CARNIAN REEF BIOTA FROM A MEGABRECCIA OF THE HAWASINA COMPLEX (AL AQIL, OMAN)

Carnian reef biota and brachiopods of the Misfah Formation (Hawasina complex) from a locality near the town of Al Aqil in Oman are described. A new brachiopod species, Oxycolpella arabica n. sp. is described. The composition of the Carnian reef biota in Oman is similar to those known from the Alpine-Mediterranean region. However, differences exist in the microfauna of reef dwellers, e.g. foraminifers. New stratigraphic data based on reef organisms and conodonts are presented.&nbsp

Permian-Triassic extinction and recovery: results from the Muscat -Gutech field meeting

International audienceThe Permian–Triassic transition has been surveyed in the Oman Mountains and new detailedsections have been presented (Baud and Bernecker, 2010), from autochthonous shallow-waterunits (Saih Hatat and Al Jabal al-Akhdar) to slope deposits in the Jabal Sumeini area (WadiMaqam units), from distal tilted block (Wadi Wasit) to oceanic deep-water deposits(Buday’ah).Middle Permian TransgressionAt the dawn of the Wordian (Middle Permian), the "Fusulinid Sea" transgressed over most ofOman with the exception of Jabal Ja'alan and the Huqf-Dhofar High. This transgressionenabled the establishment of a vast carbonate platform in Al Jabal al-Akhdar, a 700 m-thicksuccession of cyclic shallow-marine carbonate, the Saiq Formation (Middle and Late Permian,basal Triassic (Baud et al., 2001a, b, 2005; Richoz et al., 2005; Richoz, 2006). A similarsuccession occurs in Saih Hatat (Le Métour, 1988; Weidlich and Bernecker, 2003; Chauvet,2007), in the Musandam (Bih Formation, Maurer et al., 2009), as well as in the Interior Omanand in the Haushi area (Khuff Formation, Angiolini et al. 1998, 2003). Clearly, for us, thistransgression was the result of the break-up of the Neo-Tethyan rift and the associatedthermal subsidence.Following the peak of the thermal subsidence in the Wordian–Capitanian, a stable carbonateplatform became established on the Arabian Peninsula. The Saiq, Khuff and Hagil formationsshow a strong regressive tendency at the end of the Guadalupian (Middle Permian), withrestricted environment facies and a reduced biophase, mainly associated with a global fall insea level at this time and climate changes (Isozaki, 2009). During the Lopingian (LatePermian), the subsidence as recorded in the Saiq mega-cycle B (up to 300 m of shallowingupward cycles) was still well active.The most striking effect of the climax of the Neo-Tethyan extension was the formation of acontinental slope (Sumeini) and a basin (Hawasina) that constituted with the adjacentArabian Platform, the southern continental passive margin of the Neo-Tethys Ocean.Furthermore early-rifted blocks detached from the edge of the Arabian Shield formed isolatedproximal platforms along the continental slope (later they were incorporated in the HawasinaNappes). The continental margin slope deposits are clearly identified (with slumps and intraformationalbreccia) in the northwestern part of the Oman Mountains (Jabal Sumeini), wherethey form the basal part of the Maqam Formation dated as Roadian (Middle Permian).The distal isolated platform identified as nappes in Baid and Jabal Qamar areas by Béchennec(1988), Béchennec et al. (1992), Pillevuit (1993) and Pillevuit et al. (1997) are mainly made ofMiddle–Late Permian open-shelf carbonates. The Jabal Qamar unit includes a fragment of thepre-Middle Permian Basement (Rann, Ayim and Asfar formations, Pillevuit, 1993) overlain inunconformity by the late Early to early Middle Permian shallow-marine carbonate QamarFormation with its quartz-sandstone basal member. The Baid unit is truncated at the base andis made of about 100 m of the Middle–Late Permian (Capitanian–Wuchiapingian) shallowmarinecarbonate (Baid Formation, Béchennec, 1988; Pillevuit, 1993; Pillevuit et al., 1997;Baud et al., 2001b). The distal paleogeographic position of these Permian tilted blocks inregard with the Arabian Platform is documented by: (1) the differences in terms of facies(open marine with ammonoids) with those restricted to the others parts of the OmanMountains (Al Jabal al-Akhdar, Saih Hatat and Musandam); and (2) the presence of reworkedboulders originating from these isolated platforms in the calcirudites of the proximal units ofthe basinal Hawasina Nappes.Basinal facies of the Middle Permian are present in the Hawasina Nappes at the base ofnumerous tectonics units, made up of formations from the Hamrat Duru Group. Thesesuccessions generally start with thick volcanic sequences (Al Jil and Buday’ah formations).These volcanic rocks are either of MORB type or alkali basalt-related (Maury et al., 2003;Lapierre et al., 2004). The volcanic succession is filled and overlain by red ammonoidlimestones dated as Middle Permian (Capitanian) followed by radiolarian chert and shalesnewly dated as Lopingian in Buday'ah. In the Wadi Wasit area, the volcanic series is cappedby red cephalopods-bearing carbonate, dated Middle Permian (Wordian, Blendinger et al.,1992; Pillevuit et al., 1997; Baud et al., 2001b), by shales and breccia with reworked blocks ofMiddle Permian to basal Triassic platform carbonate (Béchennec et al., 1992b; Pillevuit, 1993;Pillevuit et al., 1997; Krystyn et al., 2003; Weidlich and Bernecker, 2007).Near Nahkl the volcanic series includes blocks of Middle Permian shallow-marine carbonateand is overlain by pelagic limestone (Weidlich, 2007). In the Rustaq area the volcanicsuccession is also capped by a condensed carbonate sequence (Hallstatt facies type) dated asMiddle Permian (Wordian, Blendinger et al., 1992; Pillevuit et al., 1997; Baud et al. 2001b;Richoz et al., 2005).Different types of deep-water black limestones are also identified in the basinal units of theBatain Plain (southeastern part of the Oman Mountains), the "Qarari Limestone" with a basedated as Roadian (Middle Permian, Immenhauser et al., 1998) and the top as Changhsingian.From the Permian/Triassic Transition to the Basal Triassic (Figure 1)At the end of the Permian (top of KS3 sequence of Koehrer et al., 2010), regressive conditionsup locally to emersion (?) are recorded as well on the Arabian carbonate platform (Al Jabal al-Akhdar, Saih Hatat and Musandam). On the slope of the continental margin, we observe ashallowing in the Sumeini unit deposits.Shallow tidal influenced carbonate platform is the main component of the Induandolomitized deposit in the Al Jabal al-Akhdar (Units C1 to C4 of the Saiq Formation in Baudand Bernecker, 2010, correlated with Khuff sequences KS2–KS1) that is now dated byconodonts. During the Dienerian, part of the margin was affected by a renewed extensionalregime, tilting and drowning resulting in erosive deposition and accumulation of carbonatebreccia (Unit C2 of the Saiq Formation) followed in the Al Jabal al-Akhdar by high-energy,partly oolitic dolomitized shallow-water deposits, Dienerian in age (Unit C3) and renewedbreccias (Unit C4). The Saiq-Mahil transition (correlated with the Khuff-Sudair transition) isprobably of late Induan age (chemostratigraphical correlations, Richoz, 2006).On the slope of the continental margin, a continuous carbonate deposition and shale has beenrecently precisely dated from Changsingian to Spathian. Overlying the Wuchiapingian–Changhsingian, deep-water chert and dolostone (upper Member B of the Maqam Formation),we note the deposition of upper Changsingian shallowing siliceous strongly bioturbated limemudstones. A major facies change occurs with the Griesbachian papery, laminatedcalcimicrobial mudstone overlying the boundary clay (base of C1c Member of the MaqamFormation). The calcarenite, calcirudite turbidites and avalanches with shallow water upperPermian lime clasts start in the Dienerian (instability period). The incredible thickness of theSmithian deposits (platy limestones, shales and megabreccia up to 900 m of thickness, middleand upper Member C of the Maqam Formation) indicate high carbonate productivity on theplatform and a very active subsidence at the base of slope (Watts, 1985; Baud et al., 2001b;Richoz et al., 2005; Richoz, 2006).On the Baid Exotic block, after karstification of part of the tilted Permian carbonate platformand the Dienerian drowning event, the Dienerian-Smithian deep-water red ammonoidlimestone is filling fissures and cavities (Hallstatt breccia) and is deposited over the Permianlimestones (Tozer and Calon, 1990; Pillevuit, 1993; Pillevuit et al., 1997; Baud et al., 2001a;Richoz, 2006; Wood and Baud, 2008).In the proximal deep-water basin (Wadi Wasit units) the Lopingian allodapic limestones arepartly eroded by a submarine avalanche breccia (Dienerian) containing Permian to basalTriassic mega-blocks. One of these blocks with a unique Permian–basal Triassic record hasbeen analyzed in Krystyn et al. (2003). Upper Dienerian–Smithian deep-water platy limestoneoverlay the Lower Dienerian mega-block breccia.In the distal Hawasina basin (Buday’ah), the Upper Permian radiolarian chert deposits areoverlain by Changhsingian siliceous shales and calcareous shales followed by Griebachianlaminated platy limestones and shales and Dienerian–Smithian papery limestones.ConclusionsThe Neo-Tethys Ocean opened with the northward drifting of the Iran/Mega-Lhasamicrocontinent followed a rifting extensional phase in the Roadian–Wordian. Thermalsubsidence, with the development of the continental margin, is well recorded in theWordian–Capitanian carbonate succession and continued during the Lopingian. Tectonicinstability of the margin, with block tilting, platform drowning and (fault) breccia depositsstarted at the dawn of the Triassic with the main climax during the Dienerian and theSmithian