Subsurface stratigraphy and micropaleontology of the Neogene rocks , Nile Delta , Egypt

Three wells (Naf-2, Naf-3 and Naf-101), were described and sampled in order to increase understanding of the stratigraphy and micropaleontology of the North Abu Qir Field, Nile Delta, Egypt. Lithostratigraphic studies aided recognition of the following Miocene-Pliocene rock formations (from base to top); Qantara Formation, Sidi Salim Formation, Qawasim Formation, Rosetta Formation, Abu Madi Formation, Kafr El Sheikh Formation, Baltim Formation, Mit Ghamr Formation, and Bilqas Formation. Biostratigraphic studies were based on the distribution of foraminifera through the Miocene-Pliocene succession. The environmental conditions of the Neogene rocks of the studied wells are interpreted using the results of palaeoecological parameters (e.g. the total number of foraminifera (T.N.F) and planktonic/benthonic ratio (P/B).


INTRODUCTION
The Nile Delta is one of the most well known deltas of the world, and has attracted the attention of many geologists due to its potential gas reserves.The considerable rise of oil and gas prices has lead to further exploration in order to locate new hydrocarbon fi elds.The Nile Delta has in general, a featureless surface with a northward slope, except for some limited topographic features such as the Khatatba positive structural and topographic features, and the westward Wadi El-Natrun negative element.Generally, no outcrops occur on the Delta surface, being mainly covered with recent mud and alluvial deposits (AZZAM, 1994), and also with some sand accumulations known as the Turtle-backs.
The structural setting of the Nile Delta region occupies a key position within the plate tectonic development of the eastern Mediterranean and the Levant.It lies on the northern margin of the African Plate, which extends from the subduc-tion zone adjacent to the Cretan and Cyprus arcs, to the Red Sea where it drifted apart from the Arabian plate.The Abu Qir Field consists of two culminations western and eastern.The western culmination is a four-way dip closure and the eastern culmination is a three-way dip closure and sealed from the eastern direction (cross-fault sealing) by the Kafr El Sheikh Shales, which were brought in juxtaposition with the Abu Madi Sands on the upthrown side of the fault.To the southeast, the West Abu Qir structure is separated from the Abu Qir Gas Field by a northeast-southwest narrow complex graben.This graben was formed by a northeast-southwest trending group of faults (BADRAN, 1996).Structurally, the Abu Qir and West Abu Qir fi elds were possibly formed in the same way, each being a rollover feature resulting from the slumping of post-Miocene deltaic sediments within the giant graben, which was bounded by almost two east-west major growth faults (BADRAN, 1996).
wasim Formation, with a marked unconformity.It is a marine deposit of Early Pliocene age.The shale content increas es upward and the contact with the overlying Kafr El Sheikh Formation is gradational in the studied wells.The type section is present in the Abu Madi well 1, between 3007 to 3229 m depth.The Abu Madi Formation is the gas-producing horizont of the Nile Delta (E.G.P.C., 1994).
The Kafr El Sheikh Formation is composed of soft clays with a few interbeds of poorly consolidated sands with a clay ey matrix.The development of this series appears to be rather constant over the entire Delta area.Its upper boundary is mark ed by the fi rst appearance of the El-Wastani sands which have a typical littoral fauna.The Kafr El Sheikh is dated as Early to Middle Pliocene age, according to palaeontological evidence (BARAKAT, 1982).The section has been penetrated in the Kafr El Sheikh well, located some 40 km SSW of the Abu Madi gas fi eld, in the south-central part of the onshore delta area.Its thickness is 1458 m (ISMAIL, 1984).
The El Wastani Formation consists of thick quartzose sandstone interbedded with thin clays which thin towards the top.The upper boundary of this formation is uncertain, but it is delineated where the series becomes more sandy for several tens of metres.This formation is assigned to the Late Pliocene (BARAKAT, 1982), and is 123 m thick in the El Wastani well 1 (ISMAIL, 1984).
Pleistocene-Holocene rocks are subdivided by (E.G.P.C., 1994) into two formations; the Mit Ghamr Formation at the base, and the Bilqas Formation at the top.The Mit Ghamr Formation is composed of thick layers of sands and pebbles at its base with clay interbeds.This formation grades into the overlying?Bilqas Formation by the increase of interbedded clays with sands, rich in peat, and fossiliferous, with a coastal or lagoonal fauna.The Bilqas Formation constitutes the top basin fi ll with coastal sands and deposits from the Nile fl oods.It was encountered between 20 and 484 m in the Mit Ghamr well, located in the southern part of the Delta, on the east side of the Damietta branch (SCHLUMBERGER, 1984).The Holocene rocks are represented by the intermittent marine transgressions that give rise to a few metres of marine sediments.Both constitute the Bilqas Formation.Plant remains and peat deposits are frequent (E.G.P.C., 1994).

MATERIAL AND METHODS
The Abu Qir North Field, Nile Delta, Egypt, is located to the north west of the Rosetta branch of the Nile River, and is bounded between latitudes 31° 34' N & 31° 52' N and longitudes 30° 04' E & 30° 26' E (Fig. 1).The number and depth of ditch cutting samples (in metres) for each well are given in Table 1 below.

GEOLOGIC SETTING
The Miocene rocks in the Nile Delta region were subdivided by E.G.P.C., (1994) into three formations, from base to top: the Sidi Salim, Qawasim and Rosetta.The Sidi Salem Formation is mainly composed of green-grey clays with a few interbeds of dolomitic marls, and rare occurrences of quartzose sandstones with calcareous cement and siltstones (BA- RAKAT, 1982).The age of this formation ranges from Langhi an to Tortonian.The lower limit is not known in the central part of the Delta, but was encountered in the western offshore area (Abu Qir) E.G.P.C. (1994) and also in the south and southeast.It probably overlies the Moghra Formation or older rocks (BARAKAT, 1982).The type section of this formation is represented by the bottom sequence at the Sidi Salim well 1 (located south of Lake Burullus), from 3592 to 4038 m depth.The upper limit is defi ned by the base of the thick conglomeratic series of the Qawasim Formation.Offshore the Sidi Salim is overlain directly either by the Rosetta Anhydrite or by the Lower Pliocene clays of the Kafr El Sheikh Formation.Extensive facies changes, both lateral and up-dip, occur within the Sidi Salim Formation in particular, and in Miocene sequence in general (E.G.P.C., 1994).
The Qawasim Formation overlies the Sidi Salem Formation, and underlies the Rosetta Formation.It is composed of a thick, sandy, and conglomeratic sequence, containing a typical rare Messinian fauna of the Mediterranean basin (E.G.P.C., 1994).The sequence is present in the interval from 2800 to 3733 m in the Qawasim 1 well, located some 14 km east of the Sidi Salim well 1 (SCHLUMBERGER, 1984).The upper boundary of this formation is rather diffi cult to determine if the anhydrites of Rosetta Formation are absent.Locally, it passes laterally to marine clays with Pliocene fauna of Kafr El Sheikh Formation.When the Qawasim Formation occurs within the basal sands of Abu Madi Formation, where the Rosetta Anhydrite is missing, the criteria of separation are based on palaeontological and sedimentological evidence (BARAKAT, 1982).
Large layers of anhydrite, interbedded with thin clays, represent the Rosetta Formation, observed in offshore well Rosetta 2, NE of the mouth of the Rosetta Nile branch, between 678 to 2718 m depth.The presence of the Rosetta Anhydrite seems to be limited only to the northern and offshore part of the Delta.It has not been encountered in wells drilled on the west fl ank of the Delta (Abu Qir), but was again present offshore to the north of Alexandria.A Messinian age has been attributed to the Rosetta Anhydrite because of its position below the marine shales of defi nite Early Pliocene age.The formation indicates a general starvation of the sea that affected the whole Mediterranean area and led to the deposition of evaporites SCHLUMBERGER (1984) and HSU et al. (1973,1977).
The Pliocene rocks in the Nile Delta region are subdivided by E.G.P.C., (1994) into three formations, from base to top: Abu Madi, Kafr El Sheikh, El Wastani.The Abu Madi Formation is represented by a thick series of sands, in part pebbly, with interbedded thin shales.The formation is crossbedded and overlies the Rosetta Anhydrite, and/or the Qa- 2. Identifying the foraminifera obtained from the different horizons and the distribution of the foraminiferal assemblages, for biostratigraphic studies of the Neogene sequence.
3. Delineation of palaeo-sedimentary environments, and the number of depositional cycles by using several palaeoecological parametres (e.g. the total number of foraminifera, (T.N.F.) and planktonic/benthic ratio (P/B).

STRATIGRAPHY
Correlation of the three wells located in the North Abu Qir Field revealed ten lithostratigraphic formations (based on lithological characteristics).These are, from base to top, as follows: Qantara Formation, Sidi Salim Formation, Qawasim Formation, Rosetta Formation, Abu Madi Formation, Kafr El Sheikh Formation, El Wastani Formation, Baltim Formation, Mit Ghamr Formation, and Bilqas Formation.Each rock unit is discussed below, taking into consideration the lithologic characters, stratigraphic limits, thickness, and the foraminiferal content when present.

Qantara Formation
The top of the Qantara Formation is only reached by the Naf-101 well (Figs.3, 4 and 5), which did not reach the base of this formation.The formation is unconformably overlain by the Sidi Salim Formation.Southward, in the study area, this formation is composed of shale with argillaceous sand and limestone, as revealed by the drilling data in other wells.Northward, the limestone of this formation decreases, and was replaced by clastics (shale and sand).Furthermore, this formation is dated as Early Miocene in age, according to the presence of Globigerinoides primordius as shown in (Fig. 6).This age assignment is confi rmed by the presence of the Early Miocene Dentoglobigerina altispira altispira and Globorotalia These samples were washed, picked, and the different species of foraminifera have been identifi ed and examined.The aim of this study is to analyze the encountered successions stratigraphically, in order to decipher the depositional environment, depositional processes and lateral and vertical facies changes.To achieve these objectives, the following steps were followed: 1. Identifying and recognizing the different rock units of the penetrated Miocene-Pliocene sequence based on the description of the ditch cutting samples and composite logs.obesa.Also, there are several other planktonic species associated with these fossils (e.g.Globigerinoides bisphericus, Neogloboquadrina continuosa, Globorotalia archeomerandii, Globigerina brazieri, Globigerina praebulloides, Orbulina cf.suturalis, Orbulina universa and Globigerinoides trilobus immaturus).Moreover, there are several benthic species associated with the previous planktonic species e.g.(Bolivina dilatata, Gyroidinoides soldanii, Nonionina scapha, Bulimina elongata, Lagena sulcata, Globocassidulina elongata, Uvigerina semiornata, Nonionella auris, Lenticulina cultra ta, Cibicides refulgens and Neoeponides sp).

Sidi Salim Formation
This formation unconformably overlies the Qantara Formation and underlies the Qawasim Formation.The bottom of this formation was not reached in two wells (Naf-2 and Naf-3).Its thickness in well Naf-101 is 460 m.This formation is composed of intercalations of shale, sand, clay, with rare occurrences of white, bioclastic limestone.This limestone occurs less frequently and passes gradually towards the northeast of the study area.The formation is of Middle Miocene age, based on the presence of Globigerinoides bollii at the top of this formation, which could represent a useful datum in the Mediterranean region, where the Globigerinoides fohsi lineage is not developed (BOLLI & SAUNDERS, 1985).However, the absence of the three upper biozones of Middle Miocene age (Globigerinoides ruber, Neogloboquadrina mayeri and Globorotalia menardii) biozones indicates a hiatus between the Middle Miocene and the Late Miocene as shown on the distribution chart of the Naf-101 well (Fig. 12).However, the presence of Praeorbulina glomerosa curva and Praeorbulina glomerosa glomerosa species supports the age assignment of this formation, which directly underlies the Upper Miocene sediments.This also indicates a similar hiatus in the formation as shown in the Naf-3 well (Fig. 11).Accordingly, this formation is dated from the Early Middle Miocene to Late Miocene.Also, there are several planktonic species associated with the above species (e.g.Globigerinoides pseudobesa, Globigerina ciperoensis ciperoensis, Dentoglobigerina venezuelana, Globigerina woodi, Globigerina nilotica, Orbulina universa, Orbulina bilobata, Globigerinoides trilobus immaturus, Globigerinoides obliquus extremus and Globigerinella obesa).Moreover, there are several benthic species associated with the planktonic taxa listed above (e.g.Quinqueloculina bosciana, Bolivina hebes, Ammonia beccarii, Bulimina elongata, Asterigerina planorbis, Nonionellina cf.labradorica, Gyroidinoides soldanii, Pullenia quinqueloba, Elphidium macellum and Neoeponides sp.).

Qawasim Formation
This formation overlies the Sidi Salim Formation and underlies the Rosetta Formation.The thickness of this formation increases northward (25 m in the Naf-101 well, and 100.5 m in the Naf-2 well (Fig. 3)).Also, its thickness is 34 m in Naf-3 well.This formation is composed of sand to sandstone with a few interbeds of clay.Also, there are several planktonic species associated with this formation (e.g.Globigerinoides trilobus immaturus, Globigerinoides bullatus, Globigerinoides obliquus extremus, Globigerina nilotica, and Orbulina universa).Moreover, there are several benthic species associated with the planktonics (e.g.Cibicides gibbosus, Alabamina sp., Buccella sp., Uvigerina cf.asperula, Bolivina hebes, and Nonionina scapha).The formation has been dated as Late Miocene (Messinian), according to its stratigraphic position (AZZAM, 1990; E.G.P.C., 1994; and ABU EL ENEIN, 1990) and also on both lithological and palaeontological characteristics (ISMAIL, 1984).In the present study, this formation is also dated as Late Miocene according to its stratigraphic position between the underlying Sidi Salim Formation of Early Middle Miocene to Late Miocene and the overlying Rosetta Formation of Late Miocene.

Rosetta Formation
This formation overlies the Qawasim Formation and underlies the Abu Madi Formation.The thickness of this formation decreases northward (99 m in Naf-101 well and 28 m in Naf-2 well).Also, its thickness is 50 m in Naf-3 well.It is composed of sand with occurrences of anhydrite and clay.Deposition of evaporites in this formation indicates a general regression of the Mediterranean, and this also explains the low content of planktonic foraminiferal species (e.g.Globigerinoides tenellus, Globigerinoides obliquus extremus, Globigerina nilotica, Orbulina bilobata and Orbulina universa).Also, there are few benthic species associated with the planktonics (e.g.Gyroidinoides soldanii, Alabamina sp., Uvigerina semiornata and Loxostomum pseudodigitale).The age of the Rosetta Formation is Late Miocene (Messinian) due to its stratigraphic position below the Upper Miocene-Lower Pliocene marine sediments (Abu Madi Formation).Also, the presence of Sphaeroidinellopsis disjuncta in the topmost part of this formation is further evidence for this age assignment.This species of Sphaeroidinellopsis has been used repeatedly as a zonal marker (BOLLI & SAUNDERS, 1985).The highest occurrence of Sphaeroidinellopsis disjuncta denotes the top of the Miocene (BOLLI & SAUN-DERS, 1985).

Abu Madi Formation
This formation overlies the Rosetta Formation and/or the Sidi Salim Formation with a marked unconformity and underlies the Kafr El Sheikh Formation.The thickness of this formation increases northward (138 m in Naf-101 well and 234 m in Naf-2 well).Also, its thickness attains 155 m in Naf-3 well (Fig. 4).It is mainly composed of intercalations of sand, clay, and shale.The age assignment of this formation is controversial, where it is dated as Late Miocene (Messinian), on a sedimentological basis, by EFFAT & GEZEIRY (1986) and DEIBIS et al. (1986).However, ABU EL ENEIN (1990) stated that the transgression in the Early Pliocene was responsible for deposition of the Abu Madi Formation.In the present study, this formation is dated as Early Pliocene in the studied three wells, according to the presence of Globorotalia margaritae, which is a widely recognized index species for the Pliocene (BOLLI & SAUNDERS, 1985).On palaeomagnetic evidence (CITA, 1975 andLOURENS et al., 2004), the age of this species ranges from 5.01 to 4.14 Ma.It is a cosmopolitan species occurring in both deep and shallow waters (BOLLI & SAUNDERS, 1985).The presence of Globorotalia exilis with Globorotalia margaritae terminates the Early Pliocene according to BOLLI & SAUN-DERS (1985).The occurrence of Sphaeroidinellopsis disjuncta in the top of the Abu Madi Formation in the Naf-2 well suggests that this formation is of Late Miocene age.
The Kafr El Sheikh Formation is dated as Early-Middle Pliocene according to palaeontological (BARAKAT, 1982) and geophysical data by BADRAN (1996).It is worthmentioning that during Early-Middle Pliocene, the marine transgression that began during the Early Pliocene, had been extended over the entire Mediterranean area (AZZAM, 1994).The Kafr El Sheikh Formation is ascribed to Early-Late Pliocene (DEIBIS et al., 1986).Also, EFFAT & GEZEIRY (1986) assigned the same age, to the formation based on lithology and wireline logs.RIZZINI et al. (1978) mentioned that the upper part of this formation belongs to the Middle Pliocene.

El Wastani Formation
This formation overlies the Kafr El Sheikh Formation and underlies the Baltim Formation.The thickness of this formation increases northward (156 m in Naf-101 well, and 301 m in Naf-2 well).Also, its thickness attains 124 m in Naf-3 well.This formation is composed of intercalations of sand, shale, clay, with some dolomite and limestone.The nonclastic facies (carbonates) increase northward.There are seve-Fi gu re 7: The planktonic foraminiferal distribution chart of Naf-2 well.
The age of this formation is Late Pliocene, based on geophysical data (BADRAN, 1996 and AZZAM, 1994).These authors mentioned that the regression of the sea heralded the end of the sedimentation cycle of the Pliocene.

Mit Ghamr Formation
This formation overlies the Baltim Formation and underlies the Bilqas Formation.The thickness of this formation decreases northward (661 m in Naf-101 well and 482.5 m in Naf-2 well).Also, its thickness attains 624 m in the Naf-3 well.This formation is composed of intercalations of clay, sand, and silt, with some limestone.No foraminifera have been recorded in this formation which may be partly due to the number of samples.ISMAIL (1984) dated this formation Fi gu re 9: The planktonic foraminiferal distribution chart of Naf-101 well.
as Late Pliocene to Quaternary, while AZZAM (1994) ascribed it to the Pleistocene age.Moreover, BADRAN (1996) dated it as Late Pliocene to Pleistocene in age.In the study area, this formation is dated Pleistocene to Recent throughout, based on correlation with neighbouring areas.

Bilqas Formation
This formation covers the whole Delta region.In the study area, it is present at the top of all wells.However, it is diffi cult to differentiate it from the underlying Mit Ghamr For-mation.This formation is composed of sand interbedded with clay rich in molluscan fragments.The clays contain vegetable remains and carbonaceous matter.It is dated as Holocene by BARAKAT (1982) and BADRAN (1996).AZ-ZAM (1994) mentioned that during the Holocene a marine transgression covered most of the Northern Delta area and gave rise to a few metres of marine sediments capped by agricultural soil.RIZZINI et al. (1976) and ABU EL ENEIN (1990) ascribed this formation to the same age, based on the faunal association.In the study area, this formation is dated as being Pleistocene to Recent in age.

ENVIRONMENTAL IMPLICATIONS
The environmental conditions of the Neogene rocks of the studied wells are interpreted by using the results of some palaeoecological parametres (e. g. the total number of foraminifera (T.N.F.) and planktonic/benthic ratio (P/B).The Rosetta Formation overlies the Qawasim Formation and underlies the Abu Madi Formation.This unit is extrem ely poor in foraminifera.It refl ects a decrease in water depth during its deposition.Deposition of evaporites in this formati on indicates a general regression of the whole Mediterranean.The top of this formation coincides with a general regression of sea level all over the study area, which is contemporaneous with the "Messinian Salinity Crisis" phenomenon all over the Mediterranean HSU et al. (1973,1977).
The Abu Madi Formation overlies the Rosetta Anhydrite and underlies the Kafr El Sheikh Formation.The faunal distribution shows an increase of T.N.F.values and high P/B values indicating an increase in water depth during deposi-Fi gu re 14: The paleoecologic parametres of Naf-3 well.
tion of this formation (Fig. 13).The occurrence of Bolivina hebes (as in Naf-3 well) refl ects a neritic type of bolivines (DOUGLAS, 1979).Furthermore, the occurrence of the costate Uvigerina semiornata (as in the Naf-3 well) that prefers anoxic conditions and fi ne-grained substrate (BOERSMA, 1984) suggests a shallow environment.
The Kafr El Sheikh Formation overlies the Abu Madi Formation and underlies the El Wastani Formation.The faunal distribution refl ects an increase of T.N.F.values and high P/B values mostly at the top and the base of this formation, if compared to the middle part, indicating a fl uctuating water depth which is lower for the central section of the formation.The occurrence of Cassidulina brocha, Ammonia beccarii, A. tepida, Pullenia osloensis, Bolivina dilatata, Bulimina elongata, Uvigerina pygmoidea and Vulvulineria complanata suggests a higher water depth in the lower part of the Kafr El Sheikh Formation.Also, the same conditions prevailed in the upper part of the same formation as indicated by the occurrence of Elphidium advenum, Quinqueloculina bosciana, Globocassidulina oblonga and Fursenkoina schreibersiana.
The El Wastani Formation overlies the Kafr El Sheikh Formation and underlies the Baltim Formation.The faunal distribution of this formation refl ects an increase of T.N.F. but low P/B values.This represents a lowering of the water depth during deposition of this formation as shown on Fig. 14.The top of this formation coincides with a regression of sea level all over the study area.Also, the occurrence of Ammonia-Elphidium and Valvulineria-Fursenkoina assemblages suggests a near shallow environment and a decrease in water depth through the El Wastani Formation.
The Baltim Formation overlies the El Wastani Formation and underlies the Mit Ghamr Formation.The faunal distribution of this formation is only observed for the lower part (Fig. 14) due to a lack of samples.The facies in the southern parts, of the study area, can be described as shallow marine.Intercalations of sand, shales and even carbonates were deposited, primarily by wave transport processes, in a high energetic outer shelf environment which become more quiet towards the north.
The Mit Ghamr Formation overlies the Baltim Formation and underlies the Bilqas Formation.The facies can be described as clastics and even carbonates deposited in a quiet shelf environment, where these sediments were affected by postdepositional processes forming some sort of canyon in the older sediments.
Finally, the Bilqas Formation covers the whole delta.AZZAM (1994) mentioned that during this time, the marine transgression covered most of the northern delta area and gave rise to a few metres of marine sediments capped by agricultural soil.This is repetition whereas this section is about the faunal content and depositional environment, where no samples are available in this interval.

CONCLUSION
The present work deals with the stratigraphy and micropaleontology of the sedimentary sequence in the North Abu Qir Field, Nile Delta, Egypt.Three wells (Naf-2, Naf-3 and Naf-101) were described, sampled and micropalaeontologically investigated.The lithostratigraphic studies have been carried out on the study area helped in the recognition of the Miocene-Pliocene rock units of the study area.These units are (from base to top) the Qantara Formation, Sidi Salim Formation, Qawasim Formation, Rosetta Formation, Abu Madi Formation, Kafr El Sheikh Formation, Baltim Formation, Mit Ghamr Formation, and Bilqas Formation.
The Qantara Formation is dated as Early Miocene according to the presence of Globigerinoides primordius.This age assignment is confi rmed by the presence of the Early Miocene forms such as Globoquadrina altispira altispira and Globorotalia obesa (KENNETT & SRINIVASAN, 1983).The Sidi Salim Formation is of Middle Miocene age due to the presence of Globigerinoides bollii, at the top of this formation, which could represent a useful datum in the Mediterranean, where the Globorotalia fohsi lineage is not developed (BOLLI & SAUNDERS, 1985).On the other hand, the absence of the three upper biozones of the Middle Miocene (Globigerinoides ruber, Globorotalia mayeri and Globorotalia menardii biozones) indicates a hiatus between the Middle and Late Miocene.However, the presence of Praeorbulina glomerosa curva and Praeorbulina glomerosa glomerosa species supports an Early Middle Miocene age for this formation, which is directly overlain by the Upper Miocene sediments.This indicates a hiatus between the Early Middle and Late Miocene.Accordingly, this formation is dated as being from the Early Middle to Late Miocene.The Qawasim Formation is dated to the Late Miocene according to its stratigraphic position between the underlying Sidi Salim Formation of Early Middle Miocene to Late Miocene age and the overlying Rosetta Formation of Late Miocene.This Rosetta Formation is of Late Miocene (Messinian) age, due to its stratigraphic position below the well-defi ned Early Pliocene marine sediments, together with, the presence of the defi nitive Sphaeroidinellopsis disjuncta in the topmost part of this formation.

Fi gu re 1 :Fi gu re 2 :Fi gu re 3 :
A location map showing the studied wells.The Generalized subsurface stratigraphic column of the Nile Delta region.The stratigraphic column of Naf-2 well.

Fi gu re 10 :
The benthic foraminiferal distribution chart of Naf-2 well.

1798 .
Serpula sulcata WALKER AND JACOB, p. 634, pl.14, fi g.18  1985.Lagena sulcata (WALKER AND JACOB)-LUGER, p. 81, pl. 4, fi g.6 The fi rst parameter (T.N.F) is the number of foraminiferal individuals in one gram of dry sediments.It increases with increasing water depth as mentioned by BANDY & ARNAL(1960).The planktonic/benthic ratio represents the number of planktonic foraminiferal individuals divided by the number of benthic foraminifera.It is low in near shore marine environment and increases with depth until the carbonate compensation depth (CCD) of approximately 4000 m is reached, below which only agglutinated foraminifera are found (PH-ELEGER, 1960).These parametres are graphically repre-sented to refl ect the vertical distribution of the foraminiferal fauna of the different rock units (Figs.13, 14 and 15).The environmental conditions for each recognized rock unit are mentioned below based on these aforementioned parameters.The Qantara Formation was only represented in the Naf-101 well.It underlies the Sidi Salim Formation.The facies of this formation is of non-marine clastics deposited by river currents and associated marginal marine transport processes, in a high-energy outer shelf environment.Moreover, towards the north, the environment changed to a shallow marine one where clastics and even carbonates were deposited by wave transport processes in a relatively quieter inner shelf environment.This is shown by the relatively higher values of T.N.F. and high P/B values indicating an increase in water depth as shown on Fig.15.Also, the occurrence of Bolivina dilatata, Gyroidinoides soldanii, Bulimina elongata and Globocassidulina oblonga indicates an increase of water depth (MURRAY, 1991) as in Fig.15.The Sidi Salim Formation overlies the Qantara Formation and underlies the Qawasim Formation.The faunal distribution shows considered values of T.N.F., high P/B values Fi gu re 13: The paleoecologic parametres of Naf-2 well.especially in the upper part of the formation which indicate an increase in water depth.Furthermore, the occurrence of Bolivina hebes, Bulimina elongata, Uvigerina pygmoidea, Gyroidinoides soldanii and Lenticulina antipodum suggests a deep shelf environment (MURRAY, 1991) at the upper part of the Sidi Salem Formation.Moreover, there is a decrease in these values up to the middle of this formation as shown on Fig. 14.The facies of this formation, towards north and northwest directions, can be described as shallow marine clastics deposited primarily by wave transport processes in a relatively low-energy outer shelf environment.Furthermore, it gradually changes into a high-energy deltaic environment, towards the south and southeast, which resulted in clastic deposits being deposited from several channels.The Qawasim Formation overlies the Sidi Salim Formation and underlies the Rosetta Formation.The values of T.N.F. and P/B ratio are relatively low indicating a decrease in water depth during deposition of this formation.It was deposited in a high-energy deltaic environment, towards the south and southeast directions.The occurrence of Ammonia beccarii in the Qawasim formation in the Naf-3 well suggests a near-shore environment (VAN DER ZWAAN & JOR-ISSEN, 1991).

Table 1 :
Location and number of samples taken from each well in the study area.