Maqna Gr
Type Locality and Naming
The Maqna Group consists of two evaporite-bearing formations: (1) the lower to middle Miocene Jabal Kibrit Fm; and (2) the middle Miocene Kial Fm (Hughes and Filatoff, 1995; R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). . The first published use of the name Maqna Group (after the town of Maqna on the Gulf of Aqaba) was by Hughes and Filatoff (1995) following in-house usage by Saudi Aramco since 1992. Although well exposed in the Midyan region, the definition of the Maqna Group has been based upon the better-understood subsurface stratigraphic relationship. Column: Red Sea Saudi Arabia.
Synonym:
Lithology and Thickness
The Maqna Group consists of exposed deep-marine carbonates, shallow-marine carbonates, and anhydrite. In the subsurface, it consists of deep-marine mudstones and generally fine-grained sandstones and anhydrite. At Jabal Rughama in the Midyan region, anhydrite is interbedded with soft, calcareous mudstones that overlie Burqan Fm mudstones (Figure 66). The thickness of the interbedded mudstones varies along the length of the exposure, most probably due to slumping of the anhydrite cap. A.A. Al-Laboun (Saudi Aramco, oral communication, 1998) has confirmed that some of the repeated mudstone-anhydrite sections are the result of a series of gravity slides of the poorly consolidated mudstones. There are, however, undisturbed alternations between siliciclastics and interbedded anhydrite within the Kial Fm. In the subsurface, the Maqna Gr varies in thickness from absent (Al Khurmah-1) or from a minimum of 165 ft (Yuba-1) to a maximum of 3,679 ft (Al Wajh-1). The maximum thickness in the Maqna Group seems to coincide with those areas in which the clastics of the Umm Luj Member (Jabal Kibrit Fm) are best developed (Al Wajh and Yanbu Basins). (Hughes and Johnson, 2005)
Relationships and Distribution
Lower contact
In a complete section, the Maqna Group unconformably overlies the Burqan Fm. Local variations exist due to local topographic irregularities, and include the Maqna Group lying unconformably upon siliciclastics of the Tayran Gr. Regionally, the schematic strat column indicates the next older unit as the Burgan Fm.
Upper contact
In a complete section, the Maqna Group is conformable with the overlying Mansiyah Fm. Regionally, the schematic strat column indicates the next younger unit as the Mansiyah Fm
Regional extent
The Maqna Group is exposed along the eastern and western margins of the Ifal Plain in the Midyan region whre it forms an extensive blanket of gypsum and anhydrite that covers much of the central part of the basin.
"The Maqna Group is regionally equivalent to the combined Belayim Fm and Kareem Fm of the Gulf of Suez and other areas of the Red Sea (Hughes and Beydoun, 1992; Hughes et al., 1992) and to the Abu Imama Fm and Khor Eit Fm, respectively, of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992; Hughes et al., 1992). The Maqna Gr is equivalent to the open-marine, syn-rift tectono-sedimentary unit C of Plaziat et al. (1990)." (Hughes and Johnson, 2005)
GeoJSON
Fossils
The Maqna Group was dated as early to middle Miocene based on the presence of age-diagnostic planktonic foraminifera and calcareous nannofossils (Hughes and Filatoff, 1995). Samples collected from the surface and the subsurface confirm this age. The occurrence of charred Gramineae cuticle in the palynological assemblages (the richest and most diverse in the Neogene succession) has served to differentiate the Maqna Group from underlying units. This age range is consistent with the early to middle Miocene age of the Kareem Fm, and to the middle Miocene age of the Belayim Fm, in the Gulf of Suez." (Hughes and Johnson, 2005)
Age
Depositional setting
Sediments of the Maqna Group were deposited under a variety of conditions, each of which is discussed under the various formal members. Deep- and shallow-marine carbonates and siliciclastics are present, together with evaporites that are interpreted as having a submarine origin.
Additional Information