Sedimentology and mineralogy of Kuwait Bay bottom sediments, Kuwait—Arabian Gulf

Marine Geology, 46 (1982) 71--99

71

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

SEDIMENTOLOGY AND MINERALOGY OF KUWAIT BAY BOTTOM SEDIMENTS, KUWAIT--ARABIAN GULF

F.I. KHALAF, A. AL-GHADBAN, S. AL-SALEH and L. AL-OMRAN

Environmental and Earth Sciences Division, Environmental Sciences Department, Kuwait Institute for Scientific Research, Safat (State of Kuwait) (Received November 5, 1980; revised and accepted May 1, 1981)

ABSTRACT Khalaf, F.I., AL-Ghadban, A., AL-Saleh, S. and AL-Omran, L., 1982. Sedimentology and mineralogy of Kuwait Bay bottom sediments, Kuwait--Arabian Gulf. Mar. Geol., 46: 71--99. Textural and mineralogical properties of the Recent bottom sediments of Kuwait Bay, northern Arabian Gulf, were investigated. Six sediment types were identified, namely silty clay, clayey silt, sandy mud, silt, muddy sand and sand. It was found that most of the northern shelf and the central channel of the Bay are covered with muddy sediments, while sand and sandy deposits are restricted only to the southern offshore area of the bay. Based on the textural characteristics of its sediments, Kuwait Bay environment was divided into two energy zones: (a) low-energy zone, including most of the bay area; and (b) a moderate-energy zone, restricted to the southern offshore area of the bay. The detailed mineralogical investigation of the various size classes of Kuwait Bay sediments revealed that they are of polygenetic origin. Two main sources of the bay sediments were recognized, namely: (a) autochtonous materials which are derived from the degradation of recent shells of various fauna, erosion of the submerged ancient sediments and sub-Recent coastal sediments; and (b) allochtonous materials, which are derived from the onshore desert sediments by the action of the prevailing NW winds. It was also concluded that fallout from dust storms, contributes considerably to the sediment budget of the bay. INTRODUCTION

Kuwait Bay is a relatively large tongue of shallow water in the northwestern corner of the Arabian Gulf coast. It lies between longitudes 47043 ' and 48010 ' east and latitudes 29o20 ' and 29035 ' north and covers an area of approx. 720 km:. Its m a x i m u m length is about 45 km and the width of its entrance is about 22 km (Fig.l). Although the Arabian Gulf b o t t o m sediments have been a subject of extensive studies (Purser, 1973), few published works are available on the Holocene sedimentology of the northern part of the Arabian Gulf in general and Kuwait Bay in particular. Larsen and Evans (1978) have reviewed the Holocene geological history of the Tigris--Euphrates--Karun Delta. Mohamed (1979) attempted a study on the sediment distribution in Kuwait Bay. He 0025--3227/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company

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prepared a preliminary map of the bottom sediments in Kuwait Bay based on 21 samples collected from about 19 sites only. A1-Zamel and Khalaf {1978) studied the sedimentology of the tidal flat and beach sediments, in the Ras AI-Subbiyah area, at the northeastern corner of Kuwait Bay. Hayes (1977) studied the bottom sediment of Sulalbikhat Bay, located along the southern coast of Kuwait Bay.

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In addition, few mineralogical studies have been carried out. Khalaf and Ala (1980) studied the mineralogy of the Recent intertidal m u d d y sediments of Kuwait Bay. Hilmy et al., (1971) investigated the mineralogy and fabrics of the opaque mineral grains in Kuwait beach sediments and discussed their possible sources. Khalaf (1969) studied the Recent beach sediments along the whole Coast of Kuwait, including Kuwait Bay. The present study was carried o u t as an integral part of an extensive research programme aiming at the assessment of the marine environment of the State of Kuwait. This paper presents the results of detailed textural and mineralogical investigations of the Holocene sediments of Kuwait Bay. The sources and transportation pattern of these sediments are also discussed. SAMPLING AND ANALYTICAL PROCEDURES

A b o u t a hundred and fifteen samples were collected from the b o t t o m sediments of the Kuwait Bay area (Fig.2). Samples were taken from the top 10 cm of sediments using a Van Veen grab sampler. Grain-size analyses of all collected samples were made using standard sieving and sedimentation techniques (Folk, 1974). Cumulative curves and histograms were prepared. The percentages of the main size fraction (sand-silt-clay) and the statistical size parameters for all analysed samples were calculated using the formula of Folk and Ward (1957). 28 samples were chosen for the study of the composition of the sand fractions. The various mineral grains in the very coarse, coarse, medium and fine sand fractions have been identified using a binocular microscope. The relative frequency percentage of each mineral grain was determined by counting a total of a b o u t 200 grains in each size fraction. The biogenic fragments were also studied in thin section. 17 samples were selected for the study of heavy minerals. The latter were separated from the very fine sand and coarse silt fractions using the standard b r o m o f o r m method. Light mineral fractions were stained by alizarine red to facilitate identification of carbonate mineral grains. For the study of "whole sediment" mineralogy a portion of the dried sample was finely crushed and analysed by X-ray powder diffraction. Semiquantitative estimations of the minerals present in the "whole sediment" samples were made using the method described by Bush (1973). The clay size fraction 4--2 ~m was separated by means of the sedimentation method. A suction-onto-ceramic disc method (Shaw, 1971) was used for the preparation of oriented clay samples for X-ray diffraction analysis. The analysis were carried out on a powder diffractometer using nickel-filtered Cu-K radiation. The identification of clay minerals involved the standard pretreatments of glyceration and heating at 550°C. The semi-quantitative estimates of the relative amounts of clay minerals were calculated by the method and outlined by Schultz (1964). This essentially involves using the area under the diffraction peaks as a measure of the relative concentration of the corresponding clay mineral in the sample.

78 GENERAL PHYSIOGRAPHY AND OCEANOGRAPHY

The Arabian Gulf is divided into several morphological provinces, namely: Mesopotamian shal.low shelf; Arabian Shallow shelf; central basin; western basin; central swell; eastern swell; and Hormuz region (Purser, 1973). The Mesopotamian shallow shelf occupies most of the northern part of the Arabian Gulf. Kuwait Bay lies within this shallow shelf area. Kuwait Bay can be divided physiographically into three main provinces, namely: the northern flat, the southern flat and the central channel. The northern flat occupies most of the northern half of the bay and is characterized by a very gentle slope (maximum depth is about 5 m). The southern flat is generally narrow and closer to the central channel (Fig.3). The bay is bounded at the north by Jal Az-Zor escarpment, which is formed mainly of calcareous grits. The northern coastal plain is relatively flat and grades northward from Sabkha flat to the lower terraces o f Jal Az-Zor. The southern coast of the bay is bounded mainly by flat-topped coastal plain deposits. Kuwait Bay is characterized by the occurrence of coves and promontories. Three main coves can be recognized along the southern coast of the bay, namely: Kathma Cove, Sulaibikhat Cove and Binade A1-Gar Cove (Fig.3). Kathma cove extends from the western end of the bay to Ras Ushairij headland. It has a relatively steep beach profile and is bounded by oolitic limestone ridges (Quaternary?) which are covered by coastal dunes. The tidal flat of this cove is mostly covered by an oyster bank which is partially covered by sand sheets. Sulaibikhat cove (Sulaibikhat Bay) lies to the east of Kathma cove and is bounded by Ras Ushairij at the west and Ras Ajuza at the east and is characterized b y an extensive tidal flat (Hayes, 1977). Before the recent development along Kuwait coastal area, Sulaibikhat Bay was mainly bounded by low berms of quartizitic calcarenites (Pleistocene). At present most of its coast is built of heterogenous fill. The third cove (Binade AI-Gar) is located near the entrance of the bay and is bounded to the west by Ras Ajuza and to the east by Ras A1-Ard. This cove was bordered by low beach terraces (Pleistocene) composed mainly of quartizitic calcarenites. After the recent development of Kuwait coastal area, the shore of this cove has been filled by heterogenous fill material. Ras A1-Subbiyah headland, forms the northeastern corner of Kuwait Bay. It is built of Recent oolitic and quartzitic calcarenites. Khor A1-Sabbiyah, a large tidal creek, lies to the north of the Bay. Its m o u t h is very close to the entrance of Kuwait Bay. Oyster banks (reefal flats) occur extensively along the southern coast of Kuwait Bay (A1-Akaz and Ushairij reefal flat). Oyster mounds are also present near Ras A1-Subbiyah. Kuwait Bay can almost be considered as a shallow marine environment (littoral to epineritic), its maximum water depth is a b o u t 28 m at the entrance of the bay near Ras A1-Ard. It is characterized by asymmetric bathymetrical

79 profile (N--S), with its depth axis closer to the southern coast. Most of the Bay area ranges in depth between 0 and 10 m. The water temperature of Kuwait Bay varies only little horizontally, but it shows significant seasonal variation. In winter the surface temperature ranges from about 13.3°C in the southern and western portions of the Bay to nearly 15.5°C just o f f Jazirat Failakka. The difference between the surface and b o t t o m is of the same order of magnitude, a maximum vertical temperature gradient of 1.65°C was recorded at the entrance of the Bay at a depth of a b o u t 9 m (Dubach and Wehe, 1967). In summer, surface temperature increases to 32.3°C and b o t t o m temperature to about 29.4°C. This results in a gradient thermocline which is markedly developed eastwards, in deeper waters. The salinity of Kuwait Bay shows a W--E transverse gradient. Jacob (1980) recorded a ~ange of salinity of between 41%o 42.4%0 for the surface water in winter. No significant vertical variation in salinity was recorded in the bay. Dubach and Wehe (1967) reported a gradient of only 0.4% o. through a 4.5 m depth. The tides of Kuwait are borderline between mesotidal (2--4 m) and macrotidal (> 4 m), the tidal range in Kuwait Bay is a b o u t 3.53 m for neap tides and 4.3 m for spring tides (Hayes, 1977). Currents throughout Kuwait Bay are mainly tidal. Tidal current measurements by Dubach and Wehe (1967) show that the maximum current speed was recorded near Ras A1-Ard, at the entrance of the bay, where ebb and flood currents reached 1.54 and 2.00 knots, respectively. Wind blows from two main directions, namely, the northwest and, to a lesser extent, the southwest. The northwesterly winds frequently raise dust and sand, especially when they exceed 10 m.p.h. Dust and sand storms, known locally as "Toze", are one of the most c o m m o n weather phenomena in Kuwait. (Khalaf and Ala, 1980). The shallow nature of the bay prohibits the generation of large waves. Waves larger than 50 cm are n o t c o m m o n and occur mostly during winter storms. The dominance of northwesterly winds is responsible for the relative abundance of waves along the southern coast of the Bay. There is no flow of local streams into Kuwait Bay; the nearest major fluvial source to the bay is the Shatt A1-Arab river. RESULTS Textural classes

The various textural classes of Kuwait Bay b o t t o m sediments have been determined using Folk's classification (1974), which is based on sand-siltclay percentages, with slight modification. Folk's mud textural class is divided into t w o textural classes, namely; silty clay and clayey silt. According to this classification six textural classes were identified, namely; sand, m u d d y sand, silt, sandy mud, silty clay and clayey silt. The average grain size compo-

80

TABLE I Average values o f size f r a c t i o n p e r c e n t a g e s a n d statistical size p a r a m e t e r s o f the various t y p e s o f b o t t o m s e d i m e n t s o f K u w a i t Bay Sediment Type

Sand %

Silt %

Clay %

Size p a r a m e t e r s Mz(P

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KG

Clayey silt

Max. Min. Av.

10.0 0.5 2.5

61.5 50.0 57.0

45.5 30.0 40.5

8.3 7.0 7.3

3.46 1.60 1.95

~ 0.44 --0.29 ~ 0.05

1.30 0.80 1.00

Silty clay

Max. Min. Av.

8.0 0.5 3.0

67.5 38.5 42.5

57.0 49.0 54.5

8.7 7.9 8.3

2.65 1.70 2.07

+ 0.20 -O.19 ÷0.01

1.34 0.85 1.05

Sandy mud

Max. Min. Av.

34.5 11.0 19.5

56.5 39.0 44.1

47.5 30.5 36.4

9.6 5.8 6.9

4.70 2.40 3.00

~ 0.40 --0.30 --0.07

1.21 0.80 0.95

Silt

Max. Min. Av.

70.5 69.0 71.4

28.5 23.4 26.18

7.0 5.9 6.6

2.15 1.80 2.03

+0.91 ~ 0.21 +0.39

1.00 0.79 0.88

M u d d y sand

Max. Min. Av.

80.5 46.5 64.1

29.5 13.5 20.8

24.5 6.0 15.0

4.5 1.4 3.1

4.60 2.80 3.80

~ 0.60 +~0.02 +-0.36

1.60 0.70 0.98

Sand

Max. Min. Av.

99.0 92.0 95.5

7.0 0.5 3.2

3.0 0.5 1.3

2.1 0.8 1.5

2.30 0.30 1.20

÷ 0.20 --0.07 + 0.04

1.90 0.80 1.23

6.0 0.1 2.42

sition and statistical size parameters of these textural classes are given in Table I. Mud sediments (clayey silt and silty clay} are chiefly composed of silt and clay-size fractions with a b o u t 3% of sand. Cumulative curves of these two sediment classes are characterized by the abundance of one size population that constitutes a small portion of the coarse tail of these curves. Mean size of the silty clay sediments ranges from 7.9 to 8.7¢ with an average of 8.3~, while in the clayey silt sediments it ranges between 7.0 and 8.3~ with an average of 7.3~. Mud sediments are generally poorly to very poorly sorted, symmetrically skewed and mesokurtic. Sandy mud sediments are mainly composed of silt and clay, which form about 44 and 36.5% of the average grain-size distribution of the sediment, respectively. Sand fraction is relatively more frequent and constitutes about 19.5% of the average grain-size distribution. Cumulative curves of these sediments display two saltation subpopulations and one suspension population. The saltation subpopulations include sand and coarse silt fractions. Mean size of the sandy mud sediments ranges between 5.8@ and 9.6¢. They are very poorly sorted, symmetrically skewed and platykurtic.

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85 The grain size distribution of the silt sediments reveals that they have average sand, silt and clay percentages of 2.4%, 71.4% and 26.2%, respectively. Their cumulative curves are characterized by the occurrence of one main size population, i.e., suspension population. They range in mean size between 4.5¢ and 6.7¢ with an average of 6.1~. They are poorly to very poorly sorted, positively skewed and platy- to mesokurtic. Sand deposits vary in mean size from 0.8¢ to 2.1¢, with an average of 1.5~ (medium sand). They are generally more sorted, range in sorting between 0.3¢ (very well sorted) and 2.3~ (poorly sorted) with an average of 1.2¢ (poorly sorted). Ill-sorting of the sand deposits is mostly due to abundance of shell and shell fragments of various sand sizes. They are mostly symmetrically skewed and platykurtic. Cumulative curves of these deposits display two size populations, namely saltated and suspended. The saltated population constitutes more than 90% of the sediments and its finer limit is about 3.0¢ (fine sand). The suspension population is very low (<10%) and includes all grains finer than 3.0¢. The muddy sand deposits are composed of sand (64% in average) with subordinate amounts of silt and clay. The relative abundance of mud in these sandy deposits has greatly influenced their size parameters. Their mean size ranges between 1.4¢ and 4.5¢ with an average of 3.1¢ (very fine sand). They are extremely poorly sorted (average sorting = 3.8¢) positively skewed and platy to leptokurtic. The distribution of the various textural classes in Kuwait Bay is presented in Fig.4. It was found that most of the bay is covered by mud and muddy sediments. Distribution of sediment types was found to be related to the bottom physiography and coastal geology of the area. The northern flat area of the bay is generally covered with mud (silt and clayey silt). Patches of sandy mud are also present near Ras As-Subbiyah. The clay content of these sediments increases towards the central channel of the Bay (areas deeper than 8 m) until it becomes silty clay. The southern coastal flat, on the other hand, is characterized by abundance of sandy sediments (sand, muddy sand and sandy mud). Sand commonly covers nearshore areas and also areas with rocky bottom. These sandy deposits grade to muddy sand and sandy mud towards the central channel, i.e., the mud content (silt and clay) of the sandy deposits increases with the increase of depth. Rocky bottoms, possibly submerged beach rocks and reefal banks were found in front of Ras A1-Ard, Doha and Kathma depression. Clean sand, composed mainly of shell hash, is frequently distributed over and around these rocky areas.

Clayey silt is the most abundant sediment in Kuwait Bay. It covers more than half the area of the bay. Silty clay mud is relatively less abundant than the clayey silt mud and covers only parts in the central channel of the bay. Silt sediments are mainly distributed on the very flat slopes of the bay, especially along the northern coast and in Sulaibikhat Bay. It is believed that these sediments were deposited as mud and the clay fraction was then washed out by tidal currents and agitation of the bottom by low-energy shallow waves.

86 Sand sediments are generally restricted to the southern area of the bay. Four main sandy areas have been recognized, namely, Kathma-A1-Doha cove sand, Ras-Ajuzah sand, Ras A1-Ard sand and Kathma depression sand. It was found that sand deposits are c o m m o n l y associated with the rocky b o t t o m and steep slope coasts. Muddy sand and sandy mud deposits mostly occur in the transitional zone between the southern sandy facies and the northern m u d d y facies. In Benaid A1-Gar cove, sediment facies have a circular distribution pattern where the centre of the cove is covered by silty clay mud and grades towards the shore to sandy mud, m u d d y sand and then sand. The same gradation was noticed along the offshore area of Ras Ajuza, where coastal sand grades to m u d d y sand and then sandy mud. The gradation of Kuwait Bay sediments grain size is shown by the isomean size contours (Fig.5). MINERALOGICAL COMPOSITION

Whole-sediment mineralogy The non-clay, whole-sediment mineralogy of most of the samples from Kuwait Bay is characterized by the presence of carbonates, quartz and feldspars, Table II. Generally, carbonate minerals constitute more than 70% of the non-clay mineral fraction. They are represented by low -Mg calcite, highMg calcite, aragonite and dolomite. Low-Mg calcite is the most frequent carbonate mineral, it forms about 50% of the non-clay mineral fraction and about 70% of the carbonate fraction. High-Mg calcite and aragonite, on the other hand, are present in some samples in subordinate amounts. They form 7% and 3% of the non-clay mineral fraction, respectively. Dolomite occurs in considerable amounts in all studied samples. It c o n stitutes a b o u t 12% of the whole sediments of Kuwait Bay. Quartz and feldspar are also present in considerable amounts, they have an average frequency of 17% and 12%, respectively. Therefore, it can be noted that Kuwait Bay sediments are composed mainly of low-Mg calcite, quartz, feldspars and dolomite. Most of these mineral constituents are of detrital origin.

Sand fraction The sand fraction of Kuwait Bay sediments consists mainly of biogenic grains (shells and shell fragments), quartz and rock fragments. Feldspars, oolites and pellets are present in subordinate amounts. The average relative frequency percentages o f the different mineral grains forming the various sand fractions of the examined samples are shown in Fig.6. Shells and shell fragments are the most dominant components, they constitute more than 60% of the sand fraction. They are generally represented by whole shells and shell fragments, of pelecypods, gastropods, echinoids, bryozoans, foraminifera and ostracodes. The relative frequency percentages of these biogenic components are controlled to great extent by grain size and

87

TABLE II "Whole sediment" mineralogy of the bottom sediments of Kuwait Bay (based on 100% non-clay minerals) Sample No.

Carbonate

Quartz feldspars

low-Mg calcite %

high-Mg calcite %

aragonite

dolomite

total

%

%

%

%

%

A A A A A A A A A A A A A A A A A A

53 47 58 49 45 54 46 45 55 49 46 43 61 45 43 48 46 55

-9 -12 9 13 9 12 -14 -14 -14 11 -9 10

----10 -8 11 7 -13 --------

14 10 12 14 12 9 11 10 11 12 13 11 12 12 12 15 10 10

67 66 70 75 76 76 74 78 73 75 72 68 73 71 66 63 65 75

17 17 16 14 13 15 15 12 15 14 16 15 18 16 22 22 18 15

16 17 14 11 11 9 11 10 12 11 12 17 9 13 12 15 17 10

Average

49

7

3

12

71

17

12

3 12 13 14 16 21 23 24 27 36 32 33 42 44 45 50 51 54

environment of deposition. They are generally more abundant in the coarser sand size fractions and decrease in the finer fractions. Biogenic grains in the very coarse and coarse sand fractions are mostly represented by fragments of pelecypods and gastropods shells and whole shells of microgastropods and micropelecypods. Echinoid plates and spines are also frequent in this size fraction. Medium and fine sand fractions are characterized by the relative abundance of ostracodes and echinoids spines. Foraminiferal tests are mostly concentrated in the fine and very fine sand fractions. Thin section study of biogenic sand grains showed that most of these grains are severely micritized. This indicates a high level of algal activity, especially the blue green algae. Micritization could be responsible for the breakdown of coarse sand size biogenic grains to finer sand and silt grains (Bathurst, 1966). Algal micritization in coastal areas of the Qatar Peninsula, Arabian Gulf, has altered skeletal grains to aragonitic micrite on a large scale (Taylor and Illing, 1969). I t was also noticed that some of the shells have been subjected to early stages of cementation. This is manifested b y the occurrence of fibrous aragonite cement on the interval surfaces of the shell chambers. The fabric indicates

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that some of the shells and shell fragments were derived from the submerged beach rocks which are exposed in the nearshore area of the southern coast of the bay. Quartz is mostly represented by rounded monocrystalline grains which are c o m m o n l y coated with thin, discontinuous shells of carbonates. Quartz is more frequent in the medium and fine sand fractions and less abundant in coarser fractions. Feldspar grains are present in subordinate amounts. Spatial distribution of the relative frequency percentages of both quartz and feldspar in the sand fraction of Kuwait Bay sediments indicates that they are more abundant in the northern area of the bay. Oolites and pellets are c o m m o n l y more abundant in the medium sand fraction. They are relatively frequent in the sediments o f the southern area of the bay, especially near Ras Ushairij where Pleistocene Oolitic limestone ridges are exposed along the beach.

Mineralogy o f very fine sand and coarse silt fractions 1. Light minerals The light-mineral assemblages of both very fine sand and coarse silt fractions of the investigated samples are chiefly composed of carbonate grains (mainly detrital calcite and allochems) quartz and feldspars. Gypsum, chert and mica are also present in appreciable amounts {Table III). Carbonate grains constitute an average of 50% of the light fraction which generally forms an average of a b o u t 84% of the studied samples of both the very fine sand and coarse silt fractions. They are mainly represented by detrital calcite grains and allochems. The latter are composed of fragments of various marine fauna shells (pelecypod, gastropod, echinoid and bryozoa) and whole shells o f ostracods, foraminifera and other microfauna. Detrital calcite is present as r o u n d e d to subrounded monocrystalline grains and as well-rounded polycrystaUine grains (micritic lumps). WeU-rhombohedral cal-

89

T A B L E III Relative f r e q u e n c y p e r c e n t a g e s o f t h e light m i n e r a l grains in t h e coarse silt a n d very fine sand f r a c t i o n s in t h e m a r i n e s e d i m e n t s o f K u w a i t Bay Sample No.

Carbonate

Quartz

Feldspars

Gypsum

Chert

c.s.

v.f.s,

c.s.

5A 7A 12A 17A 19A 20A 21A 22A 26A 27A 29A 30A 32A 37A 43A 45A 47A 49A 57A 61A 62A

59.8 59.4 43.0 34.1 47.6 51.1 37.0 52.4 60.7 48.6 54.7 54.4 42.7 53.3 43.5 61.2 00.0 60.6 00.0 57.0 46.9

50.6 53.3 42.3 29.8 00.0 56.2 57.9 72.8 41.1 50.3 00.0 39.4 32.8 53.5 36.9 53.0 40.8 52.4 37.2 52.8 49.9

Average

50.9

47.5

Mica

v.f.s,

c.s.

v.f.s,

c.s.

v.f.s,

c.s.

v.f.s,

c.s.

v.f.s.

20.5 18.4 26.4 37.2 25.0 22.2 34.4 19.6 22.5 21.6 22.6 21.9 22.2 25.3 33.5 21.3 00.0 16.2 00.0 20.1 25.0

21.0 25.2 23.2 29.8 00.0 22.9 14.6 12.6 15.8 20.9 00.0 23.6 22.4 23.8 39.0 24.4 22.9 25.1 27.3 29.4 16.8

07.1 09.0 11.4 09.4 11.5 08.9 09.6 09.5 08.4 10.1 10.7 10.2 09.4 11.5 10.6 07.9 00.0 08.6 00.0 12.1 11.2

11.1 07.1 08.3 13.6 00.0 08.5 07.3 07.2 14.6 07.2 00.0 07.1 16.8 10.4 12.3 12.9 14.6 11.2 12.6 08.0 09.0

08.5 08.0 03.1 02.4 06.0 12.8 05.6 10.6 05.6 04.8 04.3 05.1 03.8 07.1 06.8 05.1 00.0 07.6 00.0 05.6 03.0

06.2 05.2 06.0 08.9 00.0 06.5 04.3 02.6 08.9 04.4 00.0 07.9 07.2 06.4 08.6 04.1 04.5 03.7 04.3 04.9 06.0

02.7 04.7 06.2 10.9 07.1 04.4 04.8 04.2 02.8 05.8 06.8 07.8 11.1 01.6 04.3 03.4 00.0 05.6 00.0 03.7 06.0

09.3 08.6 11.3 06.8 00.0 05.2 09.1 04.1 09.5 07.2 00.0 00.1 12.8 04.5 02.7 05.5 13.4 07.0 10.0 04.3 12.1

01.3 00.5 09.8 06.0 00.4 00.6 08.5 03.7 00.0 09.1 00.9 00.0 10.7 01.0 01.2 01.1 00.0 01.5 00.0 01.4 07.8

01.9 00.5 08.9 11.2 00.0 00.7 06.7 01.0 10.1 09.9 00.0 11.0 08.0 01.5 00.5 00.0 03.8 00.5 08.7 00.6 00.6

24.0

23.2

09.8

10.5

06.0

05.8

05.4

08.1

03.7

04.8

N o t e : c.s. = coarse silt, v.f.s. = very fine sand

cite grains are also recorded. It was noticed that some of the detrital calcite grains have no biogenic structure. The microfaunal shells and echinoid spines form a considerable portion of the very fine sand fraction. Foraminiferal shells are usually filled with black organic matter and pyrite. Some of the pyrite-filled foraminiferal shells are present within the heavy fraction of the very fine sand and coarse silt. Quartz constitutes about 23% of the very fine sand and coarse silt fractions. It is c o m m o n l y present as subrounded to angular grains, most of which are monocrystalline and display slight undulose extension. Few quartz grains are polycrystalline with microlite inclusions as well as vacuoles. Zircon, rutile needles and tourmaline are the most frequent inclusions. Feldspars are represented mainly by potash feldspars (orthoclase and microcline) and plagioclase grains. They are generally subhedral and rounded. Most of the feldspar grains are partially altered to micaceous and calcareous material. They range in relative frequency between 7.1 to 16.8% in the very fine sand fraction with an average of 10.5%, and between 7.1 and 12.1% in the coarse silt f~action with an average of 9.8%.

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92 Gypsum is present as euhedral monoclinic crystals, commonly containing carbonate inclusions and biogenic fragments. They range in relative frequency between 2.6 and 8.9% in the very fine sand fraction and between 2.4 and 12.8% in the coarse silt fraction. In general, gypsum is relatively more frequent in the coarse silt fraction. Chert is commonly present as angular brownish grains rich in opaque inclusions. Composite grains of calcite and chert were recorded. They vary in relative frequency from 2.7 to 13.4% and from 1.6 to 11.1% in the very fine sand and coarse silt, respectively. Mica flakes are present in both light and heavy fractions. In the light fractions they are represented mainly by muscovite and leached chlorite. They form about 4% of the average light-mineral composition of both very fine sand and coarse silt fractions.

2. Heavy mineral In Kuwait Bay sediments, heavy-mineral fractions form about 17 and 14% by weight of the very fine sand and coarse silt fractions, respectively. They are represented mainly by opaques, dolomite, and several transparent heavy mineral grains (Tables IVA and B). Dolomite is the most abundant heavy mineral in all studied samples. It is present as small individual rhombs and as well-rounded to subrounded grains. Dolomite rhombs are relatively more frequent in the coarse silt fraction. A detailed microscopic investigation of these rhombs shows that they are very similar to the proto-dolomite described in Recent sabkha deposits (Kinsman, 1964; Shinn, et al., 1965). These rhombs generally have black cores which are most probably composed o f organic matter. Dolomite forms 39.4 and 36.4% of the average heavy-mineral composition of both coarse silt and very fine sand fractions, respectively. The heavy-mineral fraction of the studied sediments is characterized by relative abundance of opaque mineral grains. They constitute about 13 and 20% (in average) of the heavy-mineral fraction of the very fine sand and coarse silt fractions, respectively. The transparent heavy-mineral suite of the studied sediments are represented mainly by amphiboles, pyroxenes, epidotes and micas. Garnet, zircon, tourmaline, topaz, apatite, monazite, sillimanite, barite, rutile, fluorite, celestite, and stuarolite are also present b u t in subordinate quantities. The transparent heavy minerals constitute a b o u t 50.2 and 40.9% of the heavy mineral fractions of the very fine sand and coarse silt fractions, respectively. Amphibole grains are represented mainly by green hornblende, actinolite and glaucophane. In average, they form 22.7 and 36.0% of the transparent heavy minerals of the very fine sand and coarse silt fractions, respectively. Green hornblende is the most frequent amphibole mineral, it constitutes more than 70% of the total amphiboles. Pyroxene grains usually occur as euhedral to subhedral prismatic crystals, few are subrounded. They are represented mainly b y augite, diopside, hypersthene and enstatite. Augite is the most frequent pyroxene mineral while

93 diopside is next in relative abundance. Enstatite grains with green hornblende inclusions were recorded. Unlike amphiboles, pyroxene grains are concentrated in the very fine sand fraction. They have an average frequency of 30.2% in the very fine sand and o f 28.4% in the coarse silt. Pistachite and zoisite are the most c o m m o n epidote minerals. Pistachite is the most abundant and usually occurs as well-rounded grains with greenish turbidity, although few grains are fresh. Zoisite grains, on the other hand, are found as angular to subangular grains, where they are relatively abundant in the coarse silt fraction. Mica grains are represented by muscovite, chlorite and biotite. Chlorite is relatively more abundant, while biotite and muscovite are present in subordinate quantities. Micas are present in considerable amounts in the very fine sand fraction where they reach on average up to 25.8% of the transparent heavy minerals. Garnet is present as colorless, reddish, brownish and pinkish grains in most of the studied samples, with colorless garnet as the most c o m m o n variety. Garnet varies in relative frequency from 1.1 to 17.8% with an average of 6.8% and from 1.4 to 19.4% with an average of 6.5% in the very fine sand and coarse silt fractions, respectively. Zircon grainsrange in abundance between 0.9 and 8.5% with an average of 2.2% in the coarse silt fraction and between 1.5 and 10.7% with an average of 3.5% in the very fine sand fractions. Tourmaline c o m m o n l y occurs as elongated rounded grains and as euhedral prismatic crystals. BrowniSh and greenish tourmaline are the most c o m m o n varieties. They are concentrated in the coarse silt size fraction.

3. Clay minerals Illite, illite-montmorillonite, montomorillonite, palygorskite, kaolinite and chlorite are the main clay minerals identified in the Recent bottoni sediment of Kuwait Bay. The relative frequency percentages of the various clay minerals in Kuwait Bay sediments are summarized in Table V. Clay minerals of Kuwait Bay are characterized by the abundance o f ~llite and palygorskite. They form about 33 and 37% of the average composition of the clay mineral suite, respectively. Illite-montmorillonite mixed-layer clay and montmorillonite are present in subordinate amounts, 13% in average. It was also found that the clay mineral-suite is deficient in kaolinite and chlorite. The distribution of clay minerals in Kuwait Bay sediments agrees with the general distribution of clay minerals in the Arabian Gulf (Pilkey and Noble, 1966). One of the most significant characteristics of the clay minerals of Kuwait Bay sediments is the abundance of palygorskite. DISCUSSION AND CONCLUSIONS

Recent studies on the Quaternary geology of the Arabian Gulf reveal that Kuwait Bay is an integrated part of the submerged ancient Tigris-Euphrates delta system (Lees and Falcon, 1952; Fairbridge, 1961; Kassler,

94 TABLE V Clay m i n e r a l o g y of t h e < 2.0 p m f r a c t i o n o f t h e b o t t o m s e d i m e n t s in K u w a i t Bay Sample No.

Illite (%)

Illite-montmontomorillonite

Palygorskite (%)

Chlorite (%)

Kaolinite (%)

(%) 3A 20A 21A 23A 24A 26A 30A 32A 33A 35A 38A 40A 44A 45A 48A 50A 51A

32 37 26 36 27 37 31 43 46 33 38 32 36 31 26 15 40

38 14 2,1 5 15 7 19 2 5 11 5 14 6 5 21 25 3

22 36 32 45 41 41 33 42 26 33 38 36 39 45 41 35 42

2 9 13 4 15 10 11 8 9 7 10 15 8 10 2 10 10

6 4 5 10 2 5 6 5 14 16 9 3 11 9 10 15 5

Average

33

12

37

9

8

1973; Larsen and Evans, 1978). The extensive submerged fiat that occupies the northern part of the Bay, at about 5 m depth, could be correlated with the submerged Mesopotamia estuarine flat in the northern area of the Arabian Gulf (Kassler, 1973). The geological and geomorphological settings of Kuwait Bay indicate that it has developed as a result of tectonic and geomorphic processes that took place during the Late Pliocene--Pleistocene. The framework of the Kuwait Bay basin most probably developed during the initiation of the Jal Az-Zor disturbance (Owen and Nasr, 1958; Fuchs et al., 1968; Khalafallah, 1977). According to Fairbridge (1961) and Larsen and Evans (1978), Kuwait Bay was completely dry about 10,000 yrs. B.P. At that time, the northern flat of the bay was a part of the estuarine plain of the Tigris--Euphrates river system and Khor A1-Subbiyah was one of the distributaries. The present-day bathymetry of the bay reflects the possibility of the occurrence of an old channel system which is now occupied by the central channel of the bay and Sulaibikhat Bay channel. Kuwait Bay is mostly covered with muddy sediments. The northern flat and the central channel of the Bay, in addition to the extensive tidal flats of Sulaibikhat Bay, are mainly covered by mud (silty clay and clayey silt). Sandy sediments are generally restricted to the relatively narrow southern offshore flat and to the most western and most eastern parts of the central channel. The distribution of the various types of sediments and the variation

95 of their textural and granulometrical characteristics are controlled to a great extent by the h y d r o d y n a m i c status and the kinetic energy level of the water body, nature of coastal sediments and the ecological conditions of the bay. Based on the lithofacies map and the textural parameters of its b o t t o m sediments, two energy zones can be recognized i n K u w a i t Bay: a low-energy level environment, including most of the bay; and a moderate-energy level environment, restricted to the southern offshore area and the channel. Variation in the energy level in the Kuwait Bay environment is mainly due to difference in the speed of ebb and flood tidal currents. The southern offshore area is close to the main channel of the bay in which the tidal currents attain their maximum speed. The nature of the Recent--Sub-Recent coastal sediments also affects the textural characteristics of the Kuwait Bay b o t t o m sediments. The occurrence of calcarenitic beach sediments (Sub-Recent raised beaches) and extensive reefal oyster banks along the southern coast of Kuwait Bay are responsible for the relative abundance of sandy sediments in the offshore area of that region. The action of waves generated by the prevailing NW winds also play an important role in the development of these sediments. The biogenic c o m p o n e n t of the sand fractions in the studied sediments, shells and shell fragments, are mostly derived from both the living fauna within the bay area and the ancient shells from the coastal sub-Recent raised beach sediments, which are exposed along the southern coast of the bay. These shells, Recent and sub-Recent, are subjected to mechanical breakdown in the intertidal area of the bay and then transported by the action of ebb tidal currents to the offshore area of the bay. Bilogical breakdown of shells and shell fragments through the micritization and borrowing processes could be responsible for the development o f silt and clay-size calcareous particles. The coarser fragments of these shells will be transported in traction and saltation mode (bed load) and deposited in the near-shore areas; while the finer grains (silt size) are most probably transported as suspended matter and then deposited in the quite low-energy offshore area as calcareous mud. Shells of the in-situ benthic microfauna, foraminifera and ostracoda, contribute to the whole sediment budget by direct accumulation, especially in the m u d d y areas. Oolites and pellets are usually more frequent in the medium and fine sand fractions. Oolites mostly occur in the b o t t o m sediments proximal to oolitic limestone coastal ridges, e.g., Subbiyah and Ras Ushairij. Therefore, it is suggested that the oolitic grains in the sand fraction of Kuwait Bay b o t t o m sediments are derived mainly from the oolitic limestone coastal ridges by coastal erosion processes or could be supplied to the bay area as wind-blown sediments. Comparison between the composition of the marine b o t t o m sediments of Kuwait Bay and that o f the fallout from dust storms over Kuwait territory indicates the presenc e of considerable quantities of aeolian material in Kuwait Bay sediments. Kukal and Saadallah (1973) have indicated the occurrence of aeolian admixtures in the sediments of the northern Arabian Gulf, near Shatt A1-Arab.

96

The very fine sand and coarse silt fractions of Kuwait Bay sediments are characterised by the abundance of carbonate grains. Calcite forms about 50% of the average composition of the light-mineral suite of these size fractions. The abundance of calcite in the fine material of Kuwait Bay sediments is closely similar to that of the dust fallout and recent surface deposits of Kuwait. The same could also be applied to dolomite, quartz, feldspars and gypsum (Table VI). The texture and shape of the dolomite grains in the Kuwait Bay sediments are very similar to those present in the dust fallout over Kuwait. This indicates that fallout of dust storms has contributed considerably to the sediment budget of Kuwait Bay. This conclusion is also supported by the correlation of the heavy-mineral characteristics of both Kuwait Bay sediments and dust fallout. With regard to the transparent heavy minerals, it can be noticed that Kuwait Bay sediments are similar to the Recent Tigris--Euphrates sediments (Ali, 1976) in the abundance of mica, hornblende and pyroxenes. A ternary plot diagram with three end members, namely, dolomite, pyroxenes + amphiboles + epidotes, and tourmaline + zircon + garnet, indicates that Kuwait Bay sediments are more related to the dust fallout and recent surface deposits of Kuwait because of the similarity in the abundance of dolomite. On the other hand, they are similar to the Tigris--Euphrates recent sediments as far as the unstable heavy minerals are concerned (amphiboles and pyroxenes) (Fig.7). Pilkey and Nobel (1966) found that the sediments of the northern area of the Arabian Gulf are characterized by the abundance of illite and illitemontmorillonite mixed layers and the a m o u n t of kaolinite and chlorite increases towards the Iranian side. These results, with the exception of palygorskite, are in agreement with the result of the present study. TABLE VI The average relative frequency percentages of light-minerals in the fine size fractions of Dust Fallout, Kuwait Bay and surface coastal sediments of Kuwait "~'~

Light minerals Carbonates (mainly calcite) Quartz Feldspars Gypsum Chert Mica

Locations

Dust fallout sediments (Khalaf et al.,

1 9 8 0 ) ~ v . f . s .

Kuwait Bay sediments (present study)

Surface sediments (Khalaf et al., 1980)

v.f.s,

c.s.

v.f.s,

c.s.

c.s.

43.4

56.8

47.5

50.9

44.9

49.5

30.2 12.7 6.9 4.9 1.9

20.5 10.4 6.6 3.4 2.2

23.17 10.53 5.82 8.12 4.81

24.0 9.84 6.09 5.42 3.72

27.8 10.5 9.4 6.5 0.6

23.9 13.9 8.2 3.3 1.2

Note: v.f.s. = very fine sand fraction; c.s. = coarse silt fraction.

97 Dolomite

o • x •

0

z,/ Amphiboles Pyroxenes Epidotes

O

oo°°o •

0

•

Euphrates basin "n(jris basin Dust f a l l o u t in Kuwait Recent s u r f a c e deposits of K u w a i t Kuwait Bay sediment

0~ •

• o~\ • x. Zircon Garnet Tourmaline

Fig.7. Correlation of heavy mineral association in Kuwait Bay sediments, Tigris-Euphrates Recent surface deposits and dust fallout in Kuwait (No.8 in the 1st draft).

In their study on the distribution and source of clay minerals in sediments of the Arabian Gulf, Akoi and Oinuma (1977) found also that illite and illitemontmorillonite are the most dominant clay minerals in the northern area o f the Gulf. They attributed the constancy of the clay-mineral composition with depth to the fact that the sources of the clay minerals have remained unchanged for a long time. Stoffers and Ross (1979) recorded the occurrence of palygorskite in both dust samples and b o t t o m sediments collected from the Iranian side of the Arabian Gulf. Khalaf et al., (1980) have also reported the c o m m o n occurrence of palygorskite in the dust fallout in Kuwait. The abundance of illite and illite-montmorillonite mixed layer clay in the Kuwait Bay sediments could be attributed to the proximity to the Shatt A1Arab river system (Berry et al., 1970). The deficiency of the suspended sediments of Shatt A1-Arab in palygorskite (Berry et al., 1970) would suggest that this mineral has been developed as a diagenetic mineral resulting from the reaction o f the hypersaline water with the other ~detrital clay minerals in the sabkhatized areas of southern Iraq (Grim, 1953; Bonythen, 1956;

98 K h a l a f and Ala, 1980). T h e r e f o r e , it is suggested t h a t p a l y g o r s k i t e m the studied s e d i m e n t s i s ' m o s t p r o b a b l y derived f r o m the a n c i e n t M e s o p o t a m i a n f l o o d plains b y d u s t s t o r m s . F r o m t h e f o r e g o i n g discussion it can be c o n c l u d e d t h a t K u w a i t Bay is severely a f f e c t e d b y the f a l l o u t o f d u s t s t o r m s . T h e l a t t e r c o n t r i b u t e s c o n s i d e r a b l y to the s e d i m e n t b u d g e t o f K u w a i t B a y in p a r t i c u l a r and the n o r t h e r n area o f the A r a b i a n G u l f in general. In a d d i t i o n t o the c o n t r i b u t i o n o f d u s t f a l l o u t (aeolian sources), o t h e r p o t e n t i a l sources o f K u w a i t Bay b o t t o m s e d i m e n t s c o u l d also be c o n s i d e r e d . T h e s e are: (a) s u b m e r g e d estuarine m u d o f the a n c i e n t d e l t a o f S h a t t A1-Arab; (b) a c c u m u l a t i o n o f a u t o c h t o n o u s skeletal grains; a n d (c) matei-ial e r o d e d f r o m the coastal ridges and raised b e a c h e s o f t h e s o u t h e r n c o a s t o f the Bay. In c o n c l u s i o n , K u w a i t Bay is c o n s i d e r e d an area o f s e d i m e n t a t i o n (sedim e n t a c c u m u l a t i o n ) w i t h v e r y slight s e d i m e n t m o v e m e n t s , w i t h the exception o f the s o u t h e r n coast, especially the d e e p e r o f f s h o r e channels. T a k i n g into c o n s i d e r a t i o n t h e n a t u r e o f t h e s e d i m e n t s and t h e tidal c u r r e n t s p a t t e r n it can be suggested t h a t t h e b o t t o m s e d i m e n t s o f K u w a i t Bay, especially t h e s a n d y s e d i m e n t s , are m o v i n g slightly b a c k and f o r t h in the d i r e c t i o n o f e b b and f l o o d tidal currents. D u e to t h e f a c t t h a t t h e average speeds o f b o t h e b b a n d f l o o d c u r r e n t s are m o r e o r less equal, the n e t s e d i m e n t t r a n s p o r t in the central p a r t of t h e b a y is negligible. H o w e v e r , t h e r e are s o m e areas in the b a y w h e r e relatively active s e d i m e n t m o v e m e n t s can be r e c o g n i z e d . T h e s e are the areas o f tidal c h a n n e l where tidal c u r r e n t s are relatively m o r e active, e.g., S u l a i b i k h a t Bay c h a n n e l and P~as A1-Ard channel. In these areas net s e d i m e n t t r a n s p o r t is parallel to t h e e b b tidal currents. T h e s u b m e r g e d sill which e x t e n d s in a SSE d i r e c t i o n o u t o f Ras A s - S u b b i y a h shelters the n o r t h e r n area o f t h e bay. This sill facilitates t h e m o v e m e n t s o f s u s p e n d e d s e d i m e n t s into t h e b a y d u r i n g t h e f l o o d tides and at t h e s a m e t i m e hinders m o v e m e n t s o f t h e b o t t o m s e d i m e n t s t o w a r d s the o p e n sea area during e b b tides. REFERENCES Akoi, S. and Oinuma, K., 1977. On the distribution of clay minerals in sediments of the Persian Gulf. Clay Sci., 5: 79--85. Ali, A.J., 1976. Heavy mineral provinces of the Recent sediments of the Euphrates--Tigris basin. J. Geol. Soc. Iraq, 10: 33--46. A1-Zamel, A. and Khalaf, F.I., 1978. Tidal flat and beach sedimentation in the northern region of Arabian Gulf, Ras As-Sabbiyah, Kuwait. Fifth Iraqi Geol. Congress, Baghdad. Bathurst, R.G.C., 1966. Boring algae, micrite envelopes and lithification of molluscan biosparites. Geol. J., 5: 15--32. Berry, R.W., Brophy, G.P. and Nagash, A., 1970. Mineralogy of the suspended sediment in the Tigris--Euphrates and Shatt A1-Arab rivers of Iraq and the Recent history of the Mesopotamian plain. J. Sediment. Petrol., 40: 131--139. Bonython, C.W., 1956. The salt of Lake Eyre, its occurrence in Modigan Gulf and its possible origin. Trans. R. Soc. South Aust., 79: 6--92. Bush, P.R., 1973. In: Sedimentology and Ground Water Chemistry of some Recent Coastal Sediments, Abu-Dhabi, Trucial Coast, Persian Gulf. Ph.D. Thesis, Univ. London, London, 356 pp.

99 Dubach, H.W. and Wehe, T.J., 1967. Descriptive oceanography of Kuwait Harbor. U.S. Navy Hydrogr. Off., Washington, D.C., TR-55, 43 pp. Fairbridge, R.W., 1961. Eustatic changes in sea level. In: L.H. Ahrens et al. (Editors), Physics and Chemistry of the Earth, Vol. 4, Pergamon Press, Oxford, 185 pp. Folk, R.L., 1974. Petrology of Sedimentary Rocks. Hamphill, Texas, 182 pp. Folk, R.L. and Ward, W.L., 1957. Brazos river bar; a study in the significance of grain size parameters. J. Sediment. Petrol., 27: 3--27. Fuchs, F., Gattinger, T.E. and Hoizer, H.F., 1968. Explanatory text to the Eynoptic geologic map of Kuwait. Geol. Surv. Austria, pp. 1--87. Grim, R.E., 1953. Clay Mineralogy. McGraw Hill, New York, N.Y., 348 pp. Hayes, M.O., 1977. Preliminary investigations of coastal processes and geology of Kuwait City Waterfront. Technical Report, Kuwait Municipality (unpubl.). Hilmy, M.E., Slansky, E. and Khalaf, F.I., 1971. Opaque minerals in Recent beach sediments of Kuwait. Neues Jahrb. Geol. Palaeontol. Monatsheft., 6: 340--344. Jacob, P.G., 1980. Oceanographic Data for Kuwait Marine Environment. Inst. for Scientific Res., Techn. Rep., Kuwait, 128 pp. Kassler, P., 1973. The structural and geomorphic evolution of the Persian Gulf. In: B.H. Purser (Editor), The Persian Gulf. Springer, Berlin, 471 pp. Khalaf, F.I., 1980. Dust fallout in Kuwait. Kuwait Inst. for Scientific Res., Techn. Rep., Kuwait. Khalaf, F.I. and Ala, M., 1980. Mineralogy of the Recent intertidal m u d d y sediments of Kuwait--Arabian Gulf. Mar. Geol., 35: 331--342. Khalafallah, M.N., 1977. Applicability of the Electrical Resistivity Method for Groundwater Research and Prospection in Kuwait. M.Sc. Thesis, Kuwait University, 195 pp. (unpubl.). Kinsman, D.J.J., 1964. Recent Carbonate Sedimentation near Abu-Dhabi, Trucial Coast, Persian Gulf. Ph.D. Thesis, University of London, London. Kukal, Z. and Saadallah, A., 1973. Aeolian admixtures in the sediments of the Northern Persian Gulf. In: B.H. Purser (Editor), The Persian Gulf. Springer, Berlin, pp. 115--121. Larsen, C.E. and Evans, G., 1978. The Holocene geological history of the Tigris--EuphratesKarun Delta. In: W.C. Brice (Editor), The Environmental History of the Near and Middle East. Academic Press, London, 384 pp. Lees, G.M. and Falcon, N.L., 1952. The geographical history of Mesopotamian Plains. Geogr. J., 116: 24--39. Mohamed, M.A., 1979. Preliminary marine geological studies on Recent sediments of Kuwait Bay. J. Univ. Kuwait, 5: 161--177. Owen, R.M.S. and Nasser, S.N., 1958. Stratigraphy of the Kuwait--Basra area: Habitat of oil. Am. Assoc. Pet. Geol., 1252--1278. Pilkey, O.H. and Nobel, D., 1966. Carbonate and clay mineralogy of the Persian Gulf. Deep-Sea Res., 13: 1--16. Purser, B.H., 1973. The Persian Gulf, Holocene Carbonate Sedimentation and Diagenesis in a Shallow Epicontinental Sea. Springer, Berlin, 471 pp. Schultz, L.G., 1964. Analytical methods in geochemical investigations of the Pierre Shale. Quantitative interpretation of mineralogical composition from X-ray and chemical data for the Pierre Shale. U.S. Geol. Surv. Prof. Pap., 391 (C): 1--39. Seibold, E., Diester, L., Futterer, D., Lang, H., Muller, P. and Werner, F., 1973. Holocene sediments and sedimentary processes in the Iranian part of the Persian Gulf. In: B.H. Purser (Editor), The Persian Gulf. Springer, Berlin, pp. 57--80. Shaw, H.F., 1971. The Mineralogy of Recent Sediments in the Wash, Eastern England. Ph.D. Thesis, Univ. of London, (unpubl.). Shinn, E.A., Ginsburg, R.N. and Lloyd, R.M., 1965. Recent supratidal dolomite from Andros Island, Bahamas. In: L.C. Pary and R.C. Murray (Editors), Dolomitization and Limestone Diagenesis. S.E.P.M., Spec. Publ., 13: 112--123. Stoffers, P. and Ross, D.A., 1979. Late Pleistocene and Holocene sedimentation in the Persian Gulf--Gulf of Oman. Sediment. Geol., 23:181--208. Taylor, J.M.C. and Illing, L.V., 1969. Holocene intertidal calcium carbonate cementation, Qatar, Persian Gulf. Sedimentology, 12: 69--107.