When the highlands of Arabia were still covered with an ice shield in the latest
Carboniferous/Early Permian period, separation of Gondwana started. This led to the creation of the
Batain basin (part of the early Indian Ocean), off the northeastern margin of Oman. The rifting reactivated
an Infra-Cambrian rift shoulder along the northeastern Oman margin and detritus from this
high was shed into the interior Oman basin. Whereas carbonate platform deposits became widespread
along the margin of the Neo-Tethys (northern rim of Oman), drifting and oceanization of the Batain
basin started only in Late Jurassic/Early Cretaceous time. Extensional tectonics was followed in the
Late Cretaceous by contraction caused by the northward drift of Greater India and Afro-Arabia. This
resulted in the collision of Afro-Arabia with an intra-oceanic trench and obduction of the Semail
ophiolite and the Hawasina nappes south to southwestward onto the northern Oman margin ∼80 m.y.
ago. During the middle Cretaceous, the oceanic lithosphere (including the future eastern ophiolites of
Oman) drifted northwards as part of the Indian plate. At the Cretaceous–Palaeogene transition
(∼65 Ma), oblique convergence between Greater India and Afro-Arabia caused fragments of the early
Indian Ocean to be thrust onto the Batain basin. Subsequently, the Lower Permian to uppermost
Maastrichtian sediments and volcanic rocks of the Batain basin, along with fragments of Indian
Ocean floor (eastern ophiolites), were obducted northwestward onto the northeastern margin of
Oman. Palaeogene neo-autochtonous sedimentary rocks subsequently covered the nappe pile. Tertiary
extensional tectonics related to Red Sea rifting in the Late Eocene was followed by Miocene shortening,
associated with the collision of Arabia and Eurasia and the formation of the Oman Mountains.
Abstract--The Late Westphalian to Artinskian Haushi Group in the Sultanate of Oman consists of the glaciogenic A1 Khlata Formation and the Gharif Formation which contains marginal marine, coastal plain, and fluvial sediments. The sequence was deposited during a global-warming event following the PermoCarboniferous glaciation of Gondwana. Because of a varied subsidence history, these sediments range from the surface in the SE to almost 5000 m in the NW of the basin.Mixed-layer illite-smectite (I-S) is an important constituent of the <2 p,m size fraction of sandstone and shale samples in both formations at all depths. Different starting compositions lead to three distinct trends of illite layers in I-S versus temperature for different sedimentary environments and paleoclimatic conditions. The starting compositions of I-S at the surface range from an ordered I-S in the A1 Khlata Formation to smectite-rich in the Upper+Middle Gharif members.Physical, chemical and environmental factors were investigated as causes for the different starting compositions of I-S. Both formations share an identical burial history, paragenesis, thermal evolution, and source of detrital material. They differ only in environmental conditions during sedimentation. Thus, the variation in starting composition of I-S appears to be best explained by distinct weathering conditions during sedimentation of the three units. In particular, the expected low intensity of chemical weathering during glaciogenic conditions is marked by the presence of higher amounts of unstable volcanic and sedimentary rock fragments in the A1 Khlata Formation.
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