GEOLOGICAL STRUCTURE OF THE PRE-JURASSIC BASEMENT OF THE CENTRAL PART OF THE KRASNOLENINSKY SWELL IN THE LIGHT OF NEW GEOLOGICAL AND GEOPHYSICAL DATA

The article reviews features of the pre-Jurassic geological structure of the Krasnoleninsky Swell, located on the western edge of the West Siberian petroleum basin. New geological and geophysical materials are presented enabling significant clarifification of the relationships pattern between Precambrian, Paleozoic and Triassic formation complexes. The stratification of the pre-Jurassic section is based on previously known age determinations and datings made in recent years by high-precision methods. The analysis of mode of occurrence of Pre-Jurassic rock complexes is based on the interpretation of seismic materials and gravity and magnetic data. The proposed model of the Krasnoleninsky Swell pre-Jurassic basement is characterized by the significantly reduced volume of pre-Cambrian formations due to the expansion of the Paleozoic complexes area, local Paleozoic depressions at the base of the Yem-Yegovskaya and Kamennaya peaks and linear zones of development of Triassic terrigenous-volcanogenic rocks on the Talinskaya Terrace and in the Palyanovsky trough have been identified. The conclusion is made about the long and complex history of the basement structure formation in the zone of collision junction of divergent Ural and Central-West Siberian folded systems.

Comparative characteristics of lithogeochemical features of the upper jurassic deposits of the paksa and lower lena facies regions (north of Сentral Siberia)

A comparative analysis of lithogeochemical features of Upper Jurassic rock composition of the lower reaches of the Anabar river and the Urdyukh-Haya cape (Nordvik peninsula) was performed. Several common features, differences and regularities of changes in the section of lithogeochemical characteristics of the studied strata were revealed. The rocks of the Kimmeridgian and upper-middle Volgian have the greatest differences from the higher and lower layers. They are characterized by an increase in the content some of impurity elements (Co, Ni, Zn, U, and some TR). The identified features can be used for correlation when comparing faunal mute strata in the considered part of the sedimentary basin.

Morphology and sedimentary filling of an ancient estuarine valley in an urban environment (Gijón, NW Spain)

<p>The city of Gijón is located on the Cantabrian Coast (NW, Spain), and its subsurface is formed mainly by sand linked to an old estuarine mouth barrier (beach and dunes), sand bay and marshes. Under these sediments, there is a layer of clays related to the weathering of a Jurassic rock basement. This research addresses the setting of the estuary sediments in both the submerged area, located north of the city, and under the built-up area.</p><p>The seafloor morphology was investigated by means of a bathymetric survey with multi-beam echo sounder. A geophysical survey using high-resolution reflection seismic profiles allowed studying the thickness of the unconsolidated deposits that fill the bay of Gijón. Likewise, the distribution of coastal sediments under the city was reviewed from boreholes collected within a GIS-based geotechnical database.</p><p>The bathymetric reconstruction led to the identification of a paleo-valley supposedly excavated by the main river of the city, with N-S orientation that evolves to NNE-SSW towards the north. It shows a sandy bottom with a very low slope, a length of about 4 km and a width that ranges between 400 and 800 m. In this channel, the unconsolidated deposits reach a maximum thickness of around 15 m while at S, in the urban subsurface, the thickness exceeds 20 m locally. With these data, it was also possible to investigate the geometry of the bedrock under the sedimentary filling.</p>

Reservoir Productivity Analysis of Intercalated Limestone and Anhydrite Beds in Zagros Folded Belt, Kurdistan Region of Iraq

The Early Jurassic rock of Alan Formation in Barda Rash field has been examined using petrophysical wireline log analysis, drilling stem test, mud logging reports, drilling cutting and core samples for evaluation of reservoir potentiality and fluid production throughout heterogeneous rocks intervals in three exploration and appraisal wells. The Alan Formation consists of intercalation of light, chalky and argillaceous limestone beds with shale layers in the upper part and dominantly anhydrite layers from the middle to the lower parts of the formation. Qualitatively, weak oil shows of light brown to dark brown and blackish heavy oil have been observed while drilling. Furthermore, light brown trace oil has been recorded in the fracture surfaces of the core samples. The wireline log analysis provided an overestimated result for the hydrocarbon bearing interval identification and fluid movability index as the anhydrite layers confused the fluid distribution detection in the drilled interval. However, the combined results achieved from the mud logging reports and drilling stem tests were operated within the drilled intervals shown a limited productivity levels from the limestone beds of the Early Jurassic Alan Formation. The oil production from the studied interval does not exceed 10% and the entire production rates were composed of formation water with a trace amount of gases. As a result, the Early Jurassic Alan Formation can be considered as a tight carbonate reservoir rocks in the Barda Rash field.

Control litológico y estructural de los deslizamientos en el monte Rodiles (Asturias, España) Lithological and structural control of landslides in the Rodiles Hill (Asturias, Spain)

Resumen: El monte Rodiles, situado en el margen oriental de la ría de Villaviciosa, conserva evidencias de ocupación histórica desde sus orígenes como castro romanizado. El asentamiento está limitado en su vertiente sur por los restos de una muralla defensiva, mientras que en la ladera nororiental existen escarpes rocosos que debieron de actuar como defensa del enclave. Este trabajo realiza un análisis del relieve y revisa la estructura del sustrato geológico en el entorno próximo para determinar el origen de los escarpes en la ladera nordeste. Los datos de campo y el análisis de la topografía permiten identificar la existencia de varios deslizamientos que afectan a gran parte de la ladera nororiental del monte Rodiles. La masa deslizada aprovecha la inclinación de la sucesión litológica del Jurásico hacia el NE. La existencia de un nivel de arcillas, mecánicamente incompetentes, por debajo de los conglomerados de la Formación La Ñora, mecánicamente más competentes, permite el movimiento de la ladera hacia el mar. Estos escarpes están además alineados con la terminación lateral de una falla normal Mesozoica reactivada posteriormente como una falla inversa durante el levantamiento de la Cordillera Cantábrica. Las cicatrices de los deslizamientos, desarrolladas sobre niveles métricos de conglomerados fracturados, constituyeron por tanto una defensa natural del enclave histórico.Palabras clave: enclave histórico, deslizamientos, estabilidad de taludes, conglomerados jurásicos.Abstract: The Rodiles hill, on the eastern shores of the Villaviciosa estuary, preserves evidences of historic occupation since the romans. The settlement has a defensive wall in the south and is bounded to the north by a cragged slope to the sea. This work investigates the relief and the structure of the rocks in the area aiming at finding an origin for the crags in the northeastern slope of the hill. Field observations and the analysis of the topography reveal the presence of several landslides that affect most of the northeastern hillside. The dip of the Jurassic rock sequence to the NE and the presence of a two meter-thick layer of shales, mechanically very plastic, below the La Ñora conglomerates Formation, mechanically very competent, favours the slip of the hillside. The scarps are aligned with the lateral termination of a Mesozoic normal fault, reactivated as a reverse fault during the formation of the Cantabrian Mountains. The head scarps at the back of the landslides, developed on fractured conglomerates, constituted a natural defence during the historic settlement.Keywords: historic settlement, slides, slope stability, Jurassic conglomerates.

Post Jurassic shortening in the western Surat Basin relative to underlying basement depth and faulting

The Hutton-Wallumbilla (HWF), Merivale (MF), Kia Ora, and Injune faults are the major structures in the western Surat Basin, deforming Palaeozoic to Jurassic rock units. The authors present results from the interpretation of gridded gravity data and open-file seismic reflection data, which provide constraints on the geometry and kinematics of these faults. The interpretation of gravity data indicates that the HWF and MF are expressed by sharp lineaments in moderate to high-amplitude anomalies, indicating a deep-seated nature of the faults. The interpretation of seismic lines shows that the HWF and MF are northeast-dipping and east-dipping reverse blind faults, respectively. Some other faults also displaced and folded the rock units of the Bowen and Surat basins, such as the Kia Ora and Injune faults. The MF, Kia Ora, and the northern part of the HWF acted as normal faults during the early Permian and then have been inverted during the Late Permian–Triassic Hunter-Bowen Orogeny phases, especially during the early Late Triassic. The largest fault throws in the Bowen Basin successions are observed along the southern part of the HWF and its central splay, which are around 350 m and 480 m, respectively. The stratigraphic units of the Surat Basin above it have gently been folded over the major blind faults. The largest amount of shortening in the Surat Basin has taken place over the southern part of the HWF by 0.5%. The basement depth played an important role in the amount of contractional deformation in the Bowen and Surat basins. Where the basement is shallow, the amount of deformation along the faults in both the Bowen and Surat basins is higher.