Jubaila Fm

Period:

Jurassic

Age Interval:

Kimmeridgian, Sa (1,2), Bn1, On1

Province:
Saudi Arabia, Bahrain, Oman

Type Locality and Naming

The mudstones of the Jubaila Formation correspond to a full drowning of the epeiric carbonate platform. Type section is near al Jubaylah, Saudi Arabia. The Oman subsurface reference section is Butabul-1. Column: Saudi Arabia Outcrop, Saudi Arabia Subsurface, Bahrain, Oman Subsurface. Subdivisions include Lower Jubaila Fm, Jubaila J1, Jubaila J2, Arab D Reservoir. Uppermost formation (5 of 5) in the Sahtan Gr of Oman subsurface.

Synonym: Juballa Fm or Jubayla Fm (spellings)

Lithology and Thickness

Cream to tan, hard, dense, fine-grained limestone, mostly microcrystalline, containing a number of hard massive, partly conglomeratic, brown calcarenite layers. The sediments of the Jubaila Formation are predominantly slightly-argillaceous, fine-grained wacke-/mudstones with some fine dolomite layers, becoming ‘aphanitic’ towards the base (Figure 8.3b). The textures are, for the most part, mud-supported. This contrasts with the porous grainstones in the upper part of the underlying Hanif Fm. Several thin softer calcarenite lenses in Lower Jubaila Mbr / Jubalia J1. Dolomite layers are generally present in the upper part Jubaila J2 / Arab D Reservoir Mbr.

Lithology Pattern:

Limestone

Relationships and Distribution

Lower contact

The lower boundary is conformable onto the Hanifa Fm to the northwest but unconformable, onlapping on older Sahtan Gr units to the south and east.

Upper contact

Regionally, the schematic strat column indicates the next younger unit as Arab Fm.

In Oman, the deposition was followed by the uplift of the Oman margin, eroding deeply into the Jubaila Fm and underlying formations of the Sahtan Gr to the south and east. Therefore, the upper boundary of the Jubaila Fm "with the Rayda Fm of the Kahmah Gr is generally unconformable, but may be conformable in northern Oman, where both formations onlap the underlying older units of the Sahtan Gr, which progressively get older to the east. Hughes Clarke (1988) and Droste and van Steenwinkel (2004) document a base Cretaceous unconformity at the top of the Jubaila Formation overlain progressively by younger units towards the south (Rayda Fm to Habshan Fm). In both cases the deep-water facies of the Jubaila Fm are adjacent, if not genetically linked, to the deep-water sediments of the Rayda Fm.

Regional extent

Saudi Arabia, Bahrain, Oman. In Oman the Jubaila Fm occurs only in the extreme western subsurface, being truncated by Kahmah Gr units to the east and south. In the Lekhwair area, it is developed as an ‘aphanitic’ lime-mudstone of possibly deeper water character, which may be a precursor to deposition of the Rayda Fm.

GeoJSON

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Fossils

"In Oman, the Jubaila Formation probably represents the upper part of the Kimmeridgian F475 (Alveosepta jaccardi) Sub-biozone in Oman, and ranges up to the Tithonian F477/9 (Kurnubia jurassica/Crassicollaria spp.) Sub-biozones. It is placed in the upper part of the 4214 (Systematophora cf. areolata) Palynozone."

Age

Shown as early Kimmeridgian in Saudi Arabia as constrained by the age span of the overlying Arab Fm on the chart of Mideast Timescale 2008; but interpreted in Oman as late Kimmeridgian-early Tithonian.

Age Span:

Beginning stage:

Kimmeridgian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

154.78

Ending stage:

Kimmeridgian

Fraction up in the ending stage:

0.3

Ending date (Ma):

153.12

Depositional setting

The sediment type and microfossil content suggest a low- energy marine setting. "The mudstones of the Jubaila Fm correspond to a full drowning of the epeiric carbonate platform including the Oman margin (J70 MFS of Sharland et al., 2001, at the base of the Formation). This drowning seems to be immediately followed by uplift of the Oman margin, eroding deeply into the Jubaila Fm and underlying formations of the Sahtan Gr to the south and east."

Depositional pattern:

Additional Information

Compiler:

From Middle East Geological Timescale 2008 Al-Husseini, Journal of Middle East Petroleum Geosciences v 13, no. 4. Steineke et. al., 1958, Page 1304. And Forbes, G.A., Hansen, H.S.M., and Shreurs, J., 2010. Lexicon of Oman: Subsurface Stratigraphy. Gulf Petrolink, 371 pp. (plus enclosures and CD.