Dhofar is situated in the Southern province of the Sultanate of Oman, bordered to the South by the Arabian Sea, the Kingdom of Saudi Arabia from the north and bounded by South Yemen from the west .
The Continuos belt of Dhofar's mountain region constitutes Jabel Qamer, Jabel Qara and it reaches height of approximately 1800 m in Jabel Samhan.
Cyclonic storms Originating in the tropics reach the coast of Oman about once every 3 years, with a severe event occurring roughly every decade, they are most likely to occur in May to June and October to December and between these two periods they usually disintegrate as they pass over cool, Upwelling coastal water and do not reach land. Padgeley (1969) states that cyclones that bring rain to Dhofar every 5 years or so contribute about 20% of the average annual rainfall for that region.
1.2 ACCESS
The studied area lies in the Raysut area . In relation to the Dhofar Mountain’s the studied area is West of Salalah, bounded by Mughsayl beach from the South and the military area from the west. It is about 30 km from Salalah one can reach the area by using the Salalah-Dhalqut Road. The studied area mapped and prospected at I: I00, 000 scale, covered by four aerial photographs. The studied area is about 2 kW wide and 13 km long.
The coordinates of the study area are:
Latitude: 160 53' 30" – 160 54’ 00’’
Lonqituds: 530 47' 30 ‘’ -530 40' 30 ’’
1.3 GEOLOGICAL SETTING OF DHOFAR
Dhofar forms the southern province of the Sultanate of Qman and constitutes the southern and Of the broad monoclinal plateau, bordered to the South by the Arabian Sea .
To the West, the continuous belt of Dhofar's mountain region constitutes the Jabel Al Qamer (maximum altitude 1400 m) and to the north of Salalah by Jabel Qara (maximum altitude 1050 m) and further east by Jabel Samhan (altitude I800 m) which is bounded by a steep cliff.
The altitudes reached In the Jabels decreases greatly and regularly northwards. The Zalawt plain, extending from the foot of Jabel Samhan, is the largest one. The Salalah plain has a maximum width of 15 km and less than 60 Km in length, the port of Raysut at its western and. To the west Jabel Al Qamer constitutes a natural barrier by extending to the sea at Mughsayl.
In the Dhofar province of Oman adjacent to South
Yemen, the peneplained crystalline basement outcrops in the Murbat area along the coast east of Salalah are Overlain by a gently dipping clastic sequence of sandstone, siltstone and micaceous shales.
In Dhofar, no Jurassic is Known apart from a thin lens- shaped Outcrop of clastic, which include a thin limestone bed in the western coastal area.
Pre-Cambrian and overlain by wall-dated Lower Cretaceous (El Hota area near Cape Saiar) underlies it. No Jurassic Is recognized from boreholes in the Dhofar region, suggesting that either the area was emergent and no deposition Occurred, or more probably, that was mostly removed following the terminal Jurassic movements that affected the region, as Occurred in adjacent South Yemen.
Part of the southwest Of Oman, including much of southern Dhofar was probably emergent during Lower Cretaceous times, but the Middle Cretaceous, with the exception of the Murbat - most submerged Kuria Muria area. Elsewhere in Dhofar, however, carbonate deposition was going on in the early and middle Cretaceous, with clastic forming close to emerged areas. An example of this carbonate of the Qamer formation. (Hawkins 1981) Neritic-to-lagoonal clastic and carbonate deposition had covered the emerged parts by the Upper Cretaceous.
Differential Late Cretaceous movements led to uplift and erosion of parts of the earlier Cretaceous and older deposits in portions of the coastal area of Dhofar, so that progressively younger Cretaceous rock rest on pre-cretaceous from west to east in this southern coastal area.
The Paleocene of much of southern Arabia began with the pronouced transgression, as elsewhere in eastern Arabia. In place, there are demonstrable hiatuses with reworking of the underlying Maastrichtian deposits.
The transgression left behind a thick succession of fossiliferous, neritic carbonate of the Umm Er Radhuma formation, which extends Into the Ham of Africa region across the Gulf of Aden as the Auradhu carbonates.
The basal unit of the Umm Er Radhuma in Oman and In Dhofar province is frequently a well-developed fossiliferous marl-- shale sequence that underlies the maincliff-forming nodular--Weathering, limestone-dolomite sequence (Morton 1959.Beydoun 1964,l966). The age of the Umm Er Radhuma ranges up to the Lower Eocene. In the east, rifting in the southern Arabian margin gave rise to the progressive development of grabens along some of which the sea invaded. These were oriented WNW-ESE (and ENE-WSW in SE Dhofar) and deposits varied from either continental or shallow marine clastic and carbonates, and extended into the present plateau area. Thick turblditic Oligocene deposits accumulated in the coastal area at the foot of a submarine slop.
1.4 ROCKS EXPOSED IN THE AREA
There are seven formation exposed in the studied area, starting from the pre-Permian to the Tertiary sequence .
1- EL HOTA – AIN SARIT FOR MATION
Composed Of alternations of dark-green sandstone, greywacke and mudsatone, traversed by quartz Veins.
11- OISHN FORMATION
At the bottom is succeeded by alternations of marl And grayish, micritic, or dolomitic limestone, At the top is dolomitized limestone.
111- UMM ER RADHUMA FORMATION
* At the top, carbonate, essentially dolomitic.
IV- ASHAWO FORMATION
Green smactitic clay, locally gypsiferous or marl and ending with most commonly reefal calcarenitic limestone and sandy beds.
VI- MUGHSAYL FOMATION
Turbidite sequence comprised of rapid alteration of thin beds of fine chalky wackestone limestone, well-layered b1cmoicritic wackestone to packstons, locally well sorted, and bioclastic packstons to garniture limestone, well sorted-
V. –ADAWNIB FOMATION
Vary coarse conglomerate with calcarenitic interbeds, fine quartzes calcarenitic with conglomerate layers, pink biomicrosparitic wackestone to packestone limestone. The top Of the formation is composed Of layers of yellow to white gravel marly limestone .
Vii - NAR FORMATION (RED CONGLOMORITE VORMATION)
Brick-red conglomerate rests unconformable on karstified marine, calcarecits with nummulitids of the Mughsayl formation.
1. 5 METHODOLOGY
The B.Sc. project was done in the Raysut Area under the help of the Earth Sciences Staff. The work was divided into two, parts, and field work and laboratory work.
The fieldwork was carried out during January-1991. The purpose of the fieldwork was to produce a geological map of the Raysut area. The author and Ali khathiri produced this map.
The first three days were Spent in familiarization With the area After that, each pair of students mapped the area described rocks, logging, traverses collecting samples, And taking photos and slides.
From the collected samples, thin sections were made by departmental technician, and were studied under the microscope.
CHAPTER TWO
Pre-ermian Sequence
2.0 Introduction
Pre-Permian age, crystalline rocks And pre-Permian sedimentary, metasedimants and volcano-clastic constituting the basent, are extensively exposed In the Arabian shield which makes up the eastern half of the once-continuos Arab- Nubian shield now divided by the Red sea. Continuous exposures occur from the southern Part of Wadi Araba, at the head Of the Gulf of AQaba, in the north, to the highlands of Asir, to Yemen and Dhofar in the south (Z. R. Beydoun).
New groups and formations were created to define unit’s specific to Dhofar, the names of groups and formations defined elsewhere in the Arabian Peninsula by earlier Authors Are used. -The Pre-Permian formations are exposed throughout the Zalawt region, a broad foreland between Marbat and Hasik along the coast between Rakhiut and RAS Sajir, and in the Ayn Sarit inlier north of Mughsayl.
2.1 El Hota – Ain Sarit Formation
Dark-green sandstone, greywacke and mudsatone- Turbidite Deposits, quartz veins present along this formation .
2.1. Shalestone
Very fine grain size. The grains are fining upward, and these rocks are the basement rocks of Dhofar. Beydoun (1964) estimated that it could date to the pre-Cambrian to Cambrian.
2.1.1 Thickness
Very difficult to estimate, due to the underwent of the deposition which generated tight folds and overturned to the west, but it probably can exceed 15oo to 2,ooo m in thickness. It is only 480 a thick in the study area.
2.1.2 Lithology
It consists of alternating quartz-cemented mudstons and argillaceous siltstone and silty shales, which, include silty dolomite alternations slightly, thin bedded, cleavage become more intense upward, It Is more weathered.
2.1.3 T.ataeraI Variation
The contacts between the EI Hota-Ain Sarit formation and the Precambrian rocks are not exposed in all Places. The base of the Qishn formation overlies the El Hota-Ain Sarit.
2.1.4 FIELD OCCURRENCE
In, the studied area, this formation is Located along a big Wadi so the f0rmation was logged roughly.
At the basal part of this unit Is sandstone and shale great in color, shalestone very fine and loose, the Cleavage become More intense going upward, it is slightly weathered. Quartz veins present throughout the whole formation, Plumose structures are also found In this formation, see plate (2.3). It has undergone some deformation; it is slightly thin bedded, overlain this unit is alteration between siltstone and mudstone. This formation is Overlain by Qishn Formation and the logged part in about 480m. There are Many faults which shows that these rocks structure a lot during the shifting of Somalia from Arabia. These rocks are the basement rock of Dhofar, Yemen and Somalia. This formation overlaid by Qishn Formation which is Cretaceous, the Contact is an angular unconformity.
CHAPTER THREE
Cretaceous Sequence
3.0 Introduction
The elastic deposition that had characterized most of the Paleozoic Era up to the start of the Late Permian gave way to a predominance of Carbonate disposition in the Mesozoic. Triassic Jurassic and cretaceous carbonate build-ups and-stromatoporoid banks and Coral reefs would be expected to have developed all along be Continental Margin of the Arabian plate (Z.R.Bsydoun). The Precambrian-Paleozoic substratum was strongly deformed after the emergence. The Cretaceous deposits rest unconformable in the Ayn Sarit and AL hauta region in folded E1 Hota-Ain Sarit Formation beds, In the north of Marbat, on Permian-carboniferous detrital formations and in the east, on Precambrian Crystalline rocks. Due to the effects of subsidence, intra-cretaceous erosion and the Tertiary unconformity, the Cretaceous has a thickness ranging from about 1,500 m in the west, and 2 meters in Jabal Samhan.
3.1 Qishn Formation
The cretaceous Main transgression reached Dhofar later than in South Yemen where the Jurassic deposits occur. The formation Crops out also in the first Cliff between RAS Sajir and Al Hota, and around Ain Sarit.
3.1.1 Lithology
The Qishn Formation starts with detrital layers composed of thin beds of orange sandstone with local interbeds of small-pebble conglomerate and clay layers. There is alternations of marl and grayish, micritic or dolomitic limestone in which the fauna is not abundant. In the upper part of the formation does commonly dolomitized limestone comprise beds of cream-colored chert. Most of the beds covered with scree ruddiest are the best marker for the formation. The top of the upper part is commonly a ruddiest biostrome. Beydoun (1964).
Those grains composed of micrite and lacking any recognizable internal structure are called peloids. The thin section shows limestone in which the allochems are mainly peloids, circular to elliptical in cross section and averaging about 0.1 mm in diameter.
Such peloids are generally interpreted as faecal in origin. It is probable that Intense Micritization of bioclasts, thus accounting for their vague relict structures- formed the peloids. There are intraclasts sediments, Which was once incorporated on the sea floor of the basin deposition. The stylolites formed by the stress of the sediment weight above it contain quartz- chert fragments, and iron.
3.1.2 Thickness
The thickness is about 300 to 500 m.
3.1.3 Field Occurrence
This formation is located in the upper part of the map of the studied area just below the Umm Er Radhuma Formation.
Because of the steep cliff we found some problems in logging the formation, and also it is covered by scree.
From our observation in the field we found that this formation starts with marl of fine grain size, shale and dolomitic limestone. It is more or less horizontal unit; it is containing burrows and oysters. At the top it is yellow mudstone, dolomitized limestone and small beds of chert. The logged part is about 240 m. Ruddiest are the best marker for the formation.
3.1.4 Correlation
The Qishn formation unconformable Overlies Murbat crystalline rocks in the main part of Jabel Samhan where it in north of Murbat lies in angular unconformity On Murbat sandstone formation. The Qishn formation overlies the folded beds of EI Hota-Ain Sarit Formation in angular unconformity in the western areas. The upper part of the formation is unconformable Overlain by the Kharfot Formation.
3.1.5 Detailed Describtio
The formation is divided into three members in the unpublished Bureau de Recherché Geologiques ET Minieres (BRGM) reports, according to lithological variations:
*** Lower part (Sbabon Member)
Conglomerate at the base, followed by yellow-orange sandstone, sandy limestone and green clay.
It is about 30m thick. Well developed continental facies, near the astern limit of the Qishn formation transgression.
Clay and green course--grained sand deposition of about 15 m thick.
The member is 75 m thick at the base of the high cliff at Al Hauta. Microbreccia and dolomitized marl layers yellow to pink-gray to brown-red assemblage.
*** Middle Part (Hima Member)
Marl and grey-green biomicritic to dolomitic limestone. Bode With burrows are common in the marl. It is about 110 m thick.
The member is 35 m thick in Jabal Samhan, where it is 170m thick in the Al Hauta section.
**** Upper part (Hasher Member)
Grayish biomicritic limestone, with wackestone texture, fine grained packestone biocalcarenite, abundant bioturbations and stylolites.
In the Al Hauta section, the member is 100 m thick. The facies are beige-pink biodolomicrite with cream bedded and disrupted chert in the uppermost 30-m.
3.1.6 Palaeoenyironment
The Qishn formation was deposited in a restricted lagoon environment, supratidal to intertidal deposits indicated by ripple marks, laminites and moderate subsidence.
3.1.7 Paleontology
In this formation we found a lot of gastropods, reef, corals, crinoids and echinoids. There are a lot of microfossils observed in thin section, in this formation we found miliolids and ostracods.
CHAPTER FOUR
Tertiary Sequence
4.0 Introduction
The Tertiary period opened with a Paleocene transgression following from the Maaestrichtias open marine deposition. It covered almost the entire Arabian platform, except for the southwestern part of Arabia centered on Yemen and Dhofar, which was already emergent and undergoing a phase of extensive flood basalt outpouring.
The Paleocene deposits consist principally of neritic carbonates (Umm Er Radhuma Formation). Tertiary formations are widely exposed in the region and extensively blanket large areas of older units (Z.R.Beydoun).
The Umm Er Radhuma Formation belongs to Hadramaut Group, the local term for this formation is Jafnayan Formation, (Nolan ET al., 1990).
It Contains dominantly limestone with minor evaporates and the facies become more restricted towards the top. The Ashawq Formation is green smactitic clay, marl, calcarenitic limestone and sandy beds, The Mughsayl formation is chalky Turbidite limestone .
The Adawnib formation is very coarse conglomerate and marly limestone at the top, and the Nar Formation (Red conglomerate) is brick-red conglomerate.
4.1 Umm Er Radhuma Formation
The Umm Er Radhuma Formation constitutes the main part of the coastal range, and forms the top of Cliffs before dipping north towards the Rub' Al Khali.
4.1.1 Field occurrence
This formation is covered by scree and found in the studied area in the top cliff - It is highly pours limestone, rich in calcium Carbonate composed of carbonate, mainly limestone dolomitic at the top, alteration of marl shale and marine fauna present. Alveolina are the best indicator for this formation.
4.1.2 Petrography
Two samples were picked up from the formation during logging of thin section. F1 (9100251) and F3 (9100252) samples. Under the microscope, the descriptions of these two samples are as follows:
*** Fl (9100251)
Biomicrite limestone, fine grained calcite matrix. The thin section shows some veins filled with coarse calcite grains. There are a lot of forams, such as Alveolina, Miliolids and Textulariids. Shell Fragments also present
*** F3 (9100250)
Biomicrite limestone, fine grain, contains a lot of shale. The thin section shows many stylolites structures and calcite veins. Some of the stylolites formed after the calcite veins and visa versa. There are some vening along the stylolites and on other hand, there are some styloilites displacing the veins. In case of stylolites that indicate that the formation was deformed very soon after deposition.
In case of the formation of the calcite veins before the formation of stylolites that indicates that the formation was deformed very soon after deposition.
Tectostylolite growing through a calcite vein and cuts another stylolites, and two calcite veins cutting each other. A lot of foram are present such as Alveolina and Miliolids.
4.1.3 Correlation
Umm Er Radhuma deposits in unconformable contact with these of cretaceous. The major pre-Tertiary angular unconformity is particularly easy to see when the contact is followed from sarfait to the eastern end o f Jabal Samhan the contact with Qishn Formation is east of Al Hauta.
4.1.4 Lithology
The formation is mainly composed of a thick carbonate assemblage, and is well exposed In Jabal Qara, Jabal Al Qamer and in Jabal Samhan.
S.B. Henry and A.B. Brown (1935) unpublished report, Saudis Arabia they divide the formation into three members:
- Asyr member, composed of carbonate and marl, it is about 20-30 m in thickness.
- Hasik member, essentially carbonate assemblage, mainly limestone, it is dolomitic at the tap, very bioslastic, and alternation of marl-shale at the Up, It is about 300 to 550 m thick.
- The youngest unit, carbonate muddy member, essentially dolomite, marine funa present, maximum thickness 55 m.
4.1.5 palaeoenvironmet
The sedimentary depositional environment was marine, restricted supratidal to more open subtidal inner shelf. The little diversified fauna of small size indicates the restricted conditions.
4.1.6 Paleontology
Foraminifers are the most abundant and distributed in the marine waters the world, and live also in brackish waters. They are benthic organisms, sessile and a few are Plankton.
The Tertiary fossils in limestone which is exposed in the study area is dominated by foraminifers, In this formation we found a lot of gastropods which is common in the whole Tertiary sequence, they generally found in shallow water and little in deep water environments.
Nummulites are also common, corals, oysters, calcareous algae, and echinoids. The m1crofossils are alvaolinids, orbitolids, daviesina and some textularia.
4.2 Ashawq Formation
The Ashawq Formation constitutes the majority of terrain filling the graban that extends from east of the camp Aydim to Shahab Asaid road, to the right of Qardhait, northwest of Mughsayl. In the east, the formation crops out in the coastal plain around Taqah.
4.2.1 Thickness
About 20 m in the west of the graben, to probably more than 700 m in the east of the graben.
4.2.2 Field Occurrence
It is exposed near Mughsayl beach at the South limit of the studied area, exposed very little in our area surrounded by Mughsayl formation (fig. 4.1). It is limestone of fine grain, green marl with oysters, light green marl at the top and Some sandy to gravelly clay.
4.2.3 Petrography
The description of the picked Samples during the logs of the formation are as follows:
*** G-1 (9100253)
Micrite sppary, calcite and containing palliate of limestone, many peloids grains composed partly or entirely of micrite, extensively mictrized, and bioclasts.
Calcareous algae (coraline algae), large forms Such as Nummulitesand Textularia. Some burrows and holes filled with spary calcite.
Sponges with soft parts was preserved, and the Sponges filled with spary calcite. Angular intraclasts of low percentage.
*** G-2 (9100253)
Coarse grained calcite matrix, it is mostly biosparite and less micrite, with many peloids. There are some forms and broken shells. Calcite fibrous multi-layered chambers, sponges are less than I-cm a cross. Calcareous algae (coraline algae) that are skeletal remains of calcium carbonate depositing benthic red and green algae.
4.2.4 Lithology
The Ashawq Formation divided into two member: the Shizar Member and overlain by Nakhlit Member,
*** Shizar member crops out widely in the graben between Aydim camp and Shahab Ashaib. The collapse of Rus Formation causes bowl structure to the member. The Shizer is constituted of many sequences start with green marl with oyster lamechelle at the top, overlain by white Biomicrite limestone bad. The next sequence starts with yellow marl Changes to light green at the top. Chalky limestone layer overlies the marl then, is an intermediary thin continental sequence, which starts with a layer of sandy to gravelly clay.
The top Sequence is white marl of about 27 m thick. The Shizer member becomes thin towards the west.
*** Nakhlit Member forms rugged hills with slopes on the clay Shizer member, covered by talus commonly resulting from tectonic collapse of limestone beds.
It is lithologically thick beds of white, pale yellow to pink limestone varies from meter to several meters. It starts with biocalcarenite, bioclastic wackestone limestone ending with chalky, micritic limestone, There is discontinuities correspond to sedimentary Microbreccia, record abnormal radioactivity caused by carnoite, and are related to Continental facies. There are grayish dolomitic limestone associated with gypsiferous clay bed. Sevral layers have been fairly intensely sillcified and grey chert beds. Very similar member facies occur in the Raysut sheet area. to the west, the Lithology changes very quickly, and the member is very thin near the Aydim camp.
4.2.5 Paleoenvironment
Lagoonal marine basin created during the Oligocene transgression. Nummulitids indicate periods of clear marine openings.
4.2.6 Paleontology
The most abundant fossils and microfossils found in this formation are gastropods, corals, calcareous algae, sponges, miliolids, textularia, and nummulites.
4.3 Mughsayl Formation
Turbidite sequence comprised of rapid alteration of thin beds of fine chalky wackestone, limestone, well-layered biomicritic wackestone to packestone, fining upward with some gypsum and marl. Grading and internal structures of each bed can follow the classic sequence described by Bouma (1962). The Turbidite sediments consists largely of shallow water carbonate grains. Some finer turbidities show evidence of plucking up perennial Sediment with recognizable plankton and incorporating it as mud pellets in the final sediments.
4.3.1 Lithology
Mughsayl Formation started with accumulated megabreccia. This formation composed of different size clastic of all older formations. The braccia overlain by chalky limestone, locally wall Sorted.
The dip of Mughsayl beds is very steep, and flattens Out towards the center Of the basin,
Palaeoenvironmently the formation, was deposit on submarine slopes. The slope includes semi-pelagic deposits, Turbidite distorted slumped units, talus braccia, exotic blocks, It is 400 too 500 m thick.
The description of the Picked sample is as follows:
*** A (9100240)
Fine grained calcite matrix, with chalky limestone, micritic. A lot of forms present rounded Globigerina ooze (stacked together), shallow water and small brachiopods.
4.3.2 Corellation
The Mughsayl rests unconformable on the, Ashawq Formation west of Mughsayl. Reddish conglomerate, fine and loss mark the Contact between Mughsayl and Adawnib.
4.3.3 Field Occurrence
This formation is located at the southen Limit Of Our map in the studied area. It is Turbidite Sequence, white chalky limestone mostly fine grain fining upward, same gypsum and marl. We find different classics of many older formations. Locally, wall sorted grains of limestone. Many fossils are found in this unit, like gastropods, and bivalves.
Red conglomerate layer marks the contact between Mughsayl and Adawnib, this layer is the base of Adawnib formation
4.3.4 Palaeoenvironment
Deposited on submarine slopes and the slope sequences include hemi-palagic deposits, turbidities and distorted slumped units.
4.3.5 Paleontology
The fossils found in this formation are mostly corals and echinoids, and under the microscope, we found Globigerina.
4.4 Adawnib Formation
The formation comprises the first conglomerate intercalated in the last Tertiary marine sediment in Dhofar. It is exposed between Qardhait and Raysut.
4.4.1 Lithology
Argillaceous limestone of reddish, white and greenish color. There are conglomorate beds within the limestone layers. It is youngest marine sediment.
The Thickness of this formation varies from few meters to about 150 m in other places. There is very coarse conglomerate with caloaranitic interbeds followed by assemblage of fine quartz calcarecits.
The top of the formation is composed of layers of yellow to white gravelly marly limestone with oysters, fine conglomerate with limestone cement, and very fossiliferous limestone. The top is overlain by red silty clay of the youngest red formation (Nar.formation)
The descriptions of the picked samples during the logging of the unit are as follows:
*** C-5 (9100243)
Fine grained calcite matrix, with some Quartz and dolomite. Forms such as Nummulites, burrows filled with calcite grains. Calcareous algae (coraline algae) found and micritized shells.
*** C-6 (9100244)
Coarse grained calcite matrix with nice angular quartz. Calcareous algae (coraline algae) are very common. More quartz (more rounded) of 15%. Interclass limestone and micrite interclass, quartz rich intramicrite and a lot of dolomite.
4.4.2 Corllation
The Adawnib conglomerate rests unconformable on the underlying Tertiary or Cretaceous formations. The top of the formation is eroded, and the contact with the red conglomerate formation deposits is disconformable.
4.4.3 Field Occurrence
This formation is found along Wadi Adawnib. It is argillaceous limestone reddish to white in color. There are some intercalations of conglomeriteic beds with the formation. The thickness of the formation varies from a few meters to about 150m. The top of the formation is composed of layers of white gravelly marly limestone with oysters and geodes. It is bounded by red conglomerate formation.
4.4.4 Palaeoenvironment
The formation was deposited on subtidal, intertidal to inner shelf with a coarse detrital apron.
4.4.5 Paleontology
Corals, echinoids and gastropods are the most common fossils found in this formation. The microfossils, are miliolids, Globigerina, Nummulites and dicosyclina.
4.5 Nar Formation (red conglomerate )
Conglomerate detrital deposits, occurring in Salalah plain, and well exposed in the sides of Wadi Adawnib as seen in the studied area.
4.5.1 lithology
The red conglomerate formation made mostly of limestone clastic, the size of clastic ranging from pebbles to cobbles.
Continental sediments, the red color is due to the Oxidation by Water. Brick-red conglomerate rests unconformable on karstified marine calcarenite. The conglomerate units are more than 15m thick and occur in meter to several meters thick gradded bedded sequence, constituted of rounded limestone clastic .
The red conglomorate in Wadi Madam rests with angular unconformable contact on whitish calcareous-conglomorate.
Deposits of the Wadi Adawnib formation. The siltstone is sufficiently close to the Port of Raysut to be used as an additive in cement plant. Lateral equivalents occur in the Wadi Andorra area, red calcareous silt with conglomerate and sandstone intercalation. More description from the samples that were picked during mapping of the formation are as follows:
*** B-1 (9100241)
Rounded limestone conglomerate, matrix uprooted mainly Spary calcite. Angular quartz grains, some stylolites filled with ironstone, and some composite grains.
*** B-3 (9100242)
Coarse grain, biosparite, limestone, big clastic, composite grains all limestone with some quartz angular grains. Some clastic from Mughsayl Formation and a lot of form present such as Nummulites, Alveolina, and Miliolids. Calcareous algae (coraline algae) are also found in this thin section.
Stylolitization with some iron along the stylolites structures and calcite veins, with some quartz fillings.
4.5.2 Field Occurence
In the studied area it is exposed in the sides of Wadi Adawnib. It is mostly pebbles to cobbles limestone grains, the red color is due to oxidation. The conglomerate unit is more than 115 m thick.
4.5.3 Fossils
The formation has no macrofana. We found trace fossils and trails of small territorial gastropods.
4.5.4 Palaeoenvironment
The formation was continental alluvial deposits.
CHAPTER FIVE
Quaternary deposits
5.0 Introduction
In the Early Quaternary, pluvial phases created the present drainage system. Intense karstification of the limestone massifs, accompanied by travertine deposition, occurred during this epoch. These deposits occur throughout the coastal belt and on the desert plateau behind the escarpment, the deposits are widespread but discontinuous.
5.1 Alluvial Deposits
The drainage system in Dhofar is highly developed, and consist of a branched Wadi system .The Intense drainage system is essentially directed towards the Rub’ Al Khali desert which collects the transported alluvium.
Previous activity in the Wadi system, which is strongly modeled the relief, is indicated by deposition of a large volume of alluvium, which constitutes terrace gravel deposits and alluvial fans .
5.2 Terrace Gravel Deposits
These are slightly younger, the widespread deposits are only a few meters thick, and constituted of poorly sorted rounded essentially limestone coarse gravel. A sandy and clayey matrix weakly cements them.
5.3 Litroral Marine Deposits
These deposits are limited to a very narrow coastal strip. Occur mainly between Raysut and Murbat. The deposits correspond to the lower raised beaches of (Little, 1925; and Beydoun, 1968) and to the "Miliolitic coastal limestone" of Fox (1947). The most recent deposits occur on the present seaboard where they form narrow beaches, and barrier beaches at Wadi mouths .
5.4 Colluvial Deposits
Talus deposits have accumulated everywhere at the foot of the high scarps beside the coastal strip and along fault scaps. It is consists of angular limestone blocks, large volumea of talus braccia occur at the foot of the umm Er Radhuma Formation along the Jabal Samhan and Jabal Al Qamer escarpments. This talus has been forming since the Pleistocene.
5.5 Travertine
These are spring deposits formed by encrustation grey and buff porous occasionally carbonate, by emerge of solutions from permeable calcareous rocks containing solution channels in springs. The travertine deposited consists of light colored porous to cellular calcium carbonate (Caco3), commonly associated with accumulations of alluvial gravel. Accumulations of these travertine encrusted deposits most commonly form fan shaped flat topped bars, these bars form at the outlet of Wadi emerging from Jabal Qara. As these springs in Oman exit within the mountains, continentals flushing by frequent torrential
Runoff has precluded significant travertine development. Travertine that formed by uptake of atmospheric co2 from the hyperalkaline water is unlike other carbonates, which have been precipitated from bicarbonate groundwater. Calcite nodules sometimes found growing on the surface of travertine. Travertine can be correlated with karstification occurring everywhere in the mainly carbonate Dhofar plateau. The karstification is related to regresses at the foot of the plateau, which are responsible for the travertine deposits. The thickness of the travertine in the studied area is ranging from 3 to 5 meters.
Fox (1947) regarded the age of the travertine as Pliocene to Pleistocene and Beydoun (1968) considered the age as Recent.
5.6 Ancient beach deposits
They are a few meters fairly hard Calcarenite, very rich in marine fossils (miliolids, echinoids, gastropods ,oysters and other pelecypods) and commonly contain conglomeriteic intercalation.
5.7 Recent beach deposits
Recent beach sediments composed of mainly calcareous sand and rounded gravel build up by storms during the summer monsoon. The deposition of beach sediment is close to the Wadi mouths and small permanent brackish lagoons behind and associated fauna.
CHAPTER SIX
Structural Geology
6.0 Introduction
The Dhofar mountain’s are located in the southern province of the sultanate of Oman, and constitutes the constitutes the southern end of the broad monoclinal plateau, bordered to the south by the Arabian sea, which dip gently to the north under the sad of cretaceous and Tertiary terrain in Dhofar increases towards the coast. The axes of pre-Permian rocks in Oman are oriented approximately NE-SW, and a number of deformational phases seen to have taken place.
The opening of the Gulf of And and Red Sea has a number of deformational phases in the North Oman mountain’s and in the Dhofar Region. Rifting of the Gulf of Aden is responsible for Oligocene-Miocene deformation of the coastal border of Dhofar, which acts as a passive margin to thee volition of Indian Ocean and to spreading along the Carlsberg Ridge, which began some 35 ma. Ago. In the part of spreading activity the Sheba. Ridge was formed in the Gulf of Africa and opening up the Red sea (laghton et al., 1970)
6.1 Strucuters
Dhofar comprises two large structural domains, a broad monoclonal plateau and a coastal complex belt.
6.1.1. The monoclinal Plateau
Tilted to the north, which extends back from Jabals al Qamer, Qara and Samhan, and involves the large grabens to the south. Commonly subcircular very tight synclines in which the most recent Paleocene deposits are preserved.
Jabel Samhan escarpment is not aligned parallel with any one major fault, the direction of the escarpment indentations are related to fault distribution on the backslope.
6.1.1.1 The Ashawq Graben
The Ashawq Graben occurs in south of the plateau behind the coastal Jabals. It is about 40 km long and a maximum of 20-km Wide and extends over the Hawf and Raysut quadrangles. This broad west-east oriented structure is bounded by flexures and faults, and is occupied by mainly Oligocene deposits. The graben was initiated during the deposition of the Ashawq Formation, the variation in deposit thickness reflects differential subsidence of this basin. This graben extends into the Raysut.
6.1.2 The coastal complex belt
The Coastal Complex belt is only 20 km wide, and traversed by normal faults related to the episodes of extension which occurred during rifting of the Gulf of Aden. Generally separated from the monoclinal plateau by the high escarpment line of Umm Er Radhuma limestone.
6.1.2.1 Major South -Facing namal Spoon- faults
Inclined curved fault Plane- This passive-margin tectonic style is particularly Well expressed in the area between Al Hauta and tile Ashawq formation into contact with the Qishn Formation, which represents a throw of almost 2,000 m .
6.2 Joints
Joints have undergone no displacement in any direction Arielle to the plane of fissuring. Joints may also be considered to be products of folding or displacements by intrusions. Some joints are found only near the surface and may be attributable to freezing or water erosion.
Joints may conform to the same pattern over a wide area The large Pavements of limestone exposures usually have there blocks algained in a fixed grid system, with their water- widened joints forming a distinctive mesh of open channels.
In analyzing the joint structure of an area it is important to find the Joints which penetrate deepest, often passing through several 8trata, rather than shallow and random surface Joints, when the direction of these Joints have been plotted It is often possible to relate their formation to other tectonic phenomena by studying geometrical relationships.
Equal area analysis, preserves dip and strike by plotting the po1es to the fractures on an equal area net, This treatment properly defies the existence of sets and systems and forms the essential basis for analysis of the past and future movements of the rock.
The maximum principal stress(1) bisects the acute angle between the fractures.(3), the minimum stress is at right angles to that in the same plane (2), the intermediate principal stress , is at right angles to that plane .
Measuring joints in E Hota- Ain Sarit Formation , and also there are some measurements taken from the Mughsayl Formation in near the con tact of the Formation to the Adawnib Formation , The main stress in El-Hota Formation is nearly SE direction and it is nearly NW in the Mughsayl Formation.
Joint faces often show plumose markings, which have an axis, parallel to the bedding planes. The pigmies structure ends against a series Of small Joints arranged en echelon in the fringe, showing a SW stress direction.
6.3 Folding
Few sedimentary rocks remain for very long in their horizontally bedded position. Many of the earth’s older rocks have been subjected to deformation by forces of four main types.
Firstly, much folding results from deep-seated earth movements in approximately horizontal plane. Secondly, as a consequence of the major uplift of some landmasses into mountain ranges. A third type, by the intrusion material such as salt. Finally the slumping and compaction of partially unconsolidated, newly deposited sediments produce the fourth type, of a minor cause.
In the north limit of the study area, there are three synforms within the Adawnib Formation caused by nontectonic processes operating at or near the surface of the earth, especially in relation to erosion, may cause deformation.
Theses three folds found in Adawnib Formation exposure of about 13 m thick, Overlain by 5 meters of Nar formation .
Contemporaneous deformation takes Place as sediments are being deposited, and small folds occur in soft sediments due to sliding down gentle slopes. The hinge of the folds at right angles to the direction in which sediments glide, the axial planes of the folds dip in the direction from Which the slide comes.
*** Large Scale Folds
The studied area is represented in a large synforms fold locally it extends for around 13 kms long from north to south.
6.4 Faults
Some of the faults were clearly seen and mapped in the field while the others are not exposed but some data was provided by indications from structural thinning and changes in dips in the units.
In area (3) "Hareb & Ahmed" near the beach of Mughsayl in the Mughsayl formation there is a relatively downfaulted trough between high angle faults fomina graben shape.
6.5 Cross – Section
One cross section have been done in the mapped area N-S shows almost all the rocks that are exposed in the area, 13km long. The cross section shows also a fault indicates the uplift of the area .
6.6 Contacts
Most of the contacts between the Nar formation and were clearly seen and mapped in the field and the others are suggested according to the data provided from thinning of rock units and change in dip of the units.
The contact between Nar formation and Adawnib is disconformable. Mughsayl formation is an angular contact with Ashawq formation, the contact is more clearly seen west of our studied area. The Mughsayl formation is also overlain by Adawnib formation unconformable. The contact between El Hota Ain Sarit formation and Qishn formation is angular unconformity, also the Qishn formation is unconformable under the Umm Er Radhuma formation .
6.7 Map Describtion
The study area is dominated generally by Tertiary rocks and theses are from the bottom to top of the map, Mughsayl, Ashawq, Adawnib ,Nar, Qishn and Umm Er Radhuma formation at the very top.
Mughsayl formations strike almost N-S and gently dip towards East, the average dip of the formation is about 15o to the NE. Generally, the Ashawq formation is found in the southern part of the map as isolated hills surrounded by the Mughsayl formation.
The Adawnib formation is structurally very thinned towards East direction, strikes E-W and the average dip is about 12o to the SW. Nar formation occupies about 40% of the area in the middle part of the map. The Qishn formation is represented as a steep layer, it is overlain by the Umm Er Radhuma Formation which is forming the top cliffs of Dhofar region.
On the other hand the metasediment, El Hota Ain Sarit outcrops were mapped in the northern part of the study area. Metasediment sandstone rocks were found along Wadi Eshat, dips almost NE (35o)
CHAPTER SEVEN
ECONOMIC GEOLOGY OF DHOFAR
7.0 Introduction
The mineral exploration of Southern Dhofar, was carried out in 1985 and 1986, by the Bureau de Recheches Geologiques et Minieres (BRGM). Particular areas were considered to have special interest for some metals .
(l)- The Qitqawt area in the Marbat quadrangle was explored for bauxite clays in the upper Cretaceous sequence.
(2)- The gypsiferous basin about 40 km SW of the Muddy quadrangle.
(3)- Copper, lead, zinc, barite and fluorite in the South of the Hawf quadrangle.
(4)- phosphoric facies outcrops of lower Dammam and basal Ashawq formations.
Industrial rocks and minerals constitutes a variety of substances which can be developed various clays, bauxite clay, gypsum, building stone, phosphate, quartz sand principally known in the Tertiary terrain, which is the best exposed. The existence of numerous clay occurrences found throughout Dhofar in both cretaceous and Tertiary deposits has been established.
Attapulgite deposits in the Umm Er Radhuma formation and at the base of the Dammam, offer potential interest for production of absorbent granulates.
Bauxite-clay deposits with kaolinite predominant, constitute raw material suitable for the manufacture of ceramics or refractory material, or as additive for special aluminum cement .
7.1 Evaporite and associated deposits-
The Rus formation deposits are mainly carbonate and gypsum deposits. Mineralogical and chemical analysis of these material-s of these materials have shown the gypsum is of a qood quality > 90%gypsum this gypsum is satisfactory for the manufacture of plaster or as a setting-regulating additive for cement.
7.2 Geological_and Chemical Investigations
These data were provided for the new cement plant project, which is located in the south of the sultanate of Oman within the market area of the town of Salalah.
The aim of these investigations was to find sufficiently large reserves of calcareous and argillaceous raw material for a cement plant with an initial clinker capacity of 250,000 tons per year .
7.3 Raw Material
Calcareous component, argillaceous component, iron rich and silica rich correctives and gypsum.
7.3.1 Calcareous Comonent
The calcareous components in the study area are represented by the Adawnib formation.
Location:
Approximately 15 Km W of Salalah and 6 Km N of Raysut port, near to the aggregate and road stone dressing plant of Tarmac.
Topography:
Flat area, to the s 10 m, to the N 20-m above sea level.
Geology, Tectonics and Lithology :
Horizontally and very weakly bedded limestone rock formation, to the E eroded and covered by young beach deposits and by the sea, to the N, w and S conformably covered by a horizontally layered interbedded rocks series at limestone young lime ratio in places, raft partly very rilicenvis and gravel.
The limestone is soft to moderately hard, white and flesh to pink colored in the upper 20 to 40 m) of stratigraphicail thickness, grading into cress colored limestone-containing Mgo. Partly very fossiliferous and very porous in those parts.
Siliceous material Occurring as quartz crystal grains of up to 0.5 mm size and as quartzite pebbles. Feldspar crystals of up to 1.5-mm size do also occur.
Chemical Characteristics
The top layer consisting of suitable calcareous raw material towards the depth is followed by dolomitic Mgo rich material. The carbonate content of the calcareous material lies generally between 85 and 95% thus indicating good limestone. Whereas the amounts of the deleterious elements such as K2o, Na2o, So3 and p2o5 are negligibly small, the chloride content is rather high 0.04 to 0.10%, raw material basis. The lower the carbonate content becomes, the higher are the chloride values.
Mineralogical Characteristice
Carbonate minerals are present in the form of calcite and some dolomite (3 to 8%). Quartz is always present in notable quantities (3 to 8%) , feldspar only in traces .
Plastic clay minerals (montmorillonite and palygorskite) make up the rest.
7.3.2 Argillaceous Component
The argillaceous Components in the study area are represented by the El Hota Formation.
Location
21 Km WNW of Raysut port, from the paved road entering Wadi Adawnib and following Macadam road 12 to 13 Km westward.
Geology, Tectonics an4 Lithology
A fly chalk formation of Pre-Permian age, showing several 100 m of thickness. Striking approx. N/S and dipping at 20 to 40o to the W. lnterbedding of sandstone (arkose) and shale.
The shale has macroscopically massive aspect, but microscopically is highly foliated and disintegrating into thin platy fragments when disturbed. Very fine-grained, consisting of quartz, sericite/muscovite and chlorite mineral content of quartz, potash feldspar, plagioclase, muscovite and chlorite.
Both rock component shale and sandstone show the impact of a certain degree of metamorphism.
Chemical Characteristics
The shaley layers normally have slightly higher alumna and iron contents than the sandstone zones. The alkali contents are generally high .
Minarological Characteristics
The contents of clally minerals are remarkably high,, up to 60% in shale and 30 to 35% in sandstone, only chlorite and iIlite / rnuscovite occur, both of them practically non-plastic. The feldspar contents are comparatively high, thus leading to high alkali values within these materials.
CHAPTER EIGHT
DISCUSSION
Dhofar forms the southern province of the Sultanate of Oman, and constitutes the southern end of the broad monoclinal plateau, bordered to the South by the Arabian Sea.
To the West the continuous belt of Dhofar’s mountain region is constitutes the Jabel Al Qamer (maximum altitude 1400 m) and to the north of Salalah by Jabel Qara (maximum altitude 1050 m) and further east by Jabel Samhan (altitude 1800 m) which is bounded by a steep cliff.
During the Pre-Permian, the El Hota-Ain Sarit Formation Underwent an intense Phase of east-southeast to west-northwest compression which resulted in tight folds locally overturned to the West. Quartz veins, probably of Devonian age, traverse the formation.
There are many faults which shows that this rocks structure a lot during the shifting of Somalia from Arabia.
These rocks are the basement rock of Dhofar, Yemen and Somalia. This formation overlain unconformable by the Qishn Formation which is cretaceous. This formation is Pre- Permian.
The contact shows a missing of an interval of time between 440 and 200m.y. This formation was exposed to a lot of deformation and compression, there are the same type of rocks found in Somalia. During the cretaceous this part of Oman belonged to the Tethyan domain characterized by extensive carbonate deposition.
The Aden proto – Rift from the Middle Jurassic onwards, generated a subsidence by the extensional tectonics, and separated the Arabian from the African lithosphere plate. After the uplift of Dhofar it is followed by emergence that gave rise to weathering and erosion of all exposed rocks, during the Latest Turonian, and there are three successive phases of uplift lead to a non deposition period, during the Middle Crete Celind, during the Late Cretaceous and at the Maastrichtian boundary.
The Late cretaceous phase was the more important, probably the whole of the pre-Permian basement was emerged at this period.
In the Paleocene a major uplift associated probably with a compressive tectonic phase, counted during the latest Maastrichtian- early Paleocene.
The Hawf and Raysut quadrangles show beat the results of Paleocene tectonics, which strongly deformed Cretaceous tretaceous terrain in Dhofar into a dryad arch between Al Here and Ain Sarit. The Umm Er Radhuma rests unconformable on much different formation. The top of the arch is situated west of Ain Sarit where more than 1,000 m of Cretaceous terrain have been eroded and the Tertiary Umm Er Radhuma limestone rests uncomfortably on the Qishn formation.
In Dhofar, this tectonic phase is particularly important at the cretaceous – Tertiary boundary, however no tectonic phase was distinguished in Eocene in Dhofar. At the end of the Tertiary, rifting of the Gulf of Aden is responsible for Oligocene- Miocene deformation of the coastal border of Dhofar, which acts as a passive margin to the rift . The important phase expressed by the major uplift
Of the Arabian Peninsula followed by the end Eocene regression.
From the early Oligocene a phase of the extension progressively deformed southern Dhofar. Detrital deposits accumulations at the base of the Ashawq formation, derived from erosion of an emerged hinterland of crystalline terrain situated west of Dhofar, indicate the formation of the structural depositions.
At the end of the early Oligocene, acceleration of pre-rifting led to the formation of large faults bordering grabens. Subsequent submarine foundering of the SaIalah plain from Taqah to Mughsayl. During the Middle Oligocene a fall of sea level of 250 m affect the deposition of later formations.
Thick turbidities with megabreccia and slump-structure accumulated at the foot of the submarine slope, which extend down to a depth of more than 300m, up to the early Miocene during which ocean floor appeared in the Aden rift. The Mughsayl formation turbidities must occur at some distance from the coast. After deposition of Mughsayl formation, the last phases of the final uplift of Dhofar caused a steep drop in sea level, and strong continental erosion followed by conglomerate deposition.
Mughsayl formation is overlain by a reddish conglomerate layer of Adawnib formation, the contact between Mughsayl formation and Adawnib is marked by loss reddish conglomerate layer.
Adawnib formation is the last Tertiary marine sediments in Dhofar, this formation was overlain by Nar formation which is the continental alluvial deposits.
The contact between Nar and Adawnib is disconformable but it is can be angular conformable in some places like in east Wadi Adawnib.
Later, a major phase of uplift caused emergence of the Jabel Al Qamer, Qara, and Samhan, and tilted the whole of Dhofar to the north. More moderate uplift continued during the whole Pliocene-early Quaternary, as indicated by sheets of red conglomerates and deep arterenchment which separated layers of alluvium in Wadi gorges , behind the escarpment, and further to the north .
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