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Global Geology
 
2020 Vol.23 Issue.4
Published 2020-11-25
Articles
Articles
199 New palaeoclimatic insights on the Late Cretaceous environments of Mongolia based on the isotope data (δ13C, δ18O) of dinosaur eggshells and pedogenic carbonates from Bayn Dzak section
S. V. Naugolnykh, V. N. Kuleshov
Isotopic data obtained from the dinosaur eggshells and pedogenic nodules (pedonodules) are interpreted in terms of palaeoclimatology. The material studied originated from the Bayn Dzak locality, Southern Gobi Aimak, Mongolia, having Late Cretaceous (Campanian) age. Stratigraphically the Bayn Dzak locality belongs to the Djadokhta Formation. All the present data (lithology, type of paleosols, FPS-profiles, geochemistry), and the isotopic characteristics of the selected samples show unequivocally that the environments of the Bayn Dzak area in Late Cretaceous (Campanian) time were warm to summer-hot, seasonally dry. Wet seasons (most probably, which took place in the winter time) were not longer than two months with not more than 400 mm precipitation per year. The distribution of isotope data in the dinosaur eggshells show the main relation, which is the dependence of δ13C and δ18O values, i.e. specimens with heavy carbon isotope ratios are characterized by lighter oxygen isotope composition and conversely. Thus, the δ13C and δ18O values of the dinosaur eggshells display a clear positive correlation. It may be consequent both with the difference of the isotope composition of diet of the egg-lying animals modified by physicochemical isotope fractionation due to metabolism and changes in the isotope environment, and/or diagenetic alteration of the eggshell carbonate. Obtained isotopic data on the studied dinosaur eggshell fragments and the soil carbonates lend support to our assumption that diagenesis did not play significant role in changing the isotopic values. The distribution of δ13C and δ18O values in eggshells and in pedogenic carbonates shows the visible opposite dependencies.
2020 Vol. 23 (4): 199-213 [Abstract] ( 504 ) [HTML 1KB] [ PDF 4156KB] ( 491 )
214 A new type of Mo-bearing quartz vein by acid leaching: evidence from Dahu-Qinnan Mine, northern belt of the Xiaoqinling gold province, central China
ZHANG Yuanhou, MAO Jingwen, PIRAJNO Franco, LI Zongyan, QIAO Cuijie, ZHANG Xiaomin, HE Yue, ZHANG Shuaimin
Dahu-Qinnan molybdenum deposit, located in the northern part of the Xiaoqinling gold province, belongs to the Xiaoqinling-Waifangshan sub-zone of the eastern Qinling Mo-W metallogenic belt, central China. Molybdenite mineralization is associated with Au-bearing quartz veins. This paper is based on field observations and PIMA analytical data on the occurrences, and details textures and alteration patterns of Mo-bearing quartz veins in Dahu-Qinnan region. The Mo-bearing quartz veins exhibit friable with cream colored, vuggy, infilling texture and brecciated texture. The breccia clasts within Mo-bearing quartz veins are dominated by gneissic rocks of the Taihua Supergroup, and Mesozoic porphyritic granite dyke with stockwork and disseminated molybdenite mineralization. The breccias are replaced by clay minerals. Alteration associated with molybdenite-bearing quartz veins is characterized by K-feldspar (only in the breccias), sericite, sillicification (residual silica), kaolinite, smectite and anhydrite. Molybdenite with other sulfide minerals infills fissures and pore spaces in the quartz veins. As the results of above, and according to the observed geological events in the area and taking into account the geological setting, molybdenite-bearing quartz veins are likely to have been affected by late acid leaching. The precursor porphyry Mo ore, associated with porphyry granite dyke formed probably at ca. 245-211 Ma during the continent-continenl collision of Qinling orogeny.
2020 Vol. 23 (4): 214-224 [Abstract] ( 145 ) [HTML 1KB] [ PDF 2430KB] ( 323 )
225 Viability of high-density resistivity method for evaluating mountain slope stability in Erdaojiang District, Tonghua City, China
XIN Zhonghua, HAN Jiangtao, LI Zhuoyang, LIU Lijia
The authors employ the high-density resistivity method to image the subsurface structure of a mountain in Erdaojiang District, Tonghua City, Jilin Province, China, to evaluate the potential risk of slope failure on surrounding residential areas and infrastructure, and identify a shallow fault that extends across the center of the mountain and is perpendicular to the mountain slope and accurately locate the spatial position and depth of another fault on the southern side of the mountain. The results provide an important basis for evaluating mountain slope stability. This study also demonstrates that the high-density resistivity method is effective for detecting mountain faults.
2020 Vol. 23 (4): 225-233 [Abstract] ( 188 ) [HTML 1KB] [ PDF 2623KB] ( 355 )
234 Experimental study on parameter determination of fluid replacement equation for volcanic reservoirs
ZHOU Weiyi, PAN Baozhi, GUO Yuhang
In this study, the parameters of Gassmann equation based on fluid replacement theory are studied by measuring the acoustic velocity during the evaporation process of volcanic rocks in Nanpu area. The experimental data show that with the decrease of porosity of tight volcanic rock, the acoustic velocity difference between dry and wet rock samples increases, which is conducive for the identification of gas bearing reservoirs with acoustic log data. The fluid bulk modulus distribution of volcanic rocks in the study area conforms to Brie model, and the value of empirical coefficient e is related to lithology. The experimental results show that there is a linear relationship between the P-wave transit time of dry and wet rock samples. Using porosity to calculate the acoustic transit time of saturated rock samples, and taking it into the experimental formula, we can get the P-wave transit time and bulk modulus of dry rock samples. According to the bulk modulus of mixed fluid, dry rock and rock matrix determined by experiments, the saturation of volcanic reservoir in Nanpu area is calculated by Gassmann equation, which is in good contrast with the conclusion of gas test. This study provides an experimental basis for quantitative evaluation of volcanic gas reservoirs using seismic and acoustic logging data.
2020 Vol. 23 (4): 234-240 [Abstract] ( 93 ) [HTML 1KB] [ PDF 723KB] ( 316 )
241 Seismic data denoising based on data-driven tight frame dictionary learning method
ZHENG Jialiang, WANG Deli, ZHANG Liang
Because of various complicated factors in seismic data collection, the random noise of seismic data is too difficult to avoid. This random noise reduces the quality of seismic data and increases the difficulty of seismic data processing and interpretation. Improving the denoising technology is significant. In order to improve seismic data denoising result, a novel method named data-driven tight frame (DDTF) is introduced in this paper. First, we get the sparse coefficients of seismic data with noise by DDTF. Then we remove the smaller sparse coefficient by using the hard threshold function. Finally, we get the denoised seismic data by inverse transform. Furthermore, the DDTF is compared with curvelet transform in the stimulation and practical seismic data experiments to validate its performance. DDTF can raise the signal-to-noise ratio of seismic data denoising and protect the effective signal well.
2020 Vol. 23 (4): 241-246 [Abstract] ( 80 ) [HTML 1KB] [ PDF 552KB] ( 269 )
247 Numerical simulation of oil shale in-situ mining using fluid-thermo-solid coupling
ZHANG Tiantong, LIU Zeyu, XIE Zhixian, LI Yubo, XUE Linfu
For the in-situ gas-injection mining technology of oil shale by process, a numerical simulation method with flow-thermo-solid coupling is proposed in this paper. This method adopts separate simulations and step-by-step coupling simulation ideas combined with the advantages of the finite element method and the finite volume method. The numerical simulation of flow-thermo-solid coupling is decomposed into two parts:flow-solid coupling and thermo-solid coupling. Considering the Fuyu oil shale in-situ production test area in Songliao Basin as an example, it is concluded that the oil shale has undergone four heating stages:a rapid temperature rise, a steady temperature rise, a slow temperature rise, and heat preservation. It takes about 10 years for the stress-strain state of the oil shale layer to reach a steady-state through the thermo-solid coupling. The main strain zones of the oil shale layer are distributed near the fracturing fractures connected to the gas injection well and at the edge of the fracturing fractures. The areas with the plastic deformation in the oil shale layer predominantly appear near the gas injection wells, production wells, and fracturing channels. The areas with the largest fracture strength are mostly distributed near the edge of the fracturing fractures with low flow velocity and low temperature.
2020 Vol. 23 (4): 247-254 [Abstract] ( 108 ) [HTML 1KB] [ PDF 959KB] ( 420 )
255 Application of high-density resistivity method to evaluate safety around Minyan Tunnel, Helong City
LI Zhuoyang, HAN Jiangtao, XIN Zhonghua, LIU Lijia
By determining the distribution and extent of geological structures surrounding the Mingyan Tunnel, Xicheng Town, Helong City, Jilin Province, we can evaluate the stability of the rock mass and assess potential hazards during tunnel construction. We use the high-density resistivity method to analyze the subsurface structure of the study area. Conductive anomalies are likely to represent joint and fissure systems within strongly weathered host rocks, and the bedrock surrounding the tunnel is relatively stable and does not contain well-developed faults. High-density resistivity analysis can provide valuable information in the context of tunnel engineering and safety.
2020 Vol. 23 (4): 255-262 [Abstract] ( 149 ) [HTML 1KB] [ PDF 1328KB] ( 334 )
　

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