Lekhwair Fm
Type Locality and Naming
The Lekhwair Formation is part of the extensive shallow-marine carbonate shelf system that was established in Early Cretaceous times. Column: Oman Subsurface, Oman Outcrop, Qatar. Type section: Well Lekhwair-7 in Hughes Clarke (1988). Additional reference sections are Hazar-2 and Hasirah-1, both in Central Oman.
Synonym:
Lithology and Thickness
Limestone. "The Lekhwair Fm is a sequence of sedimentary cycles involving three main facies: an argillaceous limestone to marl facies with pyrite and some quartz silt; a varyingly chalky algal or fine skeletal wackestone; and a pelletal skeletoidal lime packstone-to-grainstone with common rudists. The argillaceous facies predominates in the cycles in the lower part of the unit, the cycles becoming less argillaceous upwards and laterally to the east. In the south, the base contains quartz sand." Sequence stratigraphy: "Davies et al. (2002) moved the K50 (Early Barremian) MFS of Sharland et al. (2001) up to the top of the Lekhwair Formation in well Lekhwair-7. Both publications indicate the K40 (Late? Hauterivian) MFS in the lower part of the Formation, both in Lekhwair-7 and in the Wadi Al Muaydin outcrop."
Relationships and Distribution
Lower contact
In Oman, the lower boundary is a disconformity, with the argillaceous lower Lekhwair Fm lying on Habshan Fm carbonates (a marked seismic discontinuity is noted by Davies et al., 2002) or overstepping older units to the south and east. This surface becomes a conformable, but diachronous boundary in more distal settings (in the Al Hajar Mountains, Le Bec et al., 2002). In Qatar, the underlying unit is the Yamama Fm.
Upper contact
" The upper boundary is transitional into the Kharaib Fm carbonates, which are chalky and non-argillaceous. The top is generally marked by a hard argillaceous limestone. . . .. The main difference from the overlying Kharaib Fm and Shu’aiba Fm is the amount of argillaceous limestones and thin shales, notably in the lower part of the Formation. The chalky limestones are only present in the upper part, and are similar to those of the Shu’aiba Fm and Kharaib Fm."
Regional extent
Oman Subsurface, Oman Outcrop, Qatar. "The Lekhwair Fm is present everywhere, except in the south and southeast, where it is eroded at younger unconformities over local highs and the Al Huqf axis. Equivalent sediments reappear to the north and west of Salalah, e.g., Jazal-1. The sequence generally becomes thinner from north to south."
GeoJSON
Fossils
The lower part of Biozone F55 (Choffatella decipiens, Salpingoporella dinarica) and Sub- biozone F553 (Salpingoporella muehlbergii) and Biozone F54 (Pseudochrysalidina arabica).
Age
Depositional setting
The Lekhwair Formation is part of the extensive shallow-marine carbonate shelf system that was established in Early Cretaceous times. The Formation is interpreted as intra-shelf carbonates that developed, in part, contemporaneously with the rapidly prograding Rayda Fm – Salil Fm - Habshan Fm, where the Rayda Fm and Salil Fm represent respectively basinal and slope sediments and the Habshan Fm the contemporaneous platform edge (Droste and Van Steenwinkel, 2004). The Lekhwair Fm represents shallow, probably restricted marine sediments everywhere, with variations in clay content probably reflecting varied fine clastic supply, but becoming overall cleaner upwards. The sediments are interpreted as the intra-basinal carbonates on a shallow marine, rapidly prograding carbonate shelf, inboard of the platform edge that is represented by the carbonates of the contemporaneous Habshan Fm. Overall progradation of the Salil-Rayda- Habshan-Lekhwair system is followed by the stable aggrading of the Kharaib Fm and Shu’aiba Fm carbonate platforms
Additional Information