Three-dimensional Reconstruction of Geological Solids Based on Section Topology Reasoning

In order to solve the dynamic reconstruction and local updating problem of three-dimensional geological solids, topology reasoning is used for three-dimensional geological modeling. This can advance the level of the corresponding section automation in implementing the 3D geological solid dynamical reconstruction by the construction of and reasoning on topology on the 3D curved surface. This method has been successfully used in the Nanjing city geological modeling and the Zijin gold mine modeling. The results prove that this method adapts to coplanar section and noncoplanar section data, and improves the efficiency of 3D geological modeling.

A comparative study on the illite crystallinity and the clay mineral reflectance spectral index for subdividing the very low-grade metamorphic belt along the Lizhou-Hekou geological section in the Youjiang sedimentary basin, Guangxi, China

To examine the application potential of hyperspectral remote sensing techniques in classifying very low-grade metamorphic belts, the composition of clay minerals and the cyrstallinity of illite from mudstones were measured using XRD and VIS-SWIR (400—2500 nm) reflectance spectroscopy. Based on the illite cyrstallinity, Kbler Index (KI), the Early Triassic LuoLou Group and the Middle Triassic lower Baifeng Formation were classified as the lower Epizone with KID2q° ranging from 0.22 to 0.25, the upper Baifeng Formation as upper anchizone with KID2q° ranging from 0.26 to 0.33, and the Hekou Formation as lower anchizone with KID2q° ranging from 0.38 to 0.40. According to a KID2q° value of 0.43, it is possible that there may exist a local diagenetic zone in the upper strata. The illite cyrstallinity Kbler index and the metamorphic grade increase from the bottom to the top of the stratigraphic sequence. The metamorphic grade boundaries nearly match the stratigraphic boundaries, indicating a burial metamorphism nature for the stratigraphic sequence. From the bottom to the top of the sequence, the spectral absorption band center of clay minerals from fresh rocks is around 2200 nm. The absorption band centers change towards shorter wavelengths: the Luolou Group being at 2220 nm, the Baifeng Formation at 2217—2213 nm, the lower member of the Hekou Formation at 2214—2206 nm, and the upper member of the Hekou Formation at 2205—2197 nm. The spectral absorption band center of illite shows the same change pattern. These results indicate that very low-grade metamorphic belts can be subdivided using spectral indices of clay minerals, which are measured by using field portable spectroradiometers. However, it may not work well with satellite and airborne sensors.

Using satellite magnetic data to divide geological tectonic units of South China Sea

The South China Sea locates at the convergence center of the Eurasian Plate,the Pacific Plate and the Indo-Australia plate. The Cenozoic seafloor spreading in the South China Sea Basin is an important part of the tectonic evolution of the South China Sea that records information of the continental margin tectonic history and its impact on regional geologic evolution. Magnetic data contains abundant geological structure information from the surface to deep. This paper reports magnetic data of the South China Sea. Through the conventional processing of these magnetic data,we report general results on the regional magnetic anomalies,such as the upward continuation graph,the polar magnetic anomaly map and the magnetic anomaly partition map. The magnetic anomaly field in the South China Sea is divided into eight areas,of which the characteristics are explained,and the tectonic evolution of the South China Sea is preliminarily discussed.

The paleoclimate environment and recent sea level change on the seashores of Thailand Gulf in Southeast Asia

This paper analyzed and researched on several significant natural geological sections from the views of stratum-sequence stratigraphy,climate stratigraphy,event stratigraphy and regional stratigraphy by the investigation of Thailand,Malaysia and Singapore. In combination with the coupling relationship between the life-temperature of regional life zone and the evolution of geological environment,this paper exactly made out the geological sediment records of paleoclimate times in different time scales of 3 kaBP,1 kaBP and 0.5 kaBP since the past glacier age of Quaternary period,and it is consecutive and authentic for the material medium and time joint. These studies definitely reflected that the sea level of Thailand Gulf area is in tendency of continually dropping in recent years. They also provided important and new information for the global change analysis.

Distribution and characteristics of gravelly soil liquefaction in the Wenchuan M_s 8.0 earthquake

In this paper,a distribution map of gravelly soil liquefaction that was caused by the Wenchuan M8.0 earthquake in China is proposed based on a detailed field investigation and an analysis of geological soil profiles. The geological background of the earthquake disaster region is summarized by compiling geological cross sections and borehole logs. Meanwhile,four typical liquefied sites were selected to conduct sample drillings,dynamic penetration tests (DPT),and shear wave velocity tests,to understand the features of liquefied gravelly soil. One hundred and eighteen (118) liquefied sites were investigated shortly after the earthquake. The field investigation showed:(1) sandboils and waterspouts occurred extensively,involving thousands of miles of farmland,120 villages,eight schools and five factories,which caused damage to some rural houses,schools,manufacturing facilities and wells,etc.; (2) the Chengdu plain is covered by a gravelly soil layer with a thickness of 0 m to 541 m according to the geological cross sections; (3) there were 80 gravelly soil liquefied sites in the Chengdu plain,shaped as five belt areas that varied from 20 km to 40 km in length,and about ten gravelly soil liquefied sites distributed within Mianyang area; and (4) the grain sizes of the sampled soil were relative larger than the ejected soil on the ground,thus the type of liquefied soil cannot be determined by the ejected soil. The gravelly soil liquefied sites are helpful in enriching the global database of gravelly soil liquefaction and developing a corresponding evaluation method in further research efforts.

Characteristics,Types,and Prospects of Geological Sweet Sections in Giant Continental Shale Oil Provinces in China

“Sweet sections”in giant shale oil provinces are preferential fields that primarily support China to increase the reserves and production of continental shale oil.Based on the study of the geological conditions of shale oil in the continental basins in China,it was found that the shale stratum in major oil generation windows generally has higher degrees of oil and gas accumulation,and mostly contains oil.Hydrocarbon generation and reservoir capacities are the two key parameters for evaluating and optimizing favorable shale oil provinces.The evaluation index(volume of shale stratum multiplied by total organic carbon(TOC)multiplied by total porosity)for the giant continental shale oil provinces is also proposed.It is optimized that the Upper Triassic Chang 7 Member in the southcentral Ordos Basin,Lower Cretaceous Qing 1 Member in the Gulong-Changling Sag in the Songliao Basin,Middle-Lower Permian in the Junggar Basin,Da’anzhai Member of the Ziliujing Formation of Lower Jurassic in the central and northern Sichuan Basin,and Paleogene oil-rich sag in the Bohai Bay Basin are the five giant continental shale oil provinces.The word“geological sweet sections”in continental shale oil provinces of China refers to favorable shale intervals which are relatively rich in oil,with superior physical properties,and more easily modified and developed commercially under applicable economic and technological conditions.After evaluation,there are mainly two types of“geological sweet sections”of giant continental shale oil developed onshore in China.One type of“geological sweet sections”is generally mudstone with optimal physical properties or a thin tight reservoir,to which the shale oil migrates a short distance.They are medium-to-high-mature zones with a thin sandy shale stratum in the Chang 7 Member in the Ordos Basin,mixed shale stratum in the mediummature Lucaogou Formation in the Jimsar Sag,and multi-layered mixed Paleogene shale stratum in the Bohai Bay Basin.The other type of“geological sweet sections”is generally shale oil residing in various shale reservoir spaces.This type was developed in the Qing 1 Member in the Gulong Sag and Da’anzhai Member in the north-central Sichuan Basin.Free shale oil mainly occurs in shale,sandycarbonate lamina,micro-lamella structure,and micro-fractures.Layers with lamina,lamination,and micro-fractures are generally shale oil“geological sweet sections.”Starting from field tests and the construction of the“geological sweet sections”in giant continental shale oil provinces,the shale oil industry has been rapidly developing and will become an important supplement to domestic oil production in China.

Plastic zone analysis and support optimization of shallow roadway with weakly cemented soft strata

Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to monitor the loose range and level of surrounding rocks. A mechanical model of weakly cemented roadway was established, including granular material based on the measured results. The model was then used to determine the plastic zone radium. The predicted results agree well with measured results which provide valuable theoretical references for the analysis of surrounding rock stability and support reinforcing design of weakly cemented roadways. Finally, a combined supporting scheme of whole section bolting and grouting was proposed based on the original supporting scheme. It is proved that this support plan can effectively control the deformation and plastic zone expansion of the roadway surrounding rock and thus ensure the long-term stable and safe mining.