Factors Controlling the Textural Characteristics of ... - kau

JKAU: Mar. Sci., Vol. 25, No. 1, pp: 61-78 (2014 A.D. / 1435 A.H.)

DOI: 10.4197/Mar. 25-1.4

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Factors Controlling the Textural Characteristics of the Lower Delta Plain Sediments, Wadi Al-Hamd,

NE Red Sea, Saudi Arabia

Ibrahim M. Ghandour a&b a Marine Geology Department, Faculty of Marine Science,

King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi Arabia (e-mail: [email protected])

b Geology Department, Faculty of Science, Tanta University, Tanta, 31527, Egypt

(e-mail: [email protected])

Abstract. The submerged lower delta plain of Wadi Al-Hamd in the NE Red Sea coastal plain of Saudi Arabia is of asymmetric type. It has a relatively narrow and low gradient high energy surf zone in the northern side and relatively flat low energy tidal flat in the southern side. Grain size analysis of 47 unconsolidated sediment samples from the subaqueous lower delta plain that were collected from alongshore 5 transects (TS A-E) running perpendicular to the shoreline were determined using dry sieving technique. The mean grain size of the sediments indicates the dominance of fine sand and rarely medium and coarse sands. The sediments at the northern side of the delta plain (TS A and B) are generally well sorted, fine sand-sized, and displaying near symmetrical distribution. On the other hand, the sediments in the southern side of the delta plain vary from moderately sorted to well sorted, fine to medium sands, and very fine to very coarse skewed. The lower delta plain sediments at the transect TSC are moderately sorted to well sorted, near symmetrical distribution to coarse skewed. Distribution and grain size characteristics in the study area are controlled mainly by the texture of the sediments available, transportation and depositional energy of the area. The available sediments from the temporarily active Wadi Al-Hamd display narrow range of grain size mainly of very fine to medium sands, with fine sands are the dominant. The sediments of the northern side were deposited under relatively higher energy comparing to those at the wadi mouth and the southern side.

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Keywords: Wadi Al-Hamd, grain size, depositional energy, arid coasts, CM Diagram, lower delta plain.

Introduction

Grain size of sediments is a fundamental physical property that can be used along with sedimentary structures and biofacies to interpret the dynamic conditions of transportation and deposition. It is an essential tool for classifying sedimentary facies and depositional environments (Abuodha, 2003; Anthony and Héquette, 2007; Yamashita et al., 2009 and Ganesh et al., 2013). In a certain depositional environment, grain sizes of the sediments depend on the size range of the available material, the geology of hinterlands and composition of source rock, prevailing weathering conditions, distance and mode of transportation, competence of transporting agent and depositional hydrodynamic energy as well as the geomorphology of the sedimentary basin (e.g. Folk and Ward, 1957; Passega and Byramjee, 1969; Visher, 1969; Friedman, 1979; Angusamy and Rajamanickam, 2006 and Bartholomä and Felmming, 2007). The grain size and lithofacies characteristics of coastal sediments have been described (e.g. Angusamy and Rajamanicam, 2006; Yamashita et al., 2009; Rajganapathi et al., 2013 and references therein). Most of these studies have been carried out in areas of humid regions with relatively high sedimentation rate and contain a wide range of sediment textures. The textural analysis of the Red Sea coastal plain and nearshore sediments was a target for many studies (e.g. Abou Ouf and El Shater, 1992; Gheith and Abou-Ouf, 1996 and Khawfany, 2009). Most of these studies were carried out on coastal sediments of the southern part of Red Sea or in the vicinity of Jeddah. Although, there are several wadis debouched into the NE Red Sea forming small deltas, sedimentological studies on these delta systems are absent.

In arid microtidal coasts, such as the Red Sea, beach sediments consist largely of sand-sized skeletal remains except at the mouth of wadis. These wadis along with aeolian supply are the main conduits for detrital siliciclastic sediments from the hinterland to the shorezone environments. Sedimentation and sediment transportation in the nearshore areas at the mouth of these wadis are intermittent and sporadic depending on rainy seasons and high magnitude of flash floods. The

Factors Controlling the Textural Characteristics of the Lower Delta Plain Sediments, …

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sediments in these areas are dynamic and subjected to continuous erosion, mixing, reworking and homogenization. Sediments distribution appears to be controlled mainly by wind induced currents and waves, and to a lesser extent by the negligible tidal and fluvial currents. The present study describes the general textural characteristics and the spatial variations in grain size parameters of nearshore sediments bordering Wadi Al-Hamd delta plain, NE Red Sea coast, Saudi Arabia (Fig.1). The major control(s) on grain size distribution and degree of sorting in such an arid microtidal coast are also of interest.

Area of Study

The study area is located in the vicinity of the mouth of Wadi Al-Hamd, where delta plain is formed, about 55 km south of Al-Wajh City (between Lat. 25o 57′ and 25o 58΄N and Long. 36o 42΄ E) NE coast of the Red Sea, Saudi Arabia (Fig. 1). The study area has a generally arid climate with low sporadic rainfall (0.5 - 116 mm/yr). Rainfall most often occurs between October and March; in the form of short duration showers; generally associated with thunderstorms. During rare flood seasons, water levels in the Wadi Al-Hamd reach about 3 m high. Temperature varies between 11 to 39.9oC and can rise in summer months to 47.5oC. Wadi Al-Hamd is responsible for the regional sediment load during floods that flow to the Red Sea. In the northern Red Sea, the NNW monsoon is controlled by the eastern Mediterranean weather system (Patzert, 1972) and the prevailing wind is blown to SSE over the entire year and the longshore drift is in the same direction.

The area is generally of medium energy microtidal range displaying a semi-diurnal microtidal regime. The area conforms to the microtidal coastal type with spring and neap tide range of 50 to 70 cm, respectively (Ghandour et al., 2013). The strength of flood currents, though relatively weak, but it is relatively stronger than ebb currents. Because of the shallow water depth, winds influence water movement especially during winter sea breezes. These breezes produce significant wave energy at the shoreline and the wind-driven waves (reach up to 2.5 m high) and currents are amplified and associated with longshore sediment transport (Ghandour et al., 2013).

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(A)

(B) Fig. 1. A) Location map for the area of study, B) simplified geomorphological map and the

location of transects.

Geomorphologically, the area takes the form of an asymmetric inactive eroding delta and their barriers flanked by a strandplain with a relatively steep foreshore profile to the north and a wide gently sloping intertidal flat to the south (Fig. 1B). The most common landforms are low relief beach ridges, submerged sand bars running parallel to slightly


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oblique to shoreline, coastal sand dunes, sabkhas, intertidal flats and system of inactive channels and associated levee. The source of the sediments is far (about tens of km to east) and therefore the size range of sediments that are transported to the coast is relatively narrow (medium to fine and rarely coarse sands). The surf zone to the north contains shore-parallel bars several decimeters high, separated by troughs. Waves tend to break at a small distance comparing to that in the southern tidal flat. Therefore, the wave and current energy are higher in the north than on the south. The sediment surface displays straight crested to bifurcate wave and currents ripples (Fig. 2A and B). The strandplain to the north contains features of relatively high energy wave and storm dominated settings such as the growth of beach ridge and runnel system; some of them are welded to the beach (Fig. 2C and 2D). These ridges are expected to be formed at the upper shoreface after storms and then migrate up-shore until they weld onto the backshore. On the other hands, the tidal flat to the south contains evidence of low energy conditions such as abundant heterolithic argillaceous deposits and mica concentration as well as continuous burrowing and sediment reworking (Fig. 2E and 2F). Straight crested, symmetrical wave ripples with crests running parallel to shoreline are abundant in the northern strandplain. In the southern tidal flat wave and current ripples are common with crests running slightly oblique to the shoreline.

Materials and Methods

Forty seven surface (~ upper 2 cm) sediment samples were collected using hand auger from 5 transects (A-E) in the littoral zone at Wadi Al-Hamd delta plain. The samples in each transect (8 to 12 samples) were collected at variable depths (0 to 120 cm) and variable distances from the shoreline (Fig. 3). The distance between successive samples ranges from 2 to 30 m within transect and the distances between transects are about 400-800 m. The samples were air dried, quartered and then mechanically sieved using successive sieves spaced at 1Φ interval. The main grain size descriptors (mean, sorting and skewness) were determined following the method of Folk and Ward (1957). Various bivariate plots between grain size parameters and the C-M diagram (Passega, 1957) were also prepared.

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Fig. 2. Field photographs showing the main sedimentary and geomorphological features in the area of study. A and B) Wave and current ripples at the locations of TS A and D, respectively, the direction of current ripples in B is to east ), C) Beach ridge migrating upshore and it is about to weld with the sand barrier (D), E) Features of sediment reworking and homogenization by burrowing crabs, F) Mica accumulation on low relief sand bar in the tidal flat (white arrows).


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363738

39 40

4142

4344 45

46

4725m

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25m

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3233

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cm

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Fig. 3. The profiles of the transects showing the sampling distances and the depths.

Results

The results of sieve analysis are summarized in Table 1. The sediments in the area of study display relatively no major difference in

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their textural parameters. Generally, the sediments are dominated by sand (>95 %) with negligible amounts of gravel and mud; generally less than 5 %. However, two samples (4 and 30) in transects A and D have gravel content of about 10%. The highest mud content (~ 4 %) was obtained from sediments of the transect D (sample 33). The sediments cover generally a narrow size range varying from fine to very fine sands and rarely medium to coarse sands. About 77 % of the samples are fine sands, 17 % medium sand, 4 % very fine sands and 2 % coarse sands.

The mean size (Mz) of the sediments in the area of study varied from 0.425 to 3.23 Φ with an average of 2.3 Φ. The average mean size values in the sediments of transects A-E were 2.7, 2.6, 2.04, 2.3 and 2.05 Φ (fine sands), respectively. The sediments of TSB is generally homogenous consisting of fine sands with 2 < Mz < 3 Φ. The lowest Mz value (0.43 Φ; coarse sands) was obtained from samples 37 in transect E, and the highest value (~ 3.2 Φ; very fine sands) was obtained from samples 9 and 35 in sediments of transects A and D, respectively. It is worth to mention that the Mz values (phi unit) are consistent within the same transect and increase generally with depth (i.e. grain size decreases; see Fig. 4A).

The standard deviation (σI) measures the degree of sorting of sediments. The majority of the samples (68 %) displayed well degree of sorting, some samples displayed moderately to moderately well sorting and few samples displayed very well and poorly sorting. The averages of standard deviation values in transects A-E were 0.52, 0.4, 0.5, 0.7 and 0.47 Φ, respectively. The sediments of transects A, B and E are mostly well sorted comparing to other transects (Fig. 4B).

The skewness (SkI) measures the asymmetry of the frequency of distribution. The values of skewness cover a wide range from very fine to very coarse skewed (Table 1). The average skewness values in the sediments of transects A - E were -0.6, 0.02, -0.17, 0.01 and -0.37 Φ, respectively. About 51 % of the samples in the area of study display near symmetrical skewness. The majority of samples in transects A and D displayed positive skewness values. The strongest negative skewness values were recorded from the samples 2 and 38 which were collected from the swash zone in transects A and E, respectively. On the other hand, the strongest positive skewness value (1.47 Φ) was obtained from sediments of the tidal flat in transect D (sample 31).


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Table 1. Results of grain size analysis.

Transect Sample Gravel% Sand% Mud% Mz σI SkI

TS

A

1 0.15 99.84 0.02 2.51 (FS) 0.45 (WS) -0.13 (CSK) 2 1.43 98.53 0.04 1.67 (MS) 1.16 (PS) -2.02 (VCSK) 3 0.05 99.83 0.12 2.84 (FS) 0.36 (WS) 0.04 (NSK) 4 10.86 88.86 0.28 2.68 (FS) 0.85 (MS) -3.63 (VCSK) 5 0.00 99.38 0.62 2.97 (FS) 0.36 (WS) 0.13 (FSK) 6 0.00 99.59 0.41 2.85 (FS) 0.42 (WS) 0.02 (NSK) 7 0.00 99.82 0.18 2.73 (FS) 0.36 (WS) 0.07 (NSK) 8 0.00 99.77 0.23 2.77 (FS) 0.35 (WS) 0.09 (NSK) 9 0.00 99.18 0.76 3.07 (VFS) 0.39 (WS) 0.00 (NSK)

TS

B

10 0.00 99.60 0.40 2.51 (FS) 0.36 (WS) 0.04 (NSK) 11 0.00 99.65 0.35 2.36 (FS) 0.36 (WS) -0.15 (NSK) 12 0.00 100.00 0.00 2.45 (FS) 0.37 (WS) -0.01 (NSK) 13 0.00 99.93 0.07 2.47 (FS) 0.43 (WS) -0.02 (NSK) 14 0.00 99.23 0.77 2.88 (FS) 0.43 (WS) 0.08 (NSK) 15 0.00 98.93 1.07 2.71 (FS) 0.55 (MWS) 0.00 (NSK) 16 0.00 99.78 0.22 2.60 (FS) 0.38 (WS) 0.09 (NSK) 17 0.00 99.83 0.17 2.48 (FS) 0.34 (VWS) 0.00 (NSK) 18 0.00 98.35 1.65 2.97 (FS) 0.46 (WS) 0.11 (FSK)

TS

C

19 0.00 99.68 0.32 2.52 (FS) 0.48 (WS) 0.05 (NSK) 20 0.38 99.58 0.00 1.12 (MS) 0.64 (MWS) 0.08 (NSK) 21 0.02 99.85 0.13 2.35 (FS) 0.83 (MS) -1.36 (VCSK) 22 0.00 99.90 0.10 1.79 (MS) 0.64 (MWS) 0.38 (VFSK) 23 0.52 99.42 0.07 1.78 (MS) 0.44 (WS) 0.05 (NSK) 24 0.03 99.93 0.07 2.11 (FS) 0.58 (MWS) -0.25 (CSK) 25 0.00 100.00 0.00 2.08 (FS) 0.53 (MWS) -0.28 (CSK) 26 0.00 99.93 0.07 2.27 (FS) 0.37 (WS) -0.13 (CSK) 27 0.00 99.93 0.07 2.37 (FS) 0.39 (WS) -0.08 (NSK)

TS

D

28 0.00 99.75 0.25 1.84 (MS) 0.34 (WS) 0.12 (FSK) 29 0.00 98.96 1.04 2.10 (FS) 0.61 (MWS) 0.37 (VFSK) 30 10.13 88.76 1.11 2.50 (FS) 0.48 (WS) 0.08 (NSK) 31 0.80 96.94 2.26 1.24 (MS) 1.10 (PS) 1.47 (VFSK) 32 0.00 97.24 2.76 2.04 (FS) 0.97 (MS) 1.00 (VFSK) 33 0.64 95.53 3.82 2.66 (FS) 0.81 (MS) -0.77 (VCSK) 34 0.00 97.40 2.70 2.74 (FS) 0.87 (MS) -1.61 (VCSK) 35 0.03 99.95 0.02 3.24 (VFS) 0.48 (WS) -0.55 (VCSK)

TS

E

36 0.09 99.91 0.00 2.07 (FS) 0.38 (WS) -0.16 (CSK) 37 3.39 96.61 0.00 0.43 (CS) 0.43 (WS) 0.14 (FSK) 38 0.00 100.00 0.00 1.53 (MS) 1.00 (PS) -4.19 (VCSK) 39 0.00 100.00 0.00 2.13 (FS) 0.44 (WS) -0.19 (CSK) 40 0.00 99.92 0.08 1.96 (MS) 0.40 (WS) 0.01 (NSK) 41 0.00 99.95 0.05 2.13 (FS) 0.41 (WS) -0.10 (CSK) 42 0.00 99.65 0.35 2.27 (FS) 0.41 (WS) -0.01 (NSK) 43 0.00 100.00 0.00 2.46 (FS) 0.44 (WS) 0.04 (NSK) 44 0.00 99.87 0.13 2.30 (FS) 0.40 (WS) -0.03 (NSK) 45 0.00 99.14 0.86 2.48 (FS) 0.44 (WS) 0.02 (NSK) 46 0.00 100.00 0.00 2.68 (FS) 0.53 (MWS) 0.05 (NSK) 47 0.15 99.84 0.02 2.26 (FS) 0.41 (WS) 0.04 (NSK)

FS: Fine sands, VFS: Very fine sands, MS: Medium sands, CS: Coarse sands, WS: Well sorted, VWS: Very well sorted, MS: Moderately sorted, MWS: Moderately well sorted, NSK: Near symmetrical, FSK: Fine skewed, CSK: Coarse skewed, VCSK: Very coarse skewed, VFSK: Very fine skewed

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1 2 3 428

29

30

31

32

33

34

35

TSD

0 1 2 336

37

38

39

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43

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47

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1 2 319

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2 3 410

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TSA TSB TSC TSD TSE

(B)

Fig. 4. Spatial variations in the grain size parameters (A) Mz and (B) σI.

Discussion and Conclusions

The grain size parameters and distribution in the lower delta plain of Wadi Al-Hamd express the characters of the available sediments from the source and dominant sedimentary processes. The sediments in the area of study are fine to medium and rarely coarse sands indicating an intermittent transportation through the temporarily active Wadi Al-Hamd to the nearshore area during flood seasons. In addition, beach and coastal sand dunes are possibly another source for sediments in the beach-dune transitional zone. The narrow spectrum and the relatively fine grain size


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indicate that the area of study is of moderate energy, with some areas to the north of the delta experienced relatively higher energy than those in the south. It is expected that further sediment reworking of the delta plain is driven by wind induced waves and currents and to a lesser extent the weak tidal currents. They are able to stir, transport, mix and rework bottom sediments. The riverine processes are of negligible effect because the wadi is usually inactive.

The sands in the updrift (northern) side are texturally mature comparing to the downdrift (southern) side. This is a general characteristic feature for most asymmetric wave influenced delta (e.g. Sf. Gheorghe Lobe in the Danube Delta; Giosan, 1993 and Bhattacharya and Giosan, 2003).

Bivariate Plots Bivariate plots of various grain size parameters against each other

may show definite trends or clustering of samples (Passega, 1977 and Rajganapathi et al., 2013). The mean size and standard deviation correlate positively with the energy of depositional environment (Griffths, 1967 and Lario et al., 2000). The relationship between the two parameters provides a good tool to reconstruct the transportation and depositional processes. The plot (Fig. 5A) shows that the best sorted sediments are those with mean sizes of about 2 to 3 Φ (fine sands). In all sedimentary environments, the best sorted sediments have mean size in the fine sand size range (Griffths, 1967 and Rajganapathi et al., 2013). The negative correlation between the mean size and the degree of sorting indicates that the finer grain size is the higher degree of sorting. The degree of storing depends on the size range of the material supplied to the depositional site. It is expected that the sediments were subjected to various processes that affected degree of sorting. The first of these processes is the natural sorting during transportation from the source until they reached to the depository. The sediments supplied from beach and coastal sand dunes are of high degree of sorting. The sediments are then affected by the processes of wave erosion, mixing and reworking during times of sea-breeze.

The relationship between standard deviation and skewness (Fig. 5B) indicates that the very well to well sorted sediments are clustered around the near symmetrical range and have positive and negative skewness values. The wide range of skewness values indicates variable direction of

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transporting currents, waves and tides as well variable depositional energy (Rajasekhara Reddy et al., 2008). Positive skewness values particularly in the tidal flat deposits indicate that the normal distribution is strongly influenced by finer sizes and low depositional energy compared to the sediments in the northern locations which were deposited under relatively higher energy conditions. The negative skewness particularly in the northern part of the delta resulted from winnowing by waves that are strong enough to remove finer particles.

A

TSA

TSBTSCTSDTSE

0 1 2 3 40.3

0.4

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Mean size (Phi)

Medium sand Fine sand Very Fine sandCoarse sand

TSATSBTSCTSDTSE

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Standard Deviation (phi)

B

Fig. 5. Bivariate plot between A) mean size and standard deviation, B) standard deviation

and skewness.


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Plots of mean size and degree of sorting with water depth help to interpret the variation in the depositional energy. The relationship between mean size and water depth indicates that the available sediments are generally fine sands and the grain size decreases with depth (Fig. 6A). The coarsest sediments however, concentrate near the shoreline (coarse and medium sands were not recorded at depths > 40 cm). The plot of standard deviation against water depth (Fig. 6B) displays clustering of very well to well sorted sediments particularly of northern transects A and B at water depths less than 40 cm. Depositional energy is relatively high at this water depth.

Mean size (phi)

40

0

-40

-80

-120

0 1 2 3 4

Coarse sand Medium sand Fine sand Very fine sand

TSA

TSB

TSC

TSD

TSE

A

40

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-40

-80

-120

TSA

TSB

TSC

TSD

TSE

0.3 0.4 0.5 0.6 0.7 0.8 10.9 1.1 1.2

Very well towell sorted

Moderately well tomoderately sorted

Poorlysorted

Standard deviation (phi)

B

Fig. 6. Bivariate plot between water depth and mean size (A) and standard deviation (B).

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C-M Diagram To understand the transporting processes and depositional

mechanisms, grain size properties of samples were analyzed on the C-M diagram (Passega, 1957; 1964; 1977). On the CM diagram, some fields characterizing different transportation and depositional modes can be identified (Passega and Byramjee, 1969). Almost all of the samples in the CM diagram fall in fields 5 and 4, and covering PQ segment suggesting transportation by suspension and rolling regime (Fig. 7).

TSA

TSB

TSC

TSD

TSE

10000

1000

10010010

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2000

4000

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III

4020

III

IVVVII

VI

S R

Q

PO

Graded suspension

Suspension & Rolling

Rolling & SuspensionUniform Suspension

Fig. 7. C-M diagram (Passega, 1957; 1964).

The sediments with mean sizes less than 1Φ were transported as bedload, those with sizes varying from 1 and 2 Φ are transported by saltation, and the sediments that have a mean size > 2 Φ are usually transported in suspension. The mode of transportation doesn’t depend only on the range of grain size. It depends also on flow intensity and water depth. It seems that sediments in the northern locations were transported mostly in suspension not only because the average mean size > 2 Φ, but also because the beach slope was relatively steeper and the depositional energy was relatively high. The delta plain to the south are of low slope angle, relatively low energy and probably experienced higher degree of sediment mixing and therefore, variable grain sizes were recorded. This is further indicated by the mica concentration and


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widespread burrowing activity. This suggests that the sediments were transported in the form of saltation and suspension.

Acknowledgments The author would like to thank Mr. Aaid Gadri (KAU) for his help

during field work and sample collection. The author benefited from reviews by the reviewers (Prof. M. Aref King Abdulaziz Univ. and Prof. A Zalat, Tanta University, Egypt). They have generously offered constructive criticism of the manuscript and provided several very useful items of information.

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الخصائص النسيجية لرواسب سهل الدلتا يالعوامل المؤثرة ف -الحمض شمال شرق البحر الأحمر يلمصب واد يالسفل

المملكة العربية السعودية

2و1إبراهيم محمد غندور جامعة الملك عبدالعزيز ،كلية علوم البحار ،قسم الجيولوجيا البحرية 1

المملكة العربية السعودية، 21589ة جد، ۸۰۲۰۷. ب.ص مصر - 31527 طنطا ،جامعة طنطا ،كلية العلوم ،قسم الجيولوجيا 2

تقـع علـى السـاحل يالتـو الحمـض يتمثل دلتا مصب واد .المستخلصحمــر جنــوب مدينــة الوجــه بالمملكــة العربيــة ي للبحــر الأالشــرق يالشــمال

تقــع شــمال المصــب يتتميــز المنطقــة التــ. الســعودية دلتــا غيــر متماثلــةالأمــــواج أمــــا و مــــع وجــــود نشــــاط ملحــــوظ للتيــــارات يبالانحــــدار النســــب

بســيطة الانحــدار يــنخفض فيهــا نشــاط إلــى المنطقــة الجنوبيــة فمنبســطةتــم عمــل دراســة . يكثــر فيهــا نشــاط الكائنــات الحيــةو الأمــواج و التيــارات

للخصـائص النســيجية للرواســب الســطحية القريبـة مــن الســاحل للمنطقــةالحمــض للتعــرف علــى أهــم يالمحيطــة بســهل الــدلتا عنــد مصــب واد

ــ يالعوامــل التــ ــدلتا يقــد تــؤثر ف وات غيــر المتماثلــة توزيــع الرواســب للتــم إجــراء التحليــل . المنــاطق الجافــة يعلــى الســواحل منخفضــة المــد فــ

اتجـــاه يمقـــاطع فـــ 5ن ســـطحية جمعـــت مـــ ٤٧عينـــة لعـــدد يالحجمـــالمقطـع الواحـد علـى يعينـة فـ ۱۲إلـى ۸مـن (علـى السـاحل يعمود

ا وعلى أعمـاق متفاوتـة متر ۳۰إلى ۲مسافات بين العينات تتراوح من تبعــد المقــاطع عــن بعضــها الــبعض بمســافة و ) ســم۱۲۰إلــى مــن صــفر

أظهــــرت . للســــاحل ياتجــــاه مــــواز يم فــــ ۸۰۰إلــــى ٤۰۰تتــــراوح مــــن بخاصــة الرمــال الناعمــة و المنطقــة يالنتــائج ســيادة الرواســب الرمليــة فــ

نســب ضــئيلة مــن الرمــال متوســطة التحبــب إلــى جيــدة الفــرز بالإضــافة

Ibrahim M. Ghandour

78

رديئة بقيـاس درجـة إلى الخشنة ذات درجات فرز تتراوح من متوسطةو الحيـــود وجـــد أن توزيـــع معظـــم العينـــات قريـــب مـــن التماثـــل مـــع وجـــود

أظهـــرت . الخشـــنةو الحبيبـــات الناعمـــة أإلـــى بعـــض العينـــات تحيـــد إمـــاالاتجــاه العــام لتوزيعهــا و درجــة فــرز الحبيبــات و نتــائج اخــتلاف أحجــام ال

حيــث كانــت الرواســب علــى أطــراف الــدلتا يمصــب الــواد يعلــى جــانبا تظهـر توزيعـو جيـدة الفـرز و الجهـة الشـمالية أكثـر تمـاثلا يبخاصة فـو

المتـاخم يالجزء الجنـوبو ا من التماثل على عكس رواسب المصب قريب انــــــت الرواســــــب خليطــــــا مــــــن الرواســــــب الناعمــــــة فك يلمصــــــب الــــــواد

ا رديئـة أحيانـو متوسـطة إلـى ذات درجة فرز جيـدةو المتوسطة التحبب و تعكـس الدراسـة الحاليـة مـدى . الناعم والخشن أإلى يحيد توزيعها إماو

أثنـاء فتــرات السـيول القليلــة يتـأثير حجـم الحبيبــات المنقولـة عبــر الـوادنقل و اج المرتبطة بنشاط الرياح على نحر الأمو و تأثير نشاط التيارات و .اعادة الترسيبو خلط و

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