Late Paleocene to Early Eocene Marine Vertebrates From Northern Saudi Arabia

7/24/2019 Late Paleocene to Early Eocene Marine Vertebrates From Northern Saudi Arabia

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0 1999 Acade mic des scien ces / tditions scientifiqu es et medica les Elsevier SAS. Tous droits rkervfk.

Palaeontology / Pal6ontologie

(Vertebrate Palaeontology / Palbontologie des Vert6br6s)

Late Paleocene to Early Eocene marine vertebrates

from the Uppermost Aruma Formation (northern

Saudi Arabia): implications for the K-T transition

Dkouverte de vert&br& marins du Pakocene suphieur b ll?oc&e inj&ieur

au sommet de la formation dtlruma dans le Nord de ltlrabie Saoudite :

implications sur la transition K-T

Herbert Thomasa*, Jack Rogerb, Mohammed Halawani, Abdallah Memeshd, Patrick Lebretb,

Chantal Bourdillon , Eric Buffetaut, Henri Cappettaf, Claude Cavelierb, Didier Dutheilg,

Haiyan Tong, Denis Vasletb

a College de France et laboratoire de palbontologie, UMR 8569, Mu&urn national dhistoire naturelle, 8, rue Buffon,

75005 Paris,France

b BRGM, SGN, 3, av. C.-Guillemin, BP 6009, 45060 Orleans cedex 2, France

c Ministry of Petroleum and Mineral Resources, Deputy Ministry for Mineral Resources, Jeddah, Kingdom of Saudi Arabia

d BRGM Mission, Ministry of Petroleum and Mineral Resources, DMMR Jeddah, Kingdom of Saudi Arabia

e UMR 5561, 16, tour du Libgat, 75013 Paris, France

f Laboratoire de palkontologie, UMR 5554, kern, Universitb Montpellier-2, CC 064, place Eugene-Ba taillon,

34095 Montpellier cedex 5, France

g Laboratoire de pakontologie, UMR 8569, MusCum national dhistoire naturelle, 8, rue Buffon 75005 Paris, France

(Received 9 September 1999, accepted after revision 8 November 1999)

Abstract-A

new assemblage of marine vertebrates from northern Saudi Arabia, east of the Nafud,

leads us

to recon-

sider the age of the top unit of the Aruma Formation, the Lina Member, hitherto referred to the Maastrichtian. This

assemblag e contains the remains of a dozen selachia n and actinopterygian fishes, as well as those of a giant sea turtle

representing a new dermochelyid taxon. It suggests a Late Paleocene to Early Eocene age for this unit. Thi s new dating

and a revision of the stratigraphic position of the Lina Member demonstrate the existence, on a regional scale, of an

important hiatus at the K-T boundary. (0 1999 Acadkmie des scien ces / iditions scientifiqu es et medicale s Elsevier SAS.)

Arabian Peninsula/ Saudi Arabia / Aruma Formation / K-T boundary / late Paleocene/ Early Eocene/ fauna/

vertebrates

R&umk - Une faune irkdite de vertkbrks marins provenant du Nord de 1Arabie Saoudite, P lest du Nafud, nous am&e 2

rajeunir lunitk sommitale de la formation dAruma, le membre de Lina, jusqualors attribuk au Maastrichtien. Cette faune, qui

comprend les restes dune douzaine de poissons selaciens et actinoptkygiens, ainsi quune tortue marine gkante, representant un

dermochelyide nouveau, permet dattribuer P cette unit6 un Pge Palko&ne supkrieur 2 Locke infkrieur. Cette nouvelle datation et

la revision de la position stratigraphique du membre de Lina demontrent lexistence, P lkchelle regionale, dun important hiatus ~3

la limite K-T. (0 1999 Acadkmie des sciences / editions scient ifiques et mkdicales Elsevier SAS.)

phimule Arabique / Arabie Saoudite / formation dAmma / limite K-T / Pal&&me suphieur / fioche infhieur /

faune / vert&br&

Version abegee (voir p. 910)

Note communicated by Yves Coppens.

* Correspondence and reprints.

C. R. Acad. Sci. Paris, Scienc es de la terre et des plan&es / Earth & Planetary Scien ces

1999.329,905-912


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H. Thoma s et al.

1. Introduction

The Cretaceous-Tertiary boundary, known for mass

extinction, has not ceased to attract the attention of a

large number of researchers over the past 20 years. On

the Arabian Peninsula , most work concerning this sub-

ject was done so me time ago, though there are rare

exceptions (see Roger et al., 1998). In addition, a degree

of confusion exists in this area of the world with respect

to the nature of the K-T boundary, usually perceived as

transitional despite some precursor biostratigraphical

work (Hasson, 1985), wh ich showed at least locally, the

existence of a major hiatus.

Recent exploration in Saudi Arabia, has led to recon-

sideration of the nature of the K-T transition in the cen-

tral region of the Arabian plate. inve stigations in this

respect were largely obscured until the present by the

paucity of fauna1 asso ciations and the absence of strati-

graphically useful faunas in beds straddling the K-T tran-

sition (Lina Member). Revision of some work was made

possib le because of the recent discovery in the northern

region of the Kingdom, to the east of the Nafud, of atypi-

cal marine vertebrate foss ils in sediments of the Lina

Member, hitherto attributed to the Maas trichtian. Analy-

sis of these fos sils, principally collected to the east of the

small village of Linah, have led us, as will be seen fur-

ther on, to considerably rejuvenate this unit, denoting

also the existence of a major hiatus at the K-T boundary,

which conforms readily to ideas which have emanated

from more recent work on the Arabian peninsula.

2. Geological setting

In centra l and northern Arabia (figure), Late Creta-

ceous deposits form arc-shaped outcrops that are

roughly draped around the Proterozoic basement to the

west. These deposits constitute a fairly continuous strip

extending from the edge of the Rubal Khali sand-sea in

the south, to the Riyadh area in central Arabia; further

north, they skirt the east and the northeast of Great

Nafud sand-sea and continue into Iraq. Studied by petro-

leum g eologists during the early days of oil exploration

in Saudi Arabia (Steineke et al., 1958; Powers et al.,

1966; Powers, 1968), these deposits were named the

Aruma Formation and attributed a Campanian to Maas-

trichtian age. Detailed mapping at 1:250 000 scale (Vas-

let et al., 1988, 1991) in the Riyadh area, contributed to

the collection biostratigraphic data that reconfirmed the

earlier conclu sions of the oil geologists, i.e., a Late Cam-

panian to Maastrichtian age for the Aruma Formation.

3. The Aruma Formation in the type

locality: description and subdivision

The first oil geologists recognised that the Aruma For-

mation, defined in a type section on the AIAramah Pla-

teau near Riyadh, was composed of two main units, the

c] Quaternary eolian sands

B Mesozoic

m Cenozoic volcanic rocks

LE Paleozoic

m Neogene m Arabian shield

FZl Paleogene

/

Figure. Geological sketch map of northern Saudi Arabia showing

fossil vertebrate localities of Linah.

Situation gkologique des gisements 2 vert6br6s fossile s de Linah

dans le Nord de IArabie Saoudite.

lower boundary of the formation being a minor uncon-

formity above the Albian to Turonian Wasia Formation

deposits. Their b asal informal Atj member was a thick

unit, mainly composed of carbonates with rudists; the

overlying informal Lina Member was principally com-

posed of shale, and was thinner than the Atj member

(Powers et al., 1966; Powers, 1968). This two-member

division was further justified by a non-conformable con-

tact between the two members, seen at outcrop but

more particularly in drill cores where it was described as

an angular discordanc e (Redmond, in Powers, 1968).

Using this work, El-Asaad (1983a, b) maintained the for-

mal Lina Member and divided the informal Atj member

into two formal members: the Khanasir Member at the

base and the Hajajah Member above.

The Aruma Formation is overlain by the Umm er

Radhuma Formation, Paleocene to Early Eocene in age

(Steineke et al., 1958; Sander, 1962; Powers et al., 1966;

Powers, 1968); this formation is composed of limestone

and dolomite deposited on a marine platform. At out-

crop, the dolomitic limestone of the Umm er Radhuma

Formation overlies the Lina Member dolomitic shale in

apparent conformity. Al-Asaad (1983a) confirmed the

conformable and gradational character of this contact.

However, a compilation of data on a regional scale

(Powers, 1968) suggested a possib le lacuna of deposits

approximately straddling the K-T transition; Powers

(1968) mentioned the possibility of a non-conformable

relationship between the Umm er Radhuma and Aruma

C. R. Acad. Sci. Paris, Scien ces de la terre et des plan&e s / Earth & Planetary Scien ces

1999.329,905-912


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Formations. This hypothesis was confirmed by Hasson

(1985) who found a major hiatus at the Cretaceous-

Tertiary boundary in the Rubal Khali.

4. The problematic Maastrichtian age

of the Lina Member

4.1. The Lina Member in central and northern Arabia

If , as mentioned above, the precise age of the onset of

the last transgression during the Late Cretaceous is still

under discussion for central and northern Arabia, most

authors agreed on the standard proposition for the Lina

Member: Maastrichtian for the oil geologists (Powers et

al., 1966; Powers, 1968), Late Maastrichtian for El-

Asaad (1983b) and Vaslet et al. (I 988, 1991).

In fact , this age is still a problem: the undoubted

Maastrichtian fauna1 association described by Powers

(1968) from subsurface samples (with Omphalocyc/us

macroporus and Lofiusia sp.), was never found again

during surface sampling by the geologists who restudied

the type sections (fi rst El-Asaad then the DMMR/BRGM

team that mapped central Arabia). Everywhere, the out-

crops were very poor in foss ils and no large benthic

foraminifera were found. Faced with this diff icul ty, El-

Asaad and Vaslet used El-Khayals work (1969, 1974)

for dating the Lina Member. They mention the presence

of Omphalocyclus in shale underlying the dolomitic

limestone of the Umm er Radhuma Formation, the latter

containing an uncontested Tertiary fauna. However, the

age of the shale was not confirmed by Hasson (1985),

who noticed that this rock was azoic and proposed an

Early Paleocene age for this unit. This contradictory re-

sult demonstrates that the question of the origin and ex-

act stratigraphic position of El Khayals facies with

Omphalocyclus is still open. Did he really sample the

Lina Member, or did the samples come from the top of

the underlying Hajajah Member? It should also be

pointed out that the exact origin of the samples studied

by El-Khayal in his PhD thesis (1969) is uncertain, and

that the precise location of his cutting samples from the

Arabian American Oil Company (ARAMCO) was not

confirmed during the paleontological study.

4.2. The lateral equivalents of the Lina Member in the

Arabian Peninsula

In central and northern Arabia, the Lina Member has a

remarkable lateral continuity , both in thickness (about

30 m) and in fac ies (predominantly alternating shale and

subsidiary dolomite). Outside this area, the data com-

piled for the Late Cretaceous and Early Tertiary deposits

in the Rubal Khali, Qatar, Oman, and Yemen (see argu-

ments presented below) demonstrate the ubiquity of a

shale or marl unit above the top of the rudist limestone

at the top of the Aruma Formation (Aruma Group in the

eastern Arabian Peninsula), and below the Paleogene

limestone of the Umm er Radhuma Formation. If it is

supposed that these units can be correlated on a regional

scale, the question of their age remains an open one; in

fact , there is strong disagreement between the different

authors. If in central to northern Arabia, this shale unit

(Lina Member) is considered as part of the Aruma For-

mation, Hasson (I 985) demonstrated that this unit, com-

posed of dark pyrit ic and carbonaceous shales with

sparse benthic fauna including Lockhartia haimei, is

younger than basal Paleogene in the Rubal Khali basin.

It is the same in Qatar, where Sugden and Standring

(1975) recognised that this shaly and marly Lockhartia-

bearing unit, the informal Shammar Shale member, cor-

responds to the base of the Umm er Radhuma Forma-

tion. This shale-marl unit was also identified on the

southern edge of the Arabian plate, in the interior of the

Sultanate of Oman (Shammar Shale member, Hughes

Clarke, 1988), in Yemen (Beydoun and Greenwood,

1968) and in Dhofar (Atayr member, Roger et al., 1989,

1994), where it consistently occupied the same strati-

graphic position at the base part of the Umm er

Radhuma Formation, and consistently contains Lockhar-

tia sp.

4.3. The Lina Member to the east of the Great Nafud and

the stratigraphic position of the fossil beds

East of the Great Nafud, the Lina Member is exposed

in small cuestas about 30 m high comprising alternating

ochre dolomitic shale, dolomitic marl and minor off -

white dolomite (figure). It was studied in detail during

the mapping of the Turubah quadrangle at 1:250 000

scale, by a joint DMMR/BRGM team (Lebret et al.,

1999). The unit, exposed to the north and northeast of

Linah town over a distance of more than 30 km, shows a

clear sequential organisation, consisting of fi ve se-

quences each several meters in thickness. The elemen-

tary cyc le, which is repeated several times , begins with

dolomitic shale grading into dolomitic highly biotur-

bated marl with a nodular aspect, and overlain by sev-

eral thin dolomitic beds that, again, are strongly biotur-

bated. Close to the top of the member, a layer occurs

that is enriched in bipyramidal quartz and siliceous nod-

ules that are interpreted as former anhydrite nodules.

The lower and middle parts of the Lina Member are very

poor in fossils, except for a few plant, coral and decalci-

fied bivalve casts. Only the upper 5 m, just below the

Tertiary Umm er Radhuma Formation dolomite, yielded

many fauna1 remains. The most diversified macrofauna

is found in the topmost dolomite bed, which also

yielded an association of various molluscs (bivalves, gas-

tropods), and reef-type colonial and solitary corals of

unspecific age. Among gastropods, which are not easily

identifiable because o f crushing, a large strongly winged

strombid is dominant, besides poorly preserved impres-

sions of cerithids and a Rostellaria cast - cf . Rostellaria

(hippochrenes) amp/a. Pelecypods are not better pre-

served, with the exception of impressions of Corbula

@icorbulal gr. exarata, recognizable by their curvature

and ornamentation. The underly ing Lina Member shale

Late Paleocene to Early Eocene marine vertebrates from the Uppermost Aruma F ormation (northern Saudi Arabia)

C. R. Acad. Sci. Paris, Scienc es de la terre et des plan&es / k&h & Planetary Scien ces

1999.329,905-912


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H. Thomas et al.

yielded hundreds of bone fragments from a giant marine

turtle associate d with many selachia n and actinoptery-

gian teeth, m ost of them sma ll and only discovered by

washing the samples .

5. The vertebrate fauna from the Lina

Member

Vertebrate remains collected in the shaley horizon of

the Lina Member contain on one hand, a relatively poor

ichthyofauna made up mainly of isolated teeth com-

monly reduced to a state of debris, and on the other, a

very large number of isolated oss icles belonging to a

dermochelyid turtle.

5.1. Selachians

The Lamniformes are represented by a single tooth,

the morphology of which resembles Cretolamna maroc-

cana which is only known from the Maastrichtian; this

tooth is however neither perfectly preserved nor particu-

larly typical. The Orectolobiformes are in quite diverse

contrast since they are represented by three different

genera; Orectolobus, Ginglymostoma sp. and Plicatoscyl-

lium sp. Whilst several very fragmentary scyliorhinid

teeth recall those from the Paleogene genus Premontreia,

the batoids constitute the most numerous and varied

group. The rhinobatoids sensu lato, are represented by

two distinct forms (Rhinobatos sp. and Rhinobatoidei in-

det.), the dental morphology of which resembles that of

certain sp ecies from the Maastrichtian of Morocco. Sev-

eral teeth with a very distinc t and original morphology,

can be attributed to Dasyatoidea. Lastly, the Mylio-

batidae are represented by large teeth or tooth debris

characterized by their greater thickness; certain teeth

show morphology close to that of Rhombodus, a genus

which does not cross the K-T boundary. Unfortunately

these teeth, in particular their roots, are consistently

damaged. In fact they may well be lateral teeth of large

Myliobatidae indet.

5.2. Actinopterygians

The Lina Member actinopterygians are represented by

more than a hundred isolated teeth and a few vertebrae

belonging to three distinct taxa, only one of which has

been identified to genus level.

About 15 grinding teeth, are diamond to sub-diamond

shaped and belong to an indeterminate pycnodontiform.

Their sizes vary from a few millimetres to 14 mm in

length. Pycnodontiform teeth have been reported from

the Paleocene Jubal Umm Himar Formation of south-

western Saudi Arabia (Madden et al., 1995).

Around ten acuminate teeth are attributed to the au-

lopiform genus fnchodus. The largest of these teeth, al-

though broken at its apex, measures 45 mm. These teeth

are very similar to those of Enchodu s libycus from the

Maastrichtian of Egypt and Morocco. The genus Encho-

dus is very common in the Upper Cretaceous on the

Arabia-African continent where it is reported from the

Maghreb, Egypt, subsaharan Africa and the Negev. A

different form of E. libycus is also present in the Moroc-

can Danian (Arambourg, 1952), as well as in interca-

lated sediments in the Deccan traps, the ages of which

are situated on both sides of the K-T boundary (Patter-

son, 1993).

The most commonly found actinopterygian remains in

the Lina Member, are represen ted by pharyngian teeth

with an eyelash shape and massive incisiform teeth.

These teeth resemble those of the genus fotrigonodon

which occurs in the Eocene of the Anglo-France-Belgian

basin and in the Eocene of Africa. Although the longest

incisiform tooth is more than 25 mm in length, other

broken teeth, mus t have attained even greater dimen-

sions. The genus Eotrigonodon is conventionally consid-

ered as a tetraodontiform. However doubt h as been cast

on its attribution to the tetraodontiforms by Patterson

(1993). In fact, teeth conventionally attributed to the Eot-

rigonodontidae are, according to this author, probably

pycnodontiform teeth, the pycnodontiforms being com-

monly found in the same dep osits.

5.3. Chelonians

Testudin es, Cryptodira, C helonioidea, Dermochelyidae:

gen. and sp. nov.

The dermochelyid remains are by far the most com-

mon foss ils yielded by the Lina Member. They are repre-

sented by several hundred isolated os sicles , polygonal in

shape, ranging from 20 to 45 mm in diameter, very

thick, some more than 20 mm in thickness, and deeply

sculptured on the external surfaces, with wrinkles and

tubercles radiating outward from the centre of each os-

sicle. These ossicles represent the epithecal shell mosaic

of a new dermochelyid sea turtle (see Tong et al., in this

issue).

The family Dermochelyidae is recorded from the Late

Cretaceous to the Recent. Two dermochelyid taxa are

known from the Late Cretaceous: Corsochelys from the

Campanian of the USA and Mesodermochelys from the

Maastrichtian of Japan. These primitive dermochelyids

have a thecal shell like other chelon ioid sea turtles,

without an epithecal shell mosaic. Few dermochelyid

turtle remains have been reported from the Paleocene :

fosphargis from the Latest Paleocene of Denmark, is the

only Paleocene record of the family. In the Eocene there

is a remarkable diversity of dermochelyids from all over

the world. Except for Eosphargis from the Lower Eocene

of Europe, which is a dermochelyid without a shell mo-

saic, and Thalas soche lys testei from the Lower Eocene

of Tunis ia, known only by a skull, in all others the thecal

shell is replaced by an epithecal shell composed of a

large number of small o ssicle s forming a shell mosaic.

908

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1999 329,90 %912


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6. Discussion and conclusions

6.1. Age of the Lina Member

Although not ver y diverse, the malacofauna seems to

indicate an Eocene age, judging by a cast of Rode//aria

ampla and impressions of Corbula (Bicorbula) gr. ex-

arata. Although the species exarata is considered as typi-

cal of the Middle Eocene, various similar forms have

been described from the Early to Middle Eocene of Paki-

stan and the northern part of Africa, from Egypt to Sene-

gal. Conversely, these species seem to be unknown in

the Upper Cretaceous, or even the Paleocene. This age

suggestion is confirmed by the malacofauna from a

much more productive locality, sampled by one of us

(C.C.) in the Lina Member in central Arabia. This site is

located south o f the Wadi as Sahba, in the Ar Riyad

quadrangle (Vaslet et al., 1991). I t has yielded internal

casts, sometimes silicified, of Pleurotomaria spp. includ-

ing P. cf . bianconii, Velates sp. af f. tibeticus, Campa-

nilopa spp., a large strombid, cf . Rostellaria (Hippo-

chrenes) ampla, cf . Arrhoges (Drepanochilus) sp., cf .

Surcula ingens, naticids (S./J, bullids, Corbula IBicor-

hula) sp., besides corals and various nautiloids identified

by H.Tintant (in Vaslet et al., 1991). With the exception

of the nautiloids, which are Maastrichtian in age and

may be reworked from the underlying Hajajah Member,

in which they are locally abundant, the malacofauna

from Wadi as Sahba, besides genera which cross the

Cretaceous-Tertiary boundary, is characterized by typi-

cally Eocene genera and species, such as Velates, Pleu-

rotomaria bianconii, Rostellaria ampla, Surcula ingens,

Corbula (Bicorbula), and, by the absence of any exclu-

sively Cretaceous, or even Paleocene, element.

The Lina Member ichthyofauna shows an unusual

composition that does not enable attribution of a precise

age. The selachians in particular, are different from both

the rich Maastrichtian fauna1 assemblages, collected

these last few years from Syria, Israel and Egypt (cur-

rently being studied) and those of the Late Paleocene of

Jordan (H.C.) . In addition, as no data exists on Early

Paleocene fauna from this region of the Middle East, it is

all the more di ffi cul t to make a categorical determination

with respect to the age of the Saudi Arabian fauna. How-

ever the presence, on one hand of Myliobatidae (al-

though this family is represented in the Campanian and

Maastrichtian, but by species showing very different

morphology) and on the other hand, the absence of spe-

cies known in the Maastrichtian of the region, tend to

favour a post-Cretaceous age. Whilst a Danian age can-

not be ruled out, i t should be stressed that the selachians

are in any case very different to those from the Danian of

Morocco.

As is the case for the selachians, the biostratigraphic

data provided by the rare actinopterygians, identified

from isolated teeth, are very ambiguous. The presence of

indeterminate pycnodontiforms does not contribute to

the argument since their remains are recorded from the

Mesozoic into the Cenozoic. Whilst the Enchodus teeth

are close to f . lybicus and suggest a Maastrichtian age,

the incis iform and pharyngian teeth, doubtfully attrib-

uted to the Tetraodontiformes, tend rather to suggest a

post-Cretaceous age because o f their large dimensions.

This said, it can be underlined that the very poor state of

preservation of the ichthyofauna suggests that it is in

part, undoubtedly reworked from a Maastrichtian hori-

zon. The existence of reworked material is manifest

when seen in the light o f the discovery, in the Lina Mem-

ber, of a rolled ammonite in the form of a cobble along

with a single fragment of a plesiosaur tooth. The major

lacuna of post K-T boundary deposits, which may corre-

spond to a major part of the Paleocene, must have re-

concentrated, along the Tertiary transgression base, nu-

merous fossi ls eroded out of the unit lying directly

below.

Be that as it may , with regard to the dermochelyid

remains, several evolutionary trends have been recogn-

ised in the history of the Dermochelyidae, including a

progressive decrease in mosaic shell thickness, a gradual

increase in the prominence of the carapace ridges and a

gradual decrease of the sculpture on the external surface

of the ossicles (Wood et al., 1996). The ossicles from

Saudi Arabia are the thickest among all the known der-

mochely id shell elements, the shell is the most deeply

sculptured and the carapace ridges are absent since no

keeled ossic les are present among the abundant material

from the locality. Thus the dermochelyid turtle from

Saudi Arabia is the most primitive known representative

of the dermochelyids possessing an epithecal shell mo-

saic. These primitive features suggest that the specimens

from Saudi Arabia are older than the Mid-Late Eocene,

at which time dermochelyids with a more advanced epi-

thecal shell mosaic are known.

Overall , taking into account all stratigraphic and

palaeontological data, we consider that the Lina Mem-

ber deposits ought to be considered as much younger

than hitherto thought, and we thus propose a Late Paleo-

cene or Early Eocene age.

6.2. Implications on the Cretaceous-Tertiary boundary

in central and northern Saudi Arabia

As we have seen previously, the shaly unit occurring

at the base and initiating the Umm er Radhuma Forma-

tion, shows a vast extension and is known throughout

the Arabian platform. It is indicat ive of major changes in

sedimentary conditions, marked by the disappearance of

rudist bearing platform carbonates and the initiation of a

new depositional cycle . The Umm er Radhuma Forma-

tion, characterized by depositional confinement, indi-

cates an inversion of the tendency which saw the end of

the progradation of the rudist platforms and the begin-

ning of a transgressive tendency which imposed itsel f at

the end of the Paleocene or beginning of the Eocene.

The maximum flooding of the firs t Tertiary transgression,

was only attained in the Early Eocene, as shown by pe-

Late Paleocene to Early Eocene marine vertebrates from the Uppermost Aruma F ormation (northern Saudi Arabia)

C. R. Acad. Sci. Paris, Sciences de la terre et des plan&es

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1999.329.905912


6/8

H. Thomas et al.

lagic argillaceous limestones with planktonic foramin-

ifera (Hasson, op. cit. ), which overlie the basal shales in

the Rubal Khali basin.

The dating of the Lina Member and the revision of its

stratigraphical position shed a quite different light on the

Cretaceous-Tertiary boundary in central and northern

Arabia. Even if they were not able to prove it, the first

researchers for a long time suspected the existence of a

depositional gap at the K-T boundary, basing this suspi-

cion on regional data, but hindered in this thought pro-

cess by the supposed Maastrichian age of the Lina

Member and its conformable contact observed with the

overlying Umm er Radhuma Formation limestones. The

Late Paleocene to Early Eocene age of this member fi -

nally brings proof of a major hiatus of about 10 Ma.

Attested to in the neighbouring regions of Arabia, for

example in the Rubal Khali basin, in Qatar and in

Oman, it also very logically affected the western margin

of the Arabian platform. Only on the collapsed margins

of the Arabian plate, for example in the Oman Moun-

tains (Roger et al., 1998) or in the Huqf (Plate1 et al.,

1992) of Oman was a continuous recording of the

Cretaceous-Tertiary transition possible, as witnessed by

the existence of Danian deposits. It is however probable,

in the absence of suffi cient ly precise dating, that the ex-

tent of the hiatus may var y quite significantly from one

region to the next, in the interior of the plate. It is rea-

sonable to suppose a degree of onlap of the Tertiary

transgression across the Cretaceous substratum. The very

marginal position of the depositional belt of the Lina

Member, close to emerged shallows (?) made up of the

Arabian shield, strongly suggests that the region was

probably transgressed later than the Rub al Khali basin,

possibly as late as the Early Eocene.

Version abegee

Introduction

Dans la pCninsule Arabique, le passage Cr&ac&Tertiaire

fai t depuis longtemps lobjet dappreciations contradictoires :

celui-ci serait transitionnel ou marque par un hiatus corres-

pondant 2 une importante lacune. Si certaines regions sont

bien documentCes, montrant, g lexemple de la marge oma-

naise, lexistence dune continuite des dep8ts (Plate1 et al.,

1992 ; Roger et al., 19981, ou au contraire, en domaine plus

interne de la plaque arabique (Rubal Khali), celle dun hia-

tus (Hasson, 1985), largumentation est en revanche moins

convaincante en Arabie Saoudite centrale et septentrionale,

bien que le passage K-T y soit diicrit comme transitionnel.

Les r&entes decouvertes de vertebr& marins 2 lest du

Nafud dans le Nord de IArabie, dans le membre de Lina, au

sommet de la formation dAruma, qui nous amsnent ici &

reconsiderer lsge de ces dep8ts jusque-12 repute Maas-

trichtien, demontrent lexistence, dans cette region, dun im-

portant hiatus 2 la limite K-T.

Le membre de Lina

Le membre de Lina represente le membre sommital de la

formation dAruma (El Asaad, 1983a et b), qui forme une

ceinture daffleurement continue depuis le grand desert du

Rubal Khali jusquau Nafud, au nord du pays. Lithologique-

ment distinct des unit& basales plus carbonatees et riches en

rudistes, le membre superieur de la formation dAruma mon-

tre une composition principalement argileuse et accessoire-

ment dolomitique ; il est repute passer transitionnellement

aux calcaires dsge Paleoc+ne 2 fioc?ne infirieur de la forma-

tion dUmm er Radhuma.

Depuis les premiers travaux des petroliers, lsge du mem-

bre de Lina est classiquement donne pour Maastrichtien

(Powers et al., 19661, ou Maastrichtien superieur (El-Khayal,

1969 ; El Asaad, 1983b ; Vaslet et al., 1988, 1991). Cet gge,

repris dun auteur B lautre, sappuie principalement sur la

presence de grands foraminif?res benthiques maastrichtiens,

Omphalocyclust Loftus ia, d&rits dans des equivalents la&

raux en subsurface, par Powers (1968) et El-Khayal (1969,

19741, mais jamais trouv Cs 2 ltieurement.

Les incertitudes quant 5 l?ige Maastrichtien du

membre de Lina

Le recours a des equivalents 1atCraux en subsurface, pour

dater le membre de Lina, sexplique par le caractere peu

fossilif ire de ces depats, jusque-12 ditpourvus, a laffleure-

ment, de toute faune dint&@t stratigraphique. Ces datations

demeuraient d& lors fragiles.

Dans le Rubal Khali, les travaux de revision biostratigra-

phique entrepris par Hasson, qui a repris le materiel fossile

recueilli en forage et r&tudie lunite argileuse sit&e 2 la

base des calcaires tertiaires de la formation dUmm er Rad-

huma, infirmaient les conclusions initiales, en suggerant un

Ige Palko&ne infkrieur pour cette uniti: argileuse, qui se

cor&le avec le membre de Lina.

Plus rCcemment, en Arabie centrale, dans le secteur de Ar

Riyad, la dkcouverte 2 Iaffleurement, dans le membre de

Lina, dune curieuse association de mollusques daf fmit& iler-

diennes et de nautiles maastrichtiens, soulevait a nouveau le

problkme de lsge du membre de Lina (Vaslet et al., 1991).

Une r&ision de lgge de cette unite semblait done nttces-

saire : elle simpose aujourdhui, g&e P la dkcouverte en

1998, dans des terrains du membre de Lina 2 lest du Nafud,

effect&e dans le cadre du lever de la feuille de Turubah,

dune faune atypique de vertebr& marins dlge Paleoc?ne

non basal.

La faune de verti?.brk du membre de Lina & Pest du

Nafud

Les dkp8ts argileux du membre de Lina, qui affleurent sur

plus de 30 km sous forme de petites cuestas au nord et au

nord-est du village de Linah, ont livre une ichthyofaune

910

C. R. Acad. Sci. Paris, Scienc es de la terre et des plan&es / Earth & Pkmefary Scien ces

1999 329,905912


7/8

Late Paleocene to Early Eocene marine vertebrates from the Uppermost Aruma Formation (northern Saudi Arabia)

marine relativement pauvre, composee de dents de selaciens

et dactinopterygiens, associee en divers endroits 2 de tr&

nombreuses plaques epithecales isolees dune tortue marine

geante.

Bien que pauvrement rep&sent&, les shlaciens sont ce-

pendant assez diversif . 11s comprennent 9 taxons dist incts ,

dont un Lamniforme Cretolamna f. maroccana), un Scylio-

rhinidae indetermint, 3 genres dOrectolobiformes (c f. Orec-

tolobus,Ginglymostoma

p. Plicatoscyllium sp.) et divers ba-

tdides, qui constituent dailleurs les restes les plus nombreux

Rbinobatossp., Rhinobatoidei indet., Dasyatoidea indet.,

Myliobatidae indet. ou Rbombodus). ette association, qui

correspond z? une faune nCritique 1 littorale, presente une

composition tr& inhabituelle, puisque les differentes espcces

demeurent inconnues P la fois dans les faunes du Maas-

trichtien de Syrie, dIsra&l ou dEgypte, comme dans celles du

PalCocgne superieur de Jordanie.

Une centaine de dents isolees appartiennent g des acti-

nopterygiens dont un Pycnodontiforme indetermine, un

Aulopiforme proche d&zcho&s

Zibycus,

onnu notamment

dans le Maastrichtien dEgypte et du Maroc, ainsi que le

genre tertiaire

Eotrigonodon

dont les restes sont les plus

frequents.

La faune des gisements de Lina se distingue surtout par

labondance des plaques osseuses &pith&ales dune tortue

marine, cara&ristiques de la famille des Dermochelyidae

representee uniquement de nos jours par la tortue luth Der-

mocbelys oriacea).Par la forte ornementation et la grande

Cpaisseur de ces plaques osseuses , ainsi que par labsence de

c&es ant&o-postCrieures, le dermochelyide dArabie se dis-

tingue clairement de toutes les autres formes fossiles (voir

Tong et al., 1999).

Discussion sur l&e des dep8ts

Alors que plusieurs Cl&ments de la faune ichthyologique

sont indicatifs dun ge Maastrichtien, en particulier Creto-

lamna cf. maroccanaet Encbodussp., dautres 61Cments

plaident plut& en faveur dun sge Tertiaire (e.g. Myliobatidae

et cf. Eotrigonodon). a tr?s mauvaise conservation de cette

faune laisse penser que celle-ci est sans doute en partie

remaniee 2 partir des niveaux maastrichtiens. Lexistence de

remaniements est manifeste, 2 en juger par la decouverte

dans le membre de Lina dune ammonite roulee sous forme

de galet et dun unique fragment de dent de pl&iosaure. La

faune ichthyologique est, par ailleurs, pauvrement rep&en-

tee, cornparke 2 la tortue marine, dont les restes sont bien

plus abondants. Les caract&ist iques uniques des plaques os-

seuses de cette tortue en font le plus pr imiti f des Dermo-

chelyidae possCdant une carapace epithkcale en mosdique.

Bien que cette famille soit connue depuis le C&ace sup&

rieur, les formes poss&dant une telle carapace epithecale en

mosaique ne sont pas connues avant ll?oc&e moyen P su-

perieur. Au total, compte tenu des don&es paleontologiques

nouvelles et aussi des donnees sedimentologiques et strati-

graphiques P la fois locales et regionales, lgge du membre

de Lina doit etre consid&ablement rajeuni. Bien que cet ge

soit diffici le a pr&iser, nous estimons quil est compris dans

lintervalle PalCocene superieur i fiocene inferieur.

Implications sur la nature de la transition

C&ac&Tertiaire en Arabic centrale et

septentrionale

La &vision de 1Pge du membre de Lina implique

Iexistence dun important hiatus, dune duree proche de

10 Ma, P la limite Cr&ac&Tertiaire, en Arabie centrale et

septentrionale. Ce rCsultat est plus conforme aux donnkes

regionales, qui montrent un contraste net entre le domaine

interne de la plaque arabique et ses marges. Ainsi, en do-

maine interne, 5 lexemple du Rubal Khali (Hasson, 19851,

du Qatar (Sugden et Standring, 19751, de 1Oman interieur

(Hughes Clarke, 19881, du Dhofar (Roger et al., 19891, du

Yemen (Beydoun et Greenwood, 1968), comme en Arabie

centrale et septentrionale, on rel?ve partout une importante

lacune des termes inferieurs du Paleogene. Seules des condi-

tions geodynamiques particulieres, liees ?t leffondrement des

marges de la plaque arabique, comme dans le Huqf (Plate1 et

al., 1992) ou dans les montagnes dOman (Roger et al.,

1998), favorisent lenregistrement du passage C&a&-

Tertiaire sans lacune.

Acknowledgements. This study was carried out within the framework of an agreement between the Saudi Arabian Deputy

Ministry for Mineral Resources and the French Bureau de recherches g6ologiques et mini&es . Publication of these results was

made possib le thanks to the support and authorization of Dr. M.A. Tawfiq (Assistant Deputy Ministry for Survey and Exploration.

Deputy Ministry for Mineral Resou rces), to whom the authors express their grateful thanks.

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Late Paleocene to Early Eocene Marine Vertebrates From Northern Saudi Arabia