bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstruction of the original organic richness in weathered Silurian shale outcrops (Murzuq and Kufra basins, southern Libya)
Authors: Lüning Sebastian , Kolonic Sadat , Loydell David K. , Craig Jonathan
Published: October 2021

The early Silurian in North Africa and Arabia was characterised by widespread deposition of organic-rich shales in palaeo-depressions. The unit represents an important hydrocarbon source rock in the region and can be detected easily in well logs because of strong uranium-related natural radiation. In exposures, however, organic matter is commonly heavily oxidised through weathering so that identification of the unit in the field is difficult. Uranium and pyrite framboids appear to be less vulnerable to weathering and may be used to identify intervals of originally organic-rich shales in exposures. Framboids are discrete spheroidal aggregates of pyrite microcrystallites and their size distribution is thought to be controlled by palaeo-depositional bottom-water redox-conditions. Analyses of fresh Silurian organic-rich shales from a core reveal a close correspondence, for the most part, between total organic carbon, total gamma-ray response, uranium content (as determined by spectral gamma-ray) and framboid parameters. Feasibility tests of the concept have been carried out at two exposures in southern Libya and may form the basis for improved Silurian organic-rich shale distribution maps and more precise age models for Silurian organic-rich depositional phases in northern Gondwana.
Aptian faulting in the Haushi-Huqf (Oman) and the tectonic evolution of the southeast Arabian platform-margin
Authors: Montenat Christian , Barrier Pascal , Soudet Henri J.
Published: October 2021

A major upper Aptian unconformity is recorded on the eastern Arabian Platform, between the lower Aptian Qishn limestone and the Albian Nahr Umr marls. The study of this hiatus, in the western homocline of the Haushi-Huqf Uplift (Eastern Central Oman) provides new data about the evolution of the eastern Arabian Platform during middle Cretaceous times. The limestones of the Qishn formed a shoaling sequence, mainly composed of matrix-rich, coarse-grained sediment with small rudistids and algal build-ups, that led to a subemergent environment. A third-order sequence is recognized in the Qishn platform carbonates, which is partitioned into three minor sequences. The Qishn carbonate was subjected to pre-lithification normal faulting. A thick ferrugineous crust (hardground) covered the top surface of the Qishn as well as the faultscarps before they were buried under the Albian Nahr Umr marls. The faults are dominantly NW-trending, SW-facing, normal faults. The significance of the faulting remains hypothetical. The syndiagenetic NW-SE normal faults may correspond to ‘en-echelon’ faults, combined with a sinistral movement of the Haushi-Nafun Fault (HNF). The HNF acted as a left-lateral, strike-slip fault during late Cretaceous, pre-Maastrichtian times. This movement possibly began earlier, during the late Aptian. It could be related to the dynamics of the eastern Arabian margin during the Cretaceous (Masirah transform margin). There are some indications testifying to the activity of the Masirah transform fault during the early-middle Cretaceous. The margin kinematics may be responsible for the reactivation of nearby large faults affecting the platform basement (for instance the HNF). A slight sinistral reactivation of the HNF may have induced the development of the Aptian NW-trending normal faults. Moreover, the occurrence of early Cretaceous strike-slip movements in the Arabian Platform have already been envisaged, at a plate-scale, as a consequence of the South Atlantic extension. On this assumption, the Aptian fault blocks may have resulted from the development of a sinistral transtension along the HNF.
Sedimentary architecture of Upper Ordovician tunnel valleys, Gargaf Arch, Libya: Implications for the genesis of a hydrocarbon reservoir
Authors: Heron Daniel Le , Sutcliffe Owen , Bourgig Khalid , Craig Jonathan , Visentin Claudio , Whittington Robert
Published: October 2021

In the Murzuq Basin, southwest Libya, as elsewhere in North Africa, Upper Ordovician glaciogenic rocks represent an important hydrocarbon reservoir. In this basin, anastomosing, potentially sand-filled palaeovalley networks within the Upper Ordovician succession have been described from seismic data that provide promising prospects for exploration. However, little is known about the origin and architecture of the palaeovalley-fills. On the Gargaf Arch, an outcrop analogue for these structures occurs and is comparable in scale to the valley networks described in the subsurface. This palaeovalley system is 30 km long with two 4 km-wide tributaries, cut into ice-distal glaciomarine mudrocks and diamictites and filled with ice-proximal sandstones and subordinate shales. It was created by subglacial meltwater erosion and glacial loading of a soft substrate during ice sheet advance. The initial stage of valley-fill involved the deposition of coarse-grained sands and conglomeratic ice-proximal, submarine outwash, as localised mass flows. The main stage of fill was characterised by axially (northerly) prograding, underflow-dominated fan lobes deposited in water depths of up to 80 m. A comparison with coeval valley systems in Mauritania, Algeria, Saudi Arabia and Jordan is provided that highlights the variable regional character of palaeovalley-fills and the influence that water-depth had on architecture.
Albian sea-level cycles in Oman: the ‘Rosetta Stone’ approach
Authors: Immenhauser Adrian , Matthews Robley K.
Published: October 2021

The Albian Nahr Umr Formation of Oman (bounded by the Shu’aiba and Natih formations) recorded high-, intermediate, and low-amplitude regressive-transgressive events. In order to reconstruct these sea-level oscillations in a semi-quantitative manner, six measured sections from different bathymetric positions were investigated across a 500-km-transect. Between these sections, discontinuity surfaces, indicative of sea-level fall and subsequent rise, were correlated. In order to asses the underlying causes of sea-level oscillations we compared the amplitudes and frequencies of the Oman events with published amplitudes and frequencies of factors that affect the water volume in the Earth’s oceans, or the shape of oceanic basins. We used the spatial array and field, chemical and petrographic properties of these rocks as a key for unraveling the unknown factors that caused sea-level change. We concluded that sea-level cycles in Oman either reflect unknown processes we do not understand, or changes in continental ice volumes. Thus, we give serious attention to the concept of orbital forcing and glacio-eustasy.

By modeling an orbital forcing sea-level curve for the Albian, and combining it with stratigraphic modeling of sedimentation response to sea-level change, a data-model comparison was possible. The match of our data-model comparison is expectedly not perfect but surprisingly good, and this approach is definitely worth pursuing. One of the main data-model differences is that the model exclusively reflects the orbital-forcing signal, whereas the Albian rock record in Oman is expected to represent an array of climatic, tectonic and local sedimentological factors. Nevertheless, the good data-model match supports the hypothesis that glacio-eustasy was the dominant driver of Albian sea-level change in Oman. This outcome might prove to be controversial in that it suggests a re-evaluation of the Cretaceous as a period of global, continuous climatic warmth, without significant ice shields at the poles.

This interaction has highlighted the many differences between the stratigrapher’s perspective and modeler’s perspective. There are good and bad points to both perspectives, which we point out and attempt to reconcile here.
Petroleum generation and migration in the Mesopotamian Basin and Zagros Fold Belt of Iraq: results from a basin-modeling study
Authors: Pitman Janet K. , Steinshouer Douglas , Lewan Michael D.
Published: October 2021

A regional 3-D total petroleum-system model was developed to evaluate petroleum generation and migration histories in the Mesopotamian Basin and Zagros fold belt in Iraq. The modeling was undertaken in conjunction with Middle East petroleum assessment studies conducted by the USGS. Regional structure maps, isopach and facies maps, and thermal maturity data were used as input to the model. The oil-generation potential of Jurassic source-rocks, the principal known source of the petroleum in Jurassic, Cretaceous, and Tertiary reservoirs in these regions, was modeled using hydrous pyrolysis (Type II-S) kerogen kinetics. Results showed that oil generation in source rocks commenced in the Late Cretaceous in intrashelf basins, peak expulsion took place in the late Miocene and Pliocene when these depocenters had expanded along the Zagros foredeep trend, and generation ended in the Holocene when deposition in the foredeep ceased. The model indicates that, at present, the majority of Jurassic source rocks in Iraq have reached or exceeded peak oil generation and most rocks have completed oil generation and expulsion. Flow-path simulations demonstrate that virtually all oil and gas fields in the Mesopotamian Basin and Zagros fold belt overlie mature Jurassic source rocks (vertical migration dominated) and are situated on, or close to, modeled migration pathways. Fields closest to modeled pathways associated with source rocks in local intrashelf basins were charged earliest from Late Cretaceous through the middle Miocene, and other fields filled later when compression-related traps were being formed. Model results confirm petroleum migration along major, northwest-trending folds and faults, and oil migration loss at the surface.
Arabian Orbital Stratigraphy: Periodic Second-Order Sequence Boundaries?
Authors: Al-Husseini Moujahed , Matthews Robley K.
Published: October 2021

A simplified model of orbital-forcing suggests that the Phanerozoic Eon may be represented by 38 periodic second-order depositional sequences (DS2) each lasting about 14.58 million years (my). The DS2s are separated by second-order sequence boundaries (SB2, maximum regression surface) that should be manifested as regional stratigraphic discontinuities (unconformity, disconformity, time hiatus). To test this simple model, the Arabian succession was reviewed to identify candidate regional stratigraphic discontinuities that might be periodic at 14.58 my. Of the 38 predicted SB2s, 34 regional stratigraphic discontinuities were identified within the uncertainty of biostratigraphic-radiometric age dating, or by stratigraphic position. One SB2 could not be positioned in the succession because of ambiguous biostratigraphic dating. One was predicted within a long-lasting hiatus, and another two were predicted within an undifferentiated formation. The four unidentified SB2s reflect on the limitations of the data sample, rather than on the viability of the model.

Because the stratigraphic discontinuities represent age spans with bounding ages that are at best believed to have accuracies of about ± 3.0 my, the model-data correlation was considered inconclusive. The resulting analysis, however, demonstrates that the ages in million years before present (Ma) of interpreted Arabian (and possibly global) sequence stratigraphic surfaces and depositional sequences, as estimated by biostratigraphic-radiometric dating techniques, are highly inaccurate (± 5–10 my). This conclusion suggests that presently used chronostratigraphic correlations across the Arabian Platform should be treated with great caution. The correlation of model SB2s to regional stratigraphic discontinuities, affords an alternative time scale that may eventually assist in the calibration of the biostratigraphic-radiometric time scale. An orbital-forcing time scale has a decided advantage in that it comes with precise third- and fourth-order stratigraphic predictions imbedded as sea-level fluctuations. The next level of testing is whether these orbital-forcing predictions hold up to precise correlation to stratigraphy.
Biostratigraphy of the Lower Palaeozoic Haima Supergroup, Oman; its application in sequence stratigraphy and hydrocarbon exploration
Authors: Molyneux Stewart , Osterloff Peter , Penney Randall , Spaak Pieter
Published: October 2021

The siliciclastic Haima Supergroup (Cambrian-Silurian) on the west flank of Al Ghabah Salt Basin in Oman is currently a target for gas exploration following the discovery of significant gas reserves. An understanding of stratigraphical and facies relationships within the Haima is crucial for their exploration and exploitation, and biostratigraphy is one of the more powerful and cost-effective tools that can be deployed to aid such understanding. The biostratigraphy of the Haima Supergroup is based primarily on palynomorphs. The pre-existing biozonation, comprising conventional interval zones, is of low resolution and incorporates misconceptions over the ranges of key species. The work reported here explicitly considered the biostratigraphy of the Haima Supergroup in the context of genetic sequence stratigraphy. It shows that each of the postulated marine-flooding events in the Haima Supergroup is characterised by a unique assemblage of marine palynomorphs. Intervening strata are characterised by low-diversity and sometimes sparse marine palynomorph assemblages, often comprising only sphaeromorph acritarchs, accompanied by terrestrial cryptospores. These low-diversity assemblages indicate proximal-marine to non-marine conditions, consistent with progradation following each marine flood. The sandy prograding deposits in the Haima Supergroup form reservoirs, which are sealed by the shales and mudstones deposited by succeeding marine-flooding events. Lateral changes in marine assemblages indicate onshore-offshore relationships, and have contributed towards mapping the extent of each marine-flooding event, critical for evaluation of the potential areal extent of seals. The result is improved biostratigraphical resolution, which enables more precise correlation between wells, and which has contributed to more detailed palaeogeographical maps and to a better assessment of the distribution of reservoir-seal pairs.
Mixed Late Permian floras and related palaeoenvironments in the Khuff Formation of central Saudi Arabia
Authors: Berthelin Martine , Broutin Jean , Vaslet Denis , Le Nindre Yves-Michel , Halawani Mohammed
Published: October 2021

In the outcrops of central Saudi Arabia, Permian flora have been recovered from the Unayzah Formation and the Midhnab Member of the Khuff Formation. The Unayzah Flora is found in the Unayzah Formation (below the Khuff Formation), and it is a true Cathaysian-Euramerican mixed palaeoflora with a probable age of Middle Permian (either Roadian or/and Wordian). The Unayzah Flora would therefore be coeval with the Gharif Flora from the Al Huqf area of Oman (uppermost Gharif Formation). The Midhnab Flora is found in the continental Midhnab Member (subunit 4) of the Khuff Formation. It is a mixed Late Permian flora related to the Gondwanan, Euramerican and Cathaysian realms. New associations of the Midhnab Flora were discovered at Jal Khartam, Jal al Watah and Wadi al Batan in the Qasim area of central Saudi Arabia. The new Midhnab Flora are systematically described here for the first time. The combination of palaeobotanical and sedimentological data led to the characterisation and organisation of the various palaeoenvironments in which each palaeofloral association was growing. Comparison between the Permian flora of Saudi Arabia, Oman, Anatolia (Turkey) and surrounding realms provides the means for reconstructing a more complete palaeogeographic setting for the Arabian Plate in a global palaeobiogeography.
First record of Permian conodont“jinogondolella”cf.altaduensisfrom the Midhnab Member, Khuff Formation, Saudi Arabia
Authors: Nicora Alda , Vaslet Denis , Le Nindre Yves-Michel
Published: October 2021

A single specimen of conodont is described for the first time from outcrops of the Khuff Formation in central Saudi Arabia. The specimen was recovered from 22 samples that were located in the maximum flooding intervals of the Khuff Formation and specifically processed for conodont research. The sample originated from the maximum flooding interval located at the lower part of the Midhnab Member of the Khuff Formation, at Jabal al Murayrah in the Ad Darma’ quadrangle. The conodont occurs in reworked lithoclastic and bioclastic calcarenites, secondary sparitized, as a single broken and corroded specimen, which belongs to the genus Mesogondolella (Jinogondolella) and is tentatively conferred to the species “Jinogondolella” cf. altaduensis. The conodont is associated with broken pieces of fauna including bivalves, gastropods, echinoids, brachiopods and bryozoans, as well as foraminifers and dasycladacean algae. This genus is rarely encountered in the open-marine deposits of the Tethyan platforms, where it appeared preferentially in semi-restrictive (saline) basins. A Late Capitanian age is interpreted for some species of the genus Jinogondolella in America (Texas), China and Oman, but this age interpretation is not firmly established for the Midhnab Member of the Khuff Formation. Also due to the reworked nature of the horizon that yielded this condont, the specimen is not considered to be age-indicative.
New records and new taxa of Permian brachiopods from the Khuff Formation, Midhnab Member, central Saudi Arabia
Authors: Angiolini Lucia , Vaslet Denis , Le Nindre Yves-Michel , Zarbo Miriam
Published: October 2021

Brachiopods are described for the first time from outcrops of the lower part of the Midhnab Member of the Khuff Formation in central Saudi Arabia. The very rare fauna discovered includes Kotlaia sp. ind. of the order Orthida and Omanilasma husseinii n. gen. n. sp. of the order Terebratulida. Besides this new taxon, another new species Omanilasma desertica n. gen. n. sp. from the Khuff Formation of Interior Oman is here erected. The brachiopods were collected from an open-marine horizon and are associated with nautiloids, bactritids, bivalves, foraminifers, algae, and ostracods. A probable Late Permian age is assigned to the lower part of the Midhnab Member based on foraminifers. The brachiopods are compared to similar faunas from the Middle Permian Khuff Formation of Interior Oman, Amb Formation of Salt Range (Pakistan) and Rat Buri Limestone of Southeast Thailand.
Review of Middle East Paleozoic plate tectonics
Authors: Ruban Dmitry A. , Al-Husseini Moujahed I. , Iwasaki Yumiko
Published: October 2021

The Paleozoic Middle East terranes, neighboring the present-day Arabian and Levant plates, are shown by most authors to consist of ten major tectonic units: (1 and 2) the Helmand and Farah terranes of Afghanistan, southwest Pakistan and southeast Turkmenistan; (3 to 6) the Alborz, Central Iran (Lut, Yazd and Tabas) and Sanandaj-Sirjan terranes of Iran, and Northwest Iran (possibly extending into eastern Turkey); (7 and 8) the Pontides and Taurides terranes of Turkey; and (9 and 10) the Greater and Lesser Caucasus terranes between the Caspian and Black seas (Armenia, Azerbaijan, Georgia and southwest Russia). Published plate-tectonic reconstructions indicate that all ten terranes may have broken off from either: (1) the Gondwana Supercontinent in the mid-Silurian as part of the Hun Superterrane; or (2) the Pangea Supercontinent during the mid-Permian - Triassic as part of the Cimmeria Superterrane. To the north of Gondwana and Pangea, three successively younger Tethyan oceans evolved: (1) Proto-Tethys (Cambrian - Devonian); (2) Paleo-Tethys (mid-Silurian - Mesozoic); and (3) Neo-Tethys (mid-Permian - Cenozoic).

Two regional Paleozoic unconformities in the Arabian Plate are generally linked to major regional-scale structural events, and commonly correlated to the Caledonian and Hercynian orogenies. These orogenies took place many thousands of kilometers away from the Arabian Plate and are considered unlikely causes for these unconformities. Instead, the breakaway of the Hun and Cimmeria superterranes are considered as alternative near-field tectonic sources. The older unconformity (middle Paleozoic event), represented by a mid-Silurian to Middle Devonian hiatus in North Arabia (Iraq and Syria), reflects an episode of epeirogenic uplift, which might be related to the mid-Silurian rift of the Hun Superterrane. The younger mid-Carboniferous Arabia-wide angular unconformity involved compressional faulting and epeirogenic uplift, and might be related to the earliest phase of subduction by the Paleo-Tethyan crust beneath Cimmeria (Sanandaj-Sirjan and nearby regions) before it broke off. Based on our review and regional considerations, we assign the Helmand, Farah, Central Iran, Alborz, Sanandaj-Sirjan, Northwest Iran, Lesser Caucasus, Taurides and Pontides to Cimmeria, whereas the Greater Caucasus is considered Hunic.
Early Silurian (Llandovery) graptolites from central Saudi Arabia: First documented record of Telychian faunas from the Arabian Peninsula
Authors: Jan Zalasiewicz , Mark Williams , Merrell Miller , Alex Page , Edward Blackett
Published: October 2021

Graptolites from three shallow core holes penetrating lower Silurian strata in central Saudi Arabia identify rocks of mid Aeronian and early Telychian age. The graptolites comprise Campograptus undulatus?, C. lobiferus?, Lituigraptus convolutus, Metaclimacograptus bohemicus, Neolagarograptus rickardsi, Normalograptus? aff. scalaris, cf. Paradiversograptuscapillaris,Petalolithusminor,P.praecursor,P.ovatoelongatus?, Pristiograptus regularis sl, Pseudorthograptus insectiformis, Pseudoretiolites perlatus? and Torquigraptus? decipiens, which identify the mid Aeronian convolutus Biozone, and Monograptus bjerreskovae, Monograptus ex gr. marri, Paradiversograptus runcinatus?, Petalolithus cf. altissimus, Pristiograptus renaudi, Stimulograptus becki and S. halli?, which indicate the early Telychian guerichi Biozone. The graptolite faunas are generally of low diversity, with most levels yielding between one and three species, occasionally rising to as many as seven species. The palaeogeography of the depositional basin, coupled with the low diversity and the abundance of Pristiograptus and Normalograptus species, suggests a marine-shelf setting. This is also indicated by the common occurrence of benthic shelly fossils, including articulated bivalves and gastropods. In general, the graptolite faunas are of much lower diversity than contemporaneous marine assemblages from the British Isles or the Czech Republic, and probably represent a graptolite biotope of “cratonic invaders.” Graptolites are very well preserved, displaying detail of fusellar banding (growth increments) and perhaps ultrastructure.
Design of a P-wave seismic vibrator with advanced performance
Authors: Wei Zhouhong
Published: October 2021

For optimal seismic imaging, the vibroseis method requires the vibrator to generate synchronous, repeatable sweeps over a broad frequency range and output the ground-force energy with minimum harmonic distortion. This requires re-evaluating each element of the vibrator system to ensure that it contributes to the success of the method. Key factors that cause the vibrator to suffer from severe harmonic distortion are fluctuations in the hydraulic power supply pressure, flexing of the baseplate, coupling or loading between the baseplate and the ground, nonlinear servo-valve flow-pressure characteristics, and servo-valve characteristics near null. This paper examines these factors and describes the design of a new P-wave vibrator by ION (previously I-O) to improve seismic resolution. Experimental results demonstrate that the newly designed vibrator dramatically reduces harmonic distortion in the ground-force signal under various coupling conditions, particularly on hard and uneven ground. With the high-frequency controller and Pelton DR valve, a broad-band sweep frequency is achieved. Cavitations in the supply pressure, a long-standing problem in vibrator mechanics, are almost completely eliminated.
Outcrop sedimentology of the Natih Formation, northern Oman: A field guide to selected outcrops in the Adam Foothills and Al Jabal al Akhdar areas
Authors: Homewood Peter , Razin Philippe , Grélaud Carine , Droste Henk , Vahrenkamp Volker , Mettraux Monique , Mattner Joerg
Published: October 2021

This field guide describes eleven outcrops of the Natih Formation in the Al Jabal al Akhdar-Jabal Shams and Adam Foothills areas, not far from Nizwa, at the foot of the Oman Mountains. The outcrops have been chosen for their accessibility, as well as for the fairly complete picture of the Natih Formation, which they piece together. To visit all eleven outcrops requires several days and the use of 4-wheel-drive vehicles, but the locations offer no serious physical difficulty, nor long hiking, to gain access.

The outcrop descriptions follow in stratigraphic order from the lower to the upper Natih members, roving back-and-forth across the outcrop area. Much of the detailed account of the sedimentology and stratigraphy of the Natih that has been used as the basis of this field guide, has been given previously by van Buchem et al. (1996, 2002), Grélaud (2005), Schwab et al. (2005) and Grélaud et al. (2006). The observations and interpretations given here come in part from those studies, but this paper is also largely the product of a subsequent project that was carried out for the Fahud Studies Team of Petroleum Development Oman (PDO), to provide detailed sedimentology and high-resolution sequence stratigraphy of the Natih Formation for further development of the Fahud field (Homewood et al. 2006). In this respect, this field guide is not so much intended to be an original contribution in terms of the science concerning the Natih Formation. The intent is to provide the ways-and-means for all to gain a first-hand personal understanding of the rocks we have enjoyed working on.

Following the outcrop descriptions, a general section provides a discussion on facies and facies associations in terms of the constraints of sequence stratigraphy, sea-level change and clay influx on the carbonate factory. With the incorporation of limited subsurface seismic and well data, geobodies and depositional assemblages, the three-dimensional objects that form the stratigraphic packages at outcrop and seismic scales, respectively, are also discussed. Facies are thus interpreted not only in terms of depositional environments, but are also placed within both geometrical (geobody, depositional assemblage) and sequence-stratigraphic frameworks.

In the conclusion, it is argued that a deeper understanding of the Natih Formation has been gained by comparison of outcrop data with subsurface data, and by contrast with modern analogs. The detail required to apply what was learned from outcrop to the nearby subsurface, in a practical manner (but also properly to reconstruct the successive Natih scenarios), requires building several facies models. This is in contrast to giving a single composite picture of Natih facies distribution in space and time, under one single facies model.
Facies in the Unayzah Formation and the Basal Khuff Clastics in subsurface, northern Kuwait
Authors: Tanoli Saifullah Khan , Husain Riyasat , Sajer Abdul Aziz
Published: October 2021

This is the first reporting of the Unayzah Formation from a northern Kuwait deep well where a 304 ft of core was cut in the upper part of the formation. The core consists of about 202 ft of the Unayzah Formation, 74 ft of the Basal Khuff Clastics and 28 ft of the Khuff Formation. Within the Unayzah Formation six major lithofacies were interpreted: (1) high-angle cross-bedded sandstone; (2) fine-grained sandstone; (3) normally graded coarse pebbly sandstone; (4) medium- to fine-grained sandstone and siltstone; (5) red mudstone and siltstone; and (6) black shale. In the Basal Khuff Clastics, four lithofacies were recognised: (1) fine- to medium-grained clean sandstone; (2) muddy bioturbated sandstone and siltstone; (3) dark grey to black carbonaceous shale with sand interbeds; and (4) interbedded sandstone, siltstone and dolomite. These lithofacies can be subdivided into four broad palaeoenvironments; ?eolian, braided fluvial, flood plain, and coastal plain. The possible eolian facies are represented by high-angle, cross-bedded sandstones of likely dune affinity. Braided fluvial facies consist of pebbly sandstones, which may grade normally to fine-grained sandstone and siltstone. Flood-plain environments are interpreted for the red mudstone, shale, and siltstone, which consist of prominent root casts and other subaerial exposure features. This facies is prominently repeated three times within the cored zone. Coastal plain environments are represented by tidal channels consisting of fine-grained and clean sandstone, crevasse splay and interfluve sediments consisting of bioturbated sandstone, siltstone and shale and by dark grey to black shale of coastal marsh in origin.

The core did not cover the lower contact of the Unayzah Formation. The upper contact of the formation with the Basal Khuff Clastics is placed at the top of the last oxidised red zone. Due to the limited palynofloral information, the age of the cored interval is not definitive but most likely is of Kazanian to Tatarian (Wordian to mid-Wuchiapingian). The Basal Khuff Clastics and the overlying Khuff Formation is equivalent to the OSPZ6 biozone and the Unayzah Formation could be in part equivalent to the OSPZ5 biozone. The sediments belonging to the Basal Khuff Clastics mark the onset of a major transgression that developed into a platform where carbonates of the overlying Khuff Formation were deposited.
Structural and tectonic evolution of the Jabal Sumeini – Al Ain – Buraimi region, northern Oman and eastern United Arab Emirates
Authors: Searle Michael P. , Ali Mohammed Y.
Published: October 2021

Four main Late Cretaceous and Tertiary phases of crustal shortening and thrust-related deformation are recognised in the northern Oman Mountains, each phase ending with a regional unconformity throughout the Oman Mountains and the UAE foreland. The earliest is the major thrust emplacement of the Semail Ophiolite, and underlying Haybi, Hawasina and Sumeini duplexes from NE to SW onto the depressed northeastern continental margin of the Arabian Plate during the Cenomanian to Campanian-early Maastrichtian (D1). A prominent widespread unconformity that places Maastrichtian Qahlah Formation laterite, sandstones and conglomerates and Simsima Formation rudist - Acteonellid gastropod limestones over all underlying allochthonous units is recognised throughout the Oman Mountains. SW-verging folds and thrusts in Triassic to Cretaceous carbonate slope facies rocks exposed in Jabal Sumeini (Sumeini Group and Hamrat Duru Group) have been emplaced over uppermost Cretaceous Juweiza Formation conglomerates at the highest level of the Aruma foreland basin. These Sumeini D1 structures are abruptly truncated by an unconformity, above which are Middle Maastrichtian beds showing up to 95% ‘death assemblage’ rudists and gastropods just below the Cretaceous – Tertiary boundary (top of Simsima Formation). A second deformation event (D2) affected the Simsima Formation and underlying Sumeini Group, Hamrat Duru complex and Semail Ophiolite rocks. This phase shows gentle folding about NW-SE fold axes (e.g. Jabal Rawdah), along a similar trend to the Late Cretaceous D1 event. This trend is also parallel to a regional set of NW-SE aligned fractures in the UAE foreland. A major angular unconformity occurs beneath the Upper Palaeocene – Eocene shallow-marine limestones (Umm Er Radhuma, Rus and Dammam formations). Many foreland jabals in eastern Abu Dhabi (Jabals Qatar, Malaqet, Mundasa) show gentle post-Eocene folding formed during the third stage of crustal shortening (D3). The large pericline of Jabal Hafit is a double-plunging, east-verging box fold that formed after deposition of the Oligocene Asmari Formation limestones and Miocene Fars Formation gypsum and clays, the youngest beds affected by the fold. This Late Miocene – Pliocene phase of crustal shortening (D4) is the youngest phase of deformation in the eastern Al Ain-Buraimi region.
The Wadi ad Dawasir “delta”, central Saudi Arabia: A relative sea-level fall of Early Bathonian age
Authors: Énay Raymond , Mangold Charles , Alméras Yves , Hughes Geraint Wyn ap Gwilym
Published: October 2021

The fluvial and deltaic deposits formerly described as the Wadi ad Dawasir “delta” have been reinterpreted on the basis of a new examination of biostratigraphic data, notably ammonites and brachiopods studied by the authors and nautilids studied by the late H. Tintant (the term “delta” as used in other documents is shown here in quotes because of insufficient evidence to confirm it as a true delta). Direct dating of the fluvial and deltaic deposits is not possible in the absence of age-indicative fossils, but the entire “delta” complex can be placed in the Lower Bathonian on the basis of Bathonian ammonite and brachiopod faunas found in underlying strata, and a Lower Bathonian nautilid found in the uppermost proximal beds. An Early Bathonian age of the “delta” revises the Middle Callovian age assumed by previous authors based on their admittedly lithostratigraphic correlation with marine strata of the Dhruma Formation. The Early Bathonian age is consistent with the alternative interpretation, which correlates the “delta” with the discontinuity in the marine sequence between units D5 and D6 of the Dhruma Formation, with a stratigraphic gap of Lower (in part) and Middle Bathonian. The nautilids and brachiopods from above and “apparently at the front” of the “delta” together with the ammonites, nautilids, brachiopods and calcareous nannoplankton from units D6 and D7, indicate a complete sequence from the Upper Bathonian (unit D6) to Upper Callovian (units T2 and T3 of the Tuwaiq Mountain Limestone) with transgressive overlap of the “delta” during Middle and Late Callovian. The Wadi ad Dawasir “delta” is here interpreted as resulting from a limited relative sea-level fall, causing progradation of a shelf deltaic wedge over the downlap surface associated with the D5–D6 discontinuity. Similar deltaic or/and paralic deposits have been described in the Lower Bathonian of northern Sinai, presumably of the same age, Negev and in the Bathonian of southern Tunisia, which indicate an event of wide extent (eustatic, climatic or tectonic) along the northern Gondwanan margin.
Evolution of fractures in a highly dynamic thermal, hydraulic, and mechanical system - (II) Remote sensing fracture analysis, Jabal Shams, Oman Mountains
Authors: Holland Marc , Saxena Nishank , Urai Janos L.
Published: October 2021

Extensive, very high quality outcrops on the southern flank of Jabal Shams, Oman Mountains, expose the complex fracture and fault network of an exhumed high-pressure cell. Veins are filled with white calcite in grey host rock, allowing 0.7 meter-resolution mapping based on satellite image interpretation, followed by ground-truthing with detailed field observation in selected areas. From Quickbird and Landsat data, a model was developed using interpreted 562 faults and 145,000 fractures in an area of 31 km2; the area of a typical 3-D seismic survey but with one hundred times higher resolution. Four generations of veins, with strikes of 130°, 000°, 090° and 045°, are overprinted by normal faults with wide cemented damage zones and offsets up to 500 m. Veins are generally a few 10s of meters long, and lack signs of strong mechanical interactions such as curving or abutting. This suggests a restoration of the bulk strength during the formation of the joints, and an anticlockwise rotation of permeability anisotropy during progressive fracturing. The spatial density of all cemented fractures is rather homogenous, but the spatial density within individual joint sets is heterogeneous, suggesting patchy fracturing during the different evolutionary stages. A weak mechanical anisotropy, caused by the veins, affects the nucleation and evolution of the anastomosing normal fault system that overprints the cemented joints.
Refinements in biostratigraphy, chronostratigraphy, and paleogeography of the Mississippian (Lower Carboniferous) Mobarak Formation, Alborz Mountains, Iran
Authors: Brenckle Paul L. , Gaetani Maurizio , Angiolini Lucia , Bahrammanesh Maryamnaz
Published: October 2021

Detailed sampling of limestones from the Mobarak Formation at the Abrendan and Abnak measured sections in the eastern and central Alborz Mountains, northern Iran, yielded a diverse assemblage of Tournaisian – Lower Visean (Mississippian/Lower Carboniferous) calcareous microfossils (foraminifers, algae, incertae sedis). The Abrendan locality contains Tournaisian foraminifers in the upper part of the formation that correlate to the Ivorian and upper Courceyan – lower Chadian substages of western Europe and the Kosvinsky Horizon of the Russian Platform. Brachiopods confirm a Tournaisian age for the lower part of the Mobarak, which lacks age-diagnostic calcareous microfossils. Lower Visean foraminifers at Abnak provide good correlation to the western European Moliniacian and Arundian substages and the Russian Bobrikovsky Horizon. Synthesis of foraminiferal data from this and other published reports indicates that the top of the Mobarak Formation becomes increasingly older across the Alborz to the southeast, caused most likely by Pennsylvanian (Upper Carboniferous) exposure and erosion in the south followed by a latest Pennsylvanian – Early Permian transgression from the north. The microbiota at both sections and the macrofossils at Abrendan show close affinity to the warm-water Paleo-Tethyan Ocean, seemingly contradicting Early Mississippian paleomagnetic reconstructions placing the Alborz region at 45–50° South latitude. The discrepancy is not resolvable at this time, but the answer may lie in the circulation of Paleo-Tethyan currents to the south along the Gondwanan shelf, rather than to repositioning the Alborz region to the northern side of the Paleo-Tethyan Ocean.
Petroleum system analysis of the Mishrif reservoir in the Ratawi, Zubair, North and South Rumaila oil fields, southern Iraq
Authors: Al-Ameri Thamer K. , Al-Khafaji Amer Jassim , Zumberge John
Published: October 2021

Five oil samples reservoired in the Cretaceous Mishrif Formation from the Ratawi, Zubair, Rumaila North and Rumaila South fields have been analysed using Gas Chromatography – Mass Spectroscopy (GC-MS). In addition, fifteen core samples from the Mishrif Formation and 81 core samples from the Lower Cretaceous and Upper Jurassic have been subjected to source rock analysis and palynological and petrographic description. These observations have been integrated with electric wireline log response. The reservoirs of the Mishrif Formation show measured porosities up to 28% and the oils are interpreted as being sourced from: (1) Type II carbonate rocks interbedded with shales and deposited in a reducing marine environment with low salinity based on biomarkers and isotopic analysis; (2) Upper Jurassic to Lower Cretaceous age based on sterane ratios, analysis of isoprenoids and isotopes, and biomarkers, and (3) Thermally mature source rocks, based on the biomarker analysis.

The geochemical analysis suggests that the Mishrif oils may have been sourced from the Upper Jurassic Najma or Sargelu formations or the Lower Cretaceous Sulaiy Formation. Visual kerogen assessment and source rock analysis show the Sulaiy Formation to be a good quality source rock with high total organic carbon (up to 8 wt% TOC) and rich in amorphogen. The Lower Cretaceous source rocks were deposited in a suboxic-anoxic basin and show good hydrogen indices. They are buried at depths in excess of 5,000 m and are likely to have charged Mishrif reservoirs during the Miocene. The migration from the source rock is likely to be largely vertical and possibly along faults before reaching the vuggy, highly permeable reservoirs of the Mishrif Formation. Structural traps in the Mishrif Formation reservoir are likely to have formed in the Late Cretaceous.
Calcimicrobe tubules in uppermost Jurassic Arab-A carbonates of Saudi Arabia
Authors: Wyn ap Gwilym Hughes G.
Published: October 2021

Uppermost Jurassic carbonates from the Arab-A Member of the Arab Formation in the subsurface of eastern Saudi Arabia reveal hollow, intertwined, locally bifurcating, microtubules consisting of a chain-like, uniserial series of inaperturate, stacked, concavo-convex crescentic chambers tentatively assigned to Gahkumella sp. Previously confined to the Oxfordian of North America, and possibly the Lower Cretaceous of Oman, this is believed to be the first observation of such forms in uppermost Jurassic carbonates. The carbonates consist of a lower, transgressive, ooid-foraminiferal lithofacies and an upper, regressive, stromatolite-ostracod lithofacies of which the microtubules are developed in the latter. Comparison of these structures with fossil and Recent cyanobacterial microborings and Oxfordian calcimicrobial tube-like forms suggests probable cyanobacterial affinity. Despite their very limited stratigraphic extent, they may contribute to improving mouldic microporosity of the Arab-A carbonate reservoir.
Calibrating Mid-Permian to Early Triassic Khuff sequences with orbital clocks
Authors: Al-Husseini Moujahed I. , Matthews Robley K.
Published: October 2021

The Middle East Geologic Time Scale (ME GTS) seeks to document and age-calibrate Arabian Plate transgressive-regressive (T-R) depositional sequences using: (1) Geological Time Scale of the International Commission on Stratigraphy (GTS), and (2) Arabian Orbital Stratigraphy time scale (AROS). AROS is based on an orbital-forcing glacio-eustatic model that offers three orbital clocks to date T-R sequences: (1) Stratons @ ca. 405 Ky; (2) Dozons @ ca. 4.86 My (12 stratons); and Orbitons @ ca. 14.58 My (36 stratons, three dozons). The Earth today is in Orbiton 0, which started ca. 1.5 Ma (SB 0); the ages of lower boundaries of orbitons can be estimated with the formula SB n = n × 14.58 + 1.5 Ma. This scheme was used to calibrate the Arabian Plate’s Mid-Permian to Early Triassic Khuff sequences, which contain one of the largest gas-bearing carbonate reservoirs in the World.

The Khuff and equivalent formations have been interpreted by several authors in terms of six long-period sequences in outcrop belts and subsurface sections (Khuff sequences KS6 to KS1 in ascending order). Their type sections are briefly reviewed with emphasis on their boundaries, higher-order architecture and stage assignments. The age calibration starts at the basal Khuff Sequence Boundary (Khuff SB, Sub-Khuff Unconformity) defined in a type section in Al Huqf outcrop in Oman. Above the Khuff SB (ca. 268.9 Ma) the type sections of the oldest Khuff sequences KS6 (ca. 268.9–264.0 Ma) and KS5 (ca. 264.0–259.1 Ma) are defined in Oman and interpreted to each consist of twelve subsequences (stratons) with the predicted architecture of two consecutive dozons. By biostratigraphy they span the Mid-Permian (Guadalupian Epoch), Wordian and Capitanian stages.

Type-Sequence KS4 (ca. 259.1–254.2 Ma) is defined in Iran and corresponds to the Wuchiapingian Stage. The Iranian type-Khuff Sequence KS3 (ca. 254.2–249.4 Ma) contains nine subsequences (stratons) grouped between two major exposure surfaces. By correlation to the Changhsingian Stage and Permian/Triassic Boundary (PTrB) type section in South China, it is interpreted as a dozon with three missing stratons. Khuff Sequence KS2 (ca. 249.4–247.8 Ma) contains the PTrB with an orbital age of ca. 249.0 Ma, compared to 251.0 ± 0.4 in GTS and 249.0–253.0 Ma by radiometric dating in its type section. Khuff sequences KS2 and KS1 contain 13 subsequences (stratons) between ca. 249.4–244.1 Ma spanning latest Permian and Early Triassic. The boundary of the Khuff with the overlying Sudair Formation, Sudair Sequence Boundary, is defined in Borehole SHD-1 (Central Saudi Arabia) and calibrated at ca. 244.1 Ma falling near the age of the Early/Mid-Triassic Boundary in GTS. The enclosed Chart shows a work-in-progress correlation of the six Khuff sequences across the Arabian Plate.
Structural architecture of a thin-skinned imbricate fan: Evidence from Mesozoic deepwater sediments in the Jabal Wahrah area of the central Oman Mountains
Authors: Cooper David J.W.
Published: October 2021

In the central Oman Mountains, Mesozoic deepwater off-margin sediments of the Hawasina Complex were emplaced from the northeast onto the Oman continental margin during the Late Cretaceous obduction of the Semail Ophiolite. Detailed field mapping and structural investigation have shown that, in the area studied, margin-ward detachment of continental rise sediments (Hamrat Duru Group) created two major thrust units in the face of the advancing ophiolite and subduction zone wedge of sediments from more distal parts of the Hawasina Ocean.

The upper unit is preserved in jabals Wahrah and Hurah as a wedge-shaped sheet, restoring to at least 60 km perpendicular to the line of emplacement but only about 500 m thick at its maximum. Its thinner leading edge (Jabal Wahrah) comprises a classic thin-skinned imbricate fan which is divided into five laterally continuous structural zones with finer-grained structures that are influenced by local stratigraphical variations in its Early Jurassic to Early Cretaceous section. The rear part of the thrust sheet (Jabal Hurah) behaved more rigidly, reflecting a thicker and more competent sedimentary sequence spanning the Early Triassic to ?mid Cretaceous. With the exception of a major duplex along its trailing edge, significant internal thrusts are rare and shortening is mostly accommodated by asymmetrical folding. This wedge was emplaced over the trailing edge of a lower thrust unit (Hammat Shulayshil), which formed through forward propagation of the Hawasina sole thrust and which was also deformed primarily through SW-directed folding with limited internal imbrication even after a translation during emplacement of at least 150 km.

A second stage of thrusting after the main emplacement phase is linked to renewed locking of the lowest thrust planes in the imbricated Hawasina sediment wedge ahead of the Semail Ophiolite and late-stage motion transferring to higher structural levels closer to the ophiolite as movement of the latter gradually ceased. This resulted in out-of-sequence re-thrusting of higher thrust sheets over lower sheets along existing thrust planes. This was accompanied by the local rotation of parts of the Jabal Wahrah imbricate fan as an effect of the heterogeneous composition of the overlying thrust units, in particular the out-of-sequence emplacement of a mountain-sized thrust block of intra-oceanic reef limestone (Jabal Kawr) over the Hamrat Duru Group immediately to the east.

A third phase of compression then folded and locally thrusted this re-thrust stack. The timing of this phase is not well constrained. It may represent the final effects of the Campanian emplacement; alternatively it may be tentatively linked to limited lateral motion (gravity sliding) of the thrust stack along the flanks of the Al Jabal al-Akhdar anticline during its main growth phase in the Oligocene.