Lexicon of Geological Terms for the Sudan

J.R. Vail

• Publisher: Routledge
• Year: 2022
• Print ISBN: 9789061917052
• eBook ISBN: 9781351435468
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

A listing of lithostratigraphic terms used by geologists in the Sudan. Including 315 rock unit names with location, age, and description. Useful for correlation with adjacent areas of North Africa.

Lexicon of lithostratigraphic units for the Sudan

A

Abbasiya granodiorite Precambrian

Foliated granodiorite occurs in the north-eastern Nuba Mountains in the vicinity of Abbasiya village. The region has not been mapped in detail, but forms part of the Precambrian basement. The granodiorite has been sampled by Harris et al. (1984).

Locality: North-east Nuba Mountains, South Kordofan Province, about 12°03’N, 31°20’E.

Stratigraphic position: The granodiorite is probably syn- to latetectonic with respect to Precambrian basement of unknown age.

Harris et al. (1984) obtained a model Sm-Nd age of 950 Ma suggesting derivation from an early Pan-African crust.

Absol Series Precambrian

The uppermost unit of the Bayuda Formation (Meinhold 1979, 1983; Barth and Meinhold 1981) consists of kyanite-staurolite-garnet-mica schists, quartzitic and graphitic schists, ferrugenous quartzites, marbles and calc-silicates, containing lenses of amphibolite and hornblende gneiss, all in amphibolite facies. This unit partly overlies and is interfingered with the middle series, the Rahaba. The Series is well foliated and folded, and occupies cores of large synclinal folds bounded by Rahaba gneisses.

These metasediments equate with the Supracrustal Metasedimentary Group of Vail (1979, 19876) and the Abu Hamed metasediments of Dawoud (1980).

Type locality: Eastern Bayuda Desert, south-west, west and north-west of Shereik, Nile Province. 18°53’N, 33°30’E.

Distribution: Confined to the eastern Bayuda Desert, but forms extensive narrow bands.

Stratigraphic position: The Absol Series itself has not been dated. However, biotite-garnet schists and amphibolites of the Abu Hamed metasediments (Dawoud 1980) yielded a Rb-Sr whole rock errorchron of 761 ± 22 Ma (MSWD꞊6.6), which Ries et al. (1985) considered to be a metamorphic age. Harris et al. (1984) obtained a model Nd age of 1000 Ma from a biotitic quartzo-feldspathic psammite.

The stratigraphic viability of the Absol Series has yet to be verified.

Abu Chushab Complex Silurian?

Meinhold (1983) described a small, possibly separate, ring-complex in the south-eastern Bayuda Desert near Singeir Complex, which is a deeply eroded alkali granite. It has not been studied in detail.

Locality: South-east Bayuda Desert, Nile Province, at about 17°57’N, 33°21’E.

Stratigraphic position: The complex is emplaced in Basement Complex rocks, and since it has not been isotopically dated its age can only be inferred by comparison with Singeir Complex to be Silurian.

Abu Dom Complex Middle Triassic

Almond et al. (1977, 1984) recognized a number of anorogenic ring-complexes in the central Bayuda Desert, and O’Halloran has mapped Abu Dom in detail (1982a,b, 1985a,b).

It comprises three centres aligned N-S over 10 km from the El Howi to the Abu Dom centre, and is composed of at least seven alkali granites, alkali quartz syenites and hedenbergite syenite, with small remnants of Abu Dom Volcanic Group rhyolites preserved. The complex is overlain by outliers of Nubian Sandstone type. The major intrusive rocks form steeply dipping ring-dykes, and smaller, irregular arcuate sheets may represent cone-sheets.

Locality: Central Bayuda Desert, south of Sultaniyat Complex, Northern Province, at about 17°57’N, 32°56’E.

Stratigraphic position: Post-Basement Complex, pre-Nubian Sandstone type. Samples from Abu Dom have been combined with those from Sultaniyat and Ras Ed Dom by Barth et al. (1983) to provide a 10 point Rb-Sr isochron age of 236 ± 3 Ma (Ri = 0.70564). Although this is a composite age of a sequence of intrusive and extrusive events (Almond et al. 1984), it is probably close to the emplacement age, which is Middle Triassic, and closely comparable to that of Abu Nahl Complex.

Abu Dom Volcanic Group Middle Triassic

O’Halloran (1982a,b) has mapped a small isolated patch of rhyolitic pyroclastic rocks in Wadi Umm Gaa east of Abu Dom Complex in central Bayuda Desert. Small rafts and xenoliths of volcanic rocks also occur within the granites and syenites of the ring-complex. These extrusive rocks are referred to as the Abu Dom Volcanic Group (Almond et al. 1984).

Locality: In and adjacent to the Abu Dom Complex, central Bayuda Desert, Northern and Nile Provinces, 17°55’N, 32°58’E.

Stratigraphic position: The volcanic rocks tend to be the earliest phase of igneous ring-complexes. Barth et al. (1983) combined samples of rocks from Abu Dom, Sultaniyat and Ras Ed Dom complexes to produce a 10 point Rb-Sr isochron which indicated an age of 236 ± 3 Ma (Ri = 0.70564); Middle Triassic.

Abu Gabra Formation Middle Cretaceous

One of the informally named sedimentary units in the lower part of the Muglad basin of south-west central Sudan is the Abu Gabra Formation. It is only known from oilwell drilling in the Tabaldi and Unity fields but information about the thickness, stratigraphy, and lithology is not available.

Type locality: Muglad Basin of Southern Darfur Province around 10°45 ‘N, 27° 10’E. The unit probably extends south-eastwards to the Unity Field in Southern Kordofan and Upper Nile Provinces around 9°30’N, 29°30’E.

Stratigraphic position: The Abu Gabra Formation underlies the Bentiu Formation and overlies the Sharaf Formation which are both Early to Middle Cretaceous, and is probably early in the Middle Cretaceous. This age is comparable to that of the Nubian Sandstone Formation.

Abu Habil Series late-Precambrian

The Abu Habil Series comprises well graded brick red arkosic sediments with slump structures made up of conglomerates, arkosic sandstones, subgraywackes, siltstones, calcareous grits and minor limestones. Pyroclastics and volcanics may be associated in the lower parts of the sequence. The rocks are unmetamorphosed, but have been discretely foliated, buckled, and preserved in fault troughs. The sequence was named by El Rabaa (19766), and the upper succession includes the previously recognized Nawa Series (Andrew and Karkanis 1945).

Type locality: Khor Abu Habil, Kordofan Province, at 12°37’N, 30°38’E(Salama 1985).

Distribution: Isolated occurrences (usually in wells and boreholes) around the north margin of the Nuba Mountains basement inlier. Similar lithologies occur in eastern Bayuda Desert (Amaki Series).

Stratigraphic position: Although unfossiliferous, the low state of metamorphism suggests a late Precambrian or early Palaeozoic age. Due to molassic nature they are considered to be a late-tectonic phase (cf. Hammamat of Egypt) and hence late Precambrian (El Rabaa 1976b).

Abu Hamed Metasediments Proterozoic

Dawoud (1980) mapped metasediments in the Abu Hamed area comprising pure and impure marbles, and quartzites, red magnetite-microcline quartzites, fine-grained quartzo-feldspathic sediments, calc-silicates, biotite-garnet schists and para-amphibolites, all in amphibolite grade of metamorphism.

They are similar to, and included within the Metasedimentary Group of Vail (1979), and the Bayuda Formation of Meinhold (1979, 1983).

Type locality: Mugrat area of north-east Bayuda Desert, south-west of Abu Hamed town, Nile Province. Around 19°25’N, 33°15’E.

Distribution: Confined to type area, but comparable metasedimentary rocks are well known throughout the eastern Bayuda Desert, especially south-west of Shereik, and in the Nubian Desert towards Wadi Haifa.

Stratigraphic position: A metamorphic age is indicated by a Rb-Sr whole rock errorchron of 761 ± 22 Ma (MSWD 6.6) (Ries et al. 1985). A Model Nd age of 1000 Ma was obtained by Harris et al. (1984). The metasediments are considered to be shelf facies, marginal to a continent prior to plate collision in early Pan-African (Middle or Late Proterozoic) times.

Abu Handal Complex Early Silurian

First recognized on air photographs and named by Vail (1971) the Abu Handal complex forms a striking feature with numerous arcuate sills forming a circular structure 30 km in diameter, with basement rocks within the ring structure. It comprises alkali granites and alkali rhyolite dykes (Meinhold 1983).

Locality: North side of Khor Abu Handal, eastern Bayuda Desert, Nile Province, at about 18°15’N, 33°23’E.

Stratigraphic position: The intrusive and extrusive rocks of the complex at Wadi Abu Handal have been isotopically studied by Barth et al. (1983) who obtained a 9 point Rb-Sr isochron yielding 432 ± 3 Ma (Ri = 0.7038).

This indicates an emplacement age of Early Silurian which is the oldest of the anorogenic alkali granite ring-complexes in the Bayuda Desert. It is comparable in age to the Gebel Kamil Porphyritic Granites of the northwestern Sudan.

Abu Harik Series Precambrian

Biotite, biotite-hornblende and hornblende gneisses, with intercalated amphibolites and rare quartzitic layers, all in amphibolite facies and suffering widespread migmatization, granitization, and isoclinal folding.

Described and named by Meinhold (1979, 1983) the Abu Harik Series was mapped by Barth and Meinhold (1981).

Type locality: West of the River Nile, between Wadi Kurmut and Wadi Abu Harik in eastern Bayuda Desert, i.e. opposite to Berber and Atbara, about 17°40’-18°10’N, 33°50’E, in Nile Province.

Distribution: Confined to within 60 km west of the Nile, but also exposed in cores of three anticlinal structures along Wadi Singeir (further north-west).

Stratigraphic position: Meinhold (1979) considered the series to be a remnant of an old basement, perhaps comparable to granitoid gneiss at Sabaloka. The gneisses are probably unconformable beneath the Kurmut Series of the Bayuda Formation. Ries et al. (1985) dated aplites, granodiorites and biotite granites from near Wadi Abu Harik by Rb-Sr errorchron at 898 ±51 Ma (MSWD 8).

Vail (1987b) considered the hornblende gneisses and amphibolitized gabbroics near Atbara to represent meta-ophiolitic remnants and the paragneisses further west to be part of a supracrustal metasedimentary unit, overlying older ‘Grey Gneiss Group’ rocks, and hence the Abu Harik unit would not be the oldest sequence in this region.

Abu Imama Formation Late Miocene

Carella and Scarpa (1962) recognized a sequence unconformably overlying Maghersum Formation and unconformably beneath Dunganab Formation beds on the Red Sea coast.

It comprises a low C Member of marly sandy matrix conglomerate containing igneous pebbles, up to 50 m, followed by B Member 25 m thick of calcarenites with subordinate marly limestone, and an upper A Member 62 m of cavernous and dolomitized reef limestones. The formation has yielded corals, Mollusca, echinoids, algae, ostrocods, fish, forams and Globigerinadae.

Type locality: Jebel Abu Imama, north-eastern flank north of Khor Shinab, (21°27’05“N, 36°37”15”E). Red Sea Province.

Distribution: Outcrops in hills behind Khor Shinab, Ras Abu Shagara, and hills on the Red Sea littoral south to Khor Eit. Also in borehole Dunganab-1.

Stratigraphic position: Carella and Scarpa (1962) considered th...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Introduction
• Geology of the Sudan
• Lexicon of the lithostratigraphic units for the Sudan
• References
• Stratigraphic index
• Location index
• Author index