Geology topics

N.C. Aspinall

Publications and source records attributed to N.C. Aspinall.

3 recordsLinked to original sources

USGS1990

Preliminary geologic map of the Wadi As Sirhan Quadrangle, sheet 30C, Kingdom of Saudi Arabia

The Wadi as Sirhan quadrangle lies in the northwestern pan of Saudi Arabia on the border with Jordan. It is located in the west-central part of the Sirhan-Turayf basin and is underlain by Silurian to Miocene-Pliocene sedimentary rocks that are partly covered by volcanic flows. The map area also contains large areas of surficial sand and gravel. The study area is mainly a structural depression formed by the Wadi as Sirhan graben complex, and it is flanked by highlands of moderate altitude. The Wadi as Sirhan graben is believed to have been formed by tensional forces associated with rifting in the Red Sea. The map area contains the Thaniyat, Ghinah, and Arqah phosphorite members, and the phosphate-bearing Sib member. Hypothetical estimates of mineral resource potential of the phosphate rock in the quadrangle are high, but most prospects are either covered with too much overburden or are too thin and of too low a grade to be considered for economic exploitation at this time. Several deep drill holes in the Wadi as Sirhan depression have penetrated thick sequences of marine rocks that are potential sources of oil and gas. Geological and geophysical conditions are favorable for the accumulation of hydrocarbons, and additional exploration is recommended.

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USGS1989

Preliminary geologic map of the Turayf Quadrangle, sheet 31C, and part of the An Nabk quadrangle, sheet 31B, Kingdom of Saudi Arabia

The An Nabk and Turayf quadrangles lie at the northern border of the Kingdom of Saudi Arabia. Middle and upper Cenozoic sedimentary and volcanic rocks form the surface of the quadrangles, and sedimentary rocks of the Paleozoic, Mesozoic, and lower Cenozoic are found in the subsurface. The Paleozoic and Mesozoic rocks, described from drill hole records, include the Tabuk, Upper Sudair, Lower Jilh and Aruma formations which are mostly of marine origin. The map area is part of the Sirhan-Turayf Basin and contains the Thaniyat, China, and Arqah Phosphorite members of the Upper Cretaceous-Tertiary Turayf group. Only the Arqah Phosphorite, the uppermost of the three members, crops out at the surface. From its outcrop along the east border of the area, the Arqah dips westward into the subsurface and passes into an argillaceous deeper water fades. The Thaniyat and China also dip westward in the subsurface and pinch out into a deeper water fades. Upper Eocene calcareous claystone and chalk mapped in the Wadi As Sirhan depression on the west side of the map area are named the Rashrashiyah formation, and may be partly equivalent to Eocene bioclastic, chert-bearing carbonate rocks of the Turayf group mapped to the east. The Sirhan formation is a new name for rocks of Miocene(?) age occurring in the Wadi As Sirhan area. These rocks are mostly sandstone of probable continental origin, and contain thin beds of fresh water limestone. However, marine limestone beds also occur, indicating periodic incursions by the sea. Al Harrah, a large Quaternary-Tertiary basalt field in the Sirhan-Turayf Basin, occupies the central part of the map area. The flows consist of silicic alkali olivine basalt, typical of the Cenozoic lava flows of Saudi Arabia. Volcanism appears to be of the continental rift-type and is related to Red Sea rifting. Quaternary calcareous and gypsiferous duricrust is found discontinuously throughout the western part of the map area. At one time it apparently formed a carapace-like cover over all surface rocks, and indicates a much wetter in northern Saudi Arabia than the present climate. The Arqah Phosphorite member is exposed in the northeast corner of the map area and contains thin beds of phosphorite grading from 18 to 30 percent P 2 O 5 - Oil shows have been reported in Cretaceous rocks of the Wadi As Sirhan depression, and oil has been discovered recently nearby in Jordan. Geologic and geophysical conditions are favorable for the entrapment of oil in the Wadi As Sirhan area and additional exploration is recommended.

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USGS1989

Preliminary geologic map of the Al Jawf Quadrangle, sheet 29D, Kingdom of Saudi Arabia

The Al Jawf quadrangle (Sheet 29 D) lies in the northwestern part of the Kingdom of Saudi Arabia about 900 km north of Jeddah. The quadrangle is located between lat 29°00'-30°00' N. and long 39°00'-40°30' E. It includes the southeastern rim of the Sirhan-Turayf basin, and is underlain by sedimentary rocks of Paleozoic to Cenozoic age. More than half of the quadrangle is covered by surficial deposits. The Phanerozoic sedimentary rocks of the map area were deposited under both marine and continental conditions. Marine deposits, produced by transgressions and regressions of the sea, are of outershelf to near-shore and coastal-lagoon origin, and the continental deposits are largely of fluvial and deltaic origin. Part of the Miocene-Pliocene rocks are believed to have been deposited in a lacustrine environment. Tensional structures, such as linear macro joints, grabens, block-faulting, and some folding are characteristic of the geology of the map area, and reflect a combination of Red Sea rifting and movement of the Hail Arch. This report introduces a new structural concept that extends the Wadi as Sirhan graben complex southeastward in the Al Jawf quadrangle into the An Nafud (Great Desert). This concept greatly increases the area of interest in the potentially oil-and-gas-bearing rocks of the Wadi as Sirhan region to include those of the An Nafud basin. Discovery of the largest specimen of Prototaxites sp. in the world, in the Al Jubah area of the northeastern part of the quadrangle, has helped solve a long-standing stratigraphic problem involving Devonian and Cretaceous rocks of the southeastern part of the Sirhan-Turayf basin. Phosphorite, a commodity of major economic interest in the Sirhan-Turayf basin, is exposed in the map area along escarpments that form the southeastern rim of the basin. The grade of the phosphorite is as much as 21 percent P 2 O 5 , but the beds are thin and lenticular.

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