bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure of the Jebel Sumeini-Jebel Ghawil area, Northern Oman
Authors: Searle M. P. , Cooper D. J. W. , Watts K. F. 
Published: April 2008

Abstract
Detailed structural mapping of the Sumeini half-window, Jebel Sumeini and Jebel Ghawil areas in northern Oman, shows that the dominant Late Cretaceous thrusting was a WSW-propagating piggy-back sequence modified by late-stage, deeper level thrusts in the Sumeini slope facies carbonates which breached up into the overlying Hamrat Duru thrust sheets. The uppermost Semail thrust carrying the complete ophiolite sequence overlaps lower Haybi thrust sheets and inverted metamorphic isograds are displayed in the footwall. Amphibolites and greenschists of the metamorphic sole have been subsequently imbricated with Haybi alkaline and tholeiitic volcanics, Triassic Oman exotic limestones and melanges of the Haybi duplex. A major E-W trending lateral ramp is inferred along the southern edge of Jebel Ghawil downthrowing the Sharm peridotite block up to 1000 m to the south. The basal Hamrat Duru thrust overlies Cretaceous Mayhah Formation slope facies carbonates and has been folded around the lower, later culminations primarily of Late Cretaceous age, enhanced by further structural growth and short-distance post-Maastrichtian (? Eocene) thrusting. Thrusts at the base of the Sumeini Group have breached through the overlying Hamrat Duru sheets and locally overthrust Maastrichtian Faiyah Formation limetones along the SW margin of Jebel Wasa. Culmination of Jebel Sumeini promoted hanging-wall drop fault development along the trailing (NE) edge of the Sumeini duplex, down-faulting Hamrat Duru rocks to the east. The amount of displacement of the Jebel Sumeini culmination increases towards the south, toward the axis of the Sumeini half-window.
Tectonics, geochronology and geochemistry of the Precambrian rocks of Oman
Authors: Gass I. G. , Ries A. C. , Shackleton R. M. , Smewing J. D. 
Published: April 2008

Abstract

precambrian rocks crop out in NE Oman (Qalhat and Jebel Ja’alan), in SE Oman (near Mirbat) and offshore on the Kuria Muria Islands. Similar rocks occur on Socotra and Abd el Kuri. In all these localities the Precambrian rocks include metasediments of greenschist or amphibolite facies, intruded by dolerites, granodiorites and granites and cut by doleritic and felsitic dykes which in the Mirbat area, form a dense swarm. Foliation trends vary but are predominantly ENE-WSW. Geochronological data show that the rocks are late Proterozoic (800-600 Ma) in age and are therefore chronologically and compositionally similar to the Pan-African rocks of the Afro-Arabian Shield. Unmetamorphosed, weakly deformed Infracambrian sediments in the Huqf-Haushi Uplift and in the Saih Hatat and Jebel Akhdar windows are not cut by the dyke swarms, which are therefore probably late Proterozoic in age although radiometric dating suggests a lower Palaeozoic age. These widely distributed late Proterozoic metamorphic rocks indicate that the middle Proterozoic (
c.
1700 Ma) gneisses in the Afif Terrain in eastern Saudi Arabia do not mark the eastern limit of the Pan-African belt. Before the breakup of Gondwanaland that limit must have lain between the Oman-Somalia region and the Archaean and middle Proterozoic terranes of the Bundelkhand and Aravalli areas of India.
Intraplatformal basin-fill deposits from the Infracambrian Huqf Group, east Central Oman
Authors: Wright V. P. , Ries A. C. , Munn S. G. 
Published: April 2008

Abstract
The Infracambrian Huqf Group, well exposed in the Huqf-Haushi area of Central Oman, is an alternating sequence of clastic (Abu Mahara and Shuram Formations) and carbonate (Khufai and Buah Formations) sequences overlain, in the subsurface, by the evaporitic Ara Formation. The Khufai and Buah Formations are dolomites whose lowest members have previously been interpreted as lagoonal deposits; they are here reinterpreted as sub-wave base deposits which were probably formed in an intraplatformal basin. The upper parts of both formations consist of shoal and back shoal (peritidal) deposits with evaporites. The intervening Shuram Formation is a mixed siliclastic-carbonate unit deposited in an extensive shallow wave and tidally-influenced setting.
Carbonate/evaporite deposition in the Late Precambrian — Early Cambrian Ara Formation of Southern Oman
Authors: Mattes B. W. , Conway Morris S. 
Published: April 2008

Abstract
The Ara Formation of southern Oman is a geological rarity — a late Proterozoic sedimentary sequence which contains rich hydrocarbon source rocks and large accumulations of oil. It consists of a cyclic sequence of carbonates and evaporites deposited in a restricted basin. The source rocks were deposited in relatively deep, anoxic parts of the basin; reservoir rocks, most of them dolomitic, were deposited in shallow water on adjacent shelf or ramp areas. Since the sedimentary sequence overlying the Ara Formation has been truncated by numerous unconformities, the Ara source rocks have never been buried very deeply and have had a long history of oil generation in many areas, they are still within the oil window. Thick evaporites provide a regional seal for the intraformational trapping of hydrocarbons. In addition, post-depositional basin inversion led to structural elevation of what had been the deeper parts of the basin along a broad NW dipping flank. Episodic down-dip salt removal along this flank allowed Ara oil to bypass the salt seal and to charge overlying reservoirs ranging in age from Cambrian to Tertiary.
The Ara Formation represents at least five third-order tectono-eustatic cycles of carbonate to evaporite sedimentation. Carbonates formed during periods of relatively high sea level; evaporites during sea level low stands, compounded by evaporative drawdown. The carbonates were deposited in a variety of marine to mesohaline environments; in addition to an abundance of cyanobacterial remains and framestone fabrics, they contain one of the earliest shelly faunas in the geologic record.
Chemical transects across intra-oceanic arcs: implications for the tectonic setting of ophiolites
Authors: Taylor Rex N. , Murton Bramley J. , Nesbitt Robert W. 
Published: April 2008

Abstract
Systematic spatial variations in Ti, Y, and Zr are found in volcanic sequences sampled as transects from back-arc, through arc, to trench within the western Pacific intra-oceanic arc systems. These correlations occur regardless of eruption age, reflecting the retention of relative positions between individual tectonic units. Concentrations of these incompatible elements are taken to reflect the nature of the underlying mantle at a particular trench-volcano distance during the subduction process. Volcanics become more depleted trenchwards, implying that progressively shallower levels melts were extracted from more refractory or harzburgitic mantle. A model is proposed whereby a subduction system is superimposed on a compositionally stratified mantle, which is a product of an earlier spreading event. On the basis of this evidence, the trench-distance variation model is applied to the Troodos ophiolite complex. Similar spatial changes in lava chemistry are found across the ophiolite, providing evidence for the relative position of the Troodos trench and direction of subduction beneath the Troodos basin. These findings have implications for studies in other orogenic terrains where structure and exposure permit their application.
Petrology and geochemistry of the plutonic rocks of the Halmahera ophiolite, eastern Indonesia, an analogue of modern oceanic forearcs
Authors: Ballantyne Paul 
Published: April 2008

Abstract
Ophiolitic rocks form the basement of the eastern part of the island of Halmahera in eastern Indonesia. The ophiolite is tectonically dismembered but all the elements of a complete ophiolite are present with the uncertain exception of a sheeted dyke complex. The ophiolite was formed in a supra-subduction zone setting before the Late Cretaceous and is interpreted to represent the forearc of a Mesozoic arc whose remnants are now found within and close to the margins of the Philippine Sea Plate. The plutonic rocks of the ophiolite include periotites interpreted as a ‘mantle sequence’ and cumulates interpreted as the deeper parts of an ophiolitic crustal sequence. The mantle sequence includes subordinate lherzolites of relatively enriched chemistry which represent upper mantle previously depleted by the extraction of MORB. A high degree of melting of the lherzolites under hydrous conditions left a mantle residue of depleted harzburgites, which are more refractory than the harzburgites of Troodos and Oman. Abundant cumulates which crystallized from the magma include peridotites and gabbroic rocks rich in orthopyroxene. The chemistry and mineralogy of the cumulates indicate open-system crystallization from a high Si, Mg, low Ti, LREE-depleted magma. Highly calcic plagioclase characteristic of island-arc plutons and found in the cumulate sequence of the Troodos ophiolite is not found in the Halmahera cumulates. The Halmahera ophiolite is interpreted as the onland analogue of the present-day Mariana forearc. Rocks dredged from the Mariana Trench, which like Halmahera is also situated at the margin of the Philippine Sea Plate, are remarkably similar to those of the Halmahera ophiolite.
Mobility of rare earth elements in zones of intense hydrothermal alteration in the Pindos ophiolite, Greece
Authors: Valsami E. , Cann J. R. 
Published: April 2008

Abstract
During the formation of the Jurassic Pindos ophiolite of northwest Greece, a convective seawater-fed hydrothermal system was initiated at or near the spreading centre. As a result, typical ophiolitic background metamorphic assemblages developed during the downward circulation of seawater, and epidosites and stockworks formed in the upwelling part of the system. The epidosites were analysed for major and trace elements including the REE. Substantial chemical changes occur during the evolution of the epidosites from their protoliths. While some elements (Ti, Zr, Y, Nb) appear immobile during this transformation, when a bulk quartz addition is taken into account, the REEs are mobile under these alteration conditions. Analyses show: (a) either enrichment of all the LREEs; or (b) ‘anomalous’ selective enrichment of certain elements (La, Pr, Eu) and depletion of others (Ce, Sm). These patterns can best be explained by: (a) greater mobility in the bulk of the alteration zone of the LREEs compared to the HREEs; (b) variable properties of Ce and Eu due to changes in their valence state; (c) variable water/rock ratio in epidosite zones; (d) heterogeneous permeability of reaction zones; (e) control of the rock alteration mineralogy on the REE distribution. Evidence for the mobility of the REE is also provided by the analyses of hydrothermal solutions from black smokers at 13°N and 21°N on the East Pacific Rise. REE can be very good indicators of the degree of water/rock interaction at high water/rock ratios.
Burial histories and hydrocarbon source rocks on the North West Seaboard
Authors: Parnell J. 
Published: April 2008

Abstract
The basins on the North West Seaboard of the British Isles had widely differing burial histories and consequently contain different successions. Basins active in the Permo-Triassic saw early maturation of Carboniferous source rocks, but Jurassic sections remain immature. Basins active in the Cretaceous — Tertiary saw later maturation of the Carboniferous, followed by maturation of the Jurassic. Potential source rocks range from Ordovician to Tertiary age, but Carboniferous source rocks are probably the most widely distributed. Samples from onshore Carboniferous outcrops in Northern Ireland and western Scotland give good pyrolysis yields, with a potential for gas and limited quantities of oil. The Jurassic rocks of the Hebrides include bitumen-impregnated sandstones where Jurassic shales have achieved maturation in the vicinity of Tertiary intrusions. The North West Irish Basin shows evidence for oil migration in Carboniferous rocks and the burial history suggests that gas may have been generated from the Carboniferous in eastern Ulster where the succession is analogous to that in the Morecambe Gas Field.
Late Triassic to Middle Jurassic stratigraphy, palaeogeography and tectonics west of the British Isles
Authors: Morton Nicol 
Published: April 2008

Abstract
The Upper Triassic to Middle Jurassic stratigraphy of the Atlantic margin basins west of the British Isles (including Celtic Sea, Porcupine, Slyne, Erris, Hebrides, and west of Shetland) is summarized in terms of six major genetic sequences, defined as packages of conformable strata separated by surfaces of abrupt major facies change. They indicate common tectonic histories and are interpreted as representing episodes of evolution comprising extensional phases with laterally variable sequences (1A Late Triassic to Early Sinemurian; 2A latest Toarcian to Late Bajocian), thermal and loading sag phases (1B mid-Sinemurian to earliest Toarcian; 2B Late Bajocian to Bathonian) and stabilization phases with sequences of reduced thicknesses and hiatuses (1C Toarcian; 2C Late Bathonian to Callovian).
The basins west of Shetlands, north of the Wyville-Thomson Ridge, have a different history, especially in the Early Jurassic. Similarly, basins south of an extension of the Clare Lineament (south of Celtic Sea and Porcupine Basins) differ in having limited Middle Jurassic subsidence. These transverse elements divide the Atlantic basin system into local subsystems, each of which has a different tectonic history.
Petrography and diagenesis of the Permo-Triassic of Scotland
Authors: McKeever Patrick J. 
Published: April 2008

Abstract
Sediments considered to be of Permian or Permo-Triassic age are exposed in many areas of Scotland and within several offshore basins. These sediments were deposited within fault-bounded, intermontane basins and represent a variety of continental facies typical of arid or semi-arid areas. A major study of the diagenetic evolution of the Scottish Permo-Triassic reveals that the basins were isochemical and experienced similar patterns of diagenesis, largely controlled by the climatic aridity of the depositional environment. Depositional pore-waters in the Permo-Triassic sediments of Scotland were well oxygenated and alkaline in nature, allowing the rapid alteration of the unstable mineral assemblage. Ionic complexes released as a result of this alteration were precipitated as a suite of eodiagenetic minerals with oxygen isotope analysis on the authigenic K-feldspar phase confirming an origin from meteoric waters in an arid climate. These eodiagenetic modifications resulted in a major loss of primary porosity. Further burial resulted in minor pressure solution while further depth-related changes have been identified in the authigenic clay mineral suite. Telodiagenetic precipitation of kaolinite and minor quartz was associated with a moderate development of secondary porosity. The hydrocarbon reservoir potential of the Scottish Permo-Triassic is low, primarily due to the early destruction of porosity.
Mid-Jurassic lagoonal delta systems in the Hebridean basins: thickness and facies distribution patterns of potential reservoir sandbodies
Authors: Harris J. P. 
Published: April 2008

Abstract
In the Inner Hebrides the facies distribution patterns and mineralogy of outcropping Great Estuarine Group (Bathonian) sandbodies indicate SSW progradation of copiously supplied lagoonal deltas in two sub-basins (Sea of the Hebrides Basin and Inner Hebrides Basin). These were both westerly tilted half graben and were probably separated by a slowly subsiding basement ridge known as the mid-Skye palacohigh. In the Bathonian these basins had an intermittent connection with the open sea and were supplied with clastic sediment from mineralogically distinct source areas in the Scottish Landmass to the east and an Outer Hebrides Landmass to the west. Fluvial-dominated and fluvial-wave interaction deltas supplied by low sinuosity rivers form successive sandbodies intercalated with lagoonal mudstones. The facies distribution patterns and mappable depositional limits of these sandbodies are dependent on the style and rate of fluvial supply, the configuration of the basins, variations in wave energy and salinity fluctuations. This demonstrates concepts which are probably applicable to the prediction of reservoir thickness and facies patterns in related sedimentary basins.
Palaeoenvironment of a Lower Carboniferous sandstone succession northwest Ireland: ichnological and sedimentological studies
Authors: Buckman J. O. 
Published: April 2008

Abstract

The shallow-marine deltaic sandstones and shales of the Lower Carboniferous Mullaghmore Sandstone, northwest Ireland, contain abundant trace fossils. A twenty-five metre thick measured section of Mullaghmore Sandstone from the northwest corner of Mullaghmore Head contains a minimum of twenty-eight ichnogenera and four informally named trace fossils. At least four coarsening-upward sequences occur within the measured section, with a possible total of six. Sedimentary structures and trace fossils indicate that each sequence represents deposition in a shallow-marine deltaic environment; prodelta-interdistributary bay passing upwards into a subaqueous channel environment. These represent a
Cruziana
-type ichnofacies, with an interbedded tempestite-associated
Arenicolites
ichnofacies, and a
Skolithos
-type ichnofacies respectively. The ichnogenus
Neonereites
, more typical of the
Nereites
ichnofacies, also occurs within the
Cruziana
ichnofacies, but only in limited numbers, and is atypical of the ichnofauna. Local lateral variation in ichnogenera and their sporadic occurrence along bedding planes indicates the need for extensive investigation, if trace fossils are to be used for detailed environmental reconstruction.
Origin of reddening and secondary porosity in Carboniferous sandstones, Northern Ireland
Authors: Wang W. H. 
Published: April 2008

Abstract
Carboniferous sandstones in the Ballycastle district of Northern Ireland were deposited in fluvio-deltaic environments. Significant secondary porosity was generated in the sandstones, particularly in red-coloured sandstones, due to the dissolution of carbonate cement. Minor secondary porosity was also created by the leaching of feldspar grains. Virtually all the observed porosity in the Carboniferous sandstones has a secondary origin. Subsequently, the precipitation of kaolinite reduced the porosity. The red-coloured sandstones are important in showing the depth of invasion of oxidising meteoric fluids following late Carboniferous-Permian uplift. The red colour is due to iron oxides liberated during the dedolomitization of a ferroan dolomite cement. Several instances of reddened Carboniferous strata across the UK probably have a similar origin and are potential oil and gas reservoirs as reddened sandstones may have a high secondary porosity.
Petroleum geology of the Slyne Trough and adjacent basins
Authors: Trueblood Stephen 
Published: April 2008

Abstract
The Slyne Trough lies to the west of Ireland, northeast of the Porcupine Basin and southeast of the margin of the Rockall Trough. The Slyne Trough can be demonstrated to have adequate source, reservoir and seal rocks, but the timing of hydrocarbon migration is more problematical. Structures exist on both large and small scales within the Central and Northern Slyne Troughs, with the possibility of hydrocarbon entrapment at a number of horizons. An excellent source rock has been identified in the Toarcian (Portree Shale Formation) with up to 7% TOC. A secondary source exists within the Sinemurian/Pleinsbachian (Pabba Shale Formation) with up to 4% TOC. Reservoir quality sands have been encountered in the Bathonian (Elgol Sandstone Formation) and Hettangian/Sinemurian (Broadford Beds Formation). A possibility for further reservoir development can be demonstrated in the Bajocian and Pleinsbachian. Sealing intervals have been found in the Bathonian (various levels in the Great Estuarine Group), the Toarcian/Aalenian (Portree Shale Formation/Dun Caan Shale Member) and the Sinemurian/Pleinsbachian (Pabba Shale Formation). The Liassic source rocks are marginally mature in the 27/13-1 well. In the deeper parts of the basin they are probably mature for generation and migration. The Lower and Middle Jurassic evolution of the basin can be estimated with fair accuracy from the 27/13-1 well. The Post-Middle Jurassic history can be interpreted from analogous basins in the region. The North Porcupine sub-basin section shows the complete erosion of the Liassic source horizons. The oil found within the Porcupine basin is believed to be sourced from the Upper Jurassic, which are mature here due to a post-Jurassic history different to that of the Slyne Trough. The Erris Trough is believed to have had a similar Jurassic evolution to the Slyne Trough, but with locally much greater erosion during the Lower Cretaceous. The Jurassic petroleum potential within this basin relies on preservation of the full Liassic sequence in downthrown fault blocks.
Early Tertiary submarine fan deposits in the Porcupine Basin, offshore Ireland
Authors: Shannon Patrick M. 
Published: April 2008

Abstract
The Porcupine Basin, offshore western Ireland, contains up to 10 km of Mesozoic and Cenozoic sediments. Seismic sequence analysis of the Palaeocene-Eocene strata on the southwestern and southeastern margins of the basin reveals a mounded and draped geometry. Four seismic sequences are defined and are coeval with a series of deltaic deposits in the northern and central parts of the basin. In the southwestern area these are interpreted as stacked submarine fan deposits. In the southeastern area the lower two sequences are interpreted as shelf-slope deposits which are overlain by two submarine fan complexes. Funnelling of the sediment was controlled by erosive channelling through interfan topographic lows. The seismic response indicates that the fans are dominated by lower fan sheet sand deposits with minor amounts of upper fan channellized sandstones. They probably developed in response to an interplay of eustatic sea level changes, tectonic uplift on the basin margins, and thermal subsidence towards the basin centre.
Evolution of Mesozoic sedimentary basins around the North Central Atlantic: a preliminary plate kinematic solution
Authors: Srivastava S. P. , Verhoef J. 
Published: April 2008

AbstractThere is significant correlation between the tectono-stratigraphic record in the sedimentary basins round the Central North Atlantic and the seafloor spreading history of the North Atlantic. This has been taken as an indication that the formation of these basins can be related to the relative motion between lithospheric plates. Based on many criteria, plate kinematics of the North Atlantic have been derived for the rifting periods of these basins. Reconstructions of the North Atlantic based on these plate kinematic solutions show a progressive overlap between the reconstituted plate boundaries. These overlaps exist because the margins of the original plates stretched during rifting: present-day plate boundaries are therefore extended beyond their pre-rift locations. From the overlaps, it is possible to calculate the amount of extension during rifting and to restore the plates and their enclosed basins to their pre-stretched configurations. The paper discusses techniques for the de-stretching of plate margins and describes a set of reconstructions showing the configuration of these basins as they evolved. For the first time, the reconstructions give a pictorial presentation of the formation of these basins.