Petrological and Tectonostratigraphic Evidence for a Mid Ordovician Rift Pulse on the Arabian Peninsula
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GeoArabia, Vol. 4, No. 4, 1999 Gulf PetroLink, Bahrain Mid Ordovician Rift, Oman Petrological and Tectonostratigraphic Evidence for a Mid Ordovician Rift Pulse on the Arabian Peninsula W. Heiko Oterdoom, Petroleum Development Oman Mike A. Worthing, Sultan Qaboos University, Oman and Mark Partington, Petroleum Development Oman ABSTRACT During late Early Ordovician times an increase in the rate of subsidence in the Ghaba Salt Basin and western South Oman Salt Basin is suggested by the thick sequence of continental clastics of the Ghudun Formation. After a phase of rift-shoulder uplift and erosion, related to a renewed pulse of extension which may have initiated diapiric growth of salt structures in the Ghaba Salt Basin, sedimentation resumed again in the Mid Ordovician. During this period, the center of deposition shifted to the Saih Hatat area in North Oman. This paper documents seismic and well data, field investigations and petrological study of potassic mafic rocks from the Huqf area which were intruded in the eastern side of the Ghaba Salt Basin. A Mid Ordovician age of 461 ± 2.4 million years has been established for these rocks by the Argon-Argon step heating method. Analogy with the petrology and setting of similar potassic mafic rocks from the Rio Grande Rift in the western United States of America suggests that they were intruded into the shoulder of an intra-continental rift. The data provide the first clear evidence of a pulse of rift-shoulder uplift in the Huqf area during the Mid Ordovician. The 3-kilometer-thick Mid to Late Ordovician clastic sediments of the Amdeh Formation in North Oman, together with the occurrence of abnormally thick sedimentary sequences and volcanics in the Tabas Graben in Iran, are consistent with a period of break-up of eastern Gondwana. Together, the Ghaba-Saih Hatat and Tabas Basins are considered to be part of a failed rift arm. These observations further improve our regional knowledge of the Early to Late Ordovician tectonic setting of Oman and will assist in unlocking the hydrocarbon potential of classical rift-related structures consisting of early-rift Early Ordovician sand-prone reservoirs sealed by syn-rift Mid to Late Ordovician marine shales. INTRODUCTION In Central and South Oman, a series of northeast-southwest to north-northeast–south-southwest trending extensional basins are developed on Precambrian crystalline basement (Figure 1). Episodic basin formation in Gondwana was initiated in Late Precambrian times following the formation of the Rodinia supercontinent (Stern, 1994). In Oman, the western margin of these basins is marked by a structurally complex compressional zone of late Early Cambrian age defined as the “Western Deformation Front” (Loosveld et al., 1996). Deformation increases in intensity towards the southwest across the South Oman Salt Basin into Yemen. This tectonic pulse probably signaled the end of the indentation of West Gondwana into East Gondwana (Stern, 1994) and is associated with regional uplift and erosion over the entire Arabian Plate (Stump et al., 1995). The eastern margin of Oman’s salt basins in contrast is less tectonized and Phanerozoic sediments offlap, onlap onto, or are truncated against, a structural high known as the Huqf High (Gorin et al., 1982). This high is located close to the present east coast of Oman. Subsequent phases of uplift of the Huqf High resulted in the present-day exposure of rocks ranging in age from the Precambrian granitoid basement to Tertiary sediments (Figure 2). The outcropping sequence contains both major and minor unconformities. Large sections of the stratigraphic column are absent, particularly in the Late Paleozoic due to lack of accommodation space and erosion during a Mid Carboniferous Hercynian event. Documented rift-shoulder uplift pulses in the Late Carboniferous to Early Permian and again in Late Triassic to Early Jurassic times preceded the break-up of Gondwana in Late Jurassic times (Blendinger et al., 1990; Immenhauser et al., 1998). In many cases, the exact nature of the unconformities, particularly the minor ones, remains to be elucidated. In this respect, 467 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/4/4/467/4553195/oterdoom.pdf by guest on 30 September 2021 Oterdoom et al. o o o 54Fahud 56 58 Yibal Salt M A ARABIAN Basin H K IG R H A GULF EM N R F O KA L D Figure 3 A Makarem-1 B E L M T ( A C T I V E ) UK Musalim RO Deep-1 AB GULF OF 24o M Saih Ghaba N. Figure 8 Nihayda O OMAN Figure 5 Qarn M UNITED ARABSaih Rawl Alam A Muscat EMIRATES N Wadi Bani Awf M O Semail Gap HAWASINAU THRUST SHEETS Saih N I Transfer Lekhwair T Fault Hatat A Dhulaima I N S Natih W. Qalhat Fahud W. Natih Figure 3 ARUMA TROUGH (Fiqa Foreland Basin) Fahud Fahud Jabel Yibal H Salt IG Ja'alan o N H 22 Basin EM MARADI Maghoul S. AR AK Makarem-1 FAULT ZONE M Andam-1 K Musalim Al- ROU Deep-1 AB Saih Ghaba N. Ashkharah M Nihayda Figure 8 Qarn Figure 5 Saih Rawl Alam Al Jobah SAUDI ARABIA Mafraq Mabrouk Barik Al Ghubar H G U ) Ghaba Salt S O G Maqtaa IN R T Basin T S U S R H T Zauliyah C ( E N Masirah NT O RA H I E L Figure 13 A T G OM C ID A IR U N D R HI S MASIRAH N Bahja GH B A A O Masirah TRANSFORM o W M L H A Bay 20 D R FAULT U T R S OMAN HIGH I Z N U Zafer-1 I A S Z N F Bahaa O A HUQF T I M Mukhaizna I L South Oman ARABIAN SEA Salt Basin Kulan-1 H NAJD TREND Jalmud IG H Rima H Hawasina Nappes A F Semail Ophiolite S Nimr A Al Noor H Runib (Para-) autochthonous -K N U Ordovician Amdeh Fm. D Amin Irad EASTERN FLANK U Birba H Inqaa G SAWQRAH Basement Marmul Mawhood SIN BA BAY Salt Basin Qaharir IARY RT o Ghudun-1 TE East Oman Ophiolite Complex 18 OBLIQUE OBDUCTION Batain Nappes Dhahaban S. WAGHALD BASIN Huqf Outcrop AYDIM Jazal Oil Field GRABEN Al Halaniyat S Ordovician mafic QARA MOUNTAINS Sills/dikes Marbat 0 100 Fault Al Hota (Coast) Ain Sarif Km Dry Well (Salalah) CRETACEOUS-TERTIARY (Approximate) Well SALALAH BASIN Figure 1: Salt distribution coincides approximately with the area of rifting in the Infracambrian. During the Mid Ordovician, the Ghaba Salt Basin and Saih Hatat experienced extension related to a renewed break-up attempt of eastern Gondwana. 468 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/4/4/467/4553195/oterdoom.pdf by guest on 30 September 2021 Mid Ordovician Rift, Oman CHRONOSTRAT. SUPER- GROUPS LITHOLOGY/ FORMATIONS CYCLES REMARKS RT Arid Continental and Marginal Marine Sediments FARS Taqa Dammam Collision Arabia Eurasia and Andhur Rus Microcontinents 50 TERTIARY HADHRAMAUT UER Carbonate Evaporite Ramp CENOZOIC Simsima Shamar Arada 2nd Thrusting Event Obduction ARUMA Emplacement of Nappes, Foredeep Fiqa Natih Fore Bulge Unconformity WASIA First-order Flooding Anoxic Events 100 Nahr Umr Shu'aiba Kharib Onset Subduction in Neo-Tethys KAHMAH Lekhwair Regional Unconformity Habshan ? Collision Turkish-Arabian Plate CRETACEOUS Salil Collapse North rift shoulder Rayda 150 Hanifa Tuwaiq Break-away India Dhruma SAHTAN Onlap onto E-rift-shoulder MESOZOIC INTRACRATONIC SETTING INTRACRATONIC 200 JURASSIC Mafraq Collision to North of Turkey-Iran Plate reorganization PLATFORMS CARBONATE Jilh EXTENSIONAL COMPRESSIONAL AKHDAR MESOZOIC CYCLE ALPINE CYCLE Sudair Khuff 250 Drifting Neo-Tethys and Rifting Batain Basin Continental Clastics HAUSHI Gharif Al Khlata Glaciation 300 Intracratonic Sag Thermal Doming and Rifting Glacial Erosion 350 HABUR CARBONIFEROUS PERMIAN TRIAS. MISFAR COMPRESSIONAL 400 DEVONIAN PALEOZOIC Sahmah First-order Flooding SILUR. Anoxic Event Sagging CYCLE PALEOZOIC 450 Glaciation L SAFIQ SETTING INTRACRATONIC Hasirah Rift Unconformity M Saih Nihayda Rifting Ghudun E Mabrouk HAIMA MAHATTA EXTENSIONAL ORDOVICIAN Barik Continental to 500 L HUMAID Al Bahsair SUPERGROUP shallow-marine Miqrat Mahwis clastics "Sag" M Amin NIMR Karim "Angudan" Tectonic Event Rifting E ARA Carbonate Evaporite System CAMBRIAN NAFUN 550 Buah Shuram Khufai HUQF ABU MAHARA Glaciation Rifting SUPERGROUP Onset escape tectonism VENDIAN 600 Onset East/West Gondwana continent-continent collision PAN AFRICAN CYCLE PAN 650 MARGIN PLATE ACTIVE PRECAMBRIAN Source STURTIAN Rocks TRANSTENTIONAL COMPRESSIONAL TO Accretion of Island Arcs 850 and Microcontinents Figure 2: Simplified tectono-stratigraphy of Oman interior basins. Time Scales: Harland et al. (1990) for Cenozoic-Silurian; Gradstein and Ogg (1996) for top Ordovician-Cambrian. 469 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/4/4/467/4553195/oterdoom.pdf by guest on 30 September 2021 Oterdoom et al. igneous rocks are important as they provide petrological and geochronological evidence pertinent to the plate-tectonic setting and dating of the extensional structural events with which they are associated (Wilson, 1994). In this paper, we initially review the regional geology and structural history of Oman during the Late Precambrian and Early Paleozoic. The paper then documents the petrology and geochronology of potassium-rich mafic intrusions exposed in the northern Huqf. These volcanics provide evidence for a subtle rift event. We integrate this information with the Early Paleozoic tectonic and sedimentological evolution of Oman and surrounding areas of the Arabian Peninsula. For the Cambrian to base Silurian, the time scale of Gradstein and Ogg (1996) has been applied (Figure 2). For the younger Phanerozoic we use the time scale of Harland et al. (1990). The main change compared to the time scale of Harland et al. (1990) is the shift in time of the base Cambrian from 570 to 545 million years ago (Ma). Presently, the base Cambrian is assigned an absolute age of 543 Ma (Knoll et al., 1995; Brasier et al., 1997).