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SUPERGROUPGROUPFORMATION
HaimaSafiqSahmah
Hasirah
Saih Nihayda
AndamGhudun
Barakat
Mabrouk
Barik
Al Bashair
Mahatta HumaidMiqrat
Mahwis
Amin
SUPERGROUPGROUPFORMATION
HaimaSafiqSahmah
Hasirah
Saih Nihayda
AndamGhudun
Barakat
Mabrouk
Barik
Al Bashair
Mahatta HumaidMiqrat
Mahwis
Amin

Authors: Von der Weid (unpublished, 1967), in which the Haima was originally defined as a Group for all the Palaeozoic clastic-dominated formations above the Buah dolomite and below the Khuff Formation. Restricted to the Lower Palaeozoic by Winkler (1975; see also Hughes Clarke, 1988) and upgraded to Supergroup by Priebe and Kapellos (1993; partly published in Boserio et al., 1995). Subsequently, revised by Droste (1997) and further revised by Droste (2001), who removed the tectonostratigraphically distinct Nimr Group from the Haima Supergroup and placed it within the Huqf Supergroup.

Introduction

The Haima Supergroup is a major siliciclastic-dominated unit of Cambrian to early Silurian age.

The basal Angudan unconformity of the Haima Supergroup reflects a major deformation/thermal event dated at about 540–520 Ma, associated with the convergence and subsequent transpressional/transtensional continent-continent collision between East Gondwanaland and West Gondwanaland (Immerz et al., 2000; van den Berg et al., 2008). This was associated with reactivation of the Maradi Fault system, localised deformation and inversion throughout Oman with resultant salt movement and dissolution. Subsequently, Oman was effectively a passive margin (Loosveld et al., 1996) throughout the early Palaeozoic. However, weak extension continued throughout deposition of the Haima Supergroup into, at least, the Late Ordovician (Oterdoom et al., 1999; Worthing and Nasir, 2008). Halokenesis and its effect on sedimentation were further enhanced by this extension.

This relatively stable phase ended with the collision of Gondwana and Laurasia during the Carboniferous (‘Hercynian’ event), in time associated with the base Haushi unconformity (Konert et al., 2001; Al-Husseini, 2004; Faqira et al., 2009), which truncates the Haima Supergroup.

It is important to stress that when considering pre-Hasirah formations that continental depositional settings and sediment composition were not influenced at all by the presence of, yet to evolve, land plants.

Type and reference sections: A combination of outcrops in the Al Huqf area and South and west Oman well sections as detailed at Group and Formation level.

Lithology: The Haima Supergroup is a major composite siliciclastic succession, locally with minor limestone development. It was deposited in both continental and marine environments. The basal part (Mahatta Humaid Group) was deposited in arid to semi-arid, continental settings and the upper part (Andam and Safiq groups) was deposited in marine, marginal marine and marine-influenced environments, with minor dolomites and limestones. It is separated from the underlying Huqf Supergroup by a major unconformity (the Angudan).

Boundaries: The Haima Supergroup unconformably overlies the siliciclastics, carbonates or evaporites of the Huqf Supergroup and is unconformably overlain by the Misfar, Haushi or younger groups.

Distribution: The Haima Supergroup is present throughout the subsurface basins of Oman, and in the Al Huqf outcrop area. The Mahatta Humaid and Andam groups are partially defined at outcrop in the northern Al Huqf area.

The Amdeh Formation outcropping in the Saih Hatat region of the Eastern Al Hajar Mountains (Lovelock et al., 1981; Le Métour et al., 1986) is at least partially age equivalent to the Haima Supergroup (see also Sansom et al., 2009; Booth, 2009).

The Rann Formation (Glennie, 1974) in the northern extension of the Al Hajar Mountains in the United Arab Emirates (Hudson et al., 1954) is a clastic unit with marine fossils indicating an Ordovician age, see Rickards et al. (in preparation). It may be a lateral equivalent of the Haima sediments, but is part of an allochthonous unit of uncertain original position. The Saq, Qasim and Qalibah clastics dominated formations in Saudi Arabia are probably lateral Haima equivalents in essentially the same depositional regime (Sharland et al., 2001; Al Husseini, 2008; Faqira et al., 2009).

Subdivision:Hughes Clarke (1988), Priebe and Kapellos (1993), Droste (1997) and Mohammed et al. (1997) included the Nimr Group within the Haima Supergroup. Tectonostratigraphically this unit belongs to the Huqf Supergroup as re-assigned by Droste (2001), an approach which is followed in this Lexicon.

A three-fold subdivision is made corresponding to the Safiq, Andam and Mahatta Humaid groups. This division and summary descriptions of the formations are provided as follows:

SupergroupGroupFormationShort Description
HaimaSafiqSahmahAbsent through erosion over most of Oman, occurring only in the westernmost parts of Central and South Oman, along the western edge of the Rub’ Al-Khali Basin and extending into Saudi Arabia. The Sahmah Formation is a major transgressive-regressive cycle, comprising organic-rich shales interbedded with sandstones stacked in a fining-coarsening upward trend. Recognition is based on the presence of the 1003 Palynozone (Latest Ordovician – early Silurian, Hirnantian – ?early Aeronian).
HasirahWidespread in North, Central and southwestern regions of Oman, the Hasirah Formation is probably a major marine transgressive-regressive cycle. It commonly fills-in significant erosional topography where it is dominated by mudrocks. Elsewhere it may comprise medium- to coarse-grained, commonly thickly bedded sandstones, interstratified with dark grey organic-rich shales, which may be capped by a thick sandstone unit. Contains the O40 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1005 Palynozone (Late Ordovician, Katian).
Saih NihaydaMost extensive in the northern region of Oman, but also extending into the northern part of the South Oman Salt Basin. The Saih Nihayda Formation can be eroded beneath the base Hasirah unconformity. It is probably a major transgressive-regressive cycle, comprising a basal sandstone, overlain by dark grey shales which are capped by another sandy unit. Contains the O30 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1098 Palynozone (Middle Ordovician, Darriwilian).
AndamGhudunThe most widespread and thickest unit of the Haima. The Ghudun Formation is primarily a cross-bedded to laminated sandstone section, which represents fluvial channel and sheet-flood deposits in a deltaic setting. To the northwest it becomes more marine, confirmed by the presence of acritarchs and bioclasts in some horizons. Typically highly feldspathic with siltstones, occasionally intercalated with shales. Occasionally yields the 1100 Palynozone (Early-Middle Ordovician, late Floian – early Dapingian) in the Upper Ghudun. The Formation is more often barren and probably ranges down to the Floian/?Tremadocian.
BarakatWidespread over Central and North Oman, the Barakat Formation is a marine transgressive-regressive cycle, incorporating a significant maximum flooding (MFS O20 of Sharland et al., 2001). The base is typically a sandstone, overlain by reddish-brown or greenish shales, which are capped by a sandy unit. Yields the 1108C and 1108B Palyno-subzones (Early Ordovician, Tremadocian).
MabroukWidespread over Central and North Oman and is dominated by shallow-marine muddy sediments that are reddish-brown interbedded with thin sandstones. Contains the O10 MFS (Sharland et al., 2001). Recognition partly based on the presence of the 1108B Palyno-subzone (Early Ordovician, Tremadocian).
BarikWidespread over Central and North Oman the Barik Formation, is dominantly a braid delta complex but grades into a shallow-marine system to the north. In-situ palynomorphs have yet to be recorded, as ditch cuttings yield is probably due to caving.
Al BashairWidespread over North Oman, the Al Bashair Formation is a shallow-marine sequence that, in its upper part comprises grey to reddish-brown mudstones intercalated with sands and in its lower part is dominated by fine-grained sandstones and argillaceous siltstones intercalated with shales and carbonates. Contains the Cm30 MFS (Sharland et al., 2001). Characterised by the 1108A Palyno-subzone (‘Late’ Cambrian*, Furongian).
Mahatta HumaidMiqrat/MahwisThe Miqrat Formation is present in North and Central Oman, whilst the Mahwis Formation, which is likely to be its lateral equivalent, occurs only in South Oman. Both were deposited in arid to semi-arid continental settings. The Miqrat Formation was deposited in playa/ephemeral lake-sabkha environments with a periphery of sheet-flood alluvial deposition, whereas the Mahwis Formation may have been deposited in distal alluvial fan with local playa environments. Both formations are barren of palynomorphs and all other marine indicators.
AminWidespread throughout Oman, the Amin Formation is a complex, arid depositional system including alluvial, fluvial and aeolian deposits. The base is a conglomeratic unit overlain by alternating sandy, conglomeratic and shaly intervals with the upper part generally a clean sandstone including some restricted aeolian units. Barren of palynomorphs and all other marine indicators.
SupergroupGroupFormationShort Description
HaimaSafiqSahmahAbsent through erosion over most of Oman, occurring only in the westernmost parts of Central and South Oman, along the western edge of the Rub’ Al-Khali Basin and extending into Saudi Arabia. The Sahmah Formation is a major transgressive-regressive cycle, comprising organic-rich shales interbedded with sandstones stacked in a fining-coarsening upward trend. Recognition is based on the presence of the 1003 Palynozone (Latest Ordovician – early Silurian, Hirnantian – ?early Aeronian).
HasirahWidespread in North, Central and southwestern regions of Oman, the Hasirah Formation is probably a major marine transgressive-regressive cycle. It commonly fills-in significant erosional topography where it is dominated by mudrocks. Elsewhere it may comprise medium- to coarse-grained, commonly thickly bedded sandstones, interstratified with dark grey organic-rich shales, which may be capped by a thick sandstone unit. Contains the O40 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1005 Palynozone (Late Ordovician, Katian).
Saih NihaydaMost extensive in the northern region of Oman, but also extending into the northern part of the South Oman Salt Basin. The Saih Nihayda Formation can be eroded beneath the base Hasirah unconformity. It is probably a major transgressive-regressive cycle, comprising a basal sandstone, overlain by dark grey shales which are capped by another sandy unit. Contains the O30 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1098 Palynozone (Middle Ordovician, Darriwilian).
AndamGhudunThe most widespread and thickest unit of the Haima. The Ghudun Formation is primarily a cross-bedded to laminated sandstone section, which represents fluvial channel and sheet-flood deposits in a deltaic setting. To the northwest it becomes more marine, confirmed by the presence of acritarchs and bioclasts in some horizons. Typically highly feldspathic with siltstones, occasionally intercalated with shales. Occasionally yields the 1100 Palynozone (Early-Middle Ordovician, late Floian – early Dapingian) in the Upper Ghudun. The Formation is more often barren and probably ranges down to the Floian/?Tremadocian.
BarakatWidespread over Central and North Oman, the Barakat Formation is a marine transgressive-regressive cycle, incorporating a significant maximum flooding (MFS O20 of Sharland et al., 2001). The base is typically a sandstone, overlain by reddish-brown or greenish shales, which are capped by a sandy unit. Yields the 1108C and 1108B Palyno-subzones (Early Ordovician, Tremadocian).
MabroukWidespread over Central and North Oman and is dominated by shallow-marine muddy sediments that are reddish-brown interbedded with thin sandstones. Contains the O10 MFS (Sharland et al., 2001). Recognition partly based on the presence of the 1108B Palyno-subzone (Early Ordovician, Tremadocian).
BarikWidespread over Central and North Oman the Barik Formation, is dominantly a braid delta complex but grades into a shallow-marine system to the north. In-situ palynomorphs have yet to be recorded, as ditch cuttings yield is probably due to caving.
Al BashairWidespread over North Oman, the Al Bashair Formation is a shallow-marine sequence that, in its upper part comprises grey to reddish-brown mudstones intercalated with sands and in its lower part is dominated by fine-grained sandstones and argillaceous siltstones intercalated with shales and carbonates. Contains the Cm30 MFS (Sharland et al., 2001). Characterised by the 1108A Palyno-subzone (‘Late’ Cambrian*, Furongian).
Mahatta HumaidMiqrat/MahwisThe Miqrat Formation is present in North and Central Oman, whilst the Mahwis Formation, which is likely to be its lateral equivalent, occurs only in South Oman. Both were deposited in arid to semi-arid continental settings. The Miqrat Formation was deposited in playa/ephemeral lake-sabkha environments with a periphery of sheet-flood alluvial deposition, whereas the Mahwis Formation may have been deposited in distal alluvial fan with local playa environments. Both formations are barren of palynomorphs and all other marine indicators.
AminWidespread throughout Oman, the Amin Formation is a complex, arid depositional system including alluvial, fluvial and aeolian deposits. The base is a conglomeratic unit overlain by alternating sandy, conglomeratic and shaly intervals with the upper part generally a clean sandstone including some restricted aeolian units. Barren of palynomorphs and all other marine indicators.
*

The Cambrian timescale is currently in a state of flux with four global series and ten international stages (Ogg et al., 2008), therefore ‘Late’, ‘Middle’ and ‘Early’ designations are used informally (these equate to Furongian, and approximately Epoch 3 and Epoch 2 - Terreneuvian respectively). Where possible a Series/Epoch or Stage/Age qualification is given.

Sequence stratigraphy: The Haima Supergroup represents the AP2 and basal AP3 Megasequences of Sharland et al. (2001). Their MFS surfaces Cm30 through to O40, and possibly S10, correlate into Omani sections.

The Haima Supergroup represents at least one and possibly two composite sequences commencing with the non-marine, arid to semi-arid siliciclastics of the Mahatta Humaid Group (a lowstand sequence set), and terminating with deeper-marine facies of the Safiq Group. A number of third- and higherorder sequences can be interpreted within this overall composite sequence, largely the Andam Group, including the transgressive and highstand successions of the Al Bashair Formation and the subsequent lowstand/transgressive-highstand sequence set of the Barik-Mabrouk formations (e.g. Millson et al., 2008).

Age: ‘Early’ Cambrian – early Silurian, Epoch 2 – ?early Aeronian, ca. 520–438 Ma.

Biostratigraphical evidence dates the Al Bashair (‘Late’ Cambrian) through to Sahmah (early Silurian) formations. No age calibration is available for the Mahatta Humaid Group, where an extremely tentative ‘Early’ Cambrian age is assigned as the oldest potential age. The application of various Sharland et al. (2001) MFS surfaces (ranging MFS Cm30 to ?S10) are noted above and further discussed at Formation level.

Biostratigraphy: Five Palynozones with nine Palyno-subzones are applied to the Haima Supergroup as follows:

ZoneSubzoneMarker species *Relative ageFormation/Unit
  Diexallophasis denticulataHirnantian – ?early Aeronian 
1003BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)Sahmah
 AVillosacapsula setosapellicula(Hirnantian) 
  Cheleutochroa spp.  
1005BCheleutochroa sppKatianHasirah
 A**Baltisphaeridium spp.  
  Stelliferidium cf. striatulum  
1098BStelliferidium cf. striatulumDarriwilianSaih Nihayda
ABuedingiisphaeridium? spp./Tylotopalla? spp.
1100 Coryphidium bohemicumlate Floian – early DapingianUpper Ghudun
  Acanthodiacrodium spp.Furongian – TremadocianAl Bashair – Barakat
1108CAcanthodiacrodium spp.(late Tremadocian)(Barakat)
BVulcanisphaera africana(Tremadocian)(Mabrouk – Barakat)
 AVeryhachium? dumontii(Furongian)(Al Bashair)
ZoneSubzoneMarker species *Relative ageFormation/Unit
  Diexallophasis denticulataHirnantian – ?early Aeronian 
1003BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)Sahmah
 AVillosacapsula setosapellicula(Hirnantian) 
  Cheleutochroa spp.  
1005BCheleutochroa sppKatianHasirah
 A**Baltisphaeridium spp.  
  Stelliferidium cf. striatulum  
1098BStelliferidium cf. striatulumDarriwilianSaih Nihayda
ABuedingiisphaeridium? spp./Tylotopalla? spp.
1100 Coryphidium bohemicumlate Floian – early DapingianUpper Ghudun
  Acanthodiacrodium spp.Furongian – TremadocianAl Bashair – Barakat
1108CAcanthodiacrodium spp.(late Tremadocian)(Barakat)
BVulcanisphaera africana(Tremadocian)(Mabrouk – Barakat)
 AVeryhachium? dumontii(Furongian)(Al Bashair)
*

Zonal index/marker species newly assigned for all Haima Palynozones (Mohiuddin et al., 2007 and Booth, 2009), original code based names no longer apply.

**

Previously Palynozone 1012.

The oldest interval in which biostratigraphic control exists is the Al Bashair Formation of the Andam Group (e.g. Droste, 1997; Molyneux et al., 2006). Over the whole of the Haima Supergroup five Palynozones are recognised, four of which are divided into a total of nine Palyno-subzones (Mohiuddin et al., 2007 and Booth, 2009, see Figure 12.1). The zonation is primarily based on marine acritarch content, but particularly in the Safiq Group significant amounts of cryptospores (from primitive plants) and marine chitinozoa are also recorded. Work on the latter Group has been fundamental in assigning more robust ages to the Palynozones in the Middle Ordovician – early Silurian sections (Paris, 2002, 2005 and 2006). Many uncertainties remain in the application of this zonation and in particular the extent of missing section between formations in the Safiq Group (Figure 12.1).

Figure 12.1.

Cambrian to Silurian biostratigraphical and chrono-stratigraphical subdivision of the Safiq and Andam groups (Booth, 2009).

Figure 12.1.

Cambrian to Silurian biostratigraphical and chrono-stratigraphical subdivision of the Safiq and Andam groups (Booth, 2009).

HAIMA SUPERGROUP SAFIQ GROUP

GROUPFORMATION
SafiqSahmah
Hasirah
Saih Nihayda
GROUPFORMATION
SafiqSahmah
Hasirah
Saih Nihayda

Authors:Winkler and Rácz (1978), see also Hughes Clarke (1988), upgraded to Group status by Priebe and Kapellos (1993), see also Droste (1997).

Introduction

The Safiq Group is only fully preserved in western parts of Interior Oman, and is interpreted to have transgressed from north to south and from the centre of the Rub’ Al-Khali Basin to its flanks between middle Ordovician and early Silurian times, by onlapping onto the eroded surface of the Ghudun Formation. The Safiq Group consists of open marine to restricted/marine sediments stacked into a number of transgressive-regressive cycles. An unconformity occurs above the Hasirah Formation, associated with the sudden influx of fluvial to deltaic sands in a deeper-marine setting, suggesting significant drops in sea-level. This has been tentatively correlated with major continental glaciations that have been reported from the Katian?/Hirnantian to ?Rhuddanian of Saudi Arabia (Droste, 1997). However, Miller and Al-Ruwaili (2007) restrict glacially-influenced sedimentation in Saudi Arabia to the Hirnantian. Oman was positioned at the margin of this glacial realm and it should be noted that to date glacial sediments have not been reported in Oman. Large-scale canyons seen on seismic of North Oman are filled with Katian sediments and are therefore considered to pre-date any proven glacial period in the region.

The potentially glacial-induced regression and subsequent transgression was followed by a rapid flooding of the Gondwana platforms with widespread accumulation of marine anoxic organic-rich mudrocks of the Sahmah Formation (Svendsen, 2004). The organic-rich beds represent the eastern extension of a thick interval of rich marine source rocks in the Silurian Qalibah Formation (Qusaiba Member) of Saudi Arabia, whose origin is linked to widespread anoxic conditions and high organic productivity, possibly as the result of the flooding of extensive shelf areas.

Type and reference sections: Composite sections from formational type wells provide a Group ‘type’ overview (Figure 12.2). These are Sahmah-1 in Central Oman (Figure 12.3), Hasirah-1 in Central Oman (Figure 12.6) and Saih Nihayda-24 in North Oman (Figure 12.10). For additional subsurface reference sections, see individual formations.

Figure 12.2.

Location map: Safiq Group/Haima Supergroup.

Figure 12.2.

Location map: Safiq Group/Haima Supergroup.

Figure 12.3.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Sahmah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.3.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Sahmah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Lithology: Fine-grained to coarse-grained, variably micaceous quartz and slightly arkosic sandstones, with lesser argillaceous sands, silts and shales. The shale-to-sand sequences show gross coarsening-upward cycles, and the shalier units may be organic-rich and yield marine palynomorphs and chitinozoa.

Subsurface recognition: Lithologically the formations of the Safiq are similar and it is impossible to differentiate between the Sahmah, Hasirah and Saih Nihayda formations on lithology alone. Recognition of the three Palynozones 1003, 1005 and 1098 is often the only way to confidently differentiate between them.

Boundaries: The upper boundary is formed by the top Haima hiatus or unconformity overlain by the Haushi Group. Haushi clastics lying upon Safiq clastics may not provide a marked lithological change, and confirmation by palynological dating may be necessary. Care should be taken as reworking may confuse the palynological signature at this boundary.

The lower boundary is also not always a marked lithological change. South of latitude 20°, the Safiq lies upon various continental clastic units of the Haima. The base of the Safiq has previously been defined as the lowest evidence of marine influence, but there are significant marine intervals in the Ghudun Formation, notably the Upper Ghudun, and this no longer strictly applies. Recognition of the usually distinctive log character of the Ghudun helps make a more reliable boundary pick. To the north, the Safiq lies upon the older formations of the Andam Group, which comprises very similar marginalmarine clastics. The boundary is often formed by the base of a transgressive-marine shale overlying sands. Palynological dating can assist in ambiguous cases. There is palynological evidence for a hiatus between Andam and Safiq marine sedimentation (Booth, 2009; Figure 12.1).

Distribution: The Safiq clastic sediments are found only in the western parts of Interior Oman and are progressively, partially to totally, truncated by the post-Haima unconformities from northwest to southeast onto the Al Huqf axis.

The youngest intervals are found in wells near Oman’s western border.

Biostratigraphic data from the Amdeh Formation outcrops in the Saih Hatat of the Al Hajar Mountains, originally documented by Lovelock et al. (1981) indicate that the ‘Upper Siltstone Member’ (Amdeh Unit 5, after Le Métour et al., 1986) is time equivalent to the Saih Nihayda Formation (see also Sansom et al., 2009 and Rickards et al., in preparation).

Deposition: The Safiq Group is a mainly marine clastic sequence with facies and age indications derived from acritarch and chitinozoan assemblages. The range of recovery from barren sands to shales with rich and diverse assemblages indicates a general interplay of regressive to transgressive cycles in an overall marginal to at times fully marine setting.

Subdivision: Three formations are defined in this Group: Sahmah, Hasirah, and Saih Nihayda.

Sequence stratigraphy: The Safiq Group corresponds to the upper part of the AP2 and the basal part of the AP3 Megasequences of Sharland et al. (2001). Their MFS surfaces O30, O40 and possibly S10 may be correlated into Omani sections.

Age: Middle Ordovician to early Silurian, Darriwilian – ?early Aeronian, ca. 467–438 Ma.

Biostratigraphy: The three formations within the Safiq Group are each characterised by conspicuously different palynological assemblages, which define the PDO Palynozones 1003, 1005 and 1098, equating to the Sahmah, Hasirah and Saih Nihayda formations respectively (Mohiuddin et al., 2007 and Booth, 2009).

ZoneSubzoneMarker speciesRelative ageFormation/Unit
1003 Diexallophasis denticulataHirnantian – ?early AeronianSahmah
BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)
AVillosacapsula setosapellicula(Hirnantian)
1005 Cheleutochroa spp.KatianHasirah
BCheleutochroa spp.
A*Baltisphaeridium spp.
1098 Stelliferidium cf. striatulumDarriwilianSaih Nihayda
BStelliferidium cf. striatulum
ABuedingiisphaeridium? spp./Tylotopalla? spp.
ZoneSubzoneMarker speciesRelative ageFormation/Unit
1003 Diexallophasis denticulataHirnantian – ?early AeronianSahmah
BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)
AVillosacapsula setosapellicula(Hirnantian)
1005 Cheleutochroa spp.KatianHasirah
BCheleutochroa spp.
A*Baltisphaeridium spp.
1098 Stelliferidium cf. striatulumDarriwilianSaih Nihayda
BStelliferidium cf. striatulum
ABuedingiisphaeridium? spp./Tylotopalla? spp.
*

Previously Palynozone 1012.

Subdivision is possible within these Palynozones and the most useful data is derived from the study of marine palynomorphs (acritarchs and chitinozoa). Consequently, biozonal resolution is at its best when sedimentation was in the marine realm. If sampling is sufficiently detailed many transgressive and regressive events can be observed through the study of variation in acritarch diversity.

Work on chitinozoa has been fundamental in assigning more robust ages to the acritarch zones in these Middle Ordovician – early Silurian sections (Paris, 2002, 2005 and 2006).

Sahmah Formation

Authors: The Sahmah was defined as a member of the then Safiq Formation by Wiemer (1981) and Oprinsen (1986), see also Hughes Clarke (1988), and upgraded to Formation status by Priebe and Kapellos (1993), see also Droste (1997).

Introduction

The early Silurian Sahmah Formation is the uppermost unit distinguished in the Safiq Group. It is a marine succession comprising micaceous, dark grey, organic-rich shales (locally orange/reddish brown) intercalated with grey sandstones. It was originally defined to include all lower Silurian sediments and is represented by Palynozone 1003 (Droste and Mohammed, 1994; Droste, 1997), although more recently it has been proposed that the sequence may also include sediments of latest Ordovician age (Svendsen 2004, discussed by Molyneux et al., 2006; Booth, 2009).

The Sahmah shales typically have a very high (>200 API) Gamma ray peak towards the base, representing a Maximum Flooding Surface, above which it generally coarsens upwards.

Droste (1997) compares the Sahmah Formation to the Qusaiba Member of the Qalibah Formation in Saudi Arabia (Mahmoud et al., 1992).

Type and reference sections: Sahmah-1 in Central Oman (Figure 12.3). Additional subsurface reference sections are Rabkha-1 in Central Oman (Figure 12.4), Wadi Qitbit-1 (Figure 12.5) and Burkanah-1 (see figure 7 of Svendsen, 2004), both in South Oman.

Figure 12.4.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Rabkha-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.4.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Rabkha-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.5.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Wadi Qitbit-1, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.5.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Wadi Qitbit-1, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Lithology: The Sahmah Formation consists of sandstones and predominantly organic-rich, micaceous, grey shales/siltstones with occasional and varying quantities of orange/reddish-brown shales. The latter seem confined to southwest South Oman. The Formation is characterised by fining- and coarsening-upward packages separated by relatively more organic-rich shales.

At the base of the Formation a sandy unit may be present. Described by Droste (1997) as fining up, it can equally have a marked blocky character (see Svendsen, 2004, where he places this sand in the Hasirah Formation). These sandstones are overlain by a very organic-rich shale bed, which can be recognised on logs by the very high Gamma peak, which is a very useful marker for correlation. Above this bed an overall coarsening-upward trend occurs from laminated micaceous shales with siltstone to finegrained sandstone streaks grading upwards into medium grained, in places medium to coarse-grained, thick-bedded sandstones with some shaly interbeds. The sandstones contain ripples, fining upwards waning-flow sequences and mudstone clasts.

Subsurface recognition: Whilst drilling, the Sahmah Formation is seen as a change from the grey shales, sandstones and diamictites of the Al Khlata Formation to finer grained, angular sandstones and micaceous, organic-rich, grey/(rarely orange/reddish-brown) shales.

The grey shales are much more micaceous than those of the Al Khlata. The Rate of Penetration log is very variable but quite accurately reflects sand/shale changes.

The base of the Sahmah Formation is picked at the base of the (typically) fining-upwards sandstone below a shaly unit. Unlike the Ghudun, the Sahmah shales are never greenish in colour.

Hotshot samples may be required to identify Palynozone 1003.

Post-drilling the Formation is recognised by detailed palynological analysis. The top of the unit is commonly marked by an abrupt transition to high Gamma ray readings and a negative drill break. The sandstones are very light grey when clean and have low Gamma values and are medium to dark grey with slightly higher Gamma values when silty and micaceous. The succession shows a distinct coarsening-upward trend.

A high Gamma shale (often 200+ API) occurs towards the base and generally overlies a sandstone of variable thickness. This sandstone is assigned to the Sahmah and forms the base of the unit.

Overall the unit features a typical upward-cleaning trend from a very high Gamma ray peak (over 200 API) at the base. The lower shale-dominated interval is slightly serrate, the upper interbedded shales and sandstones are highly serrate.

Palynological analysis will confirm a 1003 Palynozone age in the lower, more shaly part of the section.

Boundaries: The top of the Formation is generally a major unconformity at the base of the Permian – Carboniferous Al Khlata Formation.

The Sahmah overlies the Hasirah Formation (possibly unconformable, Booth, 2009), or rests unconformably on older sediments. Confusion arises from the formational assignment of the basal sand unit, which was placed in the Sahmah Formation by Droste (1997). Svendsen (2004) defines base Sahmah as the base of the high Gamma shale package, thereby placing this sand in the upper Hasirah Formation. Palynological confirmation is currently sparse and uncertain.

Distribution: The Sahmah Formation is present along the western edge of the Rub’ Al-Khali Basin and extends into Saudi Arabia. Widespread post-Haima erosion has probably removed the Sahmah Formation from much of Oman and typically only the shaly part at the base of the Formation is preserved in the north with the full succession occurring to the south (Svendsen, 2004). The Formation thickens from zero in the north to in excess of 500 m in southwest South Oman (Figure 9 of Svendsen, 2004). Oterdoom et al. (1999) and Svendsen (2004) suggested that the Sahmah Formation may also occur as an erosional outlier in the southern part of the Ghaba Salt Basin. Their argument is based on lithological criteria, but is not supported by biostratigraphy, which indicates an older, Late Ordovician age, Hasirah Formation (Mohuiddin et al., 2007).

Deposition: The Sahmah Formation consists of a major transgressive-regressive cycle. Locally it has a basal fining-upwards sandstone unit underneath the high Gamma ray shale.

The basal sandstone is interpreted to have been deposited above storm wave base in a shallow-marine setting (possibly shoreface). The major flooding, represented by the high Gamma shale above the basal sandstone, may be caused by the rising sea-level resulting from the melting of the ice cap at the end of the Late Ordovician glaciation (Vaslet, 1989; 1990; Droste, 1997; Molyneux et al., 2006).

The overlying sediments are interpreted to have been deposited in an open-marine environment below storm wave base, with sandstone beds deposited either as turbidites or as storm deposits.

The upper part of the Formation comprises intercalated 5–10 m thick, typically fining-upwards, sandstone and shale units. Palynomorphs recovered from this unit are largely continental and are associated with a marginal-marine setting (Svendsen, 2004).

Overall the depositional setting is consistent with a shelf or delta prograding from the south across Oman in the early Silurian (cf. Svendsen, 2004).

Subdivision:Svendsen (2004) divided the Sahmah Formation into a lower ‘Shale Member’ (also known as the Sahmah Shale) and an upper ‘Sandy Member’. The Shale Member comprises grey and brown organic-rich shales with a smooth Gamma-ray profile that increases with depth. Typically the base is marked by a significant Gamma-ray spike associated with the highest organic content (cf. Droste, 1997). The upper Sandy Member comprises interstratified, on a 5–10 m scale, grey, fine- to mediumgrained, pyritic and micaceous sandstones and grey and brown shales. It has a characteristically serrate Gamma-ray profile. Svendsen (2004) placed the sandstone below the high Gamma ray shale in the Hasirah Formation in well Sahmah-1, but it is included in the Sahmah Formation here. This sandstone is interpreted to represent the lowstand/transgressive system tract of the Sahmah Formation.

Age: Latest Ordovician – early Silurian, Hirnantian – ?early Aeronian, ca. 445–438 Ma. The Sahmah Formation has traditionally been considered to be early Silurian in age (e.g. Droste, 1997). However, Svendsen (2004) commented, based on unpublished biostratigraphic data, that the high Gamma shales of the basal Sahmah Formation in two wells could be Late Ordovician (Hirnantian) in age (see Molyneux et al. (2006) for discussion). Palynological data supports a general early Silurian age, with thin Hirnantian deposits found in only one well. The age assigned to the Sahmah Formation in Oman is less well constrained than the other Safiq Group formations and uncertainties remain.

While post-glacial deposition of the Sahmah Formation may have commenced in the Ordovician, the remainder of the lower part of the interval has been tentatively dated as Rhuddanian – early Aeronian on chitinozoan evidence (see Paris, 2006). In Saudi Arabia Zalasiewicz et al. (2007) describe graptolites, from an interval considered equivalent to the Sahmah Formation (Qusaiba Member of the Qalibah Formation), which provide firm evidence for a mid-Aeronian to early Telychian age. It is therefore not clear whether a slightly older section is preserved in Oman or the difference is due to the less certain dating.

Sharland et al. (2001) placed their mid-Aeronian MFS S10 in the high Gamma shales of both the Sahmah Formation and the Qusaiba Member of the Qalibah Formation. The latter is confirmed by the work of Zalasiewicz et al. (2007), but it may be that in Oman the preserved post-glacial incursion is slightly older, and the middle Aeronian MFS S10 event either did not extend into Oman or was eroded beneath the base Haushi unconformity (Molyneux et al., 2006). More detailed palynological studies may help to resolve the issue.

Biostratigraphy: The Sahmah Formation shales yield a palynoflora of acritarchs, chitinozoa and cryptospores, which is characteristic of the PDO Palyno-subzone 1003B, suggesting a questionable age of Rhuddanian – ?early Aeronian Stages (Booth, 2009; Figure 12.1). In sandier intervals acritarchs and chitinozoa are either absent or few in number and the assemblages are dominated by long-ranging cryptospores, which cannot be assigned a precise age.

A Hirnantian age (Palyno-subzone 1003A) has been noted in a single well (Booth, personal communication). This marine palynoflora seems to represent an event which predates MFS S10 of Sharland et al. (2001) and also postdates their MFS O40. It is provisionally referred to as MFS O50? (Figure 12.1) until additional work can be undertaken to further understand the stratigraphy of this interval.

Hasirah Formation

Authors: Defined as a member of the then Safiq Formation by Oprinsen (unpublished, 1986), see also Hughes Clarke (1988), upgraded to Formation status by Priebe and Kapellos (1993), see also Droste (1997).

Introduction

The Hasirah Formation is the middle depositional unit of the Safiq Group and is characterised by the Late Ordovician Palynozone 1005. The Hasirah Formation comprises a major fining and coarsening-upward succession interpreted by Droste (1997) as a full transgressive-regressive cycle of shallow marine to fluvio-marine sediments.

The basal Hirnantian coincides with an unconformity associated with the widespread Late Ordovician glaciation and with a period of mass extinction, with the loss of some 85% of all marine species. A continental ice sheet covered part of Gondwana centred over North Africa and extended onto the Arabian Shield in western Arabia. Proglacial deposits are known from many areas along the palaeo-edge of the ice sheet, and in Saudi Arabia these form the Zarqa and Sarah formations. The glaciation is marked on seismic by a major erosional surface and unconformity in Saudi Arabia, characterised by multiple valley systems that eventually were completely filled with Zarqa and Sarah sediments (Vaslet, 1990). In Oman, the glaciation is represented by a depositional hiatus correlating with the top of the Hasirah Formation and to date no glacial deposits have been recognised. Droste (1997) tentatively interpreted an erosional unconformity at the base of the upper part of the Hasirah Formation with a sea-level drop and tied the associated sequence boundary to the Hirnantian glaciation. This is now thought to occur between the Hasirah and Sahmah formations.

Abnormally thick Safiq Group shale successions have been penetrated in a number of wells across North Oman. Unpublished biostratigraphic analyses indicate that the successions are early to middle Katian (Caradoc – Ashgill) in age, corresponding to the Hasirah Formation (Mohiuddin et al., 2007; Booth, 2009). These shale sequences correspond to large erosional ‘canyons’ that have been observed from seismic, cutting deep into the underlying Ghudun Formation of the Andam Group. At least part of the canyon fill is Hasirah sediments. The canyons may be explained by a major sea-level drop between the Saih Nihayda and Hasirah, but there is also evidence of an earlier global sea-level fall in the early Darriwilian (late Arenig – early Llanvirn) (see Nielsen, 2004). The unconformities at the base of the Saih Nihayda Formation and the ‘Hasirah’ canyons are difficult to separate due to insufficient seismic and biostratigraphic resolution. In either case the canyons appear to pre-date the Hirnantian glaciation.

Type and reference sections:Droste (1997) only mentions the southwestern flank of the Ghaba Salt Basin as a type area. Subsurface reference sections are Hasirah-1 in Central Oman (Figure 12.6), Saih Rawl-31 in North Oman (Figure 12.7), and Dhahaban-2 in South Oman (Figure 12.8).

Figure 12.6.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Hasirah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.6.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Hasirah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.7.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Saih Rawl-31, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.7.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Saih Rawl-31, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.8.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Dhahaban-2, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.8.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Dhahaban-2, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Lithology: The Hasirah Formation consists of sandstones, siltstones and shales which vary in relative proportions from well to well (see Hasirah-1 and Saih Rawl-31, Figures 12.6 and 12.7).

Outside the canyons the Hasirah Formation typically consists of a basal medium- to coarse-grained, light grey sandstone (best developed in the area around the Barik field), overlain by a series of dark grey, organic-rich micaceous shales (with intercalated sand forming coarsening-upward sequences) and an upper sandstone. Within the canyons, lithologies are dominantly dark grey, organic-rich micaceous shales interbedded with centimetre-thick beds of silt and sandstone, locally with thicker packages of fine- to medium-grained sandstones which may form coarsening-up successions. Shales range locally to grey, orange and reddish-brown.

In general, consistent correlatable patterns cannot be distinguished.

The Hasirah is lithologically similar to the Sahmah and Saih Nihayda formations. However, compared to the Sahmah Formation, the shales are less organic-rich. See Droste (1997) for a more detailed lithological description.

Subsurface recognition: Where overlain by the Al Khlata Formation the Hasirah is recognised by a down-hole change from the grey shales, sandstones and diamictites of the Al Khlata to finer, angular sandstones and grey, locally orange/reddish-brown shales (if present, the reddish-brown colour is probably the most diagnostic criteria). The grey shales (Figure 12.9) are much more micaceous than those of the Al Khlata (see Figure 10.15).

Figure 12.9.

Ditch cuttings from the Safiq Group: (a) Shale from the Hasirah Formation in Saih Rawl-31; (b) Shale from the Saih Nihayda Formation in Saih Rawl-32; and (c) Sandstone from the Saih Nihayda Formation in Saih Rawl-32 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 12.9.

Ditch cuttings from the Safiq Group: (a) Shale from the Hasirah Formation in Saih Rawl-31; (b) Shale from the Saih Nihayda Formation in Saih Rawl-32; and (c) Sandstone from the Saih Nihayda Formation in Saih Rawl-32 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Post-drilling the Formation can be recognised using detailed palynological analysis and log correlation. When overlain by the Al Khlata, the top is often marked by an increase in Gamma log values of variable intensity (see Saih Rawl-31 and Dhahaban-2, Figures 12.7 and 12.8).

The shales also have a higher Gamma character than the underlying Ghudun shales.

When unconformably overlying the Ghudun, the basal Hasirah sandstones show a comparatively clean, blocky log character (low Gamma, less than 20 API) compared to the more erratic Ghudun.

Boundaries: The boundaries are difficult to define, because the sands at the top and bottom of the Formation are generally barren of palynomorphs.

Because of progressive erosion of the Safiq Group sediments eastwards, the overlying sediments vary from the basal Sahmah Formation in a complete section to the basal Al Khlata Formation where the Sahmah Formation has been fully eroded.

Where overlain by the Sahmah Formation, the top of the Hasirah Formation is picked at the base of the (generally fining-upward) Sahmah sand underlying a very high Gamma shale peak. This is a difficult pick on the basis of lithology alone due to lithological similarities. When overlying the Saih Nihayda the base Hasirah may be difficult to pick. By convention the base is placed at the base of the fining-upward sand below the lowermost Palynozone 1005 dated shale (Droste and Mohammed, 1994).

Distribution: The Hasirah Formation is the most widespread formation of the Safiq Group. Along the eastern flank of the Ghaba and South Oman Salt Basin the Formation is truncated below the base Al Khlata and younger unconformities. The Formation onlaps directly onto the Ghudun Formation in Central and South Oman. The maximum drilled thickness is on the central western margin at the border with Saudi Arabia, where it is about 550 m.

Deposition: The majority of the Hasirah Formation appears to be dominated by open-marine shales and heterolithics (Sutcliffe and Aitken, 2002). Turbidite facies/mass flow deposits are restricted to isolated pockets in the Ghaba Salt Basin with more extensive turbidite development in the west and in Saudi Arabia. The basal sandstone of Droste (1997) has been interpreted as a shallow-marine transgressive deposit (e.g. Oprinsen, 1986).

Subdivision:Droste (1997) describes three lithological units in the Hasirah Formation, starting with a clean sandstone unit at the base, overlain by middle shaly to argillaceous sandstone unit and completed by an upper thick sandstone unit. He highlights the sharp base of the upper sand unit and interprets this as a significant sequence boundary represented by an erosional surface associated with a prograding delta complex on top of deeper-marine settings. He interpreted this as a major drop in relative sea-level, and tentatively associates this with the main Late Ordovician (Hirnantian) glaciation (Vaslet, 1989; 1990). However, palynological dating now indicates that the Hasirah Formation is entirely Katian and any erosion represents an older event.

The shaly canyon fill has a very different nature and therefore it is difficult to generalise subdivisions.

Age: Late Ordovician, early – middle Katian age, ca. 455–450 Ma. Sharland et al. (2001) place their MFS O40 towards the base of the Hasirah Formation, within the middle shaly unit, in wells from the Ghaba Basin. This shale succession is considered equivalent to the well dated, graptolite rich, Ra’an Member of the Qasim Formation in Saudi Arabia (Sharland et al., 2001; Al-Husseini, 2008).

Biostratigraphy: Acritarchs, chitinozoa and cryptospores are all useful in defining Palynozone 1005, which is associated with the Hasirah Formation. Recovery in the upper part of the interval (Palyno-subzone 1005B) is relatively poor and the palaeoenvironments are generally more marginal marine. The lower part of the interval (Palyno-subzone 1005A), recorded from the middle shaley unit, incorporates MFS O40 of Sharland et al. (2001). Marine palynomorph recovery is consequently relatively good, with rich and diverse assemblages at some horizons.

A previous PDO Palynozone 1012 is cited in Droste (1997), Sharland et al. (2001) and Molyneux et al. (2006). This was renamed as Palyno-subzone 1005A by Mohiuddin et al. (2007).

Of particular note in the Hasirah Formation is the report that it has yielded fragments of the earliest land plants yet recorded (Wellman et al., 2003). These are from well Ghaba-1 well (core 21, ca. 1,575 m; note depth corrected from Wellman et al., 2003) within the uppermost part of a ca. 56 m thick shale-dominated section. The section yielded Palynozone 1005 and is of early – middle Katian age (Caradocian as originally reported). They describe large numbers of cryptospore tetrads (primitive spore clusters) encased in sporangia, and argue that these spore containing structures provide compelling evidence for the presence of small land plants in the Late Ordovician. This microscopic evidence significantly pre-dates, by some 25 My, the occurrence of land plant megafossil evidence from the Silurian (Edwards and Wellman, 2001).

It should be noted that for all older lithostratigraphical units continental depositional settings and sediment composition was not influenced at all by the presence of land plants.

Saih Nihayda Formation

Authors: Defined as a member of the then Safiq Formation by Oprinsen (unpublished, 1986), see also Hughes Clarke (1988), upgraded to Formation status by Droste (1997).

Introduction

The Saih Nihayda Formation is the lowest unit of the Safiq Group and comprises sediments assigned to Palynozone 1098 (Droste and Mohammed, 1994) of Middle Ordovician age. The unit comprises a clastic succession of fluvial to marine sands and shales. A large-scale shale-filled canyon system, as recognised from seismic and wells, cuts into the Saih Nihayda. These are mainly infilled with Hasirah sediments (see previous discussion).

Type and reference sections: Saih Nihayda-24 in North Oman (Figure 12.10). Additional reference section is Barik-8 in North Oman (Figure 12.11).

Figure 12.10.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Saih Nihayda-24, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.10.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Saih Nihayda-24, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.11.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Barik-8, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.11.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Barik-8, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Lithology: The Saih Nihayda Formation consists of medium-light grey sandstones, very micaceous and dark grey (locally orange/reddish-brown) siltstones and shales, all of which vary in relative proportions from well to well (see Saih Nihayda-24 and Barik-8, Figures 12.10 and 12.11). A fining-upward trend followed by a coarsening-upward trend, separated by a shale interval is usually observed. The Saih Nihayda occasionally has a basal sandstone characterised by a blocky Gamma ray trace.

Subsurface recognition: Whilst drilling, the Formation can be picked on the change from the grey shales, sandstones and diamictites of the Al Khlata to finer, angular sandstones (Figure 12.9) and grey/orange/reddish-brown shales (the latter are probably the most diagnostic criteria). The grey shales are much more micaceous than those of the Al Khlata. The change from the Hasirah to the Saih Nihayda is impossible to pick on the basis of lithology only.

Post-drilling the Formation can be determined by detailed palynological analysis combined with log correlation. The basal Saih Nihayda sandstones show a cleaner and blockier log character than the highly serrate and spiky Gamma log of the Ghudun Formation (Droste and Mohammed, 1994). The overlying interbedded sands and shales also have a serrate log response, occasionally with funnelshaped trends. This persists into the sandstones at the top of the unit that are overall funnel shaped.

The shales have a higher Gamma character (150 API) than the Al Khlata and the Ghudun shales.

Boundaries: The boundaries, both unconformable, are difficult to define because the sands at the top and bottom of the Formation are generally barren of palynomorphs.

The Saih Nihayda Formation is overlain by either the Hasirah Formation (predominantly) or the Al Khlata Formation towards the southeast. The boundary with the Hasirah Formation is taken at the base of the ‘sharp-based’ blocky sand, but can be difficult to pick in the absence of Saih Nihayda shales, and any palynological calibration. In such cases the boundary is picked at the bottom of the Hasirah shale section.

It unconformably overlies the clastics of the Ghudun Formation, where the boundary is picked at the base of the more blocky sand overlying the more serrate and spiky Ghudun Formation sands. If the basal sand unit is absent this boundary is taken at the base of the shale section.

Distribution: The Saih Nihayda is confined to North Oman along a trend broadly following the axis of the Ghaba Salt Basin. Its occurrence is strongly modified by the presence of Hasirah-filled incision canyons. The Saih Nihayda is truncated/eroded towards the south down to Ghudun level by younger formations. The upper part of the Amdeh Formation (Amdeh 5 of Le Métour et al., 1986) in the Saih Hatat area of the Al Hajar Mountains (Lovelock et al., 1981) is time equivalent to the Saih Nihayda Formation (see also Sansom et al., 2009).

Deposition: The Saih Nihayda Formation represents a major transgressive-regressive cycle. The blocky fining-upward sands at the base that include large sand and silt boulders are thought to be deltaic in origin (e.g. Sutcliffe and Aitken, 2002; Romine and Fryberger, 2006). Droste (1997) suggested this sand may have been deposited in erosive fluvial channels. Further to the north and overlying these sandstones the graptolitic shales and heterolithics are interpreted as open-marine deposits, with the sandstones thought to represent either distal (low density) turbidites in front of a delta or storm deposits. The sharp contact with the basal sand suggests a rapid, possibly erosive transgression. The coarsening-upward trend towards the top suggests a progradation into a shallower-marine shoreface setting.

Subdivision: None.

Age: Middle Ordovician, Darriwilian, ca. 467–461 Ma. Sharland et al. (2001) place their MFS O30 at the base of the Saih Nihayda shales in the Central Ghaba Basin.

Graptolite calibration (Didymograptus murchisoni zone, see below) indicates correlation with the Hanadir Member of the Qasim Formation in Saudi Arabia (Sharland et al., 2001; Al-Husseini, 2008).

Biostratigraphy: The palynomorph recovery at the top and base of the Saih Nihayda succession can be rather sparse, but the middle of the interval incorporates MFS O30 of Sharland et al. (2001). Its associated palynoflora, which characterises the 1098B Palyno-subzone, is rich and diverse. Graptolites from cores are also associated with this interval and have been identified as indicative of the Didymograptus murchisoni zone (Rickards et al., in preparation). An interval of relatively sparse recovery and more marginal facies can sometimes be present in the lower part of the section (Palyno-subzone 1098A).

Figures & Tables

Figure 12.1.

Cambrian to Silurian biostratigraphical and chrono-stratigraphical subdivision of the Safiq and Andam groups (Booth, 2009).

Figure 12.1.

Cambrian to Silurian biostratigraphical and chrono-stratigraphical subdivision of the Safiq and Andam groups (Booth, 2009).

Figure 12.2.

Location map: Safiq Group/Haima Supergroup.

Figure 12.2.

Location map: Safiq Group/Haima Supergroup.

Figure 12.3.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Sahmah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.3.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Sahmah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.4.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Rabkha-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.4.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Rabkha-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.5.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Wadi Qitbit-1, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.5.

Composite electrical logs, lithology and lithological description of the Sahmah Formation, Safiq Group, in well Wadi Qitbit-1, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.6.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Hasirah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.6.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Hasirah-1, Central Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.7.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Saih Rawl-31, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.7.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Saih Rawl-31, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.8.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Dhahaban-2, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.8.

Composite electrical logs, lithology and lithological description of the Hasirah Formation, Safiq Group, in well Dhahaban-2, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.9.

Ditch cuttings from the Safiq Group: (a) Shale from the Hasirah Formation in Saih Rawl-31; (b) Shale from the Saih Nihayda Formation in Saih Rawl-32; and (c) Sandstone from the Saih Nihayda Formation in Saih Rawl-32 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 12.9.

Ditch cuttings from the Safiq Group: (a) Shale from the Hasirah Formation in Saih Rawl-31; (b) Shale from the Saih Nihayda Formation in Saih Rawl-32; and (c) Sandstone from the Saih Nihayda Formation in Saih Rawl-32 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 12.10.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Saih Nihayda-24, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.10.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Saih Nihayda-24, North Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.11.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Barik-8, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

Figure 12.11.

Composite electrical logs, lithology and lithological description of the Saih Nihayda Formation, Safiq Group, in well Barik-8, South Oman (Mohammed et al., 1997). See Figure 12.2 for location.

SUPERGROUPGROUPFORMATION
HaimaSafiqSahmah
Hasirah
Saih Nihayda
AndamGhudun
Barakat
Mabrouk
Barik
Al Bashair
Mahatta HumaidMiqrat
Mahwis
Amin
SUPERGROUPGROUPFORMATION
HaimaSafiqSahmah
Hasirah
Saih Nihayda
AndamGhudun
Barakat
Mabrouk
Barik
Al Bashair
Mahatta HumaidMiqrat
Mahwis
Amin
SupergroupGroupFormationShort Description
HaimaSafiqSahmahAbsent through erosion over most of Oman, occurring only in the westernmost parts of Central and South Oman, along the western edge of the Rub’ Al-Khali Basin and extending into Saudi Arabia. The Sahmah Formation is a major transgressive-regressive cycle, comprising organic-rich shales interbedded with sandstones stacked in a fining-coarsening upward trend. Recognition is based on the presence of the 1003 Palynozone (Latest Ordovician – early Silurian, Hirnantian – ?early Aeronian).
HasirahWidespread in North, Central and southwestern regions of Oman, the Hasirah Formation is probably a major marine transgressive-regressive cycle. It commonly fills-in significant erosional topography where it is dominated by mudrocks. Elsewhere it may comprise medium- to coarse-grained, commonly thickly bedded sandstones, interstratified with dark grey organic-rich shales, which may be capped by a thick sandstone unit. Contains the O40 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1005 Palynozone (Late Ordovician, Katian).
Saih NihaydaMost extensive in the northern region of Oman, but also extending into the northern part of the South Oman Salt Basin. The Saih Nihayda Formation can be eroded beneath the base Hasirah unconformity. It is probably a major transgressive-regressive cycle, comprising a basal sandstone, overlain by dark grey shales which are capped by another sandy unit. Contains the O30 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1098 Palynozone (Middle Ordovician, Darriwilian).
AndamGhudunThe most widespread and thickest unit of the Haima. The Ghudun Formation is primarily a cross-bedded to laminated sandstone section, which represents fluvial channel and sheet-flood deposits in a deltaic setting. To the northwest it becomes more marine, confirmed by the presence of acritarchs and bioclasts in some horizons. Typically highly feldspathic with siltstones, occasionally intercalated with shales. Occasionally yields the 1100 Palynozone (Early-Middle Ordovician, late Floian – early Dapingian) in the Upper Ghudun. The Formation is more often barren and probably ranges down to the Floian/?Tremadocian.
BarakatWidespread over Central and North Oman, the Barakat Formation is a marine transgressive-regressive cycle, incorporating a significant maximum flooding (MFS O20 of Sharland et al., 2001). The base is typically a sandstone, overlain by reddish-brown or greenish shales, which are capped by a sandy unit. Yields the 1108C and 1108B Palyno-subzones (Early Ordovician, Tremadocian).
MabroukWidespread over Central and North Oman and is dominated by shallow-marine muddy sediments that are reddish-brown interbedded with thin sandstones. Contains the O10 MFS (Sharland et al., 2001). Recognition partly based on the presence of the 1108B Palyno-subzone (Early Ordovician, Tremadocian).
BarikWidespread over Central and North Oman the Barik Formation, is dominantly a braid delta complex but grades into a shallow-marine system to the north. In-situ palynomorphs have yet to be recorded, as ditch cuttings yield is probably due to caving.
Al BashairWidespread over North Oman, the Al Bashair Formation is a shallow-marine sequence that, in its upper part comprises grey to reddish-brown mudstones intercalated with sands and in its lower part is dominated by fine-grained sandstones and argillaceous siltstones intercalated with shales and carbonates. Contains the Cm30 MFS (Sharland et al., 2001). Characterised by the 1108A Palyno-subzone (‘Late’ Cambrian*, Furongian).
Mahatta HumaidMiqrat/MahwisThe Miqrat Formation is present in North and Central Oman, whilst the Mahwis Formation, which is likely to be its lateral equivalent, occurs only in South Oman. Both were deposited in arid to semi-arid continental settings. The Miqrat Formation was deposited in playa/ephemeral lake-sabkha environments with a periphery of sheet-flood alluvial deposition, whereas the Mahwis Formation may have been deposited in distal alluvial fan with local playa environments. Both formations are barren of palynomorphs and all other marine indicators.
AminWidespread throughout Oman, the Amin Formation is a complex, arid depositional system including alluvial, fluvial and aeolian deposits. The base is a conglomeratic unit overlain by alternating sandy, conglomeratic and shaly intervals with the upper part generally a clean sandstone including some restricted aeolian units. Barren of palynomorphs and all other marine indicators.
SupergroupGroupFormationShort Description
HaimaSafiqSahmahAbsent through erosion over most of Oman, occurring only in the westernmost parts of Central and South Oman, along the western edge of the Rub’ Al-Khali Basin and extending into Saudi Arabia. The Sahmah Formation is a major transgressive-regressive cycle, comprising organic-rich shales interbedded with sandstones stacked in a fining-coarsening upward trend. Recognition is based on the presence of the 1003 Palynozone (Latest Ordovician – early Silurian, Hirnantian – ?early Aeronian).
HasirahWidespread in North, Central and southwestern regions of Oman, the Hasirah Formation is probably a major marine transgressive-regressive cycle. It commonly fills-in significant erosional topography where it is dominated by mudrocks. Elsewhere it may comprise medium- to coarse-grained, commonly thickly bedded sandstones, interstratified with dark grey organic-rich shales, which may be capped by a thick sandstone unit. Contains the O40 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1005 Palynozone (Late Ordovician, Katian).
Saih NihaydaMost extensive in the northern region of Oman, but also extending into the northern part of the South Oman Salt Basin. The Saih Nihayda Formation can be eroded beneath the base Hasirah unconformity. It is probably a major transgressive-regressive cycle, comprising a basal sandstone, overlain by dark grey shales which are capped by another sandy unit. Contains the O30 MFS (Sharland et al., 2001). Recognition is based on the presence of the 1098 Palynozone (Middle Ordovician, Darriwilian).
AndamGhudunThe most widespread and thickest unit of the Haima. The Ghudun Formation is primarily a cross-bedded to laminated sandstone section, which represents fluvial channel and sheet-flood deposits in a deltaic setting. To the northwest it becomes more marine, confirmed by the presence of acritarchs and bioclasts in some horizons. Typically highly feldspathic with siltstones, occasionally intercalated with shales. Occasionally yields the 1100 Palynozone (Early-Middle Ordovician, late Floian – early Dapingian) in the Upper Ghudun. The Formation is more often barren and probably ranges down to the Floian/?Tremadocian.
BarakatWidespread over Central and North Oman, the Barakat Formation is a marine transgressive-regressive cycle, incorporating a significant maximum flooding (MFS O20 of Sharland et al., 2001). The base is typically a sandstone, overlain by reddish-brown or greenish shales, which are capped by a sandy unit. Yields the 1108C and 1108B Palyno-subzones (Early Ordovician, Tremadocian).
MabroukWidespread over Central and North Oman and is dominated by shallow-marine muddy sediments that are reddish-brown interbedded with thin sandstones. Contains the O10 MFS (Sharland et al., 2001). Recognition partly based on the presence of the 1108B Palyno-subzone (Early Ordovician, Tremadocian).
BarikWidespread over Central and North Oman the Barik Formation, is dominantly a braid delta complex but grades into a shallow-marine system to the north. In-situ palynomorphs have yet to be recorded, as ditch cuttings yield is probably due to caving.
Al BashairWidespread over North Oman, the Al Bashair Formation is a shallow-marine sequence that, in its upper part comprises grey to reddish-brown mudstones intercalated with sands and in its lower part is dominated by fine-grained sandstones and argillaceous siltstones intercalated with shales and carbonates. Contains the Cm30 MFS (Sharland et al., 2001). Characterised by the 1108A Palyno-subzone (‘Late’ Cambrian*, Furongian).
Mahatta HumaidMiqrat/MahwisThe Miqrat Formation is present in North and Central Oman, whilst the Mahwis Formation, which is likely to be its lateral equivalent, occurs only in South Oman. Both were deposited in arid to semi-arid continental settings. The Miqrat Formation was deposited in playa/ephemeral lake-sabkha environments with a periphery of sheet-flood alluvial deposition, whereas the Mahwis Formation may have been deposited in distal alluvial fan with local playa environments. Both formations are barren of palynomorphs and all other marine indicators.
AminWidespread throughout Oman, the Amin Formation is a complex, arid depositional system including alluvial, fluvial and aeolian deposits. The base is a conglomeratic unit overlain by alternating sandy, conglomeratic and shaly intervals with the upper part generally a clean sandstone including some restricted aeolian units. Barren of palynomorphs and all other marine indicators.
*

The Cambrian timescale is currently in a state of flux with four global series and ten international stages (Ogg et al., 2008), therefore ‘Late’, ‘Middle’ and ‘Early’ designations are used informally (these equate to Furongian, and approximately Epoch 3 and Epoch 2 - Terreneuvian respectively). Where possible a Series/Epoch or Stage/Age qualification is given.

ZoneSubzoneMarker species *Relative ageFormation/Unit
  Diexallophasis denticulataHirnantian – ?early Aeronian 
1003BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)Sahmah
 AVillosacapsula setosapellicula(Hirnantian) 
  Cheleutochroa spp.  
1005BCheleutochroa sppKatianHasirah
 A**Baltisphaeridium spp.  
  Stelliferidium cf. striatulum  
1098BStelliferidium cf. striatulumDarriwilianSaih Nihayda
ABuedingiisphaeridium? spp./Tylotopalla? spp.
1100 Coryphidium bohemicumlate Floian – early DapingianUpper Ghudun
  Acanthodiacrodium spp.Furongian – TremadocianAl Bashair – Barakat
1108CAcanthodiacrodium spp.(late Tremadocian)(Barakat)
BVulcanisphaera africana(Tremadocian)(Mabrouk – Barakat)
 AVeryhachium? dumontii(Furongian)(Al Bashair)
ZoneSubzoneMarker species *Relative ageFormation/Unit
  Diexallophasis denticulataHirnantian – ?early Aeronian 
1003BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)Sahmah
 AVillosacapsula setosapellicula(Hirnantian) 
  Cheleutochroa spp.  
1005BCheleutochroa sppKatianHasirah
 A**Baltisphaeridium spp.  
  Stelliferidium cf. striatulum  
1098BStelliferidium cf. striatulumDarriwilianSaih Nihayda
ABuedingiisphaeridium? spp./Tylotopalla? spp.
1100 Coryphidium bohemicumlate Floian – early DapingianUpper Ghudun
  Acanthodiacrodium spp.Furongian – TremadocianAl Bashair – Barakat
1108CAcanthodiacrodium spp.(late Tremadocian)(Barakat)
BVulcanisphaera africana(Tremadocian)(Mabrouk – Barakat)
 AVeryhachium? dumontii(Furongian)(Al Bashair)
*

Zonal index/marker species newly assigned for all Haima Palynozones (Mohiuddin et al., 2007 and Booth, 2009), original code based names no longer apply.

**

Previously Palynozone 1012.

GROUPFORMATION
SafiqSahmah
Hasirah
Saih Nihayda
GROUPFORMATION
SafiqSahmah
Hasirah
Saih Nihayda
ZoneSubzoneMarker speciesRelative ageFormation/Unit
1003 Diexallophasis denticulataHirnantian – ?early AeronianSahmah
BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)
AVillosacapsula setosapellicula(Hirnantian)
1005 Cheleutochroa spp.KatianHasirah
BCheleutochroa spp.
A*Baltisphaeridium spp.
1098 Stelliferidium cf. striatulumDarriwilianSaih Nihayda
BStelliferidium cf. striatulum
ABuedingiisphaeridium? spp./Tylotopalla? spp.
ZoneSubzoneMarker speciesRelative ageFormation/Unit
1003 Diexallophasis denticulataHirnantian – ?early AeronianSahmah
BDiexallophasis denticulata(Rhuddanian – ?early Aeronian)
AVillosacapsula setosapellicula(Hirnantian)
1005 Cheleutochroa spp.KatianHasirah
BCheleutochroa spp.
A*Baltisphaeridium spp.
1098 Stelliferidium cf. striatulumDarriwilianSaih Nihayda
BStelliferidium cf. striatulum
ABuedingiisphaeridium? spp./Tylotopalla? spp.
*

Previously Palynozone 1012.

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