Journal of Earth Science

Fractals and spatial statistics of point patterns

Frederik P. AGTERBERG

2013, 24(1): 1-11. doi: 10.1007/s12583-013-0305-6

[Abstract](2759) [FullText HTML] (128) [PDF 573KB](46)

Abstract:
The relationship between fractal point pattern modeling and statistical methods of parameter estimation in point-process modeling is reviewed. Statistical estimation of the cluster fractal dimension by using Ripley's K-function has advantages in comparison with the more commonly used methods of box-counting and cluster fractal dimension estimation because it corrects for edge effects, not only for rectangular study areas but also for study areas with curved boundaries determined by regional geology. Application of box-counting to estimate the fractal dimension of point patterns has the disadvantage that, in general, it is subject to relatively strong "roll-off" effects for smaller boxes. Point patterns used for example in this paper are mainly for gold deposits in the Abitibi volcanic belt on the Canadian Shield. Additionally, it is proposed that, worldwide, the local point patterns of podiform Cr, volcanogenic massive sulphide and porphyry copper deposits, which are spatially distributed within irregularly shaped favorable tracts, satisfy the fractal clustering model with similar fractal dimensions. The problem of deposit size (metal tonnage) is also considered. Several examples are provided of cases in which the Pareto distribution provides good results for the largest deposits in metal size-frequency distribution modeling.

Petromagnetic properties of granulite-facies rocks from the northern North China Craton: Implications for magnetic and evolution of the continental lower crust

Qingsheng LIU, Hongcai WANG, Jianping ZHENG, Qingli ZENG, Qingsong LIU

2013, 24(1): 12-28. doi: 10.1007/s12583-013-0314-5

[Abstract](713) [FullText HTML] (92) [PDF 2114KB](30)

Abstract:
This paper studies magnetic properties and composition of granulite-facies rocks of both the Neogene and Archean continental lower crust in the Neogene xenolith-bearing Hannuoba(汉诺坝) alkaline basalt and the exposed lower crustal section in the Archean Huai'an(淮安) terrain (Wayaokou (瓦窑口)-Manjinggou(蔓菁沟profile), the northern North China Craton. It provides a unique opportunity for a comparative study of magnetic properties and composition of both the Archean and Neogene continental lower crust. We measure magnetic parameters (susceptibility κ and magnetic hysteresis parameters, such as saturation magnetization J_s, saturation isothermal remanent magnetization J_rs, and intrinsic coercivity H_c) of eleven Hannuoba lower crustal xenoliths and nine terrain granulites from the Archean Huai'an terrain. Results indicate that the average values ofκ, J_s and J_rs of Archean granulites are 4 122×10⁻⁶ SI, 523.1 A/m and 74.9 A/m, respectively, which are generally higher than those of granulite-facies xenoliths (1 657×10⁻⁶ SI, 163.9 A/m and 41.9 A/m, respectively). These two types of granulites contain ilmenite, (titano) magnetite, minor hematite and some "magnetic silicates" (clinopyroxene, plagioclase and biotite). The Mg-rich ilmenite in granulite-facies xenolith is relatively higher than that in terrain granulites. We observe a more evolved character as higher magnetic as well as lower Sr/Nd, Cr/Nd, Ni/Nd, Co/Nd and V/Nd ratios in terrain granulites. These differences in magnetic characteristics reflect their different origins and evolutions. The high magnetization of granulites in the Huai'an terrain represents magnetic properties of the Archean continental lower crust, and low magnetization of granulite-facies xenoliths represents magnetic properties of the Cenozoic lower crusts in the northern North China Craton.

Zircon Hf isotope of Yingfeng Rapakivi granites from the Quanji Massif and ~2.7 Ga crustal growth

Nengsong CHEN, Songlin GONG, Xiaoping XIA, Hongyan GENG, Lu WANG, Min SUN, Timothy M. KUSKY

2013, 24(1): 29-41. doi: 10.1007/s12583-013-0309-2

[Abstract](906) [FullText HTML] (265) [PDF 1623KB](51)

Abstract:
The Quanji (全吉) Massif is located in the Northwest China, which is interpreted as a micro-continent that is composed of metamorphic basement and stable cover strata. There are some controversies of genetic relationship between the Quanji Massif and the major cratons in China. In this study, we obtained in situ zircon U-Pb and Hf isotopic compositions of the Yingfeng (鹰峰) rapakivi granites from the northwest Quanji Massif by application of LA-MC-ICP-MS technique. Twenty U-Pb age measurements points are concordant or near concordant, and their weighted mean²⁰⁷Pb/²⁰⁶Pb age is 1 793.9±6.4 Ma (MSWD= 1.09), yields an upper intercept age of 1 800±17 Ma (MSWD=0.41); 19 Hf isotope measurements yield a two-stage Hf model ages (T_DM2) of 2.63 to 2.81 Ga, with a weighted average age of about 2.70±0.02 Ga and ɛHf(t) values variate between -8.91 to -5.35. This indicates that magma source of the Yingfeng rapakivi granites were produced from partial melting of late stage of Neoarchean juvenile crust, and suggests a significant crustal growth event occurred in the Quanji Massif at that time. The Quanji Massif might be an ancient continental segment detached from the Tarim Craton based on the crustal growth history and other geological records. The Tarim Craton (including the Quanji Massif) and the North China Craton had a similar or homological early crustal evolution around ~2.7 Ga, which implies that Tarim Craton might be one of the component parts of North China Craton.

Carbon and oxygen isotope stratigraphy of the oxfordian carbonate rocks in Amu Darya basin

Rongcai ZHENG, Yanghui PAN, Can ZHAO, Lei WU, Renjin CHEN, Rui YANG

2013, 24(1): 42-56. doi: 10.1007/s12583-013-0315-4

[Abstract](716) [FullText HTML] (209) [PDF 921KB](40)

Abstract:
Based on the detailed research on petrologic and geochemical characteristics of deposition and diagenesis of Oxfordian carbonate rocks in Amu Darya Basin, Turkmenistan, carbon and oxygen isotopes were analyzed. The results show that the paleoenvironmental evolution reflected by the samples with well-preserved original carbon isotopes coincides with the carbon-isotope stratigraphic curve and is almost consistent with the global sea-level curve, the Mid-Oxfordian wide transgression, and the positive carbon-isotope excursion event. The Mid-Oxfordian continuing transgression not only laid the foundation for the development of the Oxfordian reef and shoal reservoirs in Amu Darya Basin but also provided an example for the Oxfordian global transgression and the resulting development of reefs and banks and high-speed organic carbon burial events. The response of oxygen isotopes in diagenetic environment showed that micrite limestones and granular limestones underwent weak diagenetic alteration, and the samples largely retained the original seawater features. Dolomitization and the precipitation of hydrothermal calcites filling solution vugs and fractures before hydrocarbon accumulation occurred in a closed diagenetic environment where the main controlling factor is the temperature, and the diagenetic fluids were from the deep hot brine. The chalkification of the limestones after hydrocarbon accumulation occurred in the oilfield water systems.

Compressibility and structural properties of jadeite, NaAlSi₂O₆ at high pressure

Xiuling WU, Xiaoyu FAN, Fei QIN, Dawei MENG, Xiaoling ZHANG, Long CHEN, Weiping LIU, Jianping ZHENG

2013, 24(1): 57-64. doi: 10.1007/s12583-013-0311-8

[Abstract](502) [FullText HTML] (131) [PDF 519KB](37)

Abstract:
The structural properties of jadeite at high pressures (0.000 1-30 GPa) are investigated using plane-wave pseudopotential density functional theory method. As a function of pressure, the monoclinic cell parameters were calculated and the compressibility coefficients are 0.002 6, 0.002 3 and 0.002 6 GPa⁻¹, respectively. The bond length, bond angle and distortion variation were studied in order to obtain the information of polyhedral compression. The pressure-volume equation of state was considered in order to obtain the bulk modulusK₀. Comparison between the calculated K₀ values and the experimental data suggested that the model provides reasonable insights into crystallographic and physical properties of jadeite.

Biotransformation of earthworm activity on potassium-bearing mineral powder

Xiaoling ZHU, Bin LIAN, Xue YANG, Congqiang LIU, Lijun ZHU

2013, 24(1): 65-74. doi: 10.1007/s12583-013-0313-6

[Abstract](449) [FullText HTML] (62) [PDF 405KB](39)

Abstract:
This study analyzes the biotransformation of earthworms on K in potassium-bearing mineral powder (PBMP) under different PBMP recruitments. A mixture of PBMP (10% to 60% mass fraction) and decaying cow dung was used as feed for breeding the earthworms to study the potassium-releasing ability of earthworms on PBMP in soil. The mixture containing 20% and 30% PBMP resulted in good growth and propagation of the earthworms as well as higher conversion rates of potassium. Therefore, the optimum recruitments of mineral powder are 20% and 30%. The mixture of cow dung and PBMP was compared with the mixture of cow dung and corresponding proportions of quartz powder to analyze the conversion rate of earthworms on PBMP in different combinations. After the earthworms were raised with the mixture of cow dung and PBMP (8: 2 and 7: 3) for 30 d, the contents of rapidly available K and effective K were 10 824.3±35.9 and 11 688.4±16.1 mg·kg⁻¹ as well as 10 079.6±62.2 and 10 247.5±172.7 mg·kg⁻¹, respectively. After the earthworms were raised with the mixture of cow dung and quartz powder (8: 2 and 7: 3) for 30 d, the contents of rapidly available K and effective K were 10 623.3± 41.1 and 11 385.5±13.5 mg·kg⁻¹ as well as 9 834.2±51.8 and 9 907.6±11.4 mg·kg⁻¹, respectively. Thus, the contents of rapidly available K and effective K in the mixture of cow dung and PBMP were significantly higher compared with those in the mixture of cow dung and quartz powder (P < 0.05). The increment contents of rapidly available K and effective K were 201.0 and 302.9 mg·kg⁻¹ as well as 245.4 and 339.9 mg·kg⁻¹, respectively. Therefore, earthworms can activate and trans-form K into effective K through feeding, digestion, absorption, and excretion. The results provided a new idea of using earthworms to release potassium in low-grade potassium-bearing rocks and obtain the rapidly available K and effective K needed by plants.

Sequence Stratigraphy and Sedimentary Facies in the Lower Member of the Permian Shanxi Formation, Northeastern Ordos Basin, China

Wei Du, Zaixing Jiang, Ying Zhang, Jie Xu

2013, 24(1): 75-88. doi: 10.1007/s12583-013-0308-3

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Abstract:
The Lower Permian Shanxi (山西) Formation is one of the main gas-bearing stratigraphic units in northeastern Ordos (鄂尔多斯) Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies: subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi (大牛地) Gas Field and braided channel, and shelf and lake at Heidaigou (黑岱沟) outcrop. Braided-river deposits form the lowstand systems tract (LST) in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract (TST). The location where dark gray mudstone first appears above the braided channel marks the first flooding surface (FFS), and the end of that marks the maximum flooding surface (MFS). The highstand systems tract (HST) deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.

Basin-Scale Sand Deposition in the Upper Triassic Xujiahe Formation of the Sichuan Basin, Southwest China: Sedimentary Framework and Conceptual Model

Xiucheng Tan, Qingsong Xia, Jingshan Chen, Ling Li, Hong Liu, Bing Luo, Jiwen Xia, Jiajing Yang

2013, 24(1): 89-103. doi: 10.1007/s12583-013-0312-7

[Abstract](1040) [FullText HTML] (130) [PDF 2874KB](30)

Abstract:
The Upper Triassic Xujiahe (须家河) Formation in the Sichuan (四川) Basin, Southwest China is distinctive for the basin-scale sand deposition. This relatively rare sedimentary phenomenon has not been well interpreted. Here we addressed this issue by discussing sedimentary framework and conceptual model. Analysis of sedimentary setting implied that the basin received transgression during the deposition. It had multiple provenance supplies and river networks, as being surrounded by oldlands in multiple directions including the north, east and south. Thus, the basin was generally characterized by coastal and widely open and shallow lacustrine deposition during the Late Triassic Xujiahe period. This is similar to the modern well-known Poyang (鄱阳) Lake. Therefore, we investigated the framework and conceptual model of the Sichuan Basin during the Xujiahe period with an analogue to the Poyang Lake. Results show that the conceptual model of the deposition can be divided into transgressive and regressive stages. The first, third and fifth members of the formation are in transgressive stage and the deposits are dominated by shore and shallow lacustrine mud. In contrast, the deposition is mainly of braided river channel sand deposits during the regressive stage, mainly including the second, fourth and sixth members of the formation. The sand deposited in almost the entire basin because of the lateral migration and forward moving of the cross networks of the braided rivers. The multiple alternations of short and rapid transgression and relatively long regression are beneficial to the basin-scale sand deposition. Thus, the main channel of the braided river and its extensional areas are favorable for the development of hydrocarbon reservoir. This provides practical significance to the reservoir evaluation and exploration. In addition, the results also justify the relatively distinctive sedimentary phenomenon in the study area and may also have implications for understanding the large-scale sand deposition elsewhere.

The Influence of Localized Slumping on Groundwater Seepage and Slope Stability

Hongyue Sun, Jie Zhong, Yu Zhao, Shuijin Shen, Yuequan Shang

2013, 24(1): 104-110. doi: 10.1007/s12583-013-0307-4

[Abstract](646) [FullText HTML] (90) [PDF 728KB](38)

Abstract:
Transverse cracks and localized slumps frequently occur within loose deposits slopes when the slope base is removed either from natural or manmade processes. Although the contribution of rainfall to the slope failures was intensely discussed, the influence of localized slumps on hydrogeological conditions has received less attention. Usually, loose deposits slopes are composed of soil layers with different permeability; localized slumps may cause flow paths partly blocked in the permeable layer that is adversely confined between impermeable layers. In this study, a case history of such failure, Xiaodan (小旦) landslide, is introduced in detail. The localized slump caused the pressure head in the permeable layer to increase substantially, which reduced the stability of the slope. To quantify the influence, Bernoulli equations are used to analytically study the increase of the pressure head with a hydrogeological model simplified from the slope. The factor of safety assessed by limit equilibrium methods may decrease up to 20% when the 80% of flow path is blocked. Thus, we should pay attention not only to changes of stress filed due to localized slumps but also to the influence of seepage variation on the slope stability.

Impacts of Human Activities on the Occurrence of Groundwater Nitrate in an Alluvial Plain: A Multiple Isotopic Tracers Approach

Zhonghe Pang, Lijuan Yuan, Tianming Huang, Yanlong Kong, Jilai Liu, Yiman Li

2013, 24(1): 111-124. doi: 10.1007/s12583-013-0310-9

[Abstract](894) [FullText HTML] (106) [PDF 727KB](33)

Abstract:
Nitrate pollution is a severe problem in areas with intensive agricultural activities. This study focuses on nitrate occurrence and its constraints in a selected alluvial fan using chemical data combined with environmental isotopic tracers (¹⁸O, ³H, and ¹⁵N). Results show that groundwater nitrate in the study area is as high as 258.0 mg/L (hereafter NO₃⁻) with an average of 86.8 mg/L against national drinking water limit of 45 mg/L and a regional baseline value of 14.4 mg/L. Outside of the riparian zone, nitrate occurrence is closely related to groundwater circulation and application of chemical fertilizer. High groundwater nitrate is found in the recharge area, where nitrate enters into groundwater through vertical infiltration, corresponding to high ³H and enriched ¹⁸O in the water. In the riparian zone, on the contrary, the fate of groundwater nitrate is strongly affected by groundwater level. Based on two sampling transects perpendicular to the riverbank, we found that the high level of nitrate corresponds to the deeper water table (25 m) near the urban center, where groundwater is heavily extracted. Groundwater nitrate is much lower (< 12.4 mg/L) at localities with a shallow water table (5 m), which is likely caused by denitrification in the aquifer.

Automated Rock Detection and Shape Analysis from Mars Rover Imagery and 3D Point Cloud Data

Kaichang Di, Zongyu Yue, Zhaoqin Liu, Shuliang Wang

2013, 24(1): 125-135. doi: 10.1007/s12583-013-0316-3

[Abstract](629) [FullText HTML] (163) [PDF 658KB](30)

Abstract:
A new object-oriented method has been developed for the extraction of Mars rocks from Mars rover data. It is based on a combination of Mars rover imagery and 3D point cloud data. First, Navcam or Pancam images taken by the Mars rovers are segmented into homogeneous objects with a mean-shift algorithm. Then, the objects in the segmented images are classified into small rock candidates, rock shadows, and large objects. Rock shadows and large objects are considered as the regions within which large rocks may exist. In these regions, large rock candidates are extracted through ground-plane fitting with the 3D point cloud data. Small and large rock candidates are combined and postprocessed to obtain the final rock extraction results. The shape properties of the rocks (angularity, circularity, width, height, and width-height ratio) have been calculated for subsequent geological studies.

The Drivers of Land Use Change in the Migration Area, Three Gorges Project, China: Advances and Prospects

Jiupai Ni, Jing'an Shao

2013, 24(1): 136-144. doi: 10.1007/s12583-013-0306-5

[Abstract](973) [FullText HTML] (93) [PDF 367KB](29)

Abstract:
This paper reviewed existing literatures on land use change since the demonstration phase of the Three Gorges Project and found that reservoir inundation, migration resettlement, urban relocation, and post-supporting construction were first paid more attention to, when analyzing the driving forces of land use change in the migration area. However, at the post-migration period (the end of migration resettlement), above-mentioned drivers had not obviously driven land use change, but the evolutions of "migration demands" replacing them increasingly became the major drivers of land use change in the migration area. Therefore, the future priority fields of land use explanations in the migration area, Three Gorges Project were (1) identifying the corresponding relationships between the spatial distributions of land use change and migration resettlement and indigenous inhabitants; (2) understanding the change of "migration demands" and their causing "indigenous inhabitants' demands" being how to drive land use transforms; (3) finding the driving processes of the conflict and exclusion between immigrants and indigenous inhabitants, and the transfer of immigrants and indigenous inhabitants on land use change; and (4) measuring the dynamic feedback of "migration demands" at different stages on the processes, directions and their corresponding impacts of land use change in order to building the coupling framework among "migration demands", driver behaviors, and land use. This paper presents a new access for the explanation of land use change and also supplies scientific proofs to obtain adaptive decision-making to optimize land use patterns in the migration area, Three Gorges Project.

2013 Vol. 24, No. 1

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