MICROFACIES AND ENVIRONMENTAL INTERPRETATION OF THE PLIOCENE-PLEISTOCENE CARBONATES IN THE MARSA...

155

MICROFACIES AND ENVIRONMENTAL INTERPRETATION OF etc .....

its building the coral reef terraces in the Mar-

sa Alam area. The lithostratigraphy, palaeoe-

cology and the geological history of the area

will be discussed. In order to carry out this

study, five stratigraphic successions have

been investigated, measured and sampled

(Fig. 1). The selected localities include Wadi

Abu Dabbab and Wadi Asalay (north of Marsa

Alam) and Wadi Samadai, Sharm El-Fuquiri

and Sharm El-Luli (south of Marsa Alam).

Research history:Research history:

Since the 19th century the Red Sea coastal

plain of Egypt was and still is one of the most

attractive study areas for geologists and other

workers from allover the world. First reports

on the geography and geology of the area; e.g.

Ball (1912), did not give much attention to the

INTRODINTRODUCUCTIONTIONThe study area lies along the Red Sea

coastal plain between Latitudes 24˚30’ and

25˚30' N in the Marsa Alam environ, forming a

strip that stretches 95 km along the coast and

ranging in width from 1-6 km (Fig. 1). This

stretch is bordered by the sea shore from east

and the white dazzling low hills of the Mio-

cene evaporites and the high hills of the Pre-

cambrian basement rocks from the west. The

area is covered by Miocene and younger de-

posits with conspicuous raised coral reef ter-

races of Pliocene-Pleistocene age which run

parallel to the shore line in a discontinuous

pattern and at different elevations.

The purpose of the present work is to shed

more light on the Pliocene-Pleistocene depos-

MICROFACIES AND ENVIRONMENTAL INTERPRETATION OFMICROFACIES AND ENVIRONMENTAL INTERPRETATION OFTHE PLIOCENE-PLEISTOCENE CARBONATES IN THE MARSATHE PLIOCENE-PLEISTOCENE CARBONATES IN THE MARSA

ALAM AREA, RED SEA COASTAL PLAIN, EGYPTALAM AREA, RED SEA COASTAL PLAIN, EGYPT

Mahmoud, Kora; Salah, Ayyad and Heba, El-DesoukyMahmoud, Kora; Salah, Ayyad and Heba, El-DesoukyDepartment of Geology, Faculty of Science, University of Mansoura, Egypt

ABSTRACTABSTRACT

The Pliocene-Pleistocene succession along the Red Sea coast is subdivided in the Marsa Alamarea into the Gabir, Shagra and Samadai formations in addition to the Pleistocene raised beach-es and coral reefs. The succession is represented by mixed siliciclastics and carbonates. Thirteencarbonate microfacies are recognized and described including mudstone, wackestone, packstone,grainstone, rudstone and boundstone. The coral framestone is the most common microfaciestype encountered; followed by oosparite, foraminiferal and algal biosparite. The fossil associationand the encountered microfacies indicate deposition in the intertidal to shallow subtidal environ-ments. The fossiliferous arkoses and conglomerates, alternating with the carbonates, were de-rived from the nearby Precambrian basement, transported by streams during short-lived pluvialepisodes and deposited in a very shallow intertidal- beach environment.

Keywords:Keywords: Pliocene-Pleistocene, microfacies, Egyptian Red Sea coast, Marsa Alam.

Journal of Environmental Sciences, 2013; Vol. 42, No. 1 : 155-182

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Mahmoud, Kora; et al...

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the Red Sea-Gulf of Aden rift system, includ-

ing articles studying the evolution of the Plio-

cene-Pleistocene deposits in the Egyptian Red

Sea coast. Arvidson et al. (1994) concluded

that the coralline limestones were formed dur-

ing sea level highstands when sediments were

trapped upstream, while the fluvial terraces

were formed during the sea level lowstands

where wadis cut into the sedimentary depos-

its associated with continuing uplift.

Plaziat et al. (1995) reported on a brief low-

ering of the sea level during the last intergla-

cial high stand (isotope substage 5e). Man-

sour (2000) concluded that all reef sequences

represent transgressive phases developed dur-

ing the sea level rise, whereas the alluvial sed-

iments reflect regressive phases and sea level

fall. Gheith (2001) reported that the microfa-

cies associations found in the Gabir Forma-

tion reflect a marine transgression where

mixed siliciclastics and carbonates of shallow

subtidal environments predominate. Tucker

(2003) compared a mixed clastic-carbonate

sequence from the Quaternary of Egypt with

the Carboniferous of England. In the Pleisto-

cene of Marsa Alam area, he concluded that

reefal carbonate deposition continued into the

highstand with some minor intercalation of

clastics along the shoreline from local fluvial

input under the arid climate. During the fall-

ing stage and lowstand of sea-level, terrige-

nous clastics were funneled through major

wadis and incised valleys to fan deltas and

lowstand wedges at the basin margin. Similar-

ly, El Khoriby & Anan (2006) concluded that

the coral reef terraces were formed during

high sea level while the beachrocks and the

wadi deposits were formed during sea level

fall.

Neogene-Quaternary succession but just gave

a general description for these younger depos-

its. Short geologic descriptions for the Mio-

cene and younger strata in this area were giv-

en in Hume (1916) and Beadnell (1924).

El-Akkad and Dardir (1966) studied the ge-

ology of the Red Sea coast between Ras Sha-

gra and Marsa Alam. They proposed a de-

tailed lithostratigraphic classification for the

sedimentary succession overlying the Pre-

Cambrian basement rocks in that area. They

subdivided this succession into the following

rock units from the base to top: Gabal El-

Rusas Formation, Gypsum Formation and

Samh Formation (Miocene), Gabir Formation

and Shagra Formation (Pliocene). These rock

units are overlain by the Pleistocene organic

reefs (four reef units), wadi deposits, gravel

terraces and Recent raised beaches and coral

reefs. This framework is generally accepted by

most subsequent workers with only a few em-

endations and minor revisions (Table 1), e.g.

Philobbos et al. (1989 and 1993), Said (1990),

Soliman et al. (1993), Mahran (2000), Khalil

and McClay (2009) and Issawi et al. (2009).

Philobbos et al. (1989) recognized three

lithofacies: Facies A; continental to restricted

marine facies (Samh Member of Marsa Alam

Formation), Facies B; open marine facies (Ga-

bir Member of Marsa Alam Formation and

Shagra Formation) and Facies C; continental

to sea marginal fans (Samadai Formation).

They added that the synsedimentary tectonics

played a great role in the distribution of these

facies. The Geological Society of Egypt in a

special publication edited by Philobbos &

Purser (1993) published some papers that

dealt with geodynamics and sedimentation of

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ral reefs. The lithostratigraphic classification

used in this study (Table 1) is in accordance

with that of El-Akkad & Dardir (1966) with

two modifications. 1. The Gabir Formation is

extended upward to include the lower mem-

ber of the Shagra Formation as emended later

by Said (1990) and accepted by Kora & Abdel-

Fattah (2000). 2. The formal name Samadai

Formation as introduced by Philobbos et al.(1989, 1993) was adopted to represent the

Plio-Pleistocene deposits which is equivalent

to the upper part of the upper member of the

Shagra Formation and to the lower part of the

Pleistocene organic reefs described by El-

Akkad & Dardir (1966). The field relations of

these rock units and their appearance in the

landscape are illustrated (Fig. 3). The follow-

ing comments are a brief description for these

rock units from base to top.

1. The Gabir Formation:1. The Gabir Formation:

The Gabir Formation as used here is equiv-

alent to the Ostrea-Pecten Series (Table 1) of

Beadnell (1924) and to the Gabir Formation

and the lower member of the Shagra Forma-

tion as used by El-Akkad & Dardir (1966) and

Issawi et al. (2009). It overlies conformably

the Samh Formation and underlies conforma-

bly the Shagra Formation. This unit and its

Indo-Pacific fauna is coeval with the lower

part of the Abbas Formation developed along

the shore line of the Yemeni Red Sea; to the

Waradan Formation in the Sudan and to the

Esbah Formation of the Farasan Islands in

Saudi Arabia (Khalil 2011). Other equivalent

units used by different workers are given in

Table (1).

The Gabir Formation forms relatively

high hills and cliffs of yellowish grey to yellow-

Geochronological, age dating and isotopic

composition investigations for the Pleistocene

emerged coral reef terraces have been done by

many workers including Gvirtzman et al.(1992), Strasser and Strohmenger (1997), El-

Moursi et al. (1994), El-Asmar (1997), etc.

Plaziat et al. (2008) reviewed the dating of

reefs on the coasts of the Red Sea including

those of Egypt, Jordan, Sudan, Eritrea, Saudi

Arabia and Djibouti. They suggested a revi-

sion of many datings of corals supposedly

younger or older than the age assigned to the

high-level isotopic substage MIS 5.5 (=5e).

This suggestion was confirmed then by an in-

dependent, more precise chronology of sea-

level fluctuation during the MIS 5.5 substage

(Rohling et al. 2008).

LITHOSTRATIGRAPHYLITHOSTRATIGRAPHY

The Pliocene-Pleistocene succession in the

Marsa Alam environs along the Egyptian Red

Sea coast varies in thickness from about 33 m

at Sharm El-Luli, south of Marsa Alam City to

130 m at Wadi Asalay north of it (Fig. 2). The

studied successions are represented by mixed

siliciclastics and carbonates. The succession

overlies conformably Miocene deposits com-

posed of evaporites (the Abu Dabbab For-

mation) and greyish green clastics of the

Samh Formation. The recognized rock units

are correlated with the lithostratigraphic clas-

sifications suggested for the Red Sea coastal

plain by different authors (Table 1).

The Pliocene rocks in the study area are

represented by the Gabir and the Shagra for-

mations. The Samadai Formation represents

the Plio-Pleistocene deposits that unconform-

ably overlie the Pliocene strata and are cov-

ered by the Pleistocene raised beaches and co-

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with abundant feldspathic rock fragments.

These conglomerates are partly fossiliferous

with bivalve shell fragments, red algae and co-

ral debris.

At Wadi Abu Dabbab, this rock unit is

made up mainly of clastics; sandstone, shale

and conglomerate with a few oolitic limestone

beds near the top of the formation. To the

south of Marsa Alam at Wadi Samadai, the

Gabir Formation forms the core of a small an-

ticlinal structure (Fig. 3a) where the oolitic

limestone facies dominates in this succession.

The formation is not recorded in the studied

ish brown colour and is well developed

(55m thick) around Wadi Asalay to the north

of Marsa Alam. In this particular locality,

it is composed mainly of sandstones alternat-

ing with limestone and conglomerate beds

(Fig. 2). The sandstones are usually arkosic to

sub-arkosic and show some cross bedding.

Near the top of the succession, these sand-

stones are intercalating limestone bands con-

tain some scleractinian coral debris. The con-

glomerates became conspicuous constituents

near the top of the formation which are cal-

careous, poorly sorted, coarsening upward;

from granules, pebbles, cobbles to boulders


Fig. (3): Lithology and field relations of the studied rock units:

a) Fossiliferous oolitic limestone intercalating with some shale thin beds at the base in the core of an anticlinal

structure; the Gabir Formation at Wadi Samadai.

b) Fossiliferous sandy oolitic limestone showing large scale tabular planar cross bedding, the strata are dipping

toward the sea with 42º/S70ºE; the Shagra Formation at Wadi Samadai.

c) Red algal limestone of the Shagra Formation overlain unconformably by the conglomerates of the Samadai

Formation, Wadi Abu Dabbab.

d) Red algal limestones overlain unconformably by cross bedded fossiliferous conglomerates in a fining upward

sequence; the Samadai Formation at Sharm El-Luli

e) The older reef terrace (TI) at Sharm El-Luli showing the branching scleractinian coral (Porites sp.) in growth

position.

f) Terrace (TIII) exposed at the northern side of Marsa Samadai with scleractinian coral colonies (Galaxea sp.) in

growth position.

g) General view of the lower and the middle Pleistocene raised coral reef terraces (TIII, TII) at the southern side of

Marsa Samadai showing a conglomeratic bed separating the two terraces (stippled arrow).

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of the formation especially at Wadi Asalay

where they are reddish in colour, poorly sort-

ed, with feldspar and rock fragments and fos-

siliferous with echinoid spines, clypeasteroids

and red algal encrustations. The lithology and

the fossil association indicate that, this rock

unit was mostly deposited in a shallow warm

marine environment with clear water and nor-

mal salinity. Kora & Abdel-Fattah (2000) re-

corded the Lithophaga avitensis-Pecten (Pec-ten) acuticostatus Zone from the lower part of

the Shagra Formation and the Clypeaster re-ticulates-Laganum depressum Zone from its

upper part and assigned them to a Late Plio-

cene age.

3. The Samadai Formation:3. The Samadai Formation:

This rock unit corresponds to the upper

part of the Laganum depressum-Clypeasterscutiformis Series of Beadnell (1924), the old-

er organic reefs described by El-Akkad & Dar-

dir (1966), the Wizr Formation and the older

raised reefs of Al-Rifaiy & Cherif (1989), and

to the upper part of the upper member of the

Shagra Formation of Issawi et al. (2009). Oth-

er equivalent units are given in Table (1). The

Samadai Formation has been recorded and

studied from all the measured sections. It

ranges in thickness from 9 m to 26 m and is

well developed at Sharm El-Luli, south of

Marsa Alam (Fig. 2). It unconformably overlies

the Shagra Formation (Fig. 3c), the Gabir For-

mation and even the Samh Formation and is

conformably overlain by the Pleistocene raised

beaches and coral reefs.

The Samadai Formation is one of the easily

recognizable rock units in the field with its

characteristic lithology, including two alter-

nating and discontinuous facies of unfossilif-

southern localities at Wadi Sharm El-Fuquiri

and Wadi Sharm El-Luli. The composition of

this formation refers to shallow warm agitat-

ed marine conditions. Kora & Abel-Fattah

(2000) recorded the Crassostrea gingensis-Crassostrea crassissima Zone from the Gabir

Formation and assigned it an Early Pliocene

age.

2. The Shagra Formation: 2. The Shagra Formation:

The studied unit represents the upper

member of the Shagra Formation as described

by El-Akkad & Dardir (1966) and is equiva-

lent to the lower part of the Laganum depres-sum-Clypeaster scutiformis Series of Beadnell

(1924). It overlies conformably the Gabir For-

mation and underlies unconformably the Plio-

cene-Pleistocene Samadai Formation or the

Pleistocene raised beaches and coral reefs.

The Shagra Formation forms relatively low

hills nearer to the Red Sea coast. It is more

calcareous and fossiliferous than the underly-

ing rock unit. It is composed mainly of lime-

stones intercalated with a number of sand-

stone and conglomerate beds (Fig. 2). A hard

current bedded limestone bed (5 m thick) is

prominent near the base of the formation at

Wadi Samadai (Fig. 3b). At Wadi Asalay,

where the formation shows its greatest thick-

ness (47.5m), the red algal limestones consti-

tute the lower part of the formation while at

Wadi Abu Dabbab and Wadi Samadai, it

forms its upper part followed directly by the

conglomerates of the Samadai Formation

(Fig. 3c).

The sandstones are generally calcareous,

arkosic to sub-arkosic, hard, and fossiliferous

mainly with molluscan moulds and shells.

The conglomerates increase in the upper part

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lap during different sea levels, by tectonics or

by erosion during transgression (Dullo 1990).

These reefs are characterized by fringing reef

types in comparison with their living counter-

parts. They are missing in front of the wadi

mouths where they are replaced by terrige-

nous sediments and gravels of alluvial fans.

Throughout the present study, a staircase

of three marine raised reef terraces with dif-

ferent altitudes from 12-17, 5-12 and 2-4 m

above the present sea level are recognized

(Fig. 3d-f). These terraces overlie the reefal

limestone or the conglomerates of the Sama-

dai Formation. Lithologically, they are formed

of coral and algal limestones. The primary

frame-builders are scleractinian corals, while

the secondary ones include foraminifera and

bryozoans. Crustose coralline algae are the

main frame binders. The terraces are occa-

sionally topped by a cover of thin Recent allu-

vial deposits of gravel beds or a thin fossilifer-

ous beach rock. A Pleistocene age was

assigned to these coral reef terraces as re-

vealed from age datings performed by several

authors. According to El-Moursi et al. (1994),

the three lowest terraces gave 230Th / 234U

ages between 72.1±2.5 and 131.2±4.7 ka B.P.

These age ranges match with the chronology

of the last interglacial cycle. The Recent fring-

ing reef exposed only during low tide is ex-

cluded from this study.

MICROFACIES AND ENVIRONMENTALMICROFACIES AND ENVIRONMENTAL

INTERPRETATIONINTERPRETATION

The microfacies analysis, the field observa-

tions and the fossil content are combined to-

gether to shed more light on the palaeo-

environmental conditions during deposition of

the Pliocene-Pleistocene rock units in the

erous and fossiliferous conglomerates that

grade laterally or vertically into reefal lime-

stone (Fig. 2). The conglomerate beds are in-

tercalating with minor fossiliferous sandstone

beds. The unfossiliferous conglomerates lie

away from the sea coast and are generally

composed of rock fragments that vary in size

from granules to boulders, poorly sorted, with

angular to sub-rounded clasts that were de-

rived from the adjacent Precambrian base-

ment rocks.

On the other hand, the conglomerates clos-

er to the coast are more calcareous and highly

fossiliferous. At Wadi Abu Dabbab, these con-

glomerates contain an oyster bank with Laga-num sp., gastropod moulds, etc. At Sharm El-

Luli, these fossiliferous conglomerate beds

contain scleractinian coral fragments, mollus-

can and echinoid shells. The conglomerate in-

tervals within this rock unit are indications of

pluvial periods that interrupted an otherwise

dry climate which is adequate for coral reef

growth (Said 1990). The lithology and the fos-

sil association in this rock unit suggest litto-

ral to beach environment with clear water and

normal salinity for the fossiliferous conglom-

erate, whereas the unfossiliferous conglomer-

ates were deposited under fluviatile condi-

tions. The stratigraphic position of this rock

unit and the encountered fauna suggest a Pli-

ocene-Pleistocene age.

4. The Pleistocene raised beaches and4. The Pleistocene raised beaches and

coral reefs :coral reefs :

The Pleistocene raised beaches and coral

reefs of the Red Sea coast form a discontinu-

ous strip in three morphological terraces with

different elevations above the sea level. These

morphological steps are caused either by on-

164


nate allochems are skeletal grains represent-

ed by biocalsts of calcareous red algae, ben-

thic foraminifera, echiniod spines and plates,

conistituting collectively 2-5% of the rock vol-

ume. The clastic fraction is represented by

poorly sorted, subangular to rounded, silt to

sand-sized quartz and feldspar grains, form-

ing about 24-48% of the rock volume. All

these components are embedded in a micritic

carbonate matrix, occasionally changes to mi-

crospar. This microfacies type can be allocat-

ed to FZ 8 of Wilson (1975); reflecting restrict-

ed circulation on marine platform conditions.

WackestonesWackestones

The wackestone microfacies has a very lim-

ited distribution recorded; from the middle

part of the Gabir Formation at Wadi Asa-

lay. It is represented by a sandy bio-

oomicrite (Fig. 8). Petrographically, the main

allochemical components of this microfacies

are well sorted, micritic and reworked ooids

(Fig. 4c) with quartz or amphibole nuclei, as-

sociated with some fossil bioclasts including

foraminiferal tests of Amphistegina sp., echi-

noid spines and molluscan shell fragments.

Detrital quartz and feldspar grains are also

common. All components are embedded in a

micrite matrix. According to Flügel (2010),

micritic ooids can be generated by random

growth of crystals in marine environments

characterized by reduced sedimentation (e.g.

outer ramps), growth within biofilms (FZ 8, FZ

9B) or are the result of pervasive micritization

(SMF type 15-M).

PackstonesPackstones

This microfacies has a restricted distribu-

tion in the studied succession, representing

only 2.5% of the total limestone thickness. It

Marsa Alam area. The petrographic compo-

nents are counted and described from 167

thin sections in the collected limestones and

other reef rocks. The study led to the recogni-

tion of 13 carbonate microfacies types. They

are photographed and illustrated (Figs. 4-6).

These carbonates are associated and alternat-

ing with clastic lithofacies including fossilifer-

ous petromictic orthoconglomerate, calcare-

ous and pebbly arkose, feldspathic greywacke

and rare silty shale. The information gained

through the field and laboratory investiga-

tions is summarized (Figs. 7-11).

The carbonate rocks make up about 57%

of the total thickness in the invistigated suc-

cessions. They are mostly represented by

limestones. The present study follows the

classification of carbonate rocks according to

the depositional texture proposed by Dunham

(1962) with the modification of Embry & Klo-

van (1971) to describe the different microfa-

cies. The corresponding terms of Folk (1959)

are also used for the subdivision of textural

spectra. The identified limestone microfacies

associatons are compared with the Standard

Microfacies Types (SMF) and Facies Zones

(FZ) of Wilson (1975) and their depositional

environments are interpreted and discussed

as categorized by Flügel (2010).

Carbonate mudstonesCarbonate mudstones

This mud supported microfacies is repre-

sented by silty-sandy fossiliferous micrite (Fig.

4a, b). It is of limited disribution in the stud-

ied succession, representing only 5% of the

total carbonate thickness. It is recorded from

the Pliocene Gabir and Shagra formations at

Wadi abu Dabbab and Wadi Samadai (Figs. 7,

9). Petrographically, the most common carbo-

165


Fig. (4):Fig. (4): The mudstone, wackestone, packstone and grainstone microfacies.a) Silty fossiliferous micrite. Calcareous red algal lumps scattered in a micritic groundmass, with silt sized derital

quartz grains; sample Ad 19, Shagra Formation, Wadi Abu Dabbab.b) Sandy fossiliferous micrite. Calcareous red algal lumps (b-1) and benthic foraminiferal tests (b-2) scattered in a

micritic groundmass, with abundant sand sized quartz grains; sample S 3, Gabir Formation, Wadi Samadai.c) Sandy bio-oomicrite. Well sorted, micritized and reworked ooids with rare foraminiferal tests and quartz grains,

all are embedded in a micritic matrix; sample As 4, Gabir Formation, Wadi Asalay.d) Sandy biomicrite. Bioclasts of oyster shells, bryozoa (d-1), calcareous red algal fragments (d-2), longitudinal sec-

tions of soritid foraminifera and echinoid spines (d-3), with abundant detrital quartz grains, all are embedded ina micritic matrix that is diagenetically changed into sparry calcite; sample Sh.L 7-b, the Pleistocene raised reefs(TI), Sharm El-Luli.

e) Algal biomicrite. Calcareous red algal fragments with sparse larger benthic foraminiferal tests set in a carbonatemud matrix with some dissolved red algal fragments; sample Ad 22, top Shagra Formation, Wadi Abu Dabbabsection.

f) Oosparite. Well sorted and rounded concentric ooids with detrital quartz or micritic carbonate fragment nuclei,some ooids are dissolved, producing oomouldic porosity; sample S 10, Shagra Formation, Wadi Samadai section.

g) Oosparite. Partly or totally micritized ooids, most grains exhibit the characters of peloids (g-1), while some grainsshow relicts of its original microstructures (g-2, arrowheads), all set in coarse crystalline sparry calcite cement;sample S 1, Gabir Formation, Wadi Samadai section.

166


Fig. (5): Fig. (5): The grainstone microfacies (continued)a) Bio-oosparite. Well sorted, superficial ooids with quartz, feldspar and amphibole nuclei, with long echinoid

spine (ES) in calcareous cement; sample Ad 18, Shagra Formation, Wadi Abu Dabbab section.b) Bio-oosparite. Well sorted, dissolved and micritized ooids with encrusting bryozoa (Br) set in sparry calcite ce-

ment; sample S 4, Gabir Formation, Wadi Samadai.c) Bio-oosparite. Poorly sorted, rounded to ellipsoid ooids with foraminiferal tests (Fo) cemented by sparry calcite;

sample As 3, Gabir Formation, Wadi Asalay.d) Foraminiferal biosparite. Benthic foraminiferal tests (Borelis sp.; arrowed, Amphistegina sp.) associated with

few echinoid spines, calcareous red algal fragments and rare quartz and feldspar grains, all set in a sparry ce-ment; sample Sh.L 5, Samadai Formation, Sharm El-Luli section.

e) Foraminiferal biosparite. Benthic foraminiferal tests (Borelis sp., Amphistegina sp.; arrowed, Quinqueloculinasp. and other miliolids) associated with few calcareous red algal fragments and rare quartz and feldspargrains, all set in a sparry cement; sample Ad 14, Shagra Formation, Wadi Abu Dabbab section.

f) Algal biosparite. Calcareous red algal fragments (Amphiroa spp.) associated with sparse miliolids; sample As11, Shagra Formation, Wadi Asalay section.

g) Foraminiferal algal biosparite. Calcareous red algal bioclasts (CA) associated with some benthic foraminifera(Fo), all set in a sparry calcite cement.; sample Sh.F 5, the Pleistocene raised beaches and coral reefs (TII),Sharm El-Fuquiri section.

h) Foraminiferal algal biosparite. The calcareous red algae Dermatolithon sp. encrusted by the sessile larger ben-thic foraminifera Carpenteria sp. (arrowheads); sample Sh.F 5, the Pleistocene raised beaches and coral reefs(TII), Sharm El-Fuquiri section.

167


Fig. (6): Fig. (6): The rudstone and boundstone microfaciesa) Biosparrudite. Gravel-sized intraclasts (a1) and coral fragments (a2), cemented by sparry calcite; sample As 12,

Shagra Formation, Wadi Asalay.b) Coral framestone. Transverse section of Porites sp. acting as a primary frame builder with empty intraskeletal

cavities; sample As 21, the Pleistocene raised beaches and coral reefs (TIII), Wadi Asalay section.c) Coral framestone. Longitudinal section in the scleractinian coral Favia pallida acting as a primary frame build-

er; sample Sh.L 8, the Pleistocene raised beaches and coral reefs (TII), Sharm El-Luli section.d, e) Algal framestone. Coralline red algae act as the primary frame-builders with a well preserved original micro-

structure such as conceptacles (arrowheads) which is partly filled with sparry calcite cement, bounded withscleractinian corals and other encrusters to build a rigid framework; sample Sh.L 6, Samadai Formation,Sharm El-Luli section.

f, g) Algal bindstone. Calcareous coralline red algae that encrust and bind the associated sediments composed offossiliferous mudstone with miliolids; sample Ad 20, Shagra Formation, Wadi Abu Dabbab section.

168


169


170


171


172


Wadi Abu Dabbab (Fig. 7), represented by 3 m

thick bed of reddish to buff algal limestone.

Petrographically, it is composed of poorly sort-

ed, moderately to lossely packed, fine- to large

sized bioclasts (Fig. 4e) mainly of calcareous

red algae, such as Lithothamnium sp., Am-phiroa spp. (up to 85%), larger benthic foram-

inifera (Amphistegina sp, Peneroplis sp., Bore-

lis sp. and miliolids) and rare coral and

bivalve shell fragments (about 10%). These al-

lochems are embedded in a micritic matrix

that occasionally changes diagenetically into

microspar. This allochthonous bioclastic

packstone with the reef-derived oraganisms is

comparable to SMF type 5 and FZ 4. The

dominant constituents have been formed in a

high energy environment on shoals and reef

settings and then transported down local

slopes to be deposited in a quiet water of fore-

reef slope.

GrainstonesGrainstones

This grain-supported facies is the major

carbonate microfacies, representing 46% of

the total thickness of the studied limestones.

It is recoded from all rock units in the studied

succession and is particularly best developed

in the Pliocene Shagra Formation. Five micro-

facies associations are recognized.

The oosparite microfacies (Fig.4 f,g) is re-

corded from the Gabir Formation at Wadi Abu

Dabbab and Wadi Samadai (Figs. 7, 9). It is

also well developed in the Shagra Formation

at Wadi Samadai, constituting about 16% of

the total limestone thickness. Ooids are the

main allochems. Other components include

rare molluscan shell fragments, benthic fo-

raminifera, red algae and peloids. The ooids

are moderately well sorted and have few

is recorded from the upper part of the Shagra

Formation at Wadi Abu Dabbab and from the

Pleistocene raised beaches and coral reefs (TI)

at Sharm El-Luli. The packstones are repre-

sented by sandy biomicrite and algal biomi-

crite.

The sandy biomicrite microfacies (Fig. 4d)

is encountered in the Pleistocene raised reefs

at Sharm El-Luli (Fig. 11). It consists mainly

of densely packed, poorly sorted, fine to large

sized bioclasts of benthic foraminifera (Car-penteria sp., Sorites sp., Quinqueloculinasp.), calcareous red algae (Lithothamniumsp., Amphiroa sp., Dermatolithon sp., Litho-phyllum sp. and Mesophyllum sp.), echinoid

spines, molluscan shells and rare bryozoa

(Fig. 4d1-3). These skeletal grains constitute

more than 70% of the total volume of the

rock. Fine to medium, sub-angular to sub-

rounded quartz and k-feldspar grains consti-

tute about 10%. All these components are em-

bedded in a microcrystalline calcite matrix

with some patches of sparry calcite. Some

skeletal fragments are coated by micrite enve-

lopes; others are dissolved creating biomoul-

dic porosity. The concentration of these bio-

clasts suggests that, this microfacies was

deposited in an open marine platform with

normal salinity and good circulation of a well-

oxygenated environment. They have been

transported to a low energy environment

(Flügel 2010) either in the shelf lagoon with

open circulation (FZ 2) or open sea shelf (FZ

7). However, the presence of quartz and K-

feldspar grains indicates near-shore piling up

of the sediments.

The algal biomicrite microfacies is restrict-

ed to the top part of the Shagra Formation at

173


174


supported, mud free microfacies is equivalent

to SMF type 15 of Flügel (2010) and FZ 6

(winnowed edge sands) of Wilson (1975).

The foraminiferal biosparite microfacies is

encountered mainly from the Shagra Forma-

tion at Wadi Abu Dabbab (Fig. 7). It is also re-

corded from the Samadai Formation at Sharm

El-Luli (Fig. 11), representing 8.5% of the to-

tal carbonate thickness. The main allochems

include mainly benthic foraminifera such as

Amphistegina sp., Borelis sp., Carpenteriasp., Triloculina sp., Quinqueloculina sp. and

Pyrgo sp., in addition to minor components of

calcreous algae, echinoid spines and coral

fragments (Fig. 5d,e). The skeletal grains are

coated by micritic envelopes. The non-

carbonate particles are represented by sand-

sized quartz, feldspar, in addition to some bio-

tite and amphiboles. All these components are

cemented by sparry calcite. The fossil associa-

tion suggests deposition in tidal bars and

open lagoons behind the outer platform edge

comparable to SMF type 18 of Flügel (2010)

and FZ 7 of Wilson (1975).

The algal biosparite microfacies is well de-

veloped in the Shagra and Samadai forma-

tions at Wadi Asalay and Wadi Samadai (Figs.

8, 9). It represents up to 7% of the total car-

bonate thickness. Petrographically, the domi-

nent components are calcareous red algal

lumps and fragments (Amphiroa sp., Litho-phyllum sp., Mesophyllum sp. and Archaeo-lithothamnium sp.). Most of the red algae are

well preserved and show their original mi-

crostructures (Fig. 5f). Considerable amounts

of echinoid spines and plates and less com-

mon benthic foraminiferal tests (miliolids,

Amphistegina sp.) are recorded. Sand-sized

concentric mostly superficial laminae which

are rounded to ellipsoidal. The nuclei are of-

ten quartz, feldspar or micritized shell frag-

ments. Diagenetic features observed in-

clude dissolution, micritization and

recrystallization. The microstructure of small

ooids is typically altered by micritization (Fig.

4g) resulting in the formation of pseudope-

loids. Some ooids are partially leached re-

sulting in oomouldic porosity. Few dissemi-

nated sand sized quartz and rock fragments

are also encountered. All these constituents

are bound by coarse sparry calcite cement.

This grain-supported microfacies indicates

deposition in high energy environments of oo-

litic shoals, tidal bars and beaches compara-

ble to SMF type 15 of Flügel (2010) and FZ 6

of Wilson (1975).

The bio-oosparite microfacies is well devel-

oped in the Gabir and Shagra formations

studied at Wadi Abu Dabbab, Wadi Asalay

and Wadi Samadai (Figs. 7-9), constituting

11% of the studied limestones. Petrographi-

cally, the main components are poorly to

moderately sorted, superficial to normal, con-

centric, densely packed, rounded to oval

ooids, constituting about 85% of the rock vol-

ume (Fig. 5a-c). The ooids ? nuclei are com-

posed of detrital quartz grains or skeletal frag-

ments such as foraminiferal tests or red algal

fragments. Some ooids are partly or totally

micritized and some are affected by dissolu-

tion resulting in oomouldic porosity. In addi-

tion to the ooids as the main allochems, mi-

nor components include calcareous red algal

fragments, benthic foraminifera, echinoid

spines, encrusting bryozoa and molluscan

shell fragments. All these components are ce-

mented together by sparry calcite. This grain

175


dite (Fig. 6a) is a grain supported rock com-

posed essentially of gravel-sized skeletal frag-

ments such as colonial corals, red algal frag-

ments, bryozoa, oyster shell fragments,

echinoid spines and some intraclasts. All

these components are cemented by sparry

calcite. These reef derived bioclasts were de-

posited and accumulated as a marine talus in

high energy fore-slope settings, comparable to

SMF type 6 of Flügel (2010) and FZ 4 of Wil-

son (1975).

BoundstonesBoundstones

Boundstones represent about 40% of the

total thickness of the studied limestones.

They are recorded mainly from the Pleistocene

raised reefs and the Plio-Pleistocene Samadai

Formation from all studied localities (Figs. 7-

11). They are recorded also from the Shagra

Formation at Wadi Abu Dabbab and Wadi Sa-

madai, and from the Gabir Formation at Wadi

Asalay. The differentiation between these au-

tochthonous carbonates is based on the inter-

actions between benthic sessile organisms

and sediments, including binding, baffling

and framework building (Embry & Klovan

1971). Three microfacies associations can be

recognized in the studied boundstones; coral

framestone, algal framestone and algal bind-

stone. These autochthonous carbonates indi-

cate deposition in a medium energy but high-

ly oxygenated organic reef buildup

environments to moderately high energy con-

ditions on platform margins, equivalent to

SMF type 7 of Flügel (2010) and FZ 5 of Wil-

son (1975).

The coral framestone microfacies is the

most common boundstone microfacies type

encountered in the studied succession. It is

quartz and feldspar grains are also encoun-

tered. All components are cemented in a spar-

ry calcite. This microfacies with its fossil asso-

ciation suggests deposition in areas with

normal salinity, constant wave action at or

above the wave base (winnowed platform edge

sands) comparable to SMF type 11 of Flügel

(2010) and FZ 6 of Wilson (1975).

The foraminiferal algal biosparite microfa-

cies has a very limited distribution, recorded

only from the Pleistocene raised reefs at

Sharm El-Fuquiri (Fig. 10), representing

about 3.5% of the studied limestones. Petro-

graphically, the main components (up to 56%)

are bioclasts of calcareous red algae (Derma-tolithon sp., Lithophyllum sp. and other algal

species). Appreciable amounts of larger ben-

thic foraminifera (Amphistegina sp., Carpente-ria sp., Miogypsina sp., Sorites sp., miliolids

and others), forming about 28% of the rock

volume are observed (Fig. 5g, h). Minor

amounts of molluscan shell fragments, echi-

noid spines, serpulid worm tubes and coral

fragments (forming collectively up to 10%) are

recorded. The non-carbonate particles are

represented by rare scattered quartz and pla-

gioclase grains. All these components are ce-

mented together by a sparry calcite. This mi-

crofacies is equivalent to SMF type 11 of

Flügel (2010) and FZ 6 (winnowed platform

edge sands) of Wilson (1975).

RudstonesRudstones

This microfacies is of limited distribution;

encountered from the Gabir Formation at

Wadi Asalay and from the Shagra Formation

at Wadi Asalay and Wadi Samadai (Figs. 8, 9).

The facies represents only 6% of the total

studied limestones. The recognized biosparru-

176


thic foraminifera such as; Amphistegina sp.,

Pyrgo sp. Borelis sp. and other encrusted

forms, scleractinian coral fragments, ooids

and fine to medium quartz and feldspar

grains.

DISCUSSION AND CONCLUSIONSDISCUSSION AND CONCLUSIONSIn the Marsa Alam area, the Early Pliocene

is marked by a proper marine transgression

where the Gabir Formation was deposited.

This fossiliferous rock unit yielded large-sized

oysters dominated by Crassostrea crassissi-ma, C. gingensis and Saccostrea cuccullataand other molluscs (bivalves and gastropods),

echinoids, corals, algae and foraminifera (Fig.

12). The fossil associations and the encoun-

tered bio-oosparite and oosparite microfa-

cies indicate normal salinities of warm wa-

ter in a medium to high energy environment.

The identified fauna (Kora & Abdel Fattah

2000) includes both Mediterranean and

Indo-Pacific forms suggesting that, the trans-

gression was due to opening of the Bab El

Mandab Strait which connected the Indian

Ocean with the Red Sea basin. The recorded

fossiliferous conglomerates and pebbly arkos-

es from the Gabir formation at Wadi Abu Dab-

bab and Wadi Asalay (Figs. 7, 8) reflects the

close relation between the nearby basement

rocks and the depositional basin. The encoun-

tered fossil association in these conglomerates

and pebbly arkoses implies deposition in a

shallow to very shallow intertidal-beach envi-

ronment with warm clear water (Fig. 12). This

is in accordance with Sheppard et al. (1992)

who reported that the rifting recommence in

the Pliocene. Connection with the Indian

Ocean contributing tropical deposits includ-

ing reef growth alternating with large alluvial

flows are among the geological events impor-

essentialy recorded from the Pleistocene

raised reefs and the Plio-Pleistocene Samadai

Formation from all studied localities. It is also

sporadically recorded from the top and middle

parts of the Gabir Formation at Wadi Asalay.

It is essentially composed of scleractinian co-

rals, acting as primary frame-builders in

growth position (Fig. 6b, c). The corals from

the Pleistocene raised reefs in addition to

those of the Samadai Formation retain their

original microstructure. The coral skeletons

contain inter- and intra-skeletal pores that

may be empty (in the younger fossils), partial-

ly or completely filled with latter sparry calcite

crystals (in the older skeletons). The spaces

between corallites are generally empty or may

be filled with micrite matrix.

The algal framestone microfacies is record-

ed only from the upper part of the Samadai

Formation at Sharm El-Luli section (Fig. 11).

Petrographically, it is composed entirely of co-

ralline red algae (Fig. 6d, e) acting as the pri-

mary frame-builders. It is well preserved,

keeping its original microstructure such as

conceptacles, fine-scale reticulate, cellular or

lattice work internal structure. This microfa-

cies represents a cavernous framestone in

which red algae are bounded together with bi-

oclasts of colonial corals, encrusting forami-

nifera and serpulids.

The algal bindstone microfacies is recorded

from the Shagra Formation at Wadi Abu Dab-

bab and Wadi Samadai (Figs. 7, 9). Petro-

graphically, the framework is composed main-

ly of calcareous red algae (Fig. 6f, g) that

encrust and bind sediment together during

deposition. The matrix between the red algal

crusts is mudstone to wackestone with ben-

177


dal environment. The carbonates are interca-

lated with fossiliferous arkoses and conglom-

erates (Fig. 12). The encountered fossils in-

cluding benthic foraminifera, molluscan

shells and red algae imply that the fossilifer-

ous arkoses and conglomerates were deposit-

ed in a shallow to very shallow, clear marine

environment. The feldspathic greywacke re-

corded from the top part of the Shagra Forma-

tion at Wadi Samadai (Fig. 9) is characterized

by the dominance of altered feldspars and

rock fragments indicating a humid climate

(Mahran et al. 1999). Similarly, El Asmar &

tant to Red Sea reef formation and distribu-

tion.

The opening of the Red Sea had continued

during Late Pliocene time where the bioclastic

carbonates of the Shagra Formation, contain-

ing a dominant (more than 75%) Indo-Pacific

fauna of clypeasteroids and corals were de-

posited. The fossil assemblages and the corre-

sponding microfacies types (Figs.7-10) indi-

cate deposition in open marine conditions of

warm and clear water, mostly in slopes and

winnowed platform margins of shallow subti-

178


lithologic characteristics of this unit indicate

deposition in very shallow subtidal environ-

ments of shoals and organic buildup condi-

tions with short lived pluvial episodes, which

continued to the Late Pleistocene (Kora & Ab-

del Fattah 2000).

During the Pleistocene, extensive sea level

fluctuations mostly at -30 to -80m below

present sea level resulted in two reef growth

phases, and uplift of older fringing reefs at

margins, forming terraces (Sheppard et al.

1992). During highstands, coral reefs develop

because alluvium is trapped upstream. Dur-

ing lowstands, wadis cut into the alluvium

and generate terraces (Arvidson et al. 1994).

According to Tucker (2003), the reefs were de-

posited during interglacial highstands of sea

level. The reefal carbonates are mainly coral

framestones (Fig. 12) composed mostly of

large scleractinian coral colonies up to several

meters in diameters (Fig. 3e, f). Landwards,

the reefal unit passes into foreshore/

shoreface conglomerates with a transition of

mixed carbonates and clastics. These fossilif-

erous conglomerates are interpreted as a se-

ries of prograding clastic beaches developed at

a time of sea level stillstand.

ACKNOWLEDGEMENTSACKNOWLEDGEMENTSThe authors would like to thank Prof.

Dr. Adam El Shahat, Mansoura University

and Prof. Dr. Abdel Mohsen Ziko, Zagazig Uni-

versity for the critical revision of the manu-

script.

Abdel-Fattah (2000) concluded that the lithol-

ogy and microfacies in the Neogene-

Quaternary succession in the Marsa Alam

area suggest changes in the depositional envi-

ronments from fluvial to open shallow marine

and intertidal conditions associated with cli-

matic changes from hot-dry to warm-wet. The

variability in distribution and deposition of

these rock units appear related to the rifting

of the northern Red Sea and/or sea level

changes.

The Late Pliocene / Early Pleistocene

transition is marked by deposition of the

Samadai Formation after a period of uplift

and truncation. It forms a grey ledge over-

lying unconformably the Shagra Formation

(Fig. 3c). Conglomerates are the essential

components of the Samadai Formation (up

to 57% of the total clastic thickness) alter-

nating with reefal limestones. These con-

glomerates are rich in algal lumps, coral

debris, larger benthic foraminiferal tests,

molluscan shell fragments, echinoid spines,

serpulid worm tubes and few ooids. The

fossil associations of this conglomerate

type suggest deposition in a littoral to

beach environment with warm, clear water

and normal salinity. Away from the sea, the

recorded unfossiliferous conglomerate and

gravel beds (e.g. at Wadi Sharm El-Fuquiri,

Fig. 10) are interpreted as representing pluvi-

al episodes which interrupted an otherwise

dry climate (Said 1990) favouring persistent

reef growth. The faunal association and

179


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Received on 15 / 12 / 2012

182


لخص العربى ا

السحنات الدقيقة والتفسير البيئى لكربونـات البليوسـ - بليسـتوس فى منطقـة مرسـى علم- ساحل البحر األحمر - مصر

محـمــــود قــــوره صـــــالح عـيـــــاد هبـــه الدســــوقى

ـنـصـــــورة قســــم اجليولوجــيـــا - كلـيـــة الـعــلــــــوم - جامعــــة ا

قياس ودراســة 5 قطاعــــات اسـتراتيجرافية تمثل تـتـــابع البليوس والبلـيستوس فى منطقة حــول مدينـة مرسـى علــم تمتد من وادى

) ومـتـكون صـمداى أبـو دبـاب شمـاال إلى وادى شـرم اللـولى جـنوبـا. وقـسمت إلي 3 وحدات صـخريـة تـشمل مـتكـونى جـابر والـشقـرا (بـليـوس

يكـروسكوبية لعدد 167 قطاعـا رقيقا تعريف رتـفعــة. ومن الدراسة ا رجانية ا ) باإلضافة إلى 3 مصاطب من الشعـاب ا (بليوبـليستوس

وتوصيف 13 سـحنـة صخـرية فى صـخـــور الـكربونـات التى تـمثل %57 من الـتتـابــــع وهى متـبادلـــة مع كـوجنلـوميـرات وحجـر رملى أركوزى

وقليل من الطفلة.

رجانـى هى أكثر السحنـات الدقيقة انـتشارا تتبعـها سحنات احلـجر اجليرى البطـروخى ثم الغنى بالفـورامينيفرا وتب أن سحنـة حجر اإلطار ا

والـطحالب. ومن دراسـة الصحبـة األحفوريـة تب أن هـذا التتابع قـد ترسب معـظمه في بيـئة ساحـلية تمـتد من خط الشـاطئ وحتى البـيئة الـبحرية

تبـادلة مع صخور الكربونات فهى مستمدة من صخور القـاعدة اجملاورة ونقلت بواسطة أنهار أثناء فترات مطرية الضحلة. أما الصخور الفتاتية ا

قصيرة ثم ترسبت فى بيئة شــاطئيـة.

183


MICROFACIES AND ENVIRONMENTAL INTERPRETATION OFMICROFACIES AND ENVIRONMENTAL INTERPRETATION OFTHE PLIOCENE-PLEISTOCENE CARBONATES IN THE MARSATHE PLIOCENE-PLEISTOCENE CARBONATES IN THE MARSA

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ReprintReprintfrom

Journal of Environmental Sciences, 2013; Vol. 42, No. 1 : 155-182Journal of Environmental Sciences, 2013; Vol. 42, No. 1 : 155-182

JOESE 5

http://www1.mans.edu.eg/facscim/english/MJI P-ISSN 1110-192Xhttp://www1.mans.edu.eg/facscim/english/MJI P-ISSN 1110-192Xe-ISSN 2090-9233e-ISSN 2090-9233

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