Mineralogy and Geochemistry of the Mesozoic

Mineralogy and Geochemistry of the Mesozoic- Tertiary Subsurface Sediments along BardawilLake, North Sinai, Egypt

A.M. GHEITB , M.E. EL,SHERBINI and R. HASSAB ALLAH*

* Faculty of Marine Science,

King Abdulaziz University, leddah, Saudi Arabia, and Faculty of Science, Geology Department,

Mansoura University, Egypt

ABsTRAcr. An attempt is made in the present work to elucidate the mineralogy and geochemistry of the subsurface sediments in three deep wells drilled around lake Bartlawil namely:Malha-1,EI-Mazar-1 and Bar- dawil-1-1 in north Sinai.

X-ray diffraction analysis has been used to determine the bulk mineral content in 51 raw powdered samples of shale and 1imestone. Itwasiound that kaolinite is dominant in Jurassic and Cretaceous deposits of EI-Mazar"

well and in the Cretacequs deposits of Malha well. They have been formed during a period with warm climate and lowered sea level. While illite seems to be dominant in Jurassic deposits of Malha well indicating a tectonically unstable active area. The Oligocene, Miocene and Pliocene deposits of EI- Mazar and Bardawil wells are characterized by dominance of montmorillo- nite and subordinate kaolinite, chlorite and illite revealing a humid climate with little changes. Source rocks and paleogeography are discussed.

X-ray fluorescence analysis has been carried out on the same raw samples of shale and limestone in order to determine the trace element content. The stratigraphic distribution pfthe trace element proved that Ba, Zr, Sr and Pb occur in higher concentrations in Jurassic and Cretaceous deposits of El- Mazar well, while Co;Cr, Cu, V, Pb and Ce are enriched in Plioceneatld Pleistocene sediments. Seven geochemical stratigraphic units (chemozones) are distinguished in El-Mazar well.

Introduction

From .latitude 300 to the north, alternating faulted domes, anticlines and synclines known as the Syrian arc, form a contrasting topography of low alluvial plains and

Mineralogy and Geochemistry of the Mesozoic- Tertiary. 95

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TABLE 1. Significant reflections used in the identification of bulk minerals in the studied samples JCPDS (1974)

§ASTM Identified

minerals

20 (001) Reft Bulk

minerals ^d(AO)

7,12

8,75 24,87 25,15

12.410.1 3.58 3.54

APX-9 2-462

§14 -0164 ASTM

§7 -0171 ASTM Montmorillonite

Illite Kaolinite

Chlorite Clay

minerals

3.34 3.27 3.21

5 -490

§10 -0479 ASTM

§9 -0456ASTM

26,86 27.49 27.88 Quartz

K-feldspar Plagioclase feldspar Detrital

minerals

3.04 2.89

5 -586

11-'78 Calcite

Dolomite

39.37 30.9

Carbonate minerals

.7.56 3.49 3.44

6 -,46 6-226 5"'- 448 Gypsum

Anhydrite Barite

11.70 25.52 25.89 Sulphate

2.84 2.71

5-628 6- 7.10

31.7

33.1..

Halite Pyrite

!Joint Committee on Powder Diffraction Stand'lrd!

American Society for Testing and Materials.

Geochemical analysis has been carried out on the whole rock powdered materials of 43 samples of shale and limestone composition. The common trace elementsBa, Sr, Zr, Cu, Zn, Ni, Co, Cr,V, Rb,Ga, Pb, Y, and Cehave been determined using the X-ray fluorescence techniqu~... .In addition, the relative percentage of organic matter in the rock powdered materials of El,.Mazar-l well has been determined by addingH2O2 until reaction ceased to remov~ organic matter.

Distribution and Significance of Bulk Minerals

The bulk mineral composition determined in peycentage for fifty onesamplescho~

sen from the three wel.lS; Malha~l, EI-Mazar-l. and Bardawil-l has been deter- mined. The stratigraphical variation in mineralogical composition is illustrated in Fig. 3,4 aDdS.

Clay minerals, detrit~l cpnstituents{quartz and feldspar), carb<:>nate minerals, sul~

phate minerals aQdpyrite are the bulk constituents found in the subsurface sedi:'ments in north Sinai. The principal clay minetalcomponents are montmorilloniteJ, kaolinite, illite and chlorite in decreasing order of abundance. j The carbonate minerals are here represented by calcite which dominated over dolomite, while the sulphate minerals include scarce amounts of anhydrite, gypsum

Mineralogy and Geochemistry of the Mesozoic-Tertiary. 99

and barite. Generally, the distribution of these components show lateral and vertical variation.

The type of the source rocks; climate and the paleogeography are discussed.

1 -Stratigraphic Variation in Bulk Mineralogy of EI-Mazar-l Well

EI-Mazar-1 well having an intermediate position, possibly represents a transi- tional stage between the other two wells; Malha-1 and Bardawil-1. A great number of samples were available and investigated from it. Thirty five samples of mudstone, marl and/or limestone have been analysed by X-ray diffraction. The stratigraphic variation of mineral constituents with depth is shown in Fig. 3.

In general, the clay mineralogy varied vertically with depth from Pre-Cretaceous to Quaternary. Montmorillonite is found to be the most abundant clay mineral con- stituents with minor content of kaolinite, illite and trace of chlorite. Kaolinite domi- nates in the Jurassic and Cretaceous sediments. The carbonate minerals represented by calcite which dominates over dolomite show cyclic variation with depth. Barite is very common among the mineral component of Jurassic and Cretaceous deposits.

Several transgressive and regressive cycles can be traced through late Jurassic, late Cretaceous, Eocene and middle Miocene.

The Jurassic-Cretaceous boundary here, is marked by a distinct change of carbo- nate minerals which decrease upward with increase of quartz and feldspar con- stituents. The Miocene sediments are characterised by the association of clay miner- als and carbonate minerals. The clay minerals are dominated by montmorillonite with subordinate kaolinite. At the end of the Miocene cycle it is clearly observed that there is a new association of minerals; evaporite, illite, chlorite and feldspar with considerable amount of montmorillonite.

However, the Pliocene sequence is very interesting due to the dominance of both clay minerals and the detrit,al constituents and feldspar while carbonate minerals are highly diminishing. Sediment supply was rather distinct during this period, where the continuous influx of detrital constituents took place through increased weathering of neighboring land mass. The clay minerals here are represented by montmorillonite, kaolinite, illite and chlorite in decreasing order of abundance. Feldspars show an ir- regular high content reaching up to 48%. The appearance of chlorite and illite indi- cates high latitude climatic conditions where mechanical weathering prevails. A cold-dry climate possibly alternated with humid climate at the source area during the Pliocene time. p.~fterwards,enrichment of calcite in the Pleistocene sediments, indi- cates seasonal humidity according to Biscaye (1965).

Tectonic events leading to uplifting and/or subsidence where erosion in up and down-stream areas producing rejuvenation of the relief, are also considered to be complementary factors in the differentiation of the clay mineral assemblages.

EI-Gindy and Samuel (1978) mentioned that during the pre-Cenomanian times the greater part of Egypt remained a fairly stable uplifted and well-drained peneplained

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103 Mineralogy and Geochemistry of the Mesozoic- Tertiary

Miocene and Pliocene are characterized by numerous and strong changes between humid and arid periods (Chamely and Diester-Haass 1979).

3 -Stratigraphic Variation in Bulk Mineralogy of Bardawil-l Well

Seven samples only have been anlaysed from Bardawil-l well, (Fig. 5). As far as the data permits the following general observations are recorded :.

1 It is found that montmorillonite is the domInant clay mineral component in the younger sediments (Miocene, Pliocene and Quaternary), while it become minor in the older sediments (Cretaceous).

2 -Carbonate exhibits an opposite trend of variation to montmorillonite and is enriched only in the Cretaceous sediments.

3 -Feldspar exhibits a similar behavior to montmorillonite; it is more abundant in the younger deposits.

4 -Kaolinite variation is erratic.

5 -Sulphate minerals are associated with the bulk mineral assemblage of Miocene sequence indicating an intertidal and supratidal environment where salinity increases due to a high rate of evaporation.

Trace Element Geochemistry

An attempt has been made herein to study the geochemical features regarding both abundance and vertical distribution of the trace elements in the bulk samples of the three studied wells; EI-Mazar-l, Malha-1, Bardawil-1. The effect of organic matter on the concentration of trace elements and the potential of rocks for hyd- rocarbon generation are also discussed.

The results of these anlayses of elements have been calculated and given in Tables 3,4 and 5. The trace element detected are Ba, Sr, Zr, Zn, Cu, Rb, Ga, Y, Pb, Co, Ni, Cr, Nb, and Ceo Thestra~!graphicdistributioncurvesoftheseelementsin the studied wells are shown in Fig. 6 and 8. Furthermore, the relative percentage of organic mat- ter in the rock powdered materials of EI-Mazar-1 well is presented in the variation curve shown in Fig. 8.

Trace elements can be used as indicator of environment and type of source rocks (De gens et aZ. , 1958; Hirst, 1962). Most minor elements enter the basin of deposition mainly structurally combined within the lattices of various clay minerals (Hirst 1962). Other processes possibly contributing to this concentration are association with organic carbon and association with the limonitic concretions.

These control mechanisms for concentration of trace elements, after Krauskopf (1956), are precipitation of sulphide within bottom sediments, adsorption and biological processes. Adsorption, according to Krauskopf, involves materials for which trace elements have affinity. These include clays, organic carbon and hyd- roxides.

Distribution and Significance of Trace Elements

A greater number of samples was available from EI-Mazar-l well providing a bet

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TABLE 3. Correlation coefficient of elements for EI-Malar sediments.

%I

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--Iaym

% urganicm

Ce Nb Cr Ni Co Ph y Ga Rb Cu Zn

Z,

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.0780 -0701 ~ 0115 Q477 0330 ~ Q1!2 Qd!J! -QI69 0.174 0153 -Q192 0065 QO4O 0030 QOl9 0211 0.200 0.101 -0037 Q387 -0352 -Q251 0498 0390 0387 0042 -0042 0054

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0350 -Q46-\ 0226 -0545 -0573

1131\2

Mineralogy and Geochemistry of the Mesozoic- Tertiary. 107

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Spnnger-Verlag, pp. 323-346.

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