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A Geological Study of Saudi Arabia—Particularly the Red Sea Margin

The rocks found in Saudi Arabia vary significantly in their age of formation starting from the Precambrian to the modern day. Such diverse varieties of rocks are an integral part of a greater landscape that comprises of the Arabian Peninsula, better known as the Arabian Plate. Some of Saudi Arabia’s Precambrian rocks in the peninsular area originated approximately 3 million years ago during the Archean era. However, most of the rocks found here date back to the Neoproterozoic age.

The rocks originated in the form of volcanic islands or as volcanic chains in a Neoproterozoic ocean stacked against continental edges to be finally folded and lifted up during the later part of the Precambrian to form large mountain belts. These massive mountains got eroded towards the end of the Precambrian leaving behind only the roots. In Saudi Arabia, the comparatively younger rocks belong to the Phanerozoic cover. The Phanerozoic cover comprises of Paleozoic, Mesozoic and Cenozoic ages. These types of rocks generally consist of flat beds of sedimentary rocks including volcanic rocks, evaporates, lime stones, siltstone and sandstone.

Such rocks originated as deposits in river beds, shallow seas and glacial valleys or erupted from volcanoes that were sub-aerial in nature. The rocks which are found on the eastern and the northern parts of the Arabian shield are commonly known as the Arabian Platform. The rocks found on the shield comprise mostly of harrat, which are fields of flood basalt from the Cenozoic age, while rocks located towards the west of the Arabian shield comprise of rocks from the Cenozoic age mostly lying in the basin of Red Sea. The youngest deposits of rocks include unconsolidated gravel, silt, sand and coral limestone.

The Precambrian rocks constitute of a majority of known deposits of metals including magnesium, iron, zinc, copper, silver and gold in Saudi Arabia. The Phanerozoic cover accounts for the oil reserves and bauxite deposits in addition to large quantities of silica sand, limestone and clay. Tectonically speaking, Saudi Arabia is located towards the south of the Arabian Plate, which is amongst the youngest plates on the earth’s surface. This plate consists of a crystalline base of Precambrian crust approximately 40-45 km in thickness and between 870-550 million years old.

The Arabian Plate also comprises of sedimentary rocks that originated in the periods ranging from Cambrian to the Pleistocene ages having thickness between 0-10 km. Such rocks are found as Paleocene-Holocene intra-continental and Cenozoic flood basalt located in the ocean basins of Gulf of Aden and Red Sea. The division of Saudi Arabia and Africa started approximately 25 million years ago, which was caused due to a rift created on the sea floor that spread axially along the Gulf of Aden and the Red Sea.

The rift drifted towards the northern part of the Arabian Plate which resulted in a collision with the Eurasian land mass. At the time of such tectonic developments new oceanic crusts were formed along with sedimentation in the basins of Red Sea and Gulf of Aden. The southern and the western fringes of the Arabian Plate had been lifted up and were partially covered by sub-aerial flood basalt, thereby creating the Red Sea Escarpment and lava fields (harrat).

The northern and north eastern parts were subjected to shortening of crust and the formation of the Zagros fold-and-thrust belt. The Red Sea Margin The coastal fringes of the Red Sea has a diverse history in terms of geomorphology– that brings to the fore the combination of structure formation, volcanism, erosion and uplifting of the rocks. The noteworthy features of the landscape comprises of: 1) A 0-50km wide coastal plain. 2) An escarpment borne out of erosion. 3) A hilly and mountainous region between the escarpment and the coastal plain.

4) Surfaces borne out of erosion and located towards the eastern part of the escarpment, more commonly known as the Najd Pedi plain. The structural constitution of the Red Sea margin comprises of: 1) Cenozoic Red Sea basin. 2) Continental crust made up of the Arabian shield Precambrian rocks. 3) Tiny inland basins from the Red Sea made up of Cenozoic sedimentary rocks. 4) Fractured inland originating from and running sub-parallel to the coastal margin, punctuated by intrusions due to Cenozoic dikes.

5) Vast fields ranging from the Cenozoic to Recent basalt or harrats extruded on the Arabian shield and on the Red Sea basin sedimentary rocks. The common contact areas between the Arabian shield and the Read Sea basin comprises of faults and deposits, coinciding with a crustal modification and attenuation zone where the Arabian Plate continental crust becomes progressively thinner—Beginning at 40-45 km and tapering down to 15-5 km originating from the inland and ending in the coastal regions respectively. The Structural and Topographic Characteristics

The structure and topography of the coastal margin of the Red Sea adjoining Saudi Arabia gives rise to the hypothetical school of thought that the margin has been segmented tectonically and has been subjected to various kinds of upliftments over the years. The Escarpment Located South of 21° N The escarpment located approximately 21° N ranges between 2000-3000 m above sea level in height extending to Aden, the southernmost end of Yemen and runs along Gulf of Aden’s western coast, thereby creating a continuous face of an erosional cliff 700 m in height. The lip of the cliff is the watershed region between Arabian Gulf and Red Sea.

The Escarpment Situated North of At Ta’if The escarpment situated north of At Ta’if is not continuous, is less in height and is disrupted by paleovalleys that come down from heights of 1000-1500 m above the sea level on to the coastal plain. Basalts extruded from the regions stretching from the Harrat Rahat up to the modern day Red Sea coast characterize the paleovalleys by their plentiful presence. The Erosional Surfaces Located North of At Ta’if Exactly opposite in characteristics when compared to the southern parts of the Red Sea margin, the region located towards north of At Ta’if consists of many erosional surfaces.

Harrat Rahat is situated on the northward extension of the Najd Pedi plain. The Cenozoic Sedimentary Basins The Azlam basin is an 80 km long stretch of trough, having a width of 8-15 km and extending towards the southeast from the coastal plains of Red Sea into the Arabian shield. It finally tapers away in the southeastern direction. The Hamd basin is an inland stretching 130 km and is located in a topographical and structural depression which is 20 km in width and 200 km in length, tending towards the south eastern direction.

Conclusion Saudi Arabia is geologically a hugely diverse country and fascinating in its characteristics. The physical features and geological evolution of the country is extremely complicated and varying in nature. Though a lot has been found out about the structural, topographical and the tectonic evolution of Saudi Arabia, there is a lot of work yet to be done. References: Saudi Geological Survey. Geology. Overview. Retrieved on July 6, 2009 http://www. sgs. org. sa/index. cfm? sec=16&page

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