JKAU: Mar. Sci., Vol. 22, No. 2, pp: 135-158 (2011 A.D. / 1432 A.H.) DOI : 10.4197/Mar. 22-2.8

Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, Northwest Libya

Mohamed Abdel Galil and Esmail El-Fergany Faculty of Science at El-Khums, Misratah University, Libya [email protected]

Abstract. Sabkha deposits occupy the relatively low topographic areas and are separated from the sea by coastal sand . The sabkha sediments are relatively finer compared to those of the coastal sand dunes and beach. Grain size grading with improvement in sorting occurs in the direction of sediment drift landward. The brines of the saline pans are of recent marine water origin. During spring and summer months, due to evaporation, the water level in the saline basin is lowered to a level below or nearly equal to that of the Mediterranean Sea from which the waters seep into the Salina. The brackish waters are partially or completely evaporated which lead to deposition of in the saline basins and the surrounding sabkha plains. In autumn and winter months, the Salina is filled with water and the surrounding sabkha plain is moistened with seawater seepage and sporadic rainfall. These waters led to partial dissolution of the former summer deposited and/or . The halite crusts in the coastal saline pans are subjected to dissolution during seawater and/or meteoric water flood stage, and to cementation during the desiccation stage. The resulting dissolution and re-precipitation features are diagnostics of the ephemeral saline pan halite. The salinities increase from the sea landward (46.9 g/l, up to 180.4 g/l and up to 323.8 g/l for the seawater, coastal sand dunes pans, and the sabkha brines respectively). Accompanying the increase in salinities is the very high concentration of Na+ and Cl- ions. The brines are highly saturated with NaCl, which favors a dominant halite precipitation (65.02- 78.12%), while bicarbonate salts are traces (0.13- 0.79 %).

Introduction Sabkha is an Arabic word for salt flat area. The study coastal sabkha is situated in an extensive sabkha plain about 6 Km to the east of Zuwarah 135 136 Mohamed Abdel Galil and Esmail El-Fergany city and about 50 Km to the east of Tunisia border (Fig. 1). Deposition and dissolution of the evaporite minerals in the recent deposits are interpreted using the saline pan cycle (Lowenstein and Hardie, 1985), which consists of a flood stage (brackish lake), an evaporative concentration stage (saline lake), a desiccation stage (dry saline pan) and return to a flood stage (brackish lake). As evaporation and halite crystallization continue, the saline lake shrinks, ultimately drying out (Fig. 2). According to Meteorological Authority data of Zuwarah station, the study area has a Mediterranean climate where arid to semi-arid 0 conditions are predominating. The average temperature rises to 50 C 0 during summer months, while it drops to 20 C during the winter. December and January are the wettest months and rain is often concentrated in a few heavy showers. Wind speed increases in November until April causing dust storms. The aim of the present work is to study the field relationships, textural characteristics of Zuwarah sabkha sediments and to delineate the water origin from the brine chemistry.

Materials and Methods Twelve water samples were collected from sabkha brines, from sand pans and from the seawater. The collected samples were + + ++ ++ - - - - analyzed for the major ions (Na , K , Ca , Mg , Cl , SO4 , HCO3 and - - CO3 ). All concentrations are expressed as equivalent per million (epm= ppm/ equivalent weight), whereas the salinity is expressed as gram per liter (g/l). Results of the chemical analyses were recalculated to e % of major cations and major anions (epm of specific cation or anion/sum of epm of cations or anions) to interpret the origin of brines. Moreover, fifteen sediment samples were collected from beach, coastal sand dunes and sabkha plain. The collected sediment samples were washed by distilled water several times, dried and mechanically analyzed using a Ro-Tap shaker at half phi interval according to Folk and Ward (1957). Five salt samples were examined by using X-ray diffraction analysis. Also, Scanning Electron Microscope (SEM) photographs were carried out for selected seven salt samples. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 137

Fig. 1. Location map of the study area and schematic cross-section showing the general distribution of Quaternary deposits (Anketell and Ghellali, 1991). Lithostratigraphy Ephemeral saline pans occupy the lowest topographic depressions in the sabkha plain. According to Anketell and Ghellali (1991) Jeffara, Gargaresh and the upper member of Qasr Al-Haj formations cap the Plio- Pleistocene deposits (Fig. 1). These deposits are capped by a veneer of Holocene superficial deposits comprising recent sand dunes, deposits and sabkha (El-Hinnawy and Cheshitev, 1975). Sabkha deposits occupy the relatively low topographic areas and are separated from the sea by coastal sand dunes (Fig. 2). The dry sabkha is frequent in the interdune areas and characterized by halophytes. Landward, the sabkha deposits are underlain by silt of Jeffara Formation (Fig. 3). 138 Mohamed Abdel Galil and Esmail El-Fergany

Coastal sand dune

Salt crust

Fig. 2. Coastal sand dune separated a relatively low area from the sea. Note, as evaporation continues, the saline lake shrinks.

Jeffara Formation

Salt crust

Fig. 3. A trench in the coastal sabkha showing salt crust contains crystals of evaporite minerals overlain Jeffara Formation. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 139

Lowenstein and Hardie (1985) grouped the layered in three depositional settings: (1) deep perennial (density stratified) basins, (2) shallow perennial lakes or , and ephemeral saline pans. Deposition of the evaporite minerals in Zuwarah sabkha took place in shallow and flat basins that are normally dry in summer and flooded with water in winter. These basins represent the ephemeral saline lake sub- environment of Hardie et al. (1978), and the ephemeral saline pans of Lowenstein and Hardie (1985). The saline pans range in size from a few square meters to hundreds of square meters depending on the amount of ground water seepage, the slope, and the surface area of the evaporite basin. The saline pans usually occupy the center of the evaporite basin, but may be shifted towards the margin depending on the topographic location of small depressions within the basin. The saline pans are filled with water in winter and floored with layered salt in summer (Fig. 4). As a result of continued evaporation, the saline pans are encrusted with halite crusts, hence they can be termed halite pans, similar to that described by Lowenstein and Hardie (1985) and Smoot and Lowenstein (1991). The saline pan zones are surrounded with brine saturated mudflats that are covered with scattered halophytes surround the saline pan (Fig. 5). Near the coastal saline basin, the water table is close to the surface of the sabkha sediments. The main supply to the coastal saline basin and the surrounding sabkha sediments is either through storm flooding of sea water, seawater seepage or high tide seawater spray, in addition to minor input from inflow through the highly permeable fluvial and dune sands after torrential rains. The inflow of both marine and nonmarine waters into the saline pans causes the level of groundwater to rise (Basyoni and Mousa, 2009). During spring and summer months, due to evaporation, the water level in the saline basin is lowered to a level below or nearly equal to that of the Mediterranean Sea from which the waters seep into the saline pans. The brackish waters are partially or completely evaporated which lead to deposition of evaporite minerals in the saline basins and the surrounding sabkha plains (Fig. 4 and 5). X-ray examinations show a dominant halite while bicarbonate salts are traces. In autumn and winter months, the saline pans are partially filled with water and the surrounding sabkha plain is moistened with seawater seepage and sporadic rainfall. These 140 Mohamed Abdel Galil and Esmail El-Fergany waters led to partial dissolution of the former summer deposited halite and/or gypsum (Fig. 6).

Fig. 4. Saline pan floored with layered salt in summer. This pan will be partially filled with water in winter.

Saline pan

Halophytes

Fig. 5. Scattered halophytes surround the saline pan. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 141

Fig. 6. The halite crusts are subjected to dissolution during meteoric water flood stage. Note the isolated remnant salt. Halite continues to precipitate from the groundwater brine as clear, void filling cement and displacive crystals within mud (Lowenstein and Hardie, 1985; Casas and Lowenstein, 1989; Smoot and Lowenstein, 1991). During the flood stage, dilute floodwater is pounded in the saline pan and dissolves the underlying halite crusts (Fig. 7 to 10). The textural features produced during the flood stage include: (1) Horizontal truncation surface, (2) cavities formed by dissolution, and (3) mud partings between and within evaporite crystals (Casas and Lowenstein, 1989).

Fig. 7. SEM photomicrograph cavities Fig. 8. SEM photomicrograph of partial formed by dissolution (arrows). dissolution of cubic halite crystals. 142 Mohamed Abdel Galil and Esmail El-Fergany

Fig. 9. SEM photomicrograph of the cleavage Fig. 10. SEM photomicrograph of cavities planes in halite showing dissolution. and partial surface dissolution.

During the evaporative concentration stage, the ephemeral pans reach saturation with respect to halite and turns into saline pans. Crystallization starts at the brine surface as small plates and hopper crystals, which sink to the bottom (Fig. 11), and as bottom growth of chevrons and cornets (Arthurton, 1973). When the brine reaches saturation with respect to halite, halite crystallizes at the brine-air interface as millimeter-sized rectangular and square-shaped plates and pyramidal hoppers (Arthurton, 1973). The crystals are suspended horizontally by surface tension. With continuous growth of halite at the brine-air interface, the growth sequence commences with chains, which form nets. This is similar to that described by Shearman (1970), Arthurton (1973), Aref et al. (1999), Sanford and Wood (2001), Tyler et al. (2006) and Basyoni et al. (2008). When the weight of the suspended mat overcomes the surface tension, the rafts sink to the bottom under the effects of gravity (Handford, 1991). The halite rafts may be later reworked by small currents (Warren, 1982 and Last, 1984) to form clastic halite, or may form nucleation sites for bottom growth of chevrons and comets. When the brine is slightly agitated at the early stage of nucleation of the halite crystals, waves disturb the surface tension, and the individual halite crystals settle to the bottom as aggregates of cumulus crystals (Smoot and Lowenstein, 1991). Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 143

Continuous concentration of the brine by evaporation produces supersaturated brine from which halite crystals grow on the earlier settled rafts and cumulus crystals (Fig. 11 to 16). The growth on the earlier formed crystals and the competitive growth of halite produce vertically oriented crystals that resemble the halite teeth. The morphology of the upward growing crystals depends on the attitude of the parent crystals. When syntaxial overgrowth begins on a halite cube lying on the edge, the resulting overgrowth will be chevron-shaped with an upward pointing coin (Arthurton, 1973; Lowenstein and Hardie, 1985). Zoning probably results from varying crystal growth rates where the cloudy bands are formed rapidly during periods of intense evaporation while clearer bands have crystallized more slowly during periods of lower evaporation rates (Shearman, 1970; Holser, 1979; and Roedder, 1984).

Fig. 11. Crystallization of small plates. Fig. 12. The plates become massive.

Fig. 13. Crystals of teeth shapes. Fig. 14. Vertically oriented crystals. 144 Mohamed Abdel Galil and Esmail El-Fergany

Fig. 15. Aggregates of halite and gypsum Fig. 16. Crystals grow as rosette pattern; crystals. salt rose.

The coastal sabkha pans under study receive flood and seeping seawater from the Mediterranean Sea, in addition to sporadic torrential rains in the surrounding fluvial and dune sands. During winter the lowest topographic depressions in the sabkha plains are filled with brackish water, whereas their margins are covered with microbial mats. The mats form multicolored layers (Fig. 17 to 20), similar to that described by Noffke et al. (1997) and Basyoni (2004). The multicolored zonation of the microbial laminae is due to the presence of diatoms (yellow), cyanobacteria (blue to dark green), phototrophic sulfur bacteria (purple) and sulfate-reducing bacteria inducing black iron sulfide coatings on sediment grains (Gerdes et al., 1985 and Noffke et al., 1997). Cornee et al. (1992), found that the tight and continuous microbial mats form a barrier for both gas and solute transfer between sediments and brines and thus enhances reducing conditions in the sediments. Microbial mats therefore not only generate organic matter, but may also enhance its preservation at depth (Cornee et al., 1992). Therefore, bacterial decomposition transformed the microbial mats into black sediment with a high hydrocarbon potential (Fig.21). Keine et al. (1986) believed in the enrichment of methanogenic bacteria in the deeper buried organic matter. From there, gas diffuses upwards through the sediments and becomes captured by surface microbial mats to form a crenulated leathery surface (Fig. 21). With increase in salinity, gypsum and/or halite crystallize on the mats surfaces that evolve into petee structure (Fig. 22), due to the combination of the physical forces of crystallization of gypsum and halite, and the biogenic growth effect on the microbial laminae (Gavish et al., 1985). Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 145

Fig. 18. Blue to dark green color due to the presence of cyanobacteria.

Fig. 17. Multicolored microbial laminae.

Fig. 19. At the margins of the pans, Fig. 20. Multicolored zonation of the microbial mates form multicolored microbial laminae. layers.

146 Mohamed Abdel Galil and Esmail El-Fergany

Petee structure

Fig. 21. Halite crystallizes on the black mats surface, evolves into scattered petee structure.

Fig. 22. Well developed petee structure due to the combination of the physical forces of crystallization and the biogenic growth effect. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 147

Towards the saline pans, the highly wetted surface of the mud flats is covered with microbial mats underlain by a black sapropelic layer a few centimeters thick (Fig. 21). The microbial mats are produced by cyanobacteria-dominated communities similar to those described from various hypersaline environments (Cohen et al., 1977; Thomas and Geisler, 1982; Gerdes and Krumbein, 1987). The extensive growth of the microbial mats embedded in sedimentary surfaces acts as a kind of soft tissue, which effectively affects the properties of surface structures (Reineck et al., 1990). The interplay between microbial stabilization of sediment surface and gas formation within the sediments, due to bacterial activity, results in the formation of crinkled surface (Fig. 22), which is defined as petee by Gavish et al. (1985); Gerdes et al. (1993). The petee structures were formed by surface gas accumulation (H2S, CH4) below the surficial cohesive microbial mat tissue, which over thrusts the mat surface into domes (Fig. 22). During flooding and evaporative concentration stages, the crinkled surfaces of the microbial mats are submerged by shallow saline water that precipitate surface halite and/or gypsum crust on top of the microbial mats. The microbial mats act as nucleation site for growth of halite and radial arrangement of lenticular gypsum crystals. Sediment Characteristics The grain size parameters of the studied sediments are given in Table (1). The studied sediments are subjected to different energy levels, reflected on their mean size values. The beach sediments are relatively coarser compared to those of coastal sand dunes and sabkha, with average mean size values of 1.38 Ø (medium sand), 1.47 Ø (medium sand), and 2.07 Ø (fine sand) respectively (Table 1). The average values of the graphic standard deviation are 0.66 Ø, 0.62 Ø, and 0.37 Ø for the beach sediments, the coastal sand dunes and sabkha sediments respectively, indicating improving in sorting landward. The average values of the inclusive graphic skewness are 0.02, 0.04 and 0.00 for the beach sediments, the coastal sand dunes and sabkha sediments respectively, indicating near symmetrical frequency distribution. Generally, grain size grading with improvement in sorting occurs in the direction of sediment drift landward and the coastal sand dunes 148 Mohamed Abdel Galil and Esmail El-Fergany sediments show relatively increase in the finer fractions compared with that of the beach sediments (Fig. 23).

Table 1. Description of the sediments according to their grain size parameters. Sample Location MZ σ1 SK1 Description Number Strongly Fine Moderately 1 2.30 0.63 -0.45 Coarse Sand Well Sorted Skewed Medium Moderately Strongly Fine 3 1.07 0.76 0.31 Sand Sorted Skewed Coarse Moderately 5 0.60 0.54 0.13 Fine Skewed Beach Sand Well Sorted sediments Medium Moderately Near 7 1.55 0.60 0.03 Sand Well Sorted Symmetrical Medium Moderately Near 9 1.37 0.75 0.06 Sand Sorted Symmetrical Medium Moderately Near Average 1.38 0.66 0.02 Sand Well Sorted Symmetrical Medium Moderately Near 2 1.50 0.6 0.09 Sand Well Sorted Symmetrical Medium Moderately Near 4 1.50 0.65 -0.01 Sand Well Sorted Symmetrical Medium Moderately Near 6 1.40 0.62 -0.02 Coastal Sand Well Sorted Symmetrical dunes Medium Moderately sediments 8 1.45 0.57 0.16 Fine Skewed Sand Well Sorted Medium Moderately Near 10 1.50 0.66 0.00 Sand Well Sorted Symmetrical Medium Moderately Near Average 1.47 0.62 0.04 Sand Well Sorted Symmetrical Medium Very Well Coarse 11 1.68 0.34 -0.21 Sand Sorted Skewed Medium Very Well Coarse 12 1.73 0.31 -0.13 Sand Sorted Skewed Medium Near 13 1.64 0.39 -0.05 Well Sorted Sabkha Sand Symmetrical sediments Medium Very Well 14 1.82 0.31 0.12 Fine Skewed Sand Sorted Fine Near 15 2.74 0.38 0.06 Well Sorted Sand Symmetrical Fine Near Average 2.07 0.37 0.00 Well Sorted Sand Symmetrical

Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 149

60 80

70 50 Sample Sample 60 40 (1) 50 (2)

% 30 % 40

30 20 20 10 10 0 0 60 60

50 Sample 50 Sample 40 (3) 40 (4)

% 30 % 30

20 20

10 10 0 0 90 70 80 60 70 Sample Sample 50 60 (5) (6) 50 40 % % 40 30 30 20 20 10 10 0 0 70 70 60 Sample 60 Sample 50 (7) 50 (8) 40 40 % % 30 30

20 20

10 10 0 0 50 60 45 50 40 Sample Sample 35 (9) 40 (10) 30 % % 25 30 20 20 15 10 10 5 0 0 Beach sediments Coastal dunes sediments

Coarse sand Medium sand Fine sand Very fine sand Fig. 23. Beach and coastal dunes sediment fractions. Arrows show sediment transportation landward. 150 Mohamed Abdel Galil and Esmail El-Fergany

Brine Chemistry Water salinity varies from 46.9 g/l of the sea water to 323.8 g/l of sabkha brines. Variations in salinity content (Fig. 24, 25 and Table 2) indicate that, salinity increases in the direction from the sea toward sand dune pans (up to 180.4 g/l) and sabkha brines (up to 323.8 g/l). The high salinities in the sabkha brines may be related to the high evaporation rate. Accompanying the increase in salinities is the very high - concentration of Na+ and Cl ions (Fig. 24 and 25). The variation in chloride concentration (Fig. 25) shows that, the chloride concentration increases progressively from the seaward (22491 ppm) to landward directions (up to 98616 ppm and 181661 ppm for the sand dune pans and the sabkha brines respectively). Sulphate constitutes the second predominant anion after chloride and varies in content between 8000 ppm for the Mediterranean Sea water and up to 19500 ppm and 38500 ppm for the sand dune pans and the sabkha brines respectively. Generally, the sulphate distribution pattern is similar to that of chloride and salinity contents indicating that, sulphate enrichment is associated with salinity rise.

350 300 250 200 g/L 150 100 50 0 1 2 3 4 5 6 7 8 9 10 11 12 Sample number

Fig. 24. Total Salinity distribution showing increase in salinity landward. 200000 Cl- 150000 ppm 100000

50000 Na+ 0 1 2 3 4 5 6 7 8 9 10 11 12 Sample number

Fig. 25. Increase in the concentrations of chlorine (Cl-) and sodium (Na+) ions accompanying the increase in salinities. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 151

Table 2. Chemical analysis of the collected water samples. S. T.D.S. Cations Anions Location Unit + + ++ ++ ------No. g/l Na K Mg Ca Cl SO4 HCO3 CO3 ppm 12600 310 2016 1262 22491 8000 213.5 - 1 Seawater 46.9 epm 547.8 7.9 165.8 63 634.3 166.6 3.5 - % 69.83 1.01 21.13 8.03 78.85 20.71 0.44 - ppm 19500 510 3864 922 38062 6000 579.5 -

2 epm 847.8 13 317.8 46 1073.4 124.9 9.5 - 69.4 % 69.23 1.06 25.95 3.76 88.87 10.34 0.79 - ppm 27600 1020 4968 1844 53633 12500 244 -

3 epm 1200 26.1 408.6 92 1512.5 260.3 4.0 - 101.8 % 69.50 1.51 23.66 5.33 85.12 14.65 0.23 - ppm 35500 660 3780 2525 55363 19500 213 -

4 epm 1543 16.9 310.9 126 1561 406 3.5 - 117.5 Sand dune % 77.27 0.85 15.57 6.31 79.22 20.60 0.18 - Pans ppm 36600 1000 5520 4609 74394 15000 305 -

5 epm 1591.3 25.6 453.9 230 2098 312.3 5.0 - 137.4 % 69.16 1.11 19.73 10.0 86.86 12.93 0.21 - ppm 48500 1416 9936 2765 98616 17000 336 -

6 epm 2109 36.2 817 138 2781 353.9 5.5 - 178.6 % 68.03 1.17 26.35 4.45 88.56 11.27 0.18 - ppm 49500 1330 9936 3687 98616 17500 275 -

7 epm 2152 34 817 184 2781 364.4 4.5 - 180.4 % 67.52 1.07 25.64 5.77 88.29 11.57 0.14 - ppm 76000 2800 21600 802 159169 38500 640 -

8 epm 3304 71.6 1776 40 4489 801.6 10.5 - 299.5 % 63.64 1.38 34.21 0.77 84.68 15.12 0.20 - ppm 82500 1500 18768 1844 174200 27000 519 -

9 epm 3587 38.4 1543 92 4912.6 562.1 8.5 - 306.3 % 68.19 0.73 29.33 1.75 89.59 10.25 0.16 - Sabkha ppm 84000 2000 22632 922 181661 32000 610 -

10 Brines epm 3652 51.2 1861 46 5123 666.3 10 - 323.8 % 65.10 0.91 33.17 0.82 88.34 11.49 0.17 - ppm 88000 1800 14900 5531 178200 26000 518 -

11 epm 3826 46 1225 276 5025.4 541.3 8.5 - 314.9 % 71.21 0.86 22.80 5.14 90.14 9.71 0.15 - ppm 87860 2000 16560 1844 176931 26000 427 -

12 epm 3820 51.2 1361.8 92 4989.6 541.3 7.0 - 311.6 % 71.74 0.96 25.57 1.73 90.10 9.77 0.13 -

Results of the chemical analyses were recalculated for both the major cations and major anions and plotted on Sulin graph (1946) to interpret the origin of brine. It is clear that, the brines of the saline pans are of recent marine water origin and of MgCl2 composition (Fig. 26). The main supply to the coastal saline basin and the surrounding sabkha sediments is either through storm flooding of sea water, seawater seepage or high tide seawater spray, in addition to minor input from water inflow 152 Mohamed Abdel Galil and Esmail El-Fergany through the highly permeable fluvial and dune sands after sporadic torrential rains. The inflow of both marine and non-marine waters into the Salinas causes the groundwater level to rise.

100 CaCl2 Old marine

Cl – (K+ + Na+)

MgCl2 Recent 2- marine SO4 100 100 Mg2+ Na2SO2 Deep meteoric water (K+ + Na+) - Cl

NaHCO2 Saline pan Shallow meteoric water Sand dunes

Sea water

Fig. 26. Sulin graph representing the water genesis in the study sabkha. The Hypothetical Salt Assemblage The hypothetical salt assemblages were determined and presented in Table (3). NaCl is the highly dominated salt (65.02 – 78.12 %), MgCl2 is present in a relatively high amount, while Ca (HCO3)2 is relatively trace (Table 3). The relatively high magnesium content of the study area may be attributed to local surface and subsurface environments related to the lithology of water – bearing rocks. Moreover, surface evaporites intercalated with the water – bearing sediments are a possible local source for magnesium. Sedimentological Significance and Brine Chemistry of Recent Coastal Sabkha, … 153

Halite is the predominant . As the water volume decreases, gypsum will be deposited first, but subsequently, with increasing evaporation, there will be a mixture of gypsum and halite and finally halite only (Braithwaite and Whitton, 1987).

Table 3. The hypothetical salt assemblage for the studied water samples.

Sample Location NaCl MgCl2 MgSO4 Ca SO4 Ca (HCO3)2 No. 1 Seawater 70.84 8.01 13.12 7.59 0.44 2 70.29 18.58 7.37 2.97 0.79 3 71.01 14.11 9.55 5.10 0.23 4 78.12 1.10 14.47 6.13 0.18 5 Sand dunes 70.27 16.59 3.14 9.79 0.21 6 69.20 19.35 7.00 4.27 0.18 7 68.59 19.70 5.94 5.63 0.14 8 65.02 19.58 14.63 0.57 0.20 9 68.92 20.67 8.66 1.59 0.16 10 Saline Pan 66.01 22.33 10.84 0.65 0.17 11 72.06 18.08 4.72 4.99 0.15 12 72.70 17.40 8.17 1.60 0.13

Conclusions Sabkha deposits occupy the relatively low topographic areas and are separated from the sea by coastal sand dunes where dry sabkha is frequent. The beach sediments are relatively coarser compared to those of coastal sand dunes and sabkha. Grain size grading with improvement in sorting occurs in the direction of sediment drift landward and the coastal sand dunes sediments show relatively increase in the finer fractions compared with that of the beach sediments. The saline pan zones are surrounded with brine saturated mudflats that are covered with scattered halophytes surround the saline pan. The water table is close to the surface of the sabkha sediments and the inflow of both marine and nonmarine waters into the saline pans causes the groundwater level to rise. The saline pans range in size from a few square meters to hundreds of square meters depending on the amount of ground water seepage, the slope, and the surface area of the evaporite basin. The saline pans are filled with water in winter and floored with layered salt in summer. 154 Mohamed Abdel Galil and Esmail El-Fergany

X-ray examinations show a dominant halite while bicarbonate salts are traces. SEM study shows the effect of the dilution of the brine on the texture of the evaporite crystals. During spring and summer months, the brackish waters are partially or completely evaporated which lead to deposition of evaporite minerals in the saline basins and the surrounding sabkha plains. In autumn and winter months, the saline pans are partially filled with water and the surrounding sabkha plain is moistened with seawater seepage and sporadic rainfall. These waters led to partial dissolution of the former summer deposited halite and/or gypsum. Salinity increases in the direction from shore landward, and the origin of the brines of the saline pans is interpreted as recent marine water origin of MgCl2 composition. The hypothetical salt assemblages were determined and show that NaCl is the dominated salt and the bicarbonate salts are traces. Moreover, surface evaporites intercalated with the water – bearing sediments are a possible local source for magnesium.

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