A multidisciplinary study of the sedimentology, geochemistry and mineralogy has been conducted to understand the linkage between marsh and alluvial sediments and also their potential sources in Eynak marsh, North of Iran. The influence of the upstream potential sources on recent sediment geochemistry has been discussed based on geochemical, sedimentological and mineralogical results. A spatial grain size distribution study was carried out to investigate the hydrodynamic and deposition system of the marsh. So, the surficial sediment sampling was carried out to describe the sedimentological parameters and elemental geochemistry of sediments in Eynak marsh. Mineralogical complexes are mainly made up of felsic minerals such as quartz, calcite, feldspar, pyrite, mica, and clay minerals (in very low values) indicated by high amounts of Al, Ca, and Ni. As expected, the mineralogy of sediments is controlled mainly by the rock formations. Also sediment textures are controlled by the hydrodynamic condition in the marsh. So its distribution has been influenced by distance from the entrance sediments to Eynak marsh. The results showed that there are no enrichments related to fine grain sediment distributions. An association of Al with the trace elements such as Sc, Y, La, Ce, and Zr indicates that their distributions are mainly controlled by the felsic rocks in the upstream. On the other side, due to the waste water entrance to the marsh, Ni and Pb concentration could be under the effects of anthropogenic activities around the marsh. Results represented high values for Mn concentration (min 462, max 1784 and average 1037 ppm) and it showed a significant correlation with Ca, Sr, and Mg. A redox habitat and constantly calm hydrodynamic circumstance in the study area, likely cause high concentration of Ca, Sr, and Mg, and Mn. And they are representing negative correlations with some elements such as Al, Be, Fe, K, and Na.
Eynak Marsh Sedimentology Geochemistry Element Distribution Pattern Element Correlation1. Introduction
Improvement of our understanding in the environmental and geomorphological changes’ effects on marshes and isolated waters is a critical step to address issues related to continental marshes and their responses to these changes. Also, sedimentological studies are proper tools to interpret the evolution of sedimentary environment [1] . Additionally, to assess the ecological impact of contamination to the environment, it is vitally important to understand the full extent and the level of pollution into the background in the area.
Regarding its capabilities in providing goods, marshes environments are classified as the most precious ecosystems on earth [2] [3] . Considering the effects of climate changes and human interferences, today the future of these important landforms and ecosystems seems to be at risk and it may cause possibly irreparable transformations [4] - [10] . However, despite progress about geomorphology, sedimentology, accretionary processes and geochemistry, more work needs to be done to explain the sedimentology, stratigraphy and geochemistry of sediment in marshes on the subject of the evolution of the systems [1] [11] [12] .
The particle size and morphology of sediments are the major implements to interpret the source of sediments, transportation modes and depositional environments [13] [14] . Variations in grain size distribution of isolated environments (specifically marshes habitats) may reflect air surface process such as developmental process of landforms through precipitational changes [15] . On the other side, mineral distributions are also standard tracers of regional geology, weathering characteristics in upstream and transport land mass [16] - [23] . Moreover, trace elemental compositions of sediments are controlled by lithologies, weathering, diagenesis, sedimentary sorting and human activities in catchments and it can be useful for identification of specific geochemical processes and provenance of clastic materials [24] . Also characterizing of the composition and the sedimentology of surface sediments is vital not only from geochemical point of view, but also from an environmental perspective. Thus variations in mineral compositions, trace elements and lithogenic components should be considered as valuable tools to find out the possible sediment sources and physico-chemical process affecting the geological records [23] .
Nowadays, Eynak marsh is strictly isolated from any riverine and oceanic sediment input (Figure 1). Anthropogenic effects (as an instance intense construction operation, sewage input to marsh and etc.) likely contribute to changing the circumstances and its natural habitat. Despite the importance of this area, there is no worthy investigation devoted to the study of geochemical, mineralogical and sedimentological signature of Eynak marsh. This investigation could be more momentous if we spot contamination of sewage entrance from the urban areas and also underground linking to GoharRood River. It is noteworthy that, GoharRood by itself is a fully contaminated river transporting sewage from upstream.
Because of its position regarding urban area, being one of the biggest marshes in north of Iran and tourism industry, this marsh represents a crucially important ecosystem in the region. Detailed sedimentological and geochemical investigations on these marshes can help us to improve our knowledge about its generation. Then it led to precise relationship being deducted between marsh and river sediments. As the other aquatic environments in south of Caspian Sea, Eynak marsh is situated in the migration way of different birds (Africa-Eurasia and Asia-Pacific skyways) then lots of bird spices fly to this region every year. Also this marsh is populated by various plant species like Myriphgllom verticillatum, Ceratophyllum submersum, Alisma plantago-aguatica, amphibians like frog and creepers like snake, turtle, lizard adapted to the environment.
Due to reflecting the privilege geology of the source area by the deposited sediments [25] , a comprehensive study has been conducted. This paper focuses on understanding of sedimentology, mineralogy and geochemistry variation pattern in the riverine sediment of Eynak marsh (North of Iran). So the main purposes of this paper are: 1) to provide information about the sediment size distribution, mineral composition and also the main potential source of marsh sediments; 2) to improve our understanding in trace element pattern distribution in the marsh; and 3) to assess metal contamination levels in surficial sediments and particles. To achieve these goals we have analyzed surficial sediments of the marsh thoroughly.
Geographical location and detailed sketch map of the study area in Eynak marsh
2. Study Area
Marshes and bays across the Caspian Sea that are under the impact of 3 major processes of longitudinal transfer of coastal sediments, increasing the level of Caspian water, and syncline-anticline structure [26] are considered environment passages, from land to sea. Moreover, analysis of historical aerial photography depicts a relatively dynamic system in the area in which lateral migration of main channels caused some isolated small areas. So, Eynak marsh could be considered as such environments and it is located in Rasht countryside (Gilan province) and about 17 km away from Anzali costal lagoon, North of Iran. Also it is situated from 37˚16'25"E 49˚32'18"N to 37˚16'22"E 49˚33'31"N presumably is a separated pool from flowing rivers through time. It seems the main source of sediment in this marsh located in Kacha Mountain and sediments transported through Lakan and GoharRood Rivers. Nowadays Gohar rood and Lakan Rivers drain to Anzali coastal lagoon. Estimated area is about 214,650 m2. Due to being situated in Rasht countryside and industrial activities around the marsh, irreversible changes is happening there which effects on its habitat and it may cause to destroy the marsh completely in the future. Unfortunately it has not been a comprehensive investigation in the area to discover the origination of this marsh yet. Better to know, the upstream sewage discharging to Lakan River and its probable underground linking to Eynak marsh, may cause more negative effects on the marsh habitat. Also, there are some transects cutting across Eynak marsh and separated it to smaller areas. It means there might be no more Eynak marsh in the area in future unfortunately.
Study area has a humid subtropical climate that is one of the wettest in Iran. It has certain Mediterranean features such as a drier summer, but is also relatively continental with cooler winters and higher seasonal temperature variation than in much of Iran, in spite of its marine position. The average humidity is 81.2%, contrasting heavily with cities in many other parts of Iran. Sunshine hours, averaging roughly 1520 per year, are lower than in most places in Iran and also compared to most places at this latitude.
The oldest rocks in the domain area consists of early Carboniferous made up of creamy-brown to dark-green slate to phyletic clastic sediment which in partly are calcareous and belongs to Mobarak Formation. After that, grey to green arkozic sandstone and shaly mudstone belongs to late Triassic can be seen (Figure 2). Cretaceous rocks such as massive sandy limestone, silty limestone-siltstone and dark grey basaltic-andesitic lava occurrence
Geological map and the main hydrological features of the study area
in the upstream area. Plain landscape is overlain by Quaternary deposits which [27] classified them in the area into: 1-Deltaic deposits and gravel, 2-Deluvial and fluvial deposits, 3-Old fluvial deposits, 4-Alluvium floodplain and deltaic deposits and finally 5-Blown sands (Figure 2).
3. Material and Method
Figure 1 shows the total 44 collected sediment sample locations along the marsh which sampling points took by GPS receiver. The primary distance between locations was about 40meters which it changed slightly based on convenient sampling. Sampling was carried out onboard small boat using a 4liter Van Veen grab sampler. Samples were taken onboard for sedimentology, mineralogy and geochemical analysis individually. Each sample was packed in polyethylene bags, tied, labeled and brought to GSI Lab for excess analyses. Detailed grain size, mineralogy and geochemical analysis has been carried out on all collected samples in order to recognize possible anomalies and basic pattern of sediment characteristics inside of the marsh.
Afterward, on the lab, samples were dried at 70˚ and dried bulk sediment was sieved to separate various fractions using wet sieving (based on standard test ASTM for determining average grain size). Grain size analysis of the 44 surficial sediment samples performed by Analysette 19 wet sieving instrument. Therefore, samples grouped into mud, sand and gravel fraction according to Udden and Wentworth. A detailed description of grain size <63 µm fractions executed by Laser Particle Seizer (model analysette 22).
Standard practice for total digestion of 44 sediment samples for chemical analysis of various metals (according to D-4698 preparing method) has been performed. So minor and major elements determined by inductively coupled plasma-optical emission spectrometry (ICP-OES-ES Varian 735) in Geological Survey of Iran chemistry lab. Moreover, X-Ray diffractions in 44 sediment samples in the area have been performed using an automatic powder EQUINOX 3000 X-ray diffractometer. Quantification and identification of the various minerals present in the crystalline fraction has been carried out following the standard procedure [28] .
Fractional analyses were carried out using the software package SPSS20 for windows. In addition, on all samples in Eynak marsh, detailed grain size, geochemical and mineralogical analysis have been carried out to recognize a possible correlation between their distributions and depositional environments.
4. Result4.1. Physical and Mineralogical Characteristic
Textural and size analyses are quantitative tools to determine the size frequency distribution [29] . Also, mineralogical and physical characteristics of the sediments in Eynak marsh can be influenced by rock assemblages in upstream such as basaltic-andesitic lava, dark grey limestone, slate and Arkozic sandstone which has been subjected into weathering, eroded and transported to downstream. In fact, due to terrestrial sources of sediments in Eynak marsh, it is characterized by similar mineralogical and physical features. Results showed that samples basically were angular to sub angular in shape (Figure 3), major component mineral were quartz, calcite, feldspar, and mica and minor mineral were pyroxene, evaporates along with some heavy minerals.
Grain Size Distribution
According to grading studies, 13 sedimentary types existed in surface sediments including: Gravelly Mud, Muddy Gravel, Gravelly Sand, Muddy Sandy Gravel, Gravelly Muddy Sand, Muddy Sand with a Little Gravel, Sandy Mud with a Little Gravel, Mud with a Little Gravel, Silty Sand, Muddy Sand, Sandy silt, Silt, Sandy Mud (Figure 4). Considering its pattern, east side of the marsh represented a variety of sedimentary types. Moreover, grain size distribution maps reveal that, silt and clay fractions are the most important sediment constitutes concentrated mostly in the middle and the east. Also, gravel size grains increased eastward approaching GoharRood River.
4.2. Statistical Parameters
Various statistical parameters of Eynak marsh sediments computed. Mean grain size: The variation in mean size reflects the variety of energy conditions to deposit and shows the average kinetic energy of the depositing agent [30] . Different values obtained for textural statistical parameters varying from minimum 1.5 to maximum 6.6, i.e. thus it falls between coarse sand and medium silt. Sorting: Sorting indicate the differences in kinetic
Sediment grains in Eynak marsh
Ternary plot showing the content of gravel, sand and mud fractions in the surficial sediments of Eynak marsh
energy associated with these mode of depositions. In the study area sediments ranges in 3 sorts: poorly sorted, very poorly sorted, and moderately sorted. The closer to GoharRood, the sorting number increases and sediments poorly sorted. Skewness: It measures the asymmetry of frequency distribution and marks the position of mean according to median [29] . In the present study skewness values ranges −0.43 to 0.68 with an average −0.02 represents five sorts: strongly fine skewed, fine skewed, near symmetrical, coarse skewed, strongly coarse skewed. Eastern samples showed near symmetrical to coarse skewed which it accounts as the abundance of coarse particles of energetic environment. Also, strongly fine skewed can be seen in the middle of Eynak marsh. Kurtosis: Many curves designated to minute Kurtosis and it varies from platy kurtic to mesokurtic. Also the values are among 0.5 to 2 with an average of 0.99. The platy kurtic to mesokurtic nature of sediments refers to fewer addition of finer or coarser materials to the depositional environment [30] . In general and regarding average values, sediments are fine grained (Figure 4), moderately to poorly sorted associated with very low current flow in eastern side of the marsh.
4.3. Statistical Parameters
Various statistical parameters of Eynak marsh sediments computed. Mean grain size: The variation in mean size reflects the variety of energy conditions to deposit and shows the average kinetic energy of the depositing agent [30] . Different values obtained for textural statistical parameters varying from minimum 1.5 to maximum 6.6, i.e. thus it falls between coarse sand and medium silt. Sorting: Sorting indicate the differences in kinetic energy associated with these modes of depositions. In the study area sediments ranges in 3 sorts: poorly sorted, very poorly sorted, and moderately sorted. The closer to GoharRood, the sorting number increases and sediments poorly sorted. Skewness: It measures the asymmetry of frequency distribution and marks the position of mean according to median [29] . In the present study skewness values ranges −0.43 to 0.68 with an average −0.02 represents five sorts: strongly fine skewed, fine skewed, near symmetrical, coarse skewed, strongly coarse skewed. Eastern samples showed near symmetrical to coarse skewed which it accounts as the abundance of coarse particles of energetic environment. Also, strongly fine skewed can be seen in the middle of Eynak marsh. Kurtosis: Many curves designated to minute Kurtosis and it varies from platy kurtic to mesokurtic. Also the values are among 0.5 to 2 with an average of 0.99. The platy kurtic to mesokurtic nature of sediments refers to fewer addition of finer or coarser materials to the depositional environment [29] . In general and regarding average values, sediments are fine grained (Figure 4), moderately to poorly sorted associated with very low current flow in eastern side of the marsh.
4.4. Scatter Plot
Scatter plot with mean, standard deviation and skewness can be used successfully for the distinction of the sedimentary environments, always using a large number of samples for each sedimentary body sampled [31] . Moreover, scatter plots are useful to identify geological signature of the grain size parameters [32] . Scatter plots viz. skewness versus standard deviation, mean versus standard deviation, and standard Deviation versus mean is brought in Figure 5. The scatter diagram proved that the distribution of grains belongs to fluvial and riverine sediments.
4.5. Sediment Composition
The significant correlation of elements with each other may indicate same source, chemical behavior, sediment-water interface and etc. [33] . Spearman’s correlation coefficient is a statistical measure of the strength of a monotonic relationship between paired data. Unlike Pearson’s correlation, there is no requirement of normality and hence it is a nonparametric statistic. Regarding unmorally in our data diversity, Spearman’s correlation analysis has been conducted on the calculated data to determine the relationship between various elements and sedimentary parameters as well as to find out the main sources of elements and grains.
4.5.1. Mineral Diversity
Eynak marsh sediments were mainly composed of muddy fractions (Figure 4). Mineralogically, quartz, calcite, feldspar, dolomite, and mica were the main constitutive minerals present in surficial sediments (Table 3). Considering opposite geochemical behavior in Quartz and Calcite, high values of quartz from the middle to east and
Various scatter plot of surficial sediments in the study area to show the origin of grains
west of Eynak marsh correlated to calcite and dolomite depletion. As well as, higher amounts of calcite along with pyrite and gypsum can be seen in the middle of the marsh. Also, silicates such as feldspars, mica, pyroxene and clay minerals are distributed regularly throughout the surficial sediments. Mineralogy data diversity was proofed by geochemical analysis of sediments throughout the study area.
4.5.2. Element Diversity
Usually, fine grain sediments are common hosts and controlling factor in distribution of elements, especially metals, in aquatic sediments [34] . The correlation matrix, element composition and Dendrogram using Ward method are shown in Table 1 and Table 2 and Figure 6 respectively. Trace elements incorporated in heavy minerals like Y, Zr, Th, Cr, have lower content in the finer grained sediments (Figure 7) indicating depletion of
Dendrogram using Ward Method illustrating the relationship of elements in the study area
Contour plots showing the distribution of sediment composition along the study area
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