الفهرس 
introductionOnly 14 pages are availabe for public view
 |  | from | 236 |  |  |
| | | from | 236 | | |
Abstract
SUMMARY AND CONCLUSIONS
The present work studies the exposed Eocene rocks lying in the central part of the area stretching between the Northern Galala to the south and Gabal Qattamia-Gabal Kahalyia to the north. The study includes the lithologic and microfacies investigations; rock units differentiation; micro and macropaleontologic identification, biostratigraphic and chronostratigraphic differentiation and correlation. The studied area is bounded by latitudes 29? 40´ & 30? 10´ N and longitudes 31? 47´ & 32? 10´ E (Fig. 1).
Eight stratigraphic sections were selected, measured and sampled at west Gabal Um Zeita, Gabal El Nugra, west Gabal Kahalyia, Gabal Um El Reheiat, Gabal Ghraibun, north east Gabal Ghraibun, south Gabal Sad El Naam and Wadi Um Gerfan for completing the study. The detailed field work; laboratory investigations; office work; statistical and technical methods; photographic and drawing steps; quantitative and qualitative estimations and deductions; interpretations, discussions, comparisons and correlation and conclusions were carried out with recurrent revisions. These are outlined generally in the methods of study and in details throughout the thesis. A lot of information, data, figures, tables and results have been gained. The following sentences summarise the main results.
LITHOLOGIES AND MICROFACIES
Lithologically, the studied Eocene rocks consist mainly of carbonates which are chalky and cherty in the Lower Eocene, while in the Middle Eocene, they become locally rich in alveolines and Nummulites toward the west, substituted by Dictyoconus and large miliolids that increase toward the east. In the Upper Eocene, the facies change completely to sands, marls with some shale intercalations. These marls and shales are with observed rarity of foraminiferal content rich in ostracods, and there are some compact oyster banks and Carolia beds. The detailed megascopic and microscopic investigation of 100 rocks samples and their thin sections led to the identification of 14 microfacies association in the 8 studied Lower, Middle and Upper Eocene successions. These associations include : the foraminiferal biomicrite, Dictyoconus biomicrite, biomicrite, miliolid biosparite, Nummulites – miliolid biomicrite, Dictyoconus – miliolid biosparite, silty – argillaceous biomicrite, sandy – shally dolobiomicrite, sandy – shelly pellbiomicrite, sandy – shelly biomicrite, Nummulites – Operculina biomicrite, Dolobiosparite, Nummulites biomicrite and Alveolina biomicrite. All these associations were described, referred to their stratigraphic horizons in all studied sections and attributed to their probable paleoenvironments (see the Microfacies).
ROCK UNITS
Depending on the field work, lithologic study and microfacies investigation, the studied Eocene successions in the 8 studied sections were assigned to the following rock units :
1] Thebes Formation : It is the oldest exposed Eocene rock unit in the studied area and detected from west Gabal Kahalyia section where it lies with unexposed base and reaches 66.6 m. thick. It consists of white to grayish white limestones, moderately compact to compact, chalky, dolomitic in parts, marly at the base with some chert nodules at the top. This unit is referred to the Early Eocene (Ypresian age) according to its stratigraphic position, planktonic foraminiferal content and correlation. This is the first record of Lower Eocene sediment in the whole area to the north of El Galala El Baharyia at all.
2] Minia Formation : It is detected in west Kahaliya section where it conformably overlies the Thebes Formation and reaches 91 m in thickness. The studied Minia Formation consists of grayish to yellowish white limestones, nummulitic at base, dolomitic and alveoline at top. The macrofaunal and larger foraminiferal content of this unit refer it to the Early Lutetian as the case in its type section. This is the first record of a complete Lower Lutetian (especially the lower part) in the area as a whole.
3] Observatory Formation : This unit is the thickest recorded unit in the studied area, it is found in Gabal Nugra, G. Um El Reheiat, south G. Sad El Naam and Wadi Um Gerfan sections with thicknesses of 160.4 m, 21.7 m, 49.3 m and 79.6 m, respectively. It consists fo grayish to yellowish white, compact, well bedded, biogenic limestones, argillaceous in parts, interbedded by dolomitic beds and some chert nodules in other parts. The abundant macro and microfauna with correlation of this unit attribute its studied sections to the Late Lutetian and the early time of the Bartonian.
4] Qurn Formation : It consists of lower white to grayish white marly limestone, middle marl to marly limestones and upper yellowish white limestones. This unit is represented by 22.9 m, 37.8 m, 60.5 m and 22.2 m in Wadi Um El Reheiat, Gabal Ghraibun, south Gabal Sad El Naam and Wadi Um Gerfan sections, respectively. Their stratigraphic positions, faunal contents and correlation assign the studied sections of the Qurn Formation to the middle time of the Bartonian.
5] Wadi Hof Formation : This is the youngest exposed Eocene unit recorded in studied area at north east Gabal Ghraibun and west Gabal Um Zeita with thicknesses 20.1 m and 15.2 m, respectively; it belongs to the Late Eocene (Priabonian) and lies unconformably under the Oligocene sands and gravels at west Gabal Um Zeita. This unit consists mainly of clastic sediments; mostly intercalations of grey to grayish brown sandstones, loose sands, marly sandstones and sandy limestones with several compact Carolia and oyster banks. This is the first record of Priabonian sediments in the whole area.
FOSSIL CONTENT
Faunastically, 123 micro and macrofaunal species have been identified, they include : 58 planktonic, benthonic and large foraminiferal species belonging to 31 genera, 25 families, 20 ostracod species (including 3 new ones) belonging to 15 genera, 9 families and 2 suborders; 31 Bivalvia species belonging to 24 genera, 13 families and 3 suborders; 14 gastropod species belonging to 13 genera, 9 families of the order Mesogastropoda. All these species were persuaded stratigraphically and geographically inside and outside Egypt as can as possible, their individuals were counted and statistically represented in distribution faunal charts for biostratigraphic investigation; all type specimens were photographed microscopically or/and megascopically, the foraminiferal species were microphotographed directly by SEM from the complete specimens and/or from thin sections by the polarizing microscope. All the identified species are presented in 22 photographed plates.
BIOSTRATIGRAPHY
Seventeen biozones have been recognized throughout the Lower, Middle and Upper Eocene successions in the eight studied sections. These biozones are 8 microbiozones and 9 macrobiozones, the firsts are 4 range and 4 assemblage biozones of foraminifera only because the ostracods content is not feasible for biostratigraphic differentiation; the seconds are 7 range, one assemblage and one interval. Bivalvia and gastropod biozones included within two superbiozones; stratigraphically they run as the following :
8- Epinoides schreibersi Zone (Priabonian).
7- Nonion cf. graniferum Zone (Priabonian).
6- Quinqueloculina carinata Zone (Priabonian).
5- Nummulites beaumonti – Nummulites striatus Zone (Lutetian – Bartonian).
4- Dictyoconus egyptiensis – Nummulites striatus Zone (Lutetian – Bartonian).
3- Dictyoconus egyptiensis – Nummulites beaumonti Zone (Lutetian – Bartonian).
2- Alveolina frumentiformis Zone (Early Lutetian).
1- Acarinina pentacamerata – Nummulites silvanus Zone (Latest Ypresian).
Macrobiozones :
B- Pegophysema pharaonis – Vulsella crispata super zone.
9- Cassis nilotica – Spondylus egyptiacus Zone (Lutetian – Bartonian).
8- Saxolucina rai Zone (Lutetian – Bartonian).
7- Ostrea califera Zone (Lutetian – Bartonian).
6- Cassis nilotica Zone (Lutetian – Bartonian).
5- Lucina immanis Zone (Lutetian – Bartonian).
A- Carolia placunoides – Plicatula polymorpha super zone.
4- Carolia placunoides Zone (Priabonian).
3- Ostrea reili Zone (Priabonian).
2- Mesalia shatai Zone (Priabonian).
1- Lower interval Zone (Priabonian).
The forementioned micro and macrobiozones were correlated inside the studied area and discussed, compared and correlated with similar and equivalent biozones inside and outside Egypt especially the widely extended foraminiferal biozones (see the biostratigraphy).
CHRONOSTRATIGRAPHY
The 8 studied sections were attributed to the Lower (Ypresian), Middle (Lutetian and Bartonian) and Upper (Priabonian) Eocene stages based on their macro and microfaunal content, biozones, stratigraphic positions and correlation. In ascending order, the defined stages run as the following :
1- The Lower Eocene (Ypresian) :
It comprises the lower segment of the exposed succession studied in west Gabal Kahalyia which includes the exposed part of the Thebes Formation. This segment is occupied by the Ypresian Acarenina pentacamerata – Nummulites silvanus Zone and lies conformably under a definite Lower Lutetian interval. This is the only Ypresian succession in the studied area.
2- The Middle Eocene (Lutetian – Bartonian) :
a) Lower Lutetian : It is represented by the upper segment of the exposed succession studied at west Gabal Kahalyia which belongs to the Minia Formation and occupied by the early Lutetian Alveolina frumentiformis Zone. This is the only lower part of the Lower Lutetian known in the studied area. The relation between the Lower and Middle Lutetian in the studied section is not well defined because the top of the exposed part of the first is uncomplete and the base of the second is unexposed.
b) Upper Lutetian – Bartonian : This is represented by the Eocene sediments exposed in Gabal El Nugra, Wadi Um Gerfan, south Gabal Sad El Naam and Gabal Um El Reheiat which belong to the Observatory Formation and/or Qurn Formation. These units are occupied by the Lutetian – Bartonian biozones namely Dictyoconus egyptiensis – Nummulites beaumonti Zone and Dictyoconus egyptiensis – Nummulites striatus Zone.
c) Bartonian : It is represented by the exposed part of the Qurn Formation which is occupied by Nummulites beaumonti – Nummulites striatus Zone in Gabal Ghraibun section which most likely have an occurrence in the upper part of the Bartonian, this in addition to the presence of the two Bartonian macrobiozones : Saxolucina rai Zone and Cassis nilotica – Spondylus egyptiacus Zone and their main unit Vulsella crispata – Pegophysema pharaonis super Zone.
3- The Upper Eocene (Priabonian) :
The sediments of this stage are represented by the exposed parts of Wadi Hof Formation at north east Gabal Ghraibun section and west Gabal Um Zeita section; the first is occupied by the foraminiferal biozones Quinqueloculina carinata Zone, Nonion cf. graniferum Zone, Epinoides schreibersi Zone and Carolia placunoides – Plicatula polymorpha super Zone with its two subdivisions the Mesalia shatai Zone and Ostrea reili Zone; while the second section is occupied by Carolia placunoides Zone. All these micro and macrobiozones are of Priabonian age.
Paleoecologically, the recognized microfacies and the recorded fauna indicate that, the studied Eocene successions were deposited generally within usually warm, normal shallow marine to inner neritic conditions; sometimes deep and other times littoral; protected at certain times but at others were tidal and slightly turbid with terrigenous supply from nearby landmass; sometimes calm with low energy and other times of high energy. Chronologically, these conditions reflect a gradual change from somewhat deep marine and neritic environments during the Ypresian, to the prevalence of shallow neritic and reefal conditions during the Lutetian – Bartonian, to littoral and shallow marine with terrigenous supply during the Priabonian.