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GROUPFORMATIONMEMBER
ArumaSimsima 
FiqaArada
Shargi
GROUPFORMATIONMEMBER
ArumaSimsima 
FiqaArada
Shargi

Introduction

The Aruma Group is widely used around the Gulf to comprise all units between the regional hiatus/disconformity above the Wasia Group and the Cretaceous – Cenozoic boundary, which is usually also a hiatus. In southern Iraq and Kuwait, the Group is divided into six formations, none of which extend to the southern Gulf areas. In Interior Oman, a simple two-fold subdivision of the Aruma into the Simsima and Fiqa formations is used.

Type and reference sections: Not specified, but implied to be south Iraq-Kuwait (see van Bellen et al., 1959/2005). Additional reference sections at Formation level are Suneinah-1 (Figure 5.2) and Al Huwaisah-6 (Figure 5.5) in North Oman and Hawmyat-1 in South Oman (Figure 5.3).

Figure 5.1:

Location map: Aruma Group.

Figure 5.1:

Location map: Aruma Group.

Figure 5.2.

Composite electrical logs, lithology and lithological description of the Simsima Formation, Aruma Group, in well Suneinah-1, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.2.

Composite electrical logs, lithology and lithological description of the Simsima Formation, Aruma Group, in well Suneinah-1, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.3.

Composite electrical logs, lithology and lithological description of the Simsima and Fiqa formations, Aruma Group, in well Hawmyat-1, South Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.3.

Composite electrical logs, lithology and lithological description of the Simsima and Fiqa formations, Aruma Group, in well Hawmyat-1, South Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Lithology: A very fossiliferous carbonate unit, commonly dolomitised. Significant, and also very fossiliferous, shaly facies occur in the lower Fiqa Formation (Shargi Member), particularly in North Oman.

Boundaries: The Group lies unconformably on underlying rock units - generally the Natih Formation. It is unconformably overlain by the Shammar Shale.

Distribution: The Group is widespread through Oman, although commonly cut-out over structural highs, many of which had growth phases late in the Cretaceous. It is very thick close to the Al Hajar Mountains, in a foredeep related to the Late Cretaceous nappe emplacement (Robertson 1987a,b; Warburton et al., 1990). Proximity to and involvement with this deformation is the basis for different subdivisions in this area (Boote et al., 1990; Rabu et al., 1990). To the south and east, it is a thin shallow-marine unit wedging out onto the Al Huqf-Haima High axis, but then thickening over it into the partially-offshore down-faulted blocks bounding the Arabian Sea.

Subdivision: The Simsima and Fiqa formations constitute this Group.

Sequence Stratigraphy: Megasequence AP9 (Sharland et al., 2001). Sharland et al. (2001) correlate their Late Cretaceous MFS surfaces K180 through to K150 into the Aruma Group of Oman (see formational discussions for detail).

Age: Late Cretaceous, Coniacian – Maastrichtian, ca. 88.6–65.5 Ma.

Biostratigraphy: The biostratigraphy of the Aruma Group has developed since the 1960s in quite a complex and sporadic fashion. Listed below are the most current, and best documented zonations.

Microfossil zones, originally defined by Sikkema (1991), have been revised by Osterloff et al. (2001) based on a series of reports by Packer (culminating in Packer, 2002). Much of the microfossil work is substantiated by a significant amount of nannofossil work, which has never been formally worked up into a zonation scheme (see Osterloff et al., 2001 for a summary).

ZoneMarker speciesRelative ageFormation/Member
F68Siderolites calcitrapoidesMaastrichtianSimsima
F67Globotruncana calcarataLate CampanianFiqa/Arada-Shargi
F66Pseudedomia complanata, G. elevatalate Early – early Late Campanian
F65Pseudedomia aff. multistriataEarly CampanianFiqa/Shargi
F64Dicarinella asymetricalate Early – Late Santonian
F63Whiteinella balticaConiacian – Early Santonian
ZoneMarker speciesRelative ageFormation/Member
F68Siderolites calcitrapoidesMaastrichtianSimsima
F67Globotruncana calcarataLate CampanianFiqa/Arada-Shargi
F66Pseudedomia complanata, G. elevatalate Early – early Late Campanian
F65Pseudedomia aff. multistriataEarly CampanianFiqa/Shargi
F64Dicarinella asymetricalate Early – Late Santonian
F63Whiteinella balticaConiacian – Early Santonian

Palynological scheme of Clarke and Hoogkamer (1967), as applied to the then ‘Aruma Shale Formation’:

ZoneSubzoneMarker speciesRelative age
596522Odontochitina costataCampanian – Maastrichtian
802Xenascus ceratoidesConiacian – Campanian
ZoneSubzoneMarker speciesRelative age
596522Odontochitina costataCampanian – Maastrichtian
802Xenascus ceratoidesConiacian – Campanian

Palynological Zones of Mohiuddin (2002):

ZoneMarker speciesRelative ageFormation/Member
1Fibrocysta axialis‘middle’ – Late MaastrichtianSimsima
2Hystrichodinium pulchrumEarly – ‘middle’ Maastrichtian
3Apteodinium reticulatumLate CampanianFiqa/Arada
4Cribroperidinium orthocerasEarly – Late CampanianFiqa/Shargi
5Exochosphaeridium bifidum?Turonian – Santonian
ZoneMarker speciesRelative ageFormation/Member
1Fibrocysta axialis‘middle’ – Late MaastrichtianSimsima
2Hystrichodinium pulchrumEarly – ‘middle’ Maastrichtian
3Apteodinium reticulatumLate CampanianFiqa/Arada
4Cribroperidinium orthocerasEarly – Late CampanianFiqa/Shargi
5Exochosphaeridium bifidum?Turonian – Santonian

Although used in Droste (2001), the Palynozone 596 has not been applied very often to the subsurface. The more detailed scheme of Mohiuddin (2002) is more applicable. However, as is the case for most of the Cretaceous carbonate sections, the generally more refined and practical microfaunal/nannofossil schemes are applied in preference to any palynological zonations.

Simsima Formation

Authors: Sugden (unpublished, 1956), see Dominguez (1965).

Introduction

The Simsima Formation represents the re-establishment of marine sedimentation over Oman after the disturbance caused by the nappe emplacement along Oman’s northeast margin associated with the closure of the Neo-Tethys Ocean.

Type and reference sections: Dukhan-65, Qatar, thickness drilled 148 m. Reference section in Oman is well Suneinah-1 (Figure 5.2) in North Oman. Additional reference section is Hawmyat-1 (Figure 5.3) in South Oman.

Lithology: A variable carbonate unit, containing a variety of shallow-marine limestone facies and subordinate dolomites. Commonly very fossiliferous.

Subsurface recognition: Whilst drilling, ‘hotshots’ are needed to confirm a Maastrichtian age, Biozone F68. The Simsima Formation is lithologically very similar to other limestones of the Aruma Group and thus difficult to identify. The post-drilling pick can be based on faunal content (thin sections), which is distinctly Maastrichtian, and log correlation.

Boundaries: The Simisima lies disconformably on the underlying units, generally Fiqa, with a hiatus and minor basal clastics. It is overlain by the argillaceous Shammar Member of the Umm Er Radhuma Formation, with a hiatus of latest Maastrichtian to Early Palaeocene duration.

Distribution: The sediments are everywhere of shallow-water facies in Interior Oman, although a deep facies occurs further to the northwest and into the eastern United Arab Emirates. In the reference section in the Suneinah-1 well, the Simsima lies on sediments, with much detritus from the nappes, which can be referred to the surface Juweiza Formation (Glennie et al., 1974). In the Al Hajar Mountains, the Simsima can lie directly on the nappes, although a basal clastic unit, the Qahlah Formation (Glennie et al., 1974), may be present. In South Oman, the Simsima occurs only very patchily, although dating imprecision is a constraint. It may not have been deposited over large parts of South Oman, but it is present in the west and is continuous into the Rub’ Al-Khali basin. On the east side of the Al Huqf, small outcrops of Maastrichtian pelagic carbonates suggest open, deeper-marine influence in the down-faulted Arabian Sea margins. It was only confirmed to be present in well Dhahaban South-1 (Figure 5.1, South Oman). It is assumed to be present in adjacent wells by log correlation (Hawmyat-1, Figure 5.3).

Deposition: The sediments indicate an overall shallow-marine and generally high-energy environment, but open-marine foraminifera are occasionally found in this Formation.

Age: Maastrichtian, ca. 70.6–65.5 Ma. Sharland et al. (2001) place their mid-Maastrichtian MFS K180 flooding surface within marls of the Upper Simsima Formation.

Biostratigraphy: Biozone F68, containing three subzones, is characterised by the presence of Siderolites calcitrapoides (Figure 5.4). Omphalocyclus macroporus typifies Sub-biozone F687 in the shallow-water facies. Deeper-water assemblages containing planktic foraminifera of the genera Globotruncana are seen in Sub-biozone F685, which also yields Archaecyclus midorientalis and Lebidorbitoides schenki. Globotruncana arca and Pseudotextularia elegans characterise the lowermost Sub-biozone, F683. This trend with deeper water microfauna in the older sub-biozones is at odds with Sharland et al. (2001) placing their MFS K180 in the upper Simsima Formation.

Figure 5.4.

Fossils from the Simsima Formation: (a-c) Siderolites calcitrapoides from Maastrichtian Biozone F68 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 5.4.

Fossils from the Simsima Formation: (a-c) Siderolites calcitrapoides from Maastrichtian Biozone F68 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Fiqa Formation

Authors: Standring (unpublished, 1967), see Sugden and Standring (1975).

Introduction

The Fiqa Formation comprises a new phase of sedimentation after a widespread regional emergence at the end of Natih deposition. The Fiqa Formation is interpreted to represent the deposition and fill of a foreland basin (Boote et al., 1990; Warburton et al., 1990), ahead of the southward advancing thrust sheets of the Hawasina nappes and Semail Ophiolite. These were emplaced on the northern margin of the Arabian Plate, associated with the Late Cretaceous closure of the Neo-Tethys Ocean.

Type and reference sections: Murban-44, Abu Dhabi, thickness drilled 350 m. The reference section in Oman is well Al Huwaisah-6 (Figure 5.5). Additional reference sections are Hawmyat-1 in South Oman (Figure 5.3) and Haima-3 in Central Oman (Figure 5.6).

Figure 5.5.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Al Huwaisah-6, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.5.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Al Huwaisah-6, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.6.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Haima-3, Central Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.6.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Haima-3, Central Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Lithology: The sedimentary facies varies, but essentially two facies are separated as members: a shale facies, the Shargi Member, and a carbonate facies, the Arada Member. The Arada carbonates usually overlie the shales of the Shargi Member, but alternation occurs, pointing to lateral interfingering. In North Oman a mid Shargi sand-prone level is thought to be equivalent to the Batain Coast, Fayah Formation sandstones (Shackleton et al., 1990; see also Osterloff et al., 2001 and Packer, 2002). Similarly in North Oman the basal Shargi Member has an Early Santonian silty/sandy level rich in chamosite ooids and glauconite. Locally, Coniacian clastics and lignitic shales, equivalent to the outcropping Qitqawt Formation (Platel et al., 1995), may constitute the earliest phase of Fiqa deposition.

Subsurface recognition: Whilst drilling, the Fiqa Formation can be recognised by the change from the dark grey Shammar Shale to the light grey limestones of the Arada Member.

The limestones of the Arada Member are frequently more argillaceous and greyer than the Umm Er Radhuma limestones, but the difference can be subtle. Fossils (foraminifera and ostracods) are the key to successful separation of the two.

The Shargi Member is recognised by the change from grey limestones (base of last limestone) to massive dark grey shales, marked by an increase in Rate of Penetration. It is rich in pelagic and benthonic fauna. The faunal content is similar to that in the Arada. There are no limestones in the sequence. In North Oman the base of the Shargi is marked by a glauconite-rich unit near the base, and a chamosite ooid level at the base. Locally, lignitic black shales, silts and sands may be associated with the basal Shargi.

Post-drilling the Arada Member can be picked on the faunal change from Cenozoic to Cretaceous faunas, or the decrease in Gamma at the upper boundary. The top of the Shargi Member is put at the last limestone (downhole) in cases where there is an interbedded shale/limestone sequence in the lower part of the Arada Member. The Shargi can be picked on the increase in Gamma at the boundary. The Gamma ray maintains a uniform character throughout the Shargi Member. It has a uniform Density/Neutron pattern with a consistent wide separation. A basal high Gamma reading may be associated with chamosite/glauconite occurrence. Locally black lignitic shales may also occur at the base of the Formation (below the chamosite/glauconite).

Wireline log changes through the Shargi Member can be subtle and key lithological changes can be easily missed due to a combination of poor sample quality, too wide sample spacing and lag time calculation errors.

Boundaries: The lower boundary of the Fiqa Formation with the Natih Formation is always sharp, with age and facies changes suggesting a hiatus. The upper boundary is generally sharp, with age, facies and seismic evidence of a disconformity between Fiqa and Simsima or younger Cenozoic units.

Distribution: The thick and mainly pelagic shale or chalk occurs in northern areas close to the Al Hajar Mountains. The Formation thins towards the south and southeast, becoming progressively more shallow facies throughout. Thin developments of imprecisely-dated Late Cretaceous carbonates in South Oman can represent either, or both, Fiqa and Simsima formations. The Shargi facies crops out on the extreme southern flanks of the Al Hajar Mountains, where it can contain some sandy and lithoclastic turbidite beds, showing a transition to the Muti Formation (Glennie et al., 1974) in the main Al Hajar Mountains outcrops. The Arada shallow-marine carbonate facies crops out in the Al Huqf area.

Deposition: Dominantly deeper-marine pelagic facies in the north, passing to shallow-marine carbonates in the south. In the north there are more cherts, conglomerates and calciturbidites than their equivalents in the south.

The Fiqa Formation is interpreted to represent the deposition and fill of a foreland basin (Boote et al., 1990; Warburton et al., 1990) with clastics and carbonates (marls). These were deposited ahead of the southward advancing thrust sheets of the Hawasina nappes and Semail Ophiolite that were emplaced on the northern margin of the Arabian Plate associated with the Late Cretaceous closure of the Neo-Tethys Ocean. The Muti Formation, time equivalent with the Shargi Member of the Fiqa Formation, was deposited in close proximity to these advancing thrust sheets and became partly overridden by them. In North Oman, an initial, northwards prograding, Coniacian to Santonian deltaic complex (incorporating the Qitqawt sand equivalents) ultimately gave way to deeper-marine facies in the Campanian via a widespread erosional surface at the base of sandy silty turbidites (Fayah sandstone equivalent). This surface is thought to represent the shelf break delineating the deeper foreland basin to the north, with the Hawasina and Semail thrusts defining the northern boundary of this basin (see Filbrandt et al., 2001, 2004).

Subdivision: In North and Central Oman the Fiqa Formation is subdivided into an upper limestone dominated member (Arada) and a lower shale member (Shargi). Sandstones are locally developed in the middle of the Shargi Member as the Fayah sandstone equivalent and in the basal Shargi as the Qitqawt sandstone equivalent. The Upper Fiqa in North Oman is defined as Juweiza facies (Boote et al., 1990), derived from the allochthonous wedge to the northeast, containing coarse detritus rich in chert.

In South Oman these members are not recognisable. The Fiqa is much thinner and comprises interbedded limestones, sandstones and lignitic shales. Along the Eastern Flank it is classified as undifferentiated Aruma Group.

Osterloff et al. (2001) and Packer (2002; see also Filbrandt et al., 2004) split the Shargi Member into Upper and Lower units separated by a ‘Fayah’ sand (Early Campanian, early Zone F65). They also recognise a basal succession with an Early Santonian (Sub-biozone F63a) influx of sands and siltstones with associated glauconite and chamositic ooids. This is the so-called ‘glauconite marker’ of North Oman (Figure 5.7a), which can range from 3 m to over 40 m above top Natih Formation, although the majority of occurences are less than 25 m above the Natih. This unit can be very condensed (e.g. the 3 m end member) and high Gamma/Density reading chamostic hardgrounds are recognisable. However, care should be taken with this pick as a minor influx of silt and sand within Zone F64 may also be locally glauconitic.

Figure 5.7.

Ditch cuttings from Shargi Member, Fiqa Formation, Aruma Group; (a) Glauconite Marker Bed from Badeel-1; (b) shale from Al Huwaisah-60; and (c) shale from Al Huwaisah-60 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 5.7.

Ditch cuttings from Shargi Member, Fiqa Formation, Aruma Group; (a) Glauconite Marker Bed from Badeel-1; (b) shale from Al Huwaisah-60; and (c) shale from Al Huwaisah-60 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Locally an older, basal Shargi Member, Coniacian (Sub-biozone F63b) unit is developed, which comprises black, lignite/plant-rich claystones and silts and sands of Qitqawt Formation equivalance.

Age: Coniacian – Campanian, ca. 88.6–70.6 Ma. Sharland et al. (2001) position their Santonian MFS K160 surface towards the base of the Shargi Member, and their MFS K170 (Campanian) surface in a mid-Fiqa position. The Coniacian MFS K150 surface is recognised in outcrop equivalent sections from western Oman (Laffan Formation).

Biostratigraphy: The Fiqa Formation contains Biozones F67 (Globotruncanita calcarata) to F63 (Whiteinella baltica) (see Group discussion). Recent studies (Packer, 2002) have provided a much higher resolution in the Shargi Member (F65 (Pseudedomia aff. multistriata) to F63 Biozones). See Group discussion for zonation table.

The key to the detailed breakdown of the Shargi Member is this highly refined micropalaeontological calibration (13 Sub-biozones/events) made possible by rich and varied faunal recovery. Detailed and rigorous micropalaeontological analysis is the key to the full understanding of this unit. In addition to the plant remains observed near the base (Sub-biozone F63b shales) the top (upper Zone F65) of the Shargi Member can be similarly organic/plant-rich.

Figures & Tables

Figure 5.1:

Location map: Aruma Group.

Figure 5.1:

Location map: Aruma Group.

Figure 5.2.

Composite electrical logs, lithology and lithological description of the Simsima Formation, Aruma Group, in well Suneinah-1, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.2.

Composite electrical logs, lithology and lithological description of the Simsima Formation, Aruma Group, in well Suneinah-1, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.3.

Composite electrical logs, lithology and lithological description of the Simsima and Fiqa formations, Aruma Group, in well Hawmyat-1, South Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.3.

Composite electrical logs, lithology and lithological description of the Simsima and Fiqa formations, Aruma Group, in well Hawmyat-1, South Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.4.

Fossils from the Simsima Formation: (a-c) Siderolites calcitrapoides from Maastrichtian Biozone F68 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 5.4.

Fossils from the Simsima Formation: (a-c) Siderolites calcitrapoides from Maastrichtian Biozone F68 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 5.5.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Al Huwaisah-6, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.5.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Al Huwaisah-6, North Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.6.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Haima-3, Central Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.6.

Composite electrical logs, lithology and lithological description of the Fiqa Formation, Aruma Group, in well Haima-3, Central Oman (Mohammed et al., 1997). See Figure 5.1 for location.

Figure 5.7.

Ditch cuttings from Shargi Member, Fiqa Formation, Aruma Group; (a) Glauconite Marker Bed from Badeel-1; (b) shale from Al Huwaisah-60; and (c) shale from Al Huwaisah-60 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

Figure 5.7.

Ditch cuttings from Shargi Member, Fiqa Formation, Aruma Group; (a) Glauconite Marker Bed from Badeel-1; (b) shale from Al Huwaisah-60; and (c) shale from Al Huwaisah-60 (scale grid is 1 x 1 mm) (Mohammed et al., 1997).

GROUPFORMATIONMEMBER
ArumaSimsima 
FiqaArada
Shargi
GROUPFORMATIONMEMBER
ArumaSimsima 
FiqaArada
Shargi
ZoneMarker speciesRelative ageFormation/Member
F68Siderolites calcitrapoidesMaastrichtianSimsima
F67Globotruncana calcarataLate CampanianFiqa/Arada-Shargi
F66Pseudedomia complanata, G. elevatalate Early – early Late Campanian
F65Pseudedomia aff. multistriataEarly CampanianFiqa/Shargi
F64Dicarinella asymetricalate Early – Late Santonian
F63Whiteinella balticaConiacian – Early Santonian
ZoneMarker speciesRelative ageFormation/Member
F68Siderolites calcitrapoidesMaastrichtianSimsima
F67Globotruncana calcarataLate CampanianFiqa/Arada-Shargi
F66Pseudedomia complanata, G. elevatalate Early – early Late Campanian
F65Pseudedomia aff. multistriataEarly CampanianFiqa/Shargi
F64Dicarinella asymetricalate Early – Late Santonian
F63Whiteinella balticaConiacian – Early Santonian
ZoneSubzoneMarker speciesRelative age
596522Odontochitina costataCampanian – Maastrichtian
802Xenascus ceratoidesConiacian – Campanian
ZoneSubzoneMarker speciesRelative age
596522Odontochitina costataCampanian – Maastrichtian
802Xenascus ceratoidesConiacian – Campanian
ZoneMarker speciesRelative ageFormation/Member
1Fibrocysta axialis‘middle’ – Late MaastrichtianSimsima
2Hystrichodinium pulchrumEarly – ‘middle’ Maastrichtian
3Apteodinium reticulatumLate CampanianFiqa/Arada
4Cribroperidinium orthocerasEarly – Late CampanianFiqa/Shargi
5Exochosphaeridium bifidum?Turonian – Santonian
ZoneMarker speciesRelative ageFormation/Member
1Fibrocysta axialis‘middle’ – Late MaastrichtianSimsima
2Hystrichodinium pulchrumEarly – ‘middle’ Maastrichtian
3Apteodinium reticulatumLate CampanianFiqa/Arada
4Cribroperidinium orthocerasEarly – Late CampanianFiqa/Shargi
5Exochosphaeridium bifidum?Turonian – Santonian

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