Papers by William Bosworth
The Albian – Cenomanian boundary on the southern Tethyan margin: Abu Gharadig Basin, Northern Western Desert, Egypt
Marine and Petroleum Geology, Aug 1, 2023
Geophysical Evidence for Magmatism Southwest of the Brothers Islands, Northern Red Sea (Offshore Quseir, Egypt)
Tectonics, Oct 1, 2022
The Red Sea formed as a consequence of Cenozoic rifting between the African and Arabian plates. W... more The Red Sea formed as a consequence of Cenozoic rifting between the African and Arabian plates. While continuous oceanic spreading is active in the southern and central sectors, in the northern Red Sea, exposure of oceanic crust is limited to a few along‐axis isolated deeps. However, several off‐axis magmatic edifices have been recognized in this sector, their description in terms of relative age and architectural features remains vague. One of these, offshore Quseir corresponding to a kilometer‐size structural high, was studied in detail using 3D industrial seismic data. This structure is interpreted as due to the coalescence of different volcanic edifices developed on the footwall of a major rift‐related normal fault. Magnetic and gravity data and forward modeling suggest a volcanic nature of the substratum underlying the morphological relief. A similar volcanic origin is proposed for other neighboring basement hills that show a similar magnetic signal. Relationships with the imaged seismo‐stratigraphic sequences point to a Pleistocene age for the magmatic event. Arabian alkali‐basalts, at the same latitude as Quseir, show ages comparable to those inferred for the volcano edifice studied, suggesting a similar geotectonic context. In western Arabian plate, large alkali‐lava fields (Harrats) developed along rift‐related faults since the early stages of the Red Sea rift (Late Oligocene). They display a significant northward rejuvenation trend that may be explained by the progressive propagation of the Afar mantle plume.
Red Sea rifting in central Egypt: constraints from the offshore Quseir province
Journal of the Geological Society, Feb 16, 2023
The formation of oceanic crust in the southern and central Red Sea is generally accepted to have ... more The formation of oceanic crust in the southern and central Red Sea is generally accepted to have started at c. 5 Ma. However, the nature of the crust in the northern Red Sea is still debated. This paper describes the rift architecture, dynamics and evolution of the northern Red Sea and identifies domains that relate to first-order geodynamic processes. The proximal margin domain is located onshore and is characterized by latest Oligocene–Miocene half-graben basins. New seismic interpretations show that the offshore region is a necking domain dominated by low-angle, high-offset extensional faults, which led to the exhumation of lower crustal gabbros at Brothers Islands. Two-dimensional forward models suggest that the necking domain passes into a distal margin domain, where the continental crust thins to <10 km at 120 km from the coast. Sensitivity testing of interpretations for the distal domain indicates a probable scenario where exhumed lower continental crust or serpentinized mantle is present. A comprehensive rift model for the northern Red Sea in the Quseir province accounts for magmatic underplating accompanied by half-graben development at c. 25 Ma, followed by Early Miocene crustal thinning accommodated by an east-dipping detachment fault. A Late Miocene phase with a flip of the detachment geometry led to the present day configuration.
AAPG Studies in Geology #44, Appendix C-Chapter 4: Geology and Geophysics of the Anza Graben
Investigating the Palaeoshorelines and Coastal Archaeology of the Southern Red Sea
Springer eBooks, Dec 5, 2018
Numerous palaeoshoreline features including coral platforms, beachrock and wave-cut notches are p... more Numerous palaeoshoreline features including coral platforms, beachrock and wave-cut notches are present on the Red Sea coastline of SW Saudi Arabia and on the Farasan Islands. Some are associated with prehistoric archaeological material, which has been the focus of ongoing archaeological investigations over the past decade. Dating and interpretation of these features are therefore of considerable interest and relevance to the deep history of human coastal adaptation and colonization in a key zone for the understanding of early human expansion out of Africa, as well as to the study of relative sea-level changes and tectonic movements. This chapter provides details of a field survey carried out in 2014 and presents new information on the location, geological setting, geochronological sampling and archaeological associations of these palaeoshoreline features. The results of dating are still awaited, so that some of our interpretations are still hypotheses in need of further testing. At this stage, it is clear that the most prominent shoreline features on the mainland coast are at elevations similar to those dated elsewhere in the Red Sea as belonging to MIS 5e, and that in at least one exposure Middle Stone Age artefacts can be stratigraphically linked with this period of high sea level. On the Farasan Islands, coral platforms have undergone more variable and localised rates of movement associated with salt tectonics. We set out the field data in support of these interpretations and consider their wider archaeological and tectonic implications.
Timing of Extensional Faulting Along the Magma-Poor Central and Northern Red Sea Rift Margin—Transition from Regional Extension to Necking Along a Hyperextended Rifted Margin
Springer eBooks, Dec 5, 2018
In light of voluminous Oligocene continental flood basalts in the Afar/Ethiopian region, the Red ... more In light of voluminous Oligocene continental flood basalts in the Afar/Ethiopian region, the Red Sea has often been viewed as a typical volcanic rift, despite evidence for asymmetric extension and hyperextended crust (Zabargad Island). An in-depth analysis of the timing, spatial distribution, and nature of Red Sea volcanism and its relationship to late Cenozoic extensional faulting should shed light on some of the misconceptions. Voluminous Eocene to Oligocene flood basalts in northern Ethiopia and western Yemen at ~31–30 Ma were synchronous with the onset of continental extension in the Gulf of Aden, but demonstrably predate Red Sea extensional faulting and rifting. Basaltic dike emplacement, syn-rift subsidence and sedimentation, and rapid rift-related fault block exhumation at ~23 Ma along the entire Red Sea-Gulf of Suez rift system mark the onset of Red Sea rifting. Early Miocene rifting affected a wide area (~1200 km) around the northern Red Sea with limited strain localization along the main rift axis between ~20 and 14 Ma. While the initiation of lithospheric extension in the northern and central Red Sea and Gulf of Suez was accompanied by only sparse basaltic volcanism and possible underplating, the main phase of rifting in the Miocene Red Sea/Gulf of Suez lacks significant rift-related volcanism. There appears to be no evidence for the formation of SDRs or accretion of a thick proto-oceanic crust. Rift localization and major crustal thinning continued throughout the Early Miocene. Middle Miocene onset of left-lateral displacement along the Gulf of Aqaba transform resulted in the tectonic isolation of the Gulf of Suez and a switch from rift-normal to highly oblique extension with the Red Sea. Oblique extension led to the formation of fracture zones, pull-apart basins, and crustal necking, and ultimately local crustal separation and mantle exhumation, prior to Plio-Pleistocene incipient oceanic breakup in the northern Red Sea. This clearly supports the interpretation of the northern Red Sea as a magma-poor rift system and the importance of the Middle Miocene kinematic reorganization for continental breakup.
Structural geology of the Fort Miller, Schuylerville and portions of the Schaghticoke 7½' quadrangles, eastern New York, and its implications in Taconic geology; and experimental and theoretical studies of solution transfer in deforming heterogeneous systems
Noncoaxial deformation along the northeastern edge of the Appalachian Plateau, New York: implications for faulting processes in orogenic forelands
Structural and tectonostratigraphic evolution of Matruh Basin, northern Western Desert, Egypt: An example of an inverted rift basin
Journal of African Earth Sciences, Jul 1, 2023
Structural style and tectonic evolution of the rift basins of northeast Africa
Geoscientific Research in Northeast Africa
North African Phanerozoic
Encyclopedia of Geology
Constraining the tectono-thermal evolution of the Egyptian Red Sea margin: linking observations from the proximal to the hyperextended rift domain
AGU Fall Meeting Abstracts, Dec 1, 2019
Geology of Egypt: The Northern Red Sea
The Geology of Egypt, 2019
The Red Sea and Gulf of Aden constitute parts of the Afro-Arabian rift system that are in the mos... more The Red Sea and Gulf of Aden constitute parts of the Afro-Arabian rift system that are in the most advanced stages of continental break-up. These basins have therefore received extensive scrutiny in the geoscientific literature, but several aspects of their evolution remain enigmatic. Many of their most important features lie beneath several kilometers of water, in places covered by several kilometers of evaporite deposits, and along international political boundaries. All these factors greatly complicate the acquisition and interpretation of both subsurface wellbore and geophysical datasets. Much of our understanding of the evolution of the Red Sea has therefore relied on the integration of outcrop geology and land-based analytical studies with these more difficult to obtain marine observations. While stratigraphic, radiometric and structural data indicate that extension and rifting initiated in the southern Red Sea during the Late Oligocene (~28–25 Ma), the start of rifting in the northern Red Sea is more difficult to constrain due to paucity of rift-related volcanism and reliable biostratigraphy of the oldest syn-kinematic sedimentary strata. A regional NW-SE trending alkali basalt dike swarm, with associated extensive basalt flows in the vicinity of Cairo, appears to mark the onset of crustal-scale extension and continental rifting. These dikes and scarce local flows, erupted at the Oligocene-Miocene transition (~23 Ma) and coeval with similar trending dikes along the Yemen and Saudi Arabian Red Sea margin, are interbedded with the oldest part of the paleontologically dated siliciclastic syn-rift stratigraphic section (Aquitanian Nukhul Fm.), and are associated with the oldest recognized extensional faulting in the Red Sea. Bedrock thermochronometric results from the Gulf of Suez and both margins of the Red Sea also point to a latest Oligocene onset of major normal faulting and rift flank exhumation and large-magnitude early Miocene extension along the entire length of the Red Sea rift. This early phase of rifting along the Egyptian Red Sea margin and in the Gulf of Suez resulted in the formation of a complex, discontinuous fault pattern with very high rates of fault block rotation. The rift was segmented into distinct sub-basins with alternating regional dip domains separated by well-defined accommodation zones. Sedimentary facies were laterally and vertically complex and dominated by marginal to shallow marine siliciclastics of the Abu Zenima, Nukhul and Nakheil Formations. Neotethyan faunas appeared throughout all of the sub-basins at this time. During the Early Burdigalian (~20 Ma) tectonically-driven subsidence accelerated and was accompanied by a concordant increase in the denudation and uplift of the rift shoulders. The intra-rift fault networks coalesced into through-going structures and fault movement became progressively more focused along the rift axis. This reconfiguration of the rift structure resulted in more laterally continuous depositional facies and the preponderance of moderate-to-deep marine deposits of the Rudeis, Kareem and Ranga Formations. The early part of the Middle Miocene (~14 Ma) was marked by dramatic changes in rift kinematics and sedimentary depositional environments in the Red Sea and Gulf of Suez. The onset of the left-lateral Gulf of Aqaba transform fault system, isolating the Gulf of Suez from the active northern Red Sea rift, resulted in a switch from orthogonal to oblique rifting and to hyperextension in the northern Red Sea. The open marine seaway was replaced by an extensive evaporitic basin along the entire length of the rift from the central Gulf of Suez to Yemen/Eritrea. In Egypt these evaporites are ascribed to the Belayim, South Gharib, Zeit and Abu Dabbab Formations. Evaporite deposition continued to dominate in the Red Sea until the end of the Miocene (~5 Ma) when a subaerial unconformity developed across most of the basin. With the onset of seafloor spreading in the southern Red Sea, Indian Ocean marine waters re-entered through the Bab el Mandab in the earliest Pliocene and re-established open marine conditions. During the Pleistocene, glacial-isostatic driven sea-level changes resulted in the formation of numerous coral terraces and wave-cut benches around the margins of the Red Sea, Gulf of Suez and Gulf of Aqaba. Their present elevations suggest that the Egyptian Red Sea margin has been relatively vertically stable since the Late Pleistocene. While there is general agreement that full seafloor spreading, producing well-defined magnetic stripes, has been occurring in the southern Red Sea since ~5 Ma, there is ongoing debate whether and when lithospheric break-up has occurred in the northern Red Sea. Industry wellbore and seismic data demonstrate that continental crust extends at least several tens of kilometers offshore from the present-day coastline, and that the northern Red Sea is a non-volcanic rifted margin. On the basis of integrated geophysical,…
Oceanization Starts at Depth During Continental Rupturing in the Northern Red Sea
Geological Setting, Palaeoenvironment and Archaeology of the Red Sea, 2018
We present here 3D seismic reflection and gravity data obtained from an off-axis area of the NW R... more We present here 3D seismic reflection and gravity data obtained from an off-axis area of the NW Red Sea, as well as results of a study of gabbroic rocks recovered in the same area both from an oil well below a thick evaporitic-sedimentary sequence, and from a layered mafic complex exposed on the Brothers Islets. These new data provide constraints on the composition, depth of emplacement and age of early syn-rift magma intrusions into the deep crust. The Brothers are part of a series of sub-parallel NW-striking topographic highs associated with SW-dipping extensional fault blocks with significant footwall uplift during rifting that brought early syn-rift deep crustal rocks up to the seafloor. Assuming an important role played by magmatism in the evolution of narrow rifts helps to solve the controversy on the nature of the crust in the northern/central Red Sea (i.e., the crust outside the axial oceanic cells is either oceanic or it consists of melt-intruded extended continental crust). Gabbros show petrologic and geochemical signatures similar to those of MORB-type gabbroic cumulates and are compatible with their having been emplaced either in a continental or in an oceanic context. We explored the different hypotheses proposed to explain the lack of magnetic anomalies in the presence of oceanic crust in the northern Red Sea. Our results, combined with a review of all the geophysical and geological data in the area, suggest a stretched and thinned continental crust with few isolated sites of basaltic injections, in line with a model whereby asthenospheric melt intrusions contribute to weaken the lower crust enabling some decoupling between upper and lower crust, protracting upper crust extension and delaying crustal breakup. Our findings show that continental rupture in the northern Red Sea is preceded by intrusion of basaltic melts with MORB-type elemental and isotopic signature, that cooled forming gabbros at progressively shallower crustal depths as rifting progressed toward continental separation.
Regional Geology and Petroleum Systems of the Main Reservoirs and Source Rocks of North Africa and the Middle East
The Geology of the Arab World---An Overview, 2018
Roughly 44% of the world’s total known hydrocarbon resources are located in North Africa and the ... more Roughly 44% of the world’s total known hydrocarbon resources are located in North Africa and the Middle East, from Algeria in the west to the Zagros region of Iran in the east. This includes more than 200 giant fields in the Middle East. North African basins, mainly in Algeria, Libya, and Egypt, contain 4% of the world’s oil and gas reserves and nearly 40 giants. The most recent giant field resides in the offshore Levantine Basin. In this chapter, the region’s geological history and petroleum systems are reviewed, including descriptions of the regional habitats and stratigraphy of the main reservoirs and source rocks. The Late Pre-Cambrian to Phanerozoic tectonostratigraphy is characterized by six major phases: (1) basement assembly and Infracambrian extension; (2) development of Cambrian to Carboniferous passive margins; (3) Late Carboniferous to Early Permian Hercynian orogeny; (4) post-Hercynian breakup of Gondwana; (5) collision with Eurasia; and (6) Red Sea rifting and the closing of Neotethys. For most of the Phanerozoic, the terranes of North Africa and Arabia were locked together at the northern rim of Gondwana. They shared a similar geodynamic history and generally similar climates. Their plate margins interacted over time with the water masses of three oceans: Proto-, Paleo-, and Neotethys. Throughout the Paleozoic, the region lay on a wide “ramp-like” passive margin facing northward toward Paleotethys. The main sediment source was the large hinterland to the south, with prevailing south to north and southeast to northwest-directed paleocurrents. Multiple marine transgressions across a low-relief continental platform were interrupted by at least four glacial events: Late Ordovician (Hirnantian), Silurian, Carboniferous, and Early Permian. Deposition of siliciclastics predominated throughout the Paleozoic whereas carbonates were much less common. The most important tectonic event was the mid-Carboniferous Hercynian composite-orogeny, which caused major uplift and erosion. The Hercynian represented the final closure of Paleotethys and produced many fault blocks and arches that would later host many of the major hydrocarbon accumulations of North Africa and eastern Arabia. The Mesozoic–Cenozoic sedimentary sequence similarly consists of eustatically and tectonically controlled depositional cycles along the newly formed passive margin of Neotethys. Triassic to mid-Cretaceous facies along North Africa are almost everywhere shallow marine, nearshore, deltaic, and continental. Neotethys reached its maximum extent in the Late Cretaceous at which time carbonate sequences dominated. In addition to the Hercynian Orogeny, two other compressional events had major consequences on North Africa–Arabia petroleum systems. The closing of Neotethys began in the late Santonian (~84 Ma) and the convergence between Eurasia and Africa–Arabia sent pulses of compressional deformation across the plate. This corresponded to the first phase of the complex Alpine orogenic cycle and caused folding, basin inversion, and strike-slip faulting along the African–Arabian Neotethyan margin (the “Syrian Arc”), and thrusting and ophiolite obduction in Oman. Compression was renewed at the end of the Maastrichtian and continued into the early Paleocene, followed by even stronger effects in the Late Eocene. Eruption of the Afar plume at about 31 Ma marked the beginning of a new phase of continental rifting that had dramatic effects on all aspects of the geology of the region. The Gulf of Aden ruptured first in the Early Oligocene, followed by the southern Red Sea in the Late Oligocene. At the Oligocene–Miocene transition, the remainder of the Red Sea north to the Gulf of Suez underwent a regional dike event and accompanying extensional faulting. Initiation of the Gulf of Aqaba—Dead Sea transform plate boundary occurred in the Middle Miocene, completing formation of the independent Arabian plate. The Neotethys Ocean also ceased to exist in the Middle Miocene following a collision between Eurasia and the Arabian plate to form the Bitlis–Zagros suture and fold belt. The Arabian plate was progressively tilted to the northeast as a result of both uplift and rifting of Arabia from Africa, and structural loading of the northeast margin by the Zagros fold belt. Recent tectonic activity is mainly concentrated along the Maghrebian Alpine Belt, the offshore Nile Delta, the Red Sea–East African (or “Afro-Arabian”) Rifts Province, the Aqaba–Dead Sea–Bekaa sinistral strike-slip fault zone, and some major intra-plate fault zones including the Guinean–Nubian, Aswan, and central Sinai lineaments. Our review of the petroleum systems of North Africa and Arabia is brief and includes only highlights of the hydrocarbon occurrences found across this broad and complex region. Based on the age of source rocks, it is possible to distinguish an Infracambrian Petroleum System, Palaeozoic-related Petroleum Systems, and linked Mesozoic–Cenozoic Petroleum Systems. The…
Tectonic and provenance history of the Neotethyan margin in NE Africa recorded by detrital zircon (U-Th)/He thermochronometry from a borehole in the Western Desert, Egypt
The subsurface of the Western Desert of Egypt contains multiple stacked sedimentary basin deposit... more The subsurface of the Western Desert of Egypt contains multiple stacked sedimentary basin deposits separated by major unconformities reflecting the long-lived tectonic evolution of the Neotethyan continental margin in eastern North Africa. In this study, zircon (U/Th)/He (ZHe) data were collected from cuttings from a ~15000 ft borehole that penetrated Tertiary and Cretaceous strata and a major erosional unconformity at
Geology and Geophysics of the Anza Graben
Geoscience of Rift Systems—Evolution of East Africa, 1999
The Volcanic Myths of the Red Sea - Temporal Relationship Between Magmatism and Rifting
American Journal of Science, 1985
The EGU General Assembly, 2017
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Papers by William Bosworth