Effects of the Permian–Triassic boundary on reservoir characteristics of the South Pars gas field,Persian Gulf

The Permian–Triassic boundary (PTB) is a world‐wide event characterized by the most extensive mass extinction in the history of life. In the Persian Gulf, the rock record of this time interval host one of the most important hydrocarbon reserves in the world: the South Pars Gas Field and its southern extension, the North Dome (or North Field). These carbonate and evaporite successions were sampled in eight wells for petrographic, geochemical and porosity–permeability studies. An important characteristic of the Dalan and Kangan formations is the centimetre‐scale lithological heterogeneities caused by facies changes and diagenetic imprints that led to the compartmentalization of these reservoirs. These Permian–Triassic (P‐T) sediments were deposited in a shallow marine homoclinal ramp. The PTB in this hydrocarbon field is represented by a reworked coarse‐grained intraclastic/bioclastic grainstone facies deposited during a marine transgression. Prolonged subaerial exposure in the P‐T transition caused hypersaline and meteoric diagenesis, including extensive cementation, dolomitization and some dissolution, influencing reservoir characteristics of bordering units. Both δ¹⁸O and δ¹³C values in this succession mirror worldwide excursions typical of other P‐T sections, with some variations due to diagenetic alterations. A pronounced decline in ⁸⁷Sr/⁸⁶Sr values, reflective of global seawater geochemistry for most of the Permian is evident in our data. Reservoir quality declines through the late Permian, as a result of facies change and diagenesis. The Late Permian is succeeded by a Triassic transgressive facies and decline in reservoir quality. Copyright © 2009 John Wiley & Sons, Ltd.     

Cretaceous sauropod diversity and taxonomic succession in South America

The South American sauropod dinosaurs fossil record is one of the world's most relevant for their abundance (51 taxa) and biogeographical implications. Their historical biogeography was influenced by the continental fragmentation of Gondwana. The scenery of biogeographic and stratigraphic distributions can provide new insight into the causes of the evolution of the sauropods in South America. One of the most important events of the sauropods evolution is the progressive replacement of Diplodocimorpha by the Titanosauriformes during the early Late Cretaceous. The fluctuation of the sea levels is frequently related to the diversity of sauropods, but it is necessary to take into account the geological context in each continent. During the Maastrichthian, a global sea level drop has been described; in contrast, in South America there was a significant rise in sea level (named ‘Atlantic transgression’) which is confirmed by sedimentary sequences and the fossil record of marine vertebrates. This process occurred during the Maastrichtian, when the hadrosaurs arrived from North America. The titanosaurs were amazingly diverse during the Late Cretaceous, both in size and morphology, but they declined prior to their final extinction in the Cretaceous/Paleocene boundary (65.5Yrs).     

How severely was the Persian Gulf affected by oil spills following the 1991 Gulf War?

Ostracods from 14 surface sediment samples taken from the northwest part of the Persian Gulf (Iranian side) at water depths of 32-54 m were studied to evaluate the environmental pollution caused by oil spills following the 1991 Gulf War. With the exception of two live ostracods, which show no response to the contamination, at least 58 closed carapaces from 18 taxa of herbivorous and sediment-feeding species were found containing dark brown oil. All contaminated specimens were restricted to the uppermost part of the sediments (0.0-0.5 cm). The extent of the impact and the number of affected species varies within the samples. The most heavily contaminated ostracods were encountered in samples 1, 3, 14, 21 and 26 in which 3-5% of the complete carapaces contain oil residues. Compared to a previous sampling in 1965, seven additional ostracod species occur in the modern Persian Gulf. This indicates an intact environmental state prior to the Gulf War.     

波斯湾盆地中白垩统Mishrif组碳酸盐岩储层特征及其发育模式

Mishrif组碳酸盐岩储层是波斯湾盆地最主要的储集层之一,储层岩石类型主要为礁滩相生物礁灰岩、生屑灰岩和含生屑泥灰岩,储集空间主要为粒间(溶)孔、晶间(溶)孔、铸模孔、表生期组构选择性溶蚀孔洞和基质微孔。储层多呈层状展布,横向上连续,边界受沉积相带约束; 纵向上发育多套致密隔夹层,呈强非均质性。储层发育与保存主要受沉积作用、成岩作用和构造作用影响。碳酸盐岩缓坡背景下发育的生物礁和生屑滩空间分布受盆地基底古构造格局控制,是优质储层分布相带。相对海平面升降旋回控制相带迁移和成岩作用差异,导致优质孔渗层与致密隔夹层交互发育。构造圈闭发育与油气充注时间的耦合有效抑制压实作用和胶结作用对储层的破坏,是储层得以保存的有利因素。     

Iran and the continuing crisis in the Persian Gulf

Iran is attempting to return to its pre-Islamic revolution stage of regional hegemony in the Persian Gulf. During the 1980's, Iran alienated itself from both superpowers — the USA and the USSR. More recently, Iran has began a process of regaining much of its international legitimacy. This includes the adoption of a neutral stance during the Gulf War of 1991, acting as a mediator in Afghanistan and by a — so far — policy of restrained intervention in the newly independent Central Asian Moslem states of the former Soviet Union. Iran continues to see itself as a powerful Middle Eastern state which has the right to manage affairs in the Persian Gulf. This will be difficult to achieve as long as Iran is perceived as a reactionary state by the USA and European powers, in their continued support for Saudi regional interests.     

Coral reef recovery in Florida and the Persian Gulf

Long-term observations and study of coral reef destruction by hurricanes in the Florida Keys show, surprisingly, that although corals are devastated on a grand scale during storms, recovery is rapid. Recovery occurs because of the widespread scattering of live fragments, many of which become growth sites of new colonies. Reef recovery from death by chilling in the Persian Gulf was well under way when last observed, but it is not yet known if the recovery rate was as rapid as recovery from the storm destruction in Florida. Recovery from death by chilling requires settlement of transported coral larvae and a substrate suitable for larval attachment. Such resettlement is subject to the effects of currents, predators, pollution, and competition for substrate. A growth rate of 10 cm per year combined with geometrical progression of branch formation accounts for rapidAcropora cervicornis recovery. Although calculated coral proliferation seems unusually high, it has been confirmed by serial underwater photographs spanning ten years. More precise measurements of growth and branching are needed, along with growth data for other common reef-building corals. Such data would be useful for predicting standing crop of a restocked or transplanted reef.     

Anisotropic behavior of the Bushehr carbonate sand in the Persian Gulf

The anisotropy effect is exhibited more prominently in sedimentary depositions, and it relates the soil’s mechanical specifications to the directions of imposed loads. Even though this phenomenon has been comprehensively explored in silica sands, few research has been conducted for studying the anisotropic behavior of marine carbonate sands. To bridge this gap, the present study investigates the anisotropy effect on the mechanical behavior of Bushehr carbonate sand acquired from the north shelf of the Persian Gulf in Iran. Toward this end, some undrained principal stress rotation tests are conducted using a hollow cylinder shear torsional apparatus in such a manner that the direction of the applied principal stresses are fixed along a desired orientation and the total mean stress and intermediate principal stress ratio are kept constant. Furthermore, prior to shearing, the samples are consolidated under three confining pressures and two isotropic and anisotropic states. The results show that dilative behavior is observed in all loading directions after initial contraction; this contradicts the response observed in silica sands. The anisotropy response of soil follows two different trends in the contractive and dilative phases. The relation of soil’s mechanical properties shows a descending trend with the angle of maximum principal stress in the contractive phase; on the other hand, the anisotropy behavior shows a dominant parabola trend in the dilative phase, where the maximum ultimate pore pressure and minimum soil strength occur in the stress direction with an angle of α?=?30°. By increasing the confining pressure in the soil element, the intensity of the anisotropy in some mechanical properties except the soil deformation is reduced. Furthermore, the deviatoric-to-effective mean stress ratio in the phase transformation state from contraction to dilation is independent of the loading direction and consolidation stress state, and it is considered one of the intrinsic properties of sand.     

Coupled solution of oil slick and depth averaged tidal currents on three-dimensional geometry of Persian Gulf

In this paper, simulation of oil spill due to tidal currents in Persian Gulf is performed by coupled solution of the hydrodynamics equations and an equation for convection and diffusion of the oil. The hydrodynamic equations utilized in this work consist of depth average equations of continuity and motion in two dimensional horizontal planes. The effect of evaporation is considered in the continuity equation and the effects of bed slope and friction, as well as the Coriolis effects are considered in two equations of motion. The overlapping cell vertex finite volume method is applied for solving the governing equations on triangular unstructured meshes. Using unstructured meshes provides great flexibility for modeling the flow in arbitrary and complex geometries, such as Persian Gulf flow domain. The results of the hydrodynamic model for tidal currents in Persian Gulf domain is examined by imposing tidal fluctuations to the main flow boundary during a limited period of time. Finally, the developed model is used to simulate an accidental oil spill from a point in Persian Gulf.     

New stratigraphic data on the Aptian of the Persian Gulf

During Aptian times the northeastern corner of the African plate, the Arabian craton, was in the tropics. Two-thirds of it was covered by a broad epeiric sea opening eastward into the Tethys Ocean. Carbonate sedimentation recorded several environmental perturbations caused by changes in relative sea-level and by interconnected coeval global events. A well in offshore Abu Dhabi was used as the reference because it was drilled through the whole of the interval of interest and cored strata dated Gargasian (middle Aptian sensu gallico, early late Aptian sensu anglico) downward to beds of Late Barremian age. The holostratigraphic approach employing biostratigraphy, lithostratigraphy and sequence stratigraphy, along with basic well log interpretation and δ¹³C-based chemostratigraphy, facilitated correlation with outcrops in Iran and Oman, and with other wells in Iraq, Qatar and the United Arab Emirates, over distances of several hundreds of kilometers. This approach made possible refinement of our regional model for this interval and the identification of a set of events that included several forced regressions, transgressions of varying importance (by extension in the literature those floodings of greatest magnitude have been called “drownings”), the Oceanic Anoxic Sub-Event 1a and a microbial Bacinella “bloom”.     

Evaluation of ecotourism potential in the northern coastline of the Persian Gulf

This research has identified areas located in the northern coastline of the Persian Gulf in the south of Iran, as strategic and ecological sites, based on tourism potential assessing criteria. To this end coastal limits were identified by satellite imagery in terms of shorelines and the maximum extent of water approach into the land and taking into consideration the characteristics of the nearby coastal villages. The studied region was then compared to similar international criteria and experiences. The original criteria were then divided into three main and four sub criteria. The Kangan region was found to have a potential for tourism industry according to the mentioned criteria. Naiband Gulf with a score of 20 was ranked first followed by Asalouyeh with a score of 18 and finally Taheri and Kangan Ports with scores of 16 and 15, respectively. With a high tourism industry potential in the studied region the necessity of ecotourism quality enhancement and environmental management planning for the northern shoreline of the Persian Gulf becomes of vital importance.     

The petroporphyrins of a Cretaceous oil

The petroporphyrins of a Cretaceous crude oil, La Paz, from western Venezuela are shown to be a mixture of etio and DPEP homologues (C₂₇-C₃₉) maximising at C₃₀ and C₃₁, respectively. Minor amounts of rhodoporphyrins (C₃₀-C₃₉) are also present. Thin-layer chromatography afforded fractions which have been shown by mass spectrometry to contain up to 80% of a single-molecular-weight species. Oxidative degradation of La Paz petroporphyrins to maleimides and mass-spectrometric study of t.l.c. fractions indicate that some of these porphyrins are to a great extent incompletely substituted. Dealkylation reactions have presumably played an important role in their geologic history. Furthermore, the relative simplicity of the alkyl substitution pattern of the La Paz petroporphyrins suggests that transalkylation reactions have not taken place to any significant extent.The fraction of petroporphyrins isolated from the asphaltenes contains a higher proportion of the DPEP homologues than do the total petroporphyrins isolated from the original crude oil.     

Cretaceous foraminifera from the Turonian succession at Beer, southeastern Devon, England

During Winter 2000/2001 a major cliff fall occurred at the back of the bay in Beer, southeastern Devon. In the subsequent remedial works the cliff was cleared of loose material prior to stabilisation works. This process provided a suite of samples from previously inaccessible parts of the cliff succession. By adding these samples to earlier suites of samples collected over the last 30 years it has been possible to improve our knowledge of the foraminifera of Turonian age in southwestern England.The planktic foraminifera are, perhaps, the most significant component of the assemblages as many of the taxa recorded in Devon are of southern aspect and are relatively rare in others parts of the U.K. The planktic zonation recognised in this section is, therefore, almost identical with that recorded in Tethyan areas and a precise correlation can be generated. There are relatively large numbers of important taxa such as Helvetoglobotruncana helvetica, Dicarinella imbricata, Marginotruncana sigali, M. pseudolinneiana, M. coronata and M. schneegansi. The benthic foraminifera, by comparison, are relatively rare and are represented by a low diversity assemblage. This is typical of northwestern European chalk successions of Turonian age and is coincident with the highest sea levels of the Cretaceous. In the middle to late Turonian there is a dramatic shallowing event that is recorded world-wide at this level. The assemblage changes towards the top of the accessible succession at Beer record this significant, world-wide event.     

藏南白垩纪桑日群麻木下组埃达克岩的地球化学特征及其成因

桑日群火山岩位于冈底斯南缘火山-岩浆弧的中、东段,紧邻雅鲁藏布江缝合带的北侧,包括下部麻木下组与上部比马组中的火山岩,长期以来被认为是雅鲁藏布江新特提斯洋沿冈底斯南缘向北俯冲消减的产物,但是这些火山岩还未见系统的地球化学数据,对其成因也缺乏深入的讨论。通过对桑日群火山岩详细的地球化学研究,识别出麻木下组火山岩具有典型的埃达克岩的地球化学特征：高Sr（平均为977ug／g）,低Y（平均为10．4ug／g）、Yb（平均为0．942ug／g）含量,轻重稀土强烈分异（La／Yb平均为24．8）;另外岩石还具有相对低sr和高Nd的同位素组成（^87Sr／^86Sr）i=0．703506～0．704369,（^143Nd／^144Nd）,=0．512728～0．512778,εNd（t）平均为5．58,显示出与雅鲁藏布江蛇绿岩的MORB相似的同位素特征,表明其可能来源于新特提斯雅鲁藏布江洋岩石圈的部分熔融。而相对高的MgO（平均为4．38％）、Cr（平均为198ug／g）和Ni（平均为117ug／g）含量暗示原始的埃达克质熔体在其上升过程中与上覆地幔楔发生了反应。综合考虑新特提斯洋以及冈底斯造山带的演化历史,提出麻木下组埃达克岩可能是在早白垩世时雅鲁藏布江新特提斯洋北向俯冲消减的初始阶段由洋壳部分熔融所形成的认识。     

Eustatic control of late Quaternary sea-level change in the Arabian/Persian Gulf

Accurate sea-level reconstruction is critical in understanding the drivers of coastal evolution. Inliers of shallow marine limestone and aeolianite are exposed as zeugen (carbonate-capped erosional remnants) on the southern coast of the Arabian/Persian Gulf. These have generally been accepted as evidence of a eustatically driven, last-interglacial relative sea-level highstand preceded by a penultimate glacial-age lowstand. Instead, recent optically stimulated luminescence (OSL) dating suggests a last glacial age for these deposits, requiring > 100 m of uplift since the last glacial maximum in order to keep pace with eustatic sea-level rise and implying the need for a wholesale revision of tectonic, stratigraphic and sea-level histories of the Gulf. These two hypotheses have radically different implications for regional neotectonics and land–sea distribution histories. Here we test these hypotheses using OSL dating of the zeugen formations. These new ages are remarkably consistent with earlier interpretations of the formations being last interglacial or older in age, showing that tectonic movements are negligible and eustatic sea-level variations are responsible for local sea-level changes in the Gulf. The cause of the large age differences between recent studies is unclear, although it appears related to large differences in the measured accumulated dose in different OSL samples.     

The origin of nitriles in shale oil

Because nitriles are unlikely to occur naturally in a geological environment but have been reported as being present in some shale oils their origin was investigated. A careful infrared study could find no trace of the nitriles in the shale but it was shown, by infrared and gas chromatography with a nitrogen sensitive detector, that they do occur in some but not all oils. They are formed in the pyrolysis process by the reaction of car?ylic acids and ammonia liberated from minerals such as ammonium feldspars present in the shale. If both species are not present nitriles are not formed in the product oil. Pyrolysis of a brown coal, Loy Yang, in the presence of ammonia produced nitriles but none were generated when a more mature coal (Metropolitan) was similarly treated.     

A revision of the putative Late Cretaceous triconodonts from South America

Austrotriconodon mckennai and Austrotriconodon sepulvedai, from the Campanian Los Alamitos Formation, Patagonia, Argentina were originally described as triconodont mammals and the sole members of the family Austrotriconodontidae. These mammals were represented by isolated cheek teeth originally regarded as molariforms, but their peculiar morphology later raised doubts about their purported triconodont affinities. Nevertheless, the morphological bases supporting the alternative taxonomic views have not been fully documented. We present here detailed comparisons of Austrotriconodon with other Late Cretaceous taxa and conclude that Austrotriconodon specimens should be assigned to Meridiolestida and Mesungulatoidea. These isolated teeth are likely premolars and might represent unknown dental positions of already described species or correspond to taxa that are yet to be formally recognized. According to our interpretation, there is still no record of Cretaceous triconodonts in South America, but we support the triconodont affinities for Jurassic taxa from the Cañadón Asfalto Formation in central Patagonia.     

库车前陆盆地与波斯湾盆地盐构造对比研究

通过对库车前陆盆地和波斯湾盆地的盐层发育状况、盐构造特征以及盐构造与油气关系的对比研究,认为盐底辟构造与油气密切相关。库车前陆盆地勘探程度较低,应注重寻找盐底辟构造,以及与其相关的圈闭。库车前陆盆地盐构造的形成机制与波斯湾盆地下法尔斯组/加奇萨兰组相似,与霍尔姆兹组不同。根据波斯湾盆地下法尔斯组/加奇萨兰组盐构造在油气成藏中的作用,认为库车前陆盆地南部盐层较厚的地区应加强盐下勘探的力度,寻找盐下圈闭。北部山前盐层欠发育地区应注重寻找盐上圈闭,同时兼顾盐下圈闭。库车前陆盆地具有良好的三叠系和侏罗系烃源岩,应该有很广阔的勘探前景。     

The origin of sand deposits in the South Minusa basin

The paper deals with the origin of a large number of sand massifs concentrated in the South Minusa basin. The study of the sand deposits was based on field and laboratory work. Cross sections were selected in such a way as to penetrate the deposits of ridgy sands and the underlying surface at different hypsometric levels. Cross-section studies have demonstrated that the sands formed both under subaerial and subaqueous conditions. Analysis of the work of our predecessors has shown that the formation of a thick unit of subaqueous sand deposits, including those at high hypsometric levels, might be related to the removal of large amounts of sediments by catastrophic flooding along the Yenisei River caused by the failure of an ice dam in the Darhad basin at ~ 17 ka. The overlying sand deposits, which now occur as sand bars, are of eolian genesis. These bars formed in the Late Holocene owing to eolian transport and redeposition of the underlying sand members.