6-Polyphases

10

NRIAG Journal of Geophysics, Vol. 1, No. 1, PP. 175 - 196 (2002)

POLYPHASED PALEOMAGNETIC OVERPRINTING OF PALEOZOIC

ROCKS FROM SOUTHWESTERN SINAI, EGYPT

I. A. El-Hemaly * , E. M. Abd El-All * ,

H.Odah

* , E. Krol ** and T. Aifa ***

(Received: Nov. 20, 2002; Accepted: Oct. 27, 2002)

ABSTRACT: One hundred twenty nine oriented hand samples were collected along 35 sites from four Paleozoic sedimentary formations in the Um Bogma area, east Abu-Zniema, southwestern Sinai. These formations are Sarabit El Khadim and

Adedia Formations (Cambrian), Um Bogma Formation (Lower Carboniferous) and

Abu Thora Formation (Lower to Middle Carboniferous) at the top most part.

Rock magnetic experiments show that magnetite, maghemite and hematite are the main carriers of magnetization. The studied rocks showed stable magnetization against alternating field, hence thermal demagnetization was mostly used. Both normal and reversed magnetizations were identified. Six components were obtained from the demagnetization processes revealing several phases of magnetization, including magnetizations of Ordovician and Carboniferous ages.

Ordovician magnetization for the Sarabit El-Khadim Formation has a pole position at lat. = 12°N and long. = 314°E, while the Ordovician magnetization for the

Adedia Formation has a pole position at lat.= 19°N, long. = 309°E. Lower

Carboniferous magnetization was identified with a pole position at lat. = 27°S and long. = 94°E. The obtained results show that the studied rocks were remagnetized during the Upper Carboniferous, Cretaceous and Oligo-Miocene times, that could be

connected to relevant tectonic and igneous activities.

INTRODUCTION

Understanding of the paleoposition and tectonic history of Africa and hence Gondwana is still a matter of controversy. This is because of the lack of reliable information and repeated weathering and tectonic events that mask or completely remove the majority of vital information needed for the complete understanding of its history. Paleomagnetic data could provide important information concerning the paleopositions and paleotectonics. Unfortunately, paleomagnetic data of the Egyptian

_________________________________________________________________

* National Research Institute of astronomy and Geophysics, Cairo, Helwan, Egypt.

** Institute of Geophysics, Warsaw, Poland.

***Fac. Earth Science. Rennes-1 Univ., France.

POLYPHASED PALEOMAGNETIC OVERPRINTING OF…..

______________________________________________________________________

Paleozoic rocks are very poor due to their widespread and repeated chemical alteration. One of the recent paleomagnetic studies for Egyptian

Paleozoic rocks has been made by Abdeldayem et. al. (1994) who concluded that Paleozoic rocks from southwestern Sinai were subjected to remagnetization. The question of the construction of the paleogeographic history for Gondwana is still unsolved.

The present study was planned to obtain more paleomagnetic data from Paleozoic rocks, and to reveal whether alteration and hence the remagnetization processes of the Paleozoic rocks are local or widespread along the western side of Sinai. For this reason, representative hand samples from Cambrian rocks (Sarabit El-Khadim and Adedia

Formations) and Lower to Middle Carboniferous rocks (Um Bogma and

Abu Thora Formations) were collected from Um-Bogma area, east of

Abu-Zniema (lat = 29° 00

/

N, 29° 15

/

N and long. = 33° 05

/ E, 33° 30 /

E).

GEOLOGICAL SETTING

As in other parts of northeast Africa, the Paleozoic rocks in Egypt

are predominantly clastic with interfering calcareous sediments. Surface exposures of the Paleozoic strata are recorded in the northern part of the

Eastern Desert (e.g. Wadi Dakhl, Wadi Qena and Gabal El Zeit), as well as in the area of Aswan (e.g. Wadi El Hudi, Gabal Goffa and Wadi Abu

Agag). In the south of the Western Desert and the border between Egypt and Libya, the Paleozoic rocks are exposed at Gabal Uweinat-Gelf El-

Kebir land-stretch, Abu Ballas, Aqaba pass and Abu Ras plateau.

In the Sinai peninsula, Um-Bogma area (east of Abu Zniema),

Gabal Abu Durba; Wadi Araba area and down stream of Wadi Feiran of southwestern Sinai, Wadi Quseib and Ras El-Naqb, southeastern Sinai, represent the main localities of Paleozoic exposures.

Lack of fossils in the Early Paleozoic rocks prevents conclusive dating of the most units of this age (Morgan 1990). These Paleozoic exposures were studied from the stratigraphical, paleontological and sedimentological points of view by Barron, (1907), Hassan (1967),

Weissbrod (1969 a and b),Soliman and Abu El Fetouh (1969), Issawi and

Jux (1982,), Kora and Jux (1986) and El Agami (1996). At Um Bogma area, the marine Carboniferous exposures received much attention due to

______________________________________________________________________

176 NR IAG Journal of Geophysics Vol. 1, No. 1, (2002)

I. A. El-Hemaly et al

______________________________________________________________________ the occurrence of Mn-Fe deposits, which have been intensively and economically exploited. They represent the first well date Paleozoic rocks in Egypt.

In the present study, the authors follow the nomenclature adopted by Soliman and Abu El Fetouh (1969) and modified by Kora (1984), for the Paleozoic formations of the Um Bogma area.

The Paleozoic sequence in Um Bogma area, in general about 350m thick, overlies nonconformably the Precambrian basement rocks. The subarkosic, gritty sandstone of fluviatile facies known as Sarabit El

Khadim Formation of 12-23m thickness overlain by a thin marine intercalation known as Abu Hamata Formation of 12-18m thickness composed of shale and siltstone with some trace fossils of shallow marine environment. They are in turn overlain by Nasib Formation (18-60m thick) that is made up of silty sandstone with trace fossils of intertidal to deltaic environment. The Adedia Formation (0-40m) overlies the Nasib

Formation is made up of quartz-arenite and cross-bedded sandstone of fluviatile environment. El Agami (1996) assigned the early Cambrian age for the Sarabit El Khadim Formation and middle Cambrian to pre-

Carboniferous age for the Adedia Formation. These formations are covered by the Lower Carboniferous carbonates and quartz arenites of

Um Bogma and Abu Thora Formations. Neither Silurian nor Devonian rocks have been found in Sinai (Klitzsch, 1980).

The Um Bogma Formation (0-40m) is composed of sandy dolostone, marly dolostone and pink dolostone with Mn-Fe ore of shallow to open-marine environment. The Abu Thora Formation (30-200m) is composed of kaolinitic claystone layers of coastal marine environment, at the bottom, and glass sand layers of fluviatile and swampy environment at the top, and is capped by basaltic sills.

Generally, the sampled area represents a monocline tilted in northeast direction with an average dip of 5-10°. Toward the end of the

Cambrian, a gentle block faulting resulted in the development of northnorthwest tilt of most of structural relief, which led to the erosion of most of the Cambrian sediments before deposition of Carboniferous rocks

(Klitzsch, 1970, 1980; Beyth, 1981 and El Agami, 1996).

______________________________________________________________________

NRIAG Journal o f Geophysics, Vol. 1, No. 1, (2002) 177


______________________________________________________________________

Paleozoic rocks have suffered several phases of tectonic and igneous activities. In Sinai, the Phanerozoic volcanics are represented as sporadic but frequent lava flow, sills, dykes and small irregular stocks

(Mousa, 1987). Some volcanics are located at Gabal Farsh El-Azraq,

Wadi Abu Natash and Wadi Budra and their extensions at Nagb Budra.

Late Carboniferous and Permian igneous activities that coincide with the late Hercynian orogeny, were also recorded by El Ramly (1962). Permo-

Triassic volcanics were described by Meneisy (1986) at Farsh El-Azraq, west of Sinai. These activities are coinciding with the initial break up of

Pangea and closure of Tethys.

Mesozoic volcanic activity according to Meneisy (1990 and references there in), is generally related to two main phases of igneous activity; Late Jurassic-Early Cretaceous (140 Ma) and Late Cretaceous-

Early Tertiary. These phases of igneous activity coincide with the initial refitting of the South Atlantic and the Afro-Arabian strike slip faulting.

Late Jurassic - Early Cretaceous (150 to 130 and 140 ±15 Ma respectively) magmatic events was identified by Hashad (1980) and

Meneisy (1986). Meneisy (1986) has also recorded Early Cretaceous magmatism at Wadi Araba and Abu Darag areas. Meneisy (1990) stated that the volcanic rocks which were formed in connection with Red Sea rifting show that the actual rifting appears to have begun in Late Eocene, and was under way in Late Oligocene to Early Miocene.

SAMPLLING AND MEASURMENTS

129 oriented hand samples were collected from Carboniferous and

Cambrian sedimentary rocks at 35 sites. 35 hand samples were collected from Sarabit El Khadim Formation at 7 sites, 40 samples were from

Adedia Formation at 11 sites, 31 samples were collected from Um Bogma

Formation at 8 sites and the remaining 23 samples were collected from

Abu Thora Formation at 9 sites. Locations of the sampled sites are shown in Figure (1). The orientation of the hand samples was performed in the field with the use of magnetic compass. Further coring was carried out in the laboratory to obtain standard cylindrical cores (2.4 cm diameter 2.1 cm high). At least 5 cylindrical specimens were cut from every block sample.

______________________________________________________________________



______________________________________________________________________

______________________________________________________________________



______________________________________________________________________

Measurements of the remanent magnetization were carried out using a 2-G Cryogenic magnetometer. The alternating field (AF) demagnetization was done using the attached degausser of the same magnetometer. The thermal demagnetization was done using nonmagnetic furnace of Magnetic Measurement Ltd (MMTD). All demagnetization processes and measurements were carried out in a nonmagnetic shielded space at the paleomagnetic laboratory of the Institute of Geophysics in Warsaw, Poland.

The natural remanent magnetization (NRM) of each specimen was measured first. AF and thermal demagnetization were carried out on a set of specimens from each site. Thermal demagnetization was performed up to 690 o

C using a stepwise increase of 20°-50°C steps. Bulk magnetic susceptibility was measured before and after each heating step to monitor any mineralogical changes during thermal demagnetization. Stepwise AF demagnetization was done at steps of 5-20 mT up to 120mT. The remanent magnetization was measured after each demagnetization step.

Least-squares analysis (Kirschvink 1980) was used to determine the component directions of NRM chosen by the inspection of vector end point demagnetization (Zijderveld 1967). Similar components were grouped and the site mean direction of each group was calculated.

Formation mean direction was calculated from site-means for each group.

Similar formation-means were grouped and their over-all mean direction and corresponding paleomagnetic pole positions were calculated.

ROCK MAGNETIC STUDY

In order to identify the magnetic minerals responsible for remanent magnetization and to obtain information about the stability of remanence, some rock-magnetic experiments were performed. Identification of the magnetic minerals was done through measurements of Curie temperatures and IRM acquisition curves.

Identification of Curie temperatures of the magnetic minerals contained within the studied rocks was performed using Polish-made instrument (Kadzialko-Hofmokl and Kruczyk 1976). The idea of this experiment is to continuously record of the remanent magnetization, of pre-saturated sample, during heating up to 700°C and cooling down to room temperature. Heating, cooling and measurements were performed

______________________________________________________________________



______________________________________________________________________

1.2

1

0.8

0.2

0

0 within nonmagnetic space. Examples of the obtained results are shown in

Figure (2). Figure 2-A reveals the presence of maghemite with a Curie temperature at 620°C. Figure 2-B reflects the presence of both magnetite and hematite with Curie temperatures at 575°C and 675°C, respectively.

Figure 2-C reveals the presence of titanomagnetite and hematite with

Curie temperatures at 170°C and 640°C, respectively. Figure 2-D shows the presence of magnetite with Curie temperature at 575°C. This curve shows some changes at temperature range between 350°C to 450°C. This may represent the oxidation process of maghemite to hematite that was marked by a drop of susceptibility values at those temperatures (as

1

0.8

described below).

1.2

Sarabit S12-3 -1

A

1.2

1

0.8

Adedia D 4 -2 -1

B

0.6

0.4

0.6

200 400

Temperature (°C)

600

Um Bogma B13-11

C

800

0.4

0.2

1.2

1

0 200 400

Temperature (°C)

600

Abu Thora T-11

D

800

0.8

0.6

0.6

0.4

0.2

0.4

0.2

0

0 200 400

Temperature (°C)

600 800

0 200 400

Temperature (°C)

600

Fig. 2. Normalized Saturated remanent magnetization during continuous heating.

800

______________________________________________________________________



______________________________________________________________________

Isothermal remanent magnetization acquisition curves (IRM) were measured for some representative samples from each formation using maximum applied field of about 3000mT. Figure (3) shows examples of the IRM acquisition curves. All curves show fast increase of IRM with the increase of the applied field up to 750 mT after which the slopes of the curves became lower, indicating the presence of maghemite and/or magnetite. As the saturated field of magnetite is less than this field (nearly about 120 mT), therefore, this part of curve may indicate the presence of maghemite. Generally, the obtained curves show that saturation was not approached using the maximum applied field in all samples (Fig. 3). This is an indication of the presence of magnetic mineral of high coercivity

(hematite and/or goethite). A distinction between hematite and goethite could not be performed using the available maximum field of 3T, as the saturation field of both minerals is higher than this field.

1.2

0.8

0.4

0 0

0.0

Legend

Sarabit- S2b2

Adedia D17-3

Um Bogma B11-1b

Abu Thora T7-b1

0.5

1.0

1.5

2.0

2.5

Applied Field (T)

Fig. 3. Normalized IRM acquisition curves.

3.0

______________________________________________________________________



______________________________________________________________________

Low field magnetic susceptibility for the majority of samples was measured using KLY-2 Kappa-bridge. Samples of Sarabit El Khadim

Formation exhibit very low susceptibility values ranging from 3*10 -6 to

8.7*10

-6

S.I. units, revealing very small content of magnetic minerals.

This is also confirmed by the low intensity of magnetic remanence of these rocks (ranges from 0.1 to 8



A/m). Samples of Adedia Formation show very weak and sometimes negative values of susceptibility, ranging between – 2.9*10

-6

to 6*10

-6

SI units with weak intensity of magnetization (0.1 - 4



A/m). The susceptibility values of the Um Bogma rocks range from –5* 10

-6

to 90*10

-6

S.I. units, with the intensity of their

NRM ranging from 0.25 to 3.5



A/m. In Abu Thora Formation, the susceptibility values range from –2*10

-6

to 16*10

-6

S.I. units and the

NRM intensity values range from 0.45 to 5.5



A/m. Such weak values suggest that the ferromagnetic content is very low. The negative value of susceptibility reveals the prevailing effect of diamagnetic minerals.

Magnetic susceptibility was measured after some thermal demagnetization steps in an attempt to monitor any mineralogical changes within the samples due to heating. Behavior of the susceptibility of the studied rocks after heating is represented in Figure (4). Figure 4-A shows the drop of susceptibility value after 600°C. Generally, the susceptibility values drop after 200-300°C (Fig. 4 B, C and D) and start to increase in temperature range of 400°C-600°C. The drop of susceptibility values could be attributed to oxidation of the magnetite and maghemite to hematite. Goethite also could be altered to hematite due to heating after

200°C. The increase of susceptibility value after 400°C could be attributed to the creation of new magnetic minerals within the samples from clay minerals.

Hysteresis measurements were done using the Vibrating Sample

Magnetometer (VSM). Unfortunately, no reliable information was obtained from this experiment owing to the weak magnetic signals obtained from the studied rocks.

In conclusion, the results obtained from the rock magnetic studies reveal the coexistence of magnetite, maghemite, hematite and titanomagnetite as magnetic carriers. Combination of such minerals give indication of high

______________________________________________________________________



______________________________________________________________________ alteration rocks and hence the presence of secondary magnetization that could be superimposed on the primary magnetization.

9

1

8

7

6

5

A

0

-1

B

4

Adedia D2-1

Sarabit S12-4

3

-2

0 100 200 300 400 500 600 700

Temperature (°C)

0 200 400

Temperature (°C)

40 8

C

7

38

6

36 5

4

34

32

0

Um-Bogma B13-1

3 Abu Thora T3-1

2

100 200 300 400

Temperature (°C)

500 600

0 200 400

Temperature (°C)

Fig. 4 . Behavior of susceptibility during thermal

demagnetization for representative samples.

D

600

600

______________________________________________________________________



______________________________________________________________________

PALAEOMAGNETIC STUDY

Directions of the NRM of all formations show a great scatter on the net projection indicating the presence of secondary magnetization. Both normal and reversed polarities were recorded. Demagnetization processes were performed using both AF and thermal methods. During AF demagnetization, most of the samples show stable magnetization against the field except for some samples from site 7(Sarabit El-Khadim

Formation) in which the magnetizations were successfully demagnetized at a value of 25 mT. This could indicate that the major part of magnetization is carried by high-coercivity mineral(s) (hematite and/or goethite). Consequently, only thermal demagnetization was used. Figure

(5) shows some examples of the thermal demagnetization plots for some representative samples from the studied formations. Demagnetization processes show that magnetization of the single sample consists of either a single-component (Figs.5-B and C) or two components (Fig.5-A and D).

It should be mentioned that the changes of the susceptibility values before 400°C of the heated samples were not accompanied by directional changes in magnetization. This is because the new magnetic minerals were created within non-magnetic space and consequently these minerals were not magnetized and their effects were negligible.

In spite of applying thermal demagnetization, there is a high withinsite scatter (



95

>10°) in several sites. This scatter could be attributed to incomplete demagnetization because of some mineralogical changes during heating as well as the very low intensity of remanenc at higher temperatures. Errors in azimuth orientation during the field sampling and further laboratory coring are not also excluded.

Several components were isolated from the demagnetization processes. Similar directions were gathered to represent single group of components and Site-mean direction was calculated for each group.

Formation-mean direction was calculated for each group (Table 1).

Overall mean direction for each group was calculated from corresponding formation means. Results of the formation mean directions and corresponding pole positions are given in Table (1).

______________________________________________________________________



______________________________________________________________________

Fig. 5.Examples of thermal demagnetization plots for representative

samples from the studied formations.

______________________________________________________________________



______________________________________________________________________

Table 1. Formation mean directions of the isolated groups of components,

and their corresponding pole positions for the studied formations.

Group



95

K N/n D

Acomponent

Sarabit

Adedia

7.6 54.6 7/23 18

5.2 65.2 10/41 5

Um Bogma 6.4 46.9 8/39 15

I

41

44

44 plat.

72

81

76

Plong. D1

145

179

145

6

4

5

D2

9

6

6

Pal. lat.

24

25

26

78

77

165

154

4

4

7

6

24

25

Abu Thora

Mean

Bcomponent

5.7 48.9 6/29 9

5.2 317 4/132 12

42

43

Sarabit

Adedia

12 59.2 4/18 189 -36

6.3 115.5 6/22 200 -41

Um Bogma 13.5 46.7 4/21 195 -47

B-Mean 10.6 136.5 3/61 195 -41

A+B mean 4.2 205 7 12 42

Ccomponent

75

59

76

74

77

175

128

136

151

156

8

5

11

8

3

14

8

17

13

5

-20

-23

-28

-24

24

Sarabit 7.8 97.5 5/22 325 39 58 289 6 9 22

Um Bogma 14.4 74

Abu Thora 10.8 39.3

3/19

6/22

328

323

30

41

Mean

Dcomponent

9.4 170.8 3/73 325 37

Sarabit 9.1 54.9 6/25 142 29

Um Bogma 7.7 141.6 4/18 125 43

Mean* 8.3 35.4 10/33 136 35

Ecomponent

Sarabit

Adedia*

8.9 34.5 6/20 320 -1

14.1 23.5 6/19 290 -13

Abu Thora* 10.6 53.1 5/22 307 -10

57

56

57

-30

-12

-23

-39

-12

-27

276

292

285

72

78

74

86

102

93

Mean

Mean*

24.8 25.8 3/61 306 -8

9.4 24.5 11/41 298 -12

F-component

Sarabit 15.7 19.1 6/19 273 34

Adedia 9.4 97.1 4/15 281 34

-27

-19

12

19

94

98

314

309

Mean* 9.1 28.9 10/34 280 38



95= semi- angle of cone of confidence.

20 312

K= precision parameter (Fisher, 1953).

N= number of sites in each formation (or formations for mean calculation). n= number of specimens carrying the component.

D, I = tilt corrected magnetic declination and inclination. plat, plong. = pole latitude(°N) and longitude(°E).

D1, D2= Paleopole confidence limits

Pal. lat = paleolatitude.

Mean*= Mean value calculated from site-means (only two formations)

9

8

6

4

7

5

13

5

10

6

6

16

13

11

5 10

6 10

4 9

9

14

11

25

10

18

11

11

16

23

20

15

25

19

0

-7

-5

-4

-6

19

19

21

______________________________________________________________________



______________________________________________________________________

RESULTS AND DISCUSSION

There is a clear consistency between some of the formation mean directions irrespective of age, suggesting that these rocks were remagnetized.

Six components were identified from the studied rocks (Table-1).

Demagnetization data show that A and B-components carried by coarse grain magnetite and fine grain hematite. Both components are found in all formations except for Abu Thora Formation in which the B-component is absent. It should be noted that these two components were not found in any single specimens. C-component is carried by hematite and represents high temperature components with unblocking temperature more than

600°C. It is represented in all formation except for Adedia Formation.

D-component is carried by maghemite with wide range of unblocking temperature ranges from 350°C to 620°C. It is represented in Sarabit El

Khadim and Um Bogma Formations. The E-component was absent in Um

Bogma Formation only and is carried by coarse grained magnetite with unblocking temperature around 570°C. F-component shows a wide range of unblocking temperature that may be carried by hematite with unblocking temperature more than 590°C and is represented only in

Cambrian rocks. Low temperature components carried by titanomagnetite

(and/or goethite) could not be grouped reliably due to their high scatter.

Unfortunately, fold-test could not be applied in the present study because the sampled formations are slightly tilted in the same direction.

Dating of such magnetizations could be done on the base of the comparison of their pole positions with other poles obtained from Egypt and from other parts of Gondwana.

A AND B -COMPONENTS

A-component was obtained in all studied rocks. The mean direction of this component is D=12°, I= 43° (k= 317, 

95

= 5.2) with the corresponding pole position at lat. 77° N and long. = 154° E. This direction, which is similar to the Earth’s present magnetic field (2.6°,

+41.4°) suggests a recent magnetization. The B-component, that has mean direction of D= 195°, I = -41° (k= 136.5, 

95

= 10.6), could be anti-

______________________________________________________________________



______________________________________________________________________ parallel to the A-component. The overall direction of the A and B groups is D = 12°, I= 42° (k= 205 and 

95

= 4.2) corresponding to a pole position at lat. =77° N and long. = 156° E. The presence of reversed magnetization

(B-component) in three formations demonstrates that the A-component is neither a viscous nor a chemical remanence acquired in last few million years. The obtained poles of the A and B components are similar to the pole of Oligo- Miocene age, obtained by Ibrahim et al. (1998) from the

Sant Catherine basalt (lat. = 83°N and long = 179°E). Reverse polarity of

Oligo-Miocene was also recorded by Lotfy and Odah (1998), Lotfy et al.

(1995) and Wassif (1988). Therefore, the A and B magnetization could be of Oligo-Miocene age. Such secondary magnetization may be attributed to the tectono-thermal activities associated with the opening of Red Sea and Gulf of Suez.

C-COMPONENTS

C-component is represented in Sarabit El-Khadim, Um-Bogma and

Abu Thora Formations. This group of components is carried by hematite representing the high temperature component and has a mean direction of

D = 325°, I = 37° (k= 170.8,



95

= 9.4) with a pole position at lat. = 57°

N, long. = 285° E. The comparison of the obtained C-pole with other poles from Egypt and Africa shows that Cretaceous age is the most probable age for this remanence which is consistent with the long

Cretaceous quite zone of normal polarity, lasted from Early Aptain to the

Santonian-Campanian. Similar components were obtained by El Agami et. al. (1999) from Abu Thora Formation with pole position at lat. = 59

°N, long. = 302 °E. This remanence may be attributed to the magmatic events associated with the rifting of South Atlantic.

D-COMPONENTS

D-component is represented in Sarabit El Khadim and Um Bogma

Formations. It has a mean direction (calculated from site means) of D=

136 ° I= 35° (k = 35.4, 

95

= 8.3) with corresponding paleomagnetic pole at lat.= 23°S; long. = 74°E. This pole is similar to the Upper

Carboniferous pole obtained by Abdeldayem et al., (1994) for

Carboniferous sediments of Abu Durba area, SW Sinai. Also, the normal inclination direction of this component and the general similarity of this pole with other African Upper Carboniferous pole positions (pole no.7 in

______________________________________________________________________



______________________________________________________________________

Table 2) suggest that the Upper Carboniferous-Lower Permian age is the most likely. This is confirmed by comparing this pole position with X path and Y path of the palaeozoic APWP for the Gondwana (Fig. 6). This remanence may be attributed to the remagnetization processes that could be connected with the magmatic events recorded by El Ramly (1962) and

Meneisy (1986) during Permo-Carboniferous. The age of this magnetization roughly coincides with the Late Hercynian orogeny and variscan tectonics in Europe.

E-COMPONENTS

This component is carried by magnetite and is represented in all formations except for Um Bogma. It has a mean direction of D = 306°, I=

-8° (k = 25.4,



95

= 24.8) with corresponding pole position at lat. = 27° S and long. = 94° E. The E-components, obtained from both Adedia and

Abu Thora Formations are very similar. The overall mean direction of these two formations (calculated from site-means) is D = 298°, I = -12° with pole position at lat.= 19°S and long. = 98°E (Table 2). Comparison of the obtained E-pole with other poles from Egypt and other parts of

Africa (Table 2) reveals that the Lower Carboniferous age for this magnetization is most probable. This pole is similar to the Lower

Carboniferous pole obtained by El-Agami et al. (1999) from Lower

Carboniferous sediments from Sinai (pole no. 8, Table 2). This magnetization could be primary in Abu Thora Formation of Lower to

Middle Carboniferous age, but secondary in the older rocks of Sarabit El

Khadim and Adedia Formations of Cambrian age. Comparing of this pole position with X path and Y path of the palaeozoic APWP for the

Gondwana (Fig. 6) Shows that this pole is deviated from the paths which could be attributed to the local tectonic of Sinai area.

F-COMPONENTS

This group of components is presented only in the Cambrian rocks

(Sarabit El Khadim and Adedia Formations). It has a mean direction of

D= 280°, I = 38° with pole position at lat. =20° N and long = 312° E. the obtained F-pole is located on the same latitude of the Cambro-Ordovician poles of X-path APWP (Fig. 6) wit some longitudinal drift. This pole is similar to the pole obtained from Cambro-Ordovician rocks from Sinai

(Abdeldayem et al., 1994) with lat. = 18°N and long = 341°E. The F-pole

______________________________________________________________________



______________________________________________________________________ is close to some African poles of Camberian and Ordovician ages (Table

2) suggesting that these two Cambrian formations acquired their magnetizations during Cambro-Ordovician time. This secondary magnetization could be of chemical origin related with the erosion processes lasted from Late Cambrian to Carboniferous.

Fig. 6. Palaeozoic APWP for Gondwana and poles obtained from the

present study. Numbers refer to the pole number in table 2.

______________________________________________________________________



______________________________________________________________________

Table 2. Paleozoic poles positions obtained from Africa .

N Rock unit Age Lat Long A95 References

1 Dwyka varves

2 Sabaloka complex Sudan

3 Ain-Ech Chebbi RB, Algeria

4 Hassi-Bechar RB, Algeria

5 Abu Durba Sediments Egypt

6 Carboneferous L.S, Morocco

7 Um Bogma sediments, Egypt

8 Um Bogma. SW Sinia, Egypt


10 Carbiniferous rocks,Morocco

11 Salal complex, Sudan

12 Graafwater Fm, South Africa


14 Ntonya complex, Malawi

15 Nabati Complex, Sudan

Cu

Cu

Cu

Cl

Cu

Cu

Cu

Cu

26

42

23

27

26

10

7

6

3.7

7.1

-7.4 54.5 11

-23

22

206

236

232

237

244

74

277

8.3

7.5

McElhinny&Opdyke(1968)

Soffel et. Al. (1990)

Daly and Irving (1983)

Daly and Irving (1983

Abdeldayem et. al (1994)

Salmon et. al (1988)

Present study

ElAgami, et. al (1999)

Cl

Cl

Om

Ol

-19 98 9.4

-4.8 55.5 6.1

39.6

28

329

14

Ol 20

Є.m 28

Є.l 67.9

312

345

314

9.3

8.8

9.1

5

13.6

Present study

Martin et. al. (1978)

Bachtadse and Briden (1989)

Bachtadse et. al (1987)

Present study

Briden, 1968, Briden et. al (1993)

Saradeth et. al (1989)

CONCOLUSION

The investigated rocks exhibit low content of magnetic minerals revealed by their weak susceptibility and low intensity of magnetization.

Rock magnetic study shows that hematite, magnetite and maghemite are the main magnetic carriers in the studied rocks. These minerals are of secondary origin except for some magnetite that seems to carry primary magnetization.

Thermal demagnetization was used more than AF demagnetization because of the presence of hematite as remanence carriers, which hampered the proper AF demagnetization. Demagnetization processes reveal the presence of six components, for which the mean directions and their corresponding pole positions were calculated and tabulated in table1.

From the obtained results it may be concluded that:

- The Cambrian rocks retain the Cambro-Ordovician magnetization carried by stable hematite that was acquired after deposition of both formations.

- Cambrian rocks and Lower Carboniferous rocks of Um – Bogma

area had suffered remagnetization that masks the primary magnetization.

______________________________________________________________________



______________________________________________________________________

- In case of Abu Thora Formation, the primary component of

Lower Carboniferous age is still preserved, indicating that this formation could be of Lower Carboniferous.

- The studied rocks suffered several phases of remagnetization

during the Upper Carboniferous, Cretaceous and Oligo-Miocene times. The possible source of these remagnetizations seems to be

the flowing solutions associated with tectonic and igneous activities that took place during these times.

- Remagnetization processes for the Paleozoic rocks seems to be widespread all over the western part of Sinai.

______________________________________________________________________



______________________________________________________________________

REFERENCES

Abdeldayem, A. L. Kafafy, A.M. and Tarling D. H. (1994).

Paleomagnetic studies of some Paleozoic sediments, southwest Sinai, Egypt, Tectono. 234: 217-225.

Bachtadse, V., Van der Voo, R. and Halbich, W., (1987).

Paleomagnetism of the western Cap Fold belt, South Africa and its bearing on the Paleozoic apparent polar wander path for Gondwana. Earth Planet. Sci. Lett, 84: 487-499.

Bachtadse, V. and Briden, J. C., (1989).

Paleomagnetism of the Early to Mid-

Ordovician Salala igneous complex, Red Sea Hills, Sudan. Geophys. J. Int.,

99:677-685.


Palaeomagnetism of Devonian ring complexes from the Bayuda Desert, Sudan – new constraints on the apparent polar wander path for Gondwanaland. Geophys. J. Int., 104, 635-646.

Barron, T. (1907).

The topography and geology of the Peninsula of Sinai (western portion). Egypt. Surv. Dept, 241pp.

Beyth, M., (1981).

Paleozoic vertical movement in Um Bogma area, southwestern Sinai.

Bull. Am. Assoc. Petrol. Geol.65: 160-165.

Briden, J. C., (1968).

Paleomagnetism of the Ntonya ring structure, Malawi. Geophys.

J. R. Astron. Soc., 73: 725-733.

Briden, J. C., McClelland, E. and Rex, D. C., (1993).

Proving the age of a paleomagnetic pole: The case of the Ntonya Ring Structure, Malawi. J. Geophys.

Res., 98: 1743-179.

Daly, L. and Irving, E. (1983). Paléomagnétisme des roches Carbonifères de la Pangee.

Ann Geophys, 1: 207-216.

El Agami, N. L. (1996). Geology and radioactivity studies on the Paleozoic rock units in Sinai Peninsula, Egypt: Ph.D. Thesis, Fac. Science, Mansoura University,

302pp.

El Agami, N. L. Ibrahim, H. E. and Odah H. (1999). Paleomagnetic and Geologic inferences, and probable origin of the Mn-Fe ore of Um Bogma, SW Sinai,

Egypt, Sedim. of Egypt, 7: 167-183.

El Ramly, M. F. (1962). The absolute ages of some basement rocks from Egypt. Egypt.

Geolog. Surv., 15, pp. 13.

Fisher, R., (1953).

Dispersion on a sphere. Proc. Roy. Soc., London, 217A: 295- 305.

______________________________________________________________________



______________________________________________________________________

Hashad, A. H. (1980).

Present status of geochronological data on the Egyptian

basement complex. Bull. Inst. Applied Geol. King Abdul Aziz Univ., Jeddah 3

(3):31-46.

Hassan, A. A. (1967). A new Carboniferous occurrence in Abu Durba, Sinai, Egypt. 6 th

Arab petrol Congr., Baghdad.

Ibrahim, E. H., Odah, H., El Agami, N. L. and Abu El Enen, M. M., (1998).

Paleomagnetic and geology investigations on some volcanic rocks, southern

Sinai, Egypt: Egyptian J. of Geol. V 42, pp. 237-256.

Issawi, B. & U. Jux (1982).

Contributions to the stratigraphy of the Paleozoic rocks in

Egypt. Geol. Surv. Egypt, 64, 28pp.

Kadzialko-Hofmokl, M. and Kruczyk, J., (1976). Complete and partial self-reversal of natural remanent magnetization of basaltic rock from lower Silesdia, Poland. Pure

Appl. Geophysics, 110, 2031-2040.

Kirschvink, J. L., (1980).

The least squares lines and planes and the analysis of paleomagnetic data. Geophys. J. R. Astro. Soc., 62: 699-718.

Klitzsch, E. (1970). Die Strukturgeschichte der Zentrasahara Geol. Rundschau 59: 49-

520.

Klitzsch, E. (1980). Neue stratigraphische und palaogeographische Ergebnisse aus dem

NW Sudan Berl.Geowiss. Abh. 20(A): 217-222.

Kora, M. (1984). The Paleozoic outcrops of Um Bogma area, Sinai Ph.D. Thesis,

Mansoura Univ. Mansoura, 253pp.

Kora, M. & U. Jux (1986). On the early Carboniferous macrofauna from Um Bogma

Formation, Sinai. N.Jb. Geol. Palaeontol. Mh, 2: 85-98.

Lotfy, H. I. and Odah H. H, (1998). Paleomagnetic direction of two Tertiary basaltic episodes in Northern Egypt during the Late Eocene and Early Miocene, In

Northeast Egypt: Hints of Petrochemical and Petrologic diversity. Bull. Fac. Sci,

Assiut Univ. 27 (2-f) pp. 301-320.

Lotfy, H. I., Van der Voo, R., Hall, C., M., Kamel, O. A., and Abdel Aal, A. Y.

(1995). Paleomagnetism of Early Miocene basaltic eruptions in the areas east and west of Cairo. Journal of African Earth Sciences, 21(3): 407-419.

Martin.D.L. Nairn, A.E.M., Noltimier, H.C., Petty, M.H., Schmitt, T.J. (1978).

Paleozoic and Mesozoic paleomagnetic results from Morocco. Tectonophysics,

44: 91-114.

______________________________________________________________________



______________________________________________________________________

McElhinny, M. W. and Opdyke, N. D., (1968).

The paleomagnetism of some

Carboniferous glacal varves from central Africa. J. Geophys. Res., 73: 689-696.

Meneisy M. (1986). Mesozoic igneous activity in Egypt, Qatar Univ. Sci. Bull. 6.

Meneisy M. Y. (1990). Volcanicity. In: R. Said (Editor) The Geology of Egypt.

Balkema, Rotterdam, Netherlands. 157-172.

Morgan, P. (1990). Egypt in framework of global tectonics. In: R. Said (Editor) The

Geology of Egypt. Balkema, Rotterdam and Boston, 91-111.

Mousa, H. E. (1987). Geologic studies and genetic correlation of basaltic rocks in west

Central Sinai, Egypt. Ph. D. Thesis, Ain Shams University, 308p.

Salmon, E., Edel, J.B., Pique, A. and Westphal, M. (1988). Carboniferous paleomagnetic investigations in Morocco: Permian remagnetization and possible large

Carboniferous rotations occurring in Mesetian sedimentary and Jebilets intrusive rocks.; Geophys. J., 93: 115-125.

Saradeth, S., Soffel, H.C., Horn, P., Muller-Sohnius, D. and Schult, A. (1989). Upper

Proterozoic and Phanerozoic pole position and potassium-argon (K-Ar) ages from the East Sahara craton. Geophys. J., 97:209-221.

Schmidt, P. W., Powell, C. McA., Li, Z. X. and Thrupp, G. A., (1990).

Reliability of

Palaeozoic palaeomagnetic poles and APWP of Gondwanland, Tectonophysics,

184, 87-100.

Soffel, H. C., Saradeth, S., Briden, J. C. Bachtadse, V. and Rolf, C., (1990). The

Sabaloka ring complex revisited: paleomagnetism and rock magnetism. Geophys.

J. Int., 102: 411-420.

Soliman, S. M. and M. A. El-Fetouh (1969). Petrology of the Carboniferous sandstones in west central Sinai, Egypt. J. Geol. 13: 61-143.

Wassif, N. A. (1988). Data concerning the magnetic. Paleomagnetic and mineralogical properties of some basalts from Wadi Matulla and Wadi Budra. Sinai. Egypt. Ain

Shams Science Bulletin. 27(B): 13-35.

Weissbrod, T. (1969a). The Paleozoic of Israel and adjacent countries: Part I, The subsurface Paleozoic stratigraphy of S. Israel. Bull. Geol. Surv. Isr. 47-35.

Weissbrod, T. (1969b). The Paleozoic of Israel and adjacent countries: Part II, The

Paleozoic outcrops in southwestern Sinai and their correlation with those of southern Israel Bull. Geol. Surv. Isr. 48: 1-32.

Zijderveld, J.D.A. (1967). A.C. demagnetization of rocks: Analysis of results, in:

Methods in paleomagnetism, ed. Collinson, D. W.,Creer, K.M. and Runcorn,

S.K., Elsevier, Amsterdam. 254-286.

______________________________________________________________________


10

NRIAG Journal of Geophysics, Vol. 1, No. 1, PP. 175 - 196 (2002)

REFERENCES

Abdeldayem, A. L. Kafafy, A.M. and Tarling D. H. (1994).

Paleomagnetic studies of some Paleozoic sediments, southwest Sinai, Egypt, Tectono. 234: 217-225.

Bachtadse, V., Van der Voo, R. and Halbich, W., (1987).

Paleomagnetism of the western Cap Fold belt, South Africa and its bearing on the Paleozoic apparent polar wander path for Gondwana. Earth Planet. Sci. Lett, 84: 487-499.


Paleomagnetism of the Early to Mid-

Ordovician Salala igneous complex, Red Sea Hills, Sudan. Geophys. J. Int.,

99:677-685.


Palaeomagnetism of Devonian ring complexes from the Bayuda Desert, Sudan – new constraints on the apparent polar wander path for Gondwanaland. Geophys. J. Int., 104, 635-646.

Barron, T. (1907).

The topography and geology of the Peninsula of Sinai (western portion). Egypt. Surv. Dept, 241pp.

Beyth, M., (1981).

Paleozoic vertical movement in Um Bogma area, southwestern Sinai.

Bull. Am. Assoc. Petrol. Geol.65: 160-165.

Briden, J. C., (1968).

Paleomagnetism of the Ntonya ring structure, Malawi. Geophys.

J. R. Astron. Soc., 73: 725-733.

Briden, J. C., McClelland, E. and Rex, D. C., (1993).

Proving the age of a paleomagnetic pole: The case of the Ntonya Ring Structure, Malawi. J. Geophys.

Res., 98: 1743-179.

Daly, L. and Irving, E. (1983). Paléomagnétisme des roches Carbonifères de la Pangee.

Ann Geophys, 1: 207-216.

El Agami, N. L. (1996). Geology and radioactivity studies on the Paleozoic rock units in Sinai Peninsula, Egypt: Ph.D. Thesis, Fac. Science, Mansoura University,

302pp.

El Agami, N. L. Ibrahim, H. E. and Odah H. (1999). Paleomagnetic and Geologic inferences, and probable origin of the Mn-Fe ore of Um Bogma, SW Sinai, Egypt,

Sedim. of Egypt, 7: 167-183.

El Ramly, M. F. (1962). The absolute ages of some basement rocks from Egypt. Egypt.

Geolog. Surv., 15, pp. 13.

_________________________________________________________________

* National Research Institute of astronomy and Geophysics, Cairo, Helwan, Egypt.

** Institute of Geophysics, Warsaw, Poland.

***Fac. Earth Science. Rennes-1 Univ., France.


______________________________________________________________________

Fisher, R., (1953).

Dispersion on a sphere. Proc. Roy. Soc., London, 217A: 295- 305.

Hashad, A. H. (1980).

Present status of geochronological data on the Egyptian

basement complex. Bull. Inst. Applied Geol. King Abdul Aziz Univ., Jeddah 3

(3):31-46.

Hassan, A. A. (1967). A new Carboniferous occurrence in Abu Durba, Sinai, Egypt. 6 th

Arab petrol Congr., Baghdad.

Ibrahim, E. H., Odah, H., El Agami, N. L. and Abu El Enen, M. M., (1998).

Paleomagnetic and geology investigations on some volcanic rocks, southern

Sinai, Egypt: Egyptian J. of Geol. V 42, pp. 237-256.

Issawi, B. & U. Jux (1982).

Contributions to the stratigraphy of the Paleozoic rocks in

Egypt. Geol. Surv. Egypt, 64, 28pp.

Kadzialko-Hofmokl, M. and Kruczyk, J., (1976). Complete and partial self-reversal of natural remanent magnetization of basaltic rock from lower Silesdia, Poland. Pure

Appl. Geophysics, 110, 2031-2040.

Kirschvink, J. L., (1980).

The least squares lines and planes and the analysis of paleomagnetic data. Geophys. J. R. Astro. Soc., 62: 699-718.

Klitzsch, E. (1970). Die Strukturgeschichte der Zentrasahara Geol. Rundschau 59: 49-

520.

Klitzsch, E. (1980). Neue stratigraphische und palaogeographische Ergebnisse aus dem

NW Sudan Berl.Geowiss. Abh. 20(A): 217-222.

Kora, M. (1984). The Paleozoic outcrops of Um Bogma area, Sinai Ph.D. Thesis,

Mansoura Univ. Mansoura, 253pp.

Kora, M. & U. Jux (1986). On the early Carboniferous macrofauna from Um Bogma

Formation, Sinai. N.Jb. Geol. Palaeontol. Mh, 2: 85-98.

Lotfy, H. I. and Odah H. H, (1998). Paleomagnetic direction of two Tertiary basaltic episodes in Northern Egypt during the Late Eocene and Early Miocene, In

Northeast Egypt: Hints of Petrochemical and Petrologic diversity. Bull. Fac. Sci,

Assiut Univ. 27 (2-f) pp. 301-320.

Lotfy, H. I., Van der Voo, R., Hall, C., M., Kamel, O. A., and Abdel Aal, A. Y.

(1995). Paleomagnetism of Early Miocene basaltic eruptions in the areas east and west of Cairo. Journal of African Earth Sciences, 21(3): 407-419.

Martin.D.L. Nairn, A.E.M., Noltimier, H.C., Petty, M.H., Schmitt, T.J. (1978).

Paleozoic and Mesozoic paleomagnetic results from Morocco. Tectonophysics,

44: 91-114.

______________________________________________________________________



______________________________________________________________________

McElhinny, M. W. and Opdyke, N. D., (1968).

The paleomagnetism of some

Carboniferous glacal varves from central Africa. J. Geophys. Res., 73: 689-696.

Meneisy M. (1986). Mesozoic igneous activity in Egypt, Qatar Univ. Sci. Bull. 6

Meneisy M. Y. (1990). Volcanicity. In: R. Said (Editor) The Geology of Egypt.

Balkema, Rotterdam, Netherlands. 157-172.

Morgan, P. (1990). Egypt in framework of global tectonics. In: R. Said (Editor) The

Geology of Egypt. Balkema, Rotterdam and Boston, 91-111.

Mousa, H. E. (1987). Geologic studies and genetic correlation of basaltic rocks in west

Central Sinai, Egypt. Ph. D. Thesis, Ain Shams University, 308p.

Salmon, E., Edel, J.B., Pique, A. and Westphal, M. (1988). Carboniferous paleomagnetic investigations in Morocco: Permian remagnetization and possible large

Carboniferous rotations occurring in Mesetian sedimentary and Jebilets intrusive rocks.; Geophys. J., 93: 115-125.

Saradeth, S., Soffel, H.C., Horn, P., Muller-Sohnius, D. and Schult, A. (1989). Upper

Proterozoic and Phanerozoic pole position and potassium-argon (K-Ar) ages from the East Sahara craton. Geophys. J., 97:209-221.

Schmidt, P. W., Powell, C. McA., Li, Z. X. and Thrupp, G. A., (1990).

Reliability of

Palaeozoic palaeomagnetic poles and APWP of Gondwanland, Tectonophysics,

184, 87-100.

Soffel, H. C., Saradeth, S., Briden, J. C. Bachtadse, V. and Rolf, C., (1990). The

Sabaloka ring complex revisited: paleomagnetism and rock magnetism. Geophys.

J. Int., 102: 411-420.

Soliman, S. M. and M. A. El-Fetouh (1969). Petrology of the Carboniferous sandstones in west central Sinai, Egypt. J. Geol. 13: 61-143.

Wassif, N. A. (1988). Data concerning the magnetic. Paleomagnetic and mineralogical properties of some basalts from Wadi Matulla and Wadi Budra. Sinai. Egypt. Ain

Shams Science Bulletin. 27(B): 13-35.

Weissbrod, T. (1969a). The Paleozoic of Israel and adjacent countries: Part I, The subsurface Paleozoic stratigraphy of S. Israel. Bull. Geol. Surv. Isr. 47-35.

Weissbrod, T. (1969b). The Paleozoic of Israel and adjacent countries: Part II, The

Paleozoic outcrops in southwestern Sinai and their correlation with those of southern Israel Bull. Geol. Surv. Isr. 48: 1-32.

______________________________________________________________________



______________________________________________________________________

Zijderveld, J.D.A. (1967). A.C. demagnetization of rocks: Analysis of results, in:

Methods in paleomagnetism, ed. Collinson, D. W.,Creer, K.M. and Runcorn,

S.K., Elsevier, Amsterdam. 254-286.

______________________________________________________________________


6-Polyphases

Related documents

Products

Support

6-Polyphases

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib