Mineralogical composition and potential sources of dust fallout deposits in Kuwait, Northern Arabian Gulf

Sedimentary Geology, 42 (1985) 255-278

255

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

MINERALOGICAL COMPOSITION AND POTENTIAL SOURCES OF DUST F A L L O U T D E P O S I T S IN K U W A I T , N O R T H E R N A R A B I A N G U L F

FIKRY 1. KHALAF, AHLAM AL-KADI and SAMIRA AL-SALEH Environmental and Earth Sciences Division, Kuwait Institute for Scientific Research, P.O. Box 24885 (Kuwait)

(Received January 11, 1984; revised and accepted June 12, 1984)

ABSTRACT Khalaf, F.I., AI-Kadi, A. and AI-Saleh,S., 1985. Mineralogicalcomposition and potential sources of dust fallout deposits in Kuwait, northern Arabian Gulf. Sediment. Geol., 42: 255-278. Detailed mineralogical investigations of dust fallout deposits collected at eleven locations in Kuwait during April 1979-March 1980 were carried out. The mineralogy of five size fractions, medium sand, fine sand, very fine sand, coarse silt and clay, was determined. Occurrence, frequency and potential sources of the mineral grains that form the various size fractions are discussed and the gross mineralogical composition of the dust fallout calculated. It was found that dust fallout deposited in Kuwait is quartzitic calcareous sandy silt and is mostly derived from the dry Mesopotamian flood plain in the middle and south of Iraq. The occurrence of sand-size particles is attributed to pick up from local recent surface deposits.

INTRODUCTION Dust storms are c o m m o n p h e n o m e n a in arid a n d semi-arid regions a n d are usually caused b y the action of strong, persistent winds o n dry, fine-grained, a n d loose soil. D u r i n g their occurrence, a complete aeolian s e d i m e n t a r y cycle takes place, i.e., erosion, t r a n s p o r t a t i o n a n d deposition. The A r a b i a n Peninsula, in general, a n d the n o r t h e a s t e r n part, in particular, is one of the major sand a n d dust storm regions in the world (Idso, 1976; Goudie, 1978). The n o r t h e r n A r a b i a n G u l f region includes the State of Kuwait, the southern part of Iraq, a n d the n o r t h e a s t e r n corner of Saudi Arabia. This region is located in the lower M e s o p o t a m i a n Depression, b o u n d e d o n the east b y the Zagros M o u n t a i n s , on the west b y the G r e a t N e f u d Deserts a n d the Syrian Plateau, a n d on the south a n d southwest b y the A r a b i a n Gulf. K u w a i t is located at the southern end of this Depression. The southern part of Iraq can be divided into two m a i n physiographic provinces, the lower M e s o p o t a m i a n plain a n d the southern desert (Macfayden, 1938; 0037-0738/85/$03.30

© 1985 Elsevier Science Publishers B.V.

256

Mitchell, 1956; Buringh, 1960). The lower Mesopotamian plain includes Pleistocene fluviatile terraces, Holocene flood plains, and the delta plain of the rivers Tigris and Euphrates (Fig. 2). This plain is covered mostly by deposits of silt and is extensively desertified. The southern desert of Iraq borders the western limit of the lower Mesopotamian plain and includes the southern parts of the stony Al-Hajara plain and the gravel and sand regions of Ad-Dibdibba (Al-Naqib, 1967). It is characterized by extensive belt:~ of sand dunes. Like most of the Arabian Peninsula, Kuwait has a hot and dry climate. Winds blow mainly from two directions, the northwest and, to a lesser extent, the southeast. Winds from other directions are less frequent and of shorter duration. Sand and dust storms, known locally as Toze, are frequent. Regional observations of dust storms (with a visibility less than 1 km) indicate a zone of occurrence that extends in a N W - S E direction and covers most of the lower Mesopotamian plain, the eastern side of the western desert of lraq, Kuwait and most of the coastal region of Saudi Arabia on the Gulf side. The seasonal occurrence of dust storms in Kuwait is discussed by A1-Kulaib (1977). They are mostly associated with dry, hot northwesterly winds. The amount of dust fallout in the coastal area of Kuwait during April 1979-March 1980 was estimated by Khalaf et al. (1980), who found that the mean monthly maximum and minimum fallouts were recorded in July 1979 (1002.7 t km -2) and November 1979 (9.8 t km-2), respectively. Dust fallout in Kuwait is generally sandy silt with an average composition of 32% sand, 62% silt and 6% clay (Khalaf and A1-Hashash, 1983). In spite of the importance of dust fallout and its role in aeolian sedimentation in the northern part of the Arabian Gulf, very limited information is available on the mineralogy of these deposits. Stoffers and Ross (1979) studied the mineralogy of dust fallout samples collected on board the "Atlantic II" during a 1977 cruise in the Arabian Gulf. Their study was confined to four samples, which were composed of illite, chlorite, palygorskite, quartz, calcite and dolomite. They also noticed a difference between the mineral composition of samples collected in the northern part of the Gulf and those collected at the Gulf of Oman. Kukal and Saadallah (1970) reported that the dust storm sediments in Iraq are mostly of silt-sized material and that carbonate prevails in all the fallouts increasing in amount towards finer fractions. This present paper summarizes the results of a detailed mineralogical investigation of dust fallout collected in the coastal area of Kuwait during April 1979-March 1980. Potential sources of the fallout are also discussed. SAMPLING A N D ANALYTICAL PROCEDURES

Dust fallout samples were collected in April 1979-March 1980 at eleven localities along the coastal area of Kuwait (Fig. 1), These localities are AI-Abdalli, U m m A1-Aish, AI-Mutla, AI-Sulaibikhat, Kuwait City, Salmiyah, AI-Ahmadi, Al-Fahaheel,

257

Mina Abdullah, AI-Wafra and AI-Nuwaisib. Thin sections of sand grains were investigated by polarizing microscope for mineralogical identification. The relative frequency percentages of the various mineral grains in the medium and fine sand fractions were determined by binocular stereomicroscope. About 200 mineral grains were counted and the frequency percentages of the various mineral grains were calculated in each size fraction. Heavy-mineral grains in the very fine sand (0.125-0.063 ram) and coarse silt (0.063-0.031 mm) fractions were separated using bromoform according to standard technique (Carver, 1971). Weigh~percentages of the heavy-mineral fractions were determined in each studied sample. To facilitate identification of the calcite grains, the light-mineral fraction was stained with Alizarin red-S, which stains calcite red. Heavy- and light-mineral grains were identified and their relative frequency percentages computed by counting about 200 grains from each fraction. The mineralogical composition of the clay fraction of some representative samples was determined by X-ray diffraction. The clay fraction ( < 4 tim) was separated from 47*00

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NUWAISIBO I

258 the whole sediments of the investigated samples by the sedimentation method (Folk, 1974). Oriented mounts were prepared for the clay-size fractions using the suctionto-ceramic-disc technique (Shaw, 1971). The oriented ceramic disc mounts of the clay fraction were analysed with a Philips PM 9920/05 X-ray diffractometer equipped with a linear recorder. Nickelfiltered Cu K a radiation was used with settings of 40 kV and 20 MA and a scanning speed of 1 ° (20) min a. Each oriented specimen of the clay fraction was analysed in its untreated condition [scanned from 6 to 34 ° (2 0)], after treatment with ethylene glycol [scanned from 6 to 20 ° (2 0)] and after heat treatment at 550°C for an hour [scanned from 6 to 20 ° (2 0)] (Brown, 1961). The relative abundance of the main minerals forming the clay fraction was semi-quantitatively estimated using the methods described by Schultz (1964) and Shaw (1971). RESULTS

Mineralogy of the sand-size fractions Medium sand and fine sand fractions of the studied dust fallout sediments are composed mainly of quartz, feldspar, rock fragments and gypsum. Calcareous grains, represented by biogenic fragments and fine-grained oolites, were recorded in subordinate amounts (Table I). Quartz is the most frequent mineral grain. It ranges in frequency between 66.1 and 84.9% on the average with a mean of 77.3% in the medium sand fraction, and between 60.7 and 87.1% on the average with a mean of 76.1% in the fine sand fraction. Quartz is generally represented by monocrystalline grains. Some contained acicular tourmaline and zircon inclusions. Composite grains of quartz and feldspar were also recorded in the medium sand fraction. Feldspar is represented by plagioclase, orthoclase and microcline grains. It forms about 3.5% of the sand-size fractions and is relatively more abundant in samples collected from the northern area. Plagioclase grains are mostly albitic and display characteristic polysynthetic twinning. Plagioclase grains with perthitic and graphic textures are also present. Most of the feldspar grains are partially sericitized. Rock fragments follow quartz grains in relative frequency; they constitute about 12% of the sand-size fractions. They are represented mainly by fragments of duricrust, calcareous siltstone, chert and volcanic rocks. It was noticed that duricrust fragments are more abundant in the dust fallout of the northern area, whereas chert fragments are relatively frequent in that of the southern area. Duricrust fragments are represented by smooth rounded grains of anhydrite and micrite. Anhydritic grains composed of interlocking fabric of finely crystalline anhydrite laths were also noticed. Some of these anhydritic fragments enclose fine quartz grains. Calcrete fragments are composed of microcrystalline calcite cementing

pp.259-262

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UPPER WEOIY AN PLAIN Limestone Terrain with an lotriut. Piltterns of Deep Wadis.

AD-OIBDIBBA PLAIN

KUWAIT

Pebbly and Sandy Desert Land.

ANCIENT RIVER TERRACES Mainly Silty. Gypsiferous

ITITIIIIIIJI

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b;'~!'J

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Fig. 2. Geomorphological provinces in the southern desert of Iraq. (After Buringh, 1960; with modification.)

\

80.5

77.3

AI-Nuwaisib

Average

76.1

83.0

79.0

87.1

74.6

84.0

60.7

60.7

81.1

81.7

69.9

4.5

2.4

2.0

1.2

1.6

17.6

3.6

7.3

4.9

1.4

3.1

4.2

FS

2.2

0.2

2.8

-

2.7

1.3

2.~

4.6

3.2

0.5

M S = m e d i u m s a n d ; F S = fine s a n d ; t = t r a c e s ( < 0.1%).

84.9

78.8

77.7

AI-Ahmadi

Mina Abdullah

79.4

Salmiyah

Al-Wafra

73.2

66.1

76.9

AI-Mutla

K u w a i t City

82.9

AI-Sulaibikhat

72.2

Umm Al-Aish

Feldspar MS

MS

FS

Quartz

Al-Abdalli

Location

12.2

9.7

9.0

9.3

11.7

2.9

29.2

13.5

9.9

7.6

19.7

MS

12.2

9.8

11.0

4.0

13.3

5.0

30.1

22.3

5.9

6.4

15.3

FS

Rock fragments

5.0

3.3

10.2

3.7

7.2

-

1.1

6.0

6.9

7.7

3.5

MS

Gypsum

8.6

6.2

6.9

8.3

8.8

9.6

6.6

11.5

9.7

11.2

8.7

FS

0.1

0.1

-

-

-

-

-

0.2

-

0.2

1.5

MS

0.2

0.7

-

-

-

-

-

0.7

t

0.5

FS

Biogenic f r a g m e n t s

0.4

4.0

-

0.6

0.2

-

-

-

0.1

-

-

MS

Oolite

A v e r a g e relative f r e q u e n c y p e r c e n t a g e s o f the v a r i o u s m i n e r a l g r a i n s in the m e d i u m - s a n d a n d f i n e - s a n d f r a c t i o n s of the s t u d i e d d u s t fallout

TABLE I

FS

264 a framework of fine quartz and feldspar grains. Chert is usually represented by subrounded to subangular brownish grains with abundant black inclusions. Composite chert and micrite grains are very frequent. The texture of these grains shows replacement of micrite by chert. Oolites form about 4% of the medium sand fraction of the dust fallout at AI-Nuwaisib. The majority of the oolites have a quartz nucleus. They are petrographically similar to those of the oolitic limestone coastal ridges of the southern coast (Picha, 1978). The occurrence of Recent micritized shell fragments in the dust fallout of the southern coast indicates the susceptibility of the Recent coastal sediments to dust storms. Gypsum grains average about 8% of the fine sand fraction and 5% of the medium sand fraction grains; its texture is similar to that of gypsum of the Dibdibba Formation.

Mineralogy of the very fine sand and coarse silt fractions Very fine sand and coarse silt fractions of 71 samples representing dust fallout at the northern, central and southern regions of Kuwait were mineralogically investigated with a polarizing microscope. The various mineral grains in both the heavy and light fractions were identified and their relative frequency calculated.

Light-mineral fraction The light-mineral fraction of both very fine sand and coarse silt is composed mainly of calcite, quartz, feldspar, gypsum, chert and mica. Shells and shell fragments of microfaunas were also recorded. On the average, light mineral grains form about 90% of both fractions. The average mineralogical composition of the light-mineral fraction is given in Table II. Calcite is commonly present as well-rounded polycrystalline micritic grains. Angular monocrystalline calcite grains are also present but in subordinate amounts. Composite grains of well-formed euhedral drusy calcite in the form of roses were frequently found in the dust fallout in the U m m A1-Aish area. The fabric of these calcite roses is similar to that of the calcite cement that usually develops in porous sediments. Some of the calcite roses are developed around organic fragments and appear as calcite spherules with dark cores. Calcite is the most dominant mineral in the light fraction of both very fine sand and coarse silt fractions (about 50%), but is more frequent in the coarse silt fraction, N o significant variation was noticed in the geographical or seasonal distribution of calcite. Trace amounts of shells and shell fragments of microfaunas are recorded in some of the samples. These are represented mostly by whole shells of foraminifera and diatoms, and are more frequent in the coarse silt fraction, especially in the dust fallout collected in southern localities.

9 8

9 8 7

2 9

9

5

5

71

AI-Abdali Al-Mutla

AI-Sulaibikhat Kuwait City Ahmadi

Al-Fahaheel AI-Wafra

A1-Nuwaisib

T o w e r (1)

U r n m AI-Aish T o w e r (4)

U m m Al-Aish Average

20.5

22.0

19.4

19.5

15.0 22.7

19.7 22.1 22.3

23.5 19.5

30.2

20.3

22.7

30.7

40.4 38.1

27.1 28.1 34.8

27.7 31.0

10.4

13.3

11.7

8.7

9.2 12.1

10.0 9.8 10.6

9.3 9.6

12.7

10.1

11.6

9.8

14.4 15.8

10.7 13.7 13.2

12.6 14.8

VFS

CS

CS

VFS

Feldspars

Quartz

CS = coarse silt; VFS = very fine sand; t = traces ( < 1%).

N u m b e r of samples

Location

56.8

49.9

56.0

59.2

66.2 52.3

57.8 56.3 54.6

56.6 59.1

CS

Calcite

43.4

57.4

51.7

46.0

30.0 28.6

49.6 44.2 38.9

47.1 40.1

VFS

6.6

6.1

5.7

7.1

5.8 7.3

6.8 7.1 6.9

6.9 6.3

CS

6.9

6.6

7.5

6.5

7.2 8.3

7.4 6.9 6.6

6.1 6.9

VFS

Gypsum

3.4

5.7

5.2

3.2

1.8 3.4

3.3 3.0 2.7

2.2 3.1

CS

Chert

4.9

4.1

4.6

5.2

6.1 6.4

3.3 5.1 4.6

4.9 5.3

VFS

2.2

3.0

2.0

2.1

2.1 2.1

2.4 1.6 2.8

1.5 2.4

CS

Mica

1.9

1.4

1.7

1.9

1.9 2.6

1.9 2.0 1.9

1.5 2.0

VFS

Average relative frequency percentages of the light-mineral grains in the very fine s a n d and coarse silt fractions of the studied dust fallout

T A B L E II

t

-

-

t

t

t

-

CS

t

-

-

t

t

-

VSF

Shell f r a g m e n t s

9

08.5

17.9

35.1

00.6 14.2 00.5 00.7 16.0

02.3 03.3 01.4

Number of samples

Weight percentage of heavy minerals

Opaques

Dolomite

AnthophyUite Hornblende Basaltic hornblende Others Total amphiboles

Enstatite Hypersthene Diopside

A1-Abdalli

Locations

00.7 01.6 01.7

00.7 13.8 00.7 01.4 16.6

38.1

17.2

08.2 24.4 31,5 00.3 12.9 00.7 00.6 14,4 02.0 02.8 01.8

23.2 24.8 00.5 15.4 01 .t 00.6 17,6 02.4 04.3 02.6

9

A1-Sulaibikhat

09.8

8

5

7.8

A1-Mutla

UmmAl-Aish

02.4 02.5 01.7

00.7 14.5 00.4 01.0 16.7

26.1

22.8

07.3

8

Kuwait City

02.5 03.8 02.0

00.6 ] 1.6 00.6 00.6 13.4

35.2

18.6

10.9

7

03.3 02.9 00.9

00.2 11.0 00.7 00.4 12.3

25.2

27.0

05.3

2

AI-Ahmadi A1-Fahaheel

02.1 03.9 02.7

00,5 13.9 00.8 01.1 16.4

27.2

22.4

09.9

9

02.9 03.7 02.3

00.7 12.6 00.8 00.8 14.9

34.4

19.2

10.7

9

02.3 03.2 01.9

00.5 13.3 00.7 00.8 15.3

30.8

21.4

08.7

66

AI-Wafrah AI-Nuwaisib Average

Average relative frequency percentages of the heavy-mineral grains in the v e ~ fine sand fraction of dust fallout in Kuwait

TABLE llI

o~

00.3

00.1

01.9 02.0

01.0 00.6 01.4 -

00.2

Coloured garnet

Colourless garnet Total garnet

Zircon Tourmaline Apatite Sillimanite Kyanite

Topaz

t = t r a c e s ( < 0.1%).

01.5 04.2 01.8 07.5

01.3 03.1 00.9 05.4

Biotite Chlorite Muscovite Total mica

00.5

00.8 00.5 00.9 -

02.0 02.3

00.8 03.2 04.0

00.5 03.8 04.3

Ziosite Pistacite Total epidote

05.5 10.5

07.7 14.7

Augite Total pyroxene

00.2

02.0 01.1 01.0 -

02.3 02.5

00.2

01.9 02.9 01.1 05.9

00.6 04.3 04.9

07.4 16.6

00.5

01.4 00.8 01.1 t t

01.6 01.7

00.1

01.1 03.5 01.5 06.1

00.6 04.0 04.8

05.7 12.5

00.5

02.1 01.2 01.3

02.9 03.1

00.2

01.4 05.7

01.4 02.9

00.5 04.0 04.5

08.9 15.6

00.2

01.8 00.7 01.1

00.5 01.4 01.9

01.3 04.3 02.3 07.9

00.5 03.3 03.8

05.8 14.1

00.0

02.4 01.2 00.6

01.9 02.4

00.5

02.7 02.8 00.6 06.1

00.5 05.5 06.0

10.0 16.8

00.2

t

t

00.3

01.7 00.5 00.7 t

01.9 00.8 00.9

00.0 02.4 02.4

04.8

05.4 00.1 01.3 01.5

01.6 02.3 00.9

00.7 04.0 04.6

06.9 15.7

01.8 02.7 00.9

00.8 04.7 05.5

08.4 17.1

00.3

t

t

01.6 00.8 01.0

00.2 02.0 02.2

01.6 03.2 01.3 06.1

00.6 04.1 04.7

07.4 14.8

268 Quartz is generally present as monocrystalline subangular grains, some containing minute inclusions of tourmaline, zircon, and hair-like rutile needles. Quartz constitutes about 25% of these size fractions (0.03-0.125 mm) and is more frequent in the very fine sand fraction. Feldspar is commonly represented by plagioclase and alkali feldspar grains. The latter are primarily microcline and orthoclase grains, which are mostly subrounded and display characteristic crosshatching and simple twinning. Plagioclase is mostly albitic. In general, feldspar grains are partially altered along grain borders and cleavage planes. Two main types of alteration were noticed, kaolinitization and serlc~Uzatlon. Feldspar grains form about 11.5% of these size fractions, and are more frequent in the dust fallout collected in northern areas. Gypsum and anhydrite are found in almost all the samples. Gypsum is present as subhedral to anhedral grains, which usually contain calcareous inclusions. Anhydrite occurs as elongated rectangular euhedral crystals; some are partially corroded. Gypsum and anhydrite form about 7% of the average composition of the fine-grained fraction. They are more abundant in the very fine sand, especially in samples collected at Sulaibikhat, AI-Fahaheel and Umm A1-Aish. Chert is present as brownish angular grains and forms about 4% of the fine-grained fraction of the studied samples. Composite grains of chert and calcite are frequently encountered. The fabric of such grains indicates that they are derived from chertified limestone. Mica occurs in subordinate amounts and is represented mainly by muscovite, leached biotite and chlorite. Mica flakes generally form about 2% of the average composition of the fine grained size fraction. They are more abundant in the coarse silt fraction, especially in samples collected at the A1-Ahmadi and Umm A1-Aish areas.

Heavy-mineral fraction Heavy minerals are present as accessory detrital grains in the dust fallout of Kuwait. They form about 9% by weight of both coarse silt and very fine sand fractions (Tables III and IV). The heavy-mineral fraction of the dust-fallout samples studied is mainly composed of dolomite, opaque minerals, amphiboles, pyroxenes, epidotes, mica, garnet and zircon. Traces of tourmaline, apatite, monazite, staurolite, topaz, rutile, andalusite, sillimanite, kyanite, barite and celestite are also present. Dolomite is the most abundant mineral grain (28%) in both fractions, and is generally represented by rounded to subrounded grains. Well-formed euhedral rhombs of dolomite with cores of organic matter are also present, especially in the coarse silt fraction. Their shape and fabric are very similar to the protodolomite that usually develops in sabkha deposits (Shinn, 1964). Opaque mineral grains are the next most frequent heavy minerals after dolomite.

269 They form about 20.7% of the average composition of the heavy mineral fraction. Microscopic investigation revealed that some of the opaque grains were completely or partially altered ferromagnesium minerals (pyroxene and amphiboles). Relicts of the original transparent ferromagnesium minerals were noticed in some opaque grains. The majority of the opaque grains were identified as hematite and limonite. Amphibole grains are present in considerable amounts (25% of the non-opaque minerals) and are more abundant in the very fine sand fraction. Amphiboles are represented by five varieties, anthophyllite, green hornblende, basaltic hornblende, actinolite and glaucophane. Green hornblende is the most frequent, forming about 85% of the amphibole grains. Hornblende is present as subhedral prismatic grains and cleavate shreds. Basaltic hornblende occurs in subordinate amounts, mostly as subhedral stout prismatic grains. Anthophyllite is represented by a few prismatic and fibrous grains. Tremolite and actinolite are recorded as euhedral to subhedral prismatic grains and are also represented by only a few grains. Pyroxene grains are also present in considerable amounts. They form about 20% of the non-opaque heavy minerals. Like amphiboles, pyroxenes are more abundant in the very fine sand fraction, and are mainly represented by augite, hypersthene, enstatite, and diopside. Augite is the most frequent pyroxene mineral in most of the examined samples. It forms about 50% of the grains in both coarse silt and very fine sand fractions and is commonly present as subhedral prismatic grains. Hypersthene is present as subrounded to subangular grains with marked pleochroism. It generally forms 15-20% of the pyroxene grains and is more frequent in the coarse silt size. Enstatite forms 15-20% of the total pyroxene grains and is more frequent in the very fine sand fraction. It is present as subrounded elongated grains with characteristic prismatic cleavage and frequent inclusions. Diopside is the least frequent pyroxene and constitutes less than 14% of the pyroxene minerals. A few grains of titaniferous augite were also recorded in some samples. Epidote mineral grains form about 4% of the heavy-mineral fraction. They are represented mainly by pistacite and zoisite. Pistacite is the most frequent epidote mineral; it forms more than 80% of the total epidote grains. It is present as subangular chip-like grains with the characteristic pale green colour. Zoisite is represented by a few worn euhedral grains with the characteristic deep blue interference colour. Garnet is recorded in subordinate amounts; it forms about 2% of the average heavy-mineral composition of the very fine sand and coarse silt fractions. Several varieties of garnet are recognized. Grossularite was the most abundant variety, forming about 90% of the garnet grains. It occurs as angular colourless grains. Some colourless garnet grains are present as euhedral crystals (with the characteristic dodecahedron crystal form). The coloured garnets are represented by a few grains, less than 10% of the total. Zircon forms about 1% of the average composition of the heavy minerals and is generally more frequent in the coarse silt fraction. It occurs as euhedral and rounded

00.3 15.3 00.7 00.6 16.9

01.6 01.9 01.9

22.3

Dolomite

Anthophyllite 00.2 Hornblende 15.0 Basaltic hornblende 01.3 Others 01.3 Total amphiboles 17.8

Enstatite Hypersthene Diopside

03.8 04.1 02.5

38.5

10.1 19.6

Weight percentage of heavy minerals Opaques

08.7 14.3

5

9

Number of samples

14.8 21.5 27.1 00.3 15.2 00.9 01,1 17.5 02.6 03.0 03.5

21.0 00,7 14.4 01.1 00.6 16.7 03.6 06,1 02.9

9

AI-Sulaibikhat

08.4 20.3

8

Umm AI-Aish Al-Mutla

Al-Abdalli

Locations

02.8 03.9 03.4

00.5 16.5 01,t 01.1 19,t

24.3

07.1 23.3

8

Kuwait City

03.1 03.3 03,0

00.5 14.0 00.7 01.1 16.2

25.0

10.9 27.4

7

AI-Ahmadi

07.3 04.3 01.6

00.7 17.7 01,9 00.7 20.9

10.7

05.4 20.7

2

Al-Fahaheel

Average relative frequency percentages of the heavy-mineral grains in the coarse silt fraction of dust fallout in Kuwait

TABLE IV

03.6 04.7 03,2

00.6 15.9 01.l 00.8 18.4

18.0

07.9 22.8

9

01.1 04.0 03.0

00.6 15.0 01.5 01.2 18,3

23,7

08.7 18.1

9

03.5 03.9 02.8

00,5 15.4 01.1 00.9 17.9

23.4

09.1 20.8

66

AI-Wafra AI-Nuwaisib Average

11.1

00.7 00.3

00.1

-

00.4

Colourless garnet Total garnet

Zircon Tourmaline

Apatite

Sillimanite Kyanite

Topaz

t = traces ( < 0.1%).

00.2

03.8 03.9

Coloured garnet

01.5 06.9

Muscovite Total mica

00.1

-

00.3

00.6 00.5

01.3 01.4

00.1

03.8 10.8

06.3

00.8

01.6

04.1

Biotite

Chlorite

04.6

03.7

00.9

11.8

06.4

05.0

04.5

Total epidote

00.6

Pistacite

21.4

Ziosite

Total pyroxene

Augite

11.9

00.2

t t

00.1

01.2 00.7

02.2 02.6

00.5

01.2 06.4

01.8 03.4

05.4

05.0

00.5

24.5

00.3

-

00.3 00.3

01.7 01.8

00.2

02.5 10.0

06.4

01.1

03.9

03.5

00.4

16.5

07.4

03.8 01.9 04.3

04.2 01.2

00.8 00.9 00.5 00.4 00.2

02.6 02.9 00.4 00.5

00.3

00.1

00.1

00.3

00.3

07.1

01.0 05.8

01.9

05.6

03.4

03.5

03.6

01.2

00.4

00.7

16.1

18.1

18.1

00.7

05.0 01.6 04.3

02.1

02.6

03.0

t

t t 00.5

00.2

t

t t

00.3

00.2

01.2 00.5 00.4

00.8 00.5

00.3 02.3

00.3 02.9

01.7 07.6

01.5 07.0

03.4

04.3

06.0

00.7

00.5 05.4

10.0 20.2

10.6 20.7

01.5 00.8 00.1

02.6

04.2 00.5

02.3

00.3

08.4

01.7

01.5 05.1

05.4

04.6

00.8

21.4

09.9

03.5

00.7

06.1

02.8 00.5

02.7

06.8

29.3

08.6

08.1

272 grains. The former is more frequent and occurs as prismatic crystals with pyramidal tops, and usually c o n t a i n s acicular rutile inclusions. Mica is mainly represented by chlorite, muscovite a n d biotite and constitutes a b o u t 7% of the heavy-mineral fraction. In general, mica flakes are more a b u n d a n t in the very fine sand fraction.

Mineralogy of the clay-size fraction The mineralogy of the clay-size fraction of some selected dust-fallout samples was investigated by the X-ray diffraction technique. It was f o u n d that clay minerals form only about 55% of this fraction; the rest were non-clay minerals. Both clay and non-clay minerals were identified on the basis of their characteristic reflection peaks (Table V).

Clay minerals Clay minerals in the dust fallout of Kuwait are represented m a i n l y by illite, i l l i t e / m o n t m o r i l l o n i t e mixed layer, palygorskite, kaolinite and chlorite. N o marked variation was noticed in the relative frequency of the various clay minerals in the dust fallout collected at the different sampling sites or in different seasons. In general, palygorskite, illite a n d i l l i t e / m o n t m o r i l l o n i t e mixed layer form a b o u t 85% of the clay minerals. Kaolinite a n d chlorite are present in s u b o r d i n a t e amounts. Palygorskite was f o u n d to be the most frequent; its average relative frequency ranges between 40 and 50%.

TABLE V Average relative frequencydistribution of clay and non-clay minerals in the clay-sizefraction ( < 4/t m) of the dust fallout in Kuwait Location

Number Clay minerals 55% Non-clay minerals 45% of illite+ palygorkaochloquartz albite K-feld- calcite dolomite gypsum samples illite- skite linite rite spar montmori

-

llonite AI-Abdalli A1-Mutla AI-Sulaibikhat Kuwait City AI-Ahmadi Al-Wafra AI-Nuwaisib Average

4 5 5 8 1 5 4

35 40 40 40 50 45 45

50 45 45 50 45 40 45

10 10 10 10 5 10 5

5 5 5 t 5 5

15 20 15 15 10 20 20

10 20 15 15 20 15 20

20 20 20 15 15 20 15

40 35 30 35 25 30 25

10 5 15 10 15 10 10

5 10 15 5 10

32

40

45

10

5

15

15

20

30

10

10

t = traces ( < 5%).

5 t

273

Non-clay minerals Besides the clay minerals, the clay-size fraction of the dust fallout in Kuwait contains about 45% of non-clay mineral grains. They are represented mainly by calcite, feldspar, quartz, dolomite and gypsum. Like the clay minerals, no significant variations were noticed in the frequency distribution of these minerals by locality or season. Calcite was found to be the most frequent mineral (30%). Feldspars are represented mainly by K-feldspar and albite. They form about 15 and 20% of the average composition of the studied samples, respectively. On the average, dolomite forms about 10% of the non-clay mineral fraction.

Gross mineralogy An attempt was made to calculate the gross mineralogical composition of Kuwait dust fallout on the basis of the relative abundance of the various size fractions and their mineralogical composition. It was assumed that the mineralogical composition of the coarse silt fraction is similar to that of the medium and fine silt-size fractions and that of the clay fraction is similar to the very fine silt fraction. The average grain-size distribution of dust fallout collected at the eleven sampling stations in Kuwait is given in Table VI and the calculated average gross mineralogy is given in Table VII. Kuwait dust fallout is composed mainly of calcite (about 38% of the average composition). Quartz (27%) is the second most-dominant mineral grain. The average gross mineralogical composition of the dust fallout is closely related to the grain-size distribution pattern. For example, frequency percentages of calcite are T A B L E VI Average grain-size distribution of dust fallout in Kuwait Location

Size fraction weight (%) medium sand

fine sand

very fine sand

coarse silt

medium silt

fine silt

very fine silt

clay

Al-Abdalli U m m A1-Aish AI-Mutla AI-Sulaibikhat Kuwait City Salmiyah AI-Ahmadi AI-Fahaheel Mina Abdullah AI-Wafra AI-Nuwaisib

5.4 3.0 5.2 3.4 4.0 1.5 2.0 1.5 1.8 1.5 3.5

12.0 8.5 14.0 6.3 9.0 3.3 2.7 6.1 7.2 5.7 27.4

23.5 24.4 28.6 13.5 15.5 14.4 7.0 13.0 26.6 20.4 40.3

38.2 33.0 27.0 39.0 34.7 45.4 40.4 49.2 42.5 46.5 20.0

17.2 16.3 14.4 25.0 18.7 22.8 29.7 20.7 13.5 14.8 3.7

3.4 5.0 4.0 6.6 5.6 5.0 3.5 4.0 2.8 3.1 2.0

1.8 4.6 2.6 2.0 4.7 3.6 2.0 1.2 1.4 2.3 1.0

3.5 5.4 4.0 4.3 9.0 4.3 12.6 4.2 4.3 5.6 2.2

Average

3.0

9.3

20.6

37.8

17.4

4.0

2.5

5.4

274 ]'ABLE VII Calculated average gross mineralogy of dust fallout in Kuwait Mineral grains

Location

Average

Al-Abdalli AI-Mutla AI-Sulai- Kuwait City AI-Ahmadi AI-Wafra Al-Nuwaisib bikhat Calcite Quartz Feldspar Gypsum Rock fragments Chert Mica Dolomite Opaque Amphiboles Pyroxenes Epidotes Garnet Illite+ llkite-montmorillonite Palygorskite Kaolinite Chlorite

38.4 30.0 8.6 5.9 2.8 2.0 1,5 2.2 1.4 1.4 1.6 0.4 0.2

36.8 30.8 9.7 5.9 1.2 2.7 2.0 1.8 1.7 1.3 1.7 0.4 0.2

43.6 21.8 9.2 6.2 1.7 2.5 2.5 2.7 1.8 1.4 1.4 0.4 0.1

38.3 24.0 9.3 5.9 3.5 2.3 1.5 2.4 1.8 1.4 1.3 0.3 0.3

40.3 20.8 10.1 6.2 0.5 1.9 2.6 3.0 2.1 1.3 1.4 0.2 0.1

36.7 26.1 11.2 6.4 0.7 3.2 2.3 2.2 2.0 1.5 1.7 0.4 0.2

1.0 1.4 0.3 0.2

1.4 1.6 0.3 0.2

1.4 1.4 0.3 0.2

3.0 3.7 0.8

4.0 3.6 0.4

2.0 1.7 0.4 0.2

t

31.6 37.4 6.2 5.6 2.5 2.7 1.7 2.1 1.3 1.5 1.5 0.5 0.3

t 0.8 0.1 0.1

37.9 27.3 q.1 6,(1 1,8 2,5 2.0 2.3 2.0 1.4 1.5 0~3 0.2

2.0 2.1 0.4 0.1

80 70

60 .,,. 5 0

¢n40 30

20 ------

30

:34

38 Calcite

42

46

%

Fig. 3. Relationship between average relative frequency percentage of calcite and average weight percentage of silt-size fraction in dust fallout in Kuwait.

275 80 70

N 60 "o50 C

m 4() 30

Ill

20 20

25

30

35

40

Quartz %

Fig. 4. Relationship between average relative frequency percentage of quartz and average weight percentage of sand-size fraction in dust fallout in Kuwait. related to the abundance of the silt fraction, i.e., calcite increases with the increase of silt fraction (Fig. 3), and quartz is related to the relative abundance of sand fraction (Fig. 4). DISCUSSION AND CONCLUSIONS Mineralogical investigations of the dust fallout deposits in Kuwait revealed that they are composed mainly of calcite, quartz, gypsum and feldspars. Rock fragments, chert, mica, dolomite, heavy minerals and clay minerals are present in subordinate amounts and constitute less than 20% of the average gross mineralogical composition. The medium and fine sand fractions form about 12% of the dust fallout. These size fractions are composed chiefly of quartz, which constitutes about 77% of their average composition. Rock fragments, gypsum and feldspars form 12, 6 and 3.5% of the average composition, respectively. Biogenic fragments and ooids are present in trace amounts in some localities. Rock fragments are mostly represented by fragments of calcrete and gypcrete. Because sand particles (0.5-0.125 mm) are generally transported in saltation, the sand fraction in the dust fallout deposits is mostly derived from local pick up during relatively high wind velocity. The close similarity between the mineralogical composition of this size fraction and that of local surface deposits supports this argument. The very fine sand and coarse silt fractions (0.125-0.03 mm) of the studied dust fallout are mainly composed of calcite (50%) and quartz (25%) . Heavy minerals form about 9% by weight of these size fractions and are characterized by the abundance of dolomite, amphiboles and gypcrete. Kuwait's dust fallout is similar to that of Iraq with regard to the abundance of calcite, especially in the silt fraction (Kukal and Saadallah, 1970). The fabric and morphology of the dolomite grains in

276 the examined dust fallout revealed the presence of two types of aeolian dolomite, ancient detrital dolomite and sabkha rhombohedral protodolomite. The first type is most probably derived from ancient dolomite rocks exposed in the Gazirah area and northern part of the western desert of lraq. The second type could be derived from the ancient sabkhatised river terrace deposits that occupy large areas of the Mesopotamian flood plain and are rich in magnesium (Buringh, 1960). The heavymineral suite of the Kuwait dust fallout could be correlated with that of the Mesopotamian flood-plain deposits (Phillip, 1966; Ali, 1976). The clay-mineral fraction of the studied dust fallout is characterised by a relative abundance (45%) of palygorskite. It is suggested that palygorskite is authigenically developed in the ancient Mesopotamian flood-plain deposits and the Sabkha sediments in the northern area of the Arabian Gulf as a result of reaction between detrital clays (illite/montmorilionite) and hypersaline pore water (Grim, 1953; Bonython, 1956; Khalaf and Ala, 1980). Palygorskite was reported by Stoffers and Ross (1979) in the dust fallout collected at the northern part of the Arabian Gulf. They also found that palygorskite and carbonates decrease in frequency towards the south in the Gulf of Oman. The dust fallout in Kuwait could be described as quartzitic calcareous sandy silt. Based on their textural characteristics and mineralogical composition and taking into consideration the nature of the surface deposits and the climatological conditions of the northern Arabian Gulf region, it is suggested that Kuwait's dust fallout deposits are mostly derived from the dry Mesopotamian flood-plain deposits in southern Iraq. The average gross mineralogical composition of the dust fallout deposits is significantly affected by their grain-size distribution characteristics. Dust fallout significantly influences the sediment budget in the marine environment. On the basis of the measured amount of dust fallout over Kuwait, assuming uniform deposition over the entire area of the Northern Arabian Gulf, Foda et al. (1982), and Khalaf and AI-Hashash (1983) have estimated a rate of deposition of about 1 mm yr -l. A profound similarity was found between the mineralogical characteristics of the dust fallout and Kuwait Bay bottom sediments. The light-mineral suit of the fine material (the very fine sand and coarse silt) of both sediments is characterized by a high abundance of calcite (50% of the average composition). Quartz, feldspars and gypsum come next to calcite. They form about 25, 11 and 7%, respectively, of the average composition. In the heavy-mineral suit of Kuwait-Bay bottom sediments, the texture and shape of the dolomite grains are greatly similar to those in the dust fallout. A similarity was also found in the clay minerals where palygorskite was recorded as abundant in both sediments. Hence, it is clear that Kuwait Bay is highly affected by dust storms and the resulting fallout (Khalaf et al., 1982). The amount of the dust fallout is probably related to the nature of the surface deposits. The northern desert was found to have relatively less dust fallout than the southern desert because of the gravel stone pavements of the former and the lack of

277

such a protective cover in the latter. Hence, there is a slight difference in mineralogical composition between the two areas; calcite and dolomite are more abundant in the northern area and quartz is more frequent in the southern area. ACKNOWLEDGEMENT

The field and laboratory work for this paper was carried out within the dust fallout research project financially supported by a research grant from the Kuwait Institute for Scientific Research, the Kuwait Foundation for the Advancement of Sciences and the Ministry of Public Health. REFERENCES Ali, A.J., 1976. Heavy mineral provinces of the recent sediments of the Euphrates-Tigris Basin. J. Geol. Soc. Iraq, 10: 33-46. AI-Kulaib, A.A., 1977. Weather and climate of Kuwait. Kuwait Meteorological Department, Kuwait (unpublished report). Al-Naqib, K.M., 1967. Geology of the Arabian peninsula, southwestern Iraq. U.S. Geol. Surv., Prof. Pap., 560-G: 54 pp. Bonython, C.W., 1956. The salt of Lake Eire, its occurrence in Madigan Gulf and its possible origin. Trans. R. SOc. S. Aust., 1: 6-92. Brown, G., 1961. The X-ray identification and crystal structures of clay minerals. Mineralogical Society, Britain, 544 pp. Buringh, P., 1960. The Soils of Iraq. Ministry of Agriculture, Baghdad, 313 pp. Carver, R.E., 1971. Procedures in Sedimentary Petrology. Wiley-Interscience, New York, N.Y., 653 pp. Foda, M.A. Khalaf, F.I. and Al-Kadi, A., 1982. Estimation of dust fallout rates in the Arabian Gulf. EUROMECH 156, lstanbul. Folk, R.L., 1974. Petrology of Sedimentary Rocks. Hemphill, Austin, Texas, 182 pp. Goudie, A.S., 1978. Dust storms and their geomorphological implications. J. Arid Environ., 1: 291-310. Grim, R.E., 1953. Clay Mineralogy. McGraw-Hill, New York, N.Y., 348 pp. Idso, S.B., 1976. Dust storms. Sci. Am., 2(4): 108-111,113-114. Khalaf, F.I. and Ala, M., ]980. Mineralogy of tidal flat muddy sediments of Kuwait, Arabian Gulf. Mar. Geol., 35: 331-342. Khalaf, F.I. and AI-Hashash, M.K., 1983. Aeolian sedimentation in the northwestern part of the Arabian Gulf. J. Arid Environ., 6: 319-332. Khalaf, F.I., Kadib, A., Gharib, I., AI-Hashash, M.K., AI-Saleh, S., AI-Kadi, A., Desouki, M., Al-Omran, L., AI-Ansari, L., Al-huti, F. and AI-Mudhian, L., 1980. Dust Fallout in Kuwait, 3 vols. KISR/PPll08/EES-RF-R/8016, Kuwait Institute for Scientific Research, Kuwait, 214 pp. Khalaf, F.I., Al-Ghadban, A., A1-Saleh, S. and A1-Omran, L., 1982. Sedimentology and mineralogy of Kuwait Bay bottom sediments, Kuwait-Arabian Gulf. Mar. Geol., 46: 71-99. Kukal, Z. and Saadallah, A., 1970. Composition and rate of deposition of recent dust storm sediments in Iraq. Cas. Promineral. Geol., 15, 3: 227-230. Macfayden, W.A., 1938. Water supplies in Iraq. Geological Department, Ministry of Economy and Communication, Iraq, 206 pp. Mitchell, R.C., 1956. Aspects g~oiogiques du desert occidental de rlrak. Bull. Soc. Geol. Fr., 6th S~rie, pp. 391-406. Phillip, G., 1966. Mineralogy of Recent Sediments of the Tigris and Euphrates Rivers and some other detrital deposits. Bull. Coll. Sci., Univ. Baghdad, 9: 159-173.

278 Picha, F., 1978. Depositional and diagenetic history of Pleistocene and Holocene oolitic sediments and sabkha in Kuwait, Pers,ian Gulf. Sedimentology, 25: 427-450. Schultz, E.F., 1964. Quantitative interpretation of mineralogical composition from X-ray and chemical data for the Pierre shale. U.S. Geol. Surv., Prof. Pap., 391C: 1-39. Shaw, H.F., 1971. The clay mineralogy of recent sediments in the Wash, Eastern England. Ph.D. diss., University of London, London. Shinn, E.A., 1964. Recent dolomite, Sugar It,oaf Key. Guidebook for field Trip No. 1. Geological Society of America Convention 1964, New York, N.Y., pp. 62-67. Stoffers, P. and Ross, D.A., 1979. Late Pleistocene and Holocene sedimentation in the Persian Gulf-Gulf of Oman. Sediment. Geol., 23: 181-208.