Tuwaiq Mountain Limestone Fm

Period:

Jurassic

Age Interval:

Callovian, Sa1, On1

Province:
Saudi Arabia, Oman

Type Locality and Naming

The Tuwaiq Mountain Limestone Formation is a shallow-marine aggrading carbonate platform system that was first established during underlying Dhruma Fm times. Type section is Darb al Hajaz, Saudi Arabia (see Powers, 1968). Columns: Saudi Arabia Outcrop, Oman Subsurface. Middle formation (3 of 5) in the Sahtan Gr of Oman subsurface.

Synonym: Tuwaiq Mountain Fm

Lithology and Thickness

Soft marly limestone with some interbedded calcarenite. Cream dense microcrystalline lithographic limestone, and, less dense but similar limestone with a few calcarenite layers at various levels. In Oman subsurface, it is "a single sequence evolving upwards from deep-shelf lime mudstones to shallow-marine porous pack- to grainstones (indicated as oolitic on cross-section chart) (as in Butabul -1). These are slightly, to rarely very, dolomitic, particularly in the upper part."

Lithology Pattern:

Clayey limestone

Relationships and Distribution

Lower contact

The Tuwaiq Mountain Limestone Formation is underlain almost everywhere by a thin argillaceous limestone of the uppermost Dhruma Fm.

Upper contact

Overlain with low-angle unconformity by the Hanifa Fm or, more obviously, unconformably by younger units of the Kahmah Gr. In Oman, where not eroded in the west, the Tuwaiq Mountain Limestone Fm has a constant depositional thickness with a sheet-like depositional geometry. Assuming original constant thickness suggests up to 250 m of erosion of Tuwaiq Mountain Limestone Fm and upper Dhruma Fm in the east.

Regional extent

Saudi Arabia, Oman. In Oman, The Tuwaiq Mountain Limestone Fm carbonates are present only in the western subsurface of Interior Oman; being truncated by younger unconformities to the east and south. They are absent from both Al Huqf and central Al Jabal Al Akhdar outcrop areas. An equivalent is present in the Lower Musandam Fm limestones in Ruus Al Jibal, but this has not been recognized as a separate unit.

GeoJSON

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Fossils

In Oman, the Tuwaiq Mountain Limestone Fm represents Sub-biozone F475 (lower part) and Sub-biozone F473 (Trocholina palastiniensis) and ranges down to Biozone F45 (Pfenderina salernitana, P. trochoidea) at the base. The 4009 (Ctenidodinium cf. ornatum) Palynozone generally characterises this unit, whilst Jacovides et al. (1998) also recorded Late Bajocian – Bathonian ranging dinocysts (Palynozone 4191 assemblages) within the lower Tuwaiq of a number of wells in north Oman. Woollam et al. (1999) used dinocysts to indicate an age somewhere within a general middle Bathonian – Early Callovian range for the Lower Tuwaiq in well Lekhwair-319. . . . The available data it does appear that definitive Oxfordian assemblages may be absent in both the foraminiferal and palynological recovery, thereby supporting the age interpretation of Rousseau et al. (2006). All evidence considered, a best estimate, albeit tentative, age for the Tuwaiq Mountain Formation would be a broad Late Bathonian – Callovian age." (Forbes et al., 2010)

Age

Callovian, but uncertain: In Oman, "Sikkema (1992) considers it likely that Tuwaiq Mountain Limestone Fm deposition started in the Late Callovian and in support of this Sharland et al. (2001) place their Middle Callovian J40 MFS approximately at the Tuwaiq Mountain Limestone Fm / Dhruma Fm boundary in wells Butabul-1 and Yibal-85. Conversely, Rousseau et al. (2006) group the Dhruma Fm and Tuwaiq Mountain Fm within a general Bathonian – Callovian aged episode, placing the Tuwaiq almost exclusively within the Callovian, possibly no younger than Middle Callovian. They argue that no Oxfordian deposits are preserved in Interior Oman. Palynological work in PDO (Jacovides et al., 1998; Woollam et al., 1999) suggests that the Tuwaiq Mountain Limestone Fm may range down to the Late Bathonian." (Forbes et al. 2010, who assign it as "Late Bathonian-Callovian").

Age Span:

Beginning stage:

Callovian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

165.29

Ending stage:

Callovian

Fraction up in the ending stage:

1.0

Ending date (Ma):

161.53

Depositional setting

The sediments of this Formation represent generally shallow-marine carbonate environments with a transition from relative deeper below (containing pelagic lamellibranchs) to shallower above, with algae, corals, foraminifera, etc.

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.