ABSTRACT

This paper is the first in a series dedicated to the Phanerozoic Cambrian Period, and Neoproterozoic Ediacaran and Cryogenian periods, as represented in the Middle East Geologic Time Scale (ME GTS, see enclosed Chart). It introduces the term Asfar Sequence to represent a regional Early Cambrian time-rock unit, consisting mainly of continental quartz-rich arkosic sandstone, shale and siltstone, which attain a thickness of at least 750 m in Jordan and more than 700 m in Oman. The term “Asfar”, meaning yellow in Arabic, was chosen because it is the standard color for sandstone in ME GTS. To describe its stratigraphy, four representative formations are reviewed in lexicon format: Salib Arkosic Sandstone of Jordan, Siq Sandstone of Saudi Arabia, Amin Formation of Oman and Lalun Sandstone of Iran. The stratigraphic geometry of the lower boundary of the Sequence varies considerably by locality. In some regions in Iran it is conformable above the shales of the Zaigun Formation. In other regions, such as western Jordan, it is an onlap surface over Proterozoic and/or Lower and Middle Cambrian paleohighs, or a pronounced angular unconformity (e.g. central and southern Saudi Arabia). The paleo-relief represented by the unconformity surface, in many regions, forms a regional peneplain (e.g. central and eastern Jordan) implying erosion; in other paleohigh regions, the Sequence is absent by non-deposition. The age of the base Asfar Sequence is estimated at ca. 530 Ma, based on radiometric data and depositional rates in basinal areas. The top boundary of the Sequence, in Iran, Jordan, and northern and northeastern Saudi Arabia, is represented by a sequence boundary (or its correlative unconformity), above which marine, fine-grained siliciclastics and carbonates of late Early to early Mid-Cambrian age were deposited: Mila Formation in Iran, and Burj Formation in Jordan and Saudi Arabia, implying an age older than ca. 510 Ma in GTS 2004. In Oman, however, continental rather than marine deposition (Miqrat and coeval Mahwis formations) continued above the unconformity in ?Middle Cambrian. For the purpose of regional correlations it is proposed that the Angudan Unconformity of Oman be taken as the name for the basal boundary of the Sequence and the Burj Sequence Boundary for its top.

INTRODUCTION

The Middle East Geologic Time Scale (ME GTS) was launched in late 2008 with the objective of presenting the region’s time-rock units in a multi-country chronostratigraphic framework (Al-Husseini, 2008; see Middle East Web-Lexicon at www.gulfpetrolink.com). The Early Cambrian and older rock units were particularly difficult to calibrate in ME GTS due to the paucity of age-diagnostic fossils and the limited or inaccurate radiometric age data. They are even more difficult to correlate across the Middle East because their outcrops are far apart and their great depth substantially limits borehole sampling. Another issue was whether ME GTS should carry the revised series/epochs and stages of the global Cambrian Period/System of the International Commission on Stratigraphy (ICS; see www.stratigraphy.org), which would involve dropping the terms “Early/Lower, Middle/Mid” and “Late/Upper” upon which the Middle East literature is based (e.g. Wolfart, 1981, 1983; Husseini, 1989, 1990; Sharland et al., 2001; Konert et al., 2001; see enclosed Chart).

This paper proposes that ME GTS should adopt chrono-sequences and related surfaces (unconformity, sequence boundary, maximum flooding surface) that are regionally meaningful for age constraints and correlations for the Cambrian and older rocks of the Middle East. In particular, it seeks to document the Early Cambrian Asfar Sequence, consisting mainly of continental clastics. The term “Asfar”, meaning yellow in Arabic, is proposed because it is the standard color for sandstone in ME GTS. This choice for name does not, however, imply that the sandstones are yellow; infact they are generally red, brown and purple. The Asfar Sequence plays a crucial role in ME GTS by providing a regionally correlative Early Cambrian chrono-sequence. The age for the base of the Sequence therefore serves as a limiting age for older rock units. The enclosed Chart Cambrian, Ediacaran and Cryogenian Periods depicts the estimated age and correlation of the Asfar Sequence in ME GTS. Future papers by the present and other authors will document the many other units shown here in their preliminary calibrations.

The Asfar Sequence consists mainly of a quartz-rich, arkosic sandstone and conglomerate, shale and siltstone (reaching at least 750 m in thickness in Jordan, and exceeding 700 m in Oman) that were deposited in predomimantly continental settings throughout many regions of the Middle East. The Sequence is bounded below by an angular unconformity in many regions, and it is overlain by a marine transgressive unit of late Early or, more probably, early Mid-Cambrian age (Rushton and Powell, 1995) containing maximum flooding surface MFS Cm 20 (ca. 510 Ma; Sharland et al., 2001; Konert et al., 2001).

In this paper, four formations are correlated to the Asfar Sequence. Their stratigraphy is reviewed in a lexicon format based on the works of the original authors starting with the Salib Arkosic Sandstone in Jordan, and then from west to east: Siq Sandstone of Saudi Arabia, Amin Formation of Oman and Lalun Sandstone of Iran (Figure 1 and Chart). The formations that are attributed to the Asfar Sequence also occur in other parts of the Middle East but are not reviewed here (e.g. Iraq, Syria, Pakistan, southern Turkey; see Wolfart, 1981, 1983; Husseini, 1989, 1990; Best et al., 1993; Sharland et al., 2001; Konert et al., 2001).

SALIB ARKOSIC SANDSTONE, RAM GROUP, JORDAN

Locality The type section is exposed near the village of Quwayra, Jordan (Figure 2), and the formation was named after Qa Salib by Lloyd (1969).

Authors and Nomenclature (fromPowell, 1989): The following units are synonyms of the Salib Sandstone: Basal Conglomerate and Basal Bedded Arkose (Bender, 1968, 1974), Lower Quwayra Series (Quennell, 1951) and, in part, Quwayra Sandstone (Wetzel and Morton, 1959). The Quwayra and Salib are sometimes spelled Quwaira and Saleb. The Salib Sandstone represents the lowermost formation of the Cambrian – Ordovician Ram Group. The base of the Ram Group is the Pre-Salib Unconformity.

Lithology and Thickness (fromPowell, 1989; Andrews, 1991): The Salib Formation consists of predominantly yellow-brown, red, purple, medium- to very coarse-grained pebbly, cross-bedded, arkosic and sub-arkosic sandstone. Pebble- to cobble-conglomerates are locally present, and thin beds of planar to ripple cross-laminated fine-grained sandstones are present in the Safi outcrop area (Figure 2). In the southern desert outcrop belt it is 15–60 m thick; it reaches 220 m in the Safi area, and may exceed 750 m in northeastern Jordan (Figures 1 to 3).

Reference Section (fromAndrews, 1991): In the reference well Wadi Sirhan-3 (WS-3, Figures 1 to 3), the Salib Sandstone (750 m thick) consists of a lower unit (310 m thick, between 4,460–4,150 m) of red-brown, orange and purple, poorly sorted arkosic sandstone with angular lithic clasts, feldspar and sparse mica; it has a silica cement with overgrowths; haematite and abundant kaolinite are present in the lower part and a few highly micaceous, sandy claystone stringers occur. The upper unit (440 m thick, between 4,150–3,710 m) consists of pink and red-brown, poorly- to moderately-sorted sandstone with angular to rounded clasts; haematite and rare clay stringers are present; occasional concentrations of biotitic/muscovite are also present together with sparse heavy minerals and degraded (altered) feldspars.

Lower Boundary, Pre-Salib Unconformity (fromPowell, 1989): The base of the Salib Sandstone is an erosional surface that is characterized over most of Jordan as a broad peneplain with local, low relief in the southern desert and Safi areas (Figure 2). The basal Salib Sandstone is marked by pebbly, coarse-grained sandstone or conglomerate unit, which overlies a weathered zone (0.3–1.5 m thick) of granitoids, volcanics or lithic arkose/conglomerate. In the southern desert outcrops, the Salib Sandstone overlies the Aqaba Granite Complex dated at c. 595–585 Ma Ma (Ibrahim and McCourt, 1995) (Figure 2, see Chart).

In seismic sections, the Pre-Salib Unconformity is imaged as a major ersosional surface, which truncates the older, faulted-bounded Safi Group and/or basement rocks (Andrews, 1991; Figure 4). Andrews (1991) reported that in the reference well Wadi Sirhan-3 (WS-3), the Salib Sandstone overlies a dark red-brown olivine basalt named the “Unassigned Volcanic Unit” of the Safi Group (Figure 3), and in wells North Highlands-1 (NH-1) and Al Jafr-1 (JF-1) (Figures 1 and 2) it overlies the “Unassigned Clastic Unit” of the Safi Group (Figures 2 and 4). In the Al Jafr-1, the basalmost part of the Salib Sandstone consists of a 6-m-thick conglomerate containing large pebbles of quartzitic material.

Upper Boundary, Burj Sequence Boundary: Over most of Jordan, the Salib Sandstone is overlain by the Burj Limestone-Shale Formation. The boundary is taken where the siltstones and fine-grained sandstones of the basal Burj Formation overlie the thick sandstones of the Salib Formation (Powell, 1989). Andrews (1991) indicated that in boreholes the boundary is characterized by a dipmeter log break and abrupt upward increase on gamma-ray logs (Figure 3), where thick sandstones are overlain by the Burj siltstones, shales and interbedded limestones. They interpreted the base of the Burj Formation as a disconformity, here considered the Burj Sequence Boundary (Burj SB).

In southern Jordan outcrops, the Salib Sandstone is overlain by the marginal marine clastics of the Abu Khusheiba Formation (Figure 2 and Chart), which is coeval, in part or completely, to the Burj Limestone-Shale Formation (Bender, 1968, 1974; Heimbach, 1976; Powell, 1989; Andrews, 1991).

Depositional Setting: Throughout Jordan, the Salib Sandstone was deposited in a predominantly continental environment, but with rare evidence of minor marine incursions indicated by local trace fossil horizons (Skolithos and Cruziana) (Powell, 1989; Andrews, 1991; Amireh et al., 1994). At outcrop, Selley (1972) interpreted its depositional environment as a braided-stream alluvial setting with a distant provenance to the south of Jordan. Heavy mineral studies (Weissbrod and Nachmias, 1986) indicate a mature assemblage derived from a deeply weathered granitoid terrain.

Fossils and Age (fromPowell, 1988; Powell, 1989; Andrews, 1991): No diagnostic fossils have been found in the Salib Sandstone or underlying Safi Group at outcrop or in boreholes. Rare trace fossils in Wadi Museimir and in the southern desert outcrops only indicate an early Paleozoic age. The Salib Sandstone onlaps the Dana Granite Suite and/or the Aheimir Extrusive Suite in the Dana-Feinan area (Figure 2; Araba Complex inPowell, 1989). These igneous rocks gave isochron ages of 540–530 ± 30 Ma (Ibrahim and McCourt, 1995) indicating an Early Cambrian age for the base of the Salib Sandstone.

The age of the Salib Sandstone is older than that of the overlying Burj Formation. Powell (1989) and Rushton and Powell (1995) credited papers published in 1912 and 1914 by M. Blanckenhorn for recognizing inarticulate and articulate brachiopods and trilobites and first assigning a Cambrian age to the Burj Formation. Rushton and Powell (1995) reviewed the most important age-diagnostic trilobite faunas recognized by various authors (Dienemann, 1915; King 1923; Richter and Richter, 1941; Picard, 1942; Parnes, 1971) and concluded an early Mid-Cambrian age for the Burj Formation, based on the following trilobite species: Redlichops blanckenhorni (Richter & Richter), Realaspis sp.nov., Kingaspis campbelli (King), Kingaspis cf. obliquocultus (Geyer), Onaraspis palmeri (Parnes) and Palaeolenus antiquus (Chernysheva). Cooper (1976), following Parnes’ (1971) trilobite studies, suggested a late Early Cambrian age, based on the brachiopod species Trematobolus palaestinensis (Richter & Richter), Trematosis radifer (Richter & Richter), Psiloria alata (King), and P. davi (Cooper).

A Mid-Cambrian age was also interpreted based on diagnostic palynomorph species Celtiberium cf. dedalinum from the middle carbonate Unit D of the Burj Formation (Paleoservices, 1987, unpublished report; Keegan et al., 1990; Andrews, 1991).

SIQ SANDSTONE, TAYMA GROUP, SAUDI ARABIA

Localities (fromPowers, 1968): The Siq Sandstone forms a narrow belt of discontinuous exposures bordering the Arabian Shield from the latitude of Tabuk (28°23’N) southeast to longitude 40°10’E. It also occurs in outliers above the Shield and subsurface (Figure 1).

Authors and Nomenclature: The Siq Sandstone was originally defined in northwestern Saudi Arabia by Bramkamp et al. (1963) and mapped in the northwestern part of the Kingdom by Brown et al. (1963). Powers et al. (1966) formally defined the Siq Sandstone in a type section, northwest of 28°00′°N, 36°00′E (Al Bad Quadrangle, Figure 1), about 25 km east of Sha’ib as Siq, after which the formation is named. At outcrop the Siq Sandstone is overlain by the Saq Sandstone, which was defined at Jabal Saq in the Jabal Habashi Quadrangle in central Saudi Arabia (Figure 1) by Steineke et al. (1958), and formally described by Powers (1968).

The Yatib formation was named after Jabal Yatib on the eastern border of the Ha’il Quadrangle where it overlies the Arabian Shield (Figure 1) by Ekren et al. (1986). Vaslet et al. (1987) mapped this formation in the Baq’a Quadrangle (Figure 1) and reported the contact with the overlying Saq Sandstone appears to be conformable at outcrop, but a regional disconformity at regional scale. Janjou et al. (1997, 1998), based on their field work in the Tabuk and Jibal al Misma quadrangles (Figure 1), considered the Yatib formation synonymous to the Siq Sandstone, rendering the term “Yatib” obsolete.

The Siq Sandstone is the oldest formation of the Tayma Group, which includes all Paleozoic deposits that predate the Late Ordovician glacial event (i.e. those underlying the pre-glacial angular unconformity) and post-date the Jibalah Group (Vaslet, 1990).

Subsurface Reference Section: In the Khursaniyah-81 well in eastern Saudi Arabia (Figures 1 and 5; M.D. Mahmoud, M.I. Al-Husseini and A.A. Al-Laboun, 1988, Saudi Aramco report inAl-Hajri and Owens, 2000), the Saq Sandstone (384 m) was encountered below the Mid-Carboniferous Unconformity immediately below the Permian – Lower Triassic Khuff Formation. Below the Saq Sandstone, an 18-m-thick carbonate unit was encountered between 15,480–15,540 ft and assigned to the Burj Formation. Below the Burj Formation, a 305-m-thick (15,540 to 16,540 ft at total drilled depth) succession of clastics was assigned to the Siq Sandstone. In the subsurface, northeast of the Arabian Shield, based on seismic data, the Siq Sandstone is c. 500–1,000 m thick and underlies the Burj Formation.

Lithology and Depositional Setting: During the mapping of the Jibal al Misma Quadrangle (Figure 1), Janjou et al. (1998) concluded that the Siq Sandstone, as mapped by previous authors, correlates with the Salib Sandstone (lower part of the Quwayra Sandstone of Wetzel and Morton, 1959) and the Burj Formation of Jordan. In this paper, the term “Siq Sandstone” is limited to the section below the Burj Formation or below its lateral clastic correlative Abu Khusheiba Formation of Jordan (Figure 2), as consistent with subsurface Saudi Arabia (Figure 5). D. Janjou (written communication, 2009) reported that the distinction between the Siq and Saq sandstones is always very clear at outcrop, often evident by their sharp contact and an extensive lag deposit. He also noted that the Siq Sandstone is mainly dark red to pink, whereas the Saq Sandstone is light brown to yellow.

The section corresponding to the Siq Sandstone and Burj Formation is exposed in the southeast corner of the Jibal al Misma Quadrangle (Janjou et al., 1998, Figure 1), around Jibal al Ama’ir and Jibal Shurayfah. At this locality it overlies Arabian Shield rocks and is unconformably overlain by the Saq Sandstone. The thickness of the section ranges from a few meters to 79 m in the reference section and the rocks are dark-red to pink, or yellow, locally darkened by iron oxides. Janjou et al. (1998) divided this section into seven units (Figure 6), described below in upward sequence:

  • Unit 1 (12 m thick): Red, medium- to fine-grained thinly bedded arkosic sandstone; parallel to flat medium-scale trough cross-bedding. This assemblage is not always present at the base of the section.

  • Unit 2 (14 m thick): Light-brown to pink, conglomeratic to micro-conglomeratic arkosic sandstone in beds 1–4 m thick, interbedded with coarse sandstone, and with white pebbles and fragments of sandstone and Shield rocks up to 15 cm in diameter. Trough cross-bedding indicates current directions to the west.

Lowermost Units 1 and 2 were deposited in a braided-stream environment and filled depressions on top of the Arabian Shield (Janjou et al., 1998). They are here correlated to the Salib Sandstone and assigned to the Siq Sandstone sensu subsurface.

  • Unit 3 (7 m thick): Red to violet, horizontally bedded silty claystone partly covered by scree. Thin beds of fine-grained sandstone with small-scale trough cross-bedding are intercalated near the top.

  • Unit 4 (11 m thick): Dark-red to brown microconglomeratic sandstone in meter-thick lenticular beds; large-scale cross-bedding indicates a unidirectional current to the west.

  • Unit 5 (15 m thick) Violet, yellow to white clayey siltstone with horizontal bedding, bioturbation and tigillites.

  • Unit 6 (12 m thick) Dark-brown to red, fine-grained sandstone in decimeter- to meter-thick beds with horizontal to wavy bedding, intercalated with centimeter-thick layers of silty claystone. Tigillites are abundant. The thickest beds have trough (wedge) and sigmoidal cross-stratification and wave ripples, but tigillites are rare in these beds.

Units 3 and 4 indicate a transgression involving a progression from coastal to tidal flat environment, a maximum flooding in Unit 5 and regression in Unit 6 (Janjou et al., 1998). These four units are here correlated to the Burj Formation sensu subsurface and Jordan (Abu Khusheiba Formation), with the base of Unit 3 correlated to the Burj Sequence Boundary.

  • Unit 7 (8 m thick): Red, pink to beige, fine-grained homogeneous sandstone without lag deposits and with very large (10 m) multi-directional trough cross-bedding.

The setting of the sandstones of Unit 7 was interpreted by Janjou et al. (1998) as eolian. They become thicker to the north and south (25–50 m), outside the Jibal al Misma Quadrangle (Figure 1), and in particular in the north where they lie directly on Shield rocks with giant cross-bedding eolian sandstones. Unit 7 is probably coeval to the Burj Formation and assigned to this formation.

Lower Boundary, Pre-Siq Unconformity: The lower contact of the Siq Sandstone is a regional unconformity over the Arabian Shield. In some localities, the Siq Sandstone occurs directly above the Jibalah Group. For example, in the Mashhad area, Sahl al Matran Quadrangle along the northern Shield (Figure 1), Hadley (1974) mapped the unconformable contact between the Muraykhah Formation of the Jibalah Group and the overlying Siq Sandstone (Chart).

The extent of deposition of the Siq Sandstone over the Arabian Shield is difficult to determine. One large outlier of the Siq Sandstone (250 square km) was identified by Brown et al. (1989) in the northcentral part of the Shield in the Al Hissu Quadrangle (Figure 1). It is located south of the outcrop of the Jibalah Group in the Hawaqah Basin along a Najd Fault zone (Delfour, 1981). Brown et al. (1989) considered these sandstones similar to ones located north of the Arabian Shield where diagnostic Ordovician fossils (Sajir Member of Saq Sandstone, Chart) have been obtained higher in the succession. Delfour (1981) reported that these sandstone, which have been assigned to the Siq by Brown et al. (1989), form horizontally bedded, table-like outliers. The sandstone is mainly reddish purple to whitish-beige, commonly cross-bedded with a carbonate cement. In Jabal ash Shuqran area, an unconformity separates these sandstones from the underlying weathered Proterozoic Farayh Group (older than the Jibalah Group). Above the unconformity, the sandstone alternate with and grade into polymicitc beds, 50 cm thick, with rounded pebbles (up to 10 cm in size).

Janjou et al. (1998) noted that the Late Cambrian Risha Member of the Saq Sandstone (Chart), like the Siq Sandstone, can in places directly overlie the Arabian Shield. They reported that the contact between Risha Member and Shield rocks in Jibal al Ama’ir (Jibal al Misma Quadrangle, Figure 1) corresponds to the slope of a paleo-dome (more than 100 m high), where large granite boulders (> 1 m in diameter) have been reworked in the Paleozoic sandstone down-slope. The occurrence of Saq Sandstone on the Shield implies that topograhic relief persisted into the Late Cambrian and much after the deposition of the Siq Sandstone.

Deep within the Arabian Shield in the Nuqrah Quadrangle (Delfour, 1977; Figure 1), seven outliers of Cambrian – Ordovician sandstone occur. In some outliers, the succession starts with a basal conglomeratic sandstone with pebbles of quartz. The sandstones are cross-bedded, vary in color, and may represent the Siq and/or Saq sandstones.

Upper Boundary, Burj Sequence Boundary (Burj SB): In the Jibal al Misma Quadrangle (Figure 1), the Siq Sandstone sensuJanjou et al. (1998) is overlain by the Saq Sandstone (Figure 6). As explained above, the present author separates the Siq Sandstone and Burj Formation as consistent with their equivalents in Jordan (Figure 2), as well as subsurface seismic and borehole data in Saudi Arabia (Figure 5). A similar distinction was implied by Brown et al. (1989) who reported that at the type locality of the Siq Sandstone (Al Bad Quadrangle, Figure 1), flaggy sandstone a few meters above the crystalline basement rocks contains limonite and psilomelane as well as calcareous concretions reminiscent of the magniferous and cupiferous sediments of the upper part of Burj Formation of Jordan. West of Tabuk, D. Janjou (written communication, 2009) also recognized the marine influence of the Burj transgression (e.g. worm trails) in the lowermost part of the Siq Sandstone sensuJanjou et al. (1998).

Age: In the Mashhad area (Sahl al Matran Quadrangle, Figure 1), a basalt dike that crops out unconformably below the Siq Sandstone yielded a whole rock K-Ar age of 532 ± 15 Ma (Brown et al., 1989). A core (15,504.0–15,464.0 ft, Figures 1 and 5) taken from the Burj Formation in Khursaniyah-81 yielded sphaeromorph achritarchs that suggest an Early to Mid-Cambrian age (Molyneux and Al-Hajri, 2000). Microflora recovered from the same core (Burj Formation) contained Annulum squamaceum (Volkova) Martin, which appears near the base of the Cambrian and has its highest known occurrence in the lowest Middle Cambrian. The Siq Sandstone is therefore younger than 532 ± 15 Ma and older than the Mid-Cambrian (older than ca. 510 Ma in GTS 2004).

AMIN FORMATION, MAHATTA HUMAID GROUP, HAIMA SUPERGROUP, OMAN

Locality: Al Huqf and subsurface Interior Oman (Figure 1; Droste, 1997; Forbes et al., 2010).

Authors and Nomenclature: The Amin Formation was originally defined in the subsurface by Winkler and Rácz (1978, PDO unpublished report), revised by Oprinsen (1986, PDO unpublished report), published in Hughes Clarke (1988) and described in detail in Droste (1997). The type area of the Formation crops out in Al Huqf (Buckley and Harbury, 1996; Buckley, 1967). The Amin represents the lowermost formation of the Mahatta Humaid Group, introduced by Droste (1997), of the Haima Supergroup (Forbes et al., 2010).

Lithology, Thickness and Depositional Setting: The thickness of the Amin Formation varies significantly reaching in excess of 700 m in Ara salt-withdrawal basins. Droste (1997) divided it into three informal members deposited in continental settings: (1) Sandstone member, (2) Conglomeratic Sandstone member and (3) Interbedded Siltstone and Sandstone member (Figures 7 and 8). Forbes et al. (2010) renamed the Sandstone member as the Upper Amin Member and the other two as the Lower Amin Member.

Interbedded Siltstone and Sandstone member (Lower Amin Member): This member unconformably overlies the Nimr Group (Figure 7) or older Huqf sedimentary rocks and has only been encountered in the subsurface type area along the Eastern Flank of the Ghaba Basin (Figure 1). The base of the member corresponds to the Angudan Unconformity and is often characterized by a break on dipmeter logs. It ranges in thickness from a few 10s to 90 m. The lithology is described as interbedded, fine- to occasionally coarse-grained quartz sandstone and red-brown mudstone. The sandstone is sublithic, red to red-brown, moderately hard with scattered chert fragments. The contact with the Upper Amin Member (Sandstone member of Droste, 1997) is apparently conformable and transitional (Figure 7). The depositional setting is interpreted as low-relief continental, possibly a playa to distal alluvial fan environment. Some intercalated sands may be of aeolian origin.

Conglomeratic Sandstone member (Lower Amin Member): This member overlies the Angudan Unconformity (Figure 8), and occurs above the Nimr Group or older Huqf sedimentary rocks along the Western Margin, northwestern South Oman Salt Basin, southern Ghaba Salt Basin and southern Al Huqf region. The Member consists of white to light grey, fine- to medium-grained sandstones, medium- to very coarse-grained conglomeratic sandstones, with a sand-to-silt matrix and reddish brown shales. Large-scale, fining-upwards trends exceed 100 m in thickness and have an increasing number of mudstone intercalations. The Member is overlain by the Upper Amin Member (Sandstone member of Droste, 1997) in an apparently conformable and transitional manner.

The depositional setting is interpreted as alluvial by Hughes Clarke (1988) and Droste (1997). Forbes et al. (2010) note that in the outcrop (e.g. Buckley, 1997) the conglomerates are well organized with distinct bar form development, clast imbrication locally and bar top deposits suggesting a bed-load dominated braided river environment, although these could be downdip of true alluvial fan deposits.

Sandstone member (Upper Amin Member): The Upper Amin Member (Figures 7 and 8) consists of a uniform package of clean quartz-rich sandstones with variable thickness, reaching up to 700 m. The sandstones are very well-sorted, rounded to subrounded sublithic to quartz arenites. The setting is believed to be of eolian origin with some fluvial influence at the base where they overlie the Conglomeratic Sandstone member.

Forbes et al. (2010) reported that the aeolian setting of the Amin Formation is not supported by extensive available core data. It may be more appropriate to consider the Formation to be an arid fluvial system with an aeolian component. They recognized within the sandy intervals of the Formation several sub-environments. Fluvial sheet/streamflood environments may be the most common. Others include channelled to weakly channelled braided systems, aeolian sand sheets (interdunes) and dunes, wet and dry sabkhas and ephemeral lakes/playas. Typically, individual aeolian dunes are small (1–2 m maximum thickness), although they occasionally stack into thicker intervals. In South Oman, the preserved dunes appear to be larger than in North Oman. Although the detailed distribution of the sub-environments is poorly constrained in general terms the Fahud Salt Basin appears to be dominated by fluvial facies with a minor aeolian component. In the Ghaba Salt Basin and South Oman aeolian deposits are more common, although interbedded with fluvial, sabkha and playa deposits.

Lower Boundary, Angudan Unconformity:Droste (1997) reported that the Amin Formation is one of the most widespread units of the Lower Paleozoic Haima Supergroup and oversteps the underlying truncated Nimr Group and older Huqf strata. The lower boundary is represented by the Angudan Unconformity, which is a three-tiered stratigraphic break at the formation, group and supergroup levels. In a complete succession the unconformity separates the Amin Formation, Mahatta Humaid Group, Haima Supergroup from the underlying Haradh Formation, Nimr Group, Huqf Supergroup (or undifferentiated Nimr Group). The unconformity is of regional extent and has been imaged by seismic data (Figures 1 and 9) and observed in dip-meter data.

H. Droste (written communication, 2008) reported that the Angudan Unconformity was named after the NS-trending Wadi Angudan, which joins the larger Wadi Dhahaban, both of which are part of a much larger wadi drainage system along the north flank of the Qara Mountains in Dhofar, Oman (Figure 1). In the late 1980s, prominent seismic reflectors associated with a major unconformity were recognized in southern Oman. The unconformity was first calibrated by the Angudan-1 well in 1990 where it separates deformed rocks of the Huqf Supergroup from undeformed strata of the Haima Supergroup. The unconformity was described in detail for the first time by Linskail and Teyssen in 1991 (PDO unpublished report) on the geological evolution and hydrocarbon prospectivity of the Western Margin of the South Oman Salt Basin.

The rocks below the Amin Formation vary in age from the Early Cambrian Nimr Group, Ediacaran – Early Cambrian Ara Group, Neoproterozoic Nafun and Abu Mahara groups, to the Proterozoic Crystalline Basement (older than ca. 800 Ma for granodioritic basement, Mercolli et al., 2006; Bowring et al., 2007; Forbes et al., 2010).

Upper Boundary: The Sandstone Member of the Amin Formation is overlain by either the Mahwis Formation or its coeval Miqrat Formation (Figures 7 and 8), of probable Mid- to Late Cambrian age. In Farha-1 (Figure 7), the boundary is an unconformity marked by the change from clean quartz, sublithic sandstone of the Amin to very fine micaceous sandstones of the Miqrat Formation. Forbes et al. (2010) suggested that the lower part of the Miqrat Formation may represent a minor (?non-marine) flooding event. J. Mattner, written communication, 2009) reported that in some extensive outcrop belts, the Miqrat has over several tens of meters of shale at the base immediately above the coarsegrained to conglomeratic Amin Formation. He interpreted this abrupt change to represent a regional increase of the base level/accommodation space and a marine flooding in coastal areas.

Age: The Amin Formation is unfossiliferous and no radiometric age data is available. The Mid- to Late Cambrian age established for the much higher Andam Group (above the Miqrat and Mahwis formations) and the Early Cambrian age established for the upper part of the Ara Group and Nimr Group constrain the age of the Amin Formation to Early to ?Mid-Cambrian age. An Early Cambrian age was inferred by assumed correlation to the Lalun Sandstone Formation in Iran by Hughes Clarke (1988).

LALUN SANDSTONE FORMATION, IRAN

Locality: The type section is located northwest of Zaigun city, on the eastern slope of the Lalun Valley in the Central Alborz Mountains (Figure 1). Assereto (1963) reported that the Lalun Sandstone shows no lateral variations in the surrounding area and extends over the entire Alborz Mountains, northwest Iran and northwestern Central Iran. Stöcklin (1972) observed that the Lalun Sandstone is the most persistent Paleozoic rock unit in Iran. It is known from Azerbaijan in the northwest, as far as Kerman in the southeast (Figure 1). The Lalun Sandstone also crops out throughout the Soltanieh Mountains; Derenjel Mountains and surrounding regions (Ozbak Kuh - Shirgesht - Shotori Mountains of Tabas); Ravar and surrounding regions (Bahabad and Zarand areas); Kohrud Range south of Kashan; in mountains north of Yazd (north of Ardekan) and southwest of Yazd (Shirkuh Range); and throughout the High Zagros Mountains (Figure 1).

Author and Nomenclature: The Lalun Sandstone Formation was formally named and defined by Assereto (1963), who together with Stöcklin (1972) compiled numerous synonyms including the Old Red Sandstone and Vieux Grès Rouge, which had been considered Devonian by previous authors. The Lalun Sandstone was dated as Cambrian and named Upper Hezarchal Formation (Gansser and Huber; 1962), Dahu Series (Huckriede et al., 1962), and Lalun Sandstone by A. Ruttner (inFlügel and Ruttner, 1962) and Stöcklin et al. (1964, 1965).

Lithology and Thickness: In the type section the Lalun Sandstone is a homogeneous, medium-grained, red, purple to pink, quartzitic to arkosic sandstone in regular and cross-laminated beds (40–80 cm thick). The type section is 582 m thick and divided into six units (Figures 1 and 10; Assereto, 1963). In the surrounding area it maintains a uniform thickness of c. 600 m. Stöcklin et al. (1965) described the lithology in a reference sections located at Jaghan Daghi, Soltanieh Mountains (Figures 1 and 11), where the Formation is 400–600 m thick.

Stöcklin et al. (1964, 1965) examined thin sections from a sandstone sample taken in the Zinjan area, Soltanieh Mountains. They show well-rounded grains of predominantly quartz, 10–20% plagioclase and altered orthoclase, subordinate microline, mica, and sporadic grains of zircon, garnet, iron-carbonate, and other heavy minerals. Similar red sandstones occur in the older Zaigun, Barut and Bayandor, formations (Chart); however, the sandstones of these other formations are finer grained, darker and with a much higher content of mica, which is rare or totally absent in the Lalun Sandstone.

Stöcklin (1972) reported that the Lower Cambrian Top Quartzite Member is a name commonly used in Iran for a light-colored quartzite unit occurring in the upper part of the Lalun Sandstone. The Member is about 50–60 m thick and usually separated from the underlying red sandstones, which constitute the main body of the Lalun, by a zone of purple shale that has yielded Early Cambrian trace fossils in several places. The Top Quartzite is the most persistent unit of member rank in the entire sedimentary sequence of Iran and has been recognized in practically all outcrops of the Lalun Sandstone throughout northwestern, northern, central, eastern, and southwestern Iran.

Wolfart (1981), following other authors, divided the Lalun Sandstone in the Alborz and Derenjel Mountains (Figure 1) into a lower Sandstone Member, middle Shale Member and the Top Quartzite Member. In the Derenjel Mountains (Ruttner at al., 1968), the Shale Member is 135 m thick and consists of red shale with beds of red sandstone and aranaceous dolomite. Near the basal contact, the bottom of some sandstone beds interbeds show casts of footprints, digging tracks and other trace fossils. The age significance of these trace fossils is discussed below.

Lower Boundary, Pre-Lalun Unconformity (fromStöcklin, 1972): The Lalun Sandstone overlies the Zaigun Formation. The Lalun is distinguished from the Zaigun by its coarser grain and more uniform sandy-quartzitic lithology. The contact in the type section is gradational and was drawn on top of the uppermost dark-red siltstone. The Zaigun Formation accompanies the Lalun Sandstone practically everywhere and together they can be traced through a great part of northwestern, northern, central and eastern Iran. The limit against the Lalun Sandstone is sharp and possibly marks a disconformity in the Soltanieh Mountains (Figure 1; Stöcklin et al., 1965), but in most other outcrops it is drawn rather arbitrarily because of gradational contact relations. In the Golpaygan area (Figure 1), the Zaigun facies replaces most of the Lalun Sandstone (Zaigun-Lalun Formation of Thiele et al., 1968), but the Lalun’s Top Quartzite Member is still distinguishable here (Stöcklin, 1972).

In the Kerman area, the Top Quartzite Member has been described by Huckriede et al. (1962) as White Quartzite With Lydite Pebbles, overlying the Dahu Formation.Stöcklin (1972) considered the Dahu Formation to be a “perfectly identic” with the main red part of the Lalun Sandstone. In the Ravar area north of Kerman (Figure 1, Chart), dark red shales in the upper part of the diapiric Ravar (Salt) Formation seem to be perfectly equivalent to the Zaigun Formation. The Ravar red shales are in turn overlain by the Lalun Sandstone.

Stöcklin et al. (1964, p. 19) described the Zaigun-Lalun contact in many localities in the the Alborz Mountains as appearing to be conformable and gradational. In other localities, however, the Lalun is found to be much thinner than its regional average thickness, and in contact with formations that are much older than the Zaigun Formation (see Chart for older formations). In Deh-Jalal south of Assadabad (central Soltanieh Mountains) it overlies the Barut Formation (Zaigun missing). Southwest of Algozir (eastern Soltanieh Mountains) it overlies the Bayandor Formation (Zaigun and Soltanieh formations missing), and at Qara Dagh near Falaj (eastern Soltanieh Mountains) the Lalun Sandstone overlies the Kahar Formation (Infracambrian Complex missing). Along the north-foot of the Alborz Mountains and in northern Azerbaijan, the Lalun Sandstone pinches out against a series of Proterozoic (Precambrian) basement exposures.

Taking all the evidence together, Stöcklin et al. (1964) concluded that a major disconformity associated with a pre-Lalun phase of erosion occured after the Zaigun was deposited. This phase, they suggested, may have involved pre-Lalun vertical movements. They cited as further supporting evidence the presence of very uniform, dark, varicolored shales of the Zaigun Formation found as cm-sized flakes that were evidently reworked in the lowermost part of the Lalun Sandstone. They note, however, that the disconformity is non-angular and difficult to detect because of the similar lithological character of the two formations.

The widespread distribution of the Lalun Sandstone, its coarse-grained quartzitic sandstone lithology, and the absence of one or more older formations below it, argues that its base is an unconformity:

Pre-Lalun Unconformity.

Upper Boundary, Mila Sequence Boundary: In the type section, Assereto (1963) picked the upper boundary of the Lalun at the contact between its well-bedded sandstone and the overlying slightly laminated red sandstone with abundant dolomitic cement in the lower part of the Mila Formation. The basalmost Mila sandstone is in turn covered by the black dolomite of Member 1 of the Mila Formation. Stöcklin et al. (1964) reported that the contact between the white Top Quartzite Member of the Lalun Sandsone and the yellow basal marl of the overlying Mila Formation is very sharp and distinct. In sections other than the Lalun type section, the base of the Mila is frequently a dolomitic marl bed (Stöcklin, 1972).

Wolfart (1981) reviewed the biostratigraphy of the Lalun Sandstone and its presumed correlatives as reported by Stöcklin (1972). On fossil evidence he considered the upper part of the Lalun Sandstone in the Alborz and Derenjel Mountains, to pass laterally to the Kuhbanan Formation in Kerman (see Chart). He therefore cautioned that the Lalun Sandstone and Dahu Formation may not be perfect correlatives as suggested by Stöcklin (1972),

Paleontology and Age (fromStöcklin, 1972): No fossils are known from the Zaigun Formation, and an Early Cambrian? or latest Proterozoic (“Infracambrian”) age is indicated by its stratigraphic position. Assereto (1963) did not report any fossils from the Lalun Sandstone in its type section. Stöcklin (1972) and Wolfart (1981), however, reported that Gansser and Huber (1962) and Allenbach (1966) found Cruziana-like tracks in the central Alborz Mountains. Stöcklin (1972) credited A. Seilacher (inAllenbach, 1966) for interpreting the tracks as footprints of trilobites of the Ridlichia group indicating mid Early to late Early Cambrian age for the Lalun Sandstone. In the Alborz Mountains (not at type section), the Cruziana-like tracks occur in the middle Shale Member (35 m thick) above nearly 500 m of arkosic sandstones (lower Sandstone Member). The shale is overlain by a 50-m-thick Top Quartzite Member that underlies the Mila Member 1 (Wolfart, 1981).

In the Derenjel Mountains, the middle Shale Member of the Lalun Sandstone also shows imprints of Cruziana, which A. Seilacher (inRuttner et al., 1968; Wolfart, 1981) considered identical to ones described in the Magnesian Sandstone of the Salt Range of Pakistan. In Pakistan they occur together with Redlichia and Botsfordia indicating an Early Cambrian age. Both Stöcklin (1972) and Wolfart (1981) correlated the Lalun Sandstone from the Alborz to Derenjel Mountains, a distance of c. 500 km, and assigned it to the Early Cambrian.

Above the Lalun Sandstone Formation, the Mila Formation in the Alborz type section is divided into the Members 1 to 5 in ascending order (Chart). Stöcklin et al. (1964) found no fossils in Member 1, which is 189 m thick and characterized by an alternation of gray dolomite and yellow marl. In the lower part of Member 2, H.K. Erben (inStöcklin et al., 1964) identified three genera of trilobites: Chuangia, Iranochuangia and C. cf. Iranoleesia, together with Obolus and Hyolithes, suggesting an early Late Cambrian age. H.K. Erben considered it possible that Member 2 extends to the late Mid-Cambrian, although the genus Redlichia has not been found at Mila Kuh (Alborz Mountains) or the Zenjan area (Soltanieh Mountains). T. Kobayshi (inStöcklin et al., 1964), however, found trilobites of the Lioparella and Anomocarella group, and assigned part of Member 2 to the late Mid-Cambrian. B. Kuschan (1972, inWolfart, 1981) found Dorypyge in northern Iran, which is significant as indicating Mid-Cambrian age. Mila Member 1 is therefore late Early to early Mid-Cambrian in age by stratigraphic position below Mila Member 2 and above the Lalun Sandstone.

REGIONAL CORRELATION

The Salib Sandstone, Siq Sandstone sensu subsurface, Amin Formation and Lalun Sandstone share many stratigraphic characteristics:

  • (1) Lithology: consisting mainly of quartz-rich, arkosic sandstone, with shale and siltstone beds.

  • (2) Depositional Setting: mainly continental, alluvial plain and, in part, aeolian. In Iran, and to a lesser extent in Jordan, some marine influence is evident (e.g. middle Lalun Shale Member with Cruziana tracks).

  • (3) Thickness: typically between several 100s to possibly 1,000 m, but thin to absent over local paleohighs.

  • (4) Distribution: Widespread throughout the four countries; the Lalun Sandstone is the most widespread of all Paleozoic formations in Iran; the Amin Formation is the most widespread formation of the Early Paleozoic Haima Supergroup in Oman.

  • (5) Lower Boundary: the Angudan and corresponding Pre-Salib, Pre-Siq and Pre-Lalun unconformities are one and the same unconformity. In many localities one or more older formations are absent below it.

  • (6) Upper Boundary: a sequence boundary followed by a late Early Cambrian to early Mid-Cambrian transgression, which flooded the northern and northeastern Middle East. The transgression arrived from the present-day northeast where the Proto-Tethys Ocean was located (Best et al.,1993; Konert et al., 2001; Ruban et al., 2007), and its base is recognized in Iran (Mila Sequence Boundary), Jordan (Burj Sequence Boundary) and northern and eastern Saudi Arabia (Burj SB). In Oman, the upper boundary of the Amin Formation is an unconformity (ca. Lower/Middle Cambrian boundary) marking an abrupt change from quartz-rich sandstones (Amin Formation) below, to very fine micaceous sandstones above (Miqrat and coeval Mahwis formations). The basal part of the Miqrat Formation is interpreted as a base level change (Forbes et al., 2010; J. Mattner, written communication, 2009).

The four formations represent a c. 1,500 km E-W traverse over the Middle East in which this mainly continental unit was deposited on the same unconformity (correlative disconformity) and below the same regional sequence boundary. The formations therefore form one time-rock unit, here proposed as the Early Cambrian Asfar Sequence (“Yellow Sequence”, Chart).

The correlations proposed here differ in one important aspect from those presented by Konert et al. (2001, their figure 4c, p. 415), wherein they correlated the Siq, Salib and Lalun formations to the Nimr Group of Oman. In their correlation the Angudan Unconformity of Oman was miscorrelated to the Burj Sequence Boundary and base Mila Formation, instead of the Pre-Siq, Pre-Salib and Pre-Lalun unconformities as shown in the enclosed Chart.

Unlike the Mid-Cambrian paleogeography of the Middle East (Sharland et al., 2001; Konert et al., 2001), that of the Early Cambrian is not adequately constrained. It is evident that some regions were completely eroded into a smooth peneplain before the Asfar Sequence was deposited (Figure 4), whereas others were local paleohighs onlapped by it (Figure 2). Over some paleohighs the Asfar Sequence is absent by non-deposition (Figure 2). Relatively thin outliers of Lower Cambrian sandstone (Siq Sandstone) are preserved over the northcentral part of the Arabian Shield indicating Early Cambrian deposition may have extended into paleolows within the Shield. These relationships argue that both local and semi-regional topographic relief persisted into the Early Cambrian over parts of the Middle East.

The spatial limits of the late Early to early Mid-Cambrian transgression (Burj and lowermost Mila formations; MFS Cm 20 of Sharland et al., 2001) also verify the presence of Mid-Cambrian semiregional relief. The transgression was evidently limited to the vicinity of the northern edge of the Arabian Shield as concluded by Konert et al. (2001, their figure 5). The limit is also evident by the lateral change in lithology from Burj and Mila carbonates in the north and northeast to marginal marine clastics in the south and west (Abu Khusheiba Formation in Jordan). The marine setting is also absent in Oman (Miqrat and Mahwais formations). The implication is that broad paleotopographic highs persisted into the Mid- and possibly Late Cambrian in western and southern Arabia.

The provenance of the massive quartz-rich, arkosic sandstones of the Asfar Sequence was most probably from granitic and other igneous bodies that were emplaced throughout the Middle East during the Neoproterozoic and earliest Cambrian (e.g. Alkaline Granites of the Arabian-Nubian Shield, Figure 2). This interpretation suggests that the provenance may not have been far-field from interior Gondwana (i.e. Africa) as suggested by Konert et al. (2001), but rather local and semi-regional paleohighs in southern, western and possibly central Arabia (Weissbrod and Nachmias, 1986), as well as igneous rocks along the Proto-Tethys Ocean to the far east and along the southern Caspian Sea.

AGE CONSTRAINTS

Biostratigraphic constraints for the end of deposition of the Asfar Sequence are based on the age of the overlying Burj Formation in Jordan (Rushton and Powell, 1998) and Khursaniyah-81 in Saudi Arabia (Al-Hajri and Owens, 2000; Molyneux and Al-Hajri, 2000), where the Formation is dated as early Mid-Cambrian. In Iran, Mila Member 1 is undated but the overlying Member 2 is late Mid-Cambrian (Stöcklin et al., 1964), implying Member 1 is coeval to the Burj Formation, in part or completely. Paleogeographically, the Burj Formation in Khursaniyah-81 represents a more proximal position than Mila Member 1, with the Proto-Tethys Ocean further to the present-day east (Konert et al., 2001; Ruban et al., 2007). Therefore the Burj Formation and Mila Member 1 are believed to be coeval. These considerations imply the Asfar Sequence is older than late Early Cambrian (i.e. > ca. 510 Ma in GTS 2004 and MFS Cm 20 of Sharland et al., 2001). In Oman, the Amin Formation is assigned to Lower Cambrian (below the Middle? Cambrian Miqrat and Mahwis formations) and is considered to represent the Asfar Sequence.

The only direct, but poorly constrained, biostratigraphic age for the Asfar Sequence is based on the Cruziana imprints of mid Early to late Early Cambrian age in the Middle Shale Member below the Top Quartzite Member of the Lalun Formation, and in the Salib Sandstone (Jordan). The Top Quartzite (50–60 m thick) occurs immediately below the Mila Formation (at least for over 500 km from Alborz to the Derenjel Mountains) implying it too is Early Cambrian in age.

The age for the start of deposition of the Asfar Sequence is intra-Early Cambrian as constrained by the age of the Ara Group in Oman, which straddles the Ediacaran/Cambrian Boundary (Precambrian/Cambrian Boundary – PCB) dated at 542.0 Ma (Amthor et al., 2003; see Chart). The PCB is positioned in the middle of the Ara Group, above which the upper part of the Ara and Nimr groups (together c. 1,000–1,500 m thick) were deposited below the Angudan Unconformity (older than or coincident with the base of the Asfar Sequence). The depositional time required to deposit the succession between the PCB and Angudan Unconformity may be estimated by using a typical syn-rift isopach/time conversion rate (uncompensated for compaction). Assuming c. 100–150 meter/My (e.g. Gulf of Suez syn-rift rate) implies the Angudan Unconformity is about 7–15 My younger than the PCB, or ca. 535–527 Ma. This age estimate for the Unconformity is consistent with the radiometric age of underlying igneous rocks: younger than ca. 532 ± 15 Ma for the Pre-Siq Unconformity in Saudi Arabia, and 540–530 ± 30 Ma for the Pre-Salib Unconformity in Jordan.

Assuming the Asfar Sequence is constrained between 530 and 510 Ma, then its representative Salib Formation of Jordan, with an estimated c. 1,000 m thickness near the border with Iraq, would have an isopach/time conversion of c. 50 meter/My. This rate could well be representative for basinal regions within a tectonically stable Early Cambrian Arabian Plate.

Finally, an estimate of ca. 530 Ma for the base of the Asfar Sequence is the same as that shown by Loosveld et al. (1996, their figure 3), and 10 My older than that of Konert et al. (2001, p. 415) and Sharland et al. (2001) for base Arabian Plate Megasequence 2 - AP2 at ca. 520 Ma.

CONCLUSIONS

The stratigraphy of a mainly continental Early Cambrian rock unit (typically between several 100s to possibly 1,000 m thick, but thin or absent over paleohighs) was reviewed and correlated across Jordan, Saudi Arabia, Oman and Iran. The unit can be traced over a region, some 1,500 x 1,500 km in extent, from Jordan and the northern Arabian Shield to Oman and Iran. Where present, it is bounded by sequence boundaries or unconformities. It therefore provides an important chrono-sequence in the Middle East Geologic Chart (ME GTS) – here proposed as the Asfar Sequence (“Yellow Sequence”). It is also proposed that for regional correlations its lower boundary be named the Angudan Unconformity and its upper boundary the Burj Sequence Boundary.

On fossil evidence, the age of the Asfar Sequence is Early Cambrian and older than ca. 510 Ma in GTS 2004. It is younger than ca. 530 Ma based on radiometric ages of the underlying volcanics in Jordan and Saudi Arabia, and depositional rates in Oman above the Ediacaran/Cambrian (Precambrian/Cambrian PCB) boundary (542.0 Ma). These ages provide Early Cambrian contraints for younger and older rock units in the ME GTS (see enclosed Chart).

ACKNOWLEDGEMENTS

The author thanks Darweesh Jaser, Natural Resources Authority (NRA), Jordan, and the NRA for permission to reproduce Figures 2 to 4 (with modification). He thanks the Ministry of Oil and Gas, Sultanate of Oman, and Petroleum Development Oman for providing Figures 7 to 9 to GeoArabia publications. Dominique Janjou, Huub Jansen, Joerg Mattner, John Powell and Denis Vaslet are thanked for their comments on the manuscript. The ages and correlations shown in the enclosed Chart reflect the author’s interpretations and are intended to provide a working document for future refinements. The author thanks GeoArabia’s Production Manager, Nestor Buhay II, for designing the graphics and Chart.

ABOUT THE AUTHOR

Moujahed Al-Husseini founded Gulf PetroLink in 1993 in Manama, Bahrain. Gulf PetroLink is a consultancy aimed at transferring technology to the Middle East petroleum industry. Moujahed received his BSc in Engineering Science from King Fahd University of Petroleum and Minerals in Dhahran (1971), MSc in Operations Research from Stanford University, California (1972), PhD in Earth Sciences from Brown University, Rhode Island (1975) and Program for Management Development from Harvard University, Boston (1987). Moujahed joined Saudi Aramco in 1976 and was the Exploration Manager from 1989 to 1992. In 1996, Gulf PetroLink launched the journal of Middle East Petroleum Geosciences, Geo Arabia, for which Moujahed is Editor-in-Chief. Moujahed also represented the GEO Conference Secretariat, Gulf PetroLink-GeoArabia in Bahrain from 1999-2004. He has published about 50 papers covering seismology, exploration and the regional geology of the Middle East, and is a member of the AAPG, AGU, SEG, EAGE and the Geological Society of London.

geoarabi@batelco.com.bh