Broad uplift of the Red Sea margins has extensively eroded the pre-rift sedimentary section and exhumed the Proterozoic basement in the Arabian and Nubian Shields. However, some pre-rift sedimentary rocks are preserved within rift grabens along the coast, and on top of the Arabian plateau beneath syn-rift basalts of Harrat Hadan. Previous studies on outcrops of pre- and syn-rift sedimentary rocks near Jeddah assigned them various ages and Formations leading to confusion. Moreover, no attempts were made to correlate them to the section sitting on top of the Arabian plateau.
This study redefines the stratigraphy of pre-rift sedimentary rocks in the Jeddah area (Usfan and Shumaysi Formations) and correlates them with similar rocks located 200 km east over the Arabian Shield (Khurma and Umm Himar Formations). Field work, petrographic investigation and satellite image mapping data from the central Red Sea are used to reveal new stratigraphic correlations for the pre-rift section and new insights about the uplift of the Arabian plate.
The pre-rift sedimentary rocks rest uncomfortably on the Precambrian basement, consisting of sandstones, oolitic ironstone, shale, and bioclastic limestones. Their distinguishing characteristic is the textural and compositional maturity and total absence of basement-derived lithic pebbles.
The pre-rift sedimentary rocks are disconformably overlain by a syn-rift section, reaching several kilometers thick, consisting of immature continental redbeds composed of basement-derived conglomerates, sandstones, and mudstones. They are distinguished by their brick-red color, poor sorting, and compositional immaturity. The presence of pre-rift marine sediments in Harrat Hadan over the Arabian shield and in the coastal plain of the Red Sea indicates that it was at or below sea level during the early Cenozoic. Subsequently, the rift was filled with immature continental syn-rift sediments eroded from the margins.
Some key markers, particularly oolitic ironstones, define correlative units throughout the study area. Furthermore, the presence of 28 My old basaltic lava flows at the base of the syn-rift section in both the Jeddah and Harrat Hadan areas provides, for the first time, a reliable date for the start of rifting in the central Red Sea, and clear separation of pre-rift from syn-rift sedimentary rocks
| Date of Award | Sep 2021 |
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| Original language | English (US) |
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| Awarding Institution | - Physical Sciences and Engineering
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| Supervisor | Abdulkader Alafifi (Supervisor) |
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