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The allochthonous Hawasina complex is a sedimentary sequence of both continental-slope and oceanic-basin deposits that were thrust up over shallow-water marine carbonates of the Arabian Shelf during the Late Cretaceous. The Hawasina tectonically overlies the autochthonous Hajar Super Group, and is overlain tectonically by the Samail Ophiolite and associated sedimentary rocks.
The lower thrust units, the Hamat Duru Group, and Wahrah Al Ayn Formations, are generally interpreted as limestone and sandstone turbidites deposited on the continental rise. The Wahrah Formation and lower Zulla and upper Sid'r Formations within the Hamrat Duru Group all contain thick sequences of radiolarian-bearing chert. Samples collected from the Zulla and Wahrah (lower chert member) Formations yielded radiolarian faunas assignable to the Late Triassic (Karnian/Norian) based on key species of the genera Capnodoce, Capnuchosphaera, Eptingium, Sarla, Triassocampe, and Yeharaia. Additional samples from the Zulla Formation indicate an Early Jurassic (Pliensbachian) age based on the presence of Broctus, Canoptum, Canutus, Droltus, and Pseudoheliodiscus sp.; previous investigators sugge ted a hiatus in pelagic sedimentation during Early Jurassic time. Radiolarian faunas extracted from two measured sections of the Wahrah Formation (upper chert member) range in age from the Late Jurassic (Tithonian) to Early Cretaceous (late Valanginian/Hauterivian). No suitable radiolarian faunas were obtained from cherts of the Sid'r Formation (Hamrat Duru Group).
The higher thrust units are represented by the conglomeratic Al Ayn Formation, and the deeper water Halfa and Haliw Formations. Radiolarian faunas extracted from a measured section near the type locality of the Halfa Formation range in age from the Late Jurassic (Kimmeridgian/Tithonian) to the Early Cretaceous (Hauterivian/Barremian). All the radiolarian faunas obtained thus far from the Haliw Formation are assignable to the Late Triassic (late Karnian to middle Norian) based on fragments of Capnodoce and Veghicyclia sp.
Previous biostratigraphic data suggested that the thickest sections of radiolarian chert and mudstone were deposited during Late Jurassic and Early Cretaceous time. Newly obtained paleontologic evidence based on radiolarian biostratigraphy indicates that significant pelagic sedimentation occurred also during the Late Triassic and Early Jurassic.
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