Transcript
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PALYNOFACIES ANALYSES AND PALAEOENVIRONMENTS OF SOME

LOWER CRETACEOUS ROCKS OF THE SIQEIFA 1X BOREHOLE,

NORTH WESTERN DESERT, EGYPT

Magdy S. Mahmoud*,, Mohamed A. Masoud**, Mohamed A. Tamam**, and

Miran M. Khalaf**

* Assiut University, Faculty of Science, Geology Department, Assiut, Egypt

** Sohag University, Faculty of Science, Geology Department, Sohag, Egypt Corresponding author e-mail: [email protected]

ABSTRACT

A detailed palynofacies analysis was carried out on 56 ditch-cutting samples

obtained from the lower Cretaceous of Siqeifa 1x borehole, north Western

Desert, Egypt. The main aim of this study is to identify depositional

palaeoenvironments in details, reconstruct vegetation cover and to infer

palaeoclimate conditions. Three palynofacies types were recognised;

palynofacies type (PF-1) corresponds to the lower-middle Alam El Buieb

Formation (Berriasian-Barremian). This is deposited in a deltaic (prodelta)

subenvironment during a Berriasian-early Barremian regression episode, and

the lower upper Alam El Buieb deposited in an inner shallow marine

environment during a partial regain of a late Barremian-Aptian transgression,

under prevailing dysoxic-anoxic to suboxic-anoxic conditions. The second

palynofacies (PF-2) represents the uppermost Alam El Buieb, Alamein, and

Dahab formations (late Barremian-Aptian), where the uppermost Alam El-

Buieb Formation was deposited in a distal bar of a prograding delta,

accumulated during a minor local regression. However, the carbonate of the

Alamein Formation and the shale of the Dahab Formation was deposited in a

saline lagoon environment developed during a partial regain of the local early

Aptian marine transgression. Suboxic-anoxic to dysoxic-anoxic conditions are

interpreted to prevail during deposition of the PF-2. Third palynofacies (PF-3)

represents the Kharita Formation (Albian), where the lower Kharita was

deposited in a lagoon setting, while the upper Kharita was deposited in a

deltaic environment due to a major marine regression, under dysoxic-suboxic

conditions. Local pteridophyte vegetation on low lands near the borehole and

conifers on relatively dry hinterlands is interpreted to thrive under a regional

warm and relatively dry palaeoclimate. Possible seasonal dry periods may be

developed during deposition of the uppermost Alam El Buieb, Dahab and

Alamein formations.

THE SEVENTH INTERNATIONAL CONFERENCE

ON THE GEOLOGY OF AFRICA

P-P VI-33 – VI-58 (NOV. 2013) ASSIUT-EGYPT

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VI-34 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

1. INTRODUCTION

The lower Cretaceous in the north Western Desert exhibits a major regressive

phase indicated by clastics (Said, 1990). Neocomian-Barremian sedimentation

represents a regressive phase and marginal marine sandstone and shale of the Alam

El Buieb Formation were deposited. The Aptian witnessed a transgressive phase,

which brought a shallow sea over the north Western Desert, while the carbonate

unit of the Alamein Formation was deposited. The Albian time is represented by

another regressive phase, when the north Western Desert was receiving the fluvial

(mainly coarse sands) sediments of the Kharita Formation coming from the south.

However, in the extreme north, specifically at the Matruh Basin, sedimentation of

fine silt and shale was dominant (Said, 1990).

Combaz (1964) introduced the term palynofacies as “the total complement of

acid-resistant particulate organic matter recovered from sediments by

palynological processing techniques”, and based on this term palynofacies analysis

was used to interpret palaeoenvironments. However, Tyson (1995) provided the

most recent and widely used definition of the palynofacies term as “the total

particulate organic matter assemblage contained in a body of sediment thought to

reflect a specific set of environmental conditions, or to be associated with a

characteristic range of hydrocarbon-generating potential”. The later term can be

used in palaeoenvironments interpretation as well as in source rock evaluation, and

will be used here because it links palynofacies types to sedimentary sequences.

Palynofacies analysis is interested with changes in the relative abundance of various

types of sedimentary organic matter as palynomorphs, phytoclasts, and amorphous

organic material (AOM). Because palynofacies analysis is closely linked to

sedimentology, it can thus used in identifying palaeoenvironmental and

hydrographic parameters such as distance from shoreline, hydrodynamic energy in

the water column, salinity, and oxygen regime (e.g. Tyson, 1995; Batten, 1996).

Several palynological investigations have dealt with the palaeoenvironmental

interpretations of the Egyptian Cretaceous rocks (e.g. Abdel-Kireem et al., 1996,

Ibrahim, 2002; Zobaa et al., 2013). However, the use of detailed palynofacies

analyses in interpreting palaeoenvironmental settings still lacking. Mahmoud and

Deaf (2007) studied the palynostratigraphy of the lower Cretaceous succession

penetrated by the Siqeifa 1x well borehole northern Western Desert, Egypt. The

present work aims to study the palynological facies of the Siqeifa 1x with more

detailed analyses upon the percentage distribution of the palynological organic

matter (POM) assemblages to infer the palaecological settings in terms of

depositional palaeoenvironments, palaeoclimate, and palaeovegetation covers.

2. MATERIAL AND METHODS

The present study is based on fifty-six ditch cutting samples were collected from

the lower Cretaceous of the Siqeifa 1-X borehole, Matruh Basin, northern Western

Desert (Fig. 1). The samples were processed by standard (HCl-HF) palynological

preparation technique, without oxidation or ultrasonic treatments. The palynological

residue was sieved through 10 μm nylon sieves. Three to five permanent slides were

prepared using glycerin jelly as a mounting medium. It should be noted that neither

ultrasonic nor oxidation (nitric acid) treatments were carried out, where these

analyses would results in oxidation and inevitable destroyment of the plant debris

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

Miran M. Khalaf

VI-35

and the palynomorphs. All slides and residues are stored and catalogued in the

Geological Museum, Geology Department, Faculty of Science, Sohag University,

Egypt.

Figure 1. Geographic map of Egypt showing the location of the Siqeifa 1-X well

(After Abdel Kireem et al., 1993)

Palynological slides were examined using the transmitted light microscopy

Olympus BX41 Microscope at X 200 and X 500 magnifications in order to:

establish semi quantitative analysis of the POM; determine the palynofacies types

and the palaeoenvironmental interpretations. The photomicrographs are published

in Mahmoud & Deaf (2007). For full reference to taxa refer to Mahmoud & Deaf

(op. cit.). Each slide was counted for its POM content, in which the first 200

particles were categorized as abundant >35 %, frequent 16-35 %, common 5-15 %

and rare <5 %. The palynofacies analysis is based on the percentage frequency of

different POM constituents categorised by Tyson (1995). The percentage of each

palynomaceral component is derived from the total POM frequencies. However, the

species richness and percentage of dinoflagellate cysts morphotypes were obtained

from the total dinoflagellate cysts frequencies.

3. LITHOSTRATIGRAPHY

The operating drilling company WEPCO (1970) did not recognised most of the

formations in the studied borehole, and only provided detailed information on

lithology, unit thicknesses, and tops of these lithologic units. Thus, the lithology

description, which has been provided by the company and the palynological age

dating provided by Mahmoud & Deaf (2007) will be used to identify formations in

the borehole (Fig.2). Description of the Cretaceous formations in the Stratigraphic

Lexicon of Egypt (Hermina et al., 1989) and that provided by Hantar (1990) were

consulted.

Siqeifa 1-

X

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VI-36 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

Figure 2. Lithologic column of the Siqeifa 1x borehole (After Mahmoud & Deaf, 2007)

3.1 Alam El Bueib Formation

This formation is composed of sandstone with frequent shale interbeds in its

lower part and occasional limestone in its upper part, but in the Siqeifa 1-X well, the

formation is mainly composed of thick shale unit intercalated with very minor

streaks of sands, and shows more sandy facies at its bottom and top. This shale unit

was commonly referred to as the Matruh shales or the Mersa Matruh Formation of

Norton (1967). Its type section is the interval from 3927 to 4297 m of the Alam El

Bueib-1 well (Hantar, 1990). This formation ranges in age from Barremian to

Aptian (Hantar, 1990). WEPCO (1970) referred to this unit in the investigated well

as: no information, top of Umbaraks Sands, and top of Matruh Shale. Based on the

palynology work of Mahmoud and Deaf (2007) and lithologic description provided

above, the thick 869 m (2850 ft) clastic sequence confined between depths 3463 and

2594 m (11950-9100 ft) can be identified as the Alam El Bueib Formation and

given a Berriasian-Barremian age. This formation is belived to be deposited under

shallow marine conditions with more continental influence towards the south

(Hantar, 1990).

3.2 Alamein Formation

This unit consists mainly of hard dense brown dolomite with a few thin shale

interbeds at its base and top (Hantar, 1990), but in the Siqeifa 1-X well, it is

composed of chalky limestone intercalated with minor shale streaks. It rests

conformably over the Alam El Bueib Formation and underlies the Kharita

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

Miran M. Khalaf

VI-37

Formation (Hantar, 1990). In type section it measures 84 m (276 ft) thick at depths

2489 to 2573 m of the Alamein-1 well (Hantar, 1990). The age of the formation was

reported at the type section to be Aptian to Albian age (Hantar, 1990), but in the

Siqeifa 1-X well, Mahmoud & Deaf (2007) assigned an early Aptian age for the

carbonate unit confined between depths of 2487-2427 m (8750-8550 ft). The

described unit seems to have been deposited in a shallow marine, low to moderate

energy environment (Kerdany & Cherif, 1990).

3.3 Dahab Shale

It is composed of a shale unit interbeded with thin streaks of siltstone and

sandstone at its type section. In the Siqeifa 1-X well, this unit has a similar

lithological composition, but it contains minor black carbonaceous material and

pyrite in shale, and dolomite and anhydrite streaks in the sandstone beds. This

formation is conformably underlain by the Alam El Bueib Formation and overlain

by the Kharita Formation. The type section is the interval between 3180 to 3354 m

of the Dahab-1 well. This unit is attributed an Aptian-early Albian age (Hantar,

1990). In the investigated well, this formation was not identified by WEPCO (1970)

and the palynological dating of Mahmoud & Deaf (2007) suggests sediments at

depths 2366-2076 m (8350-7400 ft) as comprising the Dahab Formation of a mid to

late Aptian age. The Dahab Formation seems to be deposited in a shallow marine

environment (Barakat & Darwish, 1987; Hantar, 1990).

3.4 Kharita Formation

This formation consists of fine to coarse-grained sandstones with interbeds of

greyish green shale and some carbonates at its type section (389 m/1276 ft) at the

Kharita-1 well. In the studied well, the formation is composed essentially of

medium to coarse-grained sandstone containing minor pyrite and frequent

carbonaceous matter, and intercalated with thin shale and siltstone streaks. It rests

conformably over the Dahab Formation and underlies the Bahariya Formation

(Hantar, 1990). The Kharita Formation is assigned to be of Albian to Cenomanian

age (Hantar, 1990). In the Siqeifa 1-X well, WEPCO (1970) referred to the section

(457 m/1500 ft) at depths from 2061 to 1604 m (7350-5850 ft) as no information.

Based on the palynostratigraphic study of Mahmoud & Deaf (2007), this sequence

can be recognized as the Kharita Formation of the Albian age. The Kharita

Formation was most probably deposited in an extensive shallow marine shelf in a

littoral setting (Hantar, 1990; Kerdany & Cherif, 1990).

4. RESULTS OF PALYNOFACIES ANALYSIS AND INTERPRETED

PALAEOENVIRONMENTS

The palaeoenvironmental interpretations presented here are mainly depending on

the semi-quantitative palynofacies characteristics of selected constituents of the

palynological matter, which are known to have a palaeoenvironmental significance.

Certain sporomorphs are indicators of specific ecological parameters and thus are

useful in identifying palaeoclimatic conditions and in reconstructing the vegetation

cover grew on the source area.

The changes in the palynofacies composition in the Siqeifa 1x well (Figs. 3 & 4),

and the AOM-palynomorphs-phytoclasts (APP) ternary plot (Fig. 5) reveal three

palynofacies types in the lower Cretaceous of the study well these are described as

follows.

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VI-38 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

Figure3. Percentage abundances of some selected palynomorphs and particulate

organic matter of the Siqeifa 1x borehole, northern Western Desert, Egypt

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

Miran M. Khalaf

VI-39

Figure 4. The percentage of dinoflagellate cyst abundances, species richness, and

different cyst morphotypes, the Siqeifa 1x borehole, northern Western Desert, Egypt

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VI-40 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

4.1 Palynofacies PF-1: Prodelta to inner shallow marine

This palynofacies (samples 1-21) is considered as the oldest one; it covers the

depth from 11950 to 9550 ft (3463-2716 m) and corresponds to the lower-middle

Alam El-Buieb Formation. It is characterized by abundant AOM (avg. 46%),

abundant phytoclast (avg. 43%) and common sporomorphs (avg. 9.8%), whereas

the marine palynomorphs are represented by rare (avg. 3 %) dinoflagellate cysts and

rare (avg. <5 %) MTLs (Fig. 3; Pl. 3, Fig. 1).

The rare dinoflagellate cysts abundances and moderate species richness (avg. 4)

of this palynofacies indicate stressed marginal marine environment of below normal

salinity (e.g. Batten, 1983; Lister & Batten, 1988). The dominance of the cavate

(avg. 35 %) and proximate (avg. 32 %) cysts such as Pseudoceratium,

Cribroperidinium, and Circulodinium characteristic of brackish water conditions

over the open marine (middle shelf) chorate (avg. 8%) cysts (Fig. 4), suggests

deposition of samples 1-15 of PF-1 in a brackish marginal marine environment (e.g.

Harding, 1986; Lister & Batten, 1988). The sporadic occurrence of the low salinity

genus Muderongia in PF-1 also supports this brackish conditions (e.g. Lister &

Batten, 1988). The abundance of the dinoflagellat cysts shows a slight rise at the

upper part (samples 16-21) of the described palynofacies, which indicates a

comparatively more distal depositional setting than that recorded for the lower part

of PF-1 (Tyson, 1995). Percentages of dinoflagellate cysts have been found to

exhibit offshore increases with increased water depth (e.g. Tyson, 1984, 1993). This

suggests that a minor marine transgression related to a loacl sea level rise took place

during deposition of this part of PF-1 (e.g. Lister & Batten, 1988). This is most

propabaly related to the global late Barremian-Aptian transgression (Vail et al.,

1977; Said, 1990). The rare occurrence (1.7 %) of MTLs in the upper part (samples

12-19) of PF-1 supports the suggested minor transgression, as MTLs are indicative

of marine conditions (e.g. Lister & Batten, 1988; Stancliffe, 1989) and typically

show very low frequencies in distal deltaic facies (Traverse, 1988).

Dominance of the continental (avg. 9.8% of total POM) over the marine (avg.

4% of total POM) palynomorphs generally indicates proximity of the depositional

site to active fluvio-deltaic systems (e.g. Tyson, 1993; Batten, 1996). The override

of pteridophyte spores (avg. 6%) over sphaeroidal (Araucariacites, Balmeiopsis,

Exesipollenites) gymnosperm pollen grains (avg. 3%) in the sporomorph

assemblage suggests deposition of PF-1 in shallow marginal marine settings, most

probably in a deltaic setting. This is based on the ecological preference and

reproduction rates of the spore-parent plants, as they thrive in swampy deltaic areas

and are known to be less productive than the gymnosperm pollen-producing plants.

In addition to the fact that pteridophyte spores have relatively limited transport

efficiency in contrast to the more buoyant and easily transported sphaeroidal pollen

grains (e.g. Tyson, 1995; Traverse, 2007).

Here, the percentage distribution of terrestrial plant debris plays a main role in

the suggestion of the possible palaeoenvironmental settings of PF-1. The high

abundance (avg. 43%) of the palynodebris (Fig. 3) generally reflects strong

terrestrial influx and deposition in marginal marine environments close to land

vegetation (e.g. Tyson, 1993; Al-Ameri et al., 2001). The frequent brown wood

(avg. 34 %) indicates deposition in a relatively low energy, distal marginal marine

setting of reducing (dysoxic-anoxic to suboxic-anoxic) conditions acording to the

Tyson’s (1995) ternary plot (Fig. 5, Tab. 1). In marine sediments, abundant brown

wood fragments were found to concentrate in the high energy, proximal sand and

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

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VI-41

silt facies and decrease in a basinward direction in the low energy finer sediments

(Habib, 1983; Firth, 1993; Tyson, 1995).

Figure 5. The Siqeifa 1x palynofacies plot in the ternary kerogen diagram of Tyson,

1995

By connecting the brown wood percentages of PF-1 to its lithology: brownish

grey to partly greenish grey shale, silty shale, and shale with minor sandstone

streaks, it is most likely that PF-1 was deposited in the subaqueous, relatively low

energy, prodelta subenvironment to inner shallow marine settings. Prodelta

sediments are shallow marginal marine clastics consist of silty clay that is

occassionally intercalated with thin streaks of coarse silt and find sands, and usually

contains marine fauna (here recognized MTLs) and frequent plant fragments (e.g.

Einsele, 1992; Nichols, 2009). High black wood percentages correlate with

relatively high energy silt and sands of fluvial and delta-top environments (Nagy et

al., 1984; Smyth et al., 1992; Williams, 1992). Thus, the low (avg. 8 %) black

woods recorded from the silty shale of PF-1 would imply a limited bacterially-

driven, in situe post-depsitional oxidation of brown wood during periodical

fluctuations in water table (Tyson, 1995) or due to seasonal low runoff and limited

supply of fresh wood fragments (Hellem et al., 1986; Marzi and Rullkotter, 1986).

Fractionation of fluvial and delta-top large black woods that were transported to

delta-front and re-deposited by wave and current actions (Tyson, 1995) and/or

directly blown by wind (e.g. Summerhayes, 1987; Ten Haven et al., 1990) into the

more distal, redcuing prodelta slope are also possible explanations for the present

low black wood frequency. Very low abundance (avg.1 %) of membranous tissue

generally indicates deposition in low energy, shallow marginal marine settings.

Membranoues tissues were found to be common in non-marine (e.g. bogs)

sediments and decrease in the brackish-marine, proximal deltaic (lower delta plain)

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VI-42 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

facies, and become rare in marine sediments (e.g. Lamberson, et al., 1991; Tyson,

1995).

The shale lithology with its very high (avg. 46 %) AOM content and the marked

dilution of the phytoclast content by AOM in PF-1 suggest high rate of

sedimentation and rapid burial in somewhat farther settings slightly removed from

active, non-marine sources, where the dysoxic-anoxic to suboxic-anoxic conditions

prevailed (Tyson, 1995).

From the above discussion, it is suggested that the silty shale of the lower-

middle Alam El Buieb Formation (samples 1-15) was deposited mainly in a

prodelta setting but with its lower upper part (samples 16-21) of the formation

deposited in an inner shallow marine setting, under dysoxic-anoxic to suboxic-

anoxic conditions.

Table 1. Key to marine palynofacies fields indicated in ternary diagram

(Modified from Tyson, 1995).

Spores:

Bisaccate

II Marginal

dysoxic-

anoxic

basin

AOM diluted by high phytoclast input, but AOM preservation

moderates to good. Amount of marine TOC dependent on basin

redox state. Generally low AOM preservation.

High Very low III (gas prone)

III Heterolithic

oxic shelf

("proximal

shelf")

Absolute phytoclast abundance dependent on actual proximity to

fluvio-deltaic sources. Oxidation and reworking common.

High Common to

abundant dinocysts

dominant

III or IV (gas

prone)

IV Shelf to

basin

transition

Passage from shelf to basin in time (i.e. increased

subsidence/water depth) or space (e.g. basin slope). Absolute

phytoclast abundance depends on proximity to source and

degree of redeposition. Amount of marine TOC depends on basin

redox state. Iva dysoxic-suboxic, IVb suboxic-anoxic.

Moderate to

high

Very low-low III or II (mainly gas

prone)

V Mud-

dominated

oxic (distal)

shelf

Low to moderate AOM (usually degraded). Palynomorphs

abundant. Light coloured biotrubated, calcareous mudstone are

typical.

Usually low Common to

abundant dinocysts

dominant

III > IV (gas prone)

VI Proximal

suboxic-

anoxic

shelf.

High AOM preservation due to reducing basin conditions.

Absolute phytoclast content may be moderate to high due to

turbiditic input and/or general proximity to source.

Variable low

to moderate

Low to common

dinocysts dominant

II (oil prone)

VII Distal

dysoxic-

anoxic

"shelf".

Moderate to good AOM preservation, low to moderate

palynomorphs. Dark-coloured slightly biotrubated mudstones are

typical.

Low Moderate to

common dinocysts

dominant

II (oil prone)

VIII Distal

dysoxic-

anoxic

shelf.

AOM-dominante assemblage, excellent AOM preservation. Low

to moderate palynomorphs (partly due to masking). Typical of

organic-rich shales deposited under stratified shelf sea conditions

Low Low to moderate

dinocysts dominant,

% prasinophytes

increasing

II >> I (oil prone)

IX Distal

suboxic-

anoxic

basin.

AOM-dominant assemblages. Low abundances of palynomorphs

partly due to masking. Frequently alginate-rich. Deep basin or

stratified shelf sea deposits, especially sediments starved basins.

Low Generally low,

prasinophyte often

dominant

II ≥ I (highly oil

prone)

III (gas prone)

Palynofacies

field and

environment

Comments Microplankton Kerogen type

I Highly

proximal

dysoxic-

anoxic

basin

High phytoclast supply dilutes all other components Usually high Very low

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

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4.2 Palynofacies PF-2: Deltaic to lagoon

Samples (22-42) recovered from depths 9450 to 7350 ft (2701-2061 m)

represents Palynofacies 2, which corresponds to the upper Alam El-Buieb

Formation, Alamein and Dahab formations. PF-2 is characterized by abundant

phytoclast (46%), frequent AOM (30%) and frequent sporomorph (19%), whereas

the marine palynomorphs are represented by rare (3%) dinoflagellate cysts and rare

(<5 %) MTLs (Fig. 3; Pl. 3, Fig. 2).

This palynofacies shows a slight decrease in marine (avg. 3%) palynomorphs in

comparison to PF-1, which indicates a comparatively more proximal depositional

setting than that recorded for PF-1 (Tyson, 1995). This decrease in species

abundance and the accumulation of alternating very fine sands and shale of samples

22-26 of PF-2 over the finer prodelta-inner shallow marine shale of PF-1 (Fig. 3),

indicates a minor regression and development of a new sedimentation cycle of a

prograding delta with its distal bar showing the coarsening upward sequence

(Boggs, 2006). On the other hand, the gradual upward increase in marine

palynomorphs and high dominance (avg. 67%) of the open marine dinoflagellate

cysts (e.g. Oligosphaeridium and Florentinia) accompanied with decreases in ratios

of the cavate (avg. 24%) and proximate (avg. 10%) cysts recorded from all samlpes

of PF-2, generally indicate development of inner open marine conditions. This may

point out to a gradual regain of the local late Barremian-Aptian transgression noted

in the underlying PF-1. The frequent presence of black carbonaceous material and

pyrite in shale and sandstone beds, and dolomite and anhydrite streaks in most

samples (27-42) of PF-2, and thick (376ft/114m) dolomite sequence indicates a

reduced distal setting that is slightly removed from high freshwater supply and is

partially isolated from normal marine water, and suggests a saline lagoon

environment (Boggs, 2006). An explanation that would justify the presence of open

marine dinocysts in the suggested lagoon is that tidal currents of the tidal channel

inlet of lagoons usually remove parts of the open marine sediments and fossils,

redistribute and concentrate them in the low energy area of the lagoons (Tyson,

1984, 1993; Boggs, 2006). Another factor that may in part contribute to this inverse

picture is the selective preservation during deposition in relatively oxic to suboxic

nearshore settings, which might overprint the original primary productivity of

cavate peridinioids. The peridinioid cysts are known to be sensitive to aerobic decay

(Zonneveld et al., 2009). The rare ocurrence of MTLs also supports the stressed

(saline) marine conditions.

The common frequencies of pteridophytes (avg. 11%) and its gradual upward

increase (samples 22-35) indicate a distal depositional setting that is relatively close

to an active deltaic system and shows gradual shifts in deposition in a basin ward

direction. The thin-walled spores such as pteridophytes are known to be controlled

hydrodinamically by their graine size and tend to increase in percentages in an

offshore direction, in the distal low energy settings of delta systems (e.g. Tyson,

1989; Dybkjaer, 1991). A further development of distal low energy settings is

suggested for the upper part (samples 36-42) of PF-2, based on the moderate

increase in the sphaeroidal pollen frequencies (avg. 6%), where these pollen grains

are known to have increase in percentage frequency in a shelfal direction (Hughes

& Moody-Stuart, 1967; Habib, 1979). The minor ocurrence of the xerophytic pollen

grain Ephedripites at the middle and upper parts of PF-2, and its complete absence

in the underlying and overlying palynofacies types, indicates ocurrence of a semi-

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VI-44 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

arid condition during deposition of these parts of PF-2 (Doyle, 1999), which

supports the suggested saline lagoon setting.

The brown wood (avg. 45%) increases in samples (22-35) at the expense of the

AOM (30%) indicate strong terrestrial influx and deposition in proximal settings

that is close to the parent land plants (Tyson, 1993). Diminishing in the brown wood

(avg. 27%) frequency in the uppermost part (samples 36-42) of PF-2 reflects more

offshore settings. The general upward decrease in black wood percentages (7%)

also supports the development of reduced, low energy distal settings, where this

wood is known to show a general offshore decline in frequency (Tyson, 1995). The

persistant low concentrations of membrance tisuue (avg. 1%) reflects the general

marine conditions and in part the dilution effect of other terrestrial and marine

components (Tyson, 1995).

AOM of PF-2 shows a significant lower frequency (avg. 30%) than that recorded

from the underlying PF-1 (avg. 46%) and supports the more proximal setting of PF-

2 (Tyson, 1993). Samples 22 to 35 reflect this proximal setting, where it still diluted

by high phytoclast input (Fig. 3), but the general upward increase in the AOM

reflects development of distal settings of dysoxic-anoxic conditions (e.g. Dow &

Pearson, 1975; Bujak et al., 1977). The plot of PF-2 in the ternary kerogen of Tyson

(1995) suggests suboxic-anoxic to dysoxic-anoxic conditions to have prevailed

during despoition of the palynofacies, and where he suggested the facies as

characteristic of shelf to basin transition.

Combining all information mentioned above, the very fine sand and shale

sediments comprising the uppermost Alam El-Buieb Formation (samples 22-26)

seem to represent a part of the distal bar of a prograding delta accumulated during a

minor local regression. The carbonates of the Alamein Formation and the overlying

shale of the Dahab Formation are suggested to be deposited in a saline lagoon

environment developed during a partial regain of the local early Aptian marine

transgression. Deposition of the PF-2 sediments is interpreted to take place under

suboxic-anoxic to dysoxic-anoxic conditions.

4.3 Palynofacies PF-3: Lagoon to deltaic

This palynofacies (samples 43-56) occupies the depth from 7250 to 5850 ft

(2030-1604 m), which corresponds to the Kharita Formation. It is characterized by

abundant phytoclast (57%), frequent AOM (20%) and frequent sporomorphs (22%),

whereas the marine palynomorphs are represented by rare dinoflagellate cysts

(<5%) and MTLs (Fig. 3; Pl. 3, fig. 3).

The sharp upward decline in the abundance (avg. 1%) and species richness (avg.

3%) of the dinoflagelate cysts in comparison to that of PF-1 and PF-2 indicates a

development of strong marine regression and deposition in a very shallow maine

grades upward into a coastal condition (e.g. Tyson, 1993). This may be related to a

local (Said, 1990) and global drop in sea level by the end of the Aptian, and

development of a major marine regression by the early Albian time (Murris, 1980).

At the base (samples 43-52) of PF-3 shale beds are alternated with fine to coarse

sandstones and grades upward (samples 53-56) into coarser sand beds intercalated

with minor shales. The whole sedimentary sequence shows a coarsining upward

sequence and contains minor black carbonaceous material, pyrite, dolomite and

anhydrite streaks in most samples of PF-3, which indicates a lagoon (samples 42-

52) grades upward into a deltaic (samples 53-56) setting. Here again the chorate

cysts percentages (avg. 60%) are greater than those of the cavate cysts (avg. 20%),

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

Miran M. Khalaf

VI-45

and this cannot be used to infer more open marine environment of the formation. As

is mentioned above, this is may be explained as due to action of tidal currents on

open marine sediments and also to the selective preservation. This in turn suggests a

development of a tide-dominated delta setting for the upper part (53-56) of PF-3.

The upwrad increase in spore concentrations from common (avg. 13 %) at the

base to abundant (40%) at the top of the palynofacies supports the regressive marine

deposition and transition form lagoon to delatic setting. The relatively higher

concentration of spores (avg. 13 %) compared to saccate pollen grains (avg. 9%)

also indicates a high energy proximal setting (Tyson, 1993).

The brown wood (avg. 37 %) is the most common phytoclast constituent, while

membranous tisuue (avg. 1 %) is very rare. The high supply of brown wood

sufficient to dilute all other components is characteristic of proximal settings, where

deposition takes place close to the parent flora (Tyson, 1993). The higher

abundance of black wood (avg. 20 %) of PF-3 in comparison to that recorded from

PF-1 and PF-2 and its upward increase suggests deposition of PF-3 in higher energy

settings than that inferred for PF-1 and PF-2. This setting indicates partial oxidation

before or during final deposition (Tyson,1995). This material as in PF-1 probably

represents the in situ post-depositional bio-oxidation of normal wood particles

during seasonal fluctutions in water table conditions, where such oxidation takes

place in littoral sediments with tidally fluctuating water tables (Pocock, 1982). In

general, the high proportions of the brown and black wood are known to

concentrate in proximal onshore settings that indicate proximity to shoreline and

deposition under dysoxic-suboxic conditions and the highest concentration of

terrestrially derived organic matter over the marine palynomorph, both

characteristics of marginal marine conditions.

The decreases in abundance of AOM (avg. 20 %) compared to the two

underlynig palynofacies types indicate shallow shelf sediments (e.g. Dow &

Pearson, 1975; Bujak et al., 1977). Plot of PF-3 constituents in the kerogen diagram

suggests deposition of the palynofcaies in a proximal basin of dysoxic-suboxic

conditions.

Combining all of these characteristics given previously, the sediments of PF-3

making up the Kharita Formation, were probably deposited in a lagoon (samples 43-

52) changed upward into a deltaic (samples 53-56) environment, during local and

global early Albian regression, under prevailing dysoxic-suboxic conditions.

5. PALAEOVEGETATION AND PALAEOCLIMATE

The study of the terrestrial palynomorphs recovered from the investiged

successions of the Siqeifa 1x borehole suggests a subtropical to tropical vegetation

cover near the study area. The abundance of the mainly fern spores represented by

pteridophytes (e.g. Deltoidospora) and Schizaeacean (Cicatricosisporites) in all

studied samples probably reflects local pteridophyte vegetation on wet lowlands

(Playford 1971; Schrank & Mahmoud 1998). The differences in percentage

frequency of terrestrial palynomorphs are mainly effected by the changes in the

sedimentation trends (i.e. transgression-regression) which is considered as the more

important parameter than any other ecological parameters on land as these fern

spores show a taxonomic stability through the analysis of the all studied sections

(Deaf, 2009). The common araucariacean pollen frequency reflects a conifer forests

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VI-46 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

on relatively dry hinterlands (Schrank & Mahmoud 1998; Schrank 2001; Mahmoud

& Moawad 2002).

The frequent occurrences of the Afropollis and Elaterate pollen grains indicate

more local coastal humid conditions near the site of the borehole (Schrank 2001).

The unusual high percentage (38 % of total palynomorphs) of the elaterate pollen

grains in a single horizon (Sample 44, depth 7100 ft/1985 m) at the lower Kharita

Formation of the Seqiefa 1x borehole indicate more local temporary short term

coastal humidity (Schrank, 2001; Mahmoud & Deaf, 2007). The consistent

occurrence of the drought resistant Cheirolepidiacean conifer pollen grains

Classopollis, which vegetate in hot subtropical latitudes (e.g. Doyle, 1999) indicates

regional hot and relatively dry conditions (e.g. Watson 1988; Doyle 1999). Doyle et

al. (1982), Schrank (1990), and Brenner (1996) all suggested relatively wetter

palaeoclimates for the African palaeotropics (e.g. Egypt and Sudan) based on the

lower frequencies of Classopollis than seen in the palaeosubtropics. The xerophytic

Ephedripites pollens (e.g. Doyle, 1999) reflect warm and relatively dry

palaeoclimate, which could imply the occurrence of seasonal dry periods during

deposition of the upper Alam El Buieb, Dahab and Alamein formations.

The Albian-Cenomanian Elaterate Phytogeographic Province of Herngreen et al.

(1996) had a paleoequatorial distribution corresponding to an arid to semi-arid

warm climate (El Beialy, 1994; Aboul Ela et al., 1996; Herngreen et al., 1996;

Ibrahim, 2002; Mahmoud & Moawad, 2002). However, the occurrence of fern

spores, mainly produced by hygrophilous plants, suggests the possibility of locally

or seasonally humid conditions (Schrank & Mahmoud, 1998) and therefore, a

regional warm and semi-arid palaeoclimate is suggested to prevail during deposition

of the sediments but with a local humid condition developed near or at the site of

the well (Mahmoud & Deaf, 2007).

6. CONCLUSIONS

Berriasian to Albian sediments of the Siqeifa1-X well have been studied

previously by Mahmoud and Deaf (2007), where they gave a preliminary

interpretation of the palaeoenvironments. Here a detailed palynofacies analysis was

carried out and enabled the recognition of various palaeoenvironments of the

formations encountered, which corresponded to three major palynofacies types. PF-

1 represents the lower-middle Alam El Buieb Formation (samples 1-15) that was

deposited in a deltaic (prodelta) setting during a Berriasian-early Barremian

regression episode, but with its lower upper part (samples 16-21) deposited in an

inner shallow marine setting during a partial regain of local and global late

Barremian-Aptian transgression episodes, under prevailing dysoxic-anoxic to

suboxic-anoxic conditions. PF-2 represents the uppermost Alam El Buieb, Alamein,

and Dahab formations (late Barremian-Aptian), where the uppermost Alam El-

Buieb Formation (samples 22-26) was deposited in the distal bar of a prograding

delta accumulated during a minor local regression. However, the carbonate of the

Alamein Formation and the shale of the Dahab Formation were deposited in a saline

lagoon environment developed during a partial regain of the local early Aptian

marine transgression. Suboxic-anoxic to dysoxic-anoxic conditions are interpreted

to prevail during deposition of the PF-2 sediments. PF-3 represents the Kharita

Formation (Albian), which was deposited in a lagoon setting (samples 43-52)

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

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VI-47

changed upward into a deltaic environment (samples 53-56) due to a major marine

regression, under prevailing dysoxic-suboxic conditions.

Local pteridophyte vegetation on low lands near the borehole and conifers

on relatively dry hinterlands is interpreted to thrive under a regional warm and

relatively dry palaeoclimate. Possible seasonal dry periods may be developed during

deposition of the uppermost Alam El Buieb, Dahab and Alamein formations.

ACKNOWLEDGEMENT

We are grateful to authorities of the Egyptian General Petroleum Corporation for

providing samples and borehole Log. Thanks are due to the reviewers for their

helpful comments to improve the quality of the manuscript.

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VI-48 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

Plate 1

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VI-49

The photomicrographs are published in Mahmoud & Deaf (2007). For full

reference to taxa refer to Mahmoud & Deaf (op. cit.).

Plate 1

(Magnification X500)

1, 6. Deltoidospora spp., 1, Slide S-31A: E.F. S48-4, 6, Slide S-36A: E.F. L11.

2. Triplanosporites sp., Slide S-31A: E.F. V41-3.

3, 20. Cicatricosisporites spp. 2, Slide S-04A: E.F. O49-4, 20, Slide S-05B: E.F. V32-2.

4. Tricolpites microreticulatus Belsky et al., 1965, Slide S-68A: E.F. X63-4.

5, 10. Balmeioposis limbatus (Balme) Archangelsky, 1979, 5, Slide S-39A: E.F. L25-4,

10, Slide S-39A: E.F. Q13-4.

7. Cicatricosisporites brevilaesuratus Couper, 1958, Slide S-02A: E.F. Y20.

8. Classopollis torosus (Reissinger) Balme, 1957, Slide S-46A: E.F. Z27.

9. Inaperturopollenites undulatus Weyland & Greifeld sensu Sultan (1987, fig. 3/28),

Slide S-12A: E.F. J22-3.

11. Arucariacites australis Cookson, 1947, Slide S-39A: E.F. Q39-1.

12. Spheripollenites sp., Slide S-05A: E.F. Z39-2.

13. Inaperturopollenites undulates Weyland & Greifeld sensu Sultan (1987, fig. 3/28),

Side S-12A: E.F. N27.

14. Afropollis zonatus Doyle et al., 1982, Slide S-39A: E.F. Z35-2.

15. Afropollis operculatus Doyle et al., 1982, Slide S-39A: E.F. N56-2.

16. Ovoidites parvus (Cookson & Dettmann) Nakoman, 1966, Slide S-45A: E.F. R47.

17. Biserial Microforaminiferal test linings, Slide S-39A: E.F. K25-2.

18, 19. Concavissimisporites punctatus (Delcourt & Sprumont) Brenner, 1963, 18,

Slide S-39B: E.F. X57-3, 19, Slide S-37A: E.F. V60-4.

21. Planispiral Microforaminiferal test linings, Slide S-02A: E.F. N56.

22-24. Ephedripites spp., 25, Slide S-37A: E.F. Z44, 26, Slide S-53B: E.F. X20, 27,

Slide S-33A: E.F. H34-3.

25. Duplexisporites generalis Deak, 1962, Slide S-30B: E.F. G34.

26. Duplexisporites sp., Slide S-35A: E.F. Y11-3.

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VI-50 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

Plate 2

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VI-51

The photomicrographs are published in Mahmoud & Deaf (2007). For full

reference to taxa refer to Mahmoud & Deaf (op. cit.).

Plate 2

(Magnification X500 for 6, 8, 10, 12-19, and the others have magnification X250)

1. Structured phytoclast of probably gymnospermous plant, composed at least of four

gymnosperm tracheids (showing bordered pits in a four serial offset arrangement).

2. Amorphous organic matter (AOM).

3. Cuticular phytoclast showing regular rectangular cell outlines of probably

gymnospermous origin.

4. Membranous phytoclast of uncertain origin because of the lack of diagnostic

structure (membranous phytoclasts are thin, highly translucent, lack of internal

structure, and tend to be relatively large).

5. Black and brown striped tracheidal phytoclat.

6. Coronifera tubulosa Cookson & Eisenack, 1974, Slide S-49B: E.F. J16.

7. Structured tracheidal phytoclast of probably gymnospermous plant (each perforated

bordered pit with a concentric thickened zone)

8. Cyclonephelium cf. vannophorum Davey, 1969, Slide S-04B: E.F. X41-3.

9. Degraded terrestrially derived phytoclast showing destruction, with original outlines

preserved.

10. Oligosphaeridium complex (White) Davey & Williams, 1966, Slide S-40A: E.F.

Z37

11. Structured phytoclast derived from gymnosperm xylem ray tissue, showing a cross

hatching structure, with thickened ribs arranged approximately at right angle to each

other.

12. Odontochitina operculata (O.Wetzel) Deflandre & Cookson, 1955, Slide S-30A:

E.F. O26-3.

13. Circulodinium distinctum Deflandre & Cookson, 1955, Slide S-03A: E.F. Y45.

14. Pseudoceratium eisenackii (Davey) Bint, 1986, Slide S-17A: E.F. S14-1.

15, 17. Subtilisphaera senegalensis Jain & Millepied, 1973, 15, Slide S-39A: E.F. N17-

3, 17, Slide S-52A: E.F.X18.

16, 18. Oligosphaeridium pulcherrimum (Deflandre & Cookson) Davey & Williams,

1966, 16, Slide S-47B: E.F. H12-3, 18, Slide S-20A: E.F. S18-3.

19. Oligosphaeridium complex (White) Davey & Williams, 1966, Slide S-32A: E.F.

B43-4.

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VI-52 Palynofacies Analyses and Palaeoenvironments of Some Lower Cretaceous Rocks...

Plate 3

1 PF-1

PF-2 2

3 PF-3

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Magdy S. Mahmoud, Mohamed A. Masoud, Mohamed A.Tamam, and

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VI-53

The photomicrographs are published in Mahmoud & Deaf (2007). For full

reference to taxa refer to Mahmoud & Deaf (op. cit.).

Plate 3

(Magnification X100)

1. Palynofacies (PF-1) dominated by brown wood and amorphous organic matter.

2. Palynofacies (PF-2) dominated by brown and black wood, with a diverse

assemblage of miospores as indicated by (Murospora florida, Deltoidospora and

Triplanosporites).

3. Palynofacies (PF-3) dominated by black wood and less abundant amorphous organic

matter.

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