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Research about Red Sea

Source-linked reports with geographic coverage including Red Sea.

At least 19 recordsLinked to original sources
USGS1992

A-type granite and the Red Sea opening

Miocene-Oligocene A-type granite intrudes the eastern side of the Red Sea margin within the zone of extension from Jiddah, Saudi Arabia south to Yemen. The intrusions developed in the early stages of continental extension as Arabia began to move slowly away from Africa (around 30–20 Ma). Within the narrow zone of extension silicic magmas formed dikes, sills, small plutons and extrusive equivalents. In the Jabal Tirf area of Saudi Arabia these rocks occur in an elongate zone consisting of late Precambrian basement to the east, which is gradually invaded by mafic dikes. The number of dikes increases westward until an igneous complex is produced parallel to the present Red Sea axis. The Jabal Tirf igneous complex consists of diabase and rhyolite-granophyre sills (20–24 Ma). Although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion (< 1 km). To the south, in the Yemen, contemporaneous with alkali basaltic eruptions (26–30 Ma) and later silicic eruptions, small plutons, dikes, and stocks of alkali granite invaded thick (1500 m) volcanic series, at various levels and times. Erosion within the uplifted margin of Yemen suggests that the maximum depth of intrusion was less than 1–2 km. Granophyric intrusions (20–30 Ma) within mafic dike swarms similar to the Jabal Tirf complex are present along the western edge of the Yemen volcanic plateau, marking a north-south zone of continental extension. The alkali granites of Yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite. These granites represent water-poor, hypersolvus magmas generated from parent alkali basalt magmas. The granophyric, two-feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension. Initial 87 Sr/ 86 Sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and metaluminous granitic magmas involved both fractiónation and partial melting as they ascended through the late Precambrian crust of the Arabian plate.

Red Sea↗
USGS1985

Reconnaissance geologic map of the Muwassam Quadrangle, sheet 16/42 D, Kingdom of Saudi Arabia

The Muwassam quadrangle, bounded by lat 16&deg;00&rsquo; and 16&deg;00&rsquo; N. and long 42&deg;30&rsquo; and 43&deg;00&rsquo; E., includes the very southernmost territory of the Kingdom of Saudi Arabia. The quadrangle is named after Muwassam, a small town and minor border-crossing point for traffic into the Yemen Arab Republic. An asphalted road from the Jizan quadrangle to the north terminates at Muwassam town. Much of the quadrangle includes part of the Yemen Arab Republic and a portion of the Red Sea. All of the mapped area is occupied by coastal plain bordering the Red Sea. The flat coastal plain is covered by Quaternary surficial deposits overlying a sequence of Tertiary rocks as much as 5 km thick. The coastal plain is separated from the Red Sea by zone of supratidal sabkha deposits, offshore bars, islands, tidal md flats, and shallow lagoons. The sea is shallow, less than 200 m deep, and forms part of the shelf marginal to the main axial trough of the Red Sea.

Red Sea↗
USGS1974

Porosity, density, grain density, and related physical properties of sediments from the Red Sea drill cores

Representative sediments from each site were chosen for examination of their dry specific gravity and grain density. The determinations were made by micropycnometer; water was used as the displacing medium, and salt corrections were based on the refractive index measurements on interstitial water. For saltier brines the "salinities" derived from index of refraction are somewhat too low but, for the most part, are adequate for these corrections. Water contents are those determined on the archived samples selected for these studies. They had been kept in cold storage (4°C) in screw-capped glass bottles with poly seal lids or in heat-sealed polyethylene bags for a period of about three months. The purpose of the measurements was to gain sufficient information on grain density to permit application of the general information or pattern to the bulk water content determinations on the small syringe samples. Bulk density, porosity, and other properties could then be calculated without using volume measurements from the syringes. Whereas the data from weight loss on drying (bulk water content) at 110-120° were considered good, the volume measurements are subject to considerable error, especially in more consolidated sediments, and are not usable at all for shales, more consolidated or cemented rocks, and anhydrite. Detailed comparisons with the GRAPE determinations were also an objective. The Red Sea cores offer a particularly good opportunity to test the validity of these measurements, which have been increasingly questioned.

Initial reports of the Deep Sea Drilling Project↗
USGS1974

Chemical analyses of Red Sea sediments

One of the prime motives for exploring the deeper subsurface sediments of the Red Sea floor was to gain information on the geochemical systems controlling the hot brine-metalliferous deposits. Accordingly, a strong effort was made to provide both shipboard and laboratory means of analysis of the recovered phases. Shipboard spectrographic analyses (semiquantitative) provided both detailed surveys of chemical properties of the cores and the ability to analyze small subsamples and separated particles such as pyrite, sphalerite, organisms, and similar minute objects. Over 5000 such analyses are provided in Tables 1 to 5. Some supplementary data provided by subsequent analyses for K, Zn, and Ag in the Denver field laboratories of the U. S. Geological Survey have been added to the tables. A second body of data is provided in Table 6, which gives quantitative data on major and minor constituents, performed by the Washington analytical laboratories of the U. S. Geological Survey. A third group of analyses are partial analyses on evaporitic rocks (anhydrite and rock salt) (Table 18, in Manheim Chapter 38, this volume). In addition to the above, a number of the collaborating laboratories are providing more specific chemical data on special phases and constituents of the Red Sea materials. Most of these data are included in chapters in the Geochemical section of this volume. The significance of the data is discussed in Manheim (Chapter 38, this volume) and in the respective reports of shipboard workers and cooperating share laboratories.

Initial reports of the Deep Sea Drilling Project↗
USGS1974

Red Sea geochemistry

The Red Sea drillings reveal a number of new facets of the hot-brine-metalliferous system and other geochemical aspects of the sea, its sediments, and its past history as follows: 1) Dark shales rich in organic material, and containing enhanced Mo and V concentrations, are characteristic of Plio-Pleistocene strata in the Red Sea. Values as high as 1500 ppm V and 500 ppm Mo were obtained in sediments containing up to 8 percent organic carbon. 2) Metalliferous sediments in the hot brine deep (Site 226) are similar in composition in both solids and interstitial water to previously analyzed sediments. However, one site (228) well south of the known hot-brine deeps shows zinc mineralization reaching 5 percent Zn in late Miocene shale-anhydrite breccias. 3) Pore fluid studies show that near-saturated (NaCl) brines having similar total salt concentration to the hot-brine fluids are associated with Miocene evaporites at Sites 225, 227, and 228. However, their chemical and isotopic composition precludes such fluids being part of the "hot brine plumbing system." Hydrogen and oxygen isotope studies demonstrate that fluids trapped between and among the evaporitic rocks have a strong meteoric water component, presumed to have entered the rocks during or shortly after formation in shallow evaporating pans. The composition of pore fluid at Site 227 suggests the presence of late-stage evaporite minerals of the tachyhydrite CaMg 2 Cl 6 • 12H 2 O series in the in situ rocks. 4) Diffusivity measurements show that the pre-Miocene strata permit dissolved salt or gas diffusion to the extent of from 1/2 to about 1/10 the rate in free solution. However, in anhydrites diffusivity is reduced more than 100-fold, and no diffusion could be detected through halite rock. The rates applied to interstitial salt gradients at Site 225 suggest that less than 1 meter of rock salt is removed per million years by diffusion processes. The diffusion of salt can already be detected a few meters below the sediment-water interface, and based on the interstitial water studies, one can affirm the presence of salt at depth at Sites 228, 230, and possibly 229, where rock salt was not encountered by the drill. 5) Isotopic measurements on leads show that both leads from Site 228 and the hot brine deep (Site 226) require input from igneous or volcanic sources (e.g., volcanic ash). Elsewhere, however, leads of sedimentary-pelagic origin are noted. 6) Isotopic and other evidence indicates that the long-distance transport of subterranean brines advocated by Craig (1969) is unlikely. Instead, it is proposed that the source of the hot brines is subevaporite clastic or other aquifers of early to middle Miocene age that have been disrupted by rifting. These discharge in the deeps by virtue of hydrodynamic continuity with heavy brines at higher positions on the nearby flanks of the Red Sea. In this case, the waters might be fossil (middle Miocene) Red Sea waters of relatively normal salinity that have acquired greater salt concentration by diffusion from overlying late Miocene evaporites. The model is consistent with the isolated nature of the brine deeps and suggests that flow might have been enhanced by increased hydraulic gradients during periods of lowered Red Sea levels. 7) Interstitial water evidence indicates that Pleistocene lowerings of sea level did not cause evaporative conditions leading to actual gypsum or other evaporite deposition in the deeper water zones, as has been postulated. This in turn suggests that sill depths were greater than have been assumed.

Initial reports of the Deep Sea Drilling Project↗
USGS1973

Red sea drillings

Recent drilling in the Red Sea has shown that much of the basin is underlain by evaporites of a similar age to that of evaporites found in the Mediterranean Sea. These evaporites and their structural positions indicate that other brine areas are present - and, indeed, several others have been discovered.

Science↗
USGS1973

Shallow structure and geologic development of the Southern Red Sea

A series of 34 shallow-penetration seismic-reflection profiles made across the Red Sea show that it developed in two main stages. Initially, an early or pre-Miocene uplift and lateral extension resulted in crustal thinning and eventual formation of the main Red Sea Basin. During Miocene time, the Red Sea was isolated from the Indian Ocean but possibly connected with the Mediterranean Sea, which, like the Red Sea, was an evaporite basin at that time. A distinct acoustic reflector (reflector S) in the Red Sea marks the top of the Miocene evaporite sequence and is correlative with reflector M in the Mediterranean, which is similarly identified with termination of evaporite conditions. In Pliocene time, connection with the Indian Ocean was re-established, the opening to the Mediterranean was closed, and normal marine conditions were resumed in the Red Sea. Sea-floor spreading first started in Pliocene-Pleistocene time, and resulted in the formation of the axial zone of the Red Sea.

GSA Bulletin↗
USGS1970

Eastern margin of the Red Sea and the coastal structures in Saudi Arabia

R esults of many investigations since 1950 show that the eastern margin of the Red Sea and associated coastal structures in Saudi Arabia have a long geologic history, starting with the deposition of Precambrian eugeosynclinal sedimentary and volcanic rocks before 1000 Ma ago and extending to recent geologic time. The northeastern flank of the Red Sea rift valley is in a shield area affected by possibly four plutonic events at 1000, 720 to 735 (?), 660 to 670, and about 570 Ma. Cratonization of the shield occurred during all or part of the span 520 to 590 Ma. Nubian-type sandstone of Cambrian and Ordovician age laps up on the shield from Jordan southeastward around the rim of the Great Nafud basin, and along the eastern edge of the shield southeastward to 45 degrees E longitude where it is overlapped by Permian limestone. The sandstone reappears to the south and extends southward and westward to the Asir Mountains at the Yemen border. Isolated sandstone outliers are present in the central shield, proving that lower Paleozoic sandstone covered most, if not all, of the basement as now exposed. The Mesozoic era was almost entirely a time of uplift and non-deposition except a middle to late Jurassic fringe marine invasion in the south and a possible narrow invasion from the Gulf of Suez at the end of the era. Marine and non-marine sedimentary deposits of middle and late Tertiary age are found along the Red Sea coast, and Oligocene basaltic flows are present at both low and high altitudes in the coastal ranges. Evidence for important volcanism during Oligocene and earliest Miocene time is widespread, and within the eastern rift fault zone early Miocene hypabyssal intrusives cut the shear zones. Major rifting occurred just before or during early Miocene when the flanks of the rift valley were ramped upward. Shortly after this volcanism a thickness on the order of 3500 m of middle Miocene marl and evaporite beds filled the Red Sea trough. Evidence also exists for widespread subaerial erosion in the Pliocene. Younger lava flows are Pliocene in age but the youngest, near Al Medinah, came as late as A.D. 1250. Lake-bed deposits are very probably in large part Pliocene throughout the shield. The Red Sea coastal plain in Saudi Arabia rises gently eastward from a 3 m littoral surface, generally underlain by dead reef from the Yemen border northward to Al Wajd, a distance of 1400 km. At Jizan, in the south, a salt dome has pushed the 3 m surface up to an elevation of about 50 m. From Al Wajd northward, Pleistocene terraces have been faulted, culminating in several surfaces as high as 520 m above the Red Sea at Tiran Island. Ramping of major fault-bounded blocks along the eastern side of the Red Sea trough-the Midian block in the north, a poorly defined central block, and the Asir block in the south-is connected with renewed movement on regional Precambrian faults. Drainage patterns of wadis in these blocks are characteristically affected by the ramping, and stream capture is common in the Midian and Asir blocks.

Red Sea↗