ORIGINAL PAPER

Stratigraphy and depositional environments of the UpperCretaceous Aruma Formation, Central Saudi Arabia

Khaled M. Al-Kahtany1 & Abdelbaset S. El-Sorogy1,2 & Mohamed Youssef1,3 &

Hisham A. Gahlan1

Received: 25 August 2015 /Accepted: 26 January 2016# Saudi Society for Geosciences 2016

Abstract The Upper Cretaceous Aruma Formation in centralSaudi Arabia is subdivided into three members. The KhanasirMember at the base is characterized by dasycladecean-rudistbiofacies. The middle Hajajah Member is characterized bycoral-stromatoporoid biofacies, while the upper Lina shaleMember contains few badly preserved molluscs. Fifty macro-fossils species have been identified from the studied section,25 of them belong to gastropods, 17 belong to scleractiniancorals, and 8 species belong to bivalves. The identified mac-rofossils have close affinity to Tethyan faunas and previouslyknown from the Cretaceous rocks in Asia, Africa, and Europe.The most recorded microfacies types are wackestones,packstones, and floatstones with green algae, benthic and rareplanktonic foraminifers, ostracods, and corals. The studiedsection revealed a major Campanian-Maastrichtian marinetransgression followed the continental siliciclastics of theWasia Formation with progressive deepening upward, froma shallow marine lagoonal environment to relatively moreopen marine conditions.

Keywords Stratigraphy . Depositional environments . UpperCretaceous . Aruma Formation . Central Saudi Arabia

Introduction

Since the old studies of Steineke and Bramkamp (1952);Steineke et al. (1958); Powers et al. (1966); Powers (1968),(El As’ad 1977, 1983a, b, 1984), and Vaslet et al. (1988), thereare no studies dealt with stratigraphy and depositional envi-ronment of the Aruma Formation in central Saudi Arabia.Skelton and El Asa’ad (1992) identified new genus and spe-cies of canaliculated rudist from of the Campanian KhanasirMember of the Upper CretaceousAruma Formation in CentralSaudi Arabia. Al-Furaih (1984a, 1984b, 1986) studied theMaastrichtian ostracods of Aruma Formation from Wadi al-Atiq. He identified, described, and illustrated one new genusand 15 new species.

Studies of Okla (1991, 1992, 1994, 1995) were onCretaceous fossil algae, especially dasycladaceans. He identi-fied new dasycladecean species from surface samples of theAruma Formation in northeast of Riyadh, Saudi Arabia.Recently, Gameil and El-Sorogy (2015) identified 15 gastro-pod species from the present section, mainly from the HajajahMember and indicated shallow marine lagoonal and relativelyopen marine environment.

None of the last mentioned studies have dealt with stratig-raphy and depositional environments; therefore, the presentwork aims to study stratigraphy and to document the deposi-tional environments of the Upper Cretaceous ArumaFormation in Central Saudi Arabia based on microfacies anal-ysis and macrofossils content.

Materials and methods

A composite section was measured and macrofossils and rocksamples were collected from Khashm Bowaibiyat area,Northeast Riyadh (Fig. 1) Gastropods, scleractinian corals,

* Khaled M. Al-Kahtanykalgatani@ksu.edu.sa

1 Department of Geology and Geophysics, College of Science, KingSaud University, P.O Box: 2455, Riyadh 11451, Saudi Arabia

2 Department of Geology, Faculty of Science, Zagazig University,Zagazig, Egypt

3 Department of Geology, Faculty of Science, South Valley University,Qena, Egypt

Arab J Geosci (2016) 9:330 DOI 10.1007/s12517-016-2361-6

Fig. 1 Outcrop of the UpperCretaceous (Coniacian-Maastrichtian) Aruma Formationin Central Saudi Arabia (afterGameil and El-Sorogy 2015)

Fig. 2 Lithostratigraphic sectionof the Aruma Formation, KhashmBowaibiyat area, NortheastRiyadh

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and bivalves were cleaned and identified. Twenty-two repre-sentative hard limestone samples were chosen for thin sec-tions. Fossils are stored in the Department of Geology andGeophysics Museum, College of Science, King SaudUniversity.

Results and discussion

Stratigraphic setting

The Aruma Formation was named for its occurrence in the Al’Aramah plateau, a broad upland surface related to the east-ernmost of the Najd escarpments (Powers et al. 1966). Rocks

of the Aruma Formation crop out from Wadi ad Dawasirin southern Saudi Arabia beyond the Iraq-Saudi Arabiaborder, a distance of more than 1600 km. Width of theAruma outcrop band is somewhat erratic, but from a re-gional point of view, it persistently increases from south-east to northwest. About 20 km wide at Wadi ad Dawasir,the formation is spread out over nearly 200 km where itpasses into Iraq.

The Aruma Formation disconformably overlies thecontinental siliciclastics of the Cenomanian WasiaFormation (Steineke et al. 1958). The upper limit is takenat the change from yellow-brown dolomitic shale below togray crystalline Lockhartia-bearing dolomite of the Ummer Radhuma Formation above. The first formal referencesto the Aruma Formation appeared in Steineke and

Fig. 3 Field photographs of theAruma Formation. a TheKhanasir Memberdisconformably overliessiliciclastics of Wasia Formation.b Close up view of the rudistlimestone in the upper most partof the lower member. c Generalview of the Hajajah Member. dSlightly massive heads ofscleractinian corals in the HajajahMember. e Small corals andstromatoporoids in the marlylimestone of the Hajajah Member.f Shale and limestone of the LinaMember

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Table 1 Invertebrate megafossilsidentified from the ArumaFormation

Class Species Khanasir Mb. Hajajah Mb. Lina Mb.

Gastropoda Pleurotomaria sp. × × ×

Keilostoma morgani (Douville) × ×

Architectonica conoideum (Sowerby) × ×

Architectonica karapandiensi (Stoliczka) × ×

Nerineopsis cuckhamsliensisWoods ×

Cerithium (Fibula?) detectum Stoliczka ×

Cerithium tenouklense Conquand × ×

Scala dupiniana (d’ Orbigny) × ×

Scala (Confusiscala) dupiniana (d’ Orbigny) × ×

Chemnitzia undosa Sowerby × ×

Aporrhais marginata (Sowerby) ×

Pterodonta deffisi Peron × ×

Pterodonta ovata d’ Orbigny × ×

Strombus bellasensis Choffat × ×

Strombus cascaensensis Choffat × ×

Strombus fischeri Choffat × ×

Cypraea cunliffei Forbes ×

Megalocypraea sp. × ×

Tylostoma pallaryi (Peron & Fourtau) × ×

Sycostoma pervinquieri (Boelenev) ×

Vasum sp. × × ×

Rostellinda pergaensis Boelenev × ×

Lyria subcrassicostata Basse × ×

Drillina morgani Douville × ×

Drilluta curta Boelenev × ×

Bivalvia Spondylus calcaratus (Forbes) ×

Spondylus subserratus × ×

Spondylus latus Sowerby × ×

Ostrea (Alectryonia) pectinata Lamarck ×

Ostrea telugensis Stoliczka ×

Gryphaea cf. oldhami Noetling × ×

Apricardia sp. × ×

Durania arnaudi Choffat ×

Anthozoa Aulosmilia cuneiformis (Milne-Edwards & Haime) ×

Aulosmilia vidali Mallada ×

Aulosmilia compressa Lamarck ×

Rennensismilia subinduta (Reuss) ×

Rennensismilia oldhami (Duncan) ×

Conicosmilotrochus parkinsoni (Edwards & Haime) ×

Conicosmilotrochus figuierensis Alloiteau ×

Acrosmilia cf. fromenteli Alloiteau ×

Stylina regularis Fromentel ×

Columactinastrea torallolensis (Reig Oriol) ×

Aulosmilia cuneiformis (Milne-Edwards & Haime) ×

Aulosmilia vidali Mallada ×

Aulosmilia compressa Lamarck ×

Rennensismilia subinduta (Reuss) ×

Rennensismilia oldhami (Duncan) ×

Conicosmilotrochus parkinsoni (Edwards & Haime) ×

Conicosmilotrochus figuierensis Alloiteau ×

Acrosmilia cf. fromenteli Alloiteau ×

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Bramkamp (1952). The type locality was described bySteineke et al. (1958).

In the type locality, the Aruma Formation is 140 mthick and composed of limestone, shales, and dolomites(Powers 1968). At first, the formation was divided intofour lithological units that were grouped into two mem-bers, namely the Atj and Lina members. Later, the forma-tion was subdivided into three members, in ascendingorder: the Khanasir Member, the Hajajah Member, andthe Lina Member (El Asa’ad 1984; Vaslet et al. 1988;Skelton and El Asa’ad 1992).

The following is a detailed description of the three mem-bers of Aruma Formation at Khashm Buwaibiyat (Lat. 25° 12′12″, Long. 46° 49′ 27″) in northeast Riyadh, central SaudiArabia (Fig. 2).

The Khanasir Member

The lowermost limestone member (up to ∼65 m) comprisesshale at the base followed by slightly dolomitized, burrow, andnodular limestone caps with 12 m of local rudist biostrome

(Fig. 3a, b). It disconformably overlies the continentalCenomanian siliciclastics of theWasia Formation with a sharpcontact and overlain by the Hajajah Member with very lowangle unconformity.

The lower ∼20 m of this member comprises a laterallyvariable association of shaley, marly, and marly limestonefacies, in which few gastropod and bivalve molds (Table 1)and badly preserved echinoids were recorded. The memberbecomes more calcareous upwards with abundantdasycladecean algae and larger foraminifers includingOmphalocyclus marcoporous (Lamarck). The top most partof the member (6–12 m) is a dense packing rudist biostrome(Fig. 3b), mostly of living position of slender rudistEodictyoptychus arumaensis (Skelton and El Asa’ad 1992).

Powers et al. (1966) reported that the lowermost bedsof the Aruma outcrop could be as old as Santonian.Powers (1968) indicated that the top of the lower ArumaFormation is Campanian, where Monolepidorbis sanctae-pelagiae Astre is found. This member ranges in age fromConiacian at its base to Campanian in its topmost fewmeters (El Asa’ad 1983a, 1983b).

a b

cd

e

f

Fig. 4 Examples of the identifiedscleractinians from Hajajahmember. a Stylina regularisFromentel, calicular view. bColumactinastrea torallolensis(Reig Oriol), calicular view. cand d Acrosmilia cf. fromenteliAlloiteau, calicular view andlower view. e and f Aulosmiliacompressa Lamarck, side viewand calicular view

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The Hajajah Member

This member disconformably overlies the KhanasirMember. It comprises shale and marl at the base followedby limestones (up to ∼75 m). The lower shale and marlypart contains abundant scleractinian corals (solitary andcolonial), stromatoporoids, gastropod molds (Figs. 3c–e,4, and 5) and few bivalve ones (Table 1). Corals are pre-dominantly domal and platy and rarely branching. Thelimestone in the upper part includes abundant benthic largerforaminifera [including Omphalocuclus macroporous(Lamarck) and Quenqueloculina sp.] and dasyclad algae(Griphoporella sp.).

The Hajajah Member falls below the level of the low-ermost definitely Maastrichtian Foraminifera and abovethe level of the uppermost definitely CampanianForaminifera. El Asa’ad (1991) proposed a LateCampanian age for Hajajah Member by discovery ofthe ammonites Manambolites amardi Collignon andRoman, Libycoseras chargense Blankenhorn andpachydiscus (P.) launayi (De Grossouvre) in the calcare-ous part of the member.

The Lina Member

The Hajajah limestone Member passes upwards gradationallyinto the Lina shaleMember (over 40m) comprising shales andmarly nodular limestones (Fig. 3f), with nautioloids,burrowing bivalves, and gastropods (Table 1). Ammonitesand foraminifera from this member suggest a lateMaastrichtian age (El Asa’ad 1983a).

Fossil record and depositional environment

Fifty invertebrates have been identified from the studied sec-tion. Twenty-five species belong to gastropods, 17 toscleractinian corals, and 8 to bivalves (Table 1). Almost allof the invertebrates are recorded from the middle HajajahMember, while the lower and upper members contain thefewest. The identified species have close affinity to Tethyanfaunas and known from Cretaceous rocks in Asia, Africa, andEurope. They were previously recorded from western India,Pakistan, Iran, Baluchistan, Iraq, North Africa, Spain, andPortugal and perhaps Western Europe (El Asa’ad 1984).

hg f

be

a c dFig. 5 Examples of the identifiedscleractinians and gastropodsfrom Hajajah member. a and bRennensismilia subinduta(Reuss), side view and calicularview. c and d Drilluta curtaBoelenev, apertural view andabapertural view. e and fCypraea cunliffei Forbes,apertural view and abaperturalview. g and h Strombus fischeriChoffat, apertural view andabapertural view

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One of the most remarkable features of the Cretaceouscarbonate platforms in tropical and subtropical environmentsof the Tethyan realm was the development of facies com-plexes dominated by rudists, with or without associated corals(Masse and Philip 1981; Ross and Skelton 1993; Gili et al.1995; Mansour 2004). The present depositional study ofAruma Formation depends on field remarks, macrofossil con-tent, and microfacies analyses.

The lithological sequence of the Khanasir Member com-prises of shale at the base followed by nodular limestone andcaps with rudist biostrome. Thin sections of the limestones ofthis member gave algal wackestone, foraminiferal algalwackestone, and algal packstone (Fig. 6a–d) with abundantdasycladacean algae (Salpingoporella arumaensis ,Dissocladella intercedens, and Griphoporella sp.). All

bioclastic fragments are recrystallized. These algal floras withthe associated macrofossils mostly indicated a shallow marinelagoonal depositional environment (Okla 1995). The occur-rence of rudist-dasyclad biofacies and benthic foraminiferaclearly supports the interpretation of deposition in a shallowmarine environment that was well within the depth limits ofthe photic zone (Filkorn and Scott 2011). Smith et al. (1995)interpreted the similar upper beds dominated by rudists of theSimsima Formation (Campanian-Maastrichtian of UnitedArab Emirates) as having been deposited on stable shoalsabove active wave base. Alsharhan et al. (2000) describedthese beds as representing a transgressive phase during thedeposition of the formation. They attributed their depositionto an open shallow shelf environment, below wave base with-out or with very rare terrigenous influx.

a

c

e

A

b

f

d

Fig. 6 Thin sections photographsof the Aruma Formation (scalebar = 1 mm, crossed nicols). aAlgal wakestone with obliquesection of Salpingoporellaarumaensis Okla. All bioclasticfragments are recrystallized,Khanasir Member. bForaminiferal algal wakestonewith oblique section ofSalpingoporella arumaensis Oklaand benthic foraminifera,Khanasir Member. c Algalpackstone with longitudinalsection of Griphoporella sp. inthe lower part, HajajahMember. dForaminiferal wackestone/packestone with miliolid test(Quinquiloculina sp.) and otherbioclasts embedded in micriticmatrix, Hajajah Member. eDismicites of the Lina Member. fForaminiferal wackestone/packstone with planktonic test(Globotruncana sp.) and otherbioclasts embedded in micriticmatrix, Lina Member

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The lithological sequence of the Hajajah Member com-prises of shale and marl at the base followed by limestoneswith abundant corals, stromatoporoids, and molluscs. Thinsections of the limestones of this member gave foraminiferalwackestone/packstone (Fig. 6e, f), coralline floatstone withabundant miliolid tests (Quinquiloculina sp). Smith et al.(1995) interpreted the similar lower beds of the SimsimaFormation (Campanian-Maastrichtian of United ArabEmirates) formed of sandy bioclastic limestone with concen-trations of solitary corals as having been deposited in shallowwater below wave base. Alsharhan et al. (2000) interpretedthese beds as having been deposited in open marine deposi-tional conditions. Also, Gameil (2005) indicated the presenceof the same hemispherical to dome-shaped morphotypes be-longing to cunnolitid corals prevailed during the deposition ofthe Simsima Formation as better adaptation to a slightlyhigher energy environment with terrestrial supply by havinglarge and elevated corallites which aided them to lie freely onthe soft substrate as well as to free themselves from the finesands and silts.

The lithological sequence of the Lina Member comprises ofshale and limestones with few badly preservedmolluscans. Thinsections of the limestones of this member gave wackestones ordismicrites with rare planktonics (Globotruncana sp.) indicatingcontinuing deepening in relatively open marine conditions.

The depositional environment of the studied threemembershas developed as a carbonate platform became deeper up-wards. They begin with rudist-dasyclad unit, which representsrelatively more restricted marine conditions, followed by themiddle coral-stromatoporoid unit, which represents relativelymore open, marine conditions and ending with dismicrites inthe upper one. This deepening has been a consequence ofdecrease in sediment accumulation with a rise in relative sealevel through deposition of the sequence. The most importantfactor causing the replacement was probably the decrease insediment flux, associated with turbidity. This change in thedepositional environment eventually favored the establish-ment of coral-stromatoporoids.

Conclusions

1. The Campanian-Maastrichtian Aruma Formation inKhashm Bowaibiyat area, Northeast Riyadh, SaudiArabia is subdivided into three members; they are in as-cending order: The Khanasir Member, the HajajahMember, and the Lina Member.

2. Fifty macrofossil species have been identified from thestudied section, 25 species of them belong to gastropods,17 to scleractinian corals, and 8 to bivalves. These fossilsare more abundant in the middle member, while the lowerand upper ones contain a few.

3. The studied section recorded a major Campanian-Maastrichtian marine transgression and drowning of thearea. It began with predominantly carbonate sedimentsabove the continental siliciclastics of the WasiaFormation and changed upward through the section fromlagoonal to back reef, rudist-dasycladecean unit, followedby a relatively deeper marine in coral-stromatoporoid inthe middle and upper units.

Acknowledgments The authors would like to extend their sincere ap-preciation to the Deanship of Scientific Research at King Saud Universityfor its funding this research group (RG-1436-036).

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