CONTRIBUTIONS TO THE FAULTED-DOWN EOCENE LIMESTONES OF THE SOUTHERN GALALA PLATEAU "ST PAUL AREA" GULF OF SUEZ, EGYPT
Second Int. Conf. Geology of the Arab World, Cairo University, 1994.
CONTRIBUTIONS TO THE FAULTED-DOWN EOCENE
LIMESTONES OF THE SOUTHERN GALALA PLATEAU
"ST. PAUL AREA", GULF OF SUEZ, EGYPT
Abou-Khadrah, A.M. ; Darwish, M. and El-Azabi, M.
Geol. Dept., Fac. Sci., Cairo Univ., Egypt
ABSTRACT
The Eocene rocks represent an important lithostratigraphic record in the geologic evolution of the Southern Galala plateau. They contain various lithofacies characters and sedimentary features unlike those well developed in the Nile Valley and Western Desert of Egypt. The faulted-down Eocene rocks of the Southern Galala plateau in St. Paul area consist of well-bedded partly massive limestones, with thin dolostone, calcar-eous shale and conglomerate interbeds and occasional thin horizons of chert bands, lenses and nodules. The Eocene limestones exhibit many characteristic sedimentary structures such as brecciation, lenticular bedding, large-scale cross-bedding, wedging- out, undulations, deformed bedding and intense contortions. Such striking syn-sedimentary features make it difficult to use the traditional and well-established nomen-clatures assigned to the other tracts of the country (e.g. upper and central parts of Egypt) to the studied Eocene limestone sequences. The recently suggested Waseiyit For-mation in the Hammam Faraun-Tanka area (facing the study area on the Sinai side of the Gulf of Suez) is more applicable and recommended.
The Eocene faulted-down blocks of St. Paul area are clearly enriched in Nummulites gizehensis Forskal of Early Lutetian age, while the basal Eocene rocks which directly overlie the Paleocene (Landanian) rocks at the scarp face of the Southern Galala pla-teau are dated as Early Eocene (Ypresian). The lithofacies characters of the studied se-quences point to deposition under shallow marine conditions alternating with a relative-ly open marine regime. Such conditions were periodically interrupted by syn-depositional tectonic activities which have strongly printed their effect on the develop-ment of the sequences.
INTRODUCTION
St. Paul area is located in the central western part of the Gulf of Suez CFig. 1). the area lies between Latitudes 28'44' and 28° 57' N (Fig. 2). Bordering the area from the west is the Southern Galala (El-Galala El-Qibliya) plateau which forms a promi-nent structural high rising some 1200m above sea level, becoming gradually lower to the west where it merges into the central plateau of the Eastern Desert of Egypt. The area is limited from the east by the Gulf of Suez coastal plain. Topographically, St. Paul area consists of faulted blocks and
ridges of relatively moderate relief. The blocks are formed of sedimentary se-quences that range in age from pre-Cenomanian to Eocene. They flank the prominent topographic high of the South-ern Galala plateau. The faulted-down blocks are onlapped uncomfortably by the Miocene-Pliocene sequence in the eastern reach of St. Paul area.
The good exposures, lithofacies charac-ters and scarcity of published studies on the Eocene faulted-down blocks of the Southern Galala plateau attracted the at-tention of the present authors to carry out this research. The present work deals with the stratigraphy, lithologic characteristics and field occurrence of the Eocene rocks exposed in St. Paul area to throw more light on their probable depositional envi-ronments and sedimentational history dur-ing the Eocene period.
PREVIOUS STUDIES
As far as the authors are aware, no comprehensive studies have been pub-lished on the stratigraphy of the Eocene rocks of St. Paul area. Most of the previ-ous studies, carried out both in St. Paul and the northern extremity of the Southern Galala plateau, had been directed to the Cretaceous-Paleocene sequence. Of these the works of Blanckenhorn (1921), Cuvil-lier (1930), Foley (1942), Irving (1945), Abdallah and El-Adindani (1963), Awad and Abdallah (1966), Abdou (1969), Ab-dallah and Eissa (1970), El-Shazly et al. (1979), Abou-Khadrah et al. (1984 & 1985), Strougo (1986), Abdel-Fattah (1987), Haggag (1991), Strougo et al. (1992) and others have to be mentioned. Few studies have dealt with the general stratigraphy of the Eocene rocks in the Southern Galala and St. Paul area. These include: Soliman et al. (1965), Ismail and
Abdallah (1966), Abdou et al. (1969), Abdallah et al. (1970), Abdel Kireem (1971), Abdel-Kireem and Abdou (1979), Mazhar et al. (1979), El - Azabi (1986), Bandel and Kuss (1987) and Abou-Khadrah et al. (1987).
In addition, subsurface data is gained from two exploratory wells (Ezz El-Orban wells, No. 1 and 2) drilled in the coastal plain of St. Paul area. The bio- and litho-stratigraphy of the subsurface Lower Pale-ogene and older sediments in Ezz El-Orban wells were studied by Ansary and Tewfik (1966), Barakat and Tewfik (1966), Barakat and Fahmy (1969) and Ansary and Fahmy (1969).
LITHOSTRATIGRAPHY
The Eocene rocks represent a remarka-ble lithostratigraphic unit among the ex-posed sedimentary sequence in St. Paul area (Fig. 3). They form the block faulted hills around and to the east of St. Paul Monastery as well as the upper scarp face and the plateau surface of the Southern Ga-lala (Fig. 2). The Eocene rocks overlie uncomfortably the Paleocene (Landanian) rocks and underlie uncomfortably the Mi-ocene rocks. The contact with the underly-ing and overlying sequences is easily trace-able due to lithologic variations. The faulted-down Eocene blocks form asym-metrical ridges, while the Eocene plateau of the Southern Galala exhibits a steep and vertical inaccessible face. The Eocene rocks consist mainly of hard well-bedded, occasionally
sequences of St. Paul area differ radically from those well exposed in the Nile Val-ley and the Western Desert of Egypt. They seem to be similar to the exposed Eocene rocks in west central Sinai "Hammam Fa-raun-Gebel Tanka area". Most of the previous works conducted in the studied area were carried out at a hill in the vicinity of St. Paul Monastery "Gebel St. Paul". Of interest is the work of Ismail and Abdallah (1966) who pointed out to the occurrence of thick conglomer-ate beds (about 20m) at the base of the Eo-cene sequence indicating a major uncon-formity between the Landanian (Upper Paleocene) foraminiferal marls and the Lower Lutetian (Middle Eocene) calcare-ous grits and "marly" limestones. Abdou et al. (1969) recognized the following foraminiferal assemblages in a hard sili-ceous limestone sequence immediately above the Upper Paleocene rocks: Num-mulites atacicus Leymerie, N. lucasi D'Arch., Alveolina cf. oblonga d'Orbigny, Operculina sp., Orthophragmina sp. and miliolids. They attributed these assem-blages to the Middle Eocene "Early Lute-tian" but did not refer to the thick Lower Eocene conglomerate beds of Ismail and Abdallah (1966).
In the present study, three main surface sections are measured to clarify the litho-stratigraphy of the Eocene rocks in St. Paul area. The stratigraphic sections are denoted as El-Deir, Wadi Girf El-Bahari and Wadi Girf. They represent suitable reference sections for the exposed Eocene rocks in St. Paul area. The first studied section (El-Deir) has been measured at the scarp face of the Southern Galala plateau, northward of St. Paul Monastery (section A, Fig. 2). It represents the lower part of the Eocene sequence which directly over-lies the Landanian rocks. The second stra- tigraphic section is a composite one, meas-ured along Wadi Girf El-Bahari (sections Bl, B2 & B3, Fig. 2) to represent most of the faulted-down Eocene limestones from the Southern Galala plateau. The third (Wadi Girt) section represents the missing part of the Eocene sequence measured along Wadi Girf El-Bahari (section C, Fig. 2). It is worth to mention that a complete and continuous stratigraphic section of the Eocene rocks could not be recorded at any locality in St. Paul area due to faulting ef-fect. Measuring a continuous section of the Eocene rocks along the eastern scarp of the Southern Galala plateau is nearly impossi-ble due to steep and vertical scarp face of the plateau. The following is a detailed de-scription of the studied Eocene sequences and their measured stratigraphic sections:
1) Lower Eocene (El-Deir) sequence.
This sequence has been sampled direct-ly above the Landanian rocks at the scarp face of the Southern Galala plateau about 1.2 km north of St. Paul Monastery (Latitude 28° 51' 38" N and Longitude 32° 32' 23" E, section A, Fig. 2). The boundary between the Paleocene and Eocene rocks can be tentatively traced, both lithological-ly and topographically where the argilla-ceous limestones of the Late Paleocene form a slope face that contrast with the overlying bedded Eocene limestones which form a conspicuous scarp with steep and vertical face. However, palaeontologically the poor preservation and reduced number of planktonic foraminifera prevent a clear recognition of the Paleocene-Eocene boun-dary (Strougo et al., 1992).
are pale yellow, yellowish brown, creamy, rarely pale grey and reddish brown, hard to moderately hard, very fine to coarse- grained lime sands, partly argillaceous and sandy, and usually form marked consecu-tive ledges, 2 to 3 m in height. The lime-stones usually contain greyish brown chert (flint) bands, lenses and nodules especially in the middle part of the sequence. The chert bands are 8 to 15 cm in thickness, while the chert nodules dispersed within the limestones have different sizes varying from 1 to 6 cm in diameter, with their el-ongation parallel to the bedding plane. The limestones are highly fossiliferous with small-sizedNummulites sp., Alveolina sp., Operculina sp., Globorotalia sp., Dis-cocyclina sp. together with many other large foraminiferal tests, thick-walled oyster shells, echinoids and shell debris. The sequence is characterized by many sedimentary structures such as brecciation, lenticular and deformed bedding, large- scale cross-bedding, wedging- out, bur-rows and reworked limestone lithoclasts especially in the lower and upper meas-ured parts of the sequence. The limestones usually alternate with thin, 1 to 5 cm thick, argillaceous limestone interbeds in the basal part. In addition, a few green to greyish brown papery shale interbeds are observed within the sequence.
The measured sequence is capped by reddish brown, fine-crystalline hard dolo-stone beds which can be traced laterally for a long distance. The sampling could not be continued elsewhere upwards due to the very steep and rough scarp face of the Southern Galala plateau. The Eocene sequence of El-Deir section extends nearly horizontal or with a very gentle dip to-wards the west and attains a total meas-ured thickness of about 56m.
The limestone conglomerate bed, de-scribed by Ismail and Abdallah (1966) at the base of the Eocene sequence of Gebel St. Paul, is not observed in the above measured section. Of significance is the fact that Gebel St. Paul located some 1.5 km to the south of El-Deir section (Fig. 2). The conglomerates (about 5 m thick) con-sist of tightly-packed hard siliceous lime-stone clasts, cheifly of cobble and boulder size, embedded in a fine sandy lime-mud matrix. The conglomerate bed was also recorded in a hill near Bir Abu-Kheleifi "Fig. 2" by Thiebaud (1939).
Another stratigraphic section measured in a hill located about 2.8 km southeast of St. Paul Monastery (Latitude 28°49' 40" N and Longitude 32 33' 24"E, Fig. 2), shows that the Eocene rocks directly overlying the Paleocene rocks are represented by yel-lowish brown sandy limestones with 10-20 cm thick calcareous sandstone interbeds (Fig. 4D). The sandy limestones are hard, thick-bedded and highly fossiliferous with small-sized Nummulites sp. which increase in size upwards. The calcareous sandstone interbeds are rich in Nummulites sp. and echinoid spines. The clear lithologic varia-tions marking the basal Eocene rocks are most probably related to the palaeotopo-graphy inherited from the Late Paleocene tectonism, named the "Velascoensis event" by Strougo (1986), and the syn-depositional block faulting.
The microfacies characters of the Eo-cene limestones of El-Deir sequence point to deposition under alternating conditions of open-marine and shallow back-shoal en-vironments. The sequence starts with an open-marine pelagic carbonate sedimenta-tion (about 17m thick) with low to moder-ate occurrence of planktonic forams (e.g. Globorotalia sp.) and rare benthonics (e. g. Textularia sp. and micron - sized
Nummulites sp.) as well as thin-walled bivalves. The faunal content is embedded in a dense lime-mud matrix (pelagic lime-mudstone to wackestone, Fig. 5 A). The pelagic carbonate deposition had been fol-lowed by three depositional cycles of fining-upward pattern (Fig. 4A), each begins with skeletal limestones of shallow back-shoal environment and terminates with pelagic limestones. The skeletal lime-stones are enriched in benthonic forami-nifera (e.g. Nummulites sp., Alveolina sp., Operculina sp., Discocyclina sp., Assilina sp., Bolivina sp., miliolids) with other less abundant skeletal particles such as small- sized gastropods, large oyster debris, algal fragments, echinoids, coral debris, ostra-cods and non skeletal peloids. This assem-blage is coupled with the scarcity of pelagic foraminifera. The wackestone, packstone and rudstone (algal Nummulitic wackstone, foraminiferal peloid wacke-stone, sandy Nummulitic wackestone/ packstone, algal Nummulitic packstone, echinoid Alveolinid Nummulitic pack- stone, sandy Alveolinid Nummilitic pack- stone / rudstone & intraclastic algal Num-mulitic rudstone) are the dominant lithofacies types in the studied skeletal
limestones (Fig. 5B & C). The presence of many sedimentary features (e.g. cross- bedding, brecciation), reworked skeletal debris and dominant packstone/rudstone lithofacies are indications of the shallow water deposition, within the range of cur-rent activity which cause winnowing and consequently the mechanical concentration and accumulation of the skeletal constit-uents. The skeletal limestones of the shal-low-water environment were terminated, in each depositional cycle, by pelagic sedi-mentation. The latter is represented by limestone rich in planktonic forams (Globorotalia wackestone/packstone, Fig. 5 D) of quiet water, open-marine conditions. The basal sandy nature of the Eocene sequence south of St. Paul Monastery is, most probably, due to its proximity to a palaeostructural high which provided the detrital sand grains. The chert nodules, lenses and bands present in the limestone sequence are of diagenetic origin. They are formed due to dissolution of some sili-ceous organisms such as radiolaria and diatoms, abundant in deep-water pelagic sediments, by silica depleted pore-fluids which is then reprecipitated within the limestones in different forms.
Fig. 5 Microfacies characters of the Waseiyit Formation in St. Paul area:
A) Planktonic foraminiferal tests randomly scattered in a dense cloudy lime-mud matri, pelagic wacke-stone, El-Deir section. Notice selective aggrading neomorphism of the foraminiferal tests (P.P.L.). B) Abundant skeletal particles (Nummulites, Alveolines, Miliolids, algal fragments, molluscon debris, echi-noids) and peloids embedded in a little, partially recrystallized, lime-mud matrix and granular sparry cal-cite cement with frequent quartz grains, sandy Alveolinid Nummulitic rudstone, El-Deir section (O.L.). C) Large reworked intraclasts tightly-packed in a little dense lime-mud matrix rich in Nummulites, Discocy: clines, Operculines and algal fragments, intraclastic algal Nummulitic rudstone, El-Deir section (O.L.). D) Tightly-packed planktonic foraminiferal tests and shell fragments embedded in a dense lime-mud matri%, Globorotalia wackestone/packstone, El-Deir section (P.P.L.). E) Abundant benthonic foraminifera (Nummulites, Operculines, miliolids) and algal fragments embedded in a sand-rich lime-mud matrix, sandy Nummulitic wackestone, Wadi Girf El-Bahari section. Notice, parallel orientation of the benthonic forams (O.L.). F) Large Nummulites, shell fragments, and peloids cemented by granular sparry calcite with a few lime-mud, Nummulitic peloid rudstone, Wadi Girf El-Bahari section. Notice the original radial fibrous structure of some Nummulites (0.L.). G) Nummulites gizehensis Forskal, small-sized Nummulites spp. and many other benthonics stacked together in a chaotic manner, Nummulites pocket, Nummulitic rudstone, Wadi Girf El-Bahari section (O.L.). H) Pelagic foraminiferal tests embedded in a dense micro- crystalline limo-mud matrix, partially recrystallized into neomorphic spar, Globorotalia wackestone, Wadi Girl El-Bahari section (P.P.L.).
All Scale bars on the microphotographs = 500 microns.
The occurrence of Lower Eocene sedi-ments was a matter of some controversy in the Southern Galala plateau, in particular at St. Paul area. Foley (1942) pointed out that "the northernmost exposure of the true basal Eocene rocks (mainly chalk and chalky limestone with flint) along the western coast of the Gulf of Suez is at Wadi Uldahal surface section, just to the south of the studied area". At Gebel St. Paul, Ismail and Abdallah (1966) assigned an Early Eocene age to the limestone con-glomerate bed based on their stratigraphic position. Later on, Abdou et al. (1969) who studied the microfaunal content of Gebel St. Paul section, mentioned that the Lower Lutetian rocks directly overlie rocks of Late Paleocene age with a major unconformity due to the absence of the Lower Eocene sequence. In the subsurface, Ansary and Fahmy (1969) described the Lower Eocene se-quence, of about 245m from Ezz El-Orban well No. 1, as composed of hard crystal-line, partly argillaceous, limestone with two main biozones: an upper "Nummulitic" zone and a lower Globorotalia marginodentata Zone of a definite Early Eocene age.
In the neighbouring Gebel Thelmet area in the extreme northeastern corner of the Southern Galala plateau, Abdallah et al. (1970) gave an Early Eocene age to the limestone sequence of their Southern Ga-lala Formation which rests conformably on the Sudr Chalk and underlies the Mid-dle Eocene "Zaafarana Marble". The lime-stone sequence (about 48m) yielded the following microfaunal assemblages : Alveolina decipiens Schwager, Alveolina ovulum Stache, Nummulites subatacicus Antiques, N. atacicus Leymerie and Assilina nili de la Harpe. Abdel-Kireem and Abdou (1979) grouped the Lower Eocene "Ypresian" rocks of Gebel Thelmet in one biozone namely the "Alveolinid" Zone with abundant Nummulites solitarius de la Harpe, Operculina libyca Schwaer, Discocyclina nudimargo (Schwager), Alveolina decipiens Schwager and A. ovulum Stache. They correlated this bio-zone with the "Nummulitic" Zone of Ansary and Fahmy (1969) recorded in Ezz El-Orban well No. 1. The Early Eocene was also given to a succession of sandstone, limestone and "marl" with chert bands and nodules, and small-sized Nummulites (Wadi Irkas Formation) unconformably overlying the Sudr Chalk along the north-ern scarp of the Southern Galala plateau (El-Shazly et al., 1979).
Mazhar et al. (1979) confirmed the field observations of Foley (1940) and stated that "the Lower Eocene rocks taper gradu-ally till they completely disappear just a few kilometers south of St. Paul Monastery (until Latitude 28° 40' N), where the Mid-dle Eocene rocks unconformably overlie the Maestrichtian-Landanian chalk further north".
As a matter of fact, all the biostrati-graphic studies carried out on the surface and subsurface sections in and around St. Paul area (Ansary and Fahmy, 1969; Abdallah et al., 1970; Abdel-Kireem and Abdou, 1979 and El-Shazly et al., 1979) revealed the presence of a Lower Eocene sequence (50-245m) above the Upper Pale-ocene rocks. Abdou et al. (1969) were the only workers who reported the presence of an unconformity between the Landanian and the overlying Early Lutetian sequence at Gebel St. Paul due to the absence of Lower Eocene rocks. In fact, they neglec-ted the limestone conglomerate bed of Early Eocene age given by Ismail and Abdallah (1966) at Gebel St. Paul. These Eocene rocks are dated recently by Haggag
(1991) and Strougo et al. (1992) as Early Eocene. However, Haggag (1991) pointed out that the rare, very small-sized and poorly preserved Eocene foraminiferal fauna prevent their use for reliable zona-tion. This may explain the reason for the contradictory opinions concerning the presence or absence of Lower Eocene rocks in St. Paul area. In conclusion, an Early Eocene age is assigned to the basal Eocene sequence which directly overlies the Upper Paleocene rocks in St. Paul area.
2) Middle Eocene Sequence.
This sequence has been measured along Wadi Girf El-Bahari to represent most of the faulted-down Eocene limestones of the Southern Galala plateau in the studied area. The sequence is widely exposed to the north of Wadi EI-Deir and extends southward as a narrow strip until the north of Wadi Uldahal (Fig. 2). The Middle Eo-cene rocks are faulted down against Creta-ceous rocks of the footslopes of the South-ern Galala plateau. While eastwards, they are onlapped unconformably by the younger Miocene-Pliocene sediments. To the north of Wadi Girf, the Middle Eocene rocks are faulted down against Lower Eo-cene sediments of the upper scarp face of the Southern Galala plateau (Fig. 2) where the fault throw dies out northwards.
Lithologically, the Eocene rocks ex-posed along Wadi Girf El-Bahari are mainly represented by thick-bedded lime-stones, slightly argillaceous, chalky and dolomitic (Fig. 4B1-B3). The limestones show different colours, mainly pale grey, cream, yellowish, pinkish and greyish brown, snow white. They are well to mod-erately indurated, fine-grained to coarse
Lime sands, thick-bedded but rarely mas-sive, thin-bedded and cross-bedded. The individual bed thickness varies from 40 to 70 cm. The limestones are partly sandy, with scattered fine to coarse-grained quartz sands. The rocks are fossiliferous with Nummulites gizehensis Forskal, small-sized Nummulites spp., Alveolina sp. and Operculina sp. with badly preserved bivalves "Ostrea sp." and gastropods as well as shell fragments. The faunal content is usually concentrated as pockets and bands within the sequence. The limestones are highly fractured, weathered and caver-neous showing numerous open fissures, sinkholes, caves, carrens and brecciation (Fig. 6) especially in the lower part of the sequence referring to effective palaeokarst conditions. Sometimes, fresh water blocky and drusy sparry calcite crystals complete-ly fill the fissures, veinlets and caves ex-hibiting dog tooth form.
The argillaceous limestones intercalat-ing the sequence are yellowish to greyish brown, moderately hard, thin-bedded and poorly fossiliferous. While, the dolostones are yellowish to reddish brown, hard, mas-sive, fine-crystalline and non-fossiliferous. The sequence is capped by moderately in-durated, snow white to violet sandy lime-stone beds rich in small-sized Nummulites sp. The detrital constituents may reach up to 35% of the total framework and vary from fine to very coarse sand size. The strata of this sequence extend nearly hori-zontal or with a very gentle angle of dip to-wards the west and reach a total thickness of about 162m.
It is noted that the top of the middle part of the Eocene sequence along Wadi Girf El Bahari section (Fig. 4B2) is missing due to faulting. The stratigraphic gap is represent-ed by fissile shale and argillaceous lime-stone interbeds as observed in the northern
Flank of Wadi Girf El-Bahari. They are present in a very reduced and highly weathered nature. The missing part of the Eocene sequence along Wadi Girf El-Bahari is measured in Wadi Girf (Latitude 28° 54' 57"N and Longitude 32° 36' 42"E, section C, Fig. 2). The sequence consists of snow white chalky limestone at the base (Fig. 4C), with chert interbeds (each is about 10 cm in thickness), followed up-wards by shale and argillaceous limestone interbeds. The shale is greyish brown, pa-pery, compact, calcareous, salty and gyp-siferous. While, the argillaceous limestone is yellowish brown, moderately hard, fine- crystalline, thin-bedded and non fossilifer-ous. These interbeds are followed upsec-tion by greyish white, thick-bedded hard limestones with thin greyish brown shale intercalations. The limestone is fossilifer-ous with small-sized Nummulites sp. This part of the sequence is believed to be equivalent to the missing part of the Eocene sequence measured along Wadi Girf El-Bahari (Fig. 4B2). It attains a measured thickness of 21m.
The upper part of Wadi Girf section (Fig. 4C) consists essentially of thick- bedded hard fossiliferous limestones with small-sized Nummulites sp. and Nummu-lites gizehensis Forskal which occur as localized pockets. In these pockets, the nummulite tests may show either chaotic stacking or parallel orientation. Generally, the limestones are highly weathered and fractured with numerous caves and sink-holes. The sequence dips toward the south-east with a low angle of dip ranges from 10 to 15°.
Southwards, the upper part of Wadi Girf sequence shows a remarkable facies change where the well-bedded limestones change laterally into massive limestone conglomerates (Fig. 4E). The maximum thickness, about 20m, is measured along a small tributary about 3km from the en-trance of Wadi El-Deir (Fig. 2). The facies change starts as conglomerate intertongues and lenses within the bedded limestones. The conglomerates are yellowish brown, well indurated, massive, grain-supported (orthoconglomerate), and entirely formed of fine-grained Eocene limestone litho-clasts, of boulder, cobble, pebble and gran-ule size which are densely - packed in a sandy lime-mud matrix (closed work tex-ture). The clasts of these poorly-sorted oligomictic conglomerates are rounded to subrounded, structureless (disorganized) and showing low sphericity, sometimes have central cavities (Fig.7) partly filled with sparry calcite. Further west, the con- Fig. 6 Highly weathered, fractured and caverneous Eocene limestones showing multi-dissolutional and depositional karstic features (e.g. caves, sinkholes, carrens, brecciation, cementation, ....etc.), Wadi Girf El-Bahari, St. Paul area.
Fig. 7 Hard indurated oligomictic limestone conglomerates entirely consisting of poorly sorted Eocene limestone pebbles, cobbles and boulders densely-packed in a sandy fossiliferous lime-mud matrix, a small tributary issues in Wadi El-Deir (about 3km from its entrance), St. Paul area.
Fig. 8 Large-scale asymmetrical undulations (antiforms and synforms) hidden by younger undisturbed Eocene sediments in a small wadi that issues in Wadi El-Deir (Lat. 28° 52' 11" N and Long. 32° 35' 24" E). Notice large-scale lenticular bedding forms one limb of the undulations (lower left side). Photo looking N 50° E.
glomerate beds change again to a pure limestone sequence. The field delineation of the conglomerate body through many traversing wadies indicates that it has a fan-like shape with its apex towards the north indicating a southward palaeocurrent flow. The conglomerates represent subma-rine fan-delta sediments built up in a shelf environment and have accumulated through successive debris-flow deposi-tional process. The conglomerate beds were recorded for the first time in the studied area by El-Azabi (1986). A similar conglomerate facies is recognized in Gebel Hammam Faraun (opposite to St. Paul area) along the eastern side of the Gulf of Suez (Barakat et al., 1985).
The faulted-down Eocene limestones of the Southern Galala plateau exhibit many characteristic primary sedimentary structures such as large-scale cross- bedding, undulations and intense contor-tions. Large-scale cross-bedding shows clearly in some carbonate sand sequences exposed between Wadi El-Deir and Wadi Girf El-Bahari. It consists of inclined dip-ping beds (foresets) bounded by subhori-zontal surfaces. The cross-bedded lime-stones acquire a lens-like form on the outcrop surface (Fig. 8) and may reach up to 2m in thickness of the individual set. They seem to represent a bank or shoal on the shallow marine shelf. Large scale asymmetrical undulations (antiforms and synforms) of localized character are also common. The undulations range in width from 2 to 5 m, rarely more (Fig. 8). The undulating limestone beds are confined to individual horizons within the undeformed sequence. The flanks of the undulating beds have angles of dip vary from 10° to 35°. The restriction of the undulating beds to a single horizon, which are bounded above and below by stratified and undis-turbed strata, ascribed them to the pene- contemporaneous deformational structures. The disturbances which produced such fea-tures took place during or shortly after deposition of sediments and before the overlying beds have been deposited.
In addition, many of the faulted-down Eocene limestone sequences show highly irregular, conspicuous and unusually con-torted bedding. Such contorted bedding be-longs also to the penecontemporaneous deformational structures. The contorted beds show peculiar shapes and arrange-ments, and commonly matched together in a confused and spectacular manner (Figs. 9 & 10). They are lithologically similar to the overlying and underlying undisturbed sediments. The contorted beds are usually several meters in thickness (2-6m). They are thought to have resulted from sliding along gentle slopes under the influence of gravity. Under such conditions, unconsoli-dated sediments which are resting on the unstable slope (i.e. tilted block), lose their stability and slide down slopes under grav-itational action as a coherent mass for some distance until they come to rest as solid and rigid deformed beds. The domi.- nance of contorted beds in the Eocene limestones indicates that the studied area was periodically interrupted by conditions of tectonic instability. Such tectonism was also responsible for the uplift and fragmen-tation of some of the Eocene rocks to form limestone conglomerate interbeds within the bedded limestone sequence.
Generally, the Eocene rocks are highly fragmented and weathered at the contact with the overlying Miocene rocks (Abu Gerfan Formation, El-Azabi, 1986; Abou-Khadrah et al., 1987; Darwish and El-Azabi, 1993) due to long erosional periods before submergence by the Miocene sea. In some localities, especially along Wadi El-Deir and Wadi Girf El-Bahari, it is difficult
or reworked Miocene clasts of the Abu Gerfan Formation. However, the in- situ fragmented clasts at the top of the Eo-cene sequence are usually well-sorted, of boulder size, homogeneous, have the same composition as the original bedrock and are often coated with calcite cement. This intense fragmentation mislead Foley (1942), who measured about 60m of lime-stone boulders with a few thin limestone interbeds at the entrance of Wadi Girf El-Bahari and erroneously considered them as Miocene in age. Actually, the sixty me-ters of limestone boulders that he meas-ured are highly fractured, weathered and karstified Eocene limestones. In this local-ity, the limestone boulders (some of which measure 50 cm in diameter) are embedded in a yellowish brown fine-grained carbo-nate matrix.
The faulted-down Eocene limestones of the Southern Galala plateau at Wadi Girf El- Bahari and surroundings seem to have been deposited in a protected shallow back-shoal environment, interrupted for short periods by low-energy, open-marine pelagic sedimentation. The relative abun-dance of large benthonic foraminifera (e.g. Nummulites, Alveolines, Operculines, miliolids) indicates deposition under well- aerated, warm and shallow-water condi-tions, that most likely to have predominat-ed in shallow marine shelf/ramp environ-ment. Faunal assemblages other than foraminiferal tests are sparse represented by coralline red algae, echinoid spines and thin-walled molluscan bioclasts. The fau-nal content is randomly embedded in a fine-grained, partly sandy, lime-mud ma-trix. The lime-mudstone and wackestone depositional textures are the most domi-nant within the sequence (foraminiferal lime - mudstone, sandy Nummulitic lime- mudstone, Nummulitic wackestone, sandy Alveolinid Nummulitic wackestone, Fig. 5E), while packstone and rudstone are also recorded in certain horizons (sandy Nummulitic packstone, Nummulitic peloid rudstone, Fig. 5F). The lime - mudstone and wackestone rocks imply deposition in a very low energy, back-shoal lagoonal environment. In-situ winnowing of lime- mud and concentration of the benthonic foraminifera by occasional high energy storms have resulted in the formation of the dense packed Nummulites pockets (Nummulitic rudstone, Fig. 5G) observed within the sequence.
The shallow-water depositional environ-ment which prevailed during the deposition of Wadi Girf El-Bahari sequence was punctuated by pulses of pelagic limestone sedimentation (Globorotalia wackestone, rarely packstone, Fig. 5H). The limestones contain abundant planktonic foraminifera with a few ostracod shells and rare ben-thonics. The intermittent pelagic deposition took place in deeper, quiet water, most probably at middle to outer neritic depths. However, the less abundant pelagic depo-sits in the studied sequence, contrary to the underlying Lower Eocene sediments, is an indication of the prevalence of a shallow- water depositional environment during the Middle Eocene time.
The Middle Eocene depositional envi-ronments were periodically interrupted by syn - depositional tectonism which has strongly affected the sedimentation pattern and resulted in the formation of penecon-temporaneous deformational structures and conglomerate interbeds that characterize the area studied.
A Middle Eocene age is assigned to the faulted-down Eocene sequence since it yields Nummulites gizehensis Forskal of a definite Early Lutetian age. In St. Paul area, the Early Lutetian age is assigned to the calcareous grit and argillaceous lime-stone interbeds occupying the summit of Gebel St. Paul (Ismail and Abdallah, 1966). While, in the subsurface, Middle Eocene (Lutetian) rocks are met with in Ezz EI-Orban well No.1 (Ansary and Fah- my, 1969). These rocks are represented by about 49m of hard argillaceous and cherty limestones with"Globorotalia bullbrooki " Zone which is more or less synchronic with the Minia Formation(Ansary and Fahmy, op. cit.).
Concerning the adjacent areas, the Middle Eocene rocks are described by Abdallah et al. (1970) at Gebel Thelmet area. They are represented by the so called "Zaafarana Marble" which consists of pink to rosy-coloured massive recrystal-lized and occasionally brecciated, lime-stones. Generally, they are poorly fossili-ferous with Nummulites gizehensis Forskal and attain a total thickness of about 90m. These brecciated and recrystallized lime-stones are quarried near Mersa Thelmet area and used commercially as ornamental stones. Abdel-Kireem and Abdou (1979) distinguished two main biozones in the Middle Eocene sequence of Gebel Thelmet area: Orbulinoides beckmanni Zone below and Truncorotaloides rohri Zone above. The present authors did not use the term Zaafarana Marble for the faulted-down Eocene rocks of St. Paul area due to clear facies differences.
Regarding the lithostratigraphic
nomenclatures of the studied Eocene sequences, it is worth mentioning that in spite of the numerous subdivisions of the well-established Lower and Middle Eocene rocks in the Nile Valley and the Western Desert of Egypt (e.g. Thebes, Manfalut, Minia, Samalut, Mokat?
tam,....etc), no proper equivalent facies and hence rock units can be used for the Eocene rocks of St. Paul area. There are many radical lithologic variations. Recen-tly, Barakat et al. (1985) introduced the term Waseiyit Formation at Gebel Hammam Faraun-Gebel Tanka area (opposite to the studied area on the Sinai side of the Gulf of Suez) to represent a hard fossilife-rous limestone sequence (about 282m) with many intraformational conglomerate interbeds and conspicuous undulations. The formation overlies con-formably the Esna Shale and underlies conformably the Rod El-Awad Formation. They assigned a Late Paleocene "Landanian"- Early Middle Eocene " Early Lutetian" age to the Waseiyit Formation at its type locality (Wadi Waseiyit) in the northern part of Gebel Hammam Faraun. The collected guide fossils in this forma-tion are: Nummulites gizehensis Forskal, Alveolina oblonga d'Orbigny, Globorotalia velascoensis Cushman and Globorotalia subbotinae Morozova. The Waseiyit Formation shows a wide areal distribution in the Hammam Faraun-Tanka area, Wadi Matulla, Wadi Nukhul and Nazzazat range where the southern extension of the forma-tion is delineated (Fig. 1). Farther south, the Eocene facies changes radically from Wadi Feiran to Gebel Qabeliyat where the Nile Valley facies prevails (Said,1962; Issawi et al., 1981 and Abdallah et al., 1988). Barakat et al. (1988) extended their newly suggested Waseiyit Formation to the western shoulder of the Gulf of Suez (Southern Galala plateau) based solely on field observations without reference to any section. They also traced the formation in all the bore holes penetrating the Eocene rocks in the central Gulf area. The present authors accepted the term Waseiyit Forma-tion for the Eocene sequences when they established the formal lithostratigraphic nomenclatures of the whole exposed
sequences in the Southern Galala (Abou-Khadrah et al., 1987), based on lithologic similarities between the exposed Eocene sequences, both in St. Paul and Gebel Hammam Faraun-Gebel Tanka areas. Consequently, the measured Eocene sequences in the studied area represent intervals from the middle and upper parts of the Waseiyit Formation, since the lower Landanian part of the formation is beyond the scope of the present study. It is believed that the Waseiyit Formation could be correlated with the Thebes, Minia, Samalut and Lower Mokattam for-mations collectively (Barakat et al., 1988).
CONCLUSIONS
The Eocene faulted-down blocks of the Southern Galala plateau at St. Paul area show many peculiar lithofacies characters similar to those of the Eocene rocks ex-posed in Hammam Faraun-Tanka area, the type locality of the recently established Waseiyit Formation. This formation has lithologic characteristics unlike those equivalent rock units in the Nile Valley and Western Desert of Egypt. In St. Paul area, the formation consists of well- bedded, partly massive limestones with thin dolostone, calcareous shale, conglom-erate and chert interbeds. It exhibits many characteristic syn-depositional structures such as brecciation, lenticular and large scale cross-bedding, wedging-out, undula-tions, deformed bedding and intense con-tortions. The prevalence of the penecon-temporaneous deformational structures (i.e. deformed bedding, undulations and intense contortions) as well as conglomer-ate interbeds in the studied limestone se-quences points to deposition under a tec-tonically active regime. These syn-tectonic limestone facies have been depo-sited under shallow to slightly deep back- shoal lagoonal conditions, alternating with a relatively open-marine environment es-pecially in the lower part of the sequence, as denoted by their microfacies characters, faunal content and primary structures. The conglomerate interbeds may also provide evidence for some structural high blocks uplifted along rejuvenated faults to form positive areas, the erosion of their Eocene rocks provides the materials which built up the submarine fan-deltas during storm epi-sodes. The restriction the syn-tectonic limestone facies in the Southern Galala, Hammam Faraun, Tanka, Matulla, Nukhul and Nazzazat range, indicates that the cen-tral province of the Gulf of Suez was tec-tonically more active than its northern and southern parts where the familiar Nile Val-ley Eocene facies prevails. This is also evi-denced by the fact that the Eocene succe-ssion reaches its maximum thicknesses in the central province and decreases in thick-ness further north and south in the Gulf area. These observations could be regarded as additive evidences that the Gulf of Suez, particularly its central part, was tectonical-ly active site during the Eocene period and before the great tectonic rifting event of the Late Oligocene-Early Miocene time.
ACKNOWLEDGEMENT
The authors are deeply indebted to Prof. Dr. A. M. Abdallah, Geology Department, Faculty of Science, Cairo University for his continuous encouragement and valu-able comments during field study.
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