Time-space relationships of Upper Precambrian volcanic and sedimentary units in the Central Arabian Shield

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Abstract
Geological and radiometric data are combined to produce time-calibrated stratigraphic columns for 7 provinces in the central Arabian Precambrian shield. Regional correlation suggests a subdivision of the stratigraphy into 3 'sequences' informally named A, B and C. 'Sequence' C ( c . 1200–950 Ma) includes rocks assigned to the Baish, Ajal, Bahah, Arafat and Hali groups, and typically consists of fine-grained clastic terrigenous sediments interbedded with volcanic/volcanoclastic deposits. These were deposited in a marine basin marginal to but some distance from a continental landmass. 'Sequence' B ( c . 950–650 Ma) includes rocks assigned to the Jiddah, Halaban, Hulayfah and Samran groups and parts of the Ablah and Urd groups. It comprises several volcano-sedimentary complexes and locally contains allochthonous mafic/ultramafic rocks which have been interpreted as ophiolites. Most of 'sequence' B was deposited in elongated basins adjacent to volcanic arcs. 'Sequence' A ( c . 650–570 Ma) includes rocks assigned to the Fatima, Murdama, Jibalah and Shammar groups, the Afif and Abt formations, and parts of the Halaban, Hulayfah and Ablah groups. It typically comprises coarse-grained terrigenous clastic sediments, locally interbedded with carbonates, deposited in fluviatile or shallow marine environments, and rhyolite-dominated volcanic units deposited subaerially. Stratigraphies of similar age and lithological character can also be recognized in E Egypt, NE Sudan and N Ethiopia.