Late cretaceous to recent palaeoenvironments of the Saudi Arabian Red Sea

Pergamon Journal of Africun Earth Scrmcrs. Vol. 22. No. 4. pp. 535.548. 1996

Copyri$ht 0 1996 Elsewer Science Ltd F’nnted in Great Britam. All rights reserved

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Late Cretaceous to Recent palaeoenvironments of the Saudi Arabian Red Sea

JOHN FILATOFF and G. WYN HUGHES

Geological Department, R and D Division, Saudi Arabian Oil Company, PO Box 5000, Dhahran 31311, Saudi Arabia

(Received 2 August 1995: revised version received 28 March 1996)

Abstract - Integrated micropalaeontological, palynological and lithological analysis of the Upper Cretaceous to Recent sedimentary succession, as observed in deep and shallow well drill cores and field samples, has revealed a highly varied history of environments of deposition. Supratidal, freshwater conditions prevailed during the Late Cretaceous, Oligocene, Early and Late Miocene to Recent. Marginal marine conditions are represented in the PalaeFene to Lower Eocene successions, but without any indication of hypersaline sabkha environments. Marginal marine conditions involving periodic hypersaline sabkha and hypersaline lake development existed during the Early and Late Miocene. In most of the studied areas, very deep, normal salinity marine conditions, within the upper bathyal regime, existed during the Early Miocene; episodes of marine suboxia are indicated by the microfaunal and organic facies character. Later, during the late Early Miocene and early Middle Miocene, similar deep marine conditions prevailed, but with episodes of hypersabnity that culminated in the late Middle Miocene. Such conditions are believed to have resulted from the isolation of the basin and the precipitation of deep marine precipitates. These changes in palaeoenvironment are considered to reflect episodes of eustatic sea level fluctuation, which are possibly linked to the structural evolution of the Red Sea.

Resume - Les analyses integrees micropalContologiques, palynologiques et lithologiques de successions s&limentaires du Cretace sup&ieur au R&cent en Arabie Saoudite, basees sur sondages profonds, superficiels ou sur les observations de terrain, y ont r6v& des evolutions d’environnements de d6pBts extrsmement importantes. Des conditions supratidales en eau deuce ont prevalu au C&ace supbrieur, Oligocene, Miocene inf&ieur ainsi que du Miocene superieur au Recent. Des conditions de mer marginale sont repr&entGes dans les successions du Pal&c&e B l’EocPne infkrieur, mais sans indication d’environnements hypersalins de type sebkha. Des conditions de mer marginale incluant le developpement periodique de sebkha et de lacs hypersalins ont exist6 au MiocPne inferieur et superieur. Dans la plupart des regions etudiees, des conditions marines t&s profondes de salinite normale, au sein d’un regime bathyal superieur, sont presentes au Miocene ir&rieur; des episodes de suboxia marine sont indiques par la microfaune et les facies organiques. Plus tard, h la transition du MiocPne inf&ieur et moyen, des conditions similaires de mer profonde ont prevalu mais avec des episodes d’hypersalinit6 culminant & la fin du Miocene moyen. De telles conditions r&.ultent probablement de l’isolation du bassin et de precipitations marines profondes. Ces changements de pal6o-environement refleteraient des episodes de fluctuations eustatiques du niveau marm qui pourraient @tre liees h l’evolution structurale de la Mer Rouge. Copyright 0 I996 Elsevier Science Ltd

INTRODUCTION

Micropalaeontological and palynological analyses have been carried out on ditch-cuttings and core samples from exploratory wells drilled along the onshore and offshore margins of the Saudi Arabian Red Sea, together with field samples collected from various parts of the coastal region (Fig. 1). The results have been utilized primarily for age determination and stratigraphical control (Hughes and Filatoff, 1995) and have additionally provided palaeoenvironmental information for the sedimentary successions of Late Cretaceous (Campanian) to Pleistocene age.

The geology of the Saudi Arabian Red Sea is complex and includes igneous, volcanic, sedimentary and

metamorphic lithologies. The sedimentary successions penetrated by the explanatory wells include a variety of siliciclastics, carbonates and evaporites (Fig. 2).

PRINCIPLES OF PALAEOENVIRONMENTAL CONTROL

Palaeoenvironmental interpretation is based on an integration of lithology and biostratigraphical evidence. Within the study, a series of palaeoenvironmental regimes were identified, each of which is characterized by a unique association of palynological and micropalaeontological features (Table 1). The palaeoenvironmental regimes recognized within the Saudi Arabian Red Sea region range from terrestrial,

535

536 J. FILATOFF and G. W. HUGHES

Wajh

Figure 1. Location map of the Red Sea basin.

marginal marine and shallow marine to deep marine. The terrestrial regime includes fluviatile and lacustrine environments. Marginal marine environments are varied and include brackish estuarine and lacustrine conditions and hypersaline lakes. The shallow marine regime includes contrasting high energy sihciclastics and lower energy carbonate-dominated lagoons and platforms. Deep marine conditions are well represented in the region, and include normal salinity, siliciclastic-dominated lithologies and also deep marine hypersaline precipitates.

Terrestrial regime

Within the terrestrial regime, even in semi-arid climates, lacustrine and fluviatile environments support and preserve plant life and hence palynology is a most valuable tool for identifying such palaeoenvironments.

Micropalaeontological forms of palaeoecological value are also sporadically preserved and include freshwater ostracods, freshwater fish teeth and charophytes.

Palynology. Within terrestrial palaeoenvironments, the most useful biostratigraphical discipline is palynology, in which fossilized spores, pollen and other acid-insoluble organic remains are extracted from the rock and identified under the microscope. Palynological assemblages from such an environment are commonly poor because of a scarcity of sufficiently anoxic, low- energy environments that facilitate palynomorph preservation. Favourable niches, however, are developed in lower flood-plain settings that include lakes and slow-flowing rivers. Within the Neogene of the Red Sea area, a further adverse influence on palynological recovery is the existence of sparse source

Late Cretaceous to Recent palaeoenvironments of the Saudi Arabian Red Sea 537

Table 1. Micropalaeontological disciplines

L

SUPRATIDAL INTERTIDAL-BRACKISH SHALLOW SUBTIDAL DEEP SUBTIDAL

ORGANIC WALLED

Sporopolleninous

Spores/pollen Green algae

Chitinous

Fungal remains

Spores/pollen (Spores/pollen) Green algae Green algae

Dinoflagellates Dinoflagellates

Fungal remains Fungal remains Microforaminifera Microforaminifera

Scolecodonts Scolecodonts

PHOSPHATIC

(Spores/pollen) Green algae

Dinoflagellates

(Fungal remains) Microforaminifera

(Scolecodonts)

Fish teeth/bones I

Fish teeth/bones I

Fish teeth/bones I

Fish teeth/bones

SILICEOUS

Diatoms I

Diatoms I Diatoms I Diatoms

CALCAREOUS

Charophytes Ostracods

Charophytes Ostracods

Benthonic foraminifera

Ostracods Ostracods Benthonic foraminifera Benthonic foraminifera Planktonic foraminifera Planktonic foraminifera

Calcareous algae Calcareous nannoplankton (Calcareous nannoplankton) Pteropods

vegetation, resulting from prevailing semi-arid to arid climatic conditions. Spore/pollen assemblages of the pre-rift section (Upper Cretaceous - Lower Palaeogene) suggest a vegetation of palms with an under-storey of lycophytes and ferns typical of a humid, tropical climate (Fig. 3). Spores of water ferns and coenobia (multicellular colonies) of planktonic green algae indicate the existence of freshwater lakes and ponds (Fig. 4). In the syn-rift section, the assemblages are dominated by grass pollen indicative of Savannah-type grass vegetation with sparse arboreal cover of Acacia and other such forms (Fig. 5). Subordinate palynofloral elements show this to be broken by more diverse riverine vegetation developed in response to seasonal rainfall (Fig. 6). Freshwater green algae and tropical/ subtropical water-fern spores are again evidence of freshwater ponding. Pollen of salt-tolerant (halophytic) plants (e.g. Chenopodiaceae) are common in parts of the Neogene section and are probably associated with sabkha development.

Micropalaeontology. Freshwater ostracods are commonly recovered from lakes and slow-running rivers and they are also present in the lithified sediments, which accumulated within such environments. They are typically thin shelled and without ornament.

Foraminifera are typically absent from such environments. The white, spirally ribbed, calcified oogonia of freshwater charophytes are often locally abundant and occur together with very small fish teeth. Freshwater diatoms, although probably present, are generally too small to be recovered from micropalaeontological preparations.

Marginal marine regime

This regime spans the brackish, tidal, lower reaches of rivers, but also includes lagoons and intertidal siliciclastic and carbonate marine environments. This diversity of niches results in a greater abundance and diversity of both palynological and micropalaeontological elements. Benthonic foraminifera, ostracods, small bivalves and gastropods are typically recovered from marginal marine sediments in the Red Sea.

Palynology. Palynological recoveries from marginal marine silts are generally fairly high and include an abundance of well-preserved, coarse, cuticular kerogen. Mangrove pollen is characteristic. In the Upper Cretaceous - Palaeogene, Spinizonocolpifes, a derivative of Nypa-type palms, is common (Fig. 3). Mangrove pollen is less common in the Neogene section, although

538 1. FILATOFF and G. W. HUGHES

Avicennia-types occur sporadically in the Al Wajh and Ghawwas Formations. Sonneratia- and Rhizophora-type pollen, that are common in more equatorial regions, are rare in the Red Sea associations. A diversity of fungal remains, as well as occasional scolecodonts (polychaete worm teeth), microforaminiferal test linings and dinocysts, also occur in this environment.

Micropalaeontology. Foraminifera are the most common group recovered from this regime. In brackish sediments from estuarine palaeoenvironments, simple agglutinated forms are often abundant, but display very low species diversity. Intertidal foraminiferal assemblages are predominantly calcareous and may be dominated by miliolids within restricted environments such as hypersaline lagoons. Many intertidal deposits contain only broken foraminiferal fragments, resulting from abrasion in the high energy conditions associated with wave action. Recovery from siliciclastic sediments is often poor, but good recovery characterizes marginal marine, intertidal carbonates.

Echinoid debris is often abundant within sediments from this regime and is typically accompanied by small gastropods and bivalves.

Shallow marine (‘shelf’) regime

The use of the term ‘shelf’ by most palaeoenvironmental. scientists engaged in micropalaeontology is largely inapplicable to regions where this submarine physical entity does not exist. This situation is based on the fact that most investigations into the ecology of palynological and microfaunal material is carried out on the continental shelves, where lateral facies variations may be more easily observed, and also where access has often been easier than in the remoter regions where submarine shelves do not exist. The publication of palynological and microfaunal distribution information related to depth on the shelf has encouraged the use of this term when, in reality, only water depth and possibly distance offshore are the interpreted parameters. In the recent biostratigraphy of Red Sea fossil material, the micropalaeontological assemblages have been interpreted in terms of water depth and have therefore substituted the physical connotation of shelf, with the bathymetric term neritic. Hence, inner neritic would imply water depth similar to that encountered in the inner shelf regime, despite the absence of such a submarine physiographical feature.

The shallow marine realm is considered to include water depths between low intertidal and approximately 200 m as this has been found to be a significant depth in controlling the distribution of certain planktonic and benthonic foraminifera. The neritic zone may be readily separated into the inner and outer provinces, based on characteristic microfaunal and, to a certain extent, palynological variations, which relate to water depths of between shallow subtidal and 100 m and between

100 m and 200 m, respectively. A further subdivision is sometimes applied at a depth of approximately 30-50 m, resulting in a three-fold categorization - inner, middle and outer neritic.

Palynology. Some of the richest palynological recoveries, including both diverse spore/ pollen and dinocyst assemblages, are derived from the shallow marine environments. The inner neritic environments are richer in land-derived phytoclasts and palynomorphs and the dinocyst associations include higher proportions of peridiniacean cysts. Restricted neritic environments with negligible terrestrial influx are not uncommon, however, especially in the northern parts of the Red Sea. The kerogen displays good oil source character, being both rich and consisting of well- preserved amorphous matter. It is typically highly impregnated with pyrite, implying anoxic conditions, at least near the sediment-water interface. The palynological assemblages include abundant thin- walled (crumpled) chorate gonyaulacoid dinocysts. Assemblages of more robust ‘open marine’ dinocysts are not common in the Red Sea Neogene.

Micropalueontology. Inner, middle and outer neritic regimes are characterized by discrete foraminiferal assemblages, the proportion of planktonic to benthonic species and the degree of species diversity. All three regimes have been interpreted in terms of the Saudi Arabian Red Sea fossil assemblages. Within the Red Sea, and with the exception of shallow marine carbonate platform environments, micropalaeontologica1 assemblages are generally insufficiently represented to enable the consistent distinction of inner from middle neritic and so the wider interpretation of inner neritic (O-100 m) is typically used.

Deep marine (bathyal/slope) regime

The bathyal (or slope) regime extends below -200 m and is well represented in the Red Sea Neogene sequences. Micropalaeontological recovery is typically excellent from such deposits, although limited palynological analyses have also provided good supportive palaeoenvironmental evidence. Only the upper bathyal regime has been recognized in the assemblages analysed, with interpreted palaeowater depths less than 500 m.

Pa1ynoZogy. Palynological recoveries from this environment are generally lean. The palynomorphs comprise rare chorate gonyaulacoid dinocysts and only the more robust and poorly preserved terrestrial forms. Corroded, inertinitic kerogen is typical of this environment.

Micropulueontology. Micropalaeontological assemblages characteristic of this deep marine


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AND DEEP MARIN CARBONATES AN SlLKXLASTlCS

m MARGINAL GHAWWAS MINE

FM. SILICICLASTKX ____-

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SUQAH COARSE 6 FINE- GRAINED

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ADAFFA BRAIDED STREAM DEPOSITS;

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INFLUENCE

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RELATIVE CHANGE OF

I

EUSTATIC CURVES COASTAL ONLAP

I

----------’ -- ------

---------- -------- ---------_c ----_ _________4+~____. --__------ ___-------

\------ -----p_-------,

N&Y Coastal onlap and eustatic data

from Haq et al., 1987

Figure 2. Event stratigraphy of the Saudi Arabian Red Sea region

540 1. FILATOFF and G. W. HUGHES

PRE-RIFT HUMID TROPICAL PALMAE PROVINCE

Maurltidlltes franclscoi

r tzonocolpites echlnatus

roxapertites 3perculatur

Figure 3. Pre-nft humid tropical Late Cretaceous - Early Tertiary Palmae Province pollen

palaeoenvironment are typically high, both in abundance and species diversity of benthonic and planktonic foraminifera. Associated microfauna are rare and restricted to pteropods, ostracods, echinoid debris and diatoms.

Planktonic foraminiferal assemblages typically contain species of Globorotalia and Globoquadrina, in addition to the Globigerina - Globigerinoides associations which characterize the neritic regime. Benthonic foraminifera include deep marine species of hispid and costate Nodosaria and Uvigerina, together with locally well-developed agglutinated forms such as Bathysiphon taurinensis Sacco.

THE SAUDI ARABIAN RED SEA LITHOLOGICAL SUCCESSION

The stratigraphical succession depicted in Fig. 2 is based upon data from some 30 exploration wells, numerous shallow wells and field exposures, in addition to comparisons with other circum-Red Sea areas, including the Gulf of Suez. Lateral variations in lithotypes are evident and can be explained as lithofacies variations in response to both the great variety of depositional environments and sediment source.

A comprehensive review of the Red Sea lithostratigraphy, with age control provided by biostratigraphy, has been presented by Hughes and Beydoun (1992) and Hughes and Filatoff (1995), while that for the Gulf of Suez has been discussed by Hughes et al. (1992). Palaeoenvironmental changes within the Red Sea during geological time have also been described by Hughes and Beydoun (1992) and Crossley et al. (1992).

The Saudi Arabian Red Sea lithostratigraphy is conveniently assignable to three main stages in the geological history and development of the Red Sea rift, in which pre-rift, early syn-rift and late syn-rift phases can be distinguished. The Saudi Arabian lithostratigraphical succession used in this presentation is currently informal; formalization according to the

conventional scheme of lithostratigraphical nomenclature is in progress.

Pre-rift

The pre-rift succession is entirely sedimentary and has been termed the Suqah Group. Two formations are recognized and are locally represented by a lower Adaffa Formation and an upper Usfan Formation.

The Adaffa Formation is of Late Cretaceous age (Campanian to Early Maastrichtian, based on palynology) and, in the Jiddah basin, consists of poorly sorted, locally kaolinitic, pebbly sandstone with minor interbedded siltstone. Sparse palynomorph yields in the lower part, in conjunction with the lithological character, enable a non-marine, braided river complex palaeoenvironment to be recognized. Marginal marine incursions in the upper part are suggested by the presence of dinoflagellates. In the Midyan basin, however, the formation consists of clean, medium- to coarse-grained, well-sorted sandstones.

The Usfan Formation is of Late Cretaceous (Maastrichtian) to Early/?Middle Eocene age (based essentially on palynological data) and contains a variety of lithotypes, including black shales and light-coloured siltstones with interbedded sandstones, rare bioclastic limestones, coals and oolitic ironstones. Basaltic rocks locally intrude the section.

Palaeoenvironmental conditions range from shallow, nearshore marine at the base (deltaic/estuarine) grading to non-marine at the top (low energy fluviatile). Palynological assemblages are generally rich, well preserved and characterized by a distinctive pollen association that allows the land palynoflora to be attributed to the tropical Late Cretaceous Palmae Province that extends east-west across central Africa and into northern South America (Herngreen and Chlonova, 1981; Fig. 3). Nypa-like palm pollen indicates the existence of mangrove vegetation fringing the coast and estuaries. Landward arborescent vegetation is evidenced by the


FRESHWATER GREEN ALGAE Pedbstfum

Mfidltes @Y-W

%dlastrum z

Figure 4. Planktonic green algae.

I SYN-RIFT lROPiCAL SEMLARBD FLORA

Figure 5. Syn-rift pollen assemblages.

SYN-RIFT “MOIST” sPoRE/PouEN

Figure 6. Syn-rift, “moist”, spore and pollen flora.

pollen of other palms. Coastal plain swamps and lakes are indicated by green algae, lycophytes and ferns, including water ferns. Some such assemblages have been described previously by Srivastava and Binda (1991), who referred them to the Shumaysi Formation.

Dinocysts are common throughout the lower and middle part of the Usfan Formation (Fig. 7). Those from

the lower part can be attributed to the tropical to subtropical Malloy Peridiniacian Suite, which has a geographical distribution similar to that of the Late Cretaceous Palmae Province mentioned above (Lentin and Williams, 1980). Palaeocene dinocyst assemblages are typified by chorate gonyaulacoid cysts and include the genera Cordosphaericlium, Fibrocysta and


PRE-RMT DINOCYSTS (USFAN FORMATtON)

Figure 7. Pre-rift dinocysts in the Usfan Formation

ORGANIC FACIES

CUTICUIAR (d&dC+lb.Whd~

Figure 8. Organic facies in the Saudi Arabian Red Sea stratigraphy

Exochosphaeridium. Similar associations have been described from West Africa and are considered to represent ‘open sea’ environments (Jan du Chene and Adediran, 1984). The uppermost dinocyst assemblages from the Usfan Formation (uppermost Palaeocene - Lower Eocene) are typified by a plexus of Apfeodinium/ Wetzeliella peridiniacean cysts similar to those that have been described from West Africa and Western Europe and considered to be indicative of estuarine/brackish waters (Downie ef al., 1971; Harland, 1979).

Kerogen typically consists of coarse, well-preserved, terrestrial vegetal fragments (Fig. 8). Microfauna are generally rare, but assemblages of small agglutinated benthonic foraminifera are sporadically distributed, together with charophytes, thus providing further evidence for brackish and freshwater environments.

Possible early syn-rift succession

The earliest syn-rift episode is considered to be represented in the central Red Sea by the Matiyah Formation and composed of purplish red to variegated weathered siltstones and fine-grained sandstones with intervening basalt flows. The unit may represent ‘proto-

rift’ sedimentation and volcanism, separated unconformably from both the pre-rift Suqah Group below and the syn-rift Tayran Group above. An Early Oligocene age (33-34 Ma) has been determined for the basalts by radiometric methods (Cocker, 1992), and the presence of the following palynomorphs: Magnasfriafites howardii Germeraad ef al., a tropical water-fern spore, which evolved at the base of the Oligocene (Fig. 6) and Pediasfrum delicafites Wilson and Hoffmeister, a freshwater colonial green alga, which evolved within the mid Eocene (Fig. 4). No microfauna have been recovered from this formation.

A low energy, oxidizing, fluvio-lacustrine regime with volcanic episodes is deduced. Palynological samples are either barren or yield very sparse assemblages strongly dominated by a freshwater green algal species (Pediasfrum delicafifes) associated with rare spores and pollen. Organic yields are very low and typically consist of fine, dispersed matter (Fig. 8).

Proven early syn-rift succession

The proven early syn-rift succession includes a high variety of lithotypes. These represent a direct response


TAYRAN GROUP, AL WAJH FORMATION: FISH TEETH

Figure 9. Fish teeth of the Al Wajh Formation, Tayran Group.

Figure 10. Early Miocene larger foraminifera, Miogypsina and Miogypsinoides, Musayr Formation, Tayran Group.

to the high diversity of palaeoenvironmental conditions related to the wider variation in subsidence rates, which the region experienced during the development of the Red Sea graben. This succession commences with a volcanic episode, represented by the Jizan Group, which is separate from that which was recognized in the early syn-rift Matiyah Formation.

The Jizan Group includes basalt, dolerite, volcaniclastics, pyroclastics and shales of Early Miocene age based on radiometric determinations (Sebai et al., 1991). These have intruded the Tayran Group and Burqan Formation.

The Tayran Group comprises three formations, namely, in upward succession, the Al Wajh, Yanbu and Musayr Formations, and was associated with the early stages of shallow marine incursion into the region.

The Al Wajh Formation consists of a sequence of interbedded, coarse- and fine-grained siliciclastics of Early Miocene age, based on palynological evidence. It rests unconformably on all older stratigraphical units. A fluvio-lacustrine palaeoenvironment with marginal marine (?estuarine) pulses is deduced based upon evidence from both palynology and micropalaeontology. Palynofloras are generally sparse, particularly towards the base, and are characterized by

terrestrial elements, including the freshwater alga Pediasfmm sp.; dinocysts are rare to absent (Figs 4, 5 and 6). The presence of Avicennia-type pollen indicates limited shoreline mangrove development. Micro- palaeontological elements include fish teeth (Fig. 9), charophytes, smooth ostracods and the benthonic foraminifera Ammonia beccurii (Linnaeus) and Elphidium sp. This association became established during the early stages of slow subsidence and shows the first effects of a gradual marine transgression.

The Yanbu Formation is of Early Miocene age, based on stratigraphical position, and consists of laminated anhydrite and halite. The palaeoenvironment is interpreted to have been hypersaline marginal marine, including sabkhas and salinas. Palynofloras from the intra-evaporitic sediments typically include Refiperiporifes sp. (a pollen believed to be derived from a halophytic plant; Fig. 5), but lack marine indicators; no microfauna are present. Strontium isotope analyses on the laminated anhydrites from this formation have yielded values which support an earliest Miocene age (Cocker and Hughes, in press).

The Musayr Formation is dated as Early Miocene based on the co-occurrence of the larger foraminiferal Miogypsinu and Miogypsinoides species (Fig. 10). The


Figure 11. Early to Middle Miocene (N8-lower N9) planktonic foraminifera, Jabal Kibrit Formation, Mayna Group.

NEOGENE CHORATE DINOCYSTS

Figure 12. Neogene chorate dinocysts

formation consists of a lower, predominantly siliciclastic interval, which is overlain by bioclastic carbonates. Intertidal (lower siliciclastic section) and shallow, inner neritic, carbonate platform (upper carbonate unit) palaeoenvironments are deduced for this formation, based on the rich, shallow, marine micro- and macrofauna. In contrast to the other formations of the Tayran Group, dinoflagellate cysts are prominent in the palynofloras and are typified by species of Systematophora and Polysphaeridium.

The Burqan Formation consists of calcareous shales and claystones with interbedded sandstones and thin limestones. Locally, these grade laterally into a turbiditic sandstone equivalent termed the Nutaysh Member. This formation disconformably overlies sediments of the Tayran Group and is dated as Early Miocene, based on planktonic foraminiferal and calcareous nannofossil evidence. The planktonic foraminiferal zones N5-N7 of Blow (1969) have been determined, together with the nannofossil zones NN2-NN4C (Martini, 1971; Dr 0. Varol, pew. comm.; Hughes and Filatoff, 1995). A deep marine, upper bathyal to deep outer neritic palaeoenvironment is deduced, based on the presence of rich and diverse planktonic foraminiferal assemblages, together with the presence of characteristic

deep marine benthonic foraminifera. Localized concentrations of agglutinated benthonic foraminifera possibly represent episodes of suboxic conditions related to transgressive pulses and reduced sedimentation rates. Palynofloras may be moderately rich and include a high proportion of dinoflagellate cysts. In deep water settings (bathyal), however, samples are commonly barren of palynomorphs and characterized by inertinitic kerogen (Fig. 8).

The Maqna Group is typified by interbedded siliciclastics and, significantly, evaporites, with local facies variations which may be either entirely siliciclastic or carbonate. The presence of interbedded evaporites is critical for the segregation of this group from the underlying deep marine siliciclastics of the Burqan Formation. The group unconformably overlies the Burqan Formation. Two formations, the Jabal Kibrit and Kial Formations, have been recognized within the Maqna Group.

The Jabal Kibrit Formation consists of a lower unit of shales interbedded with three anhydrite beds and an upper unit of calcareous shales and mudstones. These units are designated the Umluj and Wadi Waqb Members, respectively. The formation is of Early to Middle Miocene age, based on planktonic foraminiferal


NEOCEME SPORE/POLLEN MARKER SPECIES

Acmthaceae

Figure 13. Neogene spore and pollen marker species.

ACCESSORY PALYNOMORPHS

Figure 14. Accessory palynomorphs.

Figure 15. Basal Middle Miocene larger foraminifera (Borelis melo), Kial Formation, Maqna Group.

evidence, with the boundary placed within the upper siliciclastic unit. The planktonic foraminiferal zones N8- N9 (lower) are recognized (Hughes and Filatoff, 1995). Deep marine, outer neritic to possibly upper bathyal palaeoenvironmental conditions are deduced, based on the rich and diverse planktonic (Fig. 11) and benthonic foraminiferal assemblages. Palynological assemblages of the Maqna Group are the richest and most diverse of

the Neogene succession. They include high proportions of chorate dinoflagellate cysts and, in more proximal settings, a spore and pollen flora characterized by a diversity of Acanthaceae-type pollen (Figs 12 and 13). Charred Gramineae cuticle (Fig. 14), an indicator of grassland fires on the hinterland, first appears in the Maqna Group and persists throughout the overlying succession. The coarse siliciclastic and carbonate


members are considered to be the products of penecontemporaneous downslope transport from a shallow marine source. The basal evaporitic units are considered to be the result of deep marine precipitation from an extremely hypersaline environment and suggest restricted conditions and almost complete isolation from the neighbouring seas.

The overlying Kial Formation typically consists of a thinly-bedded, fine-grained, siliciclastic and evaporitic association, which includes two intervals of each. A carbonate platform equivalent is recognized and termed the Dubaybah Member. This formation lies with apparent conformity upon the Jabal Kibrit Formation of the Maqna Group. The basal Middle Miocene age is based on planktonic (zone N9, upper), larger benthonic foraminiferal evidence (Borelis melo Fichtel and Moll; Fig. 15) and nannofossil evidence (zone NN5) (Hughes and Filatoff, 1995). A moderately deep marine palaeoenvironment is deduced with shallow carbonate platform facies locally developed.

Two episodes of deep marine extreme hypersalinity caused precipitation of gypsum in the deeper marine setting. Palynofloras are similar to those of the Jabal Kibrit Formation. Organic facies vary from ‘coaly’ to ‘structured terrestrial detritus’ to ‘amorphous’, depending on the depositional setting (Fig. 8).

Late syn-rift

The Mansiyah Formation consists predominantly of evaporite, associated with sporadic, thin beds of fine- grained siliciclastics. The evaporites range from entirely halite to entirely anhydrite. This formation overlies the Kial Formation with apparent conformity; some faulted unconformable contact relationships are present in areas adjacent to the halokinetic glide planes. A Middle Miocene age is presumed on the basis of its stratigraphical position relative to the enclosing formations. In the Gulf of Suez, marine diatom evidence indicates the presence of Middle Miocene sediments within the overlying lithological unit, thus restricting the Mansiyah Formation to the Middle Miocene. Palynological age criteria in the intra-evaporitic siliciclastics are as for the Kial Formation, supplemented by the presence of the dinoflagellate cyst species Systematopho~a placacantha (Deflandre and Cookson) (extinction at the top of the Middle Miocene) and Pentadinium laticinctum Gerlach (late Middle Miocene extinction). Moderately to very deep marine, extremely hypersaline palaeoenvironmental conditions are diagnosed, leading to the precipitation of halite and gypsum. A marine environment is indicated by the presence of dinoflagellate cysts in inter-evaporitic shales, whilst anoxic conditions are suggested by an abundance of pyrite-impregnated amorphous kerogen (Fig. 8).

The Ghawwas Formation is characterized by a predominantly coarse- to fine-grained siliciclastic lithology, associated with sporadic beds of anhydrite.

This formation lies with apparent conformity upon the Mansiyah Formation. A Middle to Late Miocene age is deduced, based on its stratigraphical position beneath sediments of confirmed Pliocene age. Middle Miocene marine diatoms have been recovered from this formation in the Gulf of Suez (Rose, 1989) and may be of significance to the Saudi Arabian Red Sea equivalent, unless the Ghawwas Formation is diachronous. A Late Neogene age is suggested by the relatively common occurrences of Plurnbq+uxeae (Fig. 13), Papiliormmc and Nyctaginaceae types of pollen. Intertidal to shallow inner neritic palaeoenvironmental conditions are interpreted from the lithology, with periodic development of sabkha conditions. Palynological assemblages are normally sparse and indicative of non-marine conditions, although assemblages of dinocysts, microforammiferal test linings and scolecodonts (worm teeth; Fig. 14) are preferentially concentrated near the base and top of the formation. Pedinstwn sp. and spores of Anthoceros-type bryophytes are typical elements of the formation (Figs 4 and 13).

Late syn-rift/?drift

The Lisan Formation consists of coarse- and fine- grained siliciclastics and carbonates, which lie disconformably, possibly unconformably, upon the Ghawwas Formation. The formation is of Pliocene to Pleistocene age, based on planktonic foraminiferal and calcareous nannofossil evidence. The palaeoenvironments range from supratidal, through intertidal and shallow marine carbonate platform to upper bathyal, based on the variable character of the foraminiferal populations. Foraminifera typical of reefs and lagoons characterize the shallow marine lithofacies and rich planktonic and deep marine benthonic foraminiferal assemblages typify the basinal lithofacies to the west.

SUMMARY OF ENVIRONMENTAL EVENTS

The Saudi Arabian Red Sea may be seen to have undergone a variety of environments of deposition and rates of subsidence, with major unconformities distributed at a number of levels within the succession (Fig. 2).

The following environmental episodes can be segregated and each may have useful implications for supplementing the various tectonic models already in existence for the region. Each episode will be considered separately and followed by a discussion on the possible cause of the isolation of each episode.

Episode 1 (Campanian - ?Lower Maastrichtian)

During this episode, deposition of fluviatile to marginal marine siliciclastic sediments of the Adaffa Formation took place, with occasional minor marine transgressive episodes. The predominantly coarse elastic lithology suggests that moderately high energy fluviatile


conditions prevailed within a braided river complex, some of which may have been associated with flash floods.

Episode 2 (Maastrichtian)

This episode is inferred to have been a period of erosion and/or non-deposition and possibly related to a eustatic sea-level fall.

Episode 3 (?Upper Maastrichtian - Lower Eocene)

The sediments of this age lie with probable unconformity on the Adaffa Formation and constitute the Usfan Formation. Evidence for marine influence at the base indicates that an early marine transgression affected the area with regression through estuarine and shallow marine carbonate platform conditions ultimately leading to freshwater conditions at the top.

Episode 4 (Lower Eocene - Lower Oligocene)

This episode is based on the apparent absence of sediments of Middle to Upper Eocene age and is interpreted as a period of erosion and/or non- deposition. Exposure at this time is likely to have been related to gradual eustatic fall (Fig. 2).

Episode 5 (Lower Oligocene)

This episode is characterized by basaltic volcanism associated with siliclastic fluvio-lacustrine sedimentation (the Matiyah Formation). The episode is considered to represent extension associated with, and a precursor to, later rifting.

Episode 6 (Lower - Upper Oligocene)

This episode is interpreted as a period of erosion and/ or non-deposition based on available palynological evidence. The major eustatic regression during the basal Upper Oligocene may have influenced non-deposition during this time.

Episode 7 (basal Lower Miocene)

During this episode, marginal to shallow marine conditions (Tayran Group) encroached as a result of flooding from either, or both, the Mediterranean Sea or the Gulf of Aden, accompanying the gentle subsidence of the early syn-rifting phase. Localized volcanic activity was associated with this episode in the southern part of the area (Jizan Group). Fluviatile siliciclastics (Al Wajh Formation) represent the earliest and most extensive deposits with brackish conditions locally developed. Locally isolated lagoons became hypersaline and led to the precipitation of evaporites (Yanbu Formation). At certain localities, marginal shallow carbonate platforms (Musayr Formation) became established.

Episode 8 (Lower Miocene)

Although coarse-grained fluviatile sediments continued to be deposited along the proximal flanks of the subsiding basin, the most widespread deposits include fine-grained siliclastics, which were deposited in very deep marine conditions (Burqan Formation). This facies indicates rapid subsidence, which was associated with the rapid inundation of the region by oceanic water of normal salinity.

Episode 9 (Lower Miocene)

The evidence for this episode is based on a comparison of the succession analysed from the Saudi Arabian Red Sea with that of the Gulf of Suez. The Burqan Formation in the Red Sea area is interpreted as incomplete, due to the uppermost part (time-equivalent of lower zone N8) being absent. Within the region this episode represents a possible marine regression which resulted in erosion or non-deposition along the flanks of the basin, although contemporaneous sedimentation may have persisted deeper within the basin.

Episode 10 (Lower Miocene to basal Middle Miocene)

Interbedded evaporites and siliciclastic sediments (Jabal Kibrit Formation, lower part) indicate a renewal of deep marine conditions in which periodic restriction resulted in the precipitation of evaporites. Submarine conditions are suggested by close association of evaporites with deep marine siliciclastics. Their wide extent within the Red Sea region further suggests that they were basinal and not locally developed sabkha deposits. Fluviatile and shallow marine carbonate platforms are considered to have existed at certain localized areas at this time. A regional return to normal salinity, deep marine conditions with good water circulation (Jabal Kibrit Formation, upper part) follows this hypersaline event. The presence of a condensed section within deep marine siliciclastics suggests a possible transgressive acme within the episode. At certain localities, shallow marine carbonate platforms existed, together with fluviatile deposits, which were periodically transported into a deep marine environment. A further return to two short-lived hypersaline events is represented by the interbedded siliciclastic and evaporitic deposits (Kial Formation), which indicate that restrictive conditions became established again within the deep basin, leading to an increase in salinity and the subsequent precipitation of evaporites. As with the underlying unit, shallow marine carbonate platforms existed alongside fluviatile sedimentation.

Episode 11 (Middle Miocene)

The eleventh episode marks the onset of ‘late syn-rift’ conditions, which were associated with rapid subsidence of the basin combined with widespread precipitation of

548 I. FILATOFF and G. W. HUGHES

submarine evaporites (Mansiyah Formation). Although the restriction of open marine influence is considered to be the cause of such widespread extreme hypersaline conditions, access to the open sea, either the Mediterranean Sea or the Gulf of Aden, must have continued in order to maintain the inflow of ocean and thereby the supply of salts for subsequent precipitation.

Episode 12 (Middle - Upper Miocene)

The penultimate episode is characterized by the widespread development of marginal marine, predominantly siliciclastic sedimentation in which sabkha-type evaporitic sediments were locally deposited (Ghawwas Formation). Subsidence rates remained high, as testified by the great thickness of sediments within this episode, and were combined with rapid rates of sedimentation, which served to keep infilling the basin and to exclude, or at least severely restrict, marine influence, despite the prevailing eustatic sea-level rise.

Episode 13 (Pliocene - Pleistocene)

The base of the Pliocene is marked by a regional marine transgression that led to the deposition of a variety of rock types, which accumulated in a variety of environments (Lisan Formation). An unconformity may separate this episode from Episode 12, but lacks biostratigraphical or lithostratigraphical evidence. Deep marine, basinal conditions became established close to the margins of the Red Sea graben, suggesting that a major tectonic or eustatic event took place which permitted the invasion of the region by normal salinity sea water; the re-opening of the Bab El Mandeb Straits has been accepted as being responsible for the basal Pliocene transgression within the Red Sea and Gulf of Suez. Basinal subsidence continued, but at a rate exceeding sedimentation.

Acknowledgements

The authors gratefully acknowledge the Ministry of Petroleum and Mineral Resources and the Saudi Arabian Oil Company (Saudi Aramco) for permission to publish the information presented in this paper. Nannopalaeontological determinations were provided by Dr Osman Varol of Varol Research, UK.

REFERENCES

Blow, W. H. 1969. Late Middle Eocene to Recent planktonic foraminiferal biostratigraphy. In: Proceedings 1st lnfernafional Conference Planktonic Microfossils, 1967, 1 (Edited by Bronnimann, I’. and Renz, H. H.) ~~199-421. Geneva.

Cocker, J. D. 1992. Early Oligocene (32-24 Ma) K-Ar age for pre-rift basalts, Jiddah Basin. Saudi Aramco, Geological Department, R and D Division, Petrology

Report 43. (Unpublished). Cocker, J. D. and Hughes, G. W. (In press). Seawater

strontium stratigraphy applied to anhydrites; Tertiary basins of the Saudi Arabian Red Sea. In: Dating and correlating hiostratigraphically barren strata. Geological Society of London meeting, 25-26 May, 1993.

Crossley, R., Watkins, C., Raven, M., Cripps, D., Carnell, A. and Williams, D. 1992. The sedimentary evolution of the Red Sea and Gulf of Aden. [ournal Petroleum Geology 15(2), 157-172.

Downie, C., Hussain, M. A. and Williams, G. L. 1971. Dinoflagellate cyst and acritarch associations in the Paleogene of Southeast England. Geoscience Man 3,29-35.

Haq, B. U., Hardenbol, J. and Vail, P. R. 1987. The new chronostratigraphic basis of Cenozoic and Mesozoic sea level cycles. In: Timing and depositional history ofettstatic sequences: constraints on seismic sfratigraphy (Edited by Ross, C. A. and Harman, D.) Cushman Foundation Foraminiferal Research, Special Publication 24, 7-14.

Harland, R. 1979. Wetzeliella (Apteodinium) homomorpha plexus from the Palaeogene/earliest Eocene of North- west Europe. In: Proceedings 4th 1nterrlatio)lal Palynology Conference, 1976-77. 2, ~~59-70. Lucknow.

Herngreen, G. F. W. and Chlonova, A. F. 1981. Cretaceous microfloral provinces. Pollen Spores 23,44-555.

Hughes, G. W. and Beydoun, Z. R. 1992. The Red Sea - Gulf of Aden: biostratigraphy, lithostratigraphy and palaeoenvironments. {ownal Petroleum Geology 15(2), 135-156.

Hughes, G. W. and Filatoff, J. 1995. New biostratigraphic constraints on Saudi Arabian Red Sea pre- and syn- rift sequences. In: Selected Middle East Papers, GEO’94 (Edited by Husseini, M. I.) ~~517-528. Bahrain.

Hughes, G. W., Abdine, S. and Girgis, M. H. 1992. Miocene biofacies development and geological history of the Gulf of Suez, Egypt. Marine Petroleum Geology 9(l), 2-28.

Jan du Chene and Adediran, S. A. 1984. Late Paleocene to Early Eocene dinoflagellates from Nigeria. Cahiers Micropaleontologie 3, l-38.

Lentin, J. K. and Williams, G. L. 1980. Dinoflagellate provincialism, with emphasis on Campanian Peridiniaceans. American Association Stratigraphic Palynologists, Contribufiolz Series 7, l-47.

Martini, E. 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: Proceedings 2nd Planktorzic Conference, 1970,2 (Edited by Farinacci, A.) ~~739-785. Rome.

Rose, G. 1989. Neogene diatom biostratigraphy of the Gulf of Suez. M. SC. thesis, unpubl. 85~. University College, London.

Sebai, A., Zumbo, V., Feraud, G., Bertrand, H., Hussain, A. G., Giannerini, G. and Campredon, R. 1991. Ar/ Ar dating of alkaline and tholeiitic magmatism of Saudi Arabia related to the early Red Sea rifting. Earth Planetay Science Letters 104,473-487.

Srivastava, S. K. and Binda, P. L. 1991. Depositional history of the Early Eocene Shumaysi Formation, Saudi Arabia. Palynology 15,47-61.

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Late cretaceous to recent palaeoenvironments of the Saudi Arabian Red Sea

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