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Quartz surface textures of some cretaceous Nubian sandstone exposures, Central Eastern desert, Egypt
Journal of African Earth Sciences, Vol. 7, No. 7/8, pp. 873-878, 1988
0731 7247/88 $3.00 +0.00 Pergamon Press plc
Printed in Great Britain
Quartz surface textures of some cretaceous Nubian sandstone exposures, Central Eastern desert, Egypt. E.A. AHMED and MOHAMED A. SOLIMAN Departmentof Geology,Facultyof Science, AssiutUniversity Assiut, Egypt (Receivedfor publication March 11, 1988) Abstract - Thecommonand dominantsurfacefeaturesobservedin the quartzgrainsof the Nubia Sandstoneencompassbothmechanicaland chemicalfeatures.Suchfeatures point to a complexdepositionalhistoryof the NubiaSandstoneincludingdepositionby aeolianprocessesfollowedby fluvialsedimentation.Diagenesisin theNubiaSandstone is representedby silicaprecipitationand dissolution. INTRODUCTION
Depositional history of the Nubia Sandstone (Russeger, 1837, Youssef, 1957) h a s p u ~ l e d the geologists for a long time. F o u r t a u (1902), B a r t h o u s (1922) and Picard (1934) suggested aeolian processes. Bail (1907), S h u k r i a n d Said (1944) adovcate a shallow m a r i n e depositional environment. Barron (1907) assigns a fluvio-marine condition. Recently, b a s e d on a detailed facies studies, Klitzsch et aL, (1979), Van H o u t e n a n d B h a t t a c h a r y y a (1979), Ward and McDonald (1979), A h m e d (1983) and Soliman et aL, (1986) advocate a fluvial origin for the Nubia Sandstone. Moreover, a n impressive p h e n o m e n o n in the Nubia S a n d s t o n e is its mineralogical m a t u rity. It is essentially c o m p o s e d of ultrastable mineral c o n s i t u e n t s (quartz, zircon, tourmaline and rutile). This led m a n y a u t h o r s to predict a multicyclic s e d i m e n t a t i o n as essential factor in the depositional history of the Nubia S a n d s t o n e (Shukri a n d El Ayouti, 1953; El Shazly a n d Shata, 1960; Bishara a n d Nasr, 1973). Soliman (1983) presents indications for a direct i n p u t of clastics from the b a s e m e n t complex. The aim of this work is to introduce the findings of the investigations of the surface texture of the quartz grains a n d their contribution to the depositional history of the Nubia Sandstone. M E T H O D S OF STUDY
The studied samples were collected from four
873 AES 7 7/8--A
m e a s u r e d c o l u m n a r sections representing the Cretaceous Nubia Sandstone fYoussef, 1957: Saud, 1962) in the areas situated at Kin. 80 along QiR Quseir road, Quseir, Km. 60 along Qena-Safaga road a n d the n o r t h e m r e a c h of Wadi Qena (Figs. 1,2). Friable s a n d s t o n e samples were chosen and the quartz grains were separated using the binocular microscope. The samples were p u t in a n ultrasonic vibrator, cleaned by 30 % Hcl for 5 minutes, w a s h e d by distilled water a n d dried. Photos for the surface texture of the quartz grains were t a k e n using Philips Scanning Electron Microscope. More t h a n 300 grains representing the different m e a s u red c o l u m n a r sections were investigated. RESULTS
Two different types of surface features were observed on the quartz grains : Mechanical features (Figs. 3, 4 & 5) including m e a n d e r i n g ridges a n d grooves, oriented cleavage fractures, large scale d i s h s h a p e d pits, u p t u r n e d plates and polygonal cracks. Chemical features (Figs. 6, 7 & 8) including silica over-growths and silica globules, smooth surfaces, oriented V. shaped pits and triangular facets and surface corrosions. DISCUSSION
Intensive chemical diagnosis acting in the Nubia S a n d s t o n e is marked. This is manifested by two phases of silica precipitation and dissolution. S u c h
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Fig. 3 Mechanical features: m e a n d e r i n g ridges and groove, n o r t h ofWadi Quena. Bar length = 100 microns. Fig. 4 Mechanical features: U p t u m e d plates and d i s h - s h a p e d pits, n o r t h ofWadi Quena. Bar length = 10 microns. Fig; 5 Rounded and w o r n e d quartz grain. Note the large scale d i s h s h a p e d pits a n d smooth surface, Quseir area. Bar length = 100 microns.
Quartz surface textures of sandstone exposures c h e m i c a l f e a t u r e s r e p r e s e n t t h e final fingerprints o n t h e s u r f a c e of t h e q u a r t z g r a i n s a n d p r o b a b l y d e s t r o y e d t h e m e c h a n i c a l f e a t u r e s of t h e fluvial p r o c e s s e s a s p r e d i c t e d b y m a n y a u t h o r s (e.g. Klitzseh e t aL, 1979; W a r d a n d McDonald, 1979; A h m e d , 1983: S o l i m a n e t a l . , 1986). Nevertheless, o t h e r m e c h a n i c a l f e a t u r e s s u c h a s u p t u r n e d plates, m e a n d e r i n g ridges a n d large scale d i s h pits h a v e s u r v i v e d in spite of t h e diagenetic p r o c e s s e s . The f e a t u r e s p o i n t to a n earlier eolian p h a s e (Coch a n d Krinsley, 1971; Margolis a n d Kinsley, 1971; Krinsley a n d D o o m k a m p , 1973; Margolis a n d Krinsley, 1974; Krinsley, F r i e n d a n d Klimentidis, 1976, Krinsley a n d WeUendorf, 1980) before t h e last fluvial s e d i m e n t a t i o n of t h e N u b i a S a n d s t o n e . The r o u n d e d a n d w o r n e d e d g e s of t h e q u a r t z g r a i n s (Fig. 5) m a y c o n f i r m t h e o c c u r r e n c e of t h e aeolian phase. The origin of c h e m i c a l f e a t u r e s h a s b e e n d i s c u s s e d b y H a y e t al., (1971), Margolis (1971), Doork a m p a n d Krinsley (1971), a n d Fitzpatrich a n d S u m r n e r s o n (1971). T h e y a t t r i b u t e d t h e s o l u t i o n a n d r e p r e c i p i t a t i o n p h e n o m e n a of silica on the q u a r t z g r a i n s to t h e i r location in t h e zone of w e a t h e r i n g , w h e r e t h e y were e x p o s e d to rain water, organic a c t i o n a n d p r o b a b l y fairly rapid c h a n g e s in pH a n d t e m p e r a t u r e . A c c o r d i n g to Krinsley a n d T a k a h a s h i ( 1962), W a u g h ( 1970), H a y eta/., ( 1971) a n d Krinsley e t aL, (1976), c r a c k s a n d s m o o t h s u r f a c e s are p r o d u c e d b y precipitation of silica in h o t d e s e r t a n d indicate t h a t t h e grain w a s b u r r i e d in s e d i m e n t s for a long time. In view of t h e above m e n t i o n e d o b s e r v a t i o n s t h a t t h e silica precipitation a n d d i s s o l u t i o n r e p r e s e n t t h e last s t a g e s in t h e d e v e l o p m e n t of t h e N u b i a S a n d s t o n e , the a u t h o r s inclined to relate t h e m to in situ r e a c t i o n s of i n t r a s t r a t a l s o l u t i o n s p o s s e s s i n g different pH v a l u e s . S u c h differences in pH v a l u e s m a y have c o n t r i b u t e d to climatic c h a n g e s . CONCLUSIONS The s t u d y of t h e s u r f a c e f e a t u r e s of the q u a r t z g r a i n s in t h e Central E a s t e m D e s e r t of Egypt revealed its c o m p l e x d e p o s i t i o n a l history. Three s t a g e s are reflected; early p h a s e of a e o l i a n p r o c e s ses; s e c o n d p h a s e of fluvial s e d i m e n t a t i o n ; a n d a third p h a s e of d i a g e n e s i s b y i n t r a s t r a t a l solutions. REFERENCES Ahmed, E.A. (1983). Sedimentology and tectonic evolution ofWadi Qena area, Egypt. Ph.D. thesis : 136 p., Assiut Univ. Egypt. Ball, J. (1907). A description of the first or Aswan cataract of the Nile, Egypt. Surv. Dept. Cairo, 121 pp. Barron, T. (1907). The topography and geology of the Peninsula of Sinai (Westem Portion), Egypt. Surv. Dept. Cairo, 241 pp.
877
Barthouk, U.C. (1922). Chronologie et description des roches lgnees du D6sert arabique. MerrL Inst. Egypt, v. 52, 62 pp. Blshara, W.W. and Nasr, M. (1973). On the heavy mineral content of some Nublan Sandstone exposures in Kharga Oasis. B u l l Fac. Sci., University of Assiut, Egypt, v. 2, pp. 67-76. Coch, N. and Krinsley, D.H. (1971). Comparsion of stratlgraphic and electron microscopic studies in Virginia, Pleistocene sediments. J. Geol. 79, 426-437. Doomkamp, J. and Krinsley, D.H. (1971). Electron microscopy applied to quartz grains from a tropical environment. Sedimentology, 17, 89- I0 I. EI-Shazly, M.M. and Shata, A. (1960). Contribution to the study of the heavy minerals in the Nubian Sandstone section of the NewValley project area, part 1, E 1, Kharga Oasis. BulL Inst. Desert Egypt, v. I O, pp. 1118. Fitzpatrich, K.R. and Summerson, C.H. (1971). Some observations on electron micrographs of quartz sand grains. OhioJ. ScL 71, 106-119. Fourtau, R. (1902). Sur le Gres Nubien C.R. Acad. Sci. (Paris) n ° 19, 1, Nov. pp. 803-804. Klitzsch, E., Harms, J.C., Lejal-Nicol, A. and List, F.K. (1979. Major subdivisions and depositional environments of Nubia Strata, Southwest Egypt. B u l l Am. Assoc. Pet. GeoL, 63, 967-974. Krinsley, D.H. and Doomkamp. J. (1973). Atlas of Quartz Sand Surface Textures, Cambridge University Press. 91 pp. Krinsley, D.H., Friend, P. and Klimentidis, R. (1976). Eolian transport textures on the surfaces of sand grains of early Triassic age. BulL Geol. Soc. An. 87, 130-132. Krinsley, D.H. and Wellendorf, W. (1980). Wind velocities determined from the surface textures of sand grains. Nature, 283, n ° 5745, 372-373. Margolis, S.V. and Krinsley, D.H. (1971). Submicroscopic frosting on eolian and subaqueous quartz sand grains. BulL Geol. Soc. Am. 82, 3395-3406. Margolis, S.V. and Krinsley, D.H. (1979). Processes of formation and environmental occurrence of micro features on detrital quartz grains. Am. J. ScL 2 7 4 , 4 4 9 464. Picard, L. (1943). Structure and evolution of Palestine with comparative notes on neighbouring countries. Bull. Geol. Dep. Hebrew Univ., Jerusalem, V. 4, n ° 24, 134 pp. Russeger, J.R. (1837). Kreide Und Sandstein. Einfluss Von Granit auf letztem. N e u e s Jahrb. Mineral., pp. 665-669. Said, (1962). The geology of Egypt. 337 pp. Amsterdam/ New York, (Elsevier pub. Com.). Shukri, N.M. and Said, R. (1944). Contribution to the geology of the Nubian Sandstone. Part I. Field Observation and Mechanical Analysis. Bull. F a e . Sei. Cairo. Univ., v. 25, pp. 149-172. Shukri, N.M., and Ayouti, M.K. (1953). The mineralogy of the Nubian Sandstone in Aswan. BulL Inst. Desert Egypt. v. III, pp. 65-88. VanHouten, F.B. and Bhattacharyya, D.P. (1979). Late Cretaceous Nubia Formation et Aswan, Southeastem desert, Egypt. Ann. GeoL Surv. Egypt, v. 9, pp. 408431.
E. A. AHMEDand MOHAMEDA. SOLIMAN 878 Walter, J.I~ (1888). Die KoraUenriffe der sinahalblnsel; Waugh, B. (1970). FormaUon of quartz overgrowths In Geologlsche und Biologische Bobachtungen. Abhandl, the Penrith Sandstone (Lower Permian) of northwest Sachs, Akad. Wissleipzig, Math-Nautricki. England as revealed by scanningelcctron microscopy. Ward, W.C. and McDonald, K.C. (1979). Nubia FormaSedimentology, 14, 309-320. tion of central Eastern Desert, Egypt-Major subdiviYoussef, M.I. (1957). Upper Cretaceous rocks in Kosseir sions and deposltional setUng. AAPGBul/., v. 83, pp. area. B u l l InsL Desert Egypt, vol. 7, pp. 35-54. 975-983.
Fig. 6 Chemical features: V-shaped etched pits and silica globules, Qufft-Quseir roas. Bar length = 1 micron. Fig. 7 Chemical features: Corrosion of overgrowthed quartz, Quseir area, Red Sea. Bar length = I 0 microns. Fig. 8 Chemical features: Triangular etched V-shaped pits probably parallel to cleavage planes, and polygonal cracks, north of the Wadi Quena. Bar length --- 100 microns
0731 7247/88 $3.00 +0.00 Pergamon Press plc
Printed in Great Britain
Quartz surface textures of some cretaceous Nubian sandstone exposures, Central Eastern desert, Egypt. E.A. AHMED and MOHAMED A. SOLIMAN Departmentof Geology,Facultyof Science, AssiutUniversity Assiut, Egypt (Receivedfor publication March 11, 1988) Abstract - Thecommonand dominantsurfacefeaturesobservedin the quartzgrainsof the Nubia Sandstoneencompassbothmechanicaland chemicalfeatures.Suchfeatures point to a complexdepositionalhistoryof the NubiaSandstoneincludingdepositionby aeolianprocessesfollowedby fluvialsedimentation.Diagenesisin theNubiaSandstone is representedby silicaprecipitationand dissolution. INTRODUCTION
Depositional history of the Nubia Sandstone (Russeger, 1837, Youssef, 1957) h a s p u ~ l e d the geologists for a long time. F o u r t a u (1902), B a r t h o u s (1922) and Picard (1934) suggested aeolian processes. Bail (1907), S h u k r i a n d Said (1944) adovcate a shallow m a r i n e depositional environment. Barron (1907) assigns a fluvio-marine condition. Recently, b a s e d on a detailed facies studies, Klitzsch et aL, (1979), Van H o u t e n a n d B h a t t a c h a r y y a (1979), Ward and McDonald (1979), A h m e d (1983) and Soliman et aL, (1986) advocate a fluvial origin for the Nubia Sandstone. Moreover, a n impressive p h e n o m e n o n in the Nubia S a n d s t o n e is its mineralogical m a t u rity. It is essentially c o m p o s e d of ultrastable mineral c o n s i t u e n t s (quartz, zircon, tourmaline and rutile). This led m a n y a u t h o r s to predict a multicyclic s e d i m e n t a t i o n as essential factor in the depositional history of the Nubia S a n d s t o n e (Shukri a n d El Ayouti, 1953; El Shazly a n d Shata, 1960; Bishara a n d Nasr, 1973). Soliman (1983) presents indications for a direct i n p u t of clastics from the b a s e m e n t complex. The aim of this work is to introduce the findings of the investigations of the surface texture of the quartz grains a n d their contribution to the depositional history of the Nubia Sandstone. M E T H O D S OF STUDY
The studied samples were collected from four
873 AES 7 7/8--A
m e a s u r e d c o l u m n a r sections representing the Cretaceous Nubia Sandstone fYoussef, 1957: Saud, 1962) in the areas situated at Kin. 80 along QiR Quseir road, Quseir, Km. 60 along Qena-Safaga road a n d the n o r t h e m r e a c h of Wadi Qena (Figs. 1,2). Friable s a n d s t o n e samples were chosen and the quartz grains were separated using the binocular microscope. The samples were p u t in a n ultrasonic vibrator, cleaned by 30 % Hcl for 5 minutes, w a s h e d by distilled water a n d dried. Photos for the surface texture of the quartz grains were t a k e n using Philips Scanning Electron Microscope. More t h a n 300 grains representing the different m e a s u red c o l u m n a r sections were investigated. RESULTS
Two different types of surface features were observed on the quartz grains : Mechanical features (Figs. 3, 4 & 5) including m e a n d e r i n g ridges a n d grooves, oriented cleavage fractures, large scale d i s h s h a p e d pits, u p t u r n e d plates and polygonal cracks. Chemical features (Figs. 6, 7 & 8) including silica over-growths and silica globules, smooth surfaces, oriented V. shaped pits and triangular facets and surface corrosions. DISCUSSION
Intensive chemical diagnosis acting in the Nubia S a n d s t o n e is marked. This is manifested by two phases of silica precipitation and dissolution. S u c h
874
E . A . AHMED and MOHAMED A. SOLIMAN
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Sample locations
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\
Plant remains
J-'~ Ripple marks
Oyster bed
~Shale
~Sondstone
Horizontal lamination
Trough cross-bedding
Tabular cross- bedding
Recumbent cmss-bedd;ng
Cenomanian-Turonian AI bian- c enomanian
wadi Oena Fro.
Coniacian-componion
Age (Hendriks et. al. 1987 )
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Hawoshya Fro.
Lithostratigraphic units
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E . A . AHMED and MOHAMED A. SOLIMAN
Fig. 3 Mechanical features: m e a n d e r i n g ridges and groove, n o r t h ofWadi Quena. Bar length = 100 microns. Fig. 4 Mechanical features: U p t u m e d plates and d i s h - s h a p e d pits, n o r t h ofWadi Quena. Bar length = 10 microns. Fig; 5 Rounded and w o r n e d quartz grain. Note the large scale d i s h s h a p e d pits a n d smooth surface, Quseir area. Bar length = 100 microns.
Quartz surface textures of sandstone exposures c h e m i c a l f e a t u r e s r e p r e s e n t t h e final fingerprints o n t h e s u r f a c e of t h e q u a r t z g r a i n s a n d p r o b a b l y d e s t r o y e d t h e m e c h a n i c a l f e a t u r e s of t h e fluvial p r o c e s s e s a s p r e d i c t e d b y m a n y a u t h o r s (e.g. Klitzseh e t aL, 1979; W a r d a n d McDonald, 1979; A h m e d , 1983: S o l i m a n e t a l . , 1986). Nevertheless, o t h e r m e c h a n i c a l f e a t u r e s s u c h a s u p t u r n e d plates, m e a n d e r i n g ridges a n d large scale d i s h pits h a v e s u r v i v e d in spite of t h e diagenetic p r o c e s s e s . The f e a t u r e s p o i n t to a n earlier eolian p h a s e (Coch a n d Krinsley, 1971; Margolis a n d Kinsley, 1971; Krinsley a n d D o o m k a m p , 1973; Margolis a n d Krinsley, 1974; Krinsley, F r i e n d a n d Klimentidis, 1976, Krinsley a n d WeUendorf, 1980) before t h e last fluvial s e d i m e n t a t i o n of t h e N u b i a S a n d s t o n e . The r o u n d e d a n d w o r n e d e d g e s of t h e q u a r t z g r a i n s (Fig. 5) m a y c o n f i r m t h e o c c u r r e n c e of t h e aeolian phase. The origin of c h e m i c a l f e a t u r e s h a s b e e n d i s c u s s e d b y H a y e t al., (1971), Margolis (1971), Doork a m p a n d Krinsley (1971), a n d Fitzpatrich a n d S u m r n e r s o n (1971). T h e y a t t r i b u t e d t h e s o l u t i o n a n d r e p r e c i p i t a t i o n p h e n o m e n a of silica on the q u a r t z g r a i n s to t h e i r location in t h e zone of w e a t h e r i n g , w h e r e t h e y were e x p o s e d to rain water, organic a c t i o n a n d p r o b a b l y fairly rapid c h a n g e s in pH a n d t e m p e r a t u r e . A c c o r d i n g to Krinsley a n d T a k a h a s h i ( 1962), W a u g h ( 1970), H a y eta/., ( 1971) a n d Krinsley e t aL, (1976), c r a c k s a n d s m o o t h s u r f a c e s are p r o d u c e d b y precipitation of silica in h o t d e s e r t a n d indicate t h a t t h e grain w a s b u r r i e d in s e d i m e n t s for a long time. In view of t h e above m e n t i o n e d o b s e r v a t i o n s t h a t t h e silica precipitation a n d d i s s o l u t i o n r e p r e s e n t t h e last s t a g e s in t h e d e v e l o p m e n t of t h e N u b i a S a n d s t o n e , the a u t h o r s inclined to relate t h e m to in situ r e a c t i o n s of i n t r a s t r a t a l s o l u t i o n s p o s s e s s i n g different pH v a l u e s . S u c h differences in pH v a l u e s m a y have c o n t r i b u t e d to climatic c h a n g e s . CONCLUSIONS The s t u d y of t h e s u r f a c e f e a t u r e s of the q u a r t z g r a i n s in t h e Central E a s t e m D e s e r t of Egypt revealed its c o m p l e x d e p o s i t i o n a l history. Three s t a g e s are reflected; early p h a s e of a e o l i a n p r o c e s ses; s e c o n d p h a s e of fluvial s e d i m e n t a t i o n ; a n d a third p h a s e of d i a g e n e s i s b y i n t r a s t r a t a l solutions. REFERENCES Ahmed, E.A. (1983). Sedimentology and tectonic evolution ofWadi Qena area, Egypt. Ph.D. thesis : 136 p., Assiut Univ. Egypt. Ball, J. (1907). A description of the first or Aswan cataract of the Nile, Egypt. Surv. Dept. Cairo, 121 pp. Barron, T. (1907). The topography and geology of the Peninsula of Sinai (Westem Portion), Egypt. Surv. Dept. Cairo, 241 pp.
877
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Fig. 6 Chemical features: V-shaped etched pits and silica globules, Qufft-Quseir roas. Bar length = 1 micron. Fig. 7 Chemical features: Corrosion of overgrowthed quartz, Quseir area, Red Sea. Bar length = I 0 microns. Fig. 8 Chemical features: Triangular etched V-shaped pits probably parallel to cleavage planes, and polygonal cracks, north of the Wadi Quena. Bar length --- 100 microns