykurtic curve that indicating sands is poorly sorted maturing resulting from sedimentation in muddy or river flows (Ramanathan et al. 2009). Also coarse Skewed (less than zero) is showing environment had high energy (Feiznia, 2008;Harami, 2004).
According to the classification of standard deviations and sorting (Folk and Ward, 1957;Friedman , 1961), sediment sorting in most samples is medium to poor. Moderate to poorly sorting is seen in the sediments of rivers and mud flows (Opreanu et al., 2007;Ganjoo and Kumar, 2012). However, at the depths of 80 to 100 and 100 to 120cm, the sorting is excellent in most of the core, suggesting that the sedimentation factor in the wetland has had higher energy at this time (Lewin& Brewer, 2002;Feiznia, 2008).
The deposits have three communities. The rate of the suspension (mudd, clay) varies between %5 and 70%, and the rate of sand content is between 29% and 92%. Its gravel content is very low in most samples, and varies from 0 to 14 percent and can result from the river flow (Opreanu et al., 2007) However, at a depth of about 20 to 40 cm, suspension content increase, and the sand content reduced that probably results from mudflows (Mycielska-Dowgiałło et al., 2011;Feiznia, 1999) (Fig. 3).

Sedimentary facies in surface deposits.
The subsurface sediments (sw1 to sw12) are Gravelly Sand facies and have a high amount of sand and a low percent of mud and gravel. In some surface samples such as Sw11, the rate of gravel is more indicating higher carrying energy (Harami, 2004). This sediments are poorly sorted and have coarse Skewed (less than zero).
Also the sand content in these sediments are high (more than 70%). Slope of line of this content (in cumulative curve) is moderate, indicating moderate sorting of sand grains (Mycielska -Dowgiałło, 2004). The gravel content is negligible. Therefore, the present surface sediments are thought to be transported mainly by river branches and from the source close to the wetland (Feiznia, 1999;Opreanu et al., 2007).
3. Geochemical studies. The main elements oxides and sub-elements of the sedimentary deposits depend on factors such as the composition of the source rock, topography of region, and the weather (Day et al, 2009;Taylor & McLennan, 1985;Cullers, 1995Cullers, & 2000. Therefore, the ancient conditions of the sedimentary basin can be detected by using graphs such as Batti, Rosser, Cyrus and Michelin and so on, which are presented by different scholars (Bhatia, 1983;Bhatia & Crook;McLennan et al., 2001;. Before examining the results of geochemistry on the commonly used charts and their interpretation, it is necessary to describe the statistical processing of the decomposition of the main elements. The comparison of the oxide elements of the above samples with upper continental crust (UCC) is evident in Table 1 and  Table 1, the mean value of SiO 2 in the wetland sediments is 63.1%, which is close to but slightly less than the average of this oxide in the upper continental crust (SiO 2 = 66.6%). Its value varies from 50 (in surface sample 11 and core 10) to 69% (in core 8 and 11), which shows the Mature sediment, especially in core 8 and 11. The average of CaO is 0.8, and it is less than the average of upper continental crust. The rate of CaO On the northwest of the wetland (in core 12 and surface sediments sw11) increases and has reduced the SiO 2 (Das et al., 2006;Bhatia and Crook, 1986).

As shown in
The amount of Na 2 O and K 2 O in all samples is less than the upper continental crust that indicates the destruction of plagioclases as a result of chemical weathering in the source or during the transport process. Also, the amount of K 2 O far more than Na 2 O that can be due to the presence of Feldspar or Mica (Oni et al., 2014).
The comparison of MgO in sediment samples at different depths and upper continental crust shows that the average of this oxide is 1.2, which is lower than the upper continental crust (2.2). However, the comparison of the Fe 2 O 3 content in the samples with the upper continental crust shows that the amount of this element is higher and indicates the weathering of  iron minerals during the erosion and transport (Lee, 2005). The average of TiO 2 (1.23) in all samples is higher than the upper continental crust, which indicates the acidic and felsic source rock (Oni et al., 2014). The average of Al 2 O 3 is about 14.6, which is approximately equal to the percentage, of the upper continental crust and varies from 12 (in core11) to 17.5% (in core10 and 6).
According to Lee (2005), the decrease of CaO, Na 2 O, and SiO 2 and the increase of Al 2 O 3 and Fe 2 O 3 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. According to the studies, Babeesh, used geochemical map diagrams including the relation between Al 2 O 3 and other existing oxides for sediments (Madukwe & Obasi, 2015;Babeesh, Fig. 4. Normalization of the major oxides in comparison to the composition of the upper continental crust (UCC) (Talor & McLennan, 1985, Das et al., 2006 2017), too (Fig. 6) and the diagrams were plotted for the fine-grained sediments (Fig. 6). As can be seen, Al 2 O 3 has a positive correlation, with Fe 2 O 3 , MgO and K 2 O, and a negative relationship with SiO 2 and TiO 2 , but it has no special correlation, with P 2 O 5 , MnO, and CaO. The positive relationship between Al 2 O 3 , Fe 2 O 3 and K 2 O can be due to the presence of these elements in clay minerals and mica, which have been produced due to weathering during transportation and erosion (McLennan et al., 2001;Jin et al., 2006). Furthermore, K 2 O can represent aluminum-rich phase, especially Illite (Lee, 1999;Das et al., 2006) (Fig. 5). These changes are observed in core 10 and 12, and surface sample 11, indicating severe weathering during the transport in these two parts of the wetland.
The comparison of the sub-elements of the sediments of the studied zone with the combination of the upper continental crust (Fig. 6) shows the average of Zr, Yb, Y, Ti, Sm, Ce, Hf, Tb, Nd, U, La, Cs are higher, the average of Sr, Nb, and K are lower, but the rates of HF, TA, U, Th, Ba, and Rb are approximately equal. The only difference in the core 12 at a depth of 20 to 30 cm where the value of Ta decreases and the rate of Sr and Hf value increase (Table 1 and Fig. 6).
4. Tectonic setting. Plate tectonic is the basis for the complete development of the foreland basins in the active margins (Saengsrichan et al., 2011). Formation and evolution of foreland basins are initially accompanied by the processes of compression, accumulation, and shortening near the orogeny. The tectonic setting is influenced by sedimentation, diagenesis, and sediment composition. The plate tectonic stages have a significant share in the remaining geochemical signs (Oni et al., 2014). Thus, tried to identify the tectonic setting and the source rock by relying on the previous tectonic and geochemical findings.
Fine-grained sediments have very low permeability and can retain the composition of the source rock (Bhatia, 1983;Chamley, 1990). That is why they are of great importance in the studies of provenance (Hessler and Lowe, 2006). Therefore, geochemical studies of sediments and siliceous rocks be used for determining the tectonic setting (Nesbitt and Young, 1982;Bhatia, 1986;Roser and Korsch, 1988;Herron, 1988;Kroonenberg, 1994;Cox et al., 1995;Fedo et al.,1995).
Based on changes in the values of the main elements, it is possible to separate the clastic deposits resulting from the erosion of the oceanic archipelago, the continental arc islands, the active continental margin and the passive margin from each other (Roser & (Bhatia, 1983) two-dimensional diagram to determine the tectonic origin of sediments using Al 2 O 3 / SiO 2 versus Fe 2 O 3 + MgO b: Plots of samples on the Bathia's (Bhatia,1983) two-dimensional diagram to determine the tectonic origin of sediments using the percentage of TiO 2 versus Fe 2 O 3 + MgO Fig. 8. Plots of samples on Bathia and Crook (Bhatia & Crook, 1986;Babeesh et al., 2017;Das et al., 2008) two-dimensional diagram to determining the tectonic origin of sediments using log (K 2 O / Na 2 O) versus SiO 2 Korsch, 1988). The main oxides of K 2 O and Na 2 O, Al 2 O 3 , SiO 2 are used to determine the long-standing tectonic setting of sediments. Moreover, the Sub-elements and rare elements such as Cr, Y, Ti, Zn, Sc, Th, La are less affected due to non-mobility in weathering, diagenesis, and moderate transformation. Therefore, they remain in the sediments and are good indicators for understanding their long-standing tectonic setting (Bhatia & Crook, 1986).
Dual diagrams (Babeesh et al., 2017;Roser & Korsch,1986;Bhatia & Crook,1986) show that the sediments of this wetland are oceanic arc and continental arc, also some of the samples are active continental margins (Fig. 7,8,9). Also geochemical data of igneous rocks (Asiabanhan & Foden, 2012) confirm that the origin of these sediments are igneous rocks in continental or oceanic arcs.
Furthermore, plotting the samples on the triangular diagram diagram (such as (Bhatia & Crook, 1986;Das et al., 2006) of the sub elements confirms the tectonic origin of the continental island Arc (Fig. 9).

Conclusion.
1. Statistical data showed that sediments of Saghalak-Sar wetland have poor to moderate sorted, also most of the samples have a mesokurtic to platykurtic curve indicating that the sand has poor sorting , therefore they are carrier, and deposited by muddy flow(in rainy seasons) or river.
2. According to geochemical results, lower amount of K 2 O , Na 2 O compared to the continental crust indicated the weathering of the feldspars aslo decrease of Na 2 O, K 2 O, SiO 2 and increase of Al 2 O 3 , Fe 2 O 3 indicate intense weathering and production of iron clays.
3. The geochemical results and the correlation of a number of oxides of the main elements ( K 2 O, Na 2 O, Fe 2 O 3 , MgO, Al 2 O 3 ) and Sub-elements (Th, Zr, Sc, La) on the standard triangular and dual diagrams show the tectonic setting of these sediments with continental and oceanic arc islands and active continental margins. This multiplicity is characteristic of postcollision and near-source basins, which is the result of active tectonics of the region and the formation of the small sedimentary basins within the foreland, but inevitable the source rocks of the above sediments are formed by a subduction boundary. Fig. 9. Plots of samples on the three-dimensional graph of Sub-elements of Bathia and Crook (Bhatia & Crook, 1986;Das et al, 2006) to determine the tectonic origin of sediments. A: Oceanic island arc, B: continental island arc, C: active continental margin, D: passive continental margin