Detachment folding in a Lower Cambrian–Upper Permian karst reservoir: 3D model of the Yubei 3D area (eastern Markit Slope,Tarim Basin,Northwest China)

A three-dimensional (3D) structural modeling of the Lower Cambrian–Upper Permian Yubei 3D area was performed to understand its structural evolution. This model reproduces the present-day structure of the basin and comprises 11 horizons within Lower Cambrian to Upper Permian rocks. The analysis is based on 3D depth views and faults. The results image salt movements due to tectonics and/or burial. From these observations, this paper deduces that salt structures are correlated to the main faults and tectonic events. From the model analysis, we interpret the timing and geometry of Tarim Basin tectonics. The fault geometry can be resolved based on the strike of the fault, the morphology of hanging wall strata, and the stratigraphic distribution. Emphasis is placed on gypsum rock detachment, considering its movements during the Middle Caledonian event and decoupling effects during tectonic evolution. Moreover, we point to the structural control of the Paleozoic basement and the crustal architecture (Yubei 3D Zone) on the geometry of the Tarim Basin.     

Biostratigraphy of a Paleocene–Eocene Foreland Basin boundary in southern Tibet

This study of the Paleocene–Eocene boundary within a foreland basin of southern Tibet, which was dominated by a carbonate ramp depositional environment, documents more complex environmental conditions than can be derived from studies of the deep oceanic environment. Extinction rates for larger foraminiferal species in the Zongpu-1 Section apply to up to 46% of the larger foraminiferal taxa. The extinction rate in southern Tibet is similar to rates elsewhere in the world, but it shows that the Paleocene fauna disappeared stepwise through the Late Paleocene, with Eocene taxa appearing abruptly above the boundary. A foraminifera turnover was identified between Members 3 and 4 of the Zongpu Formation—from the Miscellanea–Daviesina assemblage to an Orbitolites–Alveolina assemblage. The Paleocene and Eocene boundary is between the SBZ 4 and SBZ 5, where it is marked by the extinction of Miscellanea miscella and the first appearance of Alveolina ellipsodalis and a large number of Orbitolites. Chemostratigraphically, the δ13C values from both the Zongpu-1 and Zongpu-2 Sections show three negative excursions in the transitional strata, one in Late Paleocene, one at the boundary, and one in the early Eocene. The second negative excursion of δ13C, which is located at the P–E boundary, coincides with larger foraminifera overturn. These faunal changes and the observed δ13C negative excursions provide new evidence on environmental changes across the Paleocene–Eocene boundary in Tibet.     

Geochemical Characteristics of Different Kinds of Crude Oils in the Tarim Basin,Northwest China

Based on the compositions and distributions of biomarkers in thirty-five representative oil samples, oils from the Tarim Basin of northwestern China are mainly divided into two oil families. One oil family contains relatively low amounts of C₁₅-C₂₀ isoprenoid hydrocarbons and shows pristane predominance with Pr/Ph ratios ranging from 1.50 to 3.00. The GC/MS analytical data of these oils show the occurrence of abundant hopanes, and low concentrations of steranes and tricyclic terpanes with hopanes/steranes ratios from 6.25 to 12.24 and tricyclic terpanes/hopanes ratios from 0.03 to 0.24. These oils contain low drimane relative to homodrimane (C₁₅/C₁₆ < 1.0) and abundant rearranged bicyclanes in bicyclic sesquiterpanes. They are dominated by low carbon number (C₁₉-C₂₁) compounds in the tricyclic terpanes, and are rich in rearranged hopanes, C₂₉Ts and an unknown C₃₀ compound in pentacyclic triterpanes. These geochemical characteristics suggest that the oils were generated mainly from terrigenous organic matter. The other oil family shows remarkably different biomarker compositions and distributions. The oils revealed Pr/Ph ratios of about 1.0, high drimane/homodrimane ratios (>1.0), low hopanes/steranes ratios (0.65–2.50), high tricyclic terpanes/hopanes ratios (0.30–2.00) and a dominant peak at C₂₃ in tricyclic tepanes, suggesting a marine organic origin. Oil-source rock correlation indicates that these two oil families seem to have been derived from Mesozoic Jurassic-Triassic terrestrial source rocks (shales and coal seams) and Lower Paleozoic Ordovician-Cambrian marine source rocks, respectively.     

Moho depth determination beneath the Zagros Mountains from 3D inversion of gravity data

Due to its geological and economic importance, the Zagros Mountains have been investigated by many researchers during the last decades. Nevertheless, in spite of all the studies conducted on the region, there are still some controversial problems concerning the structure of the Zagros Mountains, including crustal depths, demanding more insights into understanding the crustal constraints of the region. Accordingly, we have conducted a gravity study to determine Moho depth map of the Zagros Mountains region, including its major structural domains from the coastal plain of the Persian Gulf to central Iran. The employed data are the densest and most accurate terrestrial gravity data set observed until now with the precision of 5 μGal and resolution of 5 arc-minute by 5 arc-minute. To image Moho depth variations, gravity inversion software GROWTH2.0 is used, proposing the possibility to model stratified structures by means of a semi-objective exploratory 3D inversion approach. The obtained results reveal the crustal thickness of ~?30–35 km underneath the southwestern most Zagros Fold-Thrust Belt increasing northeastward to 48 km. The maximum Moho depth is estimated ~?62 km below the Zagros Mountains belt along the Main Zagros Thrust. Northeast of the study area, an average crustal thickness of 46 km is computed beneath Urumieh–Dokhtar magmatic arc and central Iran.     

Hydrogeological Characteristics of a Karst Mountainous Catchment in the Northwest of Vietnam

This paper presents a preliminary assessment of the hydrogeological characteristics of a karst mountainous catchment, the Suoi Muoi River catchment, in the northwest of Vietnam. The catchment is located at 600 -700 m a.s.l. and covers an area of 284 km. Exposed limestone occupies 32% of the total catchment area. Various types of assessments have been carried out, including geological and hydrogeological field surveys, cave surveys, dye-tracer tests, meteorological and surface water monitoring. Geological studies and cave surveys have identified the most important active cave/conduit systems within the catchment. Although these data are essential, they are insufficient to make a comprehensive appraisal of the hydrologic nature of the catchment under interest. An attempt was made to calculate a global water balance of the catchment, based on short-term (15 months) meteorological and streamflow records. The results show that, despite the existence of a number of substantial cavem conduit systems, the groun     

Facies and depositional architecture according to a jet efflux model of a late Paleozoic tidewater grounding-line system from the Itararé Group (Paraná Basin), southern Brazil

During the Late Paleozoic, the Gondwana supercontinent was affected by multiple glacial and deglacial episodes known as “The Late Paleozoic Ice Age” (LPIA). In Brazil, the evidence of this episode is recorded mainly by widespread glacial deposits preserved in the Paraná Basin that contain the most extensive record of glaciation (Itararé Group) in Gondwana. The Pennsylvanian to early Permian glaciogenic deposits of the Itararé Group (Paraná Basin) are widely known and cover an extensive area in southern Brazil. In the Doutor Pedrinho area (Santa Catarina state, southern Brazil), three glacial cycles of glacier advance and retreat were described. The focus of this article is to detail the base of the second glacial episodes or Sequence II. The entire sequence records a deglacial system tract that is represented by a proximal glacial grounding-line system covered by marine mudstones and shales associated with a rapid flooding of the proglacial area. This study deals with the ice proximal grounding-line systems herein interpreted according to lab model named plane-wall jet with jump. Detailed facies analysis allowed the identification of several facies ranging from boulder-rich conglomerates to fine-grained sandstones. No fine-grained deposits such as siltstone or shale were recorded. According to this model, the deposits are a product of a supercritical plane-wall outflow jet that changes to a subcritical jet downflow from a hydraulic jump. The hydraulic jump forms an important energy boundary that is indicated by an abrupt change in grain size and cut-and-fill structures that occur at the middle-fan. The sedimentary facies and facies associations show a downflow trend that can be subdivided into three distinct stages of flow development: (1) a zone of flow establishment (ZFE), (2) a zone of transition (ZFT), and (3) an established zone (ZEF). The proximal discharge is characterized by hyperconcentrated-to-concentrated flow due to the high energy and sediment-laden nature of the flows. At the transitional zone, a hydraulic jump produces a rapid shift of conglomeratic to sandy facies with associated scour features. Towards the distal zones, the jet detaches to originate a vertical turbulent jet characterized by more diluted flows. Discussion of fan facies and architecture within a framework of jet-efflux dynamics provides an improved understanding of grounding-line fans systems that produce coarse-grained strata commonly enclosed by fine-grained rocks. The results have clear implication in terms of prediction of facies tract and geometry of oil and gas reservoirs deposited under similar conditions. And also can be useful to identifying the position of a glacial terminus through time.     

Application of a 3D photorealistic model for the geological analysis of the Permian carbonates (Khuff Formation) in Saudi Arabia

Three dimensional (3D) photorealistic models of geological outcrops have the potential to enhance the teaching of earth sciences by providing scale models in a virtual reality environment. These models can be run on low-cost desktop computers. Photorealistic models for geological outcrops are a digital illustration of outcrop photographs with either a point cloud representation or Triangular Irregular Network (TIN) mesh of the outcrop surface. The level of detail for these models is dependent on the target resolutions (physical and optical) that were used during data acquisition. In addition, the technique in which the data is rendered as a digital model affects the level of detail that can be observed by the geologists. A colored point cloud representation is suitable for large-scale features, but fine details are lost when the geologist zooms in to view the model close up. In contrast, a photorealistic model that is constructed from photographs draped onto a triangle mesh surface derived from Light Detection and Ranging (LiDAR) point clouds provides a level of detail that is restricted only by the resolution of the photographs.     

A balanced 2D structural model of the Hammerhead Delta–Deepwater Fold-Thrust Belt,Bight Basin,Australia

The Hammerhead Delta–Deepwater Fold-Thrust Belt is located in the Ceduna Sub-Basin of the Bight Basin, offshore southern Australia. It is synonymous with the Hammerhead Supersequence and consists of three, Campanian to Maastrichtian, deltaic sediment packages. The Hammerhead Delta–Deepwater Fold-Thrust Belt is a short-lived gravity-gliding system that exhibits a distinctive spoon-shape in cross-section. The system detaches on a master horizon at the top of the Tiger Formation. Finite Element Method based two-dimensional restorations show that the Hammerhead Delta–Deepwater Fold-Thrust Belt is a near-balanced system with near equal amounts of up-dip extension and down-dip compression. Overall, there is only 2.4% additional extension in the Hammerhead Delta–Deepwater Fold-Thrust Belt. This near-balanced system is unusual in comparison with other passive margin Delta–Deepwater fold-thrust belts, which generally demonstrate large amounts of extension compared with shortening, due to the regional-scale progradational nature of the systems. The results suggest that sediment input to the Hammerhead Delta–Deepwater Fold-Thrust Belt was not sufficient to result in the regional-scale progradation of fault activity and that the sediment supply shutdown before the system could develop in an extensive passive margin Delta–Deepwater fold-thrust belt, hence demonstrating that it is sediment supply that drives ongoing gravitational deformation in Delta–Deepwater fold-thrust belts and not slope gradient.     

The Depositional Environment of the Cretaceous Kizilsu Group in Xinjiang——With a Discussion of the Lowermost Marine Horizon of the Cretaceous in the Western Tarim Basin

In this paper. it is demonstrated that there exist marine horizons in the upper part of the lower subcycleand the upper subeycle of the Kizilsu Group in Xinjiang. based on new evidence of authigenic glauconite.boron content. carbon and oxygen stablc isotopic analyses. and lithological and sedimentary features. The up-per part of the lower subeycle is the lowermost marine horizon of the Cretaceous in the western Tarim Basin,which is inferred to be of Barremian age.     

3D Numerical model of the Obama hydrothermal–geothermal system,Southwestern Japan

The Obama geothermal field is one of the most interesting geothermal areas in Kyushu Island, Southwestern Japan, because of its large number of high-temperature springs. A 3D numerical simulation study using the simulator TOUGH2 (module EOS3) was carried out to obtain a comprehensive hydrothermal model of the field. From previous geochemical studies, two main fluid sources were suggested for the Obama geothermal system: cold (sea, surface, and ground) water and deep geothermal fluids. We propose two heat sources, a lateral one at the eastern boundary of the system, near the West Unzen High Temperature Body located west of the Unzen fumarolic field, and a second one beneath the Obama geothermal field. The first source contributes the system by 150°C fluids. The second source contributes by 100°C fluids. Our model indicates that the first source has a temperature of 150°C, which agrees with the results from previous geochemical studies. The low enthalpy of the second source could be explained by the mixing of geothermal fluids with seawater, as the area is near the seashore and is highly faulted. The model that was developed can explain many of the subsurface processes active in the Obama geothermal field.     

Variation of uncertainty of drainage density in flood hazard mapping assessment with coupled 1D–2D hydrodynamics model

Coupled 1D–2D hydrodynamic models are widely utilized in flood hazard mapping. Previous studies adopted conceptual hydrological models or 1D hydrodynamic models to evaluate the impact of drainage density on river flow. However, the drainage density affects not only river flow, but also the flooded area and location. Therefore, this work adopts the 1D–2D model SOBEK to investigate the impact of drainage density on river flow. The uncertainty of drainage density in flood hazard mapping is assessed by a designed case and a real case, Yanshuixi Drainage in Tainan, Taiwan. Analytical results indicate that under the same return period rainfall, reduction in tributary drainages in a model (indicating a lower drainage density) results in an underestimate of the flooded area in tributary drainages. This underestimate causes higher peak discharges and total volume of discharges in the drainages, leading to flooding in certain downstream reaches, thereby overestimating the flooded area. The uncertainty of drainage density decreases with increased rainfall. We suggest that modeling flood hazard mapping with low return period rainfalls requires tributary drainages. For extreme rainfall events, a lower drainage density could be selected, but the drainage density of local key areas should be raised.

     

Spatial variability of the Purbeck–Wight Fault Zone—a long-lived tectonic element in the southern UK

New seamless onshore to offshore bedrock (1:10 k scale) mapping for the Lyme Bay area is used to resolve the westward termination of the Purbeck–Wight Fault Zone (PWFZ) structure, comprising one of the most prominent, long-lived (Variscan–Cimmerian–Alpine) structural lineaments in the southern UK. The study area lies south of the Variscan Frontal Thrust and overlays the basement Variscide Rhenohercynian Zone, in a region of dominant E-W tectonic fabric and a secondary conjugate NW-SE/NE-SW fabric. The PWFZ comprises one of the E-W major structures, with a typical history including Permian to early Cretaceous growth movement (relating to basement Variscan Thrust reactivation) followed by significant Alpine (Helvetic) inversion. Previous interpretations of the PWFZ have been limited by the low resolution (1:250 k scale) of the available offshore BGS mapping, and our study fills this gap. We describe a significant change in structural style of the fault zone from east to west. In the Weymouth Bay area, previous studies demonstrate the development of focussed strain associated with the PWFZ, accompanied by distributed strain, N-S fault development, and potential basement uplift in its hangingwall. In the Lyme Bay area to the west, faulting is dominantly E-W, with N-S faulting absent. Comparison of the newly mapped faulting networks to gravity data suggests a spatial relationship between this faulting variation and basement variability and uplift.     

Gas Occurrence and Accumulation Characteristics of Cambrian–Ordovician Shales in the Tarim Basin, Northwest China

The Tarim Basin is located in northwestern China and is the biggest basin in China with huge oil and gas resources. Especially the Lower to Middle Cambrian and Middle to Upper Ordovician possess the major marine source rocks in the Tarim Basin and have large shale gas resource potential. The Cambrian–Ordovician shales were mainly deposited in basin–slope facies with thicknesses between 30–180 m. For shales buried shallower than 4500 m, there is high organic matter abundance with TOC (total organic carbon) mainly between 1.0% and 6.0%, favorable organic matter of Type I and Type II, and high thermal maturity with RoE as 1.3%–2.75%. The mineral composition of these Cambrian–Ordovician shale samples is mainly quartz and carbonate minerals while the clay minerals content is mostly lower than 30%, because these samples include siliceous and calcareous shale and marlstone. The Cambrian and Ordovician shales are compacted with mean porosity of 4% and 3%, permeability of 0.0003×10?3–0.09×10?3 μm2 and 0.0002×10?3–0.11×10?3 μm2, and density of 2.30 g/m3 and 2.55 g/m3, respectively. The pores in the shale samples show good connectivity and are mainly mesopore in size. Different genetic types of pores can be observed such as intercrystal, intergranular, dissolved, organic matter and shrinkage joint. The reservoir bed properties are controlled by mineral composition and diagenesis. The maximum adsorption amount to methane of these shales is 1.15–7.36 cm3/g, with main affecting factors being organic matter abundance, porosity and thermal maturity. The accumulation characteristics of natural gas within these shales are jointly controlled by sedimentation, diagenesis, hydrocarbon generation conditions?, reservoir bed properties and the occurrence process of natural gas. The natural gas underwent short-distance migration and accumulation, in-place accumulation in the early stage, and adjustment and modification in the later stage. Finally, the Yulin (well Y1) and Tazhong (well T1) areas are identified as the targets for shale gas exploration in the Tarim Basin.     

Cyclostratigraphy across a Mississippian carbonate ramp in the Esfahan–Sirjan Basin,Iran: implications for the amplitudes and frequencies of sea-level fluctuations along the southern margin of the Paleotethys

International Journal of Earth Sciences - The Tournaisian–Visean carbonate successions of the Esfahan–Sirjan Basin (ESB) from Sanandaj–Sirjan Zone, Iran, have been used to...     

Condition of development of collapse structure in the southern–central Atlassic Tunisia case study to Gafsa Basin

The Bou Omrane is an example of southern–central Atlassic Tunisian folds, this massive is presented by an anticline delimited by a NE–SW thrust. The geometry study of this anticline (hinge and subvertical layers) associated to structural and stratigraphic correlation confirms the development of structures according to “fault propagation fold” model. Using numerical software Rampe 1.3.0, the balanced cross-sections demonstrate the complicated growth of Bou Omrane anticline. The resulted structure is obtained by thrusting on breakthrough coupled to blockage of ramp on the back limb. All these condition confirm the role of diversity of tectonics events and the inheritance tectonics notion associated with the reactivation of pre-existing faults on the genesis of folds and the development of collapse structures according to more than one decollement level.     

The evolution of a Late Cretaceous–Cenozoic intraplate basin (Duaringa Basin), eastern Australia: evidence for the negative inversion of a pre-existing fold–thrust belt

International Journal of Earth Sciences - The Duaringa Basin in eastern Australia is a Late Cretaceous?–early Cenozoic sedimentary basin that developed simultaneously with the opening of the...