مشرف منتدى الجوفيزياء
عدد المساهمات : 231
تاريخ التسجيل : 04/05/2010
العمر : 32
الموقع : khartoum north
|موضوع: hyrdology 21st يونيو 2010, 3:50 am|| |
The breicambirian basement of Sudan comprises igneous and meta morphic complexes belonging to distinct major – crustal domains Known as the Arabian – Nubian shield to the east and Nile era ton or Saharan Metacraton to the west.
The Red Sea Hills of NE Sudan is belong the eastern carton of low – grade juvenile are terrenes these terrenes formed as intra oceanic Island are (1000- 550Ma ) of variably deformed green schist facies rock units cropping out in western Saudi Arabia,yemen eastern desert of Egypt Sudan ,Ethiopia and Somalia
Stratigraphy of Red Sea –Hills:-
The main stratigraphical units were out lined by maxy out hers , In spite of lack systematic geochronology (gass1955) Ruxton(1956) kabesh (1962) and (Vail 1979)Embleton et al 1983 ELNadi , 1984Vail , 1985 , Kroner et al ,1987) .
The lastest resachers have reassed the stratigraphical succession in the Red sea and established a litho .
Stratigraphic classification compatible with the current island are modle table (2-1)
Geology of Red Sea :-
The main geological units that make up the geology of Red Sea Hills are:
1- Basement complex (Precambrian)
Paleozoic volcano- sedimentary sequences
Mesozoic sediments(crater nary)
Cenozoic sediments (Quaternary)
The Red Sea basement complex perhaps one of the most Known of the Sudan gass (1955) Ruxton(1955), white man (1962) Lutffi and Kabish (1964) . since pre- Cambrian the area has been part of the Afro-Arabian shield.It has been subjected to up lift and erosion . This basement it has been subdivided by : Elnadi (1984) , Ahmed (1993) Babiker(1993) .These subdivisions are based on the rock associations and the grade of metamorphism . The classification generally subdivided the basement rocks from old to young .
(1) Kashebib series :-
It consists of acidic gneisses, hornblendes schist , schist slates and Amphibolites , these are in high grade metamorphism , and it represents the oldest rocks.
(2) Naferdib series:
It at low grade meta – sedimentary – It consist of green schist , slate agglomerates Mate Anhorites with minor quartzite , limestone , meta dacite and grey wacks .
(3) Basic Intrusiue rocks :
The Kashelbib series is cut by gabbroic and Naferdib series cut by norites.
= Awat series :-
It consists of grey , massive silt mud stones with some Micro conglomerates ,afew adensitic laves occur at the succession it most striking feature is its fresh and unaltered state .
= In jection granite and Red granite :-
The Naferdib and awat group cut by grey – white or pink red Injection granites .
= Acid and basic dykes :-
There are suarms of acidic, inter mediate and basic dykes cut the red granite.
The thickness of sediments above 200m (area located 150km north west of Port Sudan) this sediment related to Ordovician an silurian in age , It consists of sand stone with conglomerate which thought deposited in alluvial to near coastal marine environment .
In resent studies the formation shows different age's depositional environments but generally indicates continental environment of deposition of the Mesozoic age (mainly cretaceous). In the Red sea hills the formations are recognized as iso lated out cross rest un conformate on the basement complexes The crop out sw of gebeit Nw of Nw of port Sudan . And along Kher langeib east of Durdeib village (Kabish1962)ELNadi , (1984) . It consists of conglomerate and sandstone .
The geology of Khor Arbaat is apart of the Red sea Hills geology .
The geological successions in Choir Arbaat are meta ualcano sedimentary group, diorite and granites and dykes . Generally the wadi deposite are formed by the processes of woatuering denudation and deposition of local and granites and adjacent rocks . The deposite are made up of the blocks boulders pebbles sand and silt. And rock fragment. The sediments were deposited in pleistocont and Recent age and the deposition is still continuing .
Basement Rocks :-
Corolla and sorapa (1962) , Kabesh (1962) and white man (1971) out Lind the most comprehensive account of the geology of the Red sea coastal plain . based on the result of these out hors – the main geological units comprise Arbaat valley and it surroundings area.
The metamorphic rocks represent the oldest rock group and Meta volcanic group .
The meta sedimentary group .
It consist of green chlorite. Schist. Greywacke and slate . They represent the low grade . The Meta sedimentary group appears as small patches in the Nw of area the rocks are generally fractured in Ew trend that parallel to the general trend of the Nakasib Shearzone.
The Meta volcanic group:-
It represented by Arbaat volcanic west of the upper gate (joined in N – S to NNw direction). It mainly consists of basalt . The granite in this group is highly jointed by chemical weathering thus as considered is the main lateral conduit recharging the aquifer .
Synto port tectonic diorite cover most of the southern of Khor Arbaat bet ween upper and lower gate, theyappear as the moderately elevated shills build up of medium grained rocks . The xenoliths of diorite with in the grey granite indicate that the letter is younger than diovite .
The above mentioned basement rocks intruded by intermediate to basic dykes for mine adyke swarms .
Allwial sediment (Quarter nory):-
The quarter nory sed imentsin Red Sea west is acombination of inter fingering between sea litheral sediments and continental coos tic sed iments that have been the erosion of nearby crystalline pan . African mea volcanic sediments are considered as the main water – bearing strata along the coastal plane , but their extention , depth intereatation are fuctin of space ,time .
The sed iments made up of boulders , pebble sand and site , Due to the steep slope of the drainage basin running carries different size of rock fragments and sediments so that according to grain size we can subdivided the Khor In to three parts :-
i. Upper gate : the grain size in this portion is coarse(boulders) because the intensity of of flood is light .
ii. The middle gate: generally it composed several deposits of boulder , pebbles sand and silt – The Khor with is wide the flood velocity is less than upper gate so that the medium grain size is deposited .
iii. The lower gate :
In This part the sediments (gravel – sand and silt ) are predominant than others .
At lost the sediments of Khor Arbaat are in Quaternary to the recent in age .