Habshan Fm
Type Locality and Naming
As the Lower Cretaceous platform programed, bioclastic and oolitic ‘sands’ dominate the platform edge and these are referred to as the Habshan Fm. Type section is Bab-2 in Abu Dhabi (Hassan et al., 1975). Additional surface reference section is in southeast Al Jabal Al Akhdar along the road to the Saiq Plateau (E57°41 ́30”, N23°02 ́00”), where the thickness is ca. 122 m. The Oman subsurface reference section is well Dhulaima-4. Columns: Oman Subsurface, Oman Outcrop, Oman Outcrop, United Arab Emirates.
Synonym:
Lithology and Thickness
Limestone. "The Habsan Formation is a clean carbonate unit of interbedded wacke- to grainstone textures with common ooidal and algal oncoid horizons and common shell debris. The Upper section is dominated by grainstone, with excellent reservoir quality (porosities of up to 30% and permeabilities of up to 1,500 mD), the Lower section by wackestone. Occasionally dolomites are present, which increase in abundance to the east. Meter-scale current bedded units can commonly be developed. There can be thick ooidal grainstones in the upper part, with abundant loose ooids in cuttings (e.g. Dhulaima-4)." Divided locally into Habshan 6 through Habshan 1 members.
Relationships and Distribution
Lower contact
In Oman, the Habshan Fm overlies the Salil Fm, but oversteps to the south and east to lie on various levels in the Sahtan Gr.. In the northwest of Central Oman the lower boundary with the Sahtan Gr is often difficult to identify due to the similarity of the dolomites in the lower part of the Habshan Fm with those of the Sahtan Gr. In United Arab Emirates, the underlying unit is the Arab Fm
Upper contact
Regionally, the upper boundary is relatively sharp with an upward change from clean carbonates below into argillaceous limestones and marls of the Lekhwair Fm.
Regional extent
Oman Subsurface, United Arab Emirates. In Oman, the Habshan Fm occurs only north of ca. 21°N. To the west and northwest, it thickens and passes laterally into the typical shallow- marine Habshan facies of Abu Dhabi.
GeoJSON
Fossils
"Biozone F54 (lower part) (Pseudochrysalidina arabica), F53 (Pseudocylammina lituus) and F52 (upper part as Sub-biozone F527 (Calpionellites darderi and significant numbers of tintinnids). Simon Petroleum Technology (1995) recognized a diverse calpionellid assemblage in the basal Habshan Formation of well Dhulaima-7, with probable Calpionellites darderi and the tintinnid Tintinnopsella longa (e.g., Sub-biozone F527). The nannofossil Nannoconus steinmannii steinmannii was also recorded in abundance. Both fossil groups indicate an Early Valanginian age.
Age
Depositional setting
"The Lower Cretaceous platform started to grow in Central Oman after a major transgression over a structurally collapsed Middle Jurassic carbonate platform. From here, the edge of the platform prograded 250 km to the north in ca. 10 My. This prograding carbonate belt is expressed on seismic by well-defined clinoforms (Haan et al., 1990; Driessen et al., 2006). During this phase, bioclastic and oolitic ‘sands’ dominate the platform edge and these are referred to as the Habshan Fm, whereas the interbasinal carbonates are represented by the following Lekhwair Fm." . . . The sedimentary facies of the Habshan Fm is consistent with a shallow, high- energy, probably tidal-marine setting, interpreted as the platform edge facies, time-equivalent to argillaceous limestones of the "underlying" Salil Fm that form the slope deposits and the porcellaneous Rayda Fm representing the basinal facies.
Additional Information