Cenozoic Formations Research Articles

The Strike-Slip Fault System and Its Influence on Hydrocarbon Accumulation in the Gudong Area of the Zhanhua Depression, Bohai Bay Basin

The Gudong area contains abundant petroleum resources. Previous studies have mainly focused on the extension structure in this area, with its strike-slip characteristics remaining poorly understood. In this study, the geometry of the strike-slip faults in the Gudong area was investigated using high-resolution 3D seismic reflection and drilling data, as were their associated releasing and restraining structures. Based on the profile’s flower structure and the plane’s horsetail splay pattern, the Gudong fault in the study area can be characterized as a dextral strike-slip. Three types of strike-slip fault-associated structures can be identified in the study area: (a) a restraining bend occurring in the right-stepping area of the S-shaped Gudong strike-slip fault, (b) a restraining bend identified in the left-stepping, overlapping zone of the Gudong and Kendong faults, and (c) a releasing bend seen in the extensional horsetail splay structure at the southern end of the Gudong fault. The restraining stress induced the formation of a fault-related open anticline, which led to a significant increase in fault sealing efficiency, thereby preserving an estimated 75.479231 million tons of oil and 15.28317145 billion cubic meters of gas. Conversely, releasing transtensional stress has compromised the effectiveness of the traps, preventing hydrocarbon retention. Consequently, oil and gas have migrated upward along the horsetail faults to the top of Cenozoic formations and have then dispersed.

Depth estimation of pre-Kalahari basement in Southern Angola using seismic noise measurements and drill-hole data

The remote Southern region of Angola is covered by siliciclastic Kalahari Cenozoic formations that host underground aquifers of great importance to local populations affected by water scarcity problems. These aquifers are well developed where Kalahari sands reach appropriate thicknesses. On the other hand, at the eastern end of this area, regional aeromagnetic data recently acquired suggested the possibility of the continuity of the geological structures of the Lufilian Arc, sited in the nearby Zambia and Congo, southwestwards into Angola under the Kalahari formations. Once the Lufilian Arc is associated with the presence of the so-called Central African Copperbelt, this possibility increased the interest in determining the depth to Pan-African rocks under the Kalahari basin. To estimate the thickness of Kalahari formations in this area of difficult access and poor logistics, an expedited and non-invasive geophysical method was needed. Seismic noise and the single-station Nakamura technique were chosen, but due to the large distance of the study area from the ocean, one of the major sources of seismic noise, a test survey was acquired in the Cuvelai region to assess the signal quality, where the data was calibrated using available drill-holes. >170 points of seismic ambient noise were later acquired and the horizontal/vertical (HVSR) amplitude versus frequency curves were 1D inverted for the best velocity/density model for each station. The results were compared with 1D inverted legacy vertical electrical soundings reprocessed and validated in this work, showing similar depth-to-basement, while interpreted velocities/densities of geological formations were sampled and confirmed with measurements. A depth-to-basement map was produced using seismic information, mechanical soundings, and geological information. Despite the relatively reduced geographical area covered, the map presents valuable information for hydrogeology and mineral exploration purposes and agrees with a previously available coarser map of Kalahari thickness and with observations from geological surveys simultaneously conducted at the time of the seismic surveys.

Integrated stratigraphic, sedimentological and petrographical evaluation for CERN\u2019s Future Circular Collider subsurface infrastructure (Geneva Basin, Switzerland-France)

The European Organization for Nuclear Research (CERN) is currently undertaking a feasibility study to build the next-generation particle accelerator, named the Future Circular Collider (FCC), hosted in a 90–100 km subsurface infrastructure in the Geneva Basin, extending across western Switzerland and adjacent France. This article represents a preliminary, basin-scale stratigraphic and lithotype analysis using state-of-the-art Swiss and French stratigraphic terminology, set in context with the FCC. Existing stratigraphic information, rock cores and well reports, laboratory analyses and geophysical well-logs from 661 wells representative for the construction area have been integrated to pave the way for a multidisciplinary approach across several geoscientific and engineering domains to guide the FCC’s upcoming technical design phase. Comparisons with well-log data allowed the identification of rock formations and lithotypes, as well as to formulate a preliminary assessment of potential geological hazards. Regional stratigraphic evaluation revealed the FCC’s intersection of 13 geological formations comprising 25 different lithotypes across the Geneva Basin. A lack of data remains for the western to south-western subsurface region of the FCC construction area shown by well-density coverage modelling. The main geological hazards are represented by karstic intervals in the Grand Essert Formation’s Neuchâtel Member, Vallorbe and Vuache formations, associated to fractured limestone lithotypes, and Cenozoic formations represented by the pure to clayey sandstone-bearing Transition zone and Siderolithic Formation. Potential swelling hazard is associated to the presence of anhydrite, and claystone lithotypes of the Molasse Rouge and Grès et Marnes Gris à gypse formations, yielding up to 17.2% of smectite in the Molasse Rouge formation. Hydrocarbon indices in both gaseous and bituminous forms are encountered in the majority of investigated wells, and bear a potential environmental hazard associated with the Molasse Rouge deposits and fractured limestones of the Mesozoic Jura formations.

Middle Miocene Climate Transition as reflected by changes in ichnofacies and palaeosols from Patagonia, Argentina

The ichnofacies and palaeosols from the La Pava and Collón Curá formations were studied to shed light on the evolution of terrestrial ecosystems from Patagonia (Argentina) during the Middle Miocene Climate Transition. At Paso del Sapo, Cerrito Terciario and El Petiso localities (Chubut province), the La Pava Formation included Coprinisphaera ispp., Rosellichnus patagonicus, Rebuffoichnus casamiquelai, Feoichnus challa and burrows of spiders and earthworms, representing a case of the Rosellichnus ichnoassemblage of the Coprinisphaera Ichnofacies. Some of the components of this ichnoassemblage, scarce or absent in Cenozoic formations older than La Pava, are present in extant Patagonian habitats, pointing in the direction of extant invertebrate fauna. At El Petiso locality, the Collón Curá Formation included Celliforma ispp., Rosellichnus patagonicus, Fictovichnus ispp., Teisseirei barattinia and Teisseirei paladinco isp. nov., representing a case of the Celliforma Ichnofacies. The La Pava Formation comprises brownish, argillic, granular and strongly-developed palaeosols (Mollisols and Alfisols) formed in mildly stable to long-lasting landscapes, whereas the Collón Curá Formation comprises calcic, tuffaceous, paler and weakly-developed palaeosols (Andisols, Aridisols) formed in unsteady and ashy environments. The ichnofacies and palaeosols from the La Pava Formation indicate wooded grasslands developed in seasonal, subhumid and temperate-warm conditions, whereas those from the Collón Curá Formation indicate a habitat with reduced plant cover similar to semiarid and temperate-warm dry woodlands or bushlands. This shift towards more arid conditions in Patagonian landscapes would have been coeval with climatic changes corresponding to the Middle Miocene Climate Transition, a lapse of global temperature decrease associated with extensive drying.

U–Pb Zircon Geochronological and Petrologic Constraints on the Post-Collisional Variscan Volcanism of the Tiddas-Souk Es-Sebt des Aït Ikko Basin (Western Meseta, Morocco)

The NE–SW trending Tiddas Souk Es-Sebt des Ait Ikko (TSESDAI) basin, located at 110 km southeast of Rabat, in the region of Khmesset between the village of Tiddas and Souk Es-Sebt des Ait Ikko, is the third largest late Palaeozoic continental trough in the northern Central Moroccan Meseta. It is a ~20 km long and ~2–3 km wide basin, comprising mainly mixed volcano-sedimentary reddish-purple continental Permian rocks laying with an angular unconformity on Visean deep marine siliciclastic sediments and unconformably overlain by the Triassic and Cenozoic formations. In this study we aim to better determine the age of Permian volcanics and their chemical and mineralogical characteristics, as well as assess the provenance of inherited zircons, thus contributing to the understanding of the late stages of the Variscan orogeny in Morocco. The standard volcanic succession includes the following terms: (i) andesites, lapilli tuffs and andesitic ash deposits; (ii) accumulations of rhyolitic lavas; (iii) lapilli tuffs and rhyolitic ash (formation F1); (iv) flows and breccias of dacites; (v) andesite flows; and (vi) basaltic flows. The various volcanic and subvolcanic studied rocks display calc-alkaline-series characteristics with high contents of SiO2, Al2O3, CaO, MgO, and relatively abundant alkalis, and low contents of MnO. In the classification diagram, the studied facies occupy the fields of andesites, trachy-basalts, dacites, trachydacites, and rhyolites and display a sub-alkaline behavior. These lavas would be derived from a parental mafic magma (basalts) produced by partial fusion of the upper mantle. Specific chemical analyses that were carried out on the mineralogical phases (biotite and pyroxene) revealed that the examined biotites can be classified as magnesian and share similarities with the calc-alkaline association-field, while the clinopyroxenes are mainly augites and plot on the calc-alkaline orogenic basalt field. Andesites and dacites of TSESDAI show similarities with the rocks of the calc-alkaline series not linked to active subduction and which involve a continental crust in their genesis. The existence of enclaves in the lavas of the TSESDAI massif; the abnormally high contents of Rb, Ba, Th, and La; and the systematic anomalies in TiO2 and P2O5 indicate also a crustal contamination mechanism. Three magmatic episodes are distinguished with two episodes that correspond to an eruptive cycle of calc-alkaline andesites and rhyolites followed by a basaltic episode. The SHRIMP U–Pb geochronologic data of zircons recovered from the rhyolite dome of Ari El Mahsar in TSESDAI basin show a Concordia age of 286.4 ± 4.7 Ma interpreted to date the magmatic crystallization of this dome. Thus, the rhyolite likely belongs to the third magmatic episodes of TSESDAI.

HISTORICAL AND NOMENCLATURAL REMARKS ON SOME MEGATOOTHED SHARK TEETH (ELASMOBRANCHII, OTODONTIDAE) FROM THE CENOZOIC OF NEW JERSEY (U.S.A.)

. In the second issue of Samuel Morton’s “Synopsis of the Organic Remains of the Cretaceous Group of the United States” published in June 1835, several otodontid shark teeth from Cenozoic formations of New Jersey are named with authorship of Louis Agassiz and meet the conditions of availability of the International Code of Zoological Nomenclatural. It has gone largely unnoticed that some of these names were introduced in this work before their publication in Agassiz’s masterpiece “Recherches sur les poissons fossiles”. The specimens presented by Morton were kept in the John Price Wetherill (1794-1853) collection that found its way into the paleontological collection of the Academy of Natural Sciences of Drexel University, Philadelphia, where most of them have been rediscovered. These teeth are part of the type series upon which Agassiz introduced Lamna obliqua Agassiz in Morton, 1835, Lamna lanceolata Agassiz in Morton, 1835, Carcharias lanceolatus Agassiz in Morton, 1835, Carcharias megalotis Agassiz, 1835 and Carcharias polygurus Agassiz in Morton, 1835, all of these species being referred to the genus Otodus in the present work. In order to secure the nomenclatural stability of the Otodontidae, it is established that Otodus lanceolatus is a junior synonym of Otodus obliquus, that “Carcharias” lanceolatus belongs to the genus Otodus Agassiz, 1838 and is invalid as a junior secondary homonym of Otodus lanceolatus, that Otodus megalotis is a junior synonym of Otodus auriculatus (Blainville, 1818), and that Otodus polygurus (Otodus polygyrus being an incorrect subsequent spelling) is a junior synonym of Otodus megalodon (Agassiz, 1835). Furthermore, it is shown that the date of publication of Otodus obliquus (Agassiz in Morton, 1835) is 1835 and not 1838 as previously thought.

Stratigraphy, Geometry, and pattern of Imbricated zones, NW Zagros Fold and Thrust Belt in Iraqi Kurdistan Region

The High Folded and Imbricated zones are the formalized name represent the part of the Tectonic sub-division of Iraq and Kurdistan Region of Iraq (KRI). The study of compressional deformation and Stratigraphy are the keys to identify thrust faults structures and define the sequence of thrusting in High Folded and Imbrication zones as a part of Zagros Fold and Thrust Belts. Through this study, we try to describe the compressional thrust faults and stratigraphical unit description. Thrust faults make repetition of the sequences of Jurassic-Triassic Cretaceous sequence over thrust above Cretaceous sequences. In Iran-Iraq border close to Sirwan valley the large thrust faults (Sirwan-Sazan Thrust faults) identify. The fault system makes Triassic formations over-thrust the Valanginian-Albian Balambo Formations. In Balakayati area serious thrust fault exists, which creates twice repetition of Jurassic-Cretaceous formations forming imbrication thrusting system and fault propagation fold. In Bradost-Korek anticlines the Jurassic-Cretaceous formations over-thrust Cenozoic formations. In Kamosk anticline the thrust faults are in the Cretaceous formations. The dimension and the style of the thrust faults are different but generally, most of the decollement layers of the thrusting are the Early Triassic and Middle-Late Jurassic formations. The collection of all these results constrain geological cross-section in Imbricate Zone and restore to obtain the 7.5 km distance of Shortening due to folding and faulting.

A sedimentological record of fluvial-aeolian interactions and climate variability in the hyperarid northern Namib Desert, Namibia

AbstractThe aeolian regime of the 100 km wide, hyperarid Namib Desert has been sporadically punctuated by the deposition of fluvial sediments generated during periods of higher humidity either further inland or well within the desert from Late Oligocene to Late Holocene. Four new Late Cenozoic formations are described from the northern Skeleton Coast and compared with formations further south: the Klein Nadas, Nadas (gravels, sands), Vulture’s Nest (silts) and Uniab Boulder Formations. The Klein Nadas Formation is a trimodal mass-flow fan consisting of thousands of huge, remobilised, end-Carboniferous Dwyka glacial boulders, many >3 m in length, set in an abundant, K-feldspar-rich and sandy matrix of fine gravel. Deluge rains over the smallest catchments deep within the northern Namib were the driving agent for the Klein Nadas Fan, the termination of which, with its contained boulders, rests on the coastal salt pans. These rains also resulted in catastrophic mass flows in several of the other northern Namib rivers. The Uniab Boulder Formation, being one, consists only of huge free-standing boulders. Gravelly fluvial deposition took place during global interglacial and glacial events. The Skeleton Coast Erg and other smaller dune trains blocked the rivers at times. The low-energy, thinly bedded silt deposits of the central and northern Namib are quite distinctive from the sands and gravels of older deposits. Their intermittent deposition is illustrated by bioturbation and pedogenesis of individual layers. Published offshore proxy climatological data (pollens, upwelling, wind, sea surface temperatures) point to expansion of the winter-rainfall regime of the southern Cape into southwestern Angola during strong glacial periods between the Upper Pleistocene and Holocene. In contrast to deposition initiated by short summer thunder storms, we contend that the silt successions are river-end accumulations within which each layer was deposited by runoff from comparatively gentle winter rains that lasted several days.

Water-rock interactions and origin of formation water in the Bohai Bay Basin: A case study of the Cenozoic Formation in Bonan Sag

The faulted lacustrine Bohai Basin in eastern China contains abundant hydrocarbon resources. In these reservoirs, understanding the sandstone diagenesis and the resulting formation water provides a means to unravel the evolution processes in the basin. In most cases, the lack of isotopic and trace element analysis tests in this type of basin limits the research on the origin and evolution of formation water in this area. We have used multivariate statistical methods to classify the geochemical characteristics of the formation water for the Cenozoic Formation of Bonan Sag in the Bohai Bay Basin. Analysis of correlations among the evolution processes of different ions in different types of formation water provides an understanding of the primary factors influencing the ion content. We also evaluate the water-rock interactions of different types of formation water to evaluate their geologic significance, and we find three types. Type I formation water includes a mixture of river water, lake water, and atmospheric precipitation and exhibits weak water-rock interactions. Type II formation water contains primitive freshwater and brackish lake water that has undergone an evolution process similar to that of type I formation water, but that was followed by evaporation and concentration, the dissolution and precipitation of calcite and iron calcite, and feldspar dissolution. Type III formation water, which is a product of rock reconstruction, originates from saline lake sediment water. After undergoing evolution processes similar to those of types I and II, type III formation water is also affected by dissolution of evaporite, albite, dolomite, and iron dolomite. Thus, type III formation water is the product of water-rock interactions such as precipitation, SO42− reduction, and pyrite precipitation in which the water-rock reaction controls the development mechanism and characteristics of the reservoir space.

Seismic interpretation and cenozoic tectonic evolution of the Pozuelos Basin, Andean plateau, Argentina

The Andean basin formation across the Altiplano-Puna plateau has been mostly associated with: (i) interconnected depozones within a simple eastward-migrating foreland, (ii) isolated depocenters in a broken foreland or (iii) intermontane basins within a rising plateau setting. Particularly, the regions located further east from the western orogenic belts are key to disentangle these proposals. The Pozuelos Basin is today an internally-drained depositional area located at ~22°22′S in the easternmost Andean plateau (an area known as the Puna). While this basin might be key to understanding the formation of basins at these latitudes, between belts Puna and Cordillera Oriental, during the Andean orogeny, only a few studies have been done since most of their records are in subsurface. In order to address the Cenozoic formation and evolution of the Pozuelos Basin, and support some of the Andean basin formation hypotheses, we conducted seismic data interpretation, complemented with field surveys. Data allowed the correlation of seismic reflectors, five identified tectono-sequences (two basements –non-stratified and stratified– packages and three stratified Cenozoic packages) and subsurface structures with the local outcropping geology. In contrast to other areas from the Puna and Altiplano, the Pozuelos basin seems to have been affected by basement thrusting and deformation along its eastern boundary, previous to the late Miocene plateau formation. Despite that in the basin configuration was clearly an isolated and intermontane setting since the late Miocene, seismic and stratigraphic data suggest that during the Late Oligocene - Middle Miocene the Pozuelos basin would have behaved as well as a disconnected depositional zone. Some features like sequence encroachments and stratigraphic arrangements in outcrops drove us to interpret an intermontane broken foreland.

Late Mesozoic tectonic evolution of the central Bangong–Nujiang Suture Zone, central Tibetan Plateau

ABSTRACT The Bangong–Nujiang Suture Zone (BNSZ), located in the central Tibetan Plateau, experienced a Late Mesozoic transition from oceanic closure to continent–continent collision. Based on sandstone-composition analyses, U-Pb detrital-zircon dating and structural observations, we determined that this transition occurred coeval with the accretion of the Lhasa Terrane to Eurasia. According to our newly observed stratigraphic and geochronological data, we conclude the following: (1) the Upper Triassic-Lower Jurassic Muggar Gangri Group was mainly derived from the Qiangtang Terrane; (2) the Shamuluo Formation composed of Upper Jurassic-Lower Cretaceous shallow marine strata was sourced from both the Qiangtang Terrane and recycled Muggar Gangri Group; (3) the Lower Cretaceous (~125–110 Ma) Duoni Formation shows both Lhasa and Qiangtang detrital zircon fingerprints, indicating closure of the Bangong–Nujiang Ocean at ~120 Ma; and (4) the Upper Cretaceous Abushan Formation is a suite of intramontane molasse deposited after the Qiangtang–Lhasa collision. Therefore, these sedimentary strata record the transition from oceanic closure to continent–continent collision from 125 to 90 Ma within the central BNSZ. Moreover, based on relationships among strata distributions and thrust locations, we propose that thrust movements propagated southward during this transition and controlled sedimentary basin deposition. The Late Mesozoic tectonic transition within the BNSZ occurred well before the India-Asia collision and hence profoundly influenced the Cenozoic formation of the Tibetan Plateau.

Designation and Study of Anticlines- Kurdistan Region-NE Iraq

Iraq is located in the Western Asian continent particularly in the northern Arabian promontory. Iraq approximately lies in center of Middle East. The area of investigation cover northern and northeastern parts of Iraq-Kurdistan Region. Iraq and Kurdistan region are located in the northern Arabian Platform. The study area includes the northwestern extension of the Zagros Mountain range (the Zagros Fold and Thrust belt). Through study of Tectonic analysis, Stratigraphy, Geomorphology and satellite images; we try to constrain new classification with designation of the anticlines and compression stress orientation in Zagros fold belt. The northeastern and northern Iraq contain huge anticlines and synclines. They have been formed as a result of compression stress. These forces formed by collision of Arabia and Eurasian plates during Eocene-Miocene periods. Most of the anticlines characterize by double-plunging symmetrical to semi-symmetrical fold. The shield of the anticlines in the High Folded Zone mostly compose of carbonate sequence from Cretaceous formations. The core has Jurassic-Triassic formations. In the other hand the shield of anticlines in Low Folded Zones are Cenozoic formations. The plunging and terminate anticlines was caused by Cretaceous pre-tilting extensional normal faults. These fault become barriers in front of growing the anticlines longitudinally as example in Kosrat and Shakrok anticlines. The Cretaceous lateral facies change affected on the bend of anticline axis. The northwestern of Azmar anticline and southeastern of Surdash anticline seem to be En-echelon plunging; through this study we find out they are belong to one anticline. The Surdash-Azmar fold Axis shape is Bezier line while passing through facies change between Qamchuqa and Balambo Formations. The same phenomenon can be find in Aqra-Bekhme anticlines by facies change of Aqra-Tanjero formations. In this study, we try to make two or more anticlines to be show as one large anticline. In previous studies they split anticline into two or more anticlines because of having geomorphological features such as valley and lakes. However we try to show that valleys and lake are not barriers and not affect termination of the anticline as shown in Shirin, Bradost, anticlines are one individual anticline.

Cenozoic formation and colonisation history of the New Zealand vascular flora based on molecular clock dating of the plastid rbcL gene

ABSTRACTA colonisation history for 411 extant genera and 477 lineages of the vascular flora of New Zealand was constructed using the plastid rbcL gene. Molecular clock crown ages suggest that the Eocene-Oligocene transition extinction at 33.9 Ma was critical to the development of the extant flora as few lineages, mostly ferns and conifers, predate this event. Based on crown dates, almost all extant angiosperm lineages have established after the Eocene-Oligocene transition extinction. The Oligocene marine transgression had little discernible impact on the formation of the extant flora, as at the culmination of the inundation (22.0–25.0 Ma) fifty extant lineages of vascular plant were present and another eight lineages originated during this time. The majority of extant species (89%) originated after the end of the Miocene Thermal Optimum at about 15.0 Ma. Nearly 50% of the extant species have evolved during mountain uplift and glaciation of the late Pliocene-Pleistocene (0–4.99 Ma). Therefore, despite a residual contribution from the Eocene, Oligocene and early to mid Miocene periods, the New Zealand vascular flora essentially originated in the late Miocene and after.

Deformation at the eastern margin of the Northern Canadian Cordillera: Potentially related to opening of the North Atlantic

AbstractThe Northern Canadian Cordillera (NCC) comprises the Mackenzie Mountains, which are characterized by earthquakes occurring ~1,000 km east of the western North American margin. However, no recognized convergence has occurred in this inboard region since the Mesozoic to early Cenozoic formation of the Cordillera. This lack of an obvious driver for the modern NCC deformation has generated considerable debate and various geodynamic models. We show here thermal histories derived from (U‐Th‐Sm)/He data that are interpreted to indicate reactivated deformation and formation of the eastern deformation front beginning ~30 Ma. At that time the western margin of North America was mainly a transform boundary, which typically transmits very limited amount of stress into the continent. Along the northeastern margin of North America, however, the North Atlantic was opening and may have caused horizontal forces that drove deformation far to the west where the rigid craton encountered the weak Cordillera.

Characteristics and distribution of continental tight oil in China

Tight oil in China is mainly distributed in Mesozoic-Cenozoic continental petroliferous basins, either generally occurs in tight sandstone or tight carbonate reservoirs which are paragenetic to or in contact with lacustrine petroleum source rocks. By the end of 2016, the continental tight oil in China has established an annual production capacity of 1.55 million tons, and a cumulative oil production of 2.52 million tons. In 2016, the continental tight oil production in China was about 800,000 tons. By analyzing the characterization of the tight oil in Ordos Basin, Songliao Basin, Jungar Basin, the organic-rich shale in China were formed in multiple geological periods including the Permian, Triassic, Jurassic, Cretaceous, Neogene, and Paleogene, in freshwater, semi-saline to hyper-saline lacustrine depositional setting. They are generally tens of meters to several hundreds of meters thick, have total organic carbon (TOC) contents of 0.4–16%, and thermal maturity of 0.4–1.4%. Algal bloom as results of volcanism, low sedimentation rate, transgression, and stratification of water body are prominent factors controlling the formation of organic-rich shales. Tight oil reservoirs in China mainly include tight sandstone, tight carbonate rock, tight sedimentary tuff, etc., all of which are characterized by strong heterogeneity and poor petrophysical properties, with in situ porosity and permeability generally no more 12% and 1 × 10−3 μm2 respectively. They are also characterized by tight pore-throat systems of nano- to micro-scales, with pore throat diameters in the range of 80–1800 nm, and complex pore structures. The producing reservoirs have pressure coefficients between 0.7 and 1.8, covering under-pressure to over-pressure. Crude oil properties vary greatly with densities ranging from 0.75 to 0.92 g/cm3. It is believed that the abundance and effectiveness of hydrocarbon supply controls the formation of oil saturation, and tight oil “sweet spots” are generally in or near the areas with high hydrocarbon expulsion intensities. In addition, the quality of the source rock and the type of source reservoir control the distribution of the “sweet spots”, and storage space and movable fluid guarantee the formation of the “sweet spot” area of high oil saturation. “Sweet spots” are often developed in local mini-structural highs under a broad and gentle-sloped background. Continental tight oil in China has estimated geological resource of 14.66 × 109 tons with a technically recoverable resource of 1.45 × 109 tons. Tight oil is mainly distributed in Ordos Basin, Songliao Basin, Bohai Bay Basin, Junggar Basin, and Qaidam Basin, within the Mesozoic and Cenozoic formations. Overall China has a relatively large tight oil reserve and good exploration prospect.

FACTORS AND DYNAMICS OF VARIABILITY OF ZMEINYI ISLAND ROCKS FILTRATION PROPERTIES

Problem Statement and Purpose. Transmissivity (T) is one of the most important parameters in determining aquifer productivity and generally estimated from pumping tests. This study (for the period 01.2005-04.2008) focuses on the transmissivity behavior dynamic for pressure fractured-rock aquifer in the Devonian deposits of the Zmeinyi island. It presents a temporal variations in transmissivity under the influence of sea level, distance Earth-Moon and axial rotation of the Earth.Data & Methods. In the paper have studied the data from the experimental pumping test of the exploited well No 2, situated in the northwestern part of Zmeinyi island, having a depth of 50 m. Time-recovery plots (270 plots) were analyzed by using Theis Jacob method to obtain transmissivity. The geologic setting in the study area is generally composed of the Paleozoic deposits, including the Silurian and Devonian, as well as the Cenozoic formations. The lithology of the aquifer varies widely and includes conglobreccia, sandstone, conglomerate, mudstone and siltstone. By results of well logging tests for water-bearing rocks the following thickness intervals were established: 38.0-54.6 m; 57.6-74.0 m; 80.8-109.4 m. Within the upper interval represented by conglomerates, there are two aquifer subhorizons, separated by weakly fractured rocks, that is by relatively waterproof layer. A comparison of water-bearing rocks depth intervals and static water levels shows that ground water in the upper subhorizon is under pressure.Results. On the basis of a cross-spectral analysis of time series (using frequency transfer functions, coherence spectra and phase difference) correlations were revealed between variations of transmissivity and the following factors: sea level, mean Earth-Moon distance, Earth rotation speed. Variations in the correlation between transmissivity and factors influencing it allow assessing stress-strain state of water-bearing rocks. The results obtained from cross-spectral analysis showed that in the low frequency range, transmissivity is related to these factors linearly. In the range of periods from 5.5 to 11 days the Earth-Moon distance increases, the transmissivity value decreases and vice versa, with decreasing Earth-Moon distance (T) increases. For the same periods for accelerated motion of the Earth (T) increases, and vice versa, a decrease in Earth’s rotation speed is accompanied by a decrease of (T). For the sea level, for periods from 5.5 to 11 days, transmissivity is in the antiphase with sea level variations. The increase in sea water level corresponds to a decrease of (T) and decrease of sea water level corresponds to increase of (T).

The application of seismic interferometry for estimating a 1D S-wave velocity model with the use of mining induced seismicity

Abstract The main objective of this paper is to present the usefulness of the seismic interferometry method to determine the S-wave velocity model of the rock mass affected by exploitation in the KGHM Rudna copper ore mine. The research aim was achieved on the basis of seismic data, acquired from seismograms, of 10 strong seismic events of magnitude greater than 2.6. They were recorded by a pair of seismometers deployed on mining terrain. In the first stage, the Rayleigh wave between seismometers was estimated. Then, the group velocity dispersion curves of fundamental and first higher modes were identified. Finally, inversion of the dispersion curves to a 1D S-wave velocity model up to 500 m in depth was obtained. The velocity model was determined for the part of the rock mass partially affected by mining. The results confirm similar rock mass structure and velocities of the subsurface layers as those obtained by the archival 3D model. In both models, a high degree of correlation in the boundary location between the overburden of the Cenozoic formations and the bedrock of the Triassic formations was observed. The applied methodology can be used to estimate the S-wave velocity model in other mining regions characterized by strong seismicity.

Considering seismic coefficient distributions within slopes to calculate landslide reactivation probability

Landslides can be reactivated by earthquakes, causing severe damage to intensely urbanised areas. A probability analysis of earthquake-induced landslide reactivation was performed in the intensely urbanised Avcilar-Beylikduzu Peninsula, 35 km west of Istanbul (Turkey), by considering seismic coefficient distributions within slopes instead of attributing a constant seismic coefficient value. Nine rototranslational landslides with lengths ranging from 100 to 1000 m were inventoried; all of the landslides involved heterogeneous soils ascribable to Cenozoic formations and affected intensely urbanised areas that have expanded significantly over the last decade. Sinusoidal functions characterised by different frequencies and initial phases as well as amplitudes of 0.35 g, corresponding to the peak ground acceleration for a return period of 475 years, were considered. Landslide submasses with secondary sliding surfaces were treated by performing a separate stability slope analysis from that implemented for the main sliding surfaces. Sensitivity analyses were carried out by deriving horizontal seismic coefficient distributions within the landslide masses. These took the form of sinusoidal variations, each controlled by an assumed phase and frequency. Moreover, different water pressure distributions within the landside submasses were considered to account for the possible role of increased water pore pressure during rainfall events. Probability maps were obtained by computing the percentage probability of reactivation for each landslide submass taking into account all the considered seismic coefficient distributions. According to the results obtained, about 33 % of the inventoried landslides have a >50 % probability of being reactivated.

Mössbauer studies of the spectra of 57Fe nuclei in Late Cenozoic endogenous formations of the Eastern Caucasus

Three types of manifestations of Late Cenozoic endogenous activity (pyroclastic, hydrothermal explosive, and volcanogenic sedimentary formations) have been found over the last decade in different geostructural zones of the Terek–Caspian foretrough and the Alpine fold–thrust structure in the Eastern Caucasus. The results from Mossbauer studies show that these formations contain fractions of iron and its compounds with complex crystal structures in which 57Fe atoms occupy nonequivalent positions in the lattice with respect to their magnetic and electric fields, exist in different physicochemical states, and occur in various phases of the endogenous process products.

Prediction of water-inrush risk areas in process of mining under the unconsolidated and confined aquifer: a case study from the Qidong coal mine in China

The unconsolidated Cenozoic formation is well developed in the Qidong coal mine. Water-inrushes from the bottom unconsolidated Cenozoic aquifer, which is the confined aquifer, have happened several times during mining in the north mining area of the Qidong coal mine. To predict the water-inrush risk areas in the south mining area of the Qidong coal mine where some working faces have just begun to mine, the engineering analogy method is used on basis of the Fisher’s discriminant model from the actual mining situation in the north mining area. Six main influence factors including the effective thickness, the specific yield, and the load transfer coefficient of the aquifer, the effective thickness of the protective bedrock layer, the fractal dimensional value of bedrock faults and the distance between the key hard stratum and the primary mineable coal seam are selected as discriminant indexes, and their corresponding data in the north mining area of the Qidong coal mine are served as training samples. On this basis, the Fisher’s discriminant model for water-inrush is established and water-inrush risk areas including the safety, the medium risk and the risk areas of no. 61, 82 and 9 primary mineable coal seams in the south mining area of the Qidong coal mine are predicted by the model. The model’s accuracy is 90.4 %, the scatter diagram of training samples shows obviously classified effect and the field verification indicates that the predicted type is consistent with the actual type. Results show that the discriminant model is well applied in the engineering analogy method and the water-inrush risk areas predicted by the discriminant model contribute to the subsequent mining in the south mining area in the Qidong coal mine.