1. American Journal of Earth Sciences
2015; 2(6): 236-241
Published online January 5, 2016 (http://www.openscienceonline.com/journal/ajes)
ISSN: 2381-4624 (Print); ISSN: 2381-4632 (Online)
Sedimentary Facies and Depositional Environment
of the Gedaref Formation, Eastern Sudan
Abdulrhman F. I. Osman1
, Anas Ibrahim1
, Yousif Abuobida1
, Ali A. M. Eisawi2
, Madibbo Alhadi2
,
Omer Mukhtar2
, Abdelrhim A. El Tijani2
1
Department of Development, Greater Nile Petroleum Operating Company (GNPOC), Khartoum, Sudan
2
Faculty of Petroleum and Minerals, Al Neelain University, Khartoum, Sudan
Email address
afibrahim@gnpoc.com (A. F. I. Osman)
To cite this article
Abdulrhman F. I. Osman, Anas Ibrahim, Yousif Abuobida, Ali A. M. Eisawi, Madibbo Alhadi, Omer Mukhtar, Abdelrhim A. El Tijani.
Sedimentary Facies and Depositional Environment of the Gedaref Formation, Eastern Sudan. American Journal of Earth Sciences.
Vol. 2, No. 6, 2015, pp. 236-241.
Abstract
Based on field investigation of twenty eight vertical and lateral sedimentary profiles in the Gedaref area, nine sedimentary
facies have been identified based on lithofacies analysis. The identified sedimentary facies are named: matrix-supported
massive conglomerate (Gmm), trough cross-bedded sandstone (St), planner cross-bedded sandstone (Sp), ripple
cross-lamination sandstone (Sr), horizontal-bedded sandstone (Sh), massive sandstone (Sm), laminated sandstone and
mudstone (Fl), massive mudstone (Fsm) and paleosol (P). These facies are grouped into three sedimentary facies associations:
FA1consists: Sp, Sm, Sh ± (Fsm, St, P and Fl) representing sandy fluvial channel; FA2 include: Sm, Gmm, St ± (Fsm and Sh)
representing sandy point bars and FA3 consists: Fsm, Fl ± (St and Sh) representing lake deposits. These associations indicate
that the studied sediments have been deposited under fluvial conditions (multi braided and meandering channels) in Wad Hari
and Rumeila respectively, shifted into lacustrine settings at Magareef and Rashed areas towards the basin center. Paleo-current
data indicate that the source area was located southeast of the study area.
Keywords
Gedaref Formation, Sedimentary Facies, Fluvial, Lacustrine, Sudan
1. Introduction
According to Ruxton (1956) the Gedaref Formation
consists of conglomerate, sandstones, sandy mudstones and
mudstones. Constitute a sequence of interbedded sandstones
and mudstones laid down in braided river environment
(Bussert, 1998; Wipki et al., 1993). Whiteman (1971)
proposed the name Gedaref Formation to describe the under
formed sedimentary sequence exposed in the Gedaref area.
The type locality of the Gedaref Formation is represented by
outcrops along the Atbara River valley within the area
situated between lat. 13º 30ʹ 00ʺ- 14º 00ʹ 00ʺN, and long. 35º
48ʹ 00ʺ- 36º 00ʹ 00ʺ E (Fig. 1).
A Middle to Late Jurassic age for the formation was
proposed based on lithological correlation with Adigrat
Sandstone Formation in Ethiopia (Whiteman, op. cit.).
Bussert (1998) carried out sedimentological investigation on
the intracratonic basins in north Sudan and surrounding areas.
He concluded that the depositional environments were
dominated by multiple braided channels, bars and floodplain.
Conclusive evidence about the dating of Gedaref Formation
came from Eisawi and Schrank (2009) who proposed a
Maastrichtian age for the Gedaref Formation based on
pollen/spore assemblages recovered from shallow borehole
near the Gedaref town.
The study area represents one of the potential targets for
hydrocarbon exploration in the country. Therefore,
understanding of the sedimentological and
paleo-environmental evolution of the basin is important for
hydrocarbon exploration in the area. This study attempts to
throw light on the depositional history of the exposed part of
the Gedaref Formation.

2. American Journal of Earth Sciences 2015; 2(6): 236-241 237
2. Regional Geology and Tectonic
Setting
The Gedaref area has been widely studied by several
geologists: (e.g.: Ahmed, 1968; Whiteman, 1971; Chialvo,
1975, Kröner, 1985; Eisawi and Schrank, 2009 and Eisawi et
al., 2011).
The geology of the Gedaref region is composed of
crystalline basement rocks; which is cropped out in the
northern and south western parts of the study area (Fig. 2),
namely Umm Sagatta, Qala En Nahal and Es-Subagh areas
(Eljah, 2008 and Elubid, 2012).
Fig. 1. A map showing the location of the studied profiles in the study area.
Fig. 2. Regional geological map of Gedaref region.
The Gedaref Formation rests unconformably on the
basement rocks and overlain and/or intruded by basaltic
rocks. Whiteman (1971) dated the basaltic dykes depend on
Potassium Argon date of 33 x 106
years (Oligocene). The
succession is overlain in some areas by the Umm Ruwaba
Formation. The Kerib Formation. The Kerib Formation and
black cotton soil of Quaternary age form the youngest unit in
the study area.
The Umm Ruwaba Formation consists of unconsolidated
deposits; exposed in the southwestern part of the study area
(Fig. 2). The unit was deposited in fluvial and/or lacustrine
environment (Whiteman, 1971). Masdar (1991) defined
Kerib Formation as sloping land, in which both topsoil and
subsoil have been removed to expose a surface of abundant
calcium carbonate concretions (Fadul, et al., 1999). Based on
fossils encountered within the Kerib Formation; the age of

3. 238 Abdulrhman F. I. Osman et al.: Sedimentary Facies and Depositional Environment of the Gedaref Formation, Eastern Sudan
the unit is dating to the early Pleistocene (Chialvo, 1975).
The Gedaref basin as the case of the other rift basins in
Sudan and South Sudan, has been formed due to reactivation
of the Central African Shear Zone (CASZ), which is a
northeast-southwest- trending lineaments, formed in the Late
Jurassic-Early Cretaceous time. The basin is filled by
continental deposited of Late Cretaceous- Quaternary age.
(Almond, 1984 and Adam, 1987).
According to Almond (1984) the structure of the Gedaref
basin is interpreted as a northwest-trending faulted syncline.
3. Materials and Methods
The fieldwork was concerned with the sedimentary
outcrops in the study area.
Twenty eight vertical and lateral sedimentary sections have
been examined and described in order to identify the vertical
and lateral changes in sedimentary facies. Eight vertical
sections have been carefully selected from different locations
to represent the study area. Ninety six paleo-current
directions have been measured to determine the general
paleo-current direction and the source area.
Depend on concepts of the lithofacies analysis; studied
profiles have been described in details and interpreted.
Change of the grains size, sedimentary structures and other
physical characteristics are considered to identify the
different sedimentary facies and interpret the depositional
environments. The identified sedimentary facies are grouped
into sedimentary facies associations that occur together and
are considered to be environmentally related.
Computer software programs are also used to explain and
interpret the information obtained from the field studies.
These programs include CorelDraw X5 (for profiles drawing
and final layout of the studied profiles) and Rose Diagram
(for plot of paleo-current measurements).
4. Sedimentary Facies Description
and Interpretation
4.1. Matrix-Supported Massive Conglomerate
(Gmm)
This facies is characterized by moderately sorted and
well-rounded grains conglomerate, including cobble chert in
places (Plate I. (A)). The thickness of this facies is 8.4m;
found in Al Hammra (P12). The facies abundances are 3.66%
(Fig. 3). This facies is interpreted as sand bar with a multi
braided channels (Fig. 5).
4.2. Trough Cross-Bedded Sandstone (St)
This facies is composed mainly of fine-to medium-grained
sandstone, pebbly in places. Mud clasts and argillaceous
cements are dominant. The sandstone grains are moderately
to well sorted and well- to sub-rounded, partly bioturbated
(Plate I. (B)). The thickness of this facies is 30.61m;
maximum thickness in J. Kasamor (P9), it represents 8.79%
of the facies identified within the studied profiles (Fig. 3).
This facies is a result of 3-D dunes migration in a lower flow
regime, normally association with a multi braided channels
(Fig. 5).
4.3. Planner Cross-Bedded Sandstone (Sp)
This facies is composed of sandstone pebbles and mud
clasts, fine to coarse grain size of sandstone,
moderately-sorted and sub-angular-to well- rounded in shape,
partly bioturbated. Kaolinite is the dominant cementing
material (Plate I. (C)). The thickness of this facies is 37.4m.
This facies is common in Rumeila profile, J. Kasamor and J.
Areeda; P8, P9 and P15; respectively. It represents 22.9% of
the facies identified within the studied profiles (Fig. 3). This
facies result of a 2-D dunes, interpreted as braided channels
deposits (Fig. 5).
Fig. 3. Relative sedimentary facies abundance in the study area expressed in
percentage.
4.4. Ripple Cross-Lamination Sandstone (Sr)
This facies is composed mainly of fine-to very fine-grains
sandstone, well-sorted and rounded -to well-rounded grains
shape. The dominant cementing materials are kaolinite (Plate I.
(D)). This facies is rare abundance. It represents 2.04% of the
facies identified within the studied profiles (Fig. 3), the total
thickness is 5.5m; commonly in Wad Hari Profiles (P18). This
facies formed in a lower flow regime; it is interpreted as sand
bar (Fig. 5).
4.5. Horizontal Bedded Sandstone (Sh)
This facies is composed mainly of fine-to medium-grains
sandstone, rounded- to well- rounded and well-to
moderately-sorted (Plate I. (E)). The facies attains a total
thickness of 6.05m in the studied profiles which represents in
Rumeila (P8) and Wad Hari (P18) profiles. Abundance of this
facies is 4.02% (Fig. 3). Horizontal bedded sandstones was
deposited in an upper flow regime, interpreted as sand bar (Fig.
5).

4. American Journal of Earth Sciences 2015; 2(6): 236-241 239
Fig. 4. Rose Diagram showing the paleo-current directions in the study area.
4.6. Massive Sandstone (Sm)
This facies is composed mainly of medium- to
coarse-grains sandstone, moderately- to poorly-sorted, well
rounded to angular. The dominant cementing materials are
silica and kaolinite. The grains are graded fining upward,
mud clasts and pebbly sand also observed (Plate I. (F)). The
total thickness of this facies is 56.2m in the studied profiles;
rise up to 6m in J. Kasamor (P9). It represents 16.97% of the
facies identified within the studied profiles (Fig. 3). The
massive sandstone is a result of rabid sedimentation;
therefore no structure recorded, where interpreted as sand bar
(Fig. 5).
4.7. Laminated Sandstone and Mudstone (Fl)
This facies is composed of fine-to medium grain-sand and
claystone (Plate I. (G)). The thickness of this faceis is 4.7m,
exposed in Al Hammra area (P12). This facies was deposited
in an over bank and floodplains (Fig. 5). It represents 2.0% of
the facies identified within the studied profiles (Fig. 3).
4.8. Massive Mudstone (Fsm)
This facies is the most dominant sedimentary facies with a
thickness of 71.1m, it is brecciated and ferrugenated massive
siltstone. This facies is dominant at Rashed area (P25) and
Magareef area (P20); with thick layers intercalated by thin
fine- to medium-grained sandstone in places (Plate I. (H)).
This facies is characterized by white and reddish to brown
color; it could be interpreted as lake deposits, deposited in a
reducing and/or oxidizing environments (Fig. 5). It is
abundance 38.6% of the facies identified within the studied
profiles (Fig. 3).
4.9. Paleosol Facies (P)
This facies is found in J. Kasamor (P9), composed mainly
of silt size to fine-sand size, characterized by violet color and
moderately induration (Plate I. (I)). The total thickness is
16m; it represents 0.94% of the facies identified within the
studied profiles (Fig. 3). This facies is a result of stabilizing
landscape for length episodes (Fig. 5).
Plate I. List of sedimentary facies recognized in the Gedaref Formation.
A. Matrix supported conglomerate (Gmm), north of Rumeila village; NE
Gedaref town,
B. Map view of trough cross-bedded sandstone (Sp), J. Kasamor; N of
Gedaref town,
C. Planner cross-bedded sandstone (St), north of Rumeila village; NE
Gedaref town,
D. Rippled cross-lamination sandstone (Sr), Wad Hari area; SE Gedaref
town,
E. Horizontal- bedded sandstone (Sh), Atbara River area; E Gedaref town,
F. Massive sandstone (Sm), J.Kasamor; N of Gedaref town,
G. Laminated sandstone and siltstone (Fl), Al Hammra area; S Gedaref town,
H. Massive siltstone (Fsm), north of Magareef village; NE Gedaref town and
I. Paleosol in J. Kasamor, N of Gedaref town.
5. Facies Association
These facies associations have been recognized based on
the sedimentary facies identified in the study area, which is
include:
Facies Association (FA1)
This association is composed of Sp, Sm, Sh ± (Fsm, St, P
and Fl). The association interpreted as deposits of sandy
fluvial channel. FA1 indicate that the sediments have been
deposited under fluvial conditions (multi braided channels).
Facies Association (FA2)
This Facies association consists of Sm, Gmm, St ± (Sr,
Fsm and Sh) and it is interpreted to be deposits under

5. 240 Abdulrhman F. I. Osman et al.: Sedimentary Facies and Depositional Environment of the Gedaref Formation, Eastern Sudan
meandering river system.
Facies Association (FA3)
This association consist of Fsm, Fl ± (Sr and Sh) facies,
which are identified in different locations and they
interpreted as deposits of lacustrine environment.
Fig. 5. Interpretation of the studied sedimentary profiles, Gedaref area.
Table 1. Sedimentary facies in the Gedaref area (modified after Miall, 1996).
Facies
Code
Facies
Sedimentary
Structures
Interpretation
Gmm
Matrix-supported,
massive gravel
Weak grading
Plastic debris flow (high-
strength-viscous)
St
Sand, fine to very
coarse, may be
pebbly
Solitary or
grouped trough
cross-beds
Sinuous-crested and
linguoid (3-D) dunes
Sp
Sand, fine to very
coarse, may be
pebbly
Solitary or
grouped planar
cross-beds
Transverse and linguiod
bed forms
(2-D dunes)
Sr
Sand, fine to very
coarse
Ripple
cross-lamination
Ripple (lower flow
regime)
Sh
Sand, fine to very
coarse, may be
pebbly
Horizontal
lamination parting
or streaming
lineation
Plane-bed flow (critical
flow)
Sm
Sand, fine to
coarse
Massive, or faint
lamination
Sediment-gravity flow
deposits
Fl Sand, silt, mud
Fine lamination,
very small ripples
Overbank, abandoned
channels
Fsm Silt, mud Massive
Back swamp or
abandoned channel
deposits
P
Paleosol carbonate
(calcite, siderite )
Pedogenic
features: nodules,
filaments
Soil with chemical
precipitation
6. Paleo-Current Data Analysis
Ninety six paleo-current measurements have been
measured in the study area from different vertical and lateral
sections. Most of paleo-current measurements noted in the
studied profiles indicate a general northwest direction (Fig. 4).
Eisawi et al. (2011) mentioned the paleo-current directions in
Umm Khanjer and Al Hammra is due northwest. According to
paleo-current data the source area was located southeast of the
study area (probably Ethiopia region).
7. Summary and Conclusion
Based on lithofacies analysis; nine sedimentary facies have
been identified within the outcropping part of the Gedaref
Formation, eastern Sudan. These facies are grouped into
three sedimentary facies associations: (FA1); Sp, Sm, Sh ±
(Fsm, St, P and Fl); (FA2); Sm, Gmm, St ± (Fsm and Sh) and
Fsm, Fl ± (Sr and Sh). These sedimentary facies associations
are indicate that the studied sediments have been laid down
under fluvial channels, sandy point bars and lakes;
respectively. The Sp, Sm, St and Sh sedimentary facies are
dominated in eastern and southeastern sections in the Gedaref
area (Wad Hari and Areeda profiles). Therefore; interpreted
as multi-channel low-sinuosity (braided channels) with sand
bars, it thought to be proximal braided-plains or near source
area and shifted into single-channel high sinuosity
(meandering channels) in Atbara River and Al Rumeila
sections.
Massive mudstone (Fsm) and laminated sandstone and
mudstone (Fl) sedimentary facies mainly dominated in the
western and southwestern part of the study area (Umm
Khanjer and Al Hammra profiles), which represent overbank

6. American Journal of Earth Sciences 2015; 2(6): 236-241 241
and floodplain. Shifted into lacustrine settings at Magareef
and Rashed areas towards the basin center; it signify
approximately the distal of the fluvial system.
Paleo-current measurements have confirmed the above
interpretations. The output of Rose Diagram indicate that the
general paleo-current direction toward northwest. Therefore;
the source area was located to the southeast of the study area
(probably Ethiopia).
Acknowledgements
The authors wish to thank Al Neelain University for
financial support during the field trip. Special thank go to the
staff of Faculty of Petroleum and Minerals. We are extremely
grateful to Mr. Mohamed Mahmoud, Mr. Mohamed Al fatih
and Mr. Mohamed Khidir for their unlimited help during the
field trip.
References
[1] Adam, E. G. 1987: Water Resources Evaluation of Gedaref
Basin. PhD thesis, University of Khartoum, Sudan.
[2] Ahmed, F. 1968: Geology of the J. Qeili, Butana, and Sileitat
Es-Sufur igneous complexes, Nile valley, Central Sudan. M.Sc.
thesis, University of Khartoum.
[3] Almond, D. C. 1984: Alkaline Basalt volcanism in north
eastern Sudan, a comparison of Bayoda and Gedaref areas,
Jour. of African earth Sci., Vol. 2, No. 33, p. 233-245.
[4] Bussert, R. 1998: Die Entwicklung intrakratonaler Beckenim
Nordsudan. Berliner geowissenschaftliche Abhandlungen,
Reihe A 196, 329 pp.
[5] Chialvo, J. 1975: Contribution a la geologic du confluent
Atbara Setit; Unpublished thesis, University of Grenoble,
France.
[6] Eisawi, A. and Schrank, E. 2009: Terrestrial palynology and
age assessment of the Gedaref Formation. J. Afri. Earth Sci,
54, p. 22-30.
[7] Eisawi, A. A. Babikir, I.A. and Salih K.O. 2011:
Paleoecological significance of newly discovered trace fossils
near the gedaref town, eastern Sudan.
[8] Eljah, M. A. 2008: Geology and geochemistry of El Tuwal
ophiolitic complex and environs– East Central Sudan- Faculty
of petroleum and Minerals, Khartoum, Sudan, p.200.
[9] Elubid, B. A. 2012: Application 0f remote sensing and GIS in
ground water resoursces assessment and development- Faculty
of petroleum and Minerals, Khartoum, Sudan, 15-28.
[10] Fadul, H. M., Salih A. A, Ali, I. A. and Slnanaga, 1999: Use of
remote sensing to map gully erosion along Atbara River,
Sudan. JAG, 1 (34), p. 175-180.
[11] Kröner, A. 1985. Ophiolites and the evolution of tectonic
boundaries in the late Proterozoic Arabian – Nubian Shield of
northeast Africa and Arabia. Precambrian Res.
[12] Masdar, U. K. 1991. Land use plan interim report for southern
Kassala Agricultural Development Project, Sudan.
[13] Miall, A. D. 1996: The Geology of Fluvial Deposits:
Sedimentary Facies, Basin analysis and Petroleum Geology.
Berline: Springer.
[14] Ruxton, B. P. 1956: The major rock groups of the northern
Red Sea Hills, Sudan. Geol. Mag., 93, 314-30.
[15] Wiss., Math.- naturw. 191, 11-131.
[16] Whiteman, A. J. 1971: The geology of the Sudan Republic,
Clarendon Press Oxford.
[17] Wipki, M., Germann, K., and Schwarzc, T. 1993: Alunitic
kaolins of the Gedaref region (NE Sudan). In: Thorweihe, U.,
Schandelmeier, H. (Eds.), Geoscientific Research in Northeast
Africa, pp. 509–514.