Arab J Geosci (2015) 8:9973–9992 DOI 10.1007/s12517-015-1852-1

ORIGINAL PAPER

Sediment characteristics and microfacies analysis of Jizan supratidal sabkha, coast,

Mohammed H. Basyoni & Mahmoud A. Aref

Received: 20 May 2014 /Accepted: 24 February 2015 /Published online: 30 April 2015 # Saudi Society for Geosciences 2015

Abstract Jizan sabkha extends along the southeastern coastal the brine surface and floor of saline pans, and the diagenetic plain of the Red Sea, Saudi Arabia, and is considered as one of formation of and below the sediment sur- the main problems that has a negative impact on infrastructure face as intrasediment displacive, inclusive, and replacive of buildings. Field examination of the surface of the wet growth in the wet sandflat and mudflat areas. Recognition of sabkha area indicated the presence of sedimentary surface such structural and textural features of the sediments structures produced by physical forces such as adhesion rip- helps in solving engineering geological problems in Jizan area ples, tepee polygonal ridges, efflorescent pods, and and allowed also for interpreting the similar sabkha sediments structures produced by microbial activities such as petees in the rock record. and blisters. Microfacies analysis of the siliciclastic and evap- orite lithofacies types has been done for sediment samples Keywords Lenticular . Rosette gypsum . Nodular anhydrite . from the surface, trenches, and cores. The siliciclastic Basin zonation . Jizan sabkha . Saudi Arabia lithofacies type represents the host sediments in Jizan sabkha and consists of sand and mud. The evaporite lithofacies type is distinguished into three microfacies types of gypsum, anhy- drite, and halite. The gypsum microfacies types are represent- ed by diagenetic growth of individual lenticular, twinned len- Introduction ticular, twinned complex lenticular, rosettes, nodular, poikilotopic, porphyroblastic, alabastrine, and clastic gypsum. The coastal plain of the Red Sea of Saudi Arabia contains a The anhydrite microfacies types are represented by nodular series of isolated coastal , saline pans, and supratidal and enterolithic anhydrite. The halite microfacies types are sabkhas. The coastal lagoons have salinities slightly higher represented by primary rafts, cumulates, chevrons and cornets, than the Red Sea water, and their mineralogic composition, and diagenetic overgrowth and mosaic halite cement. The sediment textures, pollution, environmental characteristics, structural and textural characteristics of the evaporite sedi- and micro- and macro-faunal assemblages were studied by ments indicated the formation of primary halite crystals at Abou Ouf and El-Shater (1991), Al-Washmi (1999), Coakley and Rasul (2001), Al-Washmi (2003), Basaham et al. (2006), Abu-Zied et al. (2011), Abu-Zied and Bantan (2013), Rasul et al. (2013), and Basaham et al. (2014). The saline pans occur only south of Jeddah and were studied by M. H. Basyoni (*) : M. A. Aref Department of Petroleum Geology and Sedimentology, Faculty of Taj and Aref (2014, 2015a). The studies carried out on the Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia supratidal sabkhas of the eastern Red Sea coast were con- e-mail: [email protected] cerned mainly with water and sediment chemistry (e.g., M. A. Aref Bahafzullah et al. 1993; Basyoni 1997; Serhan and Sabtan e-mail: [email protected] 1999; Sabtan et al. 1997; Sabtan and Shehata 2003; Banat et al. 2005; Basyoni and Aref 2014; Taj and Aref 2015b). M. A. Aref Geology Department, Faculty of Science, Cairo University, Several works were concerned with the sedimentology of the- Giza, Egypt se sabkhas (e.g., Basyoni 2004;Al-Washmietal.2005; 9974 Arab J Geosci (2015) 8:9973–9992

Gheith et al. 2005; Taj and Aref 2009, 2011; Basyoni and Aref Fig. 1 a Location map for Jizan area. b Geology of Jizan area (after„ 2007, 2009, 2010, 2011; Basyoni et al. 2008; Ginau et al. Blank et al. 1987). Note: the insert box is the studied area shown in (c). 2012; Aref and Taj 2013; Aref et al. 2014). Most studies c Surface lithology and location of the sediment samples and cores drilled in the studied Jizan sabkha. d Lithologic interpretation of the cores drilled carried out on Jizan sabkha were concerned with the engineer- in Jizan area ing geological problems of the sabkha soil (Dhowian et al. 1987; Dhowian 1990;Erol1989; Al-Shamrani and Dhowian to the heavy rainfall intensity which may happen during the 1997; Al-Mhaidib 2002; Youssef et al. 2012). However, none rainy storms, and the peak runoff flows from the East towards of these works tried to relate the behavior of the sabkha sed- West (Elsebaie et al. 2013). Abdelrahman (1997) found that iments to their mineralogy and sediment composition. the average temperature in Jizan area is 23 °C, the annual Therefore, the purposes of the present work are the examina- precipitation is 1.3 cm, and the average relative humidity tion of the sedimentary surface structures, microfacies analy- varies between 45 and 65 % in winter and 25 and 40 % in sis of the evaporite sediments, and distribution of the different summer. The annual mean rate of evaporation at Jizan is evaporitic basins in the sabkha area. The results of this paper 156 cm/year (Abdelrahman and Ahmad 1995). The prevailing may help in solving the problems of damage of the infrastruc- winds at Jizan blow from west during summer and southwest ture in the sabkha area and interpretation of the depositional during winter, with wind speeds ranging between 2 and setting and mechanism of formation of similar evaporite 50 km/h. These climatic data indicated the recharge of mete- sediments. oric water to the sabkha area during winter months and the deposition of evaporite during summer months. Location and geologic setting of Jizan sabkha

Jizan sabkha is located on the southeastern coastal plain Methods of study of the Red Sea of Saudi Arabia, between latitudes N 16° 44′ and N 16° 60′, and longitudes E 42° 32′ and E 42° 42′ The results achieved in this paper are based on the field (Fig. 1). The sabkha area occupies the lowest topographic works, trenches, cores, and thin sections. Ten-day field depression that gradually increases in height towards the trips were made to Jizan sabkha in August 2012 and east. Three topographic zones are defined in Jizan area, May 2013 for examining the surface features of the wet which run for approximately 1800 km parallel to each and dry parts of the sabkha. Several shallow trenches, up other in a NW-SE direction (Blank et al. 1987; Hussein to 150 cm in depth, that meet the water table have been and Loni 2011)(Fig.1b): (1) the dissected highland of excavatedinJizansabkha.Inthefieldwork,thesalinity, Hijaz-Asir Precambrian basement complex; (2) the central temperature, and pH values of the brines in the trenches plateau that slopes gently towards the Red Sea coast, dug in the sabkha were measured. The salinity was deter- which consists of the Cambro- Wajid mined by hydrometer glasses taking into account the mea- Sandstone that rests unconformably on peneplained suring of standard sea water. The hydrometers measure Precambrian basement rocks (Powers et al. 1966); and the Mass % NaCl in the brine up to 25 %. The density (3) the Tihama coastal plain that forms a strip of land of the brine samples was measured by using two portable extending approximately 10 km to the foothills of the hydrometer glasses; the first measures density from 1.00 Red Sea escarpment. The coastal plain is covered with to 1.10 g/cm3 and the second measures density from 1.10 Quaternary aeolian sand, alluvial sand and gravel, loess, to 1.2 g/cm3. The pH value of the brine was measured in and flood plain silt deposits. Recent wet, sabkha sedi- the field by a portable pH meter. Seven PVC plastic tubes ments are widespread near the shore of the Red Sea have been drilled to a depth of 120 cm with a hammer to (Fig. 1c). The prominent elevated relief (up to 50 m in extract core samples (Fig. 1d). The evaporite sediments height) on the coastal plain is a salt dome at the old city were selected for preparation of thin sections from the of Jizan, which has an area of 4 km2 (Fig. 1c). surface, trenches, and cores in the sabkha area. The wet and loose sediment samples were dried in the oven and impregnated with epoxy resin. The thin sections were Climate prepared under dry cool condition using paraffin oil and epoxy cement in the laboratory of Cairo University. Jizan area has a subtropical desert climate, where several Petrographic examination and mineralogic identification ephemeral systems drain to the shelf (Abdelrahman of 51 thin sections were investigated by Meiji polarizing and Ahmad 1995). Jizan city is characterized by rainfall microscope adapted with digital camera. The relative storms which vary in intensity and duration. The southern part abundance of the siliciclastic components in thin sections of the city is sometimes exposed to the risk of flash flood due was made in relation to a comparison chart. Arab J Geosci (2015) 8:9973–9992 9975

E 42° 30´ 25 E 42° 34´ E 42° 38´ E 42° 42´ 5 B Jizan 24 C A C Duba NORTH 23 N 16° 58´ EGYPT SUDI ARABIA SAUDI ARABIA 21 22 4 Jeddah RED SEA 20 RED 19 SUDAN SEA 3 Jizan 16 17 0 250 km 18 N 16° 54´ Y YEMEN Ji 15 26 6 14

7 13 Quaternary surficial deposits N 16° 50´ RED SEA Pleistocene basalt 11 12 Mesozoic & Paleozoic sedimentary rocks 10 Sediment sample Hijaz-Asir complex 7 Core location (JZ-7) 2 8 10 9 N 16° 46´ 7 Granite pluton Wet mudflat/sandflat 1 4 Al 6 Proterozoic rocks 3 5 0 3 km Dry sandflat 2

Salt dome 1

JZ-1 JZ-2 JZ-3 JZ-4 JZ-5 JZ-6 JZ-7

D

Clastic gypsum Microbial filaments 10 cm Rosette gypsum Shell fragments Lenticular gypsum Poikilotopic gypsum Sand & mud layers 0 Mud Anhydrite nodules

Sand Gypsum nodules 9976 Arab J Geosci (2015) 8:9973–9992

Discussion The cap rocks of the salt dome are gypsum, anhydrite, dolo- mite, shale, and sandstone layers (Fig. 2a). Facies description (b) Surface sediments (a) Salt dome The low land surrounding the salt dome is distinguished The highest topographic area (50 m) in the coastal plain of into three zones with different sediment compositions, Jizan is a salt dome at the old Jizan city (Fig. 2a). The salt depth, and presence or absence of evaporite min- dome consists of a massive and thin bedded clear, colorless, erals. These are (Fig. 1c) (1) the dry, partially vegetated zone mosaic, halite crystals on fresh surface and gray on weathered at east; (2) the wet, sabkha sediments near the coastal plain, surface. The halite mass has vertical dissolution lines with and (3) few saline pans at the lowest topographic depressions sharp ridges in between due to their recent dissolution by in the sabkha area. The dry land contains loess and some rainfall (Fig. 2a). Several dissolution sinkholes with a diame- scattered fields, where the groundwater is deep ter less than 4 m and depth exceeding 6 m were observed at the (>150 cm in depth). Loess forms small hills, 170 cm in height, floor of the quarries made in the area of salt dome (Fig. 2b). and consists of homogenous and compact silt to fine sand- The halite of the salt dome is usually covered with duricrust sized quartz, feldspar, and mica grains (Fig. 2d). Near the (salcrete) due to re-precipitation of halite crust on the top of the hills, displacive, white anhydrite nodules and occa- weathering surface that may form polygonal ridges (Fig. 2c). sional rootlets were recorded. Sand (barchan type) and

Fig. 2 Salt dome and surface sediments in the coastal plain of a b Jizan area. a A quarry for extraction of halite in the salt dome showing vertical dissolution lines in the halite mass at bottom that are overlain with a cap of anhydrite and clastics. b A sinkhole at the floor of the quarry due to recent dissolution by rainfalls. c A salcrete crust on salt dome showing polygonal ridges. d A loess composed of homogenous silt with fine rootlets. e Coastal, barchans dune over the wet sabkha area. f A c d dense population of forest in the shallow intertidal area

e f Arab J Geosci (2015) 8:9973–9992 9977 sand sheet form most of the eastern part of the coastal plain. to 10 km (Fig. 1c), and the water table varies from 20 to The dunes range in height from 120 cm up to 250 cm, and 150 cm in depth. The salinity of the water table ranges from length up to 30 m, and the down wind direction of the dunes 170 to 180‰, the density ranges from 1.13 to 1.142 g/cm3, point towards southeast (Fig. 2e). Wind-induced ripples cover and the pH value ranges from 6.01 to 7.45. Generally, the the stoss-side of most dunes and show elongation in NE-SW subsurface sediments of the wet sabkha area are composed direction. of interbedded yellow and brown sand and gray mud layers The coastal plain is separated from the Red Sea with dense that form the sandflat and/or mudflat areas on their exposure stands of mangrove forests that grow in the (Fig. 3a). Aggregates of dark gray lenticular and rosette gyp- (Fig. 2f). The floor of the intertidal zone is usually mud- and sum and white nodular gypsum are recorded at the depths of silt-sized bioclasts and aeolian sand grains. The wet sabkha 10, 40, and 90 cm (Figs. 1d and 3b). Spherical, elliptical and area runs parallel to the coast with a width that ranges from 4 lenticular, nodular mosaic anhydrite, 2–7 mm in size, are

Fig. 3 Subsurface sediments of the wet sabkha area. a Thin layers a b of green, brown mud and yellow sand, with white gypsum layer. The floor of the trench shows plastic, wet clay. b Aweathered surface showing displacive growth of lenticular and rosette gypsum in soft mud between sand layers. c Whitemosaicof anhydrite nodules grow displacively in brown sand. d A trench in the wet sabkha showing black, organic-rich mud, enterolithic and nodular anhydrite in sand layers

c d 9978 Arab J Geosci (2015) 8:9973–9992 common near the sediment surface of the sabkha (Fig. 3c). cornets, and cumulus crystals that may increase in thickness to Sometimes, the nodules coalesce to form enterolithic folds of coalesce with the halite rafts. The halite layer may show se- milky white, soft anhydrite at a depth of 15 cm (Fig. 3d). vere dissolution by dripping water to form comb-like halite The sedimentary surface structures of the wet sabkha area fibers. are adhesion ripples, tepee polygonal ridges, efflorescent ha- lite pods, petees, and blisters. The adhesion ripples, tepee Microfacies analysis ridges, and halite pods are found in areas where the water table is located at depths exceeding 40 cm. Petees and blisters are Petrographic examinations of 51 thin sections for the evapo- associated with green microbial mats and exist in areas with rite sediments from the surface, trenches, and cores dug in the shallow (<10 cm) water table condition. Most of the wet sabkha area allowed the recognition of two lithofacies types: sabkha area is covered with adhesion ripples that consist of (a) siliciclastic lithofacies type and (b) evaporite lithofacies small undulation of sand mounds. Below the sediment sur- type. Because of the importance of the evaporite lithofacies face, numerous, fine gypsum nodules are widespread between type, it is subdivided into several microfacies types based on the sand grains (Fig. 1d). In slightly lower topographic areas in their mineralogy, textures, and fabrics that are identified under the wet sabkha, the sediment surface evolves into small the microscope. The following is the description of these (<3 cm in height) and large (>20 cm in height) tepee polygo- lithofacies types: nal ridges (Fig. 4a). The tepee ridges are composed of gypsum and/or halite crusts that form buckling, inverted V-shaped (a) Siliciclastic lithofacies type structures (Fig. 4b). The tepee ridges form the non- orthogonal (120°) polygonal pattern (Fig. 4a). At the slightly The siliciclastic lithofacies represents the host sediments in high topographic area, the tepee structure is of the immature Jizan sabkha, where the evaporite minerals were crystallized type (Assereto and Kendall 1977) that consists of thin (<2 cm) in the capillary evaporation zone from the groundwater by the crusts low (<3 cm) in height and with small (<10 cm) diameter evaporative pumping mechanism of Hsü and Siegenthaler between polygons. At slightly low topographic areas toward (1969). Bioclasts and calcite cement were recorded occasion- the center of the sabkha, the surface evaporite layer evolves ally, in addition to microbial mats in some locations (Tables 1 into mature tepee structure that consists of thick crusts (4 cm), and 2). Sand-sized grains form laminated, rippled-cross lam- of high height (<20 cm), and with a broad area (120 cm) inated or even massive structures (Fig. 5a). The sand grains between polygons (Fig. 4b). Below the tepee crust is brownish are medium to fine size, subangular to subrounded, and mod- sand or gray sand due to the decay of subrecent microbial mats erately to poorly sorted (Fig. 5b). They consist of quartz (60– (Fig. 4b). Efflorescent halite pods are scattered on the wet 80 %), mica (10-30 %), feldspar (5–10 %), hornblende, and sabkha surface in small depressions between the tepee gyp- other igneous and metamorphic grains (<10 %) (Fig. 5b). The sum ridges. They consist of milky white aggregates of spher- mica flakes are represented by biotite flakes that generally ical nodules of spongy halite crystals (Fig. 4c). show preferred orientation (Fig. 5c) or form random orienta- Petees and blisters exist in areas either covered with a thin tion when they are associated with growth of evaporite min- film of water or the water table that is a few centimeters below erals. Feldspar is represented dominantly by fresh plagioclase the sediment surface. The sediment surface may evolve into grains (Fig. 5b). Mud clasts of coarse sand-sized grains are buckling petee crusts less than 3 cm in height (Fig. 4d). The rarely recorded between the quartz grains (Fig. 5d). The type crusts form elongated, hollow, twisted petee ridges (Fig. 3d) of the sand-dominated sediment is a lithic arenite because of and consist of interlaminations of black and green microbial the dominance of mica and lithic grains over the feldspar mats and gypsum layers. Blisters also occur in areas of grains. flourished microbial mats. They consist of miniatures of small Most of the sand grains are loose, without appreciable domes, <3 cm in height and width (Fig. 4e), and consist of thin amount of cement. However, some samples have a matrix of gypsum crust over hollow centers. The lower surface of these brown clay (Fig. 5b), which decrease their compositional and buckling features has numerous vugs of escaped gases textural maturity of the lithic arenite sediment. Patches of cal- (Fig. 4f) from subrecent decayed microbial mats. cite cement are scarcely observed (Fig. 5e). The calcite crys- The lowest topographic areas in the wet sabkha contain tals may corrode and engulf the quartz and feldspar grains. saline pans filled with a high salinity brine >250‰ and a Mud-sized sediment is next in abundance, which is mas- density >1.26 g/cm3. The pans are less than 5 m in diameter sive and brownish. It is composed of angular, poorly sorted, and <30 cm in depth. Halite crystallized in these pans at the silt-sized quartz grains, mica flakes, and brown clay minerals brine surface as thin rafts and pyramidal hoppers (Fig. 4g, h). (Fig. 5f). The mica flakes are relatively finer in size than that Rapid lowering of the brine surface favors the formation of recorded in the sand fraction. The mica may form preferred or successive rafts that form 5–10-cm-thick layers. Halite also random orientation. Sometimes, the mud-sized sediment crystallized on the floor of the pan as aggregates of chevrons, forms thin lamina that grades into laminae composed of silt- Arab J Geosci (2015) 8:9973–9992 9979 sized quartz grains and mica flakes. Brownish, massive clay Microbial mats are recorded in most of the surface sedi- sediment is recorded in some samples (Tables 1 and 2). It is ment samples, and in only one sample of the cores (Tables 1 composed mainly of clay minerals and few quartz and mica and 2), associated with quartz grains and gypsum crystals. grains. The clay may be recorded as random, angular clasts They consist of slightly and highly irregular, thin, yellowish dispersed in siltstone (Fig. 5f) or form thin laminae that inter- or brownish microbial filaments (Fig. 5g). These filaments are calated with silt laminae. recorded enveloping quartz grains and lenticular gypsum

Fig. 4 Surface features in the saline sandflat and saline pan a b areas. a Polygonal tepee structures of halite crusts with partial dissolution of the top of ridges. b Inverted, V-shaped tepee halite ridges on the sediment surface that overlie black, massive sand. c Milky white gypsum forms efflorescent nodules between the buckled dirty halite crust. d Highly contorted, small, inverted U-shaped petee structure due to microbial influence on the sediment, with white efflorescent gypsum c d crystals. e Blistered surface of thin gypsum crust due to gas migration from sub-recent decayed microbial mats. f View of the underside of the blisters showing numerous circular vugs due to escape of gases. g Thin halite rafts floating at the brine surface in a shallow depression. h Bedding plane view showing the variable sizes of pyramidal halite that form the raft e f

g h 9980

Table 1 Facies and microfacies analyses of the surface evaporite sediments in Jizan sabkha

Petrographic Host sediments Individual lenticular gypsum Rosette Nodular Complex Nodular Halite Halite Microbial Secondary Alabastrine Porphyrotopic types gypsum gypsum lenticular anhydrite cement chevron mats anhydrite gypsum gypsum Sample ClayMudSandSilt- Sand- Gravel- gypsum and cornet number sized sized sized

2mmd f 5lower m d ff 5 middle d f d m d 5 upper m m ff 6A f d m f f 6B m m m m f f f 7A d f f 7B md 14A d f f d 14B d d m 16 f r md f 17A d m m f d m 17B d f d d f m 17C d m d 22 d d d 24 d d f f rbJGoc 21)8:9973 (2015) Geosci J Arab For sample location, see Fig. 1c d dominant, m moderate, f few, r rare – 9992 rbJGoc 21)8:9973 (2015) Geosci J Arab

Table 2 Facies and microfacies analyses of the subsurface evaporite sediments from cores taken in Jizan sabkha

Petrographic Host sediments Individual Rosette Nodular Complex lenticular Nodular Halite Halite Microbial Secondary Clastic Poikilotopic types lenticular gypsum gypsum gypsum gypsum anhydrite cement chevron mats anhydrite gypsum gypsum

and cornet – Depth (cm) Calcite cement Clay Mud Sand Silt- Sand- Gravel- 9992 sized sized sized

Jz 1 (16–21) Matrix d m m Jz 1 (39–44) f d Jz 1 (53–59) f d Jz 2 (1–7) d Bioclast f d d m Jz 2 (14–20) f d f d Jz 2 (32–38) f d f d Jz 3 (18–25) f d Jz 3 (34–39) f d m Jz 3 (56–61) f d d m Jz 4 (13–18) d m m Jz 4 (42–47) m f d m d Jz 4 (85–91) d d m d Jz 5 (12–17) m m f d f d f Jz 5 (23–27) m m f Jz 5 (52–57) m m d d f m Jz 5 (70–76) d f m d m m f m Jz 6 (12–17) d f f d f Jz 6 (38–42) m m f Jz 6 (44–49) d f f f Jz 7 (18–22) d m f d Jz 7 (27–31) m f m Jz 7 (53–57) f m Jz 7 (68–71) f d m

For sample location, see Fig. 1c d dominant, m moderate, f few, r rare 9981 9982 Arab J Geosci (2015) 8:9973–9992

Fig. 5 Siliciclastic host sediments in Jizan sabkha. a a b Trough, cross-laminated, very fine sand. Polarized Light. b Poorly sorted, angular quartz and feldspar grains in brownish clay matrix. Polars crossed. c Preferred orientation of biotite flakes in fine sand. Polars crossed. d Coarse, mud fragments between poorly sorted quartz grains with brownish clay matrix. Polars 100 µm 200 µm crossed. e Patch of calcite cement between quartz grains. Polars crossed. f Clay fragments scattered in silt-sized quartz c d grains. Polars crossed. g Brown to orange microbial filaments in fine sand. Polarized Light. h Displacive lenticular gypsum in brown microbial filaments. Polarized Light

200 µm 200 µm

e f

200 µm 200 µm

g h

200 µm 100 µm

crystals, which led to their biostabilization (Noffke 2000, (b) Evaporite lithofacies types 2010), or surrounding nodules of lenticular and granular gyp- sum crystals (Fig. 5h). Sometimes, the microbial filaments are The evaporite lithofacies types are subdivided according to micritized and consist of dense aggregate of micrite grains that their dominant composition into (1) gypsum also enclose the quartz grains and gypsum crystals. microfacies types, (2) anhydrite microfacies types, and (3) Arab J Geosci (2015) 8:9973–9992 9983 halite microfacies types. Each of these microfacies types are gypsum may entrap mica flakes, clay mineral, or silt and sand- distinguished into several types (Tables 1 and 2)accordingto sized quartz grains (Fig. 6c, e). The lenticular gypsum may the fabrics and textures of the deposited crystals that are con- show growth bands marked by impurities from the host sedi- trolled by the processes acting in the depositional and diage- ment (Fig. 6g). netic environments. Individual gypsum crystals may form tabular crystals with straight crystal faces (Fig. 6f). Mees et al. (2012) found that 1. Gypsum microfacies types the tabular gypsum crystals form lozenge shape in cross- sections perpendicular to (010) and elongated parallelogram The terminologies used to describe the size of the gypsum in cross-sections parallel to (010). These tabular gypsum crys- crystals into gypslutite (silt-sized gypsum crystals), tals are recorded in a host of clay sediment (Fig. 6f) or a sand gypsarenite (sand-sized gypsum crystals), and gypsrudite sediment. These tabular gypsum crystals may disturb the pre- (gravel-sized gypsum crystals) follow the terms used by ferred orientation of mica flakes or aligned parallel to the Warren (1982a), Aref (1998), Varol et al. (2002), and Lugli preferred orientation of the mica flakes. The gypsrudite len- et al. (2007). Also, the terminologies used to describe the ticular crystals are occasionally observed to be replaced by morphology of the gypsum crystals such as lenticular, tabular, fibrous anhydrite crystals that form parallel sheaves crossing tabular-prismatic, twinned, rosette, etc., follow the terms used the gypsrudite crystal (Fig. 6h). by Cody (1976, 1979), Cody and Cody (1988), and Mees et al. (2012). The dominant microfacies types of gypsum are Twinned gypsum formed by diagenetic growth of displacive and/or inclusive gypsum during desiccation of the saline pans, or in the saline Twinned gypsum is equivalent to type Ill penetration twins of sandflat/mudflat depositional setting of Lowenstein and Cody and Cody (1988). The twinned gypsum is composed of Hardie (1985); Casas and Lowenstein (1989). The gypsum either two individuals of lenticular gypsum crystals (Fig. 7a) microfacies types are represented by (Tables 1 and 2; or hemi-bipyramidal individuals of gypsum crystals of equal Fig. 6a) individual lenticular gypsum, twinned gypsum, or subequal size. Twinning occurs along the (100) plane. The twinned complex lenticular gypsum, rosette gypsum, nodular twinned gypsum crystals occur displacively and inclusively in gypsum, poikilotopic gypsum, porphyroblastic and alabas- a host clay matrix or a sand matrix. These twinned gypsum trine gypsum, and clastic gypsum. Microbial mats are occa- crystals are characterized by the dominance of inclusions of sionally associated with some of the gypsum crystals under clastic materials within the growing crystals, or they are free the less saline water conditions close to the sea side or conti- from inclusions of the matrix material. nental side of the sabkha area. The following is the description of the microfacies types of gypsum: Twinned complex lenticular gypsum

Individual lenticular gypsum The twinned gypsum may also be more complex and have additional smaller crystal faces parallel to the two main com- Lenticular gypsum of curved crystal faces are the most com- ponent individuals (Fig. 7b). This type was referred by Cody mon type of the evaporite minerals in Jizan sabkha (Tables 1 and Cody (1988) as twin complexes. They are recorded spo- and 2). The lenticular gypsum crystals range in size from radically in the surface and subsurface sediments of the gypslutite (<80 μm in length and <10 μm in width) to sabkha (Tables 1 and 2). The individual gypsum crystals gypsarenite (200–500 μminlengthand<50μminwidth)to may have multiple terminations along only one side of the gypsrudite (2 mm to 3 cm in length and 500–1000 μmin crystals or have numerous, small terminations in both sides width). The lenticular gypsum may increase in number and (Fig. 7b). The twinned complex gypsum crystals are mostly density to form aggregates of random orientation (Fig. 6b)or enclosed matrix material from the host sediment. more commonly form individual crystals floating in the host sediment (Fig. 6c, d). The host sediment may be represented Rosette gypsum with mud rich in mica flakes that commonly form preferred orientation (Fig. 6e, f) to sand-sized quartz, feldspar, and lithic The rosette gypsum is equivalent to type V rosettes of Cody grains (Fig. 6c). The lenticular gypsum crystals may be very and Cody (1988). The rosette gypsum consists of large, parent clear and free from inclusions of the host sediment (Fig. 6d), gypsum crystals, from which smaller, individual, lenticular which indicate their displacive origin. The displacive growth gypsum crystals fan out (Fig. 6a–candd). The smaller lentic- origin of such gypsum crystals are also evidenced by the dis- ular crystals resemble the “petals” of a rose. Such small gyp- turbance of the preferred orientation of the mica flakes sum petals fan out from the central area of the large gypsum (Fig. 6d). Lenticular gypsum may also grow by the inclusive crystals, and its margin is clearly visible (Fig. 7c). Sometimes, growth of materials from the host sediment. Such inclusive the component lenticular gypsum crystals appear randomly 9984 Arab J Geosci (2015) 8:9973–9992

Fig. 6 Gypsum microfacies types. a Different crystal a b morphologies of lenticular c c gypsum: a individual lenticular, b c b b a twinned, c rosettes, d aggregates. b Random, lenticular gypslutite below brownish microbial layer. Polars crossed. c Single, c d d c b gypsarenite lenticular crystal between quartz and mica. Polars crossed. d Disturbance of the preferred orientation of mica 150 µm flakes by the displacive growth of lenticular gypsum. Polars crossed. e Preferred orientation of brownish, mica (biotite) flakes c d with displacive growth of lenticular gypsum. Polars crossed. f Tabular (T) and lenticular (L) gypsum in a clay matrix. Polars crossed. g Growth zones in lenticular gypsum is marked by impurities from the host sediment. Polars crossed. h Fibrous and felted anhydrite replacing gypsum that enclose quartz grains. Polars 200 µm 250 µm crossed

e f

T L

L

250 µm 250 µm

g h

250 µm 150 µm

intergrown to form aggregates of lenticular gypsum, rather lenticular crystals of similar sizes form the rosette gypsum of than arranged to form the rosette shape. Such aggregates of approximate symmetrical appearance. However, the radial lenticular gypsum are highly varied, but some of them may be growth of asymmetric aggregates of lenticular gypsum of var- similar to well-defined rosettes. iable sizes and orientations are also observed (Fig. 6a–c). The The petals of the smaller gypsum crystals appear as a radial host sediment of the gypsum rosettes and aggregates are com- growth of lenticular gypsum from a common center that col- monly sand- and silt-sized quartz grains. All gypsum crystals lectively form the rosette pattern (Fig. 7c). More than six of the rosettes and aggregates are grown displacively and Arab J Geosci (2015) 8:9973–9992 9985

Fig. 7 Morphologies of gypsum crystals. a Clear, twinned gypsum a b crystals surrounded with finer gypsum. Polars crossed. b Twinned complex lenticular gypsum with inclusion of mica flakes. Polars crossed. c Rosette gypsum consists of radial growth of variable sizes of lenticular crystals. Polars crossed. d Ellipsoid gypsum nodule consists of random, lenticular gypsum in 200 µm 200 µm mud sediment with preferred orientation of mica flakes. Polars crossed. e Two gypsum nodules slightly merged along concavo- c dD convex boundary in clay matrix. Polars crossed. f Large, poikilotopic gypsum crystals encloses finer, lenticular, gypsum crystals. Polars crossed. g Porphyrotopic gypsum crystals with irregular interpretation boundaries. Polars crossed. h Local reworking of lenticular gypsum and formation of matching fragments. Polars 250 µm 200 µm crossed e f

200 µm 200 µm

g h

200 µm 100 µm

enclose sand- and silt-sized quartz grains, mica flakes, and and argillaceous sediments, such as silt and clay sediment, and clay material. less commonly in sand sediment (Fig. 7d, e). Gypsum nodules may occur as individual, spherical nodules (Fig. 7d)thatare Nodular gypsum exclusively isolated from the neighboring one or show plane or concavo-convex contact with the adjacent nodules Gypsum crystals may be selectively aggregated to form nod- (Fig. 7e), or may coalesce with each other to form the ules of variable sizes and shapes in a host of fine siliciclastic enterolithic nodular structure. The nodules consist generally 9986 Arab J Geosci (2015) 8:9973–9992 of gypslutite crystals of variable shapes and densities. The This resulted into the formation of clastic gypsum grains that nodules may consist of scattered, random lenticular gypsum are composed of local reworking of lenticular gypsum crystals (Fig. 7d) or dense aggregates of tabular gypsum, or (Fig. 7h). The gypsum fragments can be easily matched, indi- fine, granular gypsum crystals (Fig. 7e). Other nodules are cating a short transportation distance. However, transportation composed of random aggregates of twinned complex lenticu- of the clastic gypsum for a relatively long distance is evi- lar gypsum crystals or a mixture of fine granular and lenticular denced by the occurrence of cleavage fragments or terminal gypsum crystals. parts of the lenticular crystals mixed with sand grains, or in a matrix of mud sediment. Poikilotopic gypsum 2. Anhydrite microfacies types Poikilotopic gypsum consists of large (>500 μm) individual crystals that enclose either finer, lenticular gypsum crystals Anhydrite microfacies types are rarely recorded in the sur- (Fig. 7f) or quartz sand and mica flakes from the surrounding face and subsurface sediments of Jizan sabkha (Tables 1 and matrix. The poikilotopic gypsum crystals have generally irreg- 2). They are represented by nodular and enterolithic anhydrite ular outline with the surrounding gypsum crystals and clastic microfacies types. The morphology and composition of nod- material. They exist as individual crystals scattered in the ma- ular anhydrite and enterolithic anhydrite nodules are similar. trix or may form aggregates of adjacent poikilotopic crystals They consist of spherical and ellipsoidal, dense aggregates of of variable optical orientations. The enclosed, fine gypsum anhydrite crystals, where the boundary of the nodules are gen- crystals are commonly found with perfect lenticular morphol- erally highly irregular (Fig. 8a), in contrast to the relatively ogy in the poikilotopic gypsum (Fig. 7f), which indicates that smooth boundary of gypsum nodules (Fig. 7e). These individ- the large gypsum crystals grow by inclusive growth and en- ual and coalesced anhydrite nodules are scattered in brownish trapment of the finer lenticular gypsum and not by the mud and fine sand-sized quartz grains (Fig. 8a). Mica flakes replacive growth. commonly show preferred orientation parallel to the outer boundary of the anhydrite nodules. Generally, the nodules Porphyrotopic and alabastrine gypsum crystals are composed of prismatic, elongated anhydrite crystals that show random orientation at the center of the nodules (Fig. 8b) Porphyrotopic and alabastrine gypsum crystals are recorded in or throughout the nodular structure. However, radial, fan-like only three sediment samples in Jizan sabkha (Tables 1 and 2). anhydrite crystals may exist at the boundary of the nodules Porphyrotopic gypsum commonly occurs as coarse (Fig. 8c ). In large nodules, 100-μm-thick zone consists of (>600 μm) crystals that form mutually interfering aggregates parallel sheaves of prismatic anhydrite crystals that are ar- (Fig. 7g) or as floating crystals within finer granular gypsum ranged parallel to the boundary of the anhydrite nodules crystals. The porphyrotopic gypsum crystals are generally (Fig. 8d). The anhydrite nodules are generally clear and free clear and free from inclusion of clastic materials that are com- from inclusion of the mud and sand sediments (Fig. 8a, b). mon in the aforementioned gypsum microfacies types. However, few, scattered quartz grains are occasionally found Alabastrine gypsum is recorded as irregular or elongated at the margin of the nodules. Lenticular gypsum and twinned patches adjacent to or within coarse lenticular and lenticular gypsum may exist close to the anhydrite nodule porphyrotopic gypsum crystals. The alabastrine gypsum con- (Fig. 8e). The existence of lenticular gypsum and the clear sists of aggregates of microcrystalline gypsum with a size less nature of the anhydrite nodules indicated the presence of pri- than 50 μm. The boundaries between the finer alabastrine mary anhydrite crystals that were formed displacively in the gypsum and the coarser gypsum are usually gradational inter- host siliciclastic sediment. penetrating contact, indicating the replacement of the coarser gypsum crystals by finer gypsum. This process of replacement 3. Halite microfacies types of the coarse gypsum crystals by finer gypsum has been de- scribed before from the Miocene of the Red Sea Halite microfacies types are recorded in the saline pans (Aref et al. 2003; Mandurah and Aref 2010), from the within Jizan sabkha. They are represented by primary halite Messinian evaporites of Italy (Testa and Lugli 2000), and from crystals (chevrons and cornets) and diagenetic halite (over- pedogenic gypsum crusts (Aref 2003). growth and cement).

Clastic gypsum Primary halite (chevrons and cornets)

During periods of aridity, intensive rainfall, or occasional Chevron and cornet halite crystals are composed of fluid flood, the displacive gypsum crystals in the sabkha sediment inclusion-rich bands and fluid inclusions-poor bands are subjected to wind or water erosion and slight reworking. (Fig. 9a, b). The chevron halite forms an upturned V-shaped Arab J Geosci (2015) 8:9973–9992 9987

Fig. 8 Anhydrite microfacies types. a Several anhydrite a b nodules grow displacively in mud sediment. Polars crossed. b Random prismatic anhydrite at center and preferred orientation of prismatic anhydrite at the boundary of anhydrite nodule. Polars crossed. c Radial growth of parallel sheaves of prismatic anhydrite at the boundary of the nodule. Polars crossed. d Parallel 100 µm 100 µm arrangement of prismatic anhydrite at the boundary of anhydrite nodule. Polars crossed. e Lenticular gypsum at top and c f anhydrite nodule at bottom in a host mud sediment. Polars crossed

100 µm

d

200 µm

100 µm

pattern that is usually pointing upward (Fig. 9a), whereas the displacively grown between quartz grains (Fig. 9c). The mo- cornet halite crystals consist of horizontal halite bands that saic halite may contain clay materials, quartz, and gypsum increase in width upward (Fig. 9b). The fluid inclusion-rich fragments from infiltrating groundwater. bands in chevron and cornet halite crystals are formed during daytime due to the increase in temperature and excess evapo- ration which favor rapid rate of halite crystallization and the Basin zonation entrapment of fluid inclusions. During night time, the decrease in temperature and evaporation favor slow crystallization of Based on field examination of the sediment surface and halite without fluid inclusions (Smoot and Lowenstein 1991). trenches in Jizan sabkha, and the structural and textural char- acteristics of the evaporite sediments, the supratidal sabkha in Diagenetic halite (overgrowth and cement) Jizan area is distinguished into three depositional basins; these are the central ephemeral saline pan, the wet sandflat/mudflat, Diagenetic halite crystallized from the capillary evaporation of and dry sandflat. Each subenvironment is characterized by the saline groundwater as overgrowth and mosaic halite ce- specific textural and structural features of the evaporite min- ment. The halite overgrowth consists of large, clear halite that erals that have been formed during flooding, evaporative con- sharply truncates the fluid inclusion-rich bands in chevron and centration, and desiccation stages. Deposition of the evaporite cornet halite (Fig. 9a). Mosaic halite cement consists of minerals in Jizan sabkha took place in a shallow, flat basin that equigranular cubic and plate-like halite crystals that are is normally dry in summer and partially flooded with seepage 9988 Arab J Geosci (2015) 8:9973–9992

Fig. 9 Halite microfacies types. a Chevron halite with inverted V- a b shaped pattern of fluid inclusion- rich bands and fluid inclusion- poor bands (black arrows)that truncated with overgrowth of clear halite cement (red arrows). Polarized Light. b Cornet halite consists of fluid inclusion-rich bands and fluid inclusion-poor bands. Polarized Light. c Mosaic halite cement with clay impurities 100 µm between cubic halite crystals. Polars crossed with mica plate c

100 µm 100 µm

seawater and meteoric water from direct rainfalls or floods in sink to the bottom under the effects of gravity, similar to ob- winter time. servation by Handford (1991) and Taj and Aref (2015a). The repeated process of raft formation and sinking of the rafts led (a) Ephemeral saline pans to the formation of thick (7 cm) halite layers composed of sequences of halite rafts. When the brine is slightly agitated The saline pans in Jizan sabkha represent the ephemeral at the early stage of nucleation of the halite crystals, the waves saline lake subenvironment of Hardie et al. (1978) and the disturb the surface tension (Smoot and Lowenstein 1991), and ephemeral saline pans of Lowenstein and Hardie (1985). the individual halite crystals settle to the bottom as aggregates Ephemeral saline pans exist in the lowest topographic depres- of cumulus crystals (Fig. 4h). These cumulus crystals accu- sion in Jizan sabkha and are filled with halite saturated brine mulate between sinking halite rafts. that is highly saline (salinity >250‰ and a density >1.26 g/ cm3) with respect to the surrounding brines of the saline mud- Chevrons and cornets flat and sandflat areas (salinity 170 to 180‰, density 1.13 to 1.142 g/cm3). Primary halite crystallized in the saline pan at Continuous concentration of the brine by evaporation, togeth- the brine-air interface as rafts and cumulus crystals and at the er with mixing with the shallow pan waters, eventually pro- floor of the pan as cornets and chevrons. duces a supersaturated brine from which halite crystals grow on the earlier settled rafts and cumulus crystals. Syntaxial Rafts and cumulates halite growth on the earlier formed crystals and the competitive growth of halite produce vertically oriented crystals that re- During summer months, when the evaporation of the brine in semble the halite “teeth” (Fig. 9a) described by Valyashko the pans is more than inflow of marine and/or meteoric water, (1952). The morphology of the upward growing crystals de- the salinity of the brine increases to the range of halite satura- pends on the attitude of the parent crystals. When syntaxial tion level. Halite crystallized at the brine-air interface as overgrowth begins on a halite cube lying on the edge, the millimeter-sized square-shaped plates (Arthurton 1973) and resulting overgrowth will be chevron-shaped with an upward pyramidal hoppers (Dellwig 1955) that are suspended hori- pointing corner (Fig. 9a) (Wardlaw and Schwerdtner 1966; zontally by surface tension. With continuous growth of halite Arthurton 1973; Lowenstein and Hardie 1985). When the par- crystals at the brine-air interface, they merge with adjacent ent cube is oriented with its face upwards, syntaxial over- crystals to form continuous rafts (Fig. 4g, h). When the weight growth results in the formation of flat-topped, upward widen- of the suspended rafts overcomes the surface tension, they ing cornet-shaped crystals (Fig. 9b) (Arthurton 1973). Arab J Geosci (2015) 8:9973–9992 9989

(b) Saline mudflat/sandflat zone (2) by incorporative (Smoot and Lowenstein 1991)orinclu- sive (Rouchy et al. 1994)growth. Saline mudflat and sandflat are broad extensive flats of Displacive growth of lenticular, tabular, and rosette gyp- siliciclastic sediments that cover most of the coast of Jizan sum (Figs. 6 and 7) occur when nucleation of the gypsum area (Fig. 1c). Saline mudflat and sandflat deposits consist crystals pushes aside the host mud and fine sand sediments, of wet silt and sand in which intrasediment, diagenetic gyp- whereas the poikilotopic growth of lenticular gypsum crystals sum, anhydrite and halite, and surface efflorescent halite were occurs when the host siliciclastic sediments are entrapped formed from the evaporation of shallow water table. Upward within the growing gypsum crystals (Fig. 6g). The incorpora- movement of moisture from the water table saturated with tive or inclusive growth of gypsum is interpreted by Rouchy respect to gypsum and/or halite, probably by the evaporative et al. (1994) to take place within relatively coarse-grained pumping mechanism of Hsü and Siegenthaler (1969), led to sediment by rapid growth of gypsum in partially lithified host the formation of (a) polygonal tepee structures, (b) diagenetic sediment. Gypsum crystals may nucleate on the surface of growth of lenticular and rosette gypsum crystals, (c) detrital grains or may push or separate the sandy grains from displacive growth of mosaic and enterolithic anhydrite nod- the cementing material. The displacive and inclusive growth ules, and (d) petee structures. of lenticular and rosette gypsum took place in a brine-soaked mud that contains the type of organic matter which inhibits the growth of (111) face (Cody and Cody 1988; Rosen and Polygonal tepee structures Warren 1990 ;Aref1998). The environmental conditions that control gypsum With increases in the salinity of the brine during summer nucleation and crystal morphology have been studied months, pervasive, displacive growth of halite cement experimentally by Cody (1976, 1979) and Cody and Cody (Fig. 9c) in the subsurface causes the surface of the saline (1988). They observed that organic compounds promote the sandflats to fracture and buckle (Fig. 4a)byvolumeexpan- lenticular habit only in an alkaline environment. The lenticular sion, resulting in the development of a network of polygonal habit is most common in warm, chloride-rich mud (Cody sutures (Warren 1982b). With continuous growth of subsur- 1979); however, the mineral content, structure, and environ- face halite, the surface crust is altered into an overthrust tepee mental setting of the mud do not influence the gypsum crystal structure (Fig. 4b). The non-orthogonal pattern of the tepee habit (Cody 1979; Rosen and Warren 1990). structure reflects a homogeneous behavior of the salt crust and an expansion in a homogeneous stress field. Similar interpre- Displacive growth of nodular mosaic and enterolithic tations were mentioned by Lachenbruch (1962), Warren anhydrite nodules (1982b), Kendall and Warren (1987), and Aref (1998, 2014). Several mechanisms were described by Kendall and Close to the sediment surface of the saline mudflat/sandflat Warren (1987) which cause crusts to expand and crumple into zones of Jizan sabkha, milky white nodular mosaic and tepee structure. The fracturing of the crust may be a response enterolithic anhydrite nodules were recorded in the vadose to thermal expansion and contraction or a response to the and upper phreatic zones (Fig. 8a, b), similar to observations buoyancy effects of a fluctuating water table. Both mecha- by Neev and Emery (1967), Gornitz and Schreiber (1981), and nisms may take place in the sabkha of Jizan area. The resulting Handford (1982). The displacive growth of anhydrite took cracks may be filled or covered with wind-blown sandy ma- place in the high-salinity brine in the capillary evaporation terial or filled with halite cement. zone as mosaic of nodular aggregates or as enterolithic folds. The association of nodular anhydrite and lenticular gypsum in Diagenetic growth of lenticular and rosette gypsum crystals some samples (Fig. 8f) may point to the primary origin of the anhydrite nodules from highly concentrated brine, whereas Gypsum and/or anhydrite were diagenetically grown below the lenticular gypsum crystals may be formed from brine with the surface in brine-soaked sediments of the saline sandflats a relatively lower salinity. and mudflats (Fig. 3), when concentrated brines diffused up- ward from shallow water table by capillary action, because of Petee structures the high rates of evaporation that prevailed during the summer months (Gornitz and Schreiber 1981), a process termed “evap- During winter time, some parts of the saline mudflat/sandflat orative pumping” (Hsü and Siegenthaler 1969). Precipitation sediments were perennially moistened by seepage of less sa- would occur at the level where gypsum, anhydrite, or halite line groundwater or rainfall. This led to extensive growth of becomes supersaturated. The saline minerals grow by two microbial mats on the sediment surface. The existence of processes: (1) by displacive growth where the surrounding green and black microbial mats are usually developed on the sediment is pushed aside by the force of crystallization and floor of very shallow (<10 cm in depth) water body. Their 9990 Arab J Geosci (2015) 8:9973–9992 locations are probably controlled by a nearby flow of ground- The highest topographic area, east of Jizan sabkha, was char- water seepage as their existence required a water salinity range acterized by a deeper water table and formation of sand sheets from 60 to 150‰ (Cornée et al. 1992). During summer and sand dunes in the dry sandflat zone. months, the shallow water table and the increase in evapora- The damage of the infrastructures of buildings in Jizan tion favor the growth of microbial mats to exhibit “petee” sabkha may be caused by (1) the crystallization pressure structure (Fig. 4d). According to Reineck et al. (1990), exerted from the diagenetic growth of gypsum and anhydrite Noffke (2010), Aref et al. (2014), and Taj et al. (2014), the below the sediment surface and possibly within pores of the petee structure was formed due to accumulation of escaped infrastructure, and (2) the corrosive effect of the sulfate ions gases beneath surficial mat layers that generate folds in the which reacted with steels from the foundation of buildings and soft, wetted microbial substrate prior to consolidation. This caused their corrosion. The factors that may have great effects gas has resulted from bacterial degradation of buried organic on the deterioration of foundation in Jizan sabkha are surface matter. Initial escaping of such gases may form blisters on the topography of the sabkha, depth of the water table, chemical sediment surface (Fig. 4e) or may be entrapped in the subsur- composition of the brine, nature and density of the diagenet- face sediments forming spherical vugs (Fig. 4f). ically grown evaporite minerals, and type of siliciclastic sed- iments. Studies of these geomorphic and sedimentologic fac- (c) Dry sandflat zone tors together with the degree of the actual damage of infra- structures may help in future planning of the best locations for Dry sandflat is located in the topographically high area expansion of Jizan city. adjacent to the saline mudflat/sandflat zone towards the east and grade outward into the high mountain of the Red Sea Acknowledgments This project was funded by the Deanship of Scien- region. It is subaerially exposed most of the time and the tific Research (DSR), King Abdulaziz University, Jeddah, under grant no. (307/145/1432). The authors, therefore, acknowledge with thanks DSR groundwater level is too deep to allow the precipitation of technical and financial support. We thank two anonymous reviewers for evaporite minerals, similar to observation and interpretation the careful reading of the manuscript and their valuable comments. by Smoot and Lowenstein (1991). Therefore, the dry sandflat is severed from the process of erosion more than the saline pans or saline mudflat and sandflat zones. The dry sandflat References zone is characterized by the abundance of halophytes. Repeated wetting and drying episodes of the dry sandflat zone Abdelrahman SM (1997) Seasonal fluctuations of mean sea level at Jizan, lead to stabilization and fixation of the sandy particles by thin Red Sea. J Coast Res 13(4):1166–1172 film of water to form a pavement of sand sheet. In windy Abdelrahman SM, Ahmad F (1995) Red Sea surface heat fluxes and areas, the dry sand flat surface is covered with sand dunes advective heat transport through Bab El-Mandab. J King Abdulaziz Univ Mar Sci 6:3–13 (Fig. 2e) that consist dominantly of quartz grains. Abou Ouf MA, El-Shater A (1991) The relationship between the envi- ronmental conditions of the Jeddah coast, Red Sea, and benthic foraminifera. 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Qatar Univ Sci J 23:5–22 sabkha area led to further diagenetic growth of gypsum and Al-Washmi HA, Gheith AM, Nabhan AI (2005) Geomorphological fea- anhydrite below the sediment surface and buckling of the tures, sediment distribution and transport along Ash Shuqayq-Al surface crusts into tepee polygonal ridges. The variable mor- Huraydah coastal area, southern Red Sea, Saudi Arabia. J King Abdulaziz Univ Mar Sci 16:57–80 phologies of the gypsum crystals were related to the variable Al-Shamrani MA, Dhowian AW (1997) Preloading for reduction of com- salinities of the groundwater and contribution of organic acids pressibility characteristics of sabkha soil profiles. Eng Geol 48(1–2): from the in the tidal flats and bushes in the sabkha. 19–41 Arab J Geosci (2015) 8:9973–9992 9991

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