bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Lower Kahmah Group of Oman: the carbonate fill of a marginal shelf basin
Authors: Haan E. A. , Corbin S. G. , Hughes Clarke M. W. , Mabillard J. E. 
Published: April 2008

Abstract
Following the rifting and spreading related to the opening of the Tethys Ocean during the Triassic and Early Jurassic, relaxation and subsidence affected its passive margins. In Iran and Oman, such subsidence of the continental margins gave rise to deeper marine, marginal shelf basins, that initially were filled with pelagic sediments, but were progressively infilled by prograding shallow shelf-derived sediments. In Oman the fill sequence is well displayed for study in surface outcrops in the Oman Mountains as well as in subsurface geological and geophysical data. This paper provides an integrated picture of the geometry and facies distribution of the sediments, which filled this marginal shelf basin. The pelagic facies comprises the Rayda Formation and the basin, therefore, is named the Rayda Basin. The prograding, shelf-derived, fill facies comprises the Salil Formation. Surface-type sections of these two formations are described from outcrops in the Oman Mountains. The last stage of the basin fill is represented by a diversified shallow marine facies, referred to as the Habshan Formation, which is defined in Abu Dhabi. This unit prograded over the entire sag basin and almost levelled the pre-existing basin topography in such a way that overlying deposits hardly reflect the original Rayda Basin outline. The Habshan shoal facies is therefore in part coeval with the Rayda and Salil and exhibits a complex interdigitation with those two formations towards the basin margin. The seismostratigraphic expression of the Habshan, Salil and Rayda Formations provides a valuable tool for defining basin outline and mode of infill. A number of seismic lines are presented in relation to well log correlation panels to highlight the complexity of the sedimentary processes affecting these units. The fill of the basin was completed by the Valanginian and the ovelying Lekhwair Formation of Hauterivian to Barremian age represents a renewed marine transgression.
Manganese occurrences in the Al Hammah Range — Wahrah Formation, Oman Mountains
Authors: Kickmaier W. , Peters Tj. 
Published: April 2008

Abstract

The host rocks of the manganese in the Al Hammah Range (125 km S of Muscat) are red radiolarian cherts of Tithonian to Neocomian age, continuously exposed over 1000 km
2
. The stratigraphic sequence starts with fine-grained turbiditic limestones followed by a transition zone of coloured silt-mudstones and cherts which grade into almost CaCO

3
−

free cherts, topped by 1–5 m of silicified limestones. The base of the Wahrah Formation is unknown. Sedimentological and geochemical features indicate that the cherts are of biogenic, non-hydrothermal origin. The stratiform manganese deposits are the result of sedimentary and tectonic enrichment processes. The single Mn-layers formed during periods of condensed sedimentation at the sediment-water interface. The different Mn-chert types (disseminated and layered ore and black Mn-rich cherts) can be explained by varying sedimentation rates of radiolaria, clay and manganese precipitation. Geochemically, the manganese deposits are characterized by high Mn/Fe ratios and by an extremely low minor element (e.g. Ni, Cu, Co) content. Using geochemical discrimination diagrams, the manganese deposits of the Wahrah Formation would be of hydrothermal origin. This contrasts with the sedimentary characteristics of the manganese-bearing cherts and with the field observations. Because of the Tithonian to Neocomian age of the Wahrah Formation cherts, the manganese enrichment can not be related to the formation of the Semail ophiolite. It is proposed that they might relate to a long distance discharge from the Owen fracture zone during the formation of the Masirah ophiolite.
Origin of culminations within the Southeast Oman Mountains at Jebel Ma-jhool and Ibra Dome
Authors: Cawood P. A. , Green F. K. , Calon T. J. 
Published: April 2008

Abstract
Structural culminations within the southeast Oman Mountains at Jebel Ma-jhool and the Ibra Dome developed through a process of multistage thrusting. This involved assembly and emplacement of the Semail and Hawasina thrust sheets over a footwall sequence of shelf carbonates and their pre-Permian basement, followed by progressive footwall collapse and breaching of the Hawasina thrust stack producing a hanging-wall anticline cored by shelf carbonates at Jebel Ma-jhool. At the Ibra Dome, foreland- and hinterland-dipping thrusts developed during the latter stages of thrusting forming a pop-up structure. Structural relations at Jebel Ma-jhool provide conclusive evidence that culminations within the Hawasina Complex are related to a decollement surface which lies at least as deep as the level of the shelf carbonates. Formation of the Ibra Dome and Jebel Ma-jhool structures was part of a widespread re-imbrication and culmination forming episode within the Oman Mountains. Major culminations, such as the Jebel Akhdar—Jebel Nakhl—Saih Hatat structures form significant morphological as well as structural highs. Slippage of the upper level Semail Ophiolite and Oman Melange sheets off these structures has resulted in truncation of the underlying Hawasina Complex thrust stack at Ibra Dome and Jebel Ma-jhool producing a break-back thrust sequence. The timing of initial thrusting, subsequent re-imbrication and culmination formation, and gravity-driven slippage of surficial thrust sheets is constrained to a 5 Ma period between the late Campanian and early Maastrichtian. This is based on the Coniacian to Campanian age of Aruma Group strata, the youngest rock unit affected by thrusting and the presence of the Maastrichtian Qahlah Formation unconformably overlying the flanks of both the Jebel Ma-jhool and Ibra Dome culminations. Broad scale folding and high-angle faulting of Maastrichtian and Tertiary strata in the southern Oman Mountains formed through regional mid-Tertiary compression and reactivation of Late Cretaceous culminations.
Metamorphism in the Oman Mountains in relation to the Semail ophiolite emplacement
Authors: El-Shazly A. K. , Coleman R. G. 
Published: April 2008

Abstract

The metamorphic rocks associated with the Semail ophiolite in the Oman Mountains represent two different facies series. Amphibolites and greenshists at the base of the Semail ophiolite constitute a metamorphic sole formed in a high-temperature, lowpressure environment. Eclogites, blueschists, lawsonite schists and other metasediments occurring at different structural levels in the basement and shelf deposits of the continental margin formed at high pressures and low temperatures. The amphibolites of the metamorphic sole formed as a result of heat transfer from the hot overthrust ophiolitic slab to the underlying oceanic sediments and volcanics shortly following intraoceanic detachment at a collapsed spreading centre about 100–90 Ma. The underlying greenschists represent sediments and volcanics that were metamorphosed farther away from the spreading centre as the ophiolitic slab became cooler and moved closer to the continental margin. Eclogites, blueschists and crossite epidote schists formed in the Saih Hatat window as a result of A-type subduction (crustal thickening) of the basement and shelf units of the Oman continental margin in response to a change in plate motion between Africa and Eurasia and transpression or collision with a fragment of Gondwanaland about 131 Ma. A-type subduction along an east-dipping zone resulted in the burial of the eastern edge of the continental margin to a minimum depth of 30 km. High
P/T
metamorphic rocks formed by this process followed ‘clockwise’
P-T
paths. The Late Cretaceous emplacement of the ophiolite onto the continental margin of Oman resulted in the imbrication of the continental shelf deposits, the development of low-grade, high-
P/T
metamorphic rocks in the ‘internal’ thrust piles due to tectonic overloading and the juxtaposition of the metamorphic rocks representing different facies series. Extensional deformation associated with culmination collapse in the Late Cretaceous and Tertiary led to the exhumation of the various high
P/T
metamorphic rocks and the distortion of the metamorphic zones.
The Maastrichtian transgression onto the northwestern flank of the Proto-Oman Mountains: sequences of rudist-bearing beach to open shelf facies
Authors: Skelton P. W. , Nolan S. C. , Scott R. W. 
Published: April 2008

Abstract
The Maastrichtian Qahlah and Simsima Formations, the first autochthonous deposits on the obducted Oman ophiolite complex, crop out in a gridle of jebels around the Oman Mountains. Those around the NW flank, between Al Dhayd (Sharjah) and Al Ayn-Buraymi (Dubai-Oman) are documented to illustrate: (1) an exposed regional reference section for the widespread Simsima Formation, at Jebel Faiyah (Sharjah); (2) the marked transgressive nature of the sequence onto the obducted complex; and (3) the rich rudist faunas there, associated with various beach to shelf facies, and their palaeoecological and palaeobiogeographical implications.
‘Basement’ (serpentinites in the north and sedimentary nappes in the south) is overlain by locally developed laterites and the dominantly siliciclastic, marginal continental to marine deposits of the Qahlah Formation, followed, with local erosion and overlap, by the carbonate-dominated Simsima Formation. The latter continues the deepening trend, passing from basal rudist-rich inshore facies to open shelf foraminiferal packstones to wackestones. The whole sequence onlaps eastwards onto the obducted complex. Its truncated top is overlain by Palaeogene slope deposits.

In the north (Jebel Faiyah area) the Maastrichtian sequence has an open, relatively high energy aspect. A shelf margin of Simsima Formation rudist limestones briefly developed in the early Maastrichtian around Qarn Murrah. Further transgression to the southeast drowned this and, by ‘mid’-Maastrichtian times, a bouldery beach conglomerate of the Qahlah Formation, with
in situ Durania
, was forming at Jebel Faiyah itself, along a cliff-backed shoreline with sandy embayments. Over this came tidally influenced rudist-rich facies and foraminiferal limestones of the Simsima Formation. In the south (Jebel Huwayyah area), in contrast, marginal fan-delta gravels and sandstones, of early Maastrichtian age, were followed by more restricted shallow marine silty marls and limestones with
Loftusia
, rudists and corals, of early to mid-Maastrichian age. These Qahlah deposits were overlapped by a relatively rudist-poor Simsima Formation sequence.

The obducted complex was thus strongly emergent at the start of the Maastrichtian, and the Aruma Sea transgressed onto its western flank, as the ophiolite subsided through that stage, forming a relatively open shelf in the north, becoming broader and more restricted further south. The rudist assemblages found on this shelf are similar to those of other open Tethyan shelves in the eastern and central Mediterranean and Middle East.
The Batain Melange of NE Oman
Authors: Shackleton R. M. , Ries A. C. , Bird P. R. , Filbrandt J. B. , Lee C. W. , Cunningham G. C. 
Published: April 2008

Abstract

Most of the Batain coast area, previously unmapped or mapped as Hawasina, is shown to be underlain by melange. This consists of blocks, up to 10 km long, of a variety of rocks in a scanty, seldom exposed sheared shaly matrix. Clasts include Triassic and younger Hawasina-type red cherts and shales; Mesozoic calciturbidites; Permian limestones and megabreccias (associated with basalts);
ammonitico rosso
type blocks (Triassic?); a limestone and pillow lava assemblage, probably Jurassic; Cretaceous ophiolite; and Upper Cretaceous sandstones with basement-derived debris flows. Deformation becomes increasingly complex northwards. WNW-vergent thrusts and folds, dominant in the south, appear to have been continuous with the south-vergent structures in the Hawasina, west of the Jebel Ja’alan basement uplift. The melange is interpreted as primarily tectonic but probably composite in origin. It is correlated with the Hawasina (Oman) Melange which underlies the Semail Ophiolite, west of the Jebel Ja’alan Uplift. It is compared with other Tethyan melanges.
A new model for the late Palaeozoic—Mesozoic tectonic evolution of Iran and implications for Oman
Authors: Şengör A. M. C. 
Published: April 2008

Abstract
It has been suggested that in a number of places such as Greece, Turkey, the Central Pamirs, and Thailand Neo-Tethys may have opened as a back-arc basin above a Palaeo-Tethyan subduction zone. The purpose of this paper is to test a similar suggestion for Oman. I review the late Palaeozoic to end-Mesozoic tectonic evolution of the Middle Eastern Tethysides in terms of a new tectonic model, whose main tenet is to regard the late Palaeozoic to Late Triassic basements of the Pontide/Dzirula/Adzharia-Trialeti/Arvin-Karabagh/Sanandaj — Sirjan zones collectively as a NNE-facing Palaeo-Tethyan magmatic arc, here named the ‘Podataksasi arc’ (or ‘zone’) whose Jurassic—Cretaceous movement with respect to Eurasia was responsible for much of the coeval deformation in Iran and Transcaucasia. The late Palaeozoic deformation of the Omani basement is regarded as a part of the retroarc fold and thrust belt of this arc and therefore independent of the Hercynides in Europe and NW Africa. The arc may have been compressional in late Carboniferous to possibly early Permian time and turned extensional in the earlier middle Permian. As a result, it rifted from NE Gondwana-Land, opening, successively, the Hawasina basin in the middle Permian and the main Neo-Tethyan ocean in the Triassic, together forming the ‘Omani Neo-Tethyan back-arc basin complex’. Nearly all of the tectonic and magmatic characteristics of this basin complex are compatible with a back-arc basin interpretation, except perhaps the anomalously far inland location of the initial rift axis. A rather complete Mesozoic tectonic history of the entire Middle Eastern Tethysides is given to justify the model presented.
GLORIA and other geophysical studies of the tectonic pattern and history of the Easter Microplate, southeast Pacific
Authors: Rusby Ruth I. 
Published: April 2008

Abstract
In October–November 1988 the RRS Charles Darwin surveyed the Easter Microplate using the GLORIA (long-range sidescan) sonar system and also obtained magnetic, bathymetric and gravity data. The aim of the cruise was to produce a sidescan mosaic covering most of the microplate, in order that a greater understanding of the region could be achieved. Previous geophysical studies of the area had enabled most of the microplate boundaries to be determined to a reasonable extent, but still little was known about the interior of the microplate, or its tectonic history.
The major objectives of the GLORIA survey were to image the whole microplate including its boundary, discover the type of plate boundary element throughout (e.g. fast or slow spreading, transform or compressional zone), calculate the spreading directions and rotation poles, and determine the complex history of the microplate from the tectonic spreading fabric, fracture zone and propagating rift traces, and magnetic anomaly data.
The GLORIA survey imaged virtually all of the Easter microplate in just 18 days, and revealed unprecedented detail and complexity in its tectonic fabric and history. There is clear evidence of rapid microplate rotation, of rapidly evolving plate boundaries and of complex deformation near the northern and southern microplate boundaries. Examination of GLORIA and magnetic data to the west of the East Rift of the Easter Microplate indicate that spreading may have been taking place for over 6 Ma and the calculation of poles of rotation for different stages of the Easter Microplate evolution have enabled a simplified history to be reconstructed.
Along-axis variations in tectonic extension and accommodation zones in the MARK Area, Mid-Atlantic Ridge 23°N latitude
Authors: Karson Jeffrey A. , Winters Alec T. 
Published: April 2008

Abstract

Multidisciplinary studies of the slow-spreading (<30 mm a
−1
) ridge axis in the MARK Area define a number of discrete spreading cells in each of which the style of seafloor spreading is distinctly different. In some cells, episodic magmatism and asymmetrical detachment faulting occur, whereas in others, a more continuous magma supply and symmetrical, steep, normal faulting dominate. Oblique-slip fault zones that link the cells are a kinematic requirement of such along-strike variations and are similar to the accommodation or transfer zones of continental rifts.
Concretionary cements in Jurassic sandstones, Isle of Eigg, Inner Hebrides
Authors: Wilkinson Mark 
Published: April 2008

Abstract

Minor element and stable isotope data are presented for calcite cements within seven decimentre-scale concretions from a single bedding plane within the Middle Jurassic Valtos Sandstone Formation of Eigg. Stable oxygen isotope data (δ
18
O = −9.3 to −11.1‰) suggest precipitation at burial depths of between 200 and 300 m at temperatures of 31–46°C, within static pore waters of meteoric origin. Mg/Ca and Mn/Ca ratios (2.5 ± 1.2 and 0.062 ± 0.008 mole percent respectively) imply that growth was predominantly transport-controlled. An average sized concretion from the horizon (
r
= 11.8 cm) is predicted to have grown in 0.36–0.84 Ma. Stratigraphic constraints show concretion growth to have been delayed by at least 15 Ma after the deposition of the sediments.

The concretions are shown to be clustered within the bedding plane; concretion nucleation is interpreted to have been controlled by the availability of suitable substrates within the sediment. The concretions probably nucleated upon aragonitic
Neomiodon
shells which had previously transformed to calcite.
Evolution of the Carboniferous Lough Allen Basin, Northwest Ireland
Authors: Philcox M. E. , Baily H. , Clayton G. , Sevastopulo G. D. 
Published: April 2008

Abstract
The Lough Allen Basin contains approximately 2.9 km of Dinantian (Courceyan) to Silesian (Arnsbergian) limestone, mudstone and sandstone, mostly of marine origin. The basin was initiated during the Courceyan Stage as a result of movement of the basin margin fault complex along the southeast side of the Ox Mountains inlier. The main rifting phase, during the late Courceyan, resulted in the deposition of a southeasterly thinning, initially non-marine, clastic wedge. The intrabasinal Dowra—Macnean High and Slisgarrow Trough developed during the Chadian Stage. Movement on the Curlew fault, which bounds the basin to the south, may have begun in the Courceyan but culminated in the Arundian. There is little direct evidence of fault-controlled sedimentation in the Holkerian and much of the Asbian, although the distribution of carbonate mudmounds of Asbian age in part coincides with earlier structural elements. During the late Asbian, there appears to have been renewed tectonic activity, which led to substantial regional differences of thickness of the lower formations of the Leitrim Group. There is little evidence of tectonic control on sedimentation from the Brigantian to the Arnsbergian.
Vitrinite reflectance determinations show that the Carboniferous rocks in the basin are supra-mature for the generation of oil but are mature with respect to the generation of gas. The maturation values for the youngest preserved rocks suggest that they have been buried under 3–5 km of Upper Palaeozoic cover.
The post-Variscan history of ireland
Authors: Naylor David 
Published: April 2008

Abstract
Permian and Mesozoic rocks are of limited distribution in Ireland, except for the Ulster Basin in the northeast of the island. This contrasts with the offshore basins, the widespread Mesozoic and Tertiary sequences of which are briefly reviewed. Onshore Permo-Triassic red-bed rocks occur in the Kingscourt Graben and in Wexford. Jurassic red clays are recorded in karstic solution hollows in Carboniferous limestones in south County Cork, and Upper Cretaceous chalk in a karstic collapse feature at Ballydeenlea, near Killarney. A growing number of Tertiary non-marine fissure and collapse deposits are being found, and where dated are of Oligocene and Neogene age. The stratigraphy and setting of the post-Carboniferous outliers are discussed. Published organic maturation data suggest that high maturation values in the Carboniferous over much of the country can be attributed to high heat flows during the Variscan episode, and to a cover of Silesian rocks. Post-Variscan burial depths appear to have been modest.
Available evidence suggests that Ireland has been a positive and largely emergent feature for much of post-Variscan time. Permo-Triassic deposits were probably never widespread onshore. The Early Jurassic and Late Cretaceous were periods of marine submergence, although rocks of this age were subsequently largely removed by erosion. Low topographic relief and the protective layers of Lias and Chalk have combined to restrict the amount of erosion of the landscape, the essential elements of which had been etched out by the end of the Triassic. The scattering of Mesozoic and Tertiary deposits at low topographic levels argue against the traditional view of the Irish landscape as a product of erosion of a high-level peneplain.
Post-Permian basin history of northeast Ireland
Authors: McCaffrey Robert J. , McCann Noel 
Published: April 2008

Abstract
Basin histories and major structures for Mesozoic and Cenozoic strata in northeast Ireland have been constrained with the help of computer-contoured isopach maps. Hand-drawn maps are included for comparison. The Highland Border Ridge, a well defined structural element since at least Lower Carboniferous times, separates the Rathlin Trough from the Lough Neagh-Larne Basin. The development of these basins was controlled by the pre-existing structures of the area, fault reactivation during late Hercynian movements and also Pangean rifting. A long-lived structural high in the Lough Neagh-Larne Basin, the Knockagh axis, is inferred to be a major block detached from the adjacent Longford-Down Massif.
Lithospheric stretching in the Porcupine Basin, west of Ireland
Authors: White Nicky , Tate Michael , Conroy John-Joe 
Published: April 2008

Abstract
The Porcupine Basin is a N-S trending Mesozoic extensional sedimentary basin situated on the continental shelf west of Ireland. All available datasets have been examined in order to see how well the stretching model accounts for the structure and evolution of the basin. Subsidence data indicates that there have been two phases of stretching: at the end of the Jurassic and during the Palaeogene. The earlier phase is of more significance; stretching factors varying from 1.2 at the northern end of the basin to greater than six at the southern end. Stretching factors for the later phase are generally less than 1.1. Crustal thinning information, determined principally from gravity data, is consistent with the above estimates. The timing of volcanism within the basin is broadly consistent with these stretching phases. Significantly, the location of a 150 km long and 20 km wide median igneous ridge is broadly consistent with the steady increase in stretching southwards.