The Buday’ah Formation, Sultanate of Oman: A Middle Permian to Early Triassic oceanic record of the Neotethys and the late Induan microsphere bloom (original) (raw)
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Palaeogeography, Palaeoclimatology Palaeoecology 191, 2003
In the Wadi Wasit area (Central Oman Mountains), Dienerian breccias are widespread. These breccias consist mostly of Guadalupian reefal blocks, often dolomitised, and some rare small-sized blocks of lowermost Triassic bivalve-bearing limestones. A unique block, with a size of about 200 m 3 , including Permian and earliest Triassic faunas has been studied in detail. The so-called Wadi Wasit block consists of three major lithological units. A basal unstratified grey limestone is rich in various reef-building organisms (rugose corals, calcareous sponges, stromatoporoids) and has been dated as Middle Permian. It is disconformably overlain by well-and thin-bedded light grey to yellowish coloured limestones rich in molluscs. Two major lithologies (Coquina Limestone respectively Bioclastic Limestone unit) characterise the shelly limestones, their contact seems gradual. These two units are welldated; they are of Griesbachian age and contain three conodont zones, the Parvus Zone, the Staeschei Zone and the Sosioensis Zone, and two ammonoid zones, the Ophiceras tibeticum Zone and an 'unnamed interval'. The third unit consists of a grey marly limestone containing Neospathodus kummeli (basal Dienerian). It is the first record of welldated basal Triassic sediments in the Arabian Peninsula. The Coquina Limestone is dominated by the bivalve Promyalina with some Claraia and Eumorphotis. This bivalve association is interpreted as a pioneering opportunistic assemblage. Towards the top of the Bioclastic Limestone unit, the faunal diversity increases and contains probably more than 20 taxa of bivalves, microgastropods, crinoids, brachiopods, ammonoids, echinoid spines, ostracods and conodonts. The generic diversity of this biofacies exceeds by far any other Griesbachian assemblage known. Our data give new evidence for the geodynamical history for the distal carbonate shelf bordering the Hawasina Basin. A break in the sedimentation characterises the Late Permian. The basal Triassic shows a steady transgression and the breccias may record a distinct gravitational collapse of platform margins linked with sea-level low stand at the end of Induan time (late Dienerian^basal Smithian). N 13 C carb isotopic analyses were performed and yield typical Permian values of around 4x for the Reefal Limestone, with a strong negative shift across the Permian^Triassic boundary. During the Griesbachian values shift positively from 0.5 to 3.1x parallel to an increase in faunal diversity and probably primary productivity. The detailed faunal analysis and the discovery of an unexpected diversity give us a new understanding of the recovery of the Early Triassic marine ecosystem. ß
The oceanic base of slope record of the Permian-Triassic crisis: view from Tethys (Oman)
2006
The Oman Mountains provide some of the best sections of Permian and Triassic sediments from ocean sea floor to base-of-slope environments related to the distal South Tethyan margin. The central part of the range exposes the Buday'ah section of oceanic sediments in the so-called "Hawasina allochtons". The locality of Wadi Maqam in the northwestern part of the Oman Mountains is among places where the thick Permian-Triassic base-of-slope sediments is exposed (Baud et al., 2001). Overlying 400 m of middle Permian limestones and dolomites, the upper Permian sediments consist of 50 m of ≈ 10 cm thick beds of cherts and dolomites rich in sponge spicules. The top of the Permian units is well bioturbated lime mudstone-wackestone, devoid of cherts and dated as late Changhsingian (Krystyn in Richoz et al., 2005). The boundary yellow shales are overlain by very thinly bedded, laminated microbial platy lime mudstone with H. parvus. The dramatic loss of the burrowing infauna indicates the appearance of oxygen-poor water. These Induan sediments are about 25 m thick and show at the top the first calcirudites, commonly clast-supported (edge-wise conglomerates), and are characterized by tabular clasts representing the sub-in situ reworking of the laminated, platy calcilutite. The very thick Smithian overlying litho-unit (up to 900 m) marks the onset on the base-of-slope of a deep-marine basin in which carbonate submarine fan deposits developed This very thick unit consists essentially of platy limestones, calcarenites and calcirudites. It comprises mainly grey-beige calcilutite, laminated and flaggy, interbedded with sparse beds of fine-grained calcarenite in cm beds. Channelized beds of intraformational calcirudite are also part of this succession which constitutes the greater part of the outcrop available. During the Spathian to Anisian, the sedimentation changes to terrigenous mudstone and siltstone that ended with Ladinian radiolarites.
Permo-Triassic Deposits: from Slope to Basin and Seamounts, a guidebook. Excursion A01
Part I-Structure and palaeogeographical evolution of the Oman passsive margin during the Permo-Triassic: an introduction to the field trip. 1-Structure of the Oman Mountains 3 2-Permian birth and evolution of the Arabian passive margin 2.1 The precursors of Neo-Tethyan tectonism 6 2.2 The first stage of the Neo-Tethyan extension 6 2.3 The climax of the Neo-Tethyan extension in Middle Permian (Murgabian) 6 3-The end-Permian-Triassic evolution of the Arabian passive margin 8 3.1 Doming of the Arabian Platform 9 3.2 Renewed Triassic extension on the Continental Slope and in the Hawasina Basin 9 Part II Introduction and description of the visited outcrops. 1-Introduction 1.1 The Permian-Triassic stratigraphic nomenclature 1.2 Magmatic evolution of the Permo-Triassic Tethyan margin in Oman 1.3 Introduction to the Carbon isotope stratigraphy 2-Description of the visited outcrops January 8 morning: the Wadi Alwa mega-block January 8 afternoon: the Wadi Musjah section 5 January 9 morning: the Wadi Wasit Permian and Triassic deep water sediments of the Hawasina units January 9 afternoon: the Upper Triassic-Lower Jurassic Al Aqil exotic blocks January10 morning: the Middle-Upper Triassic carbonate platform of the Sint section, Jabal Kawr January10 afternoon: the Jabal Misfah volcanites January 11: the Permian-Triassic shallow carbonate platform in Wadi Sahtan (Jabal Akhdar) 41 Aknowledgments References 2-. Description of the visited outcrops January 8 Morning: The Wadi Alwa mega-block Upper Permian carbonate, Lower Triassic pelagic limestone, Upper Triassic to Lower Jurassic ammonitico red limestones. Routing (fig. 4 and 5) The Ba'id window is reached via the Muscat-Nizwa highway to Bidbid and then following the Sur road through the ophiolite of Wadi Uqq. The new Wadi Tayin road follows the eastern rim of the Ba'id window. Stop 1 is located after crossing the Ba'id village, along the right flanc of the Wadi Alwa (fig. 5). January 8 Late afternoon: Wadi Musjah By A. Baud and S. Richoz Routing (2 in fig 4). The Wadi Musjah outcrops (fig. 15) are located near the main road linking Bidbid to Ibra, S of the Wadi Tayin road and NE of the Rawda village. Platty limestones Calciturbidite Slope Breccia with reefal limestones partly dolomitized Red platty limestones with ammonoids Platty limestones Tuffite with reefal limestones blocs White limestone Red platty limestone Tuffite Red micritic limestone Cherts Chert and tuffites Volcanic breccia Cherts and volcanic breccia Volcanic breccia Breccia Cherts and volcani-clastic with Permian platform blocs Volcanic breccia with syn-sedimentary fault Siliceous limestones with Permian Platform remains Calciturbidites Allodapic limestones,
Sedimentary Geology, 2008
The lower member of the Alwa Formation (Lower Olenekian), found within the Ba'id Exotic in the Oman Mountains (Sultanate of Oman), consists of ammonoid-bearing, pelagic limestones that were deposited on an isolated, drowned carbonate platform on the Neotethyan Gondwana margin. The strata contain a variety of unusual carbonate textures and features, including thrombolites, Frutexites-bearing microbialites that contain synsedimentary cements, matrix-free breccias surrounded by isopachous calcite cement, and fissures and cavities filled with large botryoidal cements. Thrombolites are found throughout the study interval, and occur as 0.5–1.0 m thick lenses or beds that contain laterally laterally-linked stromatactis cavities. The Frutexites bearing microbialites occur less frequently, and also form lenses or beds, up to 30 cm thick; the microbialites may be laminated, and often developed on hardgrounds. In addition, the Frutexites-bearing microbialites also contain synsedimentary calcite cement crusts and botryoids (typically b1 cm thick) that harbour layers or pockets of what appear to be bacterial sheaths and coccoids, and are indicative of biologically mediated precipitation of the cement bodies. Slumping following lithi"cation led to fracturing of the limestone and the precipitation of large, botryoidal aragonite cements in fissures that cut across the primary fabric. Environmental conditions, speci"cally palaeoxygenation and the degree of calcium carbonate supersaturation, likely controlled whether the thrombolites (high level of calcium carbonate supersaturation associated with vertical mixing of water masses and dysoxic conditions) or Frutexites-bearing microbialites (low level of calcium carbonate supersaturation associated with anoxic conditions and deposition below a stable chemocline) formed. The results of this study point to continued environmental stress in the region during the Early Triassic that likely contributed to the uneven recovery from the Permian–Triassic mass extinction.
Permian-Triassic extinction and recovery: results from the Muscat -Gutech field meeting
HAL (Le Centre pour la Communication Scientifique Directe), 2011
In the distal Hawasina basin (Buday'ah), the Upper Permian radiolarian chert deposits are overlain by Changhsingian siliceous shales and calcareous shales followed by Griebachian laminated platy limestones and shales and Dienerian-Smithian papery limestones. Conclusions The Neo-Tethys Ocean opened with the northward drifting of the Iran/Mega-Lhasa microcontinent followed a rifting extensional phase in the Roadian-Wordian. Thermal subsidence, with the development of the continental margin, is well recorded in the Wordian-Capitanian carbonate succession and continued during the Lopingian. Tectonic instability of the margin, with block tilting, platform drowning and (fault) breccia deposits started at the dawn of the Triassic with the main climax during the Dienerian and the Smithian.