INTRODUCTION

The purpose of this note is to present revisions to the SP2 scheme resulting either from significant errors in SP2, or from newly published data that challenges SP2, or from newly published data identifying new maximum flooding surfaces.

The publication of Arabian Plate Sequence Stratigraphy (Sharland et al., 2001), commonly referred to as SP2, provided a unifying stratigraphic interpretation of the Arabian Plate within a modern sequence stratigraphic framework. In 2002 revisions to the stratigraphic positions of some SP2 Cretaceous maximum flooding surfaces (MFS), and some resulting new interpretations, were presented by Davies et al. (2002). New interpretations of mixed carbonate-clastic systems presented by these authors have application to other parts of Middle East stratigraphy.

Since 2001, many excellent new papers have been published, and oral presentations made, containing new data and/or interpretations (e.g. Al-Eidan et al., 2001; Brew et al., 2001; Konert et al., 2001; Ziegler, 2001; Al-Suwaidi and Aziz, 2002; Nehlig et al., 2002; van Buchem et al., 2002; Boote and Mou, 2003; Price and Fell, 2003; Stephenson et al., 2003 - to name but a few). The interpretations presented here are based on this new post-SP2 literature, as well as re-interpretations of older literature in the light of this new work.

Following discussions with Gulf PetroLink, the Neftex SP2 authors have been encouraged to provide a summary chronostratigraphic up-date based on this new literature for GEO 2004 of the SP2 interpretation, with particular emphasis on (1) revisions to the published geological timescale; (2) changes to SP2 megasequence boundaries (position and dating); (3) changes to SP2 maximum flooding surfaces (position and dating); (4) the identification and dating of any new TMS and/or MFS; and (5) any proposed changes to the SP2 sequence stratigraphic nomenclature.

This GeoArabia Stratigraphic Note and the accompanying two chronostratigraphic chart enclosures (Enclosure 1 Mesozoic and Cenozoic, and Enclosure 2 Palaeozoic and Precambrian), are intended to update those in SP2. These new charts have been extended into Jordan (in the north) and southwest Oman and Yemen (in the south). Significant changes to MFS are made in the Neogene, Palaeogene and Permo-Triassic sections.

Geological Timescale

The attached chronostratigraphic chart enclosures utilise the Phanerozoic timescale of Gradstein and Ogg (1996) (G&O ’96). Over the last few years there have been potential revisions to parts of the G&O ’96 timescale, offering the potential to merge the up-dated parts with the unchanged parts resulting in a ‘hybrid’ timescale (see, for example, the more recent revisions to the Permian timescale illustrated by Stephenson et al. (2003) versus G&O ’96). However, the G&O ’96 timescale is still the most up-to-date single chart for the entire Phanerozoic. Most importantly, the G&O ’96 timescale was used in SP2, and therefore allows an easy comparison between the enclosed updated charts and those in SP2. All absolute ages given herein thus relate to G&O ’96.

We are aware that a new geological timescale, ratified by the International Commission on Stratigraphy, will be published in 2004, most likely to coincide with the International Geological Congress meeting in Florence in July 2004. This new timescale is expected to cover the entire Phanerozoic, and will thus potentially replace the G&O ’96 timescale used here and in SP2.

The only change to the G&O ’96 timescale we utilise here is a slight revision of the age of the Precambrian-Cambrian boundary from 545 Ma to 542 Ma. This change been made on the basis of some well-constrained dates from Namibia that are associated with rocks of the basal Cambrian Phycodes pedum Zone (Grotzinger et al., 1995) and, more recently, new radiometric dates from ashes associated with Late Precambrian – Cambrian faunal turnover in the Ara Group of Oman (Amthor et al., 2003; Al-Husseini et al., 2003).

Megasequence Boundary Revisions

The boundaries of the 11 Arabian Plate (AP) tectono-stratigraphic megasequences (TMS, see SP2) are plate-wide unconformity surfaces that record major changes in accommodation space, resulting from plate-scale tectonic events.

Literature published since 2001 allows the re-definition of 2 of these unconformity surfaces:

  • Top AP5 = revised from near base Wordian (255 Ma) to latest Kungurian (257 Ma);

  • Top AP4 = revised from late Stephanian (295 Ma) to earliest Westphalian (315 Ma).

Top AP5 Revision:

On the basis of new data within Stephenson et al. (2003) and Angiolini et al. (2003) the age of this TMS boundary is revised from near base Wordian (255 Ma) to latest Kungurian (257 Ma) (see Stephenson et al., 2003 for an illustration of current Perman timescales). The P20 MFS establishes the Khuff carbonate (and equivalents) across the new passive margin across much of Arabia. This revision is caused by recognition that MFS P20 is clearly Wordian (= Kazanian) in age (see below).

In Oman, Stephenson et al. (2003) show that the oldest rocks within the P20 TST above the top AP5 unconformity (comprising the Upper Gharif Member) lie within part of the poorly calibrated OPZ5 Biozone. Although this biozone is poorly chronostratigraphically-calibrated, it is dated as Roadian-Wordian, which is also supported by the occurrence of plant megafossils (Broutin et al., 1995). Correlative P20 TST rocks include the basal Khuff clastics of Saudi Arabia and its equivalents. Therefore, in most places, the oldest sediments above the top AP5 unconformity are Roadian in age, and probably slightly older (i.e. latest Kungurian at 257 Ma) in (undrilled off-structure) subsiding depocentres.

Top AP4 Revision:

Top AP4 was incorrectly located in SP2 and is revised from late Stephanian (295 Ma) to earliest Westphalian (315 Ma) because the climax of the Hercynian Orogeny associated with this TMS boundary is shown to be around 315-330 Ma by Konert et al. (2001). These authors regard the Visean–Namurian Berwath Formation of Saudi Arabia as ‘syn-Hercynian’ (i.e. it potentially onlaps Hercynian structures and may be partly deformed by them), which places a limitation on the age of this TMS boundary.

Maximum Flooding Surface Revisions

Arabian Plate Sequence Stratigraphy identified 63 MFS using a ‘decimal’ nomenclature (see SP2 and below). Two new MFS are recognised here, making 65 in total.

One of the key criteria for recognising MFS in the SP2 scheme was the fact that they could be biostratigraphically calibrated in terms of age at their Reference Section (see SP2), and were regionally extensive and thus correlatable over wide areas. Additional, probable higher frequency, surfaces (e.g. those in the Umm Er Radhuma Formation) were not given decimal MFS status due to the lack (at that time) of age-significant data, even though they were very likely to be regionally extensive surfaces. As far as possible, we feel that age-significant data should be provided to support MFS proposals – without age-diagnostic data surfaces cannot be placed on a chronostratigraphic chart.

Recent literature shows that the MFS identified in SP2 have stood the test of time relatively well, although much new work in the region is now seeing the light of day. Due to the publication of new data, or re-evaluation of existing literature (especially van Bellen et al., 1959 – the Iraq Stratigraphic Lexicon), we now revise 8 MFS and identify 2 new MFS as follows:

Oligocene-Miocene Revisions (MFS Pg40 to Ng40):

Literature covering the Oligocene – Miocene succession of the Middle East, particularly the elongate NW-trending Zagros foreland region, contains conflicting data, age and correlation interpretations (see for example the differences of opinion between Jones and Racey (1994) and Goff et al. (1995). For this succession in SP2 we incorrectly placed most emphasis on data within Motiei (1993) from southern Iran. Re-evaluation of data in the Iraq Stratigraphic Lexicon (van Bellen et al., 1959) shows that the better and more complete stratigraphic and age data exists in that work and should have been used in SP2. The extensive revisions herein to the Oligocene – Miocene MFS thus result from moving from Motiei (1993) to van Bellen et al. (1959) as the key source of published data.

In SP2, four MFS (Pg30, Ng10, Ng20 and Ng30) were recognised in the Oligocene–mid-Miocene succession of the Middle East based on Motiei (1993). However, van Bellen et al. (1959) recognise five (not four) cycles of carbonate progradation and retreat separated by widespread unconformities (see Figure 1, redrawn after van Bellen et al., 1959). This figure indicates that additional MFS are present above those recognised in SP2, and that all of the Oligo-Miocene SP2 MFS thus need revision with regard to their age and stratigraphic placement.

Whilst data in van Bellen et al. (1959) and other Iraqi literature (e.g. Ctyroky et al., 1975; Al-Hashimi and Amer, 1985) help locate and biostratigraphically calibrate the MFS in the Iraq succession, published data from adjacent areas is of too low a resolution to correlate the MFS regionally with sufficient confidence. Particularly, new sedimentological and biostratigraphic details need to be published on the Pabdeh – Asmari – Gachsaran – Mishan succession of the Iranian Zagros. However, re-evaluating regional data such as that in Motiei (1993) and Ziegler (2001), and the biostratigraphic data in papers such as Slinger and Crichton (1959) and Seyrafian et al. (1996), combined with the sequence stratigraphic principles outlined in Davies et al. (2002) for similar mixed siliciclastic-carbonate systems of the Middle East Cretaceous, has allowed revision to the SP2 scheme. It is worth stating that other authors have come to broadly similar conclusions looking at new data from Iran (e.g. Horbury et al., 2003; Noad et al., 2003).

MFS Ng40 - REVISION

Given uncertainties, in SP2, of the interpretation of the Ng40 MFS reference section in the Lower Fars of Kuwait, a new reference section for Ng40 is better defined within the Guri Member of the Mishan Formation of southern Iran. Its age is also revised in the light of more precise biostratigraphic data from late Serravalian (12 Ma) to late Langhian (15.5 Ma).

In SP2, MFS Ng40 was placed in carbonates within the Lower Fars of Kuwait, said to be late Miocene in age and correlative to the Mishan Formation of Iran (Fuchs et al., 1968). However re-examination of the data within Fuchs et al. (1968) suggests that their age interpretation is somewhat equivocal and that a better reference section is within the Guri Member of the Mishan Formation in Iran (James and Wynd, 1965; Kashfi, 1982). Fuchs et al. (1968) recorded the planktonic foraminifera Globorotalia menardii from rare carbonate beds within the Lower Fars of Kuwait, which would, if present, indicate an age probably no older than late Miocene. However, this species occurs in a sample otherwise containing foraminifera usually associated with very shallow water, perhaps even restricted, conditions (e.g. Quinqueloculina, Triloculina, Ammonia, Elphidium), conditions in which G. menardii would be unlikely to normally occur. It is most likely therefore that this species has been misidentified (it is not illustrated) and that any interpretation based on its supposed occurrence should be treated with caution. It is still likely that these carbonates represent MFS Ng40 (see discussion of MFS Ng30 below), but given that there are some uncertainties over the interpretation of the Kuwaiti section, a more precise and datable reference section is defined in Iran.

As described by James and Wynd (1965), the Mishan Formation is equivalent to the Middle Fars as described by Ion et al. (1951) and Slinger and Crichton (1959), and correlatable with marine intervals in the Middle Fars (also regarded as lower Upper Fars) of northern Iraq (van Bellen et al., 1959). The Guri Member (James and Wynd, 1965; Kashfi, 1982) is a clear open marine section within the Mishan Formation that includes MFS Ng40 and contains fauna (Miogypsina, Orbulina universa) that indicates a probable Middle Miocene age. Adams (1992) indicates that the youngest Miogypsina records should be within global planktonic zone N8 or N9. The co-occurrence of Miogypsina with Orbulina universa in the Mishan Formation thus indicates a correlation with zone N9 which equates to the Late Langhian in stage nomenclature (Berggren et al., 1995), and a date of approximately 15.5 Ma. An “Operculina swarm index bed” may locate this MFS in the data of Slinger and Crichton (1959).

MFS Ng30 - NEWLY DEFINED MFS:

This is a newly defined MFS not previously identified in SP2. A new MFS (defined here as MFS Ng30) is recognised in the early Langhian with a date of 16.3 Ma. It is located in marine carbonates (interbedded with evaporites) at the base of the Lower Fars Formation in northern Iraq (see Figure 1 and description in van Bellen et al., 1959).

For clarification, the Ng30 of SP2 was located in carbonates at the base of the Jeribe Formation in Iraq and assigned a middle Miocene, late Langhian age. Due to revisions of the Miocene MFS, this surface has now become Ng20 and is re-defined below.

Above the base Jeribe MFS, using data in van Bellen et al. (1959), Aqrawi et al. (1989), Aqrawi (1993) and Tucker (1999), a further MFS can be located in marine carbonates near the base of the Lower Fars Formation in Iraq overlying a shallowing-up succession in the underlying upper Jeribe Formation.

Van Bellen et al. (1959) regarded the Lower Fars of Iraq as being of a general middle Miocene age, whilst Jones and Racey (1994) suggested that it is probably of middle Miocene, mid-Serravalian age, following Prazak (1978) who suggested correlation with global planktonic foraminifera biozone N13 on the basis of the absence of Borelis melo curdica, but the presence of Miogypsina (see illustration of Al-Omari and Sadik, 1972). This interpretation is rejected here as Adams (1992) has shown that Miogypsina is likely to be no older than global planktonic foraminifera biozone N8 or N9 (i.e. Langhian). We thus regard this MFS as being of early Langhian age (in part also constrained by the age of underlying and overlying MFS) with an approximate date of 16.3 Ma.

Due to regional subsidence this MFS is likely to be restricted to the NW-trending Zagros Foredeep (Mesopotamian Basin) - no clear candidate for this surface is present to the west in the data of Fuchs et al. (1968) (see also isopach map and correlations of Aqrawi et al., 1989 and Aqrawi, 1993). This MFS may be located in the lower Gachsaran Formation of Lurestan, Iran, but probably not in the Gachsaran of Fars or the UAE, which are demonstrably older (Thomas, 1950; James and Wynd, 1965; Jones and Racey, 1994; Peebles, 1999). Data in Slinger and Crichton (1959) indicates a marine flooding event in Member 3 of their Lower Fars of Gachsaran field, Iran, which is equivalent to the Gachsaran Formation of modern usage.

MFS Ng20 - Revision from MFS Ng30 in SP2:

This surface was originally described as MFS Ng30 in SP2, but is renumbered here to MFS Ng20 as a result of revisions elsewhere in the Oligo-Miocene succession and the recognition of additional MFS (see above). Its age is also revised in the light of further research from late Langhian (15 Ma) to late Burdigalian (18.5 Ma).

As noted in SP2 (for Ng30 therein), this Ng20 MFS can be correlated with carbonates of the upper Asmari Formation in southern Iran. A distinctive biostratigraphic feature of both the Jeribe Formation of Iraq and the upper Asmari Formation is the presence of the larger foraminifera Borelis melo curdica (data in van Bellen et al., 1959; Slinger and Crichton, 1959; James and Wynd, 1965; Sampo, 1969; Prazak, 1978; Al-Hashimi and Amer, 1985; Seyrafian and Hamedani, 1998). According to Cahuzac and Poignant (1997),“Borelis gr. melo” (including B. melo curdica) ranges no older than Langhian, although van Bellen et al. (1959) indicate that there is some evidence for it occurring in Burdigalian strata. In the north-central part of the High Zagros as described by Seyrafian and Hamedani (1998), MFS Ng20 may be located in deeper water globigerinid wackestones lying within platform carbonates containing Borelis melo curdica. Borelis melo curdica possibly occurs in the underlying Euphrates Formation in northern Iraq (equivocal illustration in Al-Saddiqi, 1972), but in this formation Borelis melo melo is more common and Miogypsina globulina also occurs (see Ctyroky et al., 1975 and MFS Ng10 discussion below).

The precise age of this MFS is slightly uncertain given issues surrounding the range of the index fossil Borelis melo curdica. Given that the underlying MFS Ng10 is clearly Burdigalian and that overlying MFS Ng30 and Ng40 are no younger than Langhian it is likely that this MFS is late Burdigalian in age (18.5 Ma), an age supported by the occurrence of Borelis melo curdica in the Gachsaran of Fars Province (e.g. Sampo, 1969), which is Burdigalian by inference of strontium isotope data from correlative sediments in Abu Dhabi (Peebles, 1999).

MFS Ng10 - Revision from MFS Ng20 in SP2:

As part of the general revisions here to the Oligo-Miocene MFS, this surface is simply renumbered to MFS Ng10 from MFS Ng20 in SP2. It is also provided with a better reference section defined in Iraq (van Bellen et al., 1959) and its age is slightly revised from mid-Burdigalian (18 Ma) to early Burdigalian (20 Ma).

The oldest Neogene marine flooding within the Zagros foreland of Iraq occurs near the base of platform carbonates of the Euphrates Formation. These carbonates represent the near-base of a Neogene cycle of deposition in Iraq (see Figure 1 and van Bellen et al., 1959; Prazak, 1978).

Van Bellen et al. (1959) mention no age diagnostic fossils from the Euphrates Formation (it is highly dolomitised in its type section), whilst for the correlative deeper water Serikagni Formation a listing of generally early Miocene foraminifera is given (see also Al-Hashimi and Amer, 1985). Ctyroky et al. (1975), and Al-Hashimi and Amer (1985), recorded Miogypsina globulina from the Euphrates Formation indicating an early Burdigalian age (Biozone SB25 of Cahuzac and Poignant, 1997). Other distinctive taxa occurring are Borelis melo melo (Ctyroky et al., 1975) and, possibly, Borelis melo curdica (equivocal illustration in Al-Saddiqi, 1972).

MFS Ng10 is therefore early Burdigalian in age with an approximate date of 20 Ma. Correlation of this MFS into adjacent areas is problematic because of the lack of published detail on the Asmari stratigraphy of Iran. However, using regional data in Motiei (1993) and Zeigler (2001) and the sequence stratigraphic principles presented in Davies et al. (2002) (where shales in relatively shallow water mixed siliciclastic-carbonate successions are viewed as land-attached), it may be expressed in clean carbonates near the base of the Upper Asmari Formation (Slinger and Crichton, 1959; Motiei, 1993). It may lie in clean Miogypsina-bearing carbonates near the base of the exposed Asmari succession in the Dehdez area of the High Zagros as described by Seyrafian (2000).

MFS Pg50 - Revision from MFS Ng10 in SP2:

The early Miocene, Aquitanian age (23 Ma) of MFS Ng10 in SP2 is slightly revised here to a late Oligocene, Chattian age (24.5 Ma) MFS Pg50 using more precise data from north Iraq in van Bellen at al., 1959. A new reference section in north Iraq (van Bellen et al., 1959) is thus proposed for this surface instead of the Asmari of Iran (Motiei, 1993) as in SP2.

The original SP2 Ng10 MFS was defined in shales near the base of the Middle Asmari of the Ab Teymur field, southern Iran, and ascribed an Aquitanian age, using data in Motiei (1993). Using the sequence stratigraphic principles of Davies et al. (2002) in which shales in a mixed siliciclastic – carbonate system such as the Asmari (see Schlumberger Middle East Evaluation Review – Iran special supplement 1991; Motiei, 1993) are viewed as land-attached, we would now place the MFS in the overlying carbonates.

Although Motiei (1993) ascribed the Middle Asmari an Aquitanian age, and this was incorrectly followed in SP2, there is biostratigraphic evidence in both Slinger and Crichton (1959) and Motiei (1993) that the Middle Asmari (and hence its associated MFS) is in fact late Oligocene in age due to the presence of Miogypsinoides. It is worth noting that foraminiferal assemblages ascribed by some Iranian workers (James and Wynd, 1965; Motiei, 1993) to the Aquitanian are in fact better interpreted as late Oligocene. This confusion stems from the historical use of the term ‘Aquitanian’, which was used by some workers in the Middle East as being coincident (at least in part) with the late Oligocene of modern usage (see Henson, 1950; Eames, 1953).

Given the above uncertainties regarding this MFS in Iran (the SP2 reference section), we now correct SP2 and reference it to the Iraq succession of van Bellen et al. (1959), and hence change its age. MFS Pg50 is now defined near the base of the Anah Formation platform carbonates in Iraq. MFS Pg50 marks the maximum flooding surface at the base of a cycle of Oligocene deposition (see Figure 1 and van Bellen, 1956; van Bellen et al., 1959). It has equivalents near the base of the progressively deeper water Azkand and Ibrahim formations. These formations, and the Anah Formation, contain foraminiferal faunas that indicate a late Oligocene, Chattian age (24.5 Ma) for this MFS (van Bellen, 1956; van Bellen et al., 1959; Buday, 1980; Al-Hashimi and Amer, 1985, 1986). Miogypsinoides complanatus is a particularly distinctive element in platform facies, and is a clear indicator of late Oligocene age (Biozone SB23 of Cahuzac and Poignant, 1997).

For reasons given above, this MFS is probably regionally expressed in clean carbonates within the Middle Asmari of southern Iran. In some of the outcrops of the High Zagros, where the progradational base of the Asmari Limestone means that the Asmari is no older than Miocene in age (Thomas, 1950; James and Wynd, 1965), then this MFS probably lies in the underlying pelagic marls of the Pabdeh Formation. However there are other outcrops of the Asmari Limestone containing Miogypsinoides complanatus in High Zagros that may contain this MFS (Seyrafian et al., 1996).

MFS Pg40 - NEWLY DEFINED MFS:

This is a newly defined MFS not previously identified in SP2. A new MFS (defined here as MFS Pg40) is recognised in the “mid” Oligocene, late Rupelian, to early Chattian, with a date of 29 Ma. It is located near the base of Bajawan Formation carbonates in Iraq (see Figure 1, van Bellen, 1956; van Bellen et al., 1959).

This newly identified Pg40 MFS marks the base of a cycle of Oligocene deposition. It has equivalents near the base of the progressively deeper water Baba and Tarjil formations. These formations, and the Bajawan Formation, contain foraminiferal faunas that indicate a “mid” Oligocene, late Rupelian – early Chattian age (29 Ma) for this MFS (van Bellen, 1956; van Bellen et al., 1959; Al-Hashimi and Amer, 1985). The co-occurrence of Nummulites (Nummulites fichteli, Nummulites vascus) and Lepidocyclina (e.g. Lepidocyclina dilatata, Lepidocyclina elephantina) is a particularly distinctive element in outer platform facies (e.g. Baba Formation) (Al-Hashimi and Amer, 1985), and is a clear indicator of a mid-Oligocene age (Biozone SB22 of Cahuzac and Poignant, 1997). Nummulites fichteli also occurs in underlying MFS Pg30 (see SP2), but not in co-occurrence with Lepidocyclina. In more proximal facies the presence of Praerhapidionina delicata and the absence of Archaias kirkukensis characterises this MFS in the lower part of the Bajawan Formation (data in van Bellen et al., 1959).

Regionally, this MFS is probably expressed in clean carbonates within the lower Asmari of southern Iran where the Palaeogene succession is of continuous carbonate (Slinger and Crichton, 1959; Motiei, 1993; Seyrafian et al., 1996). In the outcrops of the High Zagros where the progradational base of the Asmari Limestone means that the Asmari is no older than Miocene in age (Thomas, 1950; James and Wynd, 1965), then this MFS, like Pg50 above, almost certainly lies in the underlying pelagic marls of the Pabdeh Formation that can be of mid-Oligocene age (Sampo, 1969).

MFS Tr10 - Age Revision:

Minor revision to the age of MFS Tr10, from 248 Ma in SP2 to 247 Ma here, is required following the paper by Stephenson et al. (2003), to which the reader is referred for details on the latest Permo-Triassic chronostratigraphic terminology. This MFS relates to the major transgression following the Permian/Triassic extinction event. Although in SP2 the reference section for this MFS is given as the base of the Khartam Member of the Khuff Formation in Saudi Arabia, we now place Tr10 just above the base of the formation because the underlying Tr10 unconformity occurs just within the Khartam Member (data in Le Nindre et al., 1990).

In SP2, this event was regarded as Scythian (i.e. Early Triassic) with an absolute age of 248 Ma. Data in Le Nindre et al. (1990) (occurrence of Spirorbis phylactaena), suggest this MFS lies more precisely within the Induan, although sparse faunas after the end-Permian extinction event make the chronostratigraphic calibration of this MFS difficult. Faunas elsewhere in Arabia at this MFS with Claraia bivalves (e.g. in the Iranian Zagros; Szabo and Kheradpir, 1978) confirm a general Early Triassic age. The occurrence of Densoisporites playfordii in the UAE (El-Bishlawy, 1985) is also in chronostratigraphic agreement. In conclusion, we now regard this MFS as intra-Induan in age with an absolute date of 247 Ma.

MFS P40 - Age Revision:

Minor revision to the age of MFS P40, from 249 Ma in SP2 to 249.5 Ma here, is required following the paper by Stephenson et al. (2003).

In SP2, this surface was defined within the Midhnab Member of the Khuff Formation in the outcrop of Saudi Arabia, and was regarded as latest Tatarian (latest Changhsingian) with an absolute age of 249 Ma. Sharland et al. (2001) used latest Tatarian in the sense of Latest Permian, although this concept no longer agrees with current thinking on Permian nomenclature (see, for example, Stephenson et al., 2003).

In any case, the Midhnab Member (and hence MFS P40) can be regarded as intra-Changhsingian in age on the basis of its foraminifera content using data in Manivit et al. (1983), Vaslet et al. (1985) and Le Nindre et al. (1990). Plant megafossils from this unit (the Jal Khartam flora of Broutin et al., 1995, following earlier descriptions by Hill and El-Khayal, 1983; El-Khayal et al., 1980; El-Khayal and Wagner, 1985 and Le Nindre et al., 1990) also indicate a Changhsingian age. We therefore now regard this MFS as intra-Changhsingian and therefore 249.5 Ma in age. It is likely that this MFS is locally removed by erosion associated with the overlying Tr10 SB. For example, in the Iranian Zagros, Szabo and Kheradpir (1978) and Virgone et al. (2002), indicate that the Latest Permian may be missing because of this erosion.

MFS P30 - Age Revision:

Minor revision to the age of MFS P30, from 250 Ma in SP2 to 250.5 Ma here, is required following the paper by Stephenson et al. (2003). In SP2, this surface was defined within lower Khuff C carbonates of Saudi Arabia, and was regarded as late Tatarian/basal Changhsingian with an absolute age of 250 Ma. We now regard this MFS as Wuchiapingian with an absolute age of 250.5 Ma.

P30 is now regarded as Wuchiapingian because the expression of this MFS in the Saudi outcrop (near the base of the Huqayl Member) contains Wuchiapingian foraminifera (data in Vaslet et al., 1985; Le Nindre et al., 1990), as does the overlying Duhaysan Member (data in Manivit et al., 1985, 1986; Le Nindre et al., 1990). Suggestions that the rich palynoflora of the underlying Ash Shiqqah Member are Changhsingian (Stephenson and Filatoff, 2000) are now regarded as erroneous – these assemblages may be as old as Capitanian (Stephenson et al., 2003). Further support for a Wuchiapingian age for MFS P30 comes from the Upper Dalan Formation of the Iranian Zagros, where Szabo and Kheradpir (1978) have recorded Dzulfian (= Wuchiapingian) foraminifera.

MFS Cm10 - Age Revision:

Minor revision to the age of MFS Cm10, from 540 Ma in SP2 to 542 Ma here is required in keeping with our acceptance that the Precambrian-Cambrian boundary should be dated at 542 Ma (see above) and that at its reference section in Oman, the MFS immediately overlies a radiometrically ash bed with a date of 542.0 +/- 0.3 Ma that acts as a proxy for the Precambrian-Cambrian boundary (Al-Husseini et al., 2003).

Nomenclature

The SP2 sequence stratigraphic model has resolved much lithostratigraphic confusion. The use of an up-to-date public domain sequence stratigraphic nomenclature will hopefully minimise the potential for new sequence stratigraphic confusion in the literature. For the moment we continue to use the SP2 nomenclature relating to the individual MFS (i.e. J50, K70 etc.), as it is a simple system reflecting both geological age (i.e. Jurassic, Cretaceous), and a quasi-3rd order cyclicity that works well at scales relevant to exploration and production models.

Arabian Plate Sequence Stratigraphy presented the initial SP2 model using genetic stratigraphic sequences (GSS, the reader is referred to SP2 for a full explanation of the SP2 nomenclature scheme). As these MFS gain a degree of acceptance, we are now moving to describing the sediments in depositional sequences (DS, sensuVail et al., 1977). The naming of key surfaces and system tract components in this new public domain nomenclature scheme works as follows in the example we show below (Figure 2):

  • a) the DS is named after the MFS it contains (i.e. the [J70] DS is the depositional sequence containing the [J70] MFS and bounded at its base by the [J70] sequence boundary and at its top by the overlying sequence boundary);

  • b) In basinal settings, a lowstand wedge may be present above the underlying correlative conformity (to the exposed sequence boundary on the surrounding shelf) and this is referred to as the [J70] LSW;

  • c) The transgressive systems tract sediments below the [J70] MFS are referred to as the [J70] TST;

  • d) The highstand systems tract sediments above the [J70] MFS are referred to as the [J70] HST.

At this early stage it is probably best not to be too prescriptive with this new nomenclature, as there are major ‘ordering’ issues yet to be overcome in its usage.

ACKNOWLEDGEMENTS

The authors would like to thank all those who have taken the time to stop and share their ideas at our posters at GEO2002 and AAPG 2003 (Salt Lake City and Barcelona). We are also grateful to Joerg Mattner for help with parts of the Syrian stratigraphy, and for the encouragement and support of Dr. Moujahed Al-Husseini and all the staff at Gulf PetroLink.

ABOUT THE AUTHORS

Peter Sharland is both Managing Director of Neftex Petroleum Consultants Ltd and an active member of the technical team. His role thus mixes company management with technical interpretation. Peter founded Neftex Petroleum Consultants Ltd in 2001 after leaving LASMO following the company’s acquisition by ENI. He has specific responsibility to continue to grow the company. Peter has worked on global geoscience projects, as well as projects in the Middle East, North Africa and the Former Soviet Union (Russia, Kazakhstan, Turkmenistan, Azerbaijan, and Caspian Region). Peter is in great demand both for technical projects and as a corporate strategic advisor. Peter received his BSc in Geology from London University in 1983, and has 20 years of industry experience with US (LL&E) and UK (LASMO) Independents, a Major oil company (BP), and now as a consultant. He was brought up in West Africa, was educated through university in the UK, and enjoys mixing with other cultures as part of business and family travel.

peter.sharland@neftex.com

David Casey is Technical Director and co-founder of Neftex Petroleum Consultants Ltd, and has 20 years of oil industry experience. His responsibilities include the definition and implementation of technical excellence within the company. Prior to co-founding the company in 2001, he was an independent geoscience consultant specialising in the petroleum geology of the Middle East and Greater Caspian regions. He is also a co-author of Arabian Plate Sequence Stratigraphy. Dave began his career as a petroleum geologist with BP in 1983, where he spent 11 years gaining experience on the United Kingdom and the Middle East and Caspian. Dave holds a BSc in Geology and an MSc in Hydrogeology from Reading University, as well as a PhD in Sedimentary Geology and Tectonics from Oxford University. Dave is also a facilitator with the Earth Science Education Unit (ESEU), helping to raise awareness and understanding of geoscience in the national secondary school curriculum. His interests include Tethyan structural geology, and the definition of an integrated tectono-stratigraphic history of North Africa and the Arabian Plate.

dave.casey@neftex.com

Roger Davies is New Business Director and co-founder of Neftex Petroleum Consultants Ltd. He has over 20 years of oil industry experience with a Major oil company (BP) and as an independent geoscience consultant, concentrating on the Middle East, North Sea and North America. In recent years he has specialised in high-resolution sequence stratigraphy and static reservoirs of the Middle East. Roger was a co-author of the GeoArabia Special Publication Arabian Plate Sequence Stratigraphy, and has published several other papers on Middle East geoscience and numerous company reports. His early career was spent as a Sedimentologist working worldwide on carbonate and clastic reservoirs for BP. Roger has a PhD in Carbonate Sedimentology and Micropalaeontology from Southampton University, and a BSc in Geology from Bristol University.roger.

davies@neftex.com

Michael Simmons is Director of Geoscience, in this role he promotes new company business (Neftex MENA), and develops Geoscience within the company. Mike specialises in the petroleum geology and stratigraphy of the Middle East, North Africa, the FSU and the Black Sea – Caspian Sea regions. He was previously Director and Chief Geologist of CASP at Cambridge University, and prior to that Head of the Department of Geology and Petroleum Geology at the University of Aberdeen in Scotland. Before moving to Scotland, Mike spent 11 years with BP working as a Senior Geologist and Biostratigrapher in international exploration. Mike’s experience and expertise make him a valuable member of the Neftex MENA team. Mike holds a BSc and PhD from Plymouth University, and has edited and published extensively on micropalaeontology, biostratigraphy and the geology of the Middle East and Caspian regions, and he is also a co-author of Arabian Plate Sequence Stratigraphy. He has given numerous presentations at international conferences and presented several courses to industry. His research interests include applied biostratigraphy, the geology of the Tethyan region and the use of outcrop analogues in understanding subsurface reservoirs.

mike.simmons@neftex.com

Owen Sutcliffe graduated from the University of Leeds in 1993 with a BSc (Hons) in Geological Science and was subsequently awarded a PhD from the University of Bristol in 1997. Owen’s main geological interests focus on the stratigraphic and sedimentological evolution of Palaeozoic petroleum systems in North Africa and the Middle East, but he also specialises in the application of glacial sedimentological models to the glacially-influenced Upper Ordovician reservoirs of these regions. Owen also acts as an advisor to a PhD student from the University of Wales, Aberystwyth. After 2 years post-doctoral research on the architectural character of the upper Ordovician in North Africa (University of Wales, Aberystwyth and LASMO), Owen started a 3-year career with Badley Ashton & Associates. The highlights of this position include a country-wide reappraisal of the upper Ordovician stratigraphy of Saudi Arabia and the development of architectural models for Carboniferous incised valley-fills in Algeria. Owen joined Neftex on 1st December, 2003.

owen.sutcliffe@neftex.com