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Journal of Asian Earth Sciences 19 (2001) 45±60
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Fluvial-shallow marine-glacio¯uvial depositional environments of the
Ordovician System in Jordan
B.S. Amireh a,*, W. Schneider b, A.M. Abed a
a

b

Department of Geology, University of Jordan, Amman, Jordan
Institut fuÈr Geowissenscaften, TU Braunschweig, Postfach 3329, Braunschweig, Germany

Abstract
The Ordovician System, cropping out in southern and west-central Jordan, consists entirely of a 750 m thick clastic sequence that can be
subdivided into six formations. The lower Disi Formation starts conformably above the Late Cambrian Umm Ishrin Formation. According to
Cruziana furcifera occurring in the upper third of the Disi Formation, an Early Ordovician age is con®rmed. The Disi Formation, consisting
mainly of downstream accretion (DA) ¯uvial architectural element, was deposited in a proximal braidplain ¯owing N±NE from the
southerly-located Arabian±Nubian Shield towards the Tethys Seaway. The braidplain depositional environment evolved into a braidplain-dominated delta through the middle and upper parts of the Disi Formation and the lower part of the overlying Um Saham Formation.
The delta was replaced by siliciclastic tidal ¯ats, that in turn evolved into an upper to lower shoreface environment through the upper part of
the Um Saham Formation. The depositional environment attained the maximum bathymetric depth during the deposition of the lower and

central parts of the third unit, the Hiswa Formation, where offshore graptolite-rich mudstone with intercalated hummocky cross-strati®ed
tempestites were deposited. The Tethys Seaway regressed back through the upper part of the Hiswa Formation promoting a resumption of the
lower±upper shoreface sedimentation. Oscillation between the lower to upper shoreface depositional environment characterized the entire
fourth unit, the Dubaydib Formation, as well as the Tubeiylliat Sandstone Member of the ®fth unit, the Mudawwara Formation. The
depositional history of the Ordovician sequence was terminated by a glacio¯uvial regime that ®nally was gradually replaced by a shoreface
depositional environment throughout the last unit, the Ammar Formation. q 2001 Elsevier Science Ltd. All rights reserved.

1. Introduction
An Ordovician sequence consisting invariably of sandstone and silt±mudstone sediments crops out in southern
Jordan and the area along the eastern margin of Wadi
Araba (Fig. 1). The Ordovician System in Jordan has been
studied by many authors, including Qunnel (1951), Bender
(1968), Lloyd (1968), Selley (1970), Masri (1988), Powell
(1989) and Khalil (1994). Some of these studies has been
summarized and correlated with Ordovician outcrops
throughout the Middle East countries by Alsharhan and
Nairn (1997). Most of the above studies involved lithostratigraphic subdivision of the Ordovician System into various
units, but without giving details of their depositional environments. Amireh (1993) conducted a sedimentological
investigation aimed at distinguishing between the Ordovician Disi Sandstone and the similar overlying Early Cretaceous Kurnub Sandstone, and consequently extended the
known occurrence of the Ordovician System 60 km northward of the limit recorded in the previous geologic maps.

* Corresponding author. Fax: 1962-6-5348932.
E-mail address: bamireh@sci.ju.edu.jo (B.S. Amireh).

Makhlouf (1992, 1998) determined the depositional environment of random parts of the Ordovician System.
Therefore, it appears that a comprehensive sedimentological study of the Ordovician System has not been undertaken up until now. Thus, the present work documents the
detailed sedimentology of the Ordovician System based on a
systematic facies analysis and aims to determine the development of depositional environments during the Ordovician
Period.

2. Geologic setting
In southern Jordan, the clastic Ordovician System starts
conformably above the Cambrian Umm Ishrin Formation,
and is overlain, also conformably, by the Silurian Batra
Mudstone Member of the Ordovician±Silurian Mudawwara
Formation. The contact with the underlying Cambrian sediments is problematic. It is based mainly on the color change
from brown, characteristic of the Cambrian Umm Ishrin
Sandstone, to white which is diagnostic of the Disi Sandstone (Bender, 1968).
Very likely, this lithologic contact does not represent the

1367-9120/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

Fig. 1. Outcrops of the Ordovician System in Jordan and location of the studied pro®les.

actual boundary between the Cambrian and the Ordovician
Systems, since this study proves that the ®rst reliable indicator of the Early Ordovician, Cruziana furcifera, is found
130 m above the base of the formation. Therefore, the age of
the lower 130 m of the Disi Formation may well be older
than Early Ordovician, that is Late Cambrian.
The Ordovician System attains an outcrop thickness of

750±800 m in southern Jordan and can be divided into six
formations (Powell, 1989), in ascending stratigraphic order:
Disi Formation, Umm Sahm Formation, Hiswa Formation,
Dubaydib Formation, Mudawwara Formation and Ammar
Formation. Excluding the lower Disi Formation, these

formations are exposed only in southern Jordan.
Along the eastern margin of Wadi Araba (Fig. 1), only the

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60
Table 1
Fluvial lithofacies identi®ed in the Ordovician System, Jordan, from Miall (1996), and proposed (this study) tidal and marine lithofacies
Facies code

Lithofacies

Sedimentary structures

Gmm
Gcm
Gt
Gp
St
Sp

Sr
Sh
Sm
Ss
Sl
Spo
Sto
Sf
Sw
Hcs
Scs
Fr
Fm
Fl

Matrix-supported, massive gravel
Clast-supported massive gravel
Gravel, strati®ed
Gravel, strati®ed
Sand, medium to very coarse, may be pebbly

Sand, medium to very coarse, may be pebbly
Sand, very ®ne to coarse
Sand, very ®ne to very coarse, may be pebbly
Sand, ®ne to coarse
Sand, very ®ne to coarse, may be pebbly
Sand, very ®ne to coarse, may be pebbly
Sand, ®ne to coarse
Sand, ®ne to coarse
Fine sand with mud
Fine sand with mud
Fine sand and mud
Fine sand and mud
Sand, silt, mud
Sand, silt, mud
Sand, silt, mud

Weak grading
Pseudoplastic debris ¯ow
Trough cross-beds
Planar cross-beds

Solitary or grouped trough cross-beds
Solitary or grouped planar cross-beds
Ripple marks of all types
Horizontal lamination, parting lineation
Massive or faint lamination
Broad, shallow scours
Low-angle (,158) cross-beds
Overturned planar cross-beds
Overturned trough cross-beds
Flaser-rippled strati®cation
Wavy-rippled strati®cation
Hummocky cross-strati®cation
Swaley cross-strati®cation
Ripple- to climbing ripple cross-lamination
Massive
Fine lamination, very small ripples

Disi Formation crops out and appears in a strip-like pattern
trending NNW, and extending from southwestern Jordan to
Wadi Nummeirah in central Jordan (Amireh, 1993). It rests

conformably above the Cambrian sandstones but is unconformably overlain by the Early Cretaceous Kurnub Sandstone. The other Ordovician formations and the younger
Paleozoic formations were stripped away in central and
northern Jordan during the Hercynian and the Late Jurassic±Early Cretaceous tectonic events which affected Jordan
and the adjoining areas (Saint-Marc, 1978). On the other
hand, these Paleozoic formations were not deposited in
southern Jordan since the Tethys Sea did not reach this
part of Jordan during that time (Bender, 1968).

3. Methods and terminology
Thirty-three pro®les of the Ordovician sequence across
southern and central Jordan (Fig. 1) have been studied
sedimentologically. Fig. 2 displays the variation of lithofacies, architectural elements, trace fossil content and
interpretation of the depositional environment through
the six Ordovician formations compiled from these 33
sections.
The terminology of lithofacies and ¯uvial architectural
elements follow those of Miall (1985, 1988, 1996), whereas
the geometry of tidal sand bodies is based on the terminology of Nio and Yang (1991). Some of the architectural
elements and lithofacies of tidal and marine sand bodies
and their codes are proposed in this study. Tables 1 and 2

summarize the lithofacies and architectural terms. The
Cruziana-ichnofacies analysis is based upon that of Seilacher (1990, 1992, 1994).

4. Formations description and interpretation
The lithofacies association and ichnofaunal content, as
well as the architecture of complex three-dimensional sandstone bodies, have been described and are utilized to interpret the depositional paleoenvironment of the following six
Ordovician formations.
4.1. Disi Formation
The Disi Sandstone attains a maximum thickness of 300±
320 m (Fig. 2). The formation is characterized by a spheroidal weathering morphology, the absence of horizontal
bedding, and a snow-white color for the fresh surfaces. A
Table 2
Architectural elements in ¯uvial deposits, from Miall (1985, 1996) and
from tidal sandbodies (modi®ed from Nio and Yang, 1991)
Symbol

Element

Principal lithofacies assemblage

CH
GB
SB
SG
DA

Any combination
Gm, Gp, Gt
St, Sp, Sh, Sl, Sr, Se, Ss
Sm, Sh
St, Sp, Sh, Sl, Sr, Se, Ss

LA

Channel
Gravel bars and bedforms
Sandy bedforms
Sediment gravity ¯ow
Downstream accretion
macroform

Lateral accretion macroform

LS
FF
MF
SF
SW
TB
T
TCH

Laminated sand sheet
Overbank ®ne sediments
Mixed tidal ¯ats
Sandy tidal ¯at
Sandwaves
Tidal bar
Tempestite
Tidal to subtidal channel

St, Sp, Sh, Sl, Se, Ss; minor Gm,
Gt, Gp
Sh, Sl; minor Sp, Sr
Fl, Fm
Sf, Sw, St, Sh, Fr, Fl
St, Sf, Sw, Sl, Sr
St, Sp, Sh, Sl, Sr
St, Sr, Fr, Ss, Sf, Sw
Sh, Fl, Hcs, Scs, Sw
Sm, St, Sp, Sh

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

49

Fig. 3. (A) A downstream accretion architectural element (DA) truncating an underlying, wedging-out, laminated sandstone element (LS) in the Disi
Formation. (B) Sh intercalated within St lithofacies in the Disi Formation. (C) A panorama for the Disi Formation illustrating the dominant DA element
extending for several hundred meters, and the intercalated LS containing Cruziana trace fossils. The outcrop face strikes northward from right to left. Scale bar
is 5 m.

remarkable feature of the lithology of the formation is the
ubiquitous presence of scattered well-rounded quartz
pebbles, that are restricted to the bases of a large-scale
trough cross-bedded sandstone facies, and attain a maximum diameter of 12 cm.
It can be stated here that the famous Nabatean City of
Petra (Fig. 1) was carved in the white-colored, lower part of
the Disi Formation, as well as in the reddish pink-colored,
lower Cambrian Umm Ishrin Sandstone.
4.2. Lithofacies and architectural elements
The lower third portion of the Disi Formation is generally
made up of several, up to 15 m thick sandstone bodies [Fig.
3(A)] composed predominantly of coarse-grained, trough
cross-strati®ed sandstone (St) showing northward transport
directions [Fig. 4(A)]. The individual sandstone bodies have
an erosional base and are usually composed of several
®ning-upward sequences that start with a basal conglomerate and grade upward into a coarse±medium-grained sandstone, and might be terminated by silt±mudstone.

Applying Miall's (1988, 1996) architectural elements,
downstream accretion macroforms [DA; Fig. 3(A)] dominate over lateral accretion macroforms (LA) and sandy
bedforms (SB). The individual DA element extends more
than several hundred meters in the northward transport
direction [Fig. 3(C)] and several tens of meters across this
downstream direction. The internal structures of the macroforms consist dominantly of large-scale trough crossbedding (St), normal-scale trough cross-bedding [0.1±1 m;
St; Fig. 3(B)], and less common planar tabular crossbedding (Sp) and overturned cross-bedding with various
degrees of contortion and distortion (Sto, Spo). The troughs
can be considered three-dimensional megaripples that
reveal curved crests which can be traced over several
tens of meters and which exhibit regularly asymmetric
onlap structures. An Sc lithofacies is less common and
occurs as erosive, poorly structured thin channel-®lls
(CH) associated with gravel lag deposits. Throughout the
Disi Formation, these major DA elements are eroded by
subordinate channels (CH) of a small width:depth-ratio,
which are ®lled by all types of relevant ¯uvial lithofacies

Fig. 2. Variation of the lithofacies, architectural elements, trace fossil content and interpretation of the depositional environment in the compiled 33
Ordovician sections. X indicates position of the base of the Mudawwara Formation by Makhlouf (1992). Cr ˆ Cruziana; Cr.fur. ˆ Cruzina furcifera;
Sk ˆ Skolithos; Di ˆ Diplocraterion; Gr ˆ graptolite; Cr.ac. ˆ Cruziana acacensis; Br ˆ brachiopd; Cr. p. ˆ Cruziana petraea. For symbols of
lithofacies and architectural elements, see Tables 1 and 2, respectively.

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

Disi Formation. All of these thin intercalations show a short
lateral extension due to erosion by the overlying DA macroforms [Fig. 3(C)].
The middle and upper parts of the Disi Formation display
the same lithofacies and architectural elements encountered
in the lower third, but remarkably, some pelite layers
contain well-de®ned trace fossils, among which is Cruziana
furcifera [Bender and Huckriede, 1963; Fig. 5(A)], that
indicates the Early Ordovician age. Other types of ichnofossils that can be de®ned include Gyrochorte zigzag [Seilacher, 1994; Fig. 5(C)], Cruzina sp. [Rusophycus form; Fig.
5(B)] and cf. Scolicia [Fig. 5(D)]. These Cruzina-bearing
pelites are also truncated by the overlying DA (¯uvial)
elements.
4.3. Interpretation

Fig. 4. Rose diagrams showing the paleocurrent directions of: (A) St of the
DA and LA elements in the Disi Formation. (B) St of the DA and LA
elements in the Umm Sahm Formation. (C) wave ripple crests in the Tubeiliyat Sandstone Member.

including Sm, St, Sp, Sh and even overturned cross-strati®ed units (Sto, Spo).
The DA elements may be intercalated with laminated
sand sheet (LS) element comprising decimeter-thick structureless (Sm) or laminated sandstone beds [Sh; Fig. 3(B)].
Centimeter to decimeter thick mudstones or pelite beds (Fl),
that occasionally contain poorly-de®ned trace fossils, are
associated with the Sh lithofacies in the lower part of the

Based on the absence of body fossils, the presence of
®ning-upward sequences starting with gravel lags and terminated by overbank ®nes, and the prevalence of a large-scale
trough and planar cross-bedding having unidirectional
paleocurrent trends [Fig. 4(A)], the lower third of the Disi
Formation was deposited in a ¯uvial depositional paleoenvironment (Allen, 1974; Walker and Cant, 1984). Furthermore, the sheet-like morphology, the scarcity of thick
conglomerate beds and the dominance of DA macroform
DA elements over LA macroform LA elements, SB and
channel architectural elements (CH) favor a distal braidplain setting (Turner, 1980; Miall 1985). The major lithofacies (St and three-dimensional megaripples) were
deposited by sandwaves or dunes migrating along shallow
broad channels of high width:depth ratio (sand ¯ats) under
conditions equivalent to the upper part of the lower ¯ow
regime (Harms, 1975). The entire DA macroform element
was constructed by the downstream accretion of the large
mid-channel sand ¯ats in these shallow uncon®ned channels
of low sinuosity (Miall, 1985). On the other hand, the intercalated thin Sm and Sh lithofacies constituting the LS
macroform were deposited between the sand ¯ats during
sheet or storm (¯ash) ¯oods that reached the braidplain
under upper ¯ow regime, plane bed conditions (Rust,
1978). The intercalated pelites making up the overbank
®ne sediments (FF) architectural element can be interpreted
as overbank ®nes or abandoned channel ®lls formed by
vertical aggradation under decreasing water level conditions
(low ¯ow regime; Reineck and Singh, 1986). The inferred
braided river ¯owed northwards [Fig. 4(A)], from the
Arabian±Nubian Shield towards the Tethys Seaway that
was located in northern to northwestern Jordan in the Late
Cambrian Period (Amireh et al., 1994a). The large thickness
of the DA and SB elements in the lower part of the Disi
Formation indicates a high transport energy and sediment
load. The dominant DA elements in the formation may be
similar to the sandwaves of the lower South Saskatchewan
River (Cant and Walker, 1978) and of the Brahmaputra
(Bristow, 1993).

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

51

Fig. 5. (A) Cruzina furcifera, indicating an Early Ordovician age, found in the upper 130 m of the Disi Formation. (B) Cruziana rusophycus in the Disi
Formation. (C) Gyrochorte zigzag in the Disi Formation. (D) cf. Solicia in the Disi Formation.

The dispersed quartz pebbles throughout the Disi Formation, which are concentrated at the bottom of the St facies,
were deposited at the base of the shallow channels by the
downcurrent migrating sandwaves during high energy
conditions. These clasts are more common in the southern
parts of the study area which is close to the source rock, the
Arabian±Nubian Shield, whereas they decrease in number
and size in the northern parts of the study area.
The central and upper parts of the Disi Formation
were probably deposited within a ¯uvial dominated
braidplain delta (Elliott, 1986a; Miall, 1994). This interpretation is based upon the Cruziana ichnofacies that
represents mixed ¯ats deposited in the low energy interlobe positions of the delta, where the Cruziana-producing trilobites could dwell (Elliott, 1986a). However, in
these parts of the Disi Formation, the ¯uvial architectural elements DA, SB, LA and CH were still present,
but partly as submarine extensions below the high tide level
in the form of sandwaves and tidal bars (TB; Nio and Yang,
1991).

4.4. Umm Sahm Formation
The Umm Sahm Formation crops out in the Sahl as
Suwwan area, east of Qa el Disi (Fig. 1) and consisits dominantly of cross-bedded sandstone. It attains a thickness of
250 m at Jabal el Ghuzlan [Fig. 6(A)] and starts conformably above the Disi Sandstone. Also, the top of the formation is conformable with the overlying Hiswa Formation.
The Umm Sahm Formation is distinguished from the underlying formation through horizontal bedding, dark brown to
black weathering colors, a smaller thickness of the sandstone bodies, better sorting and a distinct silici®cation by
syntaxial quartz overgrowth (Amireh et al., 1994b).
4.5. Lithofacies and architectural elements
The Umm Sahm Formation consists mainly of mediumgrained, moderately to well sorted St and a less common Sp
lithofacies. Both types of sandstone show a broad spectrum
of northward transport directions [Fig. 4(B)]. Other less

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

Fig. 6. (A) Complete section of the Umm Sahm Formation, overlain by silt±mudstone facies of the Hiswah Formation (contact is indicated by arrow). In front
of Amireh, is an upper bedding plane of a sandstone bed riddled with Planolites. (B) Planolites sp. appearing in Fig. 6(A). (C) Alternating Sw and Sh with
interbedded silt±mudstone beds in the Hiswah Formation. (D) Small Cruziana in the Hiswah Formation. (E) Hummocky cross-strati®cation (Hcs) with an
interbedded Sh in the Hiswah Formation.

abundant lithofacies include laminated sandstone (Sh) and
pelites (Fl), that become abundant in the upper part of the
Umm Sahm Formation. The major sandstone lithofacies
constitute DA and SB ¯uvial architectural elements with
interbedded TB. Internal strati®cation in the TB macroform
includes horizontal bedding varying in thickness from a few

decimeters up to 1.5 m, ¯aser±wavy±lenticulal strati®cation, ripple cross-lamination, and oscillational and interference ripples (l , 12 cm). No ichnofauna are found in the
lower part of the formation (Fig. 2). On the other hand, the
upper part of the formation is characterized by the appearance of Planolites sp. and Cruziana sp. [Fig. 6(A,B)] in ®ne

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

sand±siltstone layers. Skolithos is found only in one unit,
located about 180 m above the base of the formation (Fig.
2). The upper surfaces of these preserved ichnofacies suffer
from erosion by overlying tidal channels. However, a
considerable part is still preserved, thus they display a
remarkable lateral extension and may be regarded as marker
beds.
The upper part of the Umm Sahm Formation displays
®ning±upward sequences consisting of DA or SB elements
overlain by LS or FF elements including the Cruziana and
Skolithos-bearing pelites. Ten such cycles are counted in the
study area (Fig. 2).
4.6. Interpretation
The depositional environment of the lower part of the
Umm Sahm Formation (lower 120 m; Fig. 2), lacking the
ichnofauna but characterized by well-developed horizontal
bedding, is interpreted as a ¯uvial-dominated braidplain
delta (Elliott, 1986a) which has a continuation of that postulated for the underlying Disi Sandstone. Sp dominating over
St facies indicates a slight decrease of transport velocity
(Harms et al., 1982) in comparison with underlying Disi
Formation. DA and SB elements were deposited above
high tide whereas TB element represents deposition below
the mean high tide.
The upper part (130 m), containing marine trace fossils
and interference wave±ripple cross-strati®cation, represents
a decrease of deltaic in¯uence, and instead indicates a
setting where intertidal sand ¯ats and mixed ¯ats dominated. The latter were commonly eroded by tidal channels
of low sinuosity. Throughout the uppermost part of the
Umm Sahm Formation, the depositional paleoenvironment
became more marine, where lower foreshore to upper shoreface conditions dominated, giving rise to parallel and ripplelaminated horizontal beds of sandstone and silt±mudstone.
This interpretation is based on the appearance of Skolithos
and Diplocraterion, the abundance of sand±mud deposits
that are heavily bioturbated and ripple cross-laminated, and
the truncation of these deposits by shallower tidal channels
(Graham, 1982; Reinson, 1984; Elliott, 1986b).
4.7. Hiswah Formation
The Hiswah Formation crops out in Wadi Hiswa and Sahl
as Sawwan (Fig. 1). It begins conformably above the Umm
Sahm Sandstone, with a remarkable shaley unit easily
distinguished from the underlying competent formation
[Fig. 6(A)]. The top of the Hiswah Formation is also
conformable with the overlying Dubaydib Sandstone.
The Hiswah Formation attains a thickness of 60±70 m. Its
immediate base is characterized by a thin layer of intraformational conglomerate, followed by a red to violet colored,
thin bedded ®ne sand- to siltstone unit a few decimeters
thick.

53

4.8. Lithofacies and architectural elements
The lower part of the formation (0±20 m) consists of
alternating thin beds of siltstone and laminated (Sh),
wave±ripple, cross-strati®ed (Sw) and ¯aser±ripple strati®ed (Sf) ®ne sandstone with mud±claystone (Fl; Fig. 2). The
latter is gray and partly dark gray and reddish gray. Other
internal strati®cations include interference and linguoid
oscillational ripples and rare small-scale planar tabular
cross-bedding (Sp). On the other hand, this part of the
formation is also distinguished by the abundance of Cruziana [Fig. 6(D)] and Skolithos ichnofauna.
The middle part of the formation (20±38 m; Fig. 2)
consists of tempestite architectural element (T) composed
of a graptolite and brachiopod-bearing dark gray to green
mudstone with few intercalated siltstone thin beds. The T
architectural element is characterized by the ®rst appearance
of hummocky cross-strati®cation [Hcs; Fig. 6(E)]. The graptolite, identi®ed as Didymograptus bi®dus [Fig. 7(B)], indicates a Lanvirn age (Bender and Huckriede, 1963). The
brachiopods found are identi®ed as Elkaniidae [?Broeggeria] (Carls, personal communication, 1986).
The upper part (38±70 m) of the Hiswah Formation
consists of sand ¯at architectural element, composed of
parallel laminated (Sh) and wave±ripple-laminated (Sw)
®ne-grained sandstone with interbedded silt±mudstone
[Fig. 6(C)]. Similar to the lower part of the formation,
Cruziana and Skolithos ichnofauna are present in this
upper part. Among the former, Cruziana cf. acacensis is
identi®ed and characterized by current orientation [Fig.
7(A)]. This ichnofossil was hitherto found only in the
Lower Silurian of North Africa (Seilacher, 1992). Other
trace fossils present in this part of the Hiswah Sandstone
Formation are Scolicia and ?Arthrophycus alleghannensis.

4.9. Interpretation
The lower part of the Hiswah Formation was deposited in
the upper shoreface zone as indicated from the marine
ichnofauna and the various types of wave ripples, ¯aser±
wavy strati®cation as well as the parallel- and ripple crosslaminated ®ne sandstone (Galloway and Hobday, 1983;
Stewart et al., 1991). The depositional environment then
became deeper, reaching the lower shoreface to offshore,
as indicated from the appearance of graptolites and tempestite architectural element (T; Levell, 1980). The latter represents storm conditions that frequently offset the deep and
otherwise quiet, reducing H2S-bearing depositional conditions of the dark-colored mudstones hosting the graptolites
(Galloway and Hobday, 1983; Boggs, 1987). Finally, the
depositional environment of the upper sand ¯at element
regressed back to the shallower upper shoreface as
concluded from the appearance of Cruziana and Skolithos
and the disappearance of tempestites (T element and Hcs
lithofacies) and the graptolites.

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B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

Fig. 7. (A) Current-oriented Cruziana acacensis in the Hiswah Formation. (B) Didymograptus bi®dus graptolite in the Hiswah Formation. (C) Scolithos sp.
characterizing the Dubaydib Formation, note the bifurcation and the annulated nature. (D) Mesa morphology consisting of ¯at-topped hills (arrows) diagnostic
of the Mudawwara Formation.

4.10. Dubaydib Formation
The Dubaydib Formation crops out in Sahl al Khreim
(Fig. 1), consists mainly of ®ne-grained well sorted sandstone and attains a thickness of 120 m. The base of the
formation is delineated by the appearance of huge populations of vertical burrows of Skolithos [Fig. 7(C)], whereas
the top is considered to be below the ®rst bed of a decimeterthick silici®ed sandstone facies that gives a characteristic
landscape of mesas and cuestas to the overlying Mudawwara Formation [Fig. 7(D)]. This upper contact of the
Dubaydib Formation contrasts with former publications
(e.g. Powell, 1989; Makhlouf, 1992) which used the green
pelites that occur 30 m higher in the lithostratigraphic
section to mark this transition (position X on the log of
the overlying formation, Fig. 2). The Dubaydib Formation
can be subdivided into three parts.
4.11. Lithofacies and architectural elements
The lower part of the Dubaydib Formation (0±40 m; Fig.
2) consists of horizontally bedded, poorly sorted silty sand-

stone (Sh) penetrated by large populations of Skolithos. The
thickness of the horizontal bed varies from 0.1 to 0.4 m.
Horizontal lamination (Sh) alternates with ¯aser±wavy
ripple strati®cation (Sf±Sw) throughout this part of the
formation. Ripples on bed surfaces are abundant, which
are mainly symmetrical with straight crests or less
commonly linguoid and sinuous-crested. These facies
together make up a sand ¯at architectural element (Fig. 2).
The middle part of the formation (40±95 m) consists of
three sets of channel-®lls (TCH I±III) elements [Figs. 2 and
8(A)] intercalated within horizontally bedded sandstone. The
channel-®lls are of low sinuosity and directed northwards, but
they exhibit a wide lateral paleocurrent variation. A tempestite
architectural element (T) characterized by hummocky±
swaley cross-strati®cation [Hcs±Scs; Fig. 8(B)], rich in
Skolithos occurs between the ®rst and second channels. The
channel-®lls contain a variety of internal facies including
Sm, St, Sp and Sh. The second channel (TCH II) is overlain
by lateraly extensive sandstone beds, that are, in turn,
followed by a 10±15 m thick green sandy pelite.
The upper part of the formation (95±120) overlying the
third channel-®ll (TCH III) consists of a horizontally bedded

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

55

Fig. 8. (A) Channel-®ll occurring in the middle part of the Dubaydib Formation. (B) Swaley cross-strati®cation (Scs) in Dubaydib Formation. (C) The green
massive siltstone facies (paleoloess; PL) of the Ammar Formation overlain by the ¯uvial massive sandstone channel-®ll (CHF) facies. (D) Cruziana petraea in
the Dubaydib Formation. Bar ˆ 1 cm.

®ne-grained sandstone facies (Sh) enriched with Skolithos,
comparable with the SF element of the lower part.
Other trace fossils present in the formation include: Rusophycus, Cruziana petraea [Fig. 8(D)], Cruziana alamadenensis, Diplocraterion, and ?Planolites.

third sets of subtidal channels (CH II±III) and the sand ¯at
elements of the upper part of the formation were deposited
in the lower foreshore to the upper shoreface.

4.12. Interpretation

The Mudawwara Formation crops out in southeastern
Jordan adjacent to the Hijaz railway in the Mudawwara
area (Fig. 1). Again, the formation forms broad ¯attopped mesas and slightly inclined cuestas (ªSchichtstufenlandschaftenº) due to differential weathering of alternating beds of soft shale and competent sandstone [Fig.
7(D)].
The formation is divided by the NRA mapping project
(Powell, 1989) into three members, from bottom to top:
Tubeiliyat Sandstone, Batra Mudstone and Ratiya Sandstone. The basal part of the Batra Mudstone Member
contains graptolites indicative of the early Silurian, such
as Diplograptus modestus modestus and Glyptograptus
?tenuis (Rushton cited in Powell, 1989). Therefore, the
latter two members will be not included in this study.

According to the physical and biogenic structures
described above, the depositional paleoenvironment of the
sand ¯ats of the lower part of the Dubaydib Formation is
interpreted as a lower foreshore that deepened to the upper
shoreface (Fig. 2). The middle part of the formation represents deepening of the depositional environment, where the
®rst set of subtidal channels (CH I) eroding the sand ¯ats
was deposited. The tempestite element (T) deposited
between the ®rst and second subtidal channel system represents the highest bathymetric depth recorded in the formation, where it reached the storm±wave base in the lower
shoreface (Swift, 1984; Walker, 1984). The sea level fell
during the last phase of the formation, where the second and

4.13. Mudawwara Formation

56

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

4.14. Tubeiliyat SandstoneMember
The Tubeiliyat Sandstone Member attains a thickness of
170 m. In contrast to Andrews (1991) and Makhlouf (1992),
who regarded the base of this member as the varicolored
(green, gray, mauve and pink) pelites (position X, Fig. 2),
we consider it to be 30 m below, where the ®rst cuesta or
mesa starts, overlying the Skolithos-ichnofacies of the
Dubaydib Formation. On the other hand, the top of the
member is considered as the base of the graptolite-rich
mudstones of the overlying Batra Mudstone Member.

grained sandstone characterized by hummocky cross-strati®cation may indicate storm conditions (tempestites), that
carried and deposited sand below the wave base within
the lower shoreface (Levell, 1980; Soegaard and Eriksson,
1985). Therefore, the depositional environment of the
Tubeiliyat Sandstone Member ¯uctuated several times
between the lower and the upper shoreface. The St lithofacies within the ¯at channels encountered in the bedded sandstone facies represents the distal reaches of tidal ¯ats, or
more probably, subtidal channels.
4.17. Ammar Formation

4.15. Lithofacies and architectural elements
The Tubeiliyat Sandstone Member consists mainly of
alternating friable, poorly sorted clayey±silty sandstone
facies making up a tempestite architectural element (T)
with indurated (due to quartz cementation), well sorted,
horizontally bedded ®ne sandstone facies (Sh) constituting
a sand ¯at architectural element in the form of coarsening±
upward cycles. About 20 cycles are present in the member
(Fig. 2). The thickness of the sand ¯at element attains 3±6 m,
whereas that of the T element ranges from 0.4 to 0.8 m.
The internal strati®cation of the sandstone facies of the T
element is characterized by horizontal bedding (Sh), oscillation wave ripples (l , 0.12 m), interference and ladder±
back ripples having crests that may show several maxima,
and hummocky cross-strati®cation (Hcs). The trend of the
waves was mainly N±S and less commonly NW±SE [Fig.
4(C)]. Trough cross-strati®cation (St) within ¯at channels
constituting TCH architectural element is found in the
middle and upper parts of the Tubeiliyat Sandstone Member
(Fig. 2). On the other hand, the clayey±silty sandstone
facies of the sand ¯at element is characterized by smallscale ¯aser±wavy ripple strati®cation (Sf±Sw) and parallel
lamination (Sh). Excluding the hummocky±cross-strati®ed
units, both architectural elements are invariably penetrated
by Skolithos, but in less abundance than in the underlying
Dubaydib Formation. Cruziana petraea (Seilacher, 1992,
1994) occurs directly above the varicolored siltstones and
indicates a Late Ordovician age. Moreover, brachiopods are
found in the upper part of the Tubeiliyat Sandstone Member
(Bender and Huckriede, 1963).
4.16. Interpretation
The widely distributed horizontal bedding, the presence
of oscillation ripples, ripple cross-strati®cation, Skolithos
and Cruziana ichnofossils, the frequent occurrence of
brachiopods, and the occurrence of subtidal channel and
tempestite architectural elements indicate a shoreface
depositional paleoenvironment (Levell, 1980; Graham,
1982; Walker, 1984). The thick, bioturbated (Skolithos
and Cruziana-rich) clayey±silty sandstone facies of sand
¯at element was deposited in the upper shoreface during
fair weather conditions. On the other hand, the tempestite
architectural element (T) consisting of the thin beds of ®ne-

In southeast Jordan (Wadi Hiswa, Batn el Ghul, Sahl el
Batra and Muddawwara areas, Fig. 1), the upper part of the
Tubeiliyat Sandstone Member was incised by glacial
valleys that were later ®lled with glacio¯uvial sediments
(Abed et al., 1993). The latter have designated these sediments as the Ammar Formation and constrained its age
between the Ashgillian to early Llandoverian. The Ammar
Formation is restricted to NS-striking paleovalleys/paleodepressions distributed in a narrow belt of about 4 km width
and 70 km length (Abed et al., 1993). These ªchannelsº cut
the adjacent well-bedded Tubeiliyat Sandstone Member and
wedge out laterally over a length of about 3 km without
revealing their bases, whereas the tops are sharply overlain
by the mudstones of the Batra Mudstone Member.
4.18. Lithofacies and architectural elements
The Ammar Formation starts in most localities, such as
Barga, Kharawi and Al Hatiya, with a channel lag conglomerate facies (Gmm) ®lling an erosional surface truncating
the Tubeiliyat Sandstone Member and constituting a gravel
bedform architectural element. It ranges in thickness
between 0.2 and 1 m. The pebbles and cobbles of this facies
are composed mainly of exotic quartz and quartzite clasts,
and less commonly sandstone, mudstone lithoclasts and
granite as well as rare monomineralic microcline clasts.
The quartzitic and granitic clasts are remarkably faceted
and striated, have crushed margins and ¯atiron-shapes, indicating clearly a glacial origin (Pettijohn, 1975; Edwards,
1986).
The overlying part of the Ammar Formation consists of a
30 m thick sediment gravity ¯ow architectural element
comprised of gray-greenish, massive-structureless, well
sorted sandy±siltstone (Sm) lithofacies. No sedimentary
structure, neither macro, micro, ichnofossil or rootlets
have been found. On the other hand, the light and heavy
minerals and clay mineral content of this element are identical with that of the Tubeiliyat Sandstone Member (Abed et
al., 1993).
This lower sediment gravity ¯ow architectural element is
overlain unconformably by channel architectural element
(CH) composed mainly of massive Gcm, Sm lithofacies
and rarely of Sh lithofacies [Fig. 8(C)]. Many pebbles of
quartzite, granite, metamorphic rocks and less commonly

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

sandstone±siltstone occur as lag deposits at the base of these
channels. Most of these pebbles are striated and/or faceted.
At some places, these sandstone channel-®lls exhibit slumping structures and steeply inclined, irregular bedding along
with water escape structures. This massive sandstone facies
grades upward into the cross-strati®ed sandstone facies (St,
Sto) and less common Sp and Spo facies displaying a northward transport direction.
The upper part of the Ammar Formation consists of a
sand ¯at architectural element composed of thin, uniformly
bedded sandstone facies (Sh) with subordinate St and Sp
lithofacies. The upper bedding planes of this facies exhibit
oscillation ripples (l , 0.15), undeterminable grazing trace
fossils, and at least two forms of brachiopods. One type of
the latter is Lingula-like, the other is a large scale-ripped
form. The latter exhibits a similarity with the brachipod
faunal assemblage of Spain that appeared immediately
after the Late Ordovician glaciation, among which is Mentacella cantabrica (Villas and Cocks, 1996) that inhabited
foreshore and shoreface paleoenvironments.
4.19. Interpretation
The Ammar Formation has been interpreted by Abed et
al. (1993) to be of glacial origin. Glaciers advancing north
and northeastward from Arabia during the Late Ordovician
North African±Arabian glacial event (McClure, 1978;
Vaslet, 1990) incised deep paleovalleys in the underlying
marine Tubeiliyat Sandstone Member. These depressions
were later ®lled by transported tillites that were further
reworked and deposited by ¯uvial processes, giving rise to
a glacio¯uvial sequence exhibiting little evidence of the
glacial origin.
The basal architectural element (gravel bedform) of the
Ammar Formation, containing faceted and striated pebbles
and cobbles, represents a lodgment till transported from
Arabia, reworked by a braided stream and ®nally deposited
at the ¯oor of the paleovalleys as channel lag-deposits.
The lower sediment gravity ¯ow architectural element of
the Ammar Formation, composed of the enigmatic sandy
silty facies and devoid of any physical or biogenic structures, may be interpreted as paleoloess deposits blown from
the adjacent Tubeiliyat Sandstone Member. The glacial
paleovalleys incised this marine formation. An alternative
interpretation, proposed by Abed et al. (1993), is that it
represents a rock ¯our of the underlying Tubeiliyat Sandstone Member which was dumped quickly into the glacial
paleovalleys as indicated by the identical light, heavy and
clay minerals in both the Tubeiliyat Sandstone Member and
this facies.
The middle part of the Ammar Formation, consisting of
CH architectural element [Fig. 8(C)], was deposited by a
braided river ¯owing northward within a glacial valley. This
interpretation is based upon the truncation of the massivestructureless sandstone, the channel geometry, the absence
of body fossils and marine ichnofossils, and the dominance

57

of unimodal trough cross-bedded sandstone facies (Rust and
Gibling, 1990; Brown and Plint, 1994). The massive
conglomerate±sandstone facies (Gcm and Sm) may represent deposition under critical ¯ow conditions of ¯ash ¯oods.
The upper part of the Ammar Formation, consisting of
well-bedded, ®ne-grained sandstone, ripple cross-strati®ed
and exhibiting trace fossils and brachiopods (sand ¯at architectural element), represents the change of the previous
continental system (glacial and glacio¯uvial) into a shallow
marine regime, particularly foreshore to upper shoreface
(Walker, 1984) in advance of the early Silurian transgression that gave rise to the overlying fully marine Batra
Mudstone Member.

5. Depositional model
The Ordovician depositional events of the study area,
located on the stable shelf of the Gondwana side of the
Tethys Seaway, were in¯uenced by the preceding Cambrian
depositional history. The latter was characterized in Jordan
by several ¯uctuations from braided rivers to shallow
marine depositional environments (Amireh et al., 1994a).
Subsequently, the Ordovician System evolved from braided
rivers to a braidplain-dominated delta, then to foreshore±
shoreface and further to offshore depositional environments.
Finally, the depositional history terminated by glacial to
glacio¯uvial conditions that were gradually replaced by
foreshore±shoreface sedimentation in preparation for the
regional Silurian transgression that affected Jordan and the
entire region (Andrews, 1991). The depositional model of
the Ordovician System is portrayed as a series of six-block
diagrams (Fig. 9).
The lower 140 m of the ®rst Ordovician formation, the
Disi Sandstone, consisting of sandstone sheets (DA architectural element) with few intercalated beds of siltstone±
mudstone (LS, FF) devoid of identi®able trace fossils,
were deposited by a braided river ¯owing northward from
the Arabian±Nubian Massif towards the north±northwestlocated Tethys Seaway [Fig. 4(A,B)]. The DA macroform
was constructed by downstream accretion of mid-channel
sand ¯ats whereas the LS and FF architectural elements
represent vertical aggradation of sands and ®nes after
decline of storm ¯oods. This initial event of the Ordovician
Period sedimentation is shown in Fig. 9(A).
The middle part of the Disi Formation witnessed the ®rst
marine in¯uence where Cruziana ichnofacies were deposited in the form of thin silt±mudstone intercalations within
the DA ¯uvial sandstone bodies. The Cruziana-producing
trilobites dwelled in mixed ¯ats (MF) located in the low
energy interlobes of a braidplain-dominated delta. On the
other hand, these deltaic tidal bars and sandwaves elements
probably represent a submarine continuation of adjacent
continental sandy bodies [DA; Fig. 9(B)]. The marine in¯uence increased slightly in the upper part of the Disi Formation where more Cruziana ichnofacies are encountered and

58

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

Fig. 9. Depositional Model of the Ordovician System in Jordan. (A) Depositional environment of the lower part of the Disi Formation. (B) Depositional
environment of the middle±upper parts of the Disi Formation and the lower part of the Umm Sahm Formation. (C) Depositional environment of the middle and
upper parts of the Umm Sahm Formation. (D) Depositional environment of the Hiswah Formation. (E) Depositional environment of the Dubaydib Formation
and the Tubeiliyat Sandstone Member of the Mudawwara Formation. (F) Depositional environment of the glacio¯uvial Ammar Formation. S ˆ Skolithos;
D ˆ Diplocraterion; G ˆ graptolite; Br ˆ brachiopod; T ˆ tempestite; W ˆ wind blown sediments.

horizontal bedding is well developed in the braidplaindominated deltaic deposits [Fig. 9(B)].
The braidplain-dominated deltaic depositional environment of the upper part of the Disi Formation
persisted through the lower 120 m of the overlying
Umm Sahm Formation [Fig. 9(B)]. Afterwards, the
depositional environment underwent a gradual marine
inundation through the remaining 130 m of the Umm
Sahm Formation where sand and mixed sand±mud tidal
¯ats replaced the preceding braidplain-dominated delta.
These were followed by upper to lower shoreface ®ne

sand and silt±mudstone deposits containing Skolithos
and Diplocraterion and dissected by several tidal channels [Fig. 9(C)].
The marine depositional environment continued deepening below the lower shoreface, where it achieved a maximum water depth during deposition of the offshore
graptolite- and brachiopod-bearing mudstone with the intercalated tempestite sandstone beds (T architectural element)
of the Hiswah Formation [Fig. 9(D)]. Afterwards, and
during deposition of the upper part of this formation (sand
¯at architectural element), the offshore depositional

B.S. Amireh et al. / Journal of Asian Earth Sciences 19 (2001) 45±60

environment changed back to the shallow lower shoreface
and, further, to the upper shoreface [Fig. 9(D)].
Oscillation between the lower and upper shoreface
continued through deposition of the Dubaydib Formation
and the Tubeiliyat Sandstone Member of the Mudawwara
Formation [Fig. 9(E)]. The lower shoreface depositional
environment was characterized by sedimentation within
subtidal channels (CH architectural element) with intercalated hummocky cross-strati®ed sandstone beds of a
tempestite origin (T architectural element), whereas the
upper shoreface depositional environment was dominated
by sand ¯at architectural elements. The tempestite architectural element represents deposition in the lowermost shoreface (Levell, 1980; Reineck and Singh, 1986).
The Ordovician Period closed with a glacial/glacio¯uvial
event where the Ammar Formation terminated the Ordovician System. Glaciers advancing north and northeastward
from northern Arabia during the Late Ordovician glacial
event incised the marine Tubeiliyat Sandstone Member,
forming paleovalleys that were later ®lled with reworked
tillites by a braided river ¯owing northward towards the
Tethys Seaway. A channel lag conglomerate facies with
diagnostic striated and faceted pebbles and cobbles was
deposited at the base of these glacial paleovalleys [Fig.
9(F)]. Aeolian deposits blown from the neighboring Tubeiliyat Sandstone Member gave rise to the green massive silt±
mudstone facies above the conglomerates [Fig. 9(F)]. A
braided river system persisted throughout the middle interval of the Ammar Formation. Subsequently, the sea gradually returned to the region and foreshore to upper shoreface
clastics were deposited, forming the upper part of the
Ammar Formation. Ultimately, the Tethys inundated the
entire study area during the regional early Silurian transgression and the offshore Batra Mudstone Member of the
Mudawwara Formation was deposited.
Acknowledgements
Thanks are due to Professor A. Seilacher for help in the
identi®cation of the ichnofossils. Professors K. Burke and
P. Eriksson are greatly acknowledged for the comments that
improved the paper. The ®nancial support of the research by
the Deutsche Forschungsgemeinschaft and the University of
Jordan is greatly appreciated.
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