Depositional model and sequence stratigraphy of the Paleocene-Lower Eocene succession in the Farafra Oasis, Western Desert, Egypt

Journal Pre-proof Depositional model and sequence stratigraphy of the Paleocene-Lower Eocene succession in the Farafra Oasis, Western Desert, Egypt H.A. Wanas, A.M. Abu Shama, S.A. El-Nahrawy PII:

S1464-343X(19)30361-9

DOI:

https://doi.org/10.1016/j.jafrearsci.2019.103706

Reference:

AES 103706

To appear in:

Journal of African Earth Sciences

Received Date: 7 August 2019 Revised Date:

31 October 2019

Accepted Date: 5 November 2019

Please cite this article as: Wanas, H.A., Abu Shama, A.M., El-Nahrawy, S.A., Depositional model and sequence stratigraphy of the Paleocene-Lower Eocene succession in the Farafra Oasis, Western Desert, Egypt, Journal of African Earth Sciences (2019), doi: https://doi.org/10.1016/ j.jafrearsci.2019.103706. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Depositional model and sequence stratigraphy of the Paleocene-

1

Lower Eocene succession in the Farafra Oasis, Western Desert,

2

Egypt

3 4

Wanas, H. A1,2. ; Abu Shama, A. M.3; El-Nahrawy, S. A.3

5 6

1

Department of Petroleum Geology and Sedimentology, Faculty of

7

Earth Science, King AbdulAziz University, Jeddah, Saudi Arabia, E-

8

mail: [email protected]

9

2

10

Geology Department, Faculty of Sciences, Menoufiya University,

Shebin El-Kom, Egypt, E-mail: [email protected]

11

3

12

Geology Department, Faculty of Sciences, Kafrelsheikh University,

13

Egypt

14 Abstract

15

This work is to reconstruct a depositional model and establish a sequence

16

stratigraphic framework for the exposed Paleocene-Lower Eocene succession

17

in the Farafra Oasis, Western Desert, Egypt. This has been performed by an

18

integration of the microfacies analysis with aid of the nannofossils and P/B

19

foraminiferal ratio in the studied rocks. The identified microfacies and their

20

related palaeoenvironments suggest a deposition in a carbonate shelf (inner,

21

middle and outer shelf) environment. The Paleocene deposits (Dakhla,

22

Tarawan and lower part of Esna formations) were laid down in a mid-to

23

outer-shelf setting, whereas the deposits of Early Eocene age (Farafra

24

Formation and upper part of Esna Formation) were deposited in an inner

25

shelf setting. An integration of the resultant microfacies, nannofossils and

26

P/B foramineferal ratio in the studied four stratigraphic sections led to record

27

five 3rd order depositional sequences (SQs) separated by six sequence

28

boundaries (SBs). Each sequence consists of transgressive (TST) and

29

1

highstand (HST) systems tracts. The TST consists of a retrogradational

30

package of facies (planktonic foraminiferal wackstones /packstones, as well

31

as shales and marls rich in planktonic foraminifera) ended by marine

32

flooding surface (MFS). The HST is made up of aggradational package of

33

facies (nummulitic bioclastic packstone, algal alveoline packstone, alveoline-

34

miliolid packstone and shale with a relatively low P/B foraminiferal ratio)

35

topped by sequence boundary (SB). The sequence boundaries are

36

distinguished by lithologic and paleontologic criteria. The recognized

37

lithologic criteria comprise calcretes, iron-stained surface, extensive

38

bioturbation and erosional irregular surfaces. The paleontologic criteria are

39

evidenced by the time gaps (hiatus). The maximum flooding surfaces (mfs)

40

are recognized where there are a relatively high P/B foraminiferal ratio in the

41

studied facies. The integrated results suggest that sedimentation regime of

42

the studied Paleocene-Lower Eocene rocks was mainly controlled by tectonic

43

activities and subsequent sea-level changes that were a result of a

44

reactivation of the Syrian Arc System during Early Paleogene time.

45 46

1.

Introduction

47

Paleocene-Eocene sequences of the entire world are significant

48

because they contain evidences of Paleocene-Eocene Thermal Maximum,

49

PETM, (Zachos et al., 2001; Singh et al., 2016) that affected on the various

50

biotas (Aubry et al., 1998). Egypt has good outcrops of the Paleocene-

51

Eocene stratigraphic successions, Farafra Oasis, in particular (Said, 1990).

52

This led the authors to carry out detailed study of the Paleocene-Eocene

53

sequences in the Farafra Oasis, Western Desert of Egypt. The Paleocene-

54

2

Eocene outcrops in the Farafra Oasis attracted attention of many authors

55

who studied their general geology and litho- and bio-stratigraphy (e. g.,

56

Hewaidy, and Strougo, 2001; Obaidalla et al., 2006; Farouk, 2016, Abu

57

Shama et al., 2019; Farouk et al., 2019; Sherif et al., 2019). However, a few

58

studies have been done on the detailed analysis of the depositional

59

environments and sequence stratigraphy of the exposed Paleocene-Lower

60

Eocene rocks in the Farafra Oasis (Khalil and El-Younsy, 2003; Hewaidy et

61

al., 2006). Therefore, the main objectives of this study are to reconstruct a

62

depositional model and establish a sequence stratigraphic framework for the

63

Paleocene-Lower Eocene succession exposed at Farafra Oasis on the basis

64

of its microfacies, with the aid of its nannofossils and P/B foraminiferal

65

ratio.

66

2- Geological Setting

67

The Farafra Oasis occurs on the southern Neo-Tethyan shelf (Said,

68

1990). It is an oval-shaped depression in the central part of the Egyptian

69

Western Desert (Fig.1). The Farafra area is situated between longitudes 27°

70

20' and 28° 59' E and latitudes 26° 18' and 27° 42' N (Fig. 1). Studies of the

71

Upper Cretaceous-Eocene strata in the Farafra Oasis indicate that the

72

Farafra Oasis was subjected to three syndepositional tectonic events at

73

various stages before the end of the Cretaceous to the late middle Eocene

74

(Obaidalla et al., 2006). These syndepositional tectonic events were led to

75

the formation of unconformities and responsible for the variations in

76

thicknesses and facies of the Upper Cretaceous-Eocene strata. The Syrian

77

Arc Folding System (NE–SW direction) led to the structural highs and lows

78

in the Farafra Oasis (Omara et al., 1970). The Farafra Oasis represents the

79

3

southernmost extinction of the Syrian Arc System (Omara et al., 1970). The

80

eastern part of the depression is covered by the sand dunes. The western

81

scarp is represented by El Guss Abu Said syncline (Omara et al., 1970).

82

This synclinal structure is located between El Maqfi anticline in the east

83

and Ain Dalla anticline in the west.

84 85

3. Materials and Methods

86

Four well-exposed stratigraphic sections representing the Paleocene-

87

Lower Eocene rock units (Dakhla, Tarawan, Esna and Farafra formations)

88

have been described and measured at four localities ( North Gunna, South

89

Gunna, Ain Ramla-ElQuss Abu Said and Bir Karawin; Fig. 1). The exposed

90

strata are described in terms of their thicknesses, rock types, facies changes,

91

stacking patterns and paleontological criteria. Fifty thin sections of different

92

rock types (carbonates and clastic rocks) are prepared for petrographic

93

investigation under standard polarizing microscope (Olympus model TH4-

94

200) that connected to a digital camera (Olympus UC-30). Representative

95

uncovered thin sections have been stained by Alizarin red and potassium

96

ferro-cyanide to distinguish between non ferroan calcite, ferroan calcite and

97

ferroan dolomite as described by Dickson (1965). The limestone

98

microfacies are named following the classification of Dunham (1962).

99

Dolomite textures are described using the textural classification of Sibley

100

and Gregg (1987). The identified microfacies are compared with the

101

standard microfacies types (SMF) of Wilson (1975) and Flügel (2010). The

102

XRD patterns were identified using scheme of Moore and Reynold (1997).

103

The bulk samples of the clay fractions were examined by PANalytical X-

104

4

ray diffraction equipment (type X-pert pro) with Cu radiation, λ= 1.542 Å

105

at 50 KV 40 MA at the Egyptian mineral resources authority (central

106

laboratories sector). The diffraction charts are compared with ICDD

107

database. The clay fractions (˂ 2µm) were separated out from the sample

108

by centrifugation and were dried on glass slides at air temperature. The

109

glass slides were prepared as air-dried, wetted with ethylene glycol and

110

heated up to 550̊ c for 2 hours.

111 112

4. Litho- and Bio-stratigraphy

113

Lithostratigraphically, the studied Paleocene-Eocene succession comprises

114

four rock units that are from base to top: the Dakhla, Tarawan, Esna and

115

Farafra formations (Figs. 2-5). The Dakhla Formation is Early Paleocene

116

(Danian) in age, and is unconformably overlies the Khoman Formation. It is

117

composed mainly of greyish white, flaky, gypsiferous, nodular calcareous

118

shales that are intercalated with yellow marls and argillaceous limestone.

119

The Dakhla Formation attains its maximum thickness (16 m) at North

120

Gunna section, whereas its minimum thickness (6 m) is recorded at Ain

121

Ramla-ElQuss Abu Said section. The Tarawan Formation is Late Paleocene

122

(Early Thanetian) in age, and it unconformably overlies the Dakhla

123

Formation. It is a cliff-forming, and consists mainly of white massive

124

chalky limestone, graded upward to flaky marly limestone. The maximum

125

thickness of the Tarawan Formation reaches to 8.5 meters at Ain Ramla-

126

ElQuss Abu Said section. The Esna Formation is Late Paleocene-Early

127

Eocene (Late Thanetian- Ypresian) in age, and it unconformably overlies

128

the Tarawan Formation. It is mainly made up of grey, gypsefeous, fissile

129

5

shale that has limestones (dolomites?) at its uppermost part. The limestones

130

(dolomites?) display a concretionally-like beds in parts and in others occurs

131

as thin beds. The Esna Formation varies in thickness from 15.5 m to 40 m

132

(Figs. 2-5). The Farafra Formation is Early Eocene (Ypresian) in age, and it

133

conformably overlies the Esna Formation. It is composed of greyish white,

134

highly fossiliferous, massive limestone. The limestone is nodular in parts

135

and riches in Alveoline sp and Nummulite sp. The Farafra Formation is only

136

recorded at ElQuss Abu Said and Bir Karawin sections (15-20 m thick,

137

respectively), whereas at North Gunna and South Gunna sections, the

138

Farafra Formation is not observed, where there is grey stromatolitic

139

limestone unit (6-8 m thick).This stromatolitic limestone unit directly

140

overlies the Esna Formation (Figs. 2, 3). It is considered as fresh water

141

continental carbonates of post-Eocene age (Strougo, 1996; Wanas and

142

Armenteros, 2019).

143

Biostratigraphically, because of the minor hiatus throughout the

144

stratigraphic successions help in detecting the sequence boundaries (Sarg,

145

1988; Catuneanu, 2006), the authors followed the recently biostratigraphic

146

(nannofossils) study of Abu Shama et al. (2019) who detected minor hiatus

147

in the studied stratigraphic sections (Figs. 2-5). Abu Shama et al. (2019)

148

concluded that the Paleocene-Eocene succession in the Farafra Oasis

149

unconformably overlies the Maastrichtian Khoman Formation, where the

150

latest Maastrichtian Micula prinsii (CC 26b) subzone in the uppermost part

151

of the Khoman Formation is directly overlain by Paleocene calcareous

152

nannofossil Zone NP 4 that is recorded in the base of the Dakhla

153

Formation. They also recorded a minor hiatus at the Danian/Selandian

154

6

boundary, and traced it in the uppermost part of Zone NP 4 (near the top of

155

the Dakhla Formation) at North Gunna and South Gunna sections. Also,

156

they found a pronounced hiatus after the base of Selandian to the base of

157

the Thanetian (lower part of the Tarawam Formation) at North Gunna and

158

South Gunna sections. A hiatus between the Late Paleocene (Thanetian)

159

and the Early Eocene (Ypresian) is observed in the lower part of the Esna

160

Formation at North Gunna section.

161 162

5. Facies Analysis and Depositional Environments

163

Different microfacies of carbonate rocks are identified in the studied Paleocene-Lower

Eocene

succession

(Figs.

2-5).

The

164

recognized

165

microfacies and their related paleoenvironments are outlines and discusses

166

in the following:

167

5.1. Lime mudstone Microfacies

168

Two types of lime mudstone microfacies are recorded; planktonic

169

foraminiferal lime mudstone and dolomitic lime mudstone. The planktonic

170

foraminiferal lime mudstone (PfM) microfacies is recorded in the Tarawan

171

Formation at South Gunna (Fig. 3) and Ain Ramla-El-Quss Abu Said (Fig.

172

4) with 0.5m in thickness. Rocks of this microfacies are greyish white,

173

massive limestones. Microscopically, the planktonic foraminiferal lime

174

mudstone microfacies (Plate 1A) is made up of planktonic foraminiferal

175

tests (5%) embedded in micrite (95%). The foraminiferal tests are filled

176

with pseudosparite and floating in the micritic groundmass. The dolomitic

177

lime mudstone microfacies (DM) occurs at the middle part of the Esna

178

Formation at Ain Ramla-El-Quss Abu Said and Bir Karawin sections (Figs.

179

7

4, 5). Rocks of this microfacies are yellowish white limestones (30 - 50 cm

180

thick), and occur as concretions within the grey shale of the upper part of

181

the Esna Formation. In thin section, the dolomitic lime mudstone

182

microfacies (DM) is subdivided into dolomitic non-fossiliferous lime

183

mudstone and dolomitic fossiliferous lime mudstone. The dolomitic non-

184

fossiliferous lime mudstone microfacies is composed of micrite enclosing

185

fine- to medium-crystalline, euhedral to subhedral scattered ferroan

186

dolomite rhombs (Plate 1B). The dolomitic fossiliferous lime mudstone

187

microfacies occur near the upper part of the Esna Formation at Bir Karawin

188

and Ain Ramla-El-Quss Abu Said sections. Rocks of this microfacies are

189

greyish white, nodular and attaining 0.5m thick. This microfacies is made

190

up of allochems (8%) embedded in micrite matrix. The allochems are

191

mainly represented by Nummulites sp (Plate 1C) and echinoid debris. The

192

micritic groundmass is partially replaced by fine-crystalline dolomite

193

rhombs.

194

Interpretation: Planktonic foraminiferal lime mudstone with low

195

planktonic forams (5%) is interpreted to indicate a deposition in middle,

196

proximal outer, shelf with very low energy conditions below storm wave

197

base (Wilson, 1975). The dominance of micrite groundmass also suggests a

198

low energy environment below storm wave base (Burchette and Wright,

199

1992). The dolomitic lime mudstone microfacies is interpreted to have been

200

deposited in low energy restricted tidal flat environment, inner shelf setting,

201

(equivalent to SMF23 and FZ8 of Wilson, 1975). Also, the occurrence of

202

fine-crystalline dolomite in the lime-mudstone suggests a subjection of the

203

8

lime mud to dolomitization process during an early diagenetic stage in a

204

peritidal environment, inner shelf setting, (Wanas, 2008).

205 206

5.2. Wackstone Microfacies

207

Wackstone microfacies is well distributed in the Dakhla, Tarawan and

208

Farafra formations. It has different types of skeletal components. Three

209

types of wackstones are identified on the basis of their skeletal components:

210

5.2.1. Nummulitic wackstone (NW)

211

The nummulitic wackstone is recognized in the limestone beds of the

212

upper part of the Esna Formation at El-Quss Abu Said section (Fig. 4). This

213

microfacies overlies the nummulitic operculine packstone microfacies and

214

underlies the dolomitized bioclastic nummulitc packstone microfacies.

215

Rocks of this microfacies attain a thickness ranges from 2 m to 2.5 m. They

216

are greyish white to grey in color, hard, fossiliferous and argillaceous in

217

some parts. In thin section, this microfacies consists of framework grains

218

(20%-40%) embedded in micrite groundmass (60%-80%). The framework

219

grains include tests of Nummulite sp. (15%), Operculina sp. (5%), Assilina

220

sp. (5%) and Discocylina sp. (3%) in addition to pelecypod, echinoid and

221

bryozoan shell fragments (5-7%) (Plate 1.D, E, F). The nummulite tests are

222

larger in size (Plate 1D). The bryozoan shells exhibit cellular structure with

223

voids filled with sparry calcite (Plate 1E). The micritic groundmass has

224

scattered fine-crystalline dolomite rhombs.

225

Interpretation: The association of Nummulite sp. with other large benthic

226

foraminfera (Operculina sp., Assilina sp. and Discocylina sp.) can refer to

227

banks or reefal flat environment (Aigner, 1983; Geel, 2000). It also

228

9

indicates a deposition in an inner ramp environment (Beavington-Penney

229

and Racey, 2004; Adabi et al., 2008; Sallam et al., 2015). The occurrence of

230

gypsum veins suggests evaporative phase under an arid climatic condition

231

during their development (Srivastava et al., 2019).

232 233

5.2.2. Planktonic foraminiferal wackstone (PfW)

234

This microfacies is widely recorded in the limestones of the Dakhla and

235

Tarawan formations at North Gunna, South Gunna and Ain Ramla-El-Quss

236

Abu Said sections (Figs. 2, 3, 4). In the Dakhla Formation, rocks of this

237

microfacies occur within the calcareous shales. At the Tarawan Formation,

238

rocks of this microfacies are white, yellowish white, massive and nodular

239

limestone (0.5m to 2m thick.). Petrographically, this microfacies is made up

240

of planktonic foraminifera (35-40%), echinoid and pelecypod shell debris

241

(1-5%) embedded in micrite (60-65%) (Plate 2A). The planktonic forams

242

are filled with sparry calcite.

243

Interpretation: Planktonic foraminiferal wackstone with high planktonic

244

forams (35-40%) indicates an open deep marine environment with low

245

energy conditions (Flügel, 2010). It is also equivalent to SMF3 and FZ3 of

246

the distal outer shelf that took place below storm wave base (Wilson, 1975;

247

Flügel, 2010; Geel, 2000).

248

5.2.3. Bioclastic wackstone (BW)

249

This microfacies is well encountered in the Farafra Formation at Ain

250

Ramla-El-Quss Abu Said and Bir Karawin sections (Figs. 4, 5). Rocks of

251

this microfacies are marly limestone, white to yellowish white in color,

252

massive,

253

hard,

fossiliferous

10

and

argillaceous

in

some

parts.

Microscopically, this microfacies contains recrystallized pelecypod shell

254

fragments (10-20%) floated in 80% micritic groundmass (Plate 2C).

255

Interpretation: The presence of large-sized pelecypod shell fragments

256

indicates an inner shelf environment of well-oxygenated open marine

257

environment (Kulm et al., 1975; Harris et al., 1997). The bioclastic

258

wackstone microfacies are also equivalent to SMF9 and FZ7 of the open

259

lagoons, inner shelf setting, (Wilson, 1975; Flügel, 2010).

260 261

5.3. Packstones Microfacies

262

The packstone is the widely distributed microfacies in the studied

263

formations (Figs. 2-5). It is recorded in the Dakhla, Tarawan and Farafra

264

formations. According to their skeletal components, the packstone

265

microfacies are classified to:

266

5.3.1. Alveoline miliolid packstone (AmP)

267

The alveoline miliolid packstone microfacies occurs in the upper part of

268

the Farafra Formation at El-Quss Abu Said section (Fig. 4). This

269

microfacies overlies the bioclastic wackstone microfacies and underlies the

270

algal alveoline packstone microfacies. Rocks of this microfacies are

271

bedded, hard and yellowish white in colour, attaining about 1m thick. In

272

thin section, this microfacies consists of 20% miliolid tests (Triloculina sp.,

273

Quienqueloculina sp. and Spiroloculina sp.), Alveolina sp. (15%), small

274

uniserial and biserial benthic foraminifera (1-5%), calcareous algae (5%)

275

and few pelecypod shell debris that are embedded in micrite matrix (Plate 2

276

B, D, E).

277

11

Interpretation: The presence of alveoline tests indicates very shallow

278

marine environment in an inner shelf setting (Reichel, 1964). The

279

dominance of miliolids and other small benthic foraminifera may reflect a

280

restricted shallow subtidal quiet water conditions probably lagoon in an

281

inner shelf setting (Hottinger, 1997; Sallam et al., 2015).

282

5.3.2. Algal alveoline packstone (AVP)

283

The algal alveoline packstone is recorded in the upper part of the Farafra

284

Formation at El-Quss Abu Said section (Fig. 4). This microfacies underlies

285

by alveoline miliolid packstone. The rocks of this microfacies are 2 m in

286

thickness, and are yellowish white in color. They are nodular limestone

287

fossiliferous with Lucina sp. Petrographically, it is composed of skeletal

288

carbonates (75%) embedded in micrite matrix (25%). The skeletal

289

carbonates include tests of Alveolina sp. (25%), calcareous algae (25%)

290

(Plate 2E), pelecypod shell fragments (15%) and echinod plates (5%).

291

Miliolid tests and shell fragments of ostracod and gastropod are also

292

observed (5%). The molluscan shell fragments are filled with large crystals

293

of sparry calcite. The echinoderm plates are surrounded by very thin layer

294

of syntaxial calcite overgrowth.

295

Interpretation: The occurrence of large benthic foraminifera (Alveolina

296

sp.) with calcareous algae indicates an intertidal distal back shoal (lagoon

297

with open circulation) at shallow inner shelf setting (Flügel, 2010). This

298

type of facies was interpreted to reflect a deposition in open lagoons that

299

refer to SMF18, FZ7 of Wilson (1975). The algal alveoline packstone

300

microfacies can be considered to reflect a deposition in an inner ramp

301

setting (Khalil and El-Younsy, 2003; Sallam et al., 2015).

302

12

5.3.3. Planktonic foraminiferal packstone (PfP)

303

Planktonic foraminiferal packstone microfacies is recorded in the middle

304

and upper parts of the Tarawan Formation and in the middle part of the

305

Dakhla Formation at North Gunna and south Gunna sections (Figs. 2, 3).

306

Rocks of this microfacies are massive chalky limestone and nodular

307

argillaceous limestone of yellowish brown to white in color. Their thickness

308

ranges from 2.5 m to 3.5 m. It is overlain and underlain by planktonic

309

foraminiferal wackstone microfacies. Petrographically, this microfacies is

310

made up of planktonic foraminiferal tests (75-90%) embedded in micrite

311

(10-25%). The dominant planktonic species are Globigerina, Morzovella,

312

Acarinina and Globigerinoids tests (55-60%) with chambers filled with

313

non-ferroan sparry calcite except at the upper parts of the Tarawan

314

Formation, it is ferroan type (Plate 2F). Calcareous warm tubes and

315

echinoderm spines (2-5%) are also recorded.

316

Interpretation: This type of microfacies reflects a deposition in an outer

317

shelf with low energy conditions below normal wave base (Wilson, 1975;

318

Harris et al., 1997). It also reflects a deposition in open circulated, high

319

oxygenated marine waters (Wilson, 1975; Flügel, 2010).

320

5.3.4. Nummilitic operculine packstone (NOP)

321

The nummulitic operculine packstone microfacies occur in the upper part

322

of the Esna Formation and the lower part of the Farafra Formation at El-

323

Quss Abu Said section (Fig. 4). It is overlain by nummulitic wackstone

324

microfacies and underlain by shale lithofacies (Fig. 4). Rocks of this

325

microfacies are yellowish white in color, and attain 1m thick. They are

326

argillaceous

327

and

intercalated

13

with

thin

layers

of

grey

shale.

Petrographically, the main skeletal components are tests of Operculina sp.

328

(30%), small- sized Nummulite sp. (10-15%), Discocylina and Assilina

329

species (5%) (Plate 3.A, B). It also contains pelecypod, bryozoan and

330

echinod shell fragments (10%). These allochems are embedded in 30%

331

micrite matrix containing microsparry calcite patches and scattered

332

dolomite rhombs.

333

Interpretation: The occurrence of Nummulite sp. indicates warm shallow

334

water or shallow neritic zone (Arni, 1965; Blondeau, 1972). The association

335

of Nummulite sp., Operculina sp. and Discocylina sp. indicates a bank

336

setting (Arni, 1965; Arni and Lanterno, 1972; Khalifa and Zaghloul, 1990).

337

This microfacies can be compared with SMF4 and FZ4 of Wilson (1975)

338

and Flügel (2010) which refers to a deposition in a fore slope area. It also

339

reflects a deposition in an inner ramp setting (Sallam et al., 2015).

340

5.3.5. Dolomitized nummulitic bioclastic packstone (DNP)

341

This microfacies occurs in the uppermost part of the Esna Formation at

342

El-Quss Abu Said (Fig. 4). The rocks of this microfacies occur as interbeds

343

within shale and mudrocks lithofacies. Petrographically, this microfacies

344

(Plate 3.C) contains nummulite tests (10-20%) and shell fragments of

345

pelecypod (15%), echinod (5-10%), gastropod (5-10 %), ostracod (1-2%)

346

and bryozoan (1-2%). Its matrix is micrite containing fine-crystalline

347

dolomite rhombs.

348

Interpretation: The presence of large nummilite tests with pelecypod and

349

echinoid shell fragments represents a back bank facies on an inner shelf

350

setting (Pomar, 2001; C´osovic´ et al., 2004). This type of facies is similar

351

to SMF10 and FZ7 of Wilson (1975) and Flügel (2010). The association of

352

14

nummulite debris with micritic matrix indicates extensive transportation

353

and reworking from high to low energy conditions (Dunham, 1962).

354 355

5.4. Dolomicrite (D)

356

The dolomicrite microfacies is recorded in the upper part of the Esna

357

Formation at El-Quss Abu Said and Bir Karawin sections (Figs. 4, 5). It

358

occurs as thin interbeds within shale/mudrocks lithofacies. The rocks of this

359

microfacies are yellow to yellowish white in color and attain thickness

360

ranges from 30 cm to 1m. In some parts, the rocks of this microfacies occur

361

as concretions. Microscopically, this microfacies consists of fine-crystalline

362

unzoned dolomite rhombs with anhedral, xenotopic, non-planar habit (Plate

363

3D).

364

Interpretation: Dolomicrite reflects dolomitization in an early diagenetic

365

stage in a peritidal environment of an inner shelf setting (Tucker and

366

Wright, 1990; Wanas, 2008).

367 368

5.5. Calcareous Quartz Arenite

369

This microfacies is recorded in the caliche bed (1m thick) that lies at the

370

contact between the Esna Formation and the overlying stromatolitic

371

limestone unit in the North and South Gunna sections (Figs. 2, 3). Rocks of

372

this microfacies are white in color. Petrographically, this microfacies

373

consists of monocrystalline quartz grains floating in poiklotopic calcite

374

cement (Plate 3E). The margins of quartz grains are corroded and partially

375

replaced by calcite cement. This can be described as corona texture (Plate

376

3E).

377

15

Interpretation: Quartz grains with corona texture and sparry calcite cement

378

in this calcareous quartz arenite are similar to non-pedoegenic calcretes that

379

form during a deposition of continental carbonates (Alonso-Zarza, 2003;

380

Wanas and Soliman, 2014).

381 382

5.6. Recrystallized Limestone

383

This mirofacies forms the stromatolitic limestone unit that overlies the

384

Esna Formation at North and South Gunna sections (Figs. 2, 3). The rocks

385

of this microfacies range in thickness from 4m to 8m at South Gunna and

386

North Gunna respectively. They show regular banding of light and dark

387

colors (stromatolitic-like structure). Microscopically, this microfacies is

388

composed of radiaxial fibrous calcite with dark micrite substrate (Plate 3F).

389

Silicification in some parts was observed.

390

Interpretation: This type of microfacies is similar to FZ10 of Wilson

391

(1975) and microfacies of Wanas and Armenteros (2019) that indicate

392

meteorically-induced continental carbonates. The regular light and dark

393

lamina may reflect repeated variations in aqueous geochemical conditions

394

within the depositional system (Scholle and Ulmer-Scholle, 2003).

395 396

5.7. Shale/Mudrocks Lithofacies

397

Because of their difficulty to study under the polarized microscope, the

398

encountered shales/mudrocks are investigated by using X-ray diffraction

399

analysis (XRD).

Smectite and kaolinite are the most abundant clay

400

minerals detected in the studied shale and mudrock samples (Table 1, Fig.

401

6). Also, the distribution of P/B foraminiferal ratio in shale/mudrock

402

16

lithofacies (Figs. 2, 3, 4, 5), showed that most of shale have a relatively

403

high (≥ 40%) to medorate (20-35%) P/B forminiferal ratio, whereas a few

404

of them have a relatively low (5%) P/B foraminiferal ratio.

405

Interpretation: Changes of clay minerals are mainly in a response with

406

climatic changes (Singer, 1984). The kaolinite could be a result of a

407

chemical weathering of feldspars in a more humid period and acidic water

408

(Singer, 1984). The smectite is the weathering products of mafic silicates in

409

an arid to semi-arid climate and alkaline water (Singer, 1984). Therefore,

410

changes in climatic conditions from humid to arid may reflect sea-level

411

fluctuations, from sea-level rise to sea-level fall, respectively. This is in an

412

agreement with the opinion of Millot (1970). The shale with high P/B

413

foraminiferal ratio (≥40%) indicates a deposition in a deep marine water (a

414

distal outer shelf environment), whereas shale with a relatively moderate

415

P/B foraminiferal ratio (20-35%) suggests a deposition in a relatively

416

shallower marine water (a middle, proximal outer, shelf environment) (Van

417

Der Zwaan et al., 1990). On the other hand, the shale with a relatively low

418

P/B foraminiferal ratio (1-5%) can reflect relatively very shallower marine

419

water- deposits in an inner shelf setting (Van Der Zwaan et al., 1990).

420 421

6. Depositional Model

422

The above interpreted microfacies (section 5) allow us to recognize an

423

occurrence of three main facies associations that are assignable to shelf

424

environments (inner, middle and upper shelf; Fig. 7). The inner shelf facies

425

association includes dolomicrite (tidal flat), alveoline miliolid packstone

426

(inner lagoon), algal alveoline packstone/bioclastic wackstone (outer

427

17

lagoon),

dolomitized

nummulitic

bioclastic

packstone

(back-reef),

428

nummulitic wackstone (reef patches), nummulitic operculine packstone

429

(fore reef) and shales with a relatively low P/B forminiferal ratio. The

430

middle, proximal outer, shelf facies association is represented by shales

431

with a relatively moderate P/B foraminiferal ratio. Outer shelf facies

432

association comprises the planktonic foraminifera-rich shales, packstone,

433

wackstone and lime mudstone.

434

In the studied rock units, the basal parts of Dakhla, Tarawan and Esna

435

formations are mainly dominated by foraminiferal-rich lime mudstone,

436

wackstone and shale with high P/B ratio. These criteria may point out a

437

deep subtidal shelf (outer shelf). On the other hand, the upper parts of the

438

Dakhla and Tarawan formations are dominated by shales, marls and

439

limestones that have a relatively moderate P/B ratio that indicates a

440

deposition in middle, proximal outer, shelf environment. This middle shelf

441

environment is also recoded in the middle part of the Esna Formation that

442

consists of marl and calcareous shale with moderate P/B foraminiferal ratio

443

(~ 30%). The characterization of the upper part of the Esna Formation by

444

shale with a relatively low P/B foraminiferal ratio (5-10%) %) and pertidal

445

dolomicrite interbeds suggests a deposition in a shallow shelf (an inner

446

shelf). The Farfara Formation is generally represented by packstones enrich

447

with tests of alveolines, nummulites, miliolids and algae and echinoderm

448

fragments. These packstone types reflect a deposition in warm shallow

449

marine environments (lagoon, back reef, fore reef, bank) that characterize

450

to the inner shelf setting. In conclusions, the studied deposits of the

451

Paleocene age (Dakhla, Tarawan and lower part of Esna formations) were

452

18

laid down in a mid-to outer-shelf setting, whereas the deposits of Early

453

Eocene age (Farafra and upper part of Esna formations) were deposited in

454

an inner shelf setting. This could be in an agreement with those deduced by

455

the previously benthonic-planktonic foraminiferal studies in the Paleocene-

456

Lower Eocene successions of Egypt (Farouk, 2016 and references therein).

457

7. Depositional Sequences and Sequence Boundaries

458

According to the principles of sequence stratigraphy of siliciclastic

459

(Catuneanu, 2006) and carbonate (Sarg, 1988) rocks, the vertical and lateral

460

facies of the studied formations allow us to recognize five 3rd order

461

depositional sequences (SQ 1, SQ 2, SQ 3, SQ 4 and SQ 5) which exhibit

462

transgressive and regressive packages of facies (systems tracts). These

463

sequences are bounded by six sequence boundaries (SB 1, SB 2, SB 3, SB

464

4, SB 5 and SB 6). In the present study, the age constrains of the identified

465

sequences depends on their fossil contents and previously published

466

paleontological studies. In the studied successions, the lowstand systems

467

tracts are absent. The sequence boundaries are delineated by lithologic

468

criteria with the aid of the paleontological (nannofossils) ones of Abu

469

Shama et al. (2019). The maximum flooding surfaces (mfs) were recorded

470

where there are high planktonic foraminifera in the identified facies. The

471

identified sequences and their boundaries will be described and discussed in

472

the following paragraphs:

473

7.1. Sequence Boundaries

474

7.1.1. The first sequence boundary (SB 1)

475

This boundary is delineated at the base of the Paleocene succession. The

476

SB 1 is only traced at North Gunna section (Fig. 2). This surface separates

477

19

the uppermost part of the Khoman Formation (Maastrichtian) from the

478

lowermost part of the Paleocene Dakhla Formation. Lithologically, it is

479

marked by abrupt facies changes from chalk of the Khoman Formation to

480

the calcareous shale of the Dakhla Formation. Also, the SB 1 is also

481

indicated by the occurrence of irregular iron-stained surface and gypsum

482

layer (30cm thick) (Plate 4A) at the uppermost part of the Khoman

483

Formation. Paleontologically, this boundary (SB1) is recognized by missing

484

of NP 1, NP 2 and NP 3 calcareous nannofossil zones of Early Paleocene

485

whereas NP 4 Zone of the Late Danian is overlying the Late Cretaceous CC

486

26b subzone (Fig. 2). The recognized SB 1 could be equivalent to the K/Pg

487

boundary in Egypt (El-Azabi and Farouk, 2011; Farouk, 2016), and that

488

was recorded in other countries of the Middle East (Farouk et al., 2014;

489

Alhejoj et al., 2020). Globally, this sequence boundary (SB1) may be

490

equivalent to the global sea level fall recorded between the Late

491

Maastrichtian and Early Paleocene time (Haq et al., 1988; Hardenbol et al.,

492

1998). This SB1 could be related to the syn-sedimentary tectonic event of

493

the Syrian Arc System that started at Santonian time and continued to the

494

Miocene (Moustafa et al., 2003).

495

7.1.2. The second sequence boundary (SB 2)

496

The second sequence boundary lies in the uppermost part of the Dakhla

497

Formation, and directly at the base of the Tarawan Formation. SB 2 is

498

recorded at North Gunna (Fig. 2), South Gunna (Fig. 3) and its correlative

499

conformity at Ain Ramla-El-Quss Abu Said section (Fig. 4). The lithologic

500

evidences for this sequence boundary (SB2) are irregular surface and iron

501

oxide layer (3cm thick) separating the Danian/Selandian strata (Plate 4B).

502

20

This layer is similar to the organic rich pinkish layer which is recorded by

503

Sprong et al. (2009) and Soliman and Obaidalla (2010) at the

504

Danian/Selandian boundary at Gebel Qreiya section, Nile Valley, Egypt.

505

Also, this boundary (SB2) is also noticed by the occurrence of thin layer of

506

brown-colored chert pebbles at the base of the Tarwan limestone in North

507

Gunna section. By using the zonation of calcareous nannofossil, the SB 2 is

508

recorded where there is a missing of the last part of Danian (hiatus) (Fig. 2,

509

3, 4, 5). This hiatus coincides with hiatus recorded in the Danian/Selandian

510

successions in the entire Western Desert of Egypt by biostratigraphers

511

(Farouk, 2016 and references therein). This hiatus could be in response with

512

the weak tectonic event that was related to deformation of the Syrian Arc

513

System in the Western Desert (Moustafa et al., 2003). Also, this hiatus is in

514

consistence with the global drop in relative sea-level during the Late

515

Danian (Haq et al., 1988).

516

7.1.3. The third sequence boundary (SB 3)

517

This sequence boundary (SB 3) occurs in the lowermost part Tarawan

518

Formation between the Selandian/Thanetian strata at North Gunna and

519

south Gunna (Figs. 2, 3). Lithologically, this boundary is evidenced by the

520

occurrence of extensive bioturbation forming Thalassinoides (Plate 4C).

521

According to calcareous nannofossil zonation, this boundary is marked by

522

missing part of Thanetian (NP 6 Zone) at South Gunna section as NP 5 is

523

overlain by NP 7/8. At North Gunna section, SB 3 is marked where there is

524

a missing of the latest part of Selandian and the lowest part of Thanetian

525

due to missing of NP 5 and NP 6 zones. The correlative conformity of the

526

studied SB 3 seems to be developed locally in Ain Ramla-El-Quss Abu

527

21

Said section as the NP 6 Zone is recorded and underlying by NP 5 Zone.

528

The correlative conformity of SB 3 at Ain Ramla-El-Quss Abu Said section

529

indicates submergence of this locality relative to the other localities (North

530

and South Gunna sections) that were in an emergence. This emergence may

531

be due to tectonic uplift and subsequent sea level falling. This boundary is

532

similar to that recorded by many authors in the Western Desert of Egypt

533

(e.g. El-Azabi and El-Arabi, 2000; El-Azabi and Farouk, 2011; Hewaidy et

534

al., 2006; Farouk, 2016). This boundary may confirm tectonic velasconsis

535

event of Strougo (1996).

536

7.1.4. The fourth sequence boundary (SB 4)

537

This boundary occurs at the base of Eocene succession at North Gunna

538

section (Fig. 2). It occurred within the Esna Formation and separates the

539

latest Thanetian part from the base of Ypresian. Lithologically, the SB 4 is

540

recognized by the occurrence of a gypsiferous shale layer (Plate 4D).

541

Paleontologically, this sequence bounadry is indicated by missing NP 9b

542

calcareous nannofossil subzone of Early Eocene. This boundary can be

543

correlated with that recorded in the Esna Formation by Dupuis et al. (2003),

544

Hewaidy et al. (2006), Obaidalla et al. (2008), El-Azabi and Farouk (2011)

545

and King (2013) at Dababiya Quarry Member, Farafra Oasis, Naqb Assuit

546

and Kharga Oasis, respectively. El-Azabi and Farouk (2011) mark this

547

boundary by reworked pebbles, red coloration and irregular surface.

548

Obaidalla et al. (2008) mark this boundary by an irregular surface, pebbles

549

and bioturbated sands, which indicate the occurrence of short hiatus.

550

Dupuis et al. (2003) and King (2013) distinguished this boundary by an

551

incised erosional surface which indicate eustatic sea level fall in the

552

22

Dababiya Quarry Member. Globally, this boundary may coincide with the

553

Paleocene/Eocene transition that known as the Paleocene/Eocene Thermal

554

Maximum.

555

7.1.5. The fifth sequence boundary (SB 5)

556

This sequence boundary is only recognized within the Esna Formation at

557

El-Quss Abu Said (Fig. 4) and Bir Karawin (Fig. 5) sections. SB 5 is

558

delineated at the basal part of the Early Ypresian. Lithologically, SB5 is

559

recorded within the upper part of the Esna Formation by the presence of

560

dolomicrite that can be represented discontinuity surface if there is lack in

561

subaerial exposure (Wanas, 2008). A similar sequence boundary was

562

described by Hewaidy et al. (2006) within the Esna Formation at the

563

northern slope of El-Quss Abu Said section.

564

7.1.6. The sixth sequence boundary (SB 6)

565

This boundary is recognized at the uppermost part of the Esna Formation

566

at North Gunna and South Gunna sections. Lithologically, this sequence

567

boundary is easily recognized by a caliche bed (Plate 4E) (1m to 10cm

568

thick) with red coloration at the uppermost part of the Esna Formation.

569

Also, this boundary is delineated by the abrupt facies change from the Esna

570

Shale below and the stromatolitic limestone above. Moreover, this

571

boundary is traced through the undulatory irregular erosional surface

572

separating the Esna Formation from stromatolitic limestone unit (Plate 4F).

573

The correlative conformity of this boundary occurs at Ain Ramla-El-Quss

574

Abu Said and Bir Karawin sections (Figs. 4, 5). This correlative conformity

575

lies between the Esna Formation and the Farafra Formation.

576 577

23

7.2. Depositional Sequences

578

The vertical and lateral facies change of the studied formations and their

579

time duration reflects the recognition of five 3rd order depositional

580

sequences that are subdivided into system tracts as the following:

581 582

7.2.1. The first depositional sequence (SQ 1)

583

The first depositional sequence (SQ1) in the studied stratigraphic

584

successions comprises the Late Danian part of the Dakhla Formation where

585

the Ellipsolithus macellus (NP 4) Zone occurs. SQ1 is marked at its base by

586

Cretaceous/Paleogene boundary which corresponds with the missing of the

587

Early Danian sequence (NP 1, NP 2 and NP 3 zones). The first depositional

588

sequence (SQ 1) is ended by SB2 that is marked by iron oxide layer (3 cm

589

thick) in the upper part of the Dakhla Formation. SQ1 has a thickness

590

approximately 15m at both North Gunna and South Gunna sections (Figs.

591

2, 3). The duration of SQ 1 was between 62.2 and 59.9m.y.

592

Generally, this sequence begins with retrogradational package of facies

593

(TST) that comprises outer shelf shales, marls and wackestones rich in

594

planktonic foraminifera. This passes upward to aggraditional facies (HST)

595

that are represented by mid-to inner-shelf shales with relatively moderate to

596

low planktonic forams (Figs. 2, 3). TST is marked at its base by SB1 which

597

also considered as transgressive surface (TS). It is topped by maximum

598

flooding surface (MFS) (Figs. 2, 3). The MFS is recorded in the middle part

599

of Dakhla Formation at North Gunna and South Gunna sections (Figs. 2, 3).

600

The MFS is placed at 8m from the base of the Dakhla Formation. It is

601

marked where there is a very high percentage of planktonic foraminifera.

602

24

7.3.2. The second depositional sequence (SQ 2)

603

The second depositional sequence (SQ2) in the studied sections comprises

604

the uppermost part of the Dakhla Formation and the lowermost part of the

605

Tarawan Formation (Figs. 2, 3, 4). SQ 2 is recorded at North Gunna, South

606

Gunna and Ain Ramla-El-Quss Abu Said sections. It includes the Selandian

607

NP 5 Zone. The duration of this sequence reaches about 1.5-2 my. At North

608

Gunna section, the SQ 2 is bounded by SB 2 and SB 3. At this locality, it

609

has 2.5m thick and is composed of aggradational package of facies (HST)

610

that include mid-shelf bioclastic foramineferal wackestones. At South

611

Gunna and Ain Ramla-El-Quss Abu Said sections, this depositional

612

sequence (SQ 2) is bounded by SB 2 and SB 3. It reaches about 12m in

613

thickness and starts with a retrogradational package of facies (TST) that are

614

represented by outer shelf planktonic foraminiferal packstone. This TST

615

grades upward to aggradational to prograditional package of facies (HST)

616

that consists mainly of middle shelf bioclastic foraminiferal wackstone and

617

mudstone.

618

7.3.3. The third depositional sequence (SQ 3)

619

This depositional sequence covers the Thanetian deposits that comprise the

620

upper part of the Tarawan Formation and the lower part of the Esna

621

Formation at North Gunna section (Fig. 2). It contains Heliolithus kleinpelii

622

(NP 6), Discoaster mohleri (NP 7/8) and Discoaster multiradiatus (NP 9a)

623

zones. The duration of this sequence ranges from 3.7 to 2.5 my. This SQ 3

624

is defined at its base by SB 3 which described in the previous sequence and

625

ended by subaerial exposure and regional unconformity which corresponds

626

with Paleocene-Eocene boundary that is also considered as a transgressive

627

25

surface (TS). At North Gunna (Fig. 2), the top of this sequence is

628

gypsiferous and characterizes by the missing of the latest Eocene NP 9b

629

subzone. The stacking pattern of SQ 3 starts with retrogradational facies

630

(TST, 2m to 6m thick) of middle shelf foraminiferal packstones to deep

631

outer shelf foraminiferal wackstones. The uppermost of this TST is

632

characterized by well-preserved planktonic foraminifera with high

633

abundance of P/B foraminiferal ratio (80-90%) that refers to the maximum

634

flooding surface (MFS). This TST graded upward to HST that consists of

635

moderate planktonic- shale of mid-shelf deposition. This shale forms the

636

lower part of the Esna Formation. A similar progradational facies (HST) are

637

recorded at latest Thanetian time in Garra Formation at Gabal Um El-

638

Ghanayim and Naqb Assuit with 10-20 m thick (El-Azabi and Farouk,

639

2011). At South Gunna and Ain Ramla-El-Quss Abu Said sections (Figs. 3,

640

4), the depositional sequence (SQ 3) is bounded by SB 2 and SB 3. Its

641

thickness ranges from 3 m to 15 m at Ain Ramla-El-Quss Abu Said section

642

and South Gunna section, respectively (Figs. 3, 4). At these localities, the

643

SQ 3 consists only of a retrogradational package of facies (TST) that is

644

represented by outer shelf planktonic foraminiferal wackestone/packstone.

645

7.3.4. The fourth depositional sequence (SQ 4)

646

This sequence (SQ4) is recorded in the Early Ypresian (middle and upper

647

parts of the Esna Formation) at all the studied sections (Figs. 2, 3, 4, 5), and

648

attains a thickness ranges from15 to 35 m. It contains the Early Ypresian

649

NP 10a subzone. At North Gunna section, the gap between Paleocene and

650

Eocene is estimated of about 0.5my. At this section, SQ4 is marked at its

651

base by ferruginous and gypsiferous contact which marks the Paleocene-

652

26

Eocene boundary. In the other sections the basal contact of this sequence is

653

not recognized because they are composite. At the Paleocene-Eocene

654

boundary, an abrupt disappearance of planktonic foraminifera is recorded

655

(Fig. 2). At Ain Ramla-El-Quss Abu Said and Bir Karawin, the top of SQ 4

656

is characterized by dolomitized nodular marl (dolomicrite) that represents

657

the SB 5. While at the North Gunna and South Gunna sections, the SQ 4

658

ended by undulatory surface and caliche layer (SB 6) separating it from the

659

overlying post-Eocene stromatolitic limestone unit (SB 6). At all the

660

studied sections, the SQ 4 is made up of alternating retrogradational facies

661

(TST) and aggredational facies (HST) that may be a fluctuation of sea-level

662

during Early Ypresian in the areas of study. The TST is composed of

663

middle, proximal outer shelf pelagic shales and wackstone with moderate

664

planktonic foraminifera. The HST is characterized by inner-shelf shales

665

with low planktonic foraminifera and lower intertidal dolomitic lime

666

mudstone of shallow inner shelf deposits. This indicates relative shallowing

667

in the sea-level.

668

7.3.5. The fifth depositional sequence (SQ 5)

669

This depositional sequence occupies the uppermost part of the Esna

670

Formation and the Farafra Formation. It is only recorded at Bir Karawin

671

and El-Quss Abu Said sections. SQ 5 has a thickness ranging from 13 m to

672

40 m at Bir Karawin and Ain Ramla-El-Quss Abu Said, respectively. This

673

sequence (SQ 5) comprises TST and HST. The TST consists of low

674

planktonic-shale,

and

675

bioclastic wackstone that characterize the mid- to deep inner- shelf

676

environments. The HST is characterized by shallow inner shelf facies

677

alveoline

wackstone,

27

nummulitic

wackstone

(nummulitic bioclastic packstone, algal alveoline packstone and alveoline-

678

miliolid packstone) enriched by large benthonic foraminifera and barren in

679

planktonic foraminifera (Figs. 4, 5).

680 681

8. Sedimentation Regime and Tectonic/Sea level Characterization

682

Integrated study of field observation, facies analysis, sequence stratigraphy

683

and biostratigraphic (nannofossils) permitted us to recognize an occurrence

684

of tectonic pulses and subsequent sea level changes during deposition of the

685

studied Paleocene-Lower Eocene rocks. These tectonic pulses are

686

distinguished by: 1) the presence of hiatuses (as recorded by nannofossils

687

distribution) within the studied successions (Figs. 2, 3, 4 ); 2) thickness and

688

facies variations of the studied rock units from one locality to others in the

689

study area (Figs. 2, 3, 4, 5); 3) unconformity surfaces at the contacts

690

between the studied rock units (Figs. 2, 3, 4); 4) changes of the depositional

691

setting from one rock unit to another superimposed unit, such as a transition

692

from outer shelf Dakhla, Tarwan and Esna formations to inner shelf (shoal-

693

lagoonal- peritidal) Esna and Farafra formations through mid-shelf Esna

694

Formation (Fig. 7); 5) absence of the Farafra Formation in North and South

695

Gunna successions, where the Upper Paleocene-Lower Eocene Esna

696

Formation is directly overlain by Post-Eocene continental carbonates (Figs.

697

2, 3), and 6) Recording the Selandian/Thanetian hiatus in the North Gunna

698

and south Gunna successions, and its absence in the Ain Ramla-El-Quss

699

Abu Said succession. This may indicate a low land at Ain Ramla-El-Quss

700

Abu Said locality relative to the other localities (North and South Gunna)

701

28

where high lands were prevailed. This may be due to tectonic uplift and

702

subsequent sea level falling.

703

The above distinguished criteria of tectonic pulses can be related to a

704

reactivation of the Syrian Arc System (SAS) during the Early Paleogene in

705

Egypt (Moustafa et al., 2003; Scheibner et al., 2003; El-Ayyat and

706

Obaidalla, 2016; Farouk, 2016). This SAS was a result of the convergence

707

between the Afro-Arabian and Eurasian Plates that started at Santonian

708

time and continued to the Miocene (Said, 1990; Moustafa et al., 2003).

709

Consequently, the authors can suggest that sedimentation of the studied

710

rocks was mainly controlled by tectonic activities that were formulated the

711

basins of deposition and subsequent sea-level changes. In terms of sea-level

712

changes, relative sea-level curve of the studied area (Figs. 2, 3, 4, 5) is in

713

correspondence to the Paleocene-Early Eocene global sea-level curve of

714

Haq et al. (1988) and relative sea-level changes at the nearby areas of the

715

Western Desert of Egypt (Jain and Farouk, 2017; Farouk et al., 2019).

716 717

9. Conclusions

718

A detail facies analysis with the aid of P/B foraminiferal ratio and

719

Nannofossils of the Paleocene-Lower Eocene succession in the Farafra

720

Oasis, Western Desert, Egypt led to the recognition of different microfacies

721

and five 3rd order depositional sequences. The identified microfacies

722

indicate a deposition in inner, middle and upper shelf environments. The

723

inner shelf environment is represented by lagoonal (Alveoline-miliolid

724

packstone, algal alveoline packstone and nummulitic bioclast packstone),

725

tidal flat (dolomicrite) and patch reef facies (nummulitic wackstone). These

726

29

inner shelf facies are dominated in the Farafra Formation and the upper part

727

of Esna Formation. The middle shelf environment comprises the calcareous

728

shales, and planktonic foraminiferal wackstone/packstone with a relatively

729

moderate P/B ratio. These middle shelf facies are recorded in the middle

730

part of the Dakhla, Tarawan and Esna formations. The outer shelf

731

environment was recognized where there are planktonic foraminiferal–rich

732

shales, marls, lime mudstone, wackestone and packestone. These outer

733

shelf facies are mainly recorded in the basal parts of Dakhla, Tarawan and

734

Esna formations.

735

The recorded five depositional sequences (SQ1, SQ2, SQ3, SQ4 and SQ5)

736

are made up of transgressive (TST) and highstand (HST) systems tracts.

737

These sequences are bounded by six sequence boundaries (SB 1, SB 2, SB

738

3, SB 4, SB 5 and SB 6). These sequence boundaries are recognized by

739

lithologic and paleontologic criteria. The lithologic criteria include criteria

740

as calcretes, iron stained surface, bioturbation and erosional irregular

741

surfaces. The paleontologic evidences were detected where there are time

742

gaps (hiatus) as detected by nannofossils. The transgressive systems tract

743

(TST) comprises the retrogradational package of facies that indicate sea

744

level rise. This retrogradational facies are mainly represented by outer shelf

745

facies such as planktonic foraminiferal-rich packstone, mudstone and

746

wackstone, shales and marls. The highstand systems tract consists of

747

aggraditional to prograditional package of facies that reflect relative sea-

748

level fall. This aggraditional to prograditional facies includes inner shelf

749

facies such as alveoline miliolid packstone, algal alveoline packstone and

750

molluscan wackstone, dolomitized nummulitic bioclastic packstone,

751

30

nummulitic wackstone and nummulitic operculine packstone microfacies,

752

as well as shales with low P/B ratio.

753

Integrated results of field observation, facies analysis, sequence stratigraphy

and

biostratigraphy

(nannofossils)

indicate

that

754

the

755

sedimentation regime of the studied rocks was mainly controlled by

756

tectonic activities and subsequent sea-level changes.

757 758 759 760

Acknowledgements

761

We thank the anonymous reviewers for their constructive comments and

762

suggestions. Special thanks extend to editor of JAES for his help in editorial

763

support.

764 765

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766

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965

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966

693.

967 968

38

Figures Caption

969

Fig. 1: Geological and location map of the Farafra area, Western

970

Desert (after Hermina, 1990 and Abu Shama et al., 2019).

971

Fig. 2: Lithological characteristics, microfacies types, depositional

972

environments, planktonic percentage ratio, sequence stratigraphic elements

973

and relative sea-level change of the Paleocene-Lower Eocene succession in

974

North Gunna.

975

Fig. 3: Lithological characteristics, microfacies types, depositional

976

environments, planktonic percentage ratio, sequence stratigraphic elements

977

and relative sea-level change of the Paleocene-Lower Eocene succession in

978

South Gunna.

979

Fig. 4: Lithological characteristics, microfacies types, depositional

980

environments, planktonic percentage ratio, sequence stratigraphic elements

981

and relative sea-level change of the Paleocene-Lower Eocene succession in

982

Ain Ramla-El-Quss Abu Said.

983

Fig. 5: Lithological characteristics, microfacies types, depositional

984

environments, planktonic percentage ratio, sequence stratigraphic elements

985

and relative sea-level change of the Lower Eocene succession in Bir

986

Karawin.

987

Fig. 6: X-ray diffraction pattern of clay fractions of representative shale sample (K-18) in the Esna Formation at Bir Karawin. Table 1:

X-ray diffraction data for oriented clay fractions of shale

samples in the Esna Formation at the studied localities.

988 989 990 991 992

Plate 1. Photomicrographs showing:

39

993

A- Planktonic

foraminiferal

lime

mudstone.

Sample

33,

South

Gunna. Stained, Plane Polarized Light (PPL).

995

B- Dolomitic lime mudstone. Note the ferroan dolomite rhombs within

the

micrite

997

neomorphosed to microsparite. Sample Q 16, Esna Formation, Ain

998

Ramla-El-Quss

999

Said

(arrow).

section.

The

Stained,

micrite

crossed

was

996

partially

Abu

matrix

994

nicoel

(CN

view).

1000

C- Dolomitic fossiliferous lime mudstone. Nummulites sp. (arrow)

1001

is embedded in micrite with fine scattered dolomite rhombs. Sample

1002

K 10, Esna Formation, Bir Karawin section. Stained, (CN view).

1003

D- E, F- Nummulitic wackstone. Nummulites tests (NM) are the

1004

dominant allochems. Note that the microfacies contains Assilina sp.

1005

(AS), bryozoa (BY) and echinoderm spines and plates (EC). D-

1006

Sample Q 60, E, F- Sample no. Q 63, the upper part of the Esna

1007

Formation, Ain Ramla-El-Quss Abu Said section. D- Unstained,

1008

plane polarized light (PPL). E, F- Stained, (CN view).

1009 1010 1011 1012 1013

Plate 2. photomicrographs showing:

1014

A- Planktonic foraminiferal wackstone. This microfacies includes

1015

planktonic foraminifera with spar filled chambers. Sample G 30, Dakhla

1016

Formation,North Gunna section. Stained, CN view.

1017

40

B- Bioclastic wackstone. The main framework grains are Alveolina sp.

1018

(AV) as well as echinoderm (EC), Sample No. Q72, Farafra Formation, El-

1019

Quss Abu Said. Stained, PPL.

1020

C- Bioclastic wackstone. Note the internal cavity is dissolved and the void is filled with sparry calcite.

Sample No. K39, Esna Formation, Bir

Karawin. Stained, CN view.

1021 1022 1023

D- Alveoline miliolid packstone. Alveolina sp. (AV) and miliolid

1024

foraminifera (MI) are the main components. Sample Q75, Farafra

1025

Formation, El-Quss Abu Said. Stained, CN view.

1026

E- Algal alveoline packstone. This microfacies includes calcareous algae

1027

(arrow), Alveolina sp. (AV) and bryozoa (BY). Sample Q74, Farafra

1028

Formation, Ain Ramla-El-Quss Abu Said. Stained, CN view.

1029

F- Planktonic foraminiferal packstone. This microfacies is made up of

1030

packed planktonic foraminifera with micrite matrix. The chambers of

1031

planktonic foraminifera are filled with ferroan sparry calcite. Sample 35,

1032

Tarawan Formation, North Gunna section. Stained, CN view.

1033 1034

Plate 3. Photomicrographs showing:

1035

A, B- Nummulitic operculine packstone. This microfacies includes

1036

Nummulites Sp. (NM), Operculina sp. (OP), Discocyclina sp. (DI) and

1037

many of fragmented microfossils. Sample Q58, Esna Formation, El-Quss

1038

Abu Said. Stained, A- CN view, B- PPL.

1039

C- Dolomitized nummulitic bioclast packstone. This microfacies contains

1040

nummulites tests (yellow arrow), pelecypod shell fragments (green arrow)

1041

as well as echinoderm plates and spines (red arrow) and brachiopods (blue

1042

41

arrow) in dense micrite enclosing fine crystalline dolomite rhombs. Sample

1043

No. Q66, Esna Formation, El-Quss Abu Said. Stained, CN view.

1044

D- Dolomicrite. Note the dolomite rhombs are fine crystalline, anhedral

1045

and ferroan. Sample Q50, El-Quss Abu Said section, Esna Formation.

1046

Stained, CN view.

1047

E- Calcareous quartz arenite. Note that the medium to coarse quartz

1048

grains floating on poiklotopic calcite cement. Notice also the corona texture

1049

around the quartz grains.

1050

Sample 53, caliche bed at the base of the

limestone unit capping South Gunna section. Stained, CN view.

1051

F- Recrystallized limestone. This microfacies contains void filling

1052

radiaxial fibrous calcite. Sample 54, South Gunna section. Stained, CN

1053

view.

1054 1055

Plate 4: photomicrographs showing:

1056

A- Undulatory surface that represents the first sequence boundary (SB 1).

1057

It lies between the Khoman and Dakhla formations (yellow arrow). It is

1058

overlain by thin gypsum layer (green arrow) at North Gunna section.

1059

B- Iron oxide layer (see arrow) represents the SB 2 that seperates between SQ 1 from SQ 2 within the Dakhla Formation at South Gunna section. C- Thalassinoides trace fossil at the base of the Tarawan Formation at North Gunna.

1060 1061 1062 1063

D- Ferruginous and gypsiferous shale between SQ 3 and SQ 4 at the

1064

Paleocene/Eocene boundary in the basal part of the Esna Formation at

1065

North Gunna section

1066

42

E- A close-up of the caliche layer overlying the Esna Formation at North Gunna section.

1067 1068

F- Undulatory surface (SB 6) separating SQ 4 from the overlying stromatolitic limestone unit (see arrows) at North Gunna section.

43

1069 1070

Table (1): Age

Fm

Section

S. No.

Smectite d- spacing (A°)

E s n a

Ypresian

North Gunna South Gunna

El-Quss Abu Said

Bir Karawin

Un

Gl

H

G 89

14.02

17

9.9

G 52

14.4

16.9

43

14.5

Q 50

Kaolinite Smq

d- spacing (A°)

Smq

Un

Gl

H

72

7.23

7.19

-

28

9.7

43

7.23

6.7

-

57

17.2

10

60

7.18

7.32

-

40

14.6

16.8

9.8

89

7.2

7.07

-

11

Q 42

14.8

16.6

9.9

89

7.1

7.2

-

11

Q7

14.16

17

10.1

62

7.2

7.2

-

38

K 18 K9

14.5 14.8

17 16.8

9.9 10.1

53 70

7.2 7.05

7.1 7.05

-

47 30

Fm = Formation, S. No. = Sample number, Smq = Semi-quantitative %, Un = Untreated, Gl = Glycolated, H = Heated

Assilina

dle

- Shale with low planktonic foraminifera

Alveolines

a an dF (Ear arafra f ly E oce ormatio ne) ns

Mid - NOP

Esn

- Do l num omitize d bioc mulitic lasti pac c k (DN stone P)

P)

- Nummulitic wackstone (NW)

- Dolomitic lime mudstone

NW

Esna Fm.

Bryozoa Calcareous algae

Nummulites

Dolomite rhombs

Operculina

Echinoderm fragments

Pelecypod fragments

Miliolids

Plankton foraminifera

NO

she

lf Out

er s

helf

- Sh fora ale rich min ifera in plank toni c Dak hla and T (Pal arawan Esn e a Fo fo o rma cene) rmatio ns tion (Ear ly E oce ne)

( e n o st P) f k c (P e pa n ) e to in W l s f k u (P M) rc ac e e f p op (P on al t r c s e ife iti ck ton in ul a m am al w uds m or u r f m N ife ic e n n i m o i t am ral l nk r a o f fe Pl ic ni i n o m kt ra n o a f Pl ic n o kt n a Pl

This study aims to reconstruct depositional environments and establish the sequence stratigraphic framework of the exposed Paleocene-Lower Eocene succession Microfacies analysis indicates a deposition in a carbonate shelf (inner, middle and outer) environment Five depositional sequences (SQs) separated by six sequence boundaries are recognized.

Prof. Wanas, H. A. PhD. (Geology)

Department of Geology, Faculty of Sciences Menoufiya University, Egypt Email: [email protected] Mobile: (+2) 01007902156

Date: 19/0/2019

Dear Editor-in-Chief of J. African Earth Sciences We are pleased to inform you that we are interest in Sedimentology and sequence stratigraphy of both carbonate and clastic rocks

Yours Sincerely, H.A. Wanas Abu Shama Sara El-Nahrawy