Sedimentological and Structural Evolution of the Arabian Continental Margin in the Musandam Mountains and Dibba Zone, United Arab Emirates
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Sedimentological and structural evolution of the Arabian continental margin in the Musandam Mountains and Dibba zone, United Arab Emirates M. P. SEARLE ] N. P. JAMES \ Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3X5 Canada T. J. CALON ) J. D. SMEWING Earth Sciences and Resources Institute, University of South Carolina, Columbia, South Carolina 29208 ABSTRACT gressively removed all of the Lower Creta- first subjected to stratigraphie and structur- ceous. al studies by Iraq Petroleum Company The northernmost extremity of the Oman The Tethyan basinal and ophiolitic rocks geologists (Hudson and others, 1954b; Mountains, the Musandam Peninsula, is of the Dibba zone were emplaced from the Hudson and Chatton, 1959; Hudson, 1960) composed of an allochthonous sequence of east-southeast during the Turonian to lower and later mapped by Shell International Permian to middle Cretaceous shelf carbo- Maastrichtian. After emplacement of these Petroleum Company geologists (Glennie nates. These are separated from ophiolitic allochthonous units, compressional defor- and others, 1974) and in more detail by Elf rocks to the south by a northeast-south- mation in the mid-Tertiary resulted in large- Oil Company (Biehler and others, 1975; west-trending belt known as the Dibba scale, open, "whaleback" folds with wave- Ricateau and Riche, 1980). zone. This structurally complex belt is lengths as much as 15 km, generally with The Dibba zone is a northeast-southwest- composed of allochthonous slope- and north-south axes. In places, these folds, trending belt of tectonic complexity that basin-facies sediments, Haybi volcanic which affect the complete shelf and alloch- separates the Musandam platform sequence rocks, "Oman Exotic" limestones, sub- thonous sequences, are overturned toward to the north from the Late Cretaceous ophiolitic metamorphic rocks, and ultra- the west, and thrusting has caused pre- Semail ophiolite rocks of the Oman Moun- mafic slices. viously lower tectonic units of the Late Cre- tains to the south (Fig. 1). It consists of Lithofacies correlation confirms that taceous stacking order to be thrust over allochthonous sheets of Tethyan slope- fragmentation and rifting of a vast east- previously higher tectonic units, thus revers- facies carbonates (Sumeini Group), pelagic facing carbonate platform occurred in Mid- ing the Late Cretaceous tectonostratig- basinal sediments (Hawasina Complex), dle to Late Triassic time, resulting in the raphy. The maximum amount of transla- alkaline and tholeiitic basalts, "Oman Ex- establishment of a shelf edge and small tion on the later thrusts is in excess of 5 km otic" limestones, subophiolitic metamorphic ocean basin. This margin was typified from on the Hagab thrust, where the complete rocks, and mélanges, all constituting the northwest to southeast by ooid-skeletal lime shelf carbonate sequence of the Musandam Haybi Complex (Searle and Malpas, 1980). sand shoals or small bioherms on the shelf Mountains has been thrust west-northwest These rocks tectonically overlie the shelf edge, a bypass foreslope of well-laminated over the previously higher Hawasina and carbonate sequence, underlie the 10- to 14- periplatform ooze, and basin-margin ac- Haybi thrust sheets. The Tertiary folding km-thick Semail ophiolite sequence, and cumulations of carbonate turbidites or and thrusting can be correlated in time and were emplaced from the east and east- debris flows. The shelf edge now coincides space with the Zagros fold belt of south- southeast during the Late Cretaceous. The with the northern boundary of the Dibba western Iran. only previous specific studies of the Dibba zone and appears to have remained station- zone were made by Alleman and Peters ary from Middle Triassic to Late Jurassic INTRODUCTION (1972), Searle (1980), and Lippard and oth- time. Periods of arrested carbonate sedi- ers (1982). mentation on the platform either because of The Musandam Peninsula forms the This study was undertaken to unravel the exposure (Late Triassic and middle Cre- northern extremity of the 600-km-long stratigraphie and structural history of the taceous) or because of drowning (Late arcuate Oman Mountain belt (Fig. 1) and Musandam and Dibba zones. We first pre- Jurassic) are represented in the basin by continues southeastward from the Tethyan sent an outline of the stratigraphie evolution starved sedimentation and deposition of Zagros crush zone at a major orogenic syn- of the Arabian continental margin, incorpo- radiolarian cherts. A spectacular platform taxis. This area of approximately 3,000 km2 rating new data gained from work in the margin collapse occurred in the middle and is a mid-Permian to Late Cretaceous car- western Ruus al Jibal (Ras al Khaimah) and Late Cretaceous, as represented by massive bonate platform, overlapped on the west by the southern margin of the Musandam (AI conglomerates, with clasts as young as Tertiary shallow-marine and Holocene flu- Fujairah). This is followed by structural Albian, above an unconformity that pro- viatile and eolian deposits. The area was analysis of the emplacement and post Geological Society of America Bulletin, v. 94, p. 1381-1400, 15 figs., December 1983. 1381 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/94/12/1381/3444585/i0016-7606-94-12-1381.pdf by guest on 26 September 2021 1382 SEARLE AND OTHERS emplacement folding and thrusting of all stratigraphy similar to that of the autoch- beneath the Jebel Qamar South Exotic in units of the Musandam and Dibba zones. thonous carbonates to the south, but in the Dibba zone (see Fig. 8). Ordovician- Musandam they pass southward along Silurian quartzose sandstones containing PALEOGEOGRAPHIC AND strike into shelf-edge or slope deposits. The Cruziana trilobite trails (Rann Formation STRATIGRAPHIC FRAMEWORK platform rim that coincides with the north- of Hudson and others, 1954a) pass upward ern boundary of the Dibba zone appears to to thin phosphatic bone beds and ferrugi- From late Paleozoic to late Mesozoic have remained stationary from at least nous limestones containing abundant ortho- time, the Arabian Shield lay along the Middle Triassic to Late Jurassic time. cone cephalopods, ostracods, and bryozoa southern margin of the southern Tethys A geologic map of the Musandam Moun- of possible Devonian age. The unconform- Ocean. The outer parts of the continental tains and Dibba zone is shown in Figure 1, ably overlying Permian-Triassic massive shelf and adjacent Tethyan deep-sea floor and a stratigraphic correlation table is given limestone of the Jebel Qamar is the only are now exposed as a series of thrust sheets in Figure 2. For a detailed description of all exotic in the Oman Mountains that shows a emplaced southwestward onto a passive units, the reader is referred to Glennie and Paleozoic continental clastic substrate and continental margin during the Late Cre- others (1974). Owing to the tectonized and has been interpreted as a carbonate buildup taceous (Alleman and Peters, 1972; Glennie detached nature of the deep-water slope on a horst of basement subsequently rifted and others, 1973; Searle and Malpas, 1980). (Sumeini Group) and basin (Hawasina away from the continental platform (Searle Similar allochthonous Tethyan rocks are Complex) sediments, Glennie and others and Graham, 1982). The whole exotic lime- known from a belt stretching at least from (1974) assigned separate formation names stone and its basement now form an Cyprus through the Zagros Mountains of to contemporaneous strata in different tec- enormous slab in a mélange that is tenta- Iran to Baluchistan and Makran and prob- tonic slices. Consequently, a unique strati- tively correlated with the Aruma Group. ably continuing eastward along the Indus- graphic sequence cannot be applied to Tsangpo suture zone north of the Hima- allochthonous units; each major thrust slice Permian-Triassic layas. This belt is thought to represent part has a different stratigraphic sequence, ac- of a larger, Mesozoic, southern (Neo-) cording to its pretectonic position within The late Paleozoic and early Mesozoic in Tethys Ocean that rifted during Permian- the basin. This has resulted in some confu- this region were times of prolonged aridity, Triassic time and closed during the Late sion when mapping, and we have found it followed in the Late Triassic by rifting and Cretaceous and Tertiary (Smith, 1971). more useful to use lithofacies criteria for plate fragmentation. A vast, shallow plat- The Tethyan zone in the Middle East is distinguishing sedimentary packages. A form existed across Arabia, with the impli- bounded to the north by the stable, seismi- sedimentary-profile reconstruction of shelf, cation of a west-to-east shoreline to outer cally mainly inactive block of central Iran slope, and basin facies with the formations shelf transition, illustrated by the passage along the Zagros crush zone (Stocklin, of Glennie and others (1974) in their from arid, alluvial-plain, terrigenous clastic 1974). Seismic evidence from the Gulf of approximate paleotectonic positions is sediments to shallow-water evaporite to Oman (White and Klitgord, 1976; White, sketched in Figure 3. This has been facili- carbonate sediments (Murris, 1980). The 1977) indicates that northward underthrust- tated by the detailed paleontological dating carbonates in the Musandam Peninsula are ing of oceanic crust beneath Makran has made by Glennie and others (1974), by the dolomites of the Bih, Hagil, and Ghail resulted in a large