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Recent pelletoidal carbonate sediments off Alexandria, Egypt
Marine Geology, 34 (1980) M1--M8 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
M1
Letter Section RECENT PELLETOIDAL CARBONATE SEDIMENTS O F F ALEXANDRIA, EGYPT*
PETER STOFFERS I,COLIN P. S U M M E R H A Y E S ~I"and JANUSZ DOMINIK I 11nstitutf~r Sedimentforschung, UniversitgtHeidelberg (F.R.G.) 2Woods Hole Oceanographic Institution, Woods Hole, Mass. (U.S.A.) (Received July 18, 1979; accepted August 21, 1979)
ABSTRACT Stoffers, P., Summerhayes, C.P. and Dominik, J., 1980. Recent pelletoidal carbonate sediments off Alexandria, Egypt. Mar. Geol., 34: M1--M8. Sand-sized pellets of aragonite from the continental shelf off Alexandria, Egypt, are modern lithified fecal pellets. They have not been derived from the pseudo-oolitic coastal limestones, nor are they ooids. We believe that they are derived from fresh aragonitic mud with which they are intimately associated. Aragonitic mud is much more common in this area than previous work had suggested.
INTRODUCTION Oolitic and pelletoidal sands occur nearshore along parts of the Mediterranean Coast of North Africa (Hilmy, 1951; Shukry et al., 1955; Lucas, 1955; Fabricius and Klingele, 1970; Emelyanov, 1972). The ooids are assumed to be Tertiary or Quaternary, and the single available radiocarbon date shows that some are early Holocene (Fabricius et al., 1970). On the continental shelf off the Alexandria Coast of Egypt, where sediments are rich in carbonate, oolitic sands have been reported by E1Wakeel et al. (1974). According to E1 Sayed (1974) these Sediments, like those of the beaches in the area, are pseudo-oolitic, their constituents having been eroded from the pseudo-oolitic Tertiary limestones of the nearby coast (Hilmy, 1951). To resolve the confusion about the nature of these sand-sized particles, we studied grains extracted from carbonate sediments that we collected on the continental shelf off Alexandria during " C h a i n " cruise 119, in 1975 (Fig. 1). PELLET DISTRIBUTION, AGE AND CHARACTER Alexandria shelf sediments are highly calcareous, mostly containing more than 7 5 % CaCO3 (Fig. 2a). According to Summerhayes et al. (1977) the *Woods Hole Oceanographic Institution Contribution No. 4395. 1"Present address: Exxon Production Research Company, Houston, Texas (U.S.A.).
M2 29030 ' E
I
50°00 I
I
30°50 i
1
SAMPLE LOCATIONS 32o00 '
N
f j S
~.~
/
31"30
•
.......
II ~i~
E
~i-
j
/' -
29"30'
•
~_10
~
Mouth
..........
30•00 '
30o30 '
Fig. 1. Location map of sample stations.
sand fraction of these sediments contains a varied mixture of the whole and fragmented remains of many different organisms (mainly mollusks, echinoids, bryozoans, coralline algae, benthonic foraminifera, planktonic foraminifera, and pteropods). Noteworthy are the abundant pteropods present which are not at all c o m m o n elsewhere in shelf sediments. On the middle shelf at depths of 25--40 fathoms, these skeletal carbonates are mixed with carbonate pellets of medium to fine sand size, that dominate the sand fraction in some samples (Fig. 2b). Samples with a pelletoidal carbonate assemblage are usually muddy sand containing 6--60% of silt and clay. The carbonate content of the clay fraction is about 70%. The predominant c o m p o n e n t is aragonite (Table I). The aragonite consists of 1--2 ~m long needles as revealed by SEM (Fig. 3a). The pellets are mainly ellipsoidal (Fig. 3b) although some cylindrical grains with rounded ends are also present. The pellets range in length from 0.2 to I m m but are usually 0.3--0. 5 m m in length, with diameters between 0.1 and 0.3 ram. Colours are generally greyish white. In thin sections the opaque nature of the grains can be seen (Fig. 3e). Each pellet c o n m t s of an irreinflar aggregate of micritic carbonate with none of the internal structures typical of ooids, such as an obvious nucleus. The carbonate mineralogy of characteristic pellets is given in Table I. As can be seen the pellets are aragonitic with only small amounts of high-magnesian calcite and calcite. Analyses of the pellets by scanning electron microscopy show that very small aragonite needles comprise the matrix of the pellets. The needles are clustered around numerous pores, 1--3/~m in diameter (Fig. 3d). The inter-
M3 2~30' E
I
~
[
30~0' I
i
i
30"30' i
•
o-5
- [~
~
N
mOllusclecl~nold/ benlhl¢ forommlfero mollusc lolcJOl troflSl~iC
moeri
IJ:~l rnoilusc / B~'yozoor~ - i i
- ~
Z,I"ZIO'
mollusc/plonkfonic foromm~fero fronsiho pelleto~d
blodetrltol
51°30
~
~ 30"00'
Mouth 30°~0 '
29"30' E
30*(X)'
3(T30'
Fig. 2. a. Distribution of calcium carbonate in sediments from the continental shelf off Alexandria. b. Distribution of different assemblages of carbonate organism in the sand fraction of sediments after Summerhayes and Marks (1975).
granular cement in the pore space is composed of larger aragonite needles (Fig. 3e, f). The relationship between the composition of pellets and fine-grained sediments is demonstrated best by the strontium content which is about 1% in both sediment types (Table I). The unconsolidated sediments in which the pellets occur contain substantial amounts of organic matter (0.5--1.1% org. C). The organic carbon content of the pellets is around 1.3%. Almost none of the pellets are fragmented, which suggests that they are : not allochthonous extraclasts. This is confirmed by radio-carbon dates of separated pellets which show that the pellets in the surface sediments are of recent age (Table II). The pellets are n o t restricted to the surface sediments only. They are present throughout b o x core Kast. 5. For the b o t t o m of the core a radio-carbon age of 2,060 + 50 years B.P. was found indicating that continuous pellet sedimentation has occurred on the shelf off Alexandria since 2,000 years at least. DISCUSSION Pellets from pelletoidal carbonate sediments on the continental shelf off Alexandria are aragonitic and are forming at present. From the shape of the pelletoids and their relatively high organic carbon content we infer that they are likely to be fecal pellets such as those clearly illustrated by Koonicker and P u n y (1957). Although identification of the pellet~producing organisms is difficult, the pellets are probably produced by mollusks, crustacea and
69
87
CHN 119 GR 41 0--'I 0 cm 250--354 um sep. pellets
84
Total carbonate content (%)
CHN 119 KAST 5 0--2 cm < 2 um
CHN 119 KAST 5 0 - - 2 cm 250--354 #m sep. pellets
Sample
95
96
96
5
2
4
2
tr
Carbonate mineralogy arago nite/Mg-calcite/calcite = 100%
0.35
0.81
0.34
0.84 (0.96)
0.67 (0.99)
0.83 (0.99)
Trace elements Mg Sr (%) (%)
Mineralogy and elemental composition of characteristic pellet and clay samples Data in parentheses refer to 100% carbonate
TABLE I
1.3
org.C (%)
0.06
PO, (%)
Fe (ppm)
0.06 3900
N (%)
50
Mn (ppm)
10
Zn (ppm)
M5
Fig. 3. 84 SEM picture of the clay fraction (< 2 ~m) of sample KAST 5 0--1 cm showing abundant aragonite needles. b. Pelletoidal carbonate sand. Sample KAST 5 0--1 cm. c. Reflected light photomicrograph of pelletoids sample GRAB 41. d. SEM picture of the surface of a pelletoid revealing larger pores. e+f. SEM pictures of pore space within a pelletoid showing larger aragonite crystals.
0-10
0-1
104--108
C H N 119 KAST 5
CHN 1 1 9 KAST 5
(cm)
Depth interval
CHN 1 1 9 G R 41
Sample No.
31°16.0'N
31°16.0'N
31°37.1'N
Latitude
14C d a t e s o f pellets a n d b u l k s e d i m e n t s
T A B L E II
29°44.9'E
29°44.9'E
30°31.7'E
Longitude
73.5 ± 0.4
97.4 ± 0.4
87.6 ± 0.6
" C c o n t e n t (%)
2 0 6 0 ± 50
recent
6 5 0 ± 55
Age (years B.P.)
separated pellets 250--354 ~m separated pellets 250--354 ~m bulk sediment
H 4520-3733 H 5577-5107
Comment
H 5460-5016
Source l ' C Lab. Umweltphysik
M7 worms. We assume that bacterial decomposition of the organic material within the pellets led to intergranular lithification and hardening of the pellets, a process discussed in detail by Purdy (1963, 1968). An interesting aspect is the accumulation of aragonitic needles (1--2 pm long) on the shelf off Alexandria. Aragonite needle muds are known from the Andros Islands, Bahamas (e.g. Cloud, 1962), Florida Bay (e.g. Miiller and Milller, 1967), the Persian Gulf (e.g. Wells and Illing, 1963), to mention the most important deposits. In many cases an organic source is obvious. Desintegrated codiacean algae or abraded mollusks and foraminifera are often the major sediment source; however, the aragonite can also be deposited by inorganic precipitation in hypersaline environments as suggested from the Persian Gulf (Kinsman, 1969). Lucas (1955) mentioned whitings occurring on the Alexandrian shelf which are caused by suspended matter. The aragonitic Alexandrian shelf muds have strontium values of more than 0.9% Sr which indicates that the muds are probably not products of shell desintegration, as mollusks, especially pteropods, have rather low St-contents ranging from about 0.08 to 0.4% Sr. Also codiacean algae which commonly contain 0.7 to 0.9% Sr are scarce in the study area. Thus the high strontium content of the aragonite needles would suggest a possible inorganic precipitation. The mode of precipitation, however, is not understood at present, especially as the hydrographic and climatic conditions on the Alexandrian shelf are not comparable to the hypersaline environment in the Persian Gulf area. ACKNOWLEDGEMENTS The ~4C age determinations were performed by the Institut of Umwelt~ physik, University of Heidelberg. The manuscript has benefited from the criticism of Dr. R.G.C. Bathurst and Dr. J.D. MiUiman, which is gratefully appreciated. "Chain" cruise 119 was part of a joint U.S.A.--Egyptian study of the Eastern Mediterranean funded by the National Sciences Foundation through grants GA 13212 and OIP 75-02516 to the Woods Hole Oceanographic Institution; part of this work was funded by the "Deutsche Forschungsgemeinschaft" (DFG). REFERENCES Cloud, P.E., 1962. Environment of calcium carbonate deposition west of Andros Island, Bahamas. U.S. Geol. Surv. Prof. Pap., 3 5 0 : 1 3 8 pp. EI-Sayed, M.IC, 1974. Littoral and Shallow Water Deposits of the Continental Shelf Area of Egypt, off Alexandria Thesis, University of Alexandria, 15 pp. (unpublished). El-Wakeel, S.IC, Abdon, H.F. and Mohamed, M.A., 1974. Texture and distribution of recent marine sediments of the continental shelf off the Nile Delta. J. Geol. Soc. Iraq, 7: 15--34.
M8 Emelyanov,. E.M., 1972. Principal types of recent bottom sediments in the Mediterranean Sea: their mineralogy and geochemistry. In: D.J. Stanley (Editor), The Mediterranean Sea : A Natural Sedimentation Laboratory. Dowen, Hutchinson and Ross, Stroudsburg, Pa., pp. 335--386. Fabricius, F.H., Berdau, D. and Mfinnich, K.O., 1970. Early Holocene ooids in modern littoral sands reworked from a coastal terrace, southern Tunisia. Science, 169:757--760. Fabricius, F.H. and Klingele, H., 1970. Ultrastrukturen yon Ooiden und Oolithen: Zur Genese und Diagenese Quart~rer Flachwasserkarbonate des Mittelmeeres. Verh. Geol. Bundesanst., 4: 595--617. Hilmy, M.W., 1951. Beach sands of the Mediterranean coast of Egypt. J. Sediment. Petrol., 21: 109--120. Kinsman, D.J.J., 1969. Interpretation of Sr 2÷ concentrations in carbonate minerals and rocks. J. Sediment. Petrol., 39: 486--508. Kornicker, L.S. and Purdy, E.G., 1957. A Bahamian faecal-pellet sediment. J. Sediment. Petrol., 27: 126--128. Lucas, G., 1955. Oolithes marines actuelles et calcaires oolithiques r~cents sur le revage african de la m~diterran~e orientale (Egypte et le Tun~sie sud). Bull. Stn. Oc~anogr., Salmmb5 (Tun~sie), 52: 19--38. M{lller, G. and Mtiller, J., 1967. Mineralogisch-sedimentpetrographische und chemische Untersuchungen an einem Bank-Sediment (Cross Bank) des Florida Bay, USA. Neues Jahrb. Mineral. Abhandl., 106: 257--286. Purdy, E.G., 1963. Recent calcium carbonate facies of the Great Bahama Bank. 1. Petrography and reaction groups; 2. Sedimentary facies. J. Geol., 71: 334--335; 472--497. Purdy, E.G., 1968. Carbonate diagenesis: An environmental survey. Geol. Rom., 7: 183-228. Shukry, N.M., Philip, G. and Said, R., 1955. The geology of the Mediterranean coast between Rosetta and Bardia. Part I, Recent sediments, mechanical analysis and mineral composition. Part If,Pleistocene sediments and geomorphology. Part Ill,Pleistocene sediments, mineral analysis. Bull. Inst. Egypt, 37: 377--386; 395--427. Summerhayes, C.P. and Marks, N., 1975. Nile Delta. Nature, evolution, and collapse of continental shelf sediment system. A preliminary report. Proc. U N E S C O , Sere. Nile Delta Sed., Alexandria, October 25--29, 1975. Summerhayes, C.P., Sestini,G., Misdorp, R. and Marks, N., 1978. Nile Delta: nature and evolution of continental shelf sediments. Mar. Geol., 27 : 43--65. Wells, A.J. and Illing,L.V., 1963. Present-day precipitation of calcium carbonate in the Persian Gulf. In: L.M.J.U. van Straaten (Editor), Deltaic and Shallow Marine Deposits. Developments in Sedimentology, 1 : Elsevier, Amsterdam, pp. 429--435.
M1
Letter Section RECENT PELLETOIDAL CARBONATE SEDIMENTS O F F ALEXANDRIA, EGYPT*
PETER STOFFERS I,COLIN P. S U M M E R H A Y E S ~I"and JANUSZ DOMINIK I 11nstitutf~r Sedimentforschung, UniversitgtHeidelberg (F.R.G.) 2Woods Hole Oceanographic Institution, Woods Hole, Mass. (U.S.A.) (Received July 18, 1979; accepted August 21, 1979)
ABSTRACT Stoffers, P., Summerhayes, C.P. and Dominik, J., 1980. Recent pelletoidal carbonate sediments off Alexandria, Egypt. Mar. Geol., 34: M1--M8. Sand-sized pellets of aragonite from the continental shelf off Alexandria, Egypt, are modern lithified fecal pellets. They have not been derived from the pseudo-oolitic coastal limestones, nor are they ooids. We believe that they are derived from fresh aragonitic mud with which they are intimately associated. Aragonitic mud is much more common in this area than previous work had suggested.
INTRODUCTION Oolitic and pelletoidal sands occur nearshore along parts of the Mediterranean Coast of North Africa (Hilmy, 1951; Shukry et al., 1955; Lucas, 1955; Fabricius and Klingele, 1970; Emelyanov, 1972). The ooids are assumed to be Tertiary or Quaternary, and the single available radiocarbon date shows that some are early Holocene (Fabricius et al., 1970). On the continental shelf off the Alexandria Coast of Egypt, where sediments are rich in carbonate, oolitic sands have been reported by E1Wakeel et al. (1974). According to E1 Sayed (1974) these Sediments, like those of the beaches in the area, are pseudo-oolitic, their constituents having been eroded from the pseudo-oolitic Tertiary limestones of the nearby coast (Hilmy, 1951). To resolve the confusion about the nature of these sand-sized particles, we studied grains extracted from carbonate sediments that we collected on the continental shelf off Alexandria during " C h a i n " cruise 119, in 1975 (Fig. 1). PELLET DISTRIBUTION, AGE AND CHARACTER Alexandria shelf sediments are highly calcareous, mostly containing more than 7 5 % CaCO3 (Fig. 2a). According to Summerhayes et al. (1977) the *Woods Hole Oceanographic Institution Contribution No. 4395. 1"Present address: Exxon Production Research Company, Houston, Texas (U.S.A.).
M2 29030 ' E
I
50°00 I
I
30°50 i
1
SAMPLE LOCATIONS 32o00 '
N
f j S
~.~
/
31"30
•
.......
II ~i~
E
~i-
j
/' -
29"30'
•
~_10
~
Mouth
..........
30•00 '
30o30 '
Fig. 1. Location map of sample stations.
sand fraction of these sediments contains a varied mixture of the whole and fragmented remains of many different organisms (mainly mollusks, echinoids, bryozoans, coralline algae, benthonic foraminifera, planktonic foraminifera, and pteropods). Noteworthy are the abundant pteropods present which are not at all c o m m o n elsewhere in shelf sediments. On the middle shelf at depths of 25--40 fathoms, these skeletal carbonates are mixed with carbonate pellets of medium to fine sand size, that dominate the sand fraction in some samples (Fig. 2b). Samples with a pelletoidal carbonate assemblage are usually muddy sand containing 6--60% of silt and clay. The carbonate content of the clay fraction is about 70%. The predominant c o m p o n e n t is aragonite (Table I). The aragonite consists of 1--2 ~m long needles as revealed by SEM (Fig. 3a). The pellets are mainly ellipsoidal (Fig. 3b) although some cylindrical grains with rounded ends are also present. The pellets range in length from 0.2 to I m m but are usually 0.3--0. 5 m m in length, with diameters between 0.1 and 0.3 ram. Colours are generally greyish white. In thin sections the opaque nature of the grains can be seen (Fig. 3e). Each pellet c o n m t s of an irreinflar aggregate of micritic carbonate with none of the internal structures typical of ooids, such as an obvious nucleus. The carbonate mineralogy of characteristic pellets is given in Table I. As can be seen the pellets are aragonitic with only small amounts of high-magnesian calcite and calcite. Analyses of the pellets by scanning electron microscopy show that very small aragonite needles comprise the matrix of the pellets. The needles are clustered around numerous pores, 1--3/~m in diameter (Fig. 3d). The inter-
M3 2~30' E
I
~
[
30~0' I
i
i
30"30' i
•
o-5
- [~
~
N
mOllusclecl~nold/ benlhl¢ forommlfero mollusc lolcJOl troflSl~iC
moeri
IJ:~l rnoilusc / B~'yozoor~ - i i
- ~
Z,I"ZIO'
mollusc/plonkfonic foromm~fero fronsiho pelleto~d
blodetrltol
51°30
~
~ 30"00'
Mouth 30°~0 '
29"30' E
30*(X)'
3(T30'
Fig. 2. a. Distribution of calcium carbonate in sediments from the continental shelf off Alexandria. b. Distribution of different assemblages of carbonate organism in the sand fraction of sediments after Summerhayes and Marks (1975).
granular cement in the pore space is composed of larger aragonite needles (Fig. 3e, f). The relationship between the composition of pellets and fine-grained sediments is demonstrated best by the strontium content which is about 1% in both sediment types (Table I). The unconsolidated sediments in which the pellets occur contain substantial amounts of organic matter (0.5--1.1% org. C). The organic carbon content of the pellets is around 1.3%. Almost none of the pellets are fragmented, which suggests that they are : not allochthonous extraclasts. This is confirmed by radio-carbon dates of separated pellets which show that the pellets in the surface sediments are of recent age (Table II). The pellets are n o t restricted to the surface sediments only. They are present throughout b o x core Kast. 5. For the b o t t o m of the core a radio-carbon age of 2,060 + 50 years B.P. was found indicating that continuous pellet sedimentation has occurred on the shelf off Alexandria since 2,000 years at least. DISCUSSION Pellets from pelletoidal carbonate sediments on the continental shelf off Alexandria are aragonitic and are forming at present. From the shape of the pelletoids and their relatively high organic carbon content we infer that they are likely to be fecal pellets such as those clearly illustrated by Koonicker and P u n y (1957). Although identification of the pellet~producing organisms is difficult, the pellets are probably produced by mollusks, crustacea and
69
87
CHN 119 GR 41 0--'I 0 cm 250--354 um sep. pellets
84
Total carbonate content (%)
CHN 119 KAST 5 0--2 cm < 2 um
CHN 119 KAST 5 0 - - 2 cm 250--354 #m sep. pellets
Sample
95
96
96
5
2
4
2
tr
Carbonate mineralogy arago nite/Mg-calcite/calcite = 100%
0.35
0.81
0.34
0.84 (0.96)
0.67 (0.99)
0.83 (0.99)
Trace elements Mg Sr (%) (%)
Mineralogy and elemental composition of characteristic pellet and clay samples Data in parentheses refer to 100% carbonate
TABLE I
1.3
org.C (%)
0.06
PO, (%)
Fe (ppm)
0.06 3900
N (%)
50
Mn (ppm)
10
Zn (ppm)
M5
Fig. 3. 84 SEM picture of the clay fraction (< 2 ~m) of sample KAST 5 0--1 cm showing abundant aragonite needles. b. Pelletoidal carbonate sand. Sample KAST 5 0--1 cm. c. Reflected light photomicrograph of pelletoids sample GRAB 41. d. SEM picture of the surface of a pelletoid revealing larger pores. e+f. SEM pictures of pore space within a pelletoid showing larger aragonite crystals.
0-10
0-1
104--108
C H N 119 KAST 5
CHN 1 1 9 KAST 5
(cm)
Depth interval
CHN 1 1 9 G R 41
Sample No.
31°16.0'N
31°16.0'N
31°37.1'N
Latitude
14C d a t e s o f pellets a n d b u l k s e d i m e n t s
T A B L E II
29°44.9'E
29°44.9'E
30°31.7'E
Longitude
73.5 ± 0.4
97.4 ± 0.4
87.6 ± 0.6
" C c o n t e n t (%)
2 0 6 0 ± 50
recent
6 5 0 ± 55
Age (years B.P.)
separated pellets 250--354 ~m separated pellets 250--354 ~m bulk sediment
H 4520-3733 H 5577-5107
Comment
H 5460-5016
Source l ' C Lab. Umweltphysik
M7 worms. We assume that bacterial decomposition of the organic material within the pellets led to intergranular lithification and hardening of the pellets, a process discussed in detail by Purdy (1963, 1968). An interesting aspect is the accumulation of aragonitic needles (1--2 pm long) on the shelf off Alexandria. Aragonite needle muds are known from the Andros Islands, Bahamas (e.g. Cloud, 1962), Florida Bay (e.g. Miiller and Milller, 1967), the Persian Gulf (e.g. Wells and Illing, 1963), to mention the most important deposits. In many cases an organic source is obvious. Desintegrated codiacean algae or abraded mollusks and foraminifera are often the major sediment source; however, the aragonite can also be deposited by inorganic precipitation in hypersaline environments as suggested from the Persian Gulf (Kinsman, 1969). Lucas (1955) mentioned whitings occurring on the Alexandrian shelf which are caused by suspended matter. The aragonitic Alexandrian shelf muds have strontium values of more than 0.9% Sr which indicates that the muds are probably not products of shell desintegration, as mollusks, especially pteropods, have rather low St-contents ranging from about 0.08 to 0.4% Sr. Also codiacean algae which commonly contain 0.7 to 0.9% Sr are scarce in the study area. Thus the high strontium content of the aragonite needles would suggest a possible inorganic precipitation. The mode of precipitation, however, is not understood at present, especially as the hydrographic and climatic conditions on the Alexandrian shelf are not comparable to the hypersaline environment in the Persian Gulf area. ACKNOWLEDGEMENTS The ~4C age determinations were performed by the Institut of Umwelt~ physik, University of Heidelberg. The manuscript has benefited from the criticism of Dr. R.G.C. Bathurst and Dr. J.D. MiUiman, which is gratefully appreciated. "Chain" cruise 119 was part of a joint U.S.A.--Egyptian study of the Eastern Mediterranean funded by the National Sciences Foundation through grants GA 13212 and OIP 75-02516 to the Woods Hole Oceanographic Institution; part of this work was funded by the "Deutsche Forschungsgemeinschaft" (DFG). REFERENCES Cloud, P.E., 1962. Environment of calcium carbonate deposition west of Andros Island, Bahamas. U.S. Geol. Surv. Prof. Pap., 3 5 0 : 1 3 8 pp. EI-Sayed, M.IC, 1974. Littoral and Shallow Water Deposits of the Continental Shelf Area of Egypt, off Alexandria Thesis, University of Alexandria, 15 pp. (unpublished). El-Wakeel, S.IC, Abdon, H.F. and Mohamed, M.A., 1974. Texture and distribution of recent marine sediments of the continental shelf off the Nile Delta. J. Geol. Soc. Iraq, 7: 15--34.
M8 Emelyanov,. E.M., 1972. Principal types of recent bottom sediments in the Mediterranean Sea: their mineralogy and geochemistry. In: D.J. Stanley (Editor), The Mediterranean Sea : A Natural Sedimentation Laboratory. Dowen, Hutchinson and Ross, Stroudsburg, Pa., pp. 335--386. Fabricius, F.H., Berdau, D. and Mfinnich, K.O., 1970. Early Holocene ooids in modern littoral sands reworked from a coastal terrace, southern Tunisia. Science, 169:757--760. Fabricius, F.H. and Klingele, H., 1970. Ultrastrukturen yon Ooiden und Oolithen: Zur Genese und Diagenese Quart~rer Flachwasserkarbonate des Mittelmeeres. Verh. Geol. Bundesanst., 4: 595--617. Hilmy, M.W., 1951. Beach sands of the Mediterranean coast of Egypt. J. Sediment. Petrol., 21: 109--120. Kinsman, D.J.J., 1969. Interpretation of Sr 2÷ concentrations in carbonate minerals and rocks. J. Sediment. Petrol., 39: 486--508. Kornicker, L.S. and Purdy, E.G., 1957. A Bahamian faecal-pellet sediment. J. Sediment. Petrol., 27: 126--128. Lucas, G., 1955. Oolithes marines actuelles et calcaires oolithiques r~cents sur le revage african de la m~diterran~e orientale (Egypte et le Tun~sie sud). Bull. Stn. Oc~anogr., Salmmb5 (Tun~sie), 52: 19--38. M{lller, G. and Mtiller, J., 1967. Mineralogisch-sedimentpetrographische und chemische Untersuchungen an einem Bank-Sediment (Cross Bank) des Florida Bay, USA. Neues Jahrb. Mineral. Abhandl., 106: 257--286. Purdy, E.G., 1963. Recent calcium carbonate facies of the Great Bahama Bank. 1. Petrography and reaction groups; 2. Sedimentary facies. J. Geol., 71: 334--335; 472--497. Purdy, E.G., 1968. Carbonate diagenesis: An environmental survey. Geol. Rom., 7: 183-228. Shukry, N.M., Philip, G. and Said, R., 1955. The geology of the Mediterranean coast between Rosetta and Bardia. Part I, Recent sediments, mechanical analysis and mineral composition. Part If,Pleistocene sediments and geomorphology. Part Ill,Pleistocene sediments, mineral analysis. Bull. Inst. Egypt, 37: 377--386; 395--427. Summerhayes, C.P. and Marks, N., 1975. Nile Delta. Nature, evolution, and collapse of continental shelf sediment system. A preliminary report. Proc. U N E S C O , Sere. Nile Delta Sed., Alexandria, October 25--29, 1975. Summerhayes, C.P., Sestini,G., Misdorp, R. and Marks, N., 1978. Nile Delta: nature and evolution of continental shelf sediments. Mar. Geol., 27 : 43--65. Wells, A.J. and Illing,L.V., 1963. Present-day precipitation of calcium carbonate in the Persian Gulf. In: L.M.J.U. van Straaten (Editor), Deltaic and Shallow Marine Deposits. Developments in Sedimentology, 1 : Elsevier, Amsterdam, pp. 429--435.