Iftikhar Ahmed Abbasi

Tectonic Evolution of the Oman Mountains

The Oman Mountains contain one of the worlds best- exposed and best-understood fold–thrust belts and the largest, best-exposed and most intensively studied ophiolite complex on Earth. This volume presents new international research from authors currently active in the field focusing on the geology of the Oman Mountains, the foreland region, the carbonate platforms of Northern and Central Oman and the underlying basement complex. In addition there is a particular focus on geoconservation in the region. The volume is divided into three main sections that discuss the tectonics of the Arabian plate using insights from geophysics, petrology, structural geology, geochronology and palaeontology; the petrology and geochemistry of the Oman Ophiolite and the sedimentary and hydrocarbon systems of Oman, drawing on the geophysics, structure and sedimentology of these systems. The volume is enhanced by numerous colour images provided courtesy of Petroleum Development Oman.

Late Cretaceous Conglomerates of the Qahlah Formation, north Oman

Abstract Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian–Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusia-bearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.

Tectonic evolution of the Oman mountains: An introduction

It is now more than 20 years since the GeologicalSociety published The Geology and Tectonics ofthe Oman Region (Robertson et al. 1990) as oneof its early special publications. That volume, the‘blue book’ as it became fondly known to multiplegenerations of undergraduates, has been a majorreference on the geology of Oman for many whowork in the region. This present volume, moremodest in its size compared to its illustrious prede-cessor, is the fruit of a conference on The Geologyof the Arabian Plate and the Oman Mountainsheld in January 2012 at Sultan Qaboos Universityin Muscat, organized by Professor Sobhi Nasirwith colleagues from Sultan Qaboos University,the Oman Government and the Geological Societyof Oman. Since the first comprehensive study ofthe geology of the Oman Mountains during thelate 1960s and early 1970s by Ken Glennie and histeam from Shell, the Oman Mountains have beenknown to contain some of the most spectacularand best-exposed geology not only in the MiddleEast but across the world. A summary of the geo-logy and the lithostratigraphy is given in Figure 1.The publications of Glennie et al. (1973, 1974),building on many earlier Shell geologists’ internalreports (notably D. M. Morton, R. H. Tschopp,H. H. Wilson, B. M. Reinhardt and M. W. Hughes-Clarke) set out the major stratigraphic frameworkfor the whole area, defined the major structuresand critically interpreted the Semail Ophiolite as athrust sheet of oceanic crust and upper mantleemplaced onto the previously passive continentalmargin of Arabia. Since the Glennie et al. (1974)memoir was published, oil companies have carriedout increasingly more intensive work comparingwell sections in the interior with the Permian–Mesozoic shelf carbonates so beautifully exposedalong numerous wadis cutting through the JebelAl-Akhdar and Saih Hatat massifs.During the late 1970s and 1980s two majorresearchteamsfromtheUSGS(ledbyBobColemanand Cliff Hopson) and the Open University, UK(led by Ian Gass, John Smewing and Steve Lip-pard) conducted detailed geological surveys acrossthe ophiolite in the Muscat–Ibra transect (USGS)and northern ophiolite (OU), respectively. Theirresults were published in a Special Issue of theJournal of Geophysical Research (volume 86,editors Coleman & Hopson 1981) and the Geologi-cal Society of London Memoir no. 11 (Lippard etal.1986). Major systematic mapping of the OmanMountains as well as the interior, Batain coast andDhofar region has been carried out by the Bureaude Recherches Ge´ologiques et Minieres (BRGM),France, the Geological Survey of Japan and theUniversity of Berne, Switzerland (see for examplePeters et al. (1991)) and the whole UAE part of thenorthern Oman Mountains was recently mapped bythe British Geological Survey (UAE Ministry ofEnergy Petroleum & Mineral Resources 2012).During the last 20 years major research groupsfrom France, Japan, USA and the UK have con-ducted research projects in the country. Detailedfield studies of the Oman Ophiolite have beencombined with geochemical and isotopic studiesto determine the tectonic setting and evolution ofthe Late Cretaceous oceanic crust and upper mantle(Boudier & Juteau 2000). Field-based studies havealso been linked to ocean drilling sites, in particularthe East Pacific rise, to compare the ophiolite toregions of active fast spreading. Key to the obduc-tion–emplacement story are the amphibolite andgreenschist facies rocks in the metamorphic solethat record an inverted metamorphic field gradientalong the base of the ophiolite. The ophiolite hasbeen the source of recent detailed studies involvingthe possible sequestration of CO

Stratigraphic evolution and depositional system of Lower Cretaceous Qishn Formation, Dhofar, Oman

Abstract The Barremian(?)–Aptian Qishn Formation of Dhofar (Oman) is represented by eastward (landward) thinning strata that onlap Marbat palaeohigh basin margin. The formation includes Shabon, Hinna and Hasheer members, in ascending order. The Shabon Member consists of massive and cross-bedded, locally conglomeratic arkose and quartzarenite. The Hinna Member has a lower part of rhythmically arranged bioclastic wackestones/mudstones that grade to fine crystalline dolomudstone and an upper part of cyclic units of nodular, marly, rudistic floatstone/rudstone lithofacies capped by normally grading, intraclastic, bioclastic packstone/grainstone lithofacies. Mudcracks, teepee structures and microbial laminations occur in the lower part. The member terminates with 10-m-thick discoidal orbitolinid- and rudist-bearing marls envisaged as the deepest facies of the formation. The Hasheer Member consists of partly dolomitized strata of bioclastic packstones, grainstones and rudstones. Cross-bedding and erosional surfaces are present. The overall depositional system of the formation evolved from high-energy clastic-dominated, marginal marine environment through tidal carbonate mudflat and lagoonal setting to high-energy carbonate sand shoals. The overall stratigraphic arrangement of the formation suggests a third-order transgressive-regressive system with superimposed fourth- and fifth-order cycles. Shabon and Hinna members represent lowstand to transgressive systems tracts whereas Hasheer Member represents highstand to falling stage systems tracts. Terminal platform-wide exposure resulted in an unconformity at the Qishn–Kharfot contact.

Early Eocene orthophragminids and alveolinids from the Jafnayn Formation, N Oman: significance of Nemkovella stockari Less & Özcan, 2007 in Tethys

The upper member of the Jafnayn Formation in Wadi Rusayl and Al Khoud, Seeb Area in north Oman contains Nemkovella stockari Less & Özcan, 2007, an Early Eocene orthophragminid recorded here for the first time from the Arabian Peninsula. N. stockari, the only orthophragminid identified in Jafnayn Formation, is quite distinct from any other species from Tethys in having spiral and orbitoidiform chambers around the isolepidine embryon developed before the onset of annular chambers. The Oman specimens exhibit equal-sized principal auxiliary chambers and symmetrical spirals and are assigned to N. stockari bejaensis Özcan, Boukhalfa & Scheibner, 2014, an advanced form of the N. stockari lineage. The associated alveolinids, revised in this study, rotaliids and other age-diagnostic foraminiferal taxa in the transgressive basal part of the upper member have enabled us to revise the age as middle Ilerdian (Early Eocene), assignable to SBZ 7/8 and 8; OZ 3/4. Integrating a new record of this species from Arabian Plate margin in Belen, S Turkey, and previous records from north Africa, N. stockari appears to be a diagnostic marker for the Early Eocene along the southern peri-Tethys platforms, facilitating the Tethyan correlation by orthophragminids. The palaeobiogeographic distribution of N. stockari is discussed.

Nature, genesis and industrial properties of the kaolin from Masirah Island, Oman

Abstract Kaolin deposits >10 m thick overlie unconformably a Mesozoic ophiolite sequence at Jabal Humr, Masirah Island, Oman. The clay’s mineralogical and chemical composition, plasticity and moisture content were measured to determine its genesis and suitability for commercial usage. The clayrich raw material contains 76-94% kaolinite and varying amounts of quartz (micro sheets coating kaolinite) and calcite as well as secondary sulfates. The mode of occurrence, an associated shallowmarine iron oolite/pisolite unit, various secondary minerals which can only form in a gossan environment (oxidation zone of a much older sulfide deposit), and minerals such as gypsum that are highly unstable within a laterite, have led to the conclusion that the Jabal Humr kaolinite deposit cannot have the lateritic origin that has been suggested previously. Rather, it must have formed in a coastal marine environment with a subsequent strong geochemical overprint from the underlying gossan environment, after being enveloped by Tertiary carbonates. A high plasticity and its light colour after firing indicate that this material is suitable for industrial use, especially in pottery. Occasional high contents of up to ∼25% extremely fine-grained quartz (sheet-like, <50 nm thick) reduce the need for quartz addition during the processing for ceramic materials; such natural kaolinite-quartz mixtures already produce a suitable blend of materials. The possible occurrence of spalling during or after firing, caused by the sporadic presence of accessory calcite, can be avoided by by further addition of quartz which leads to the formation of calcium silicate.

Mud Volcanoes in an Active Fore-Arc Setting: A Case Study from the Makran Coastal Belt, SW Pakistan

The Makran coastal belt is over 1000 km long stretching from Iran to east of Karachi in Pakistan. A major active subduction zone known as Makran subduction zone defined by the under thrusting of the Arabian plate beneath the Eurasian plate runs parallel to the coastline. The subduction zone is associated with a thick accretionary sedimentary wedge deposited in an active fore-arc basin containing very thick detrital sediments contributed by the accretion of the subducting plate since Late Eocene time. The sediments in the fore-arc basin are fine-grained usually of clay size fraction deposited in highly fluidized conditions trapping methane gas. The fluidized mud diapirically moves upward along weak zones as mud volcanoes due to high sedimentation rates and escaping gas pressure piercing through the overlying sediment layers. The development of mud volcanoes shows a close relationship between the sedimentation rates, gas escape from sediments and tectonic activity. Mud volcanoes are found in abundance both onshore and offshore of the Makran Coast. Most of the onshore mud volcanoes are associated with active fault zones and are believed to be triggered by tectonic activity. Located in the hanging wall of an active subduction zone, the region is seismically highly active and occurrence of major earthquakes exceeding magnitude 7 is a common phenomenon (e.g., Mw = 7.7 2013 Awaran, Mw = 8.2 1945 Makran). The seismic activity of this scale is likely the major triggerer for the emergence of new islands off the Makran coast in the Arabian Sea on regular basis in the past history. The latest of these emerged in 2013 immediately after the Mw = 7.7 Awaran earthquake.