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2000 Vol. 11, No. 1

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Stratigraphic Correlation of Middle Triassic Sequences among Different Paleogeographic Sedimentary Facies in South China
Jinnan Tong, Shiyu Xiao, Zhili Liu
2000, 11(1): 1-8.

Affected by the Indosinian movement, the sediments in the main part of South China, Yangtze platform, started to transform from marine to continental during the Middle Triassic. In the meantime, a noticeable paleogeographic and sedimentary facies differentiation occurred in the marginal regions of the platforms and produced completely different lithologic and paleontologic sequences in various paleogeographic gradients and sedimentary facies areas, which brought about the difficulties for the stratigraphic correlation based on the traditional stratigraphies. This paper proposes to use some characteristic environmental events as the markers of the stratigraphic correlation across various paleogeographic sedimentary facies, considering that some distinctive regional environmental events should have affected at the same time on the entire basin or the connected sedimentary regions and produced some closely related sedimentary records in the stratigraphic sequences though the affected intensity and recorded pattern might be different among the regions. The change of violent relative sea level (generally water depth) and the alteration of tectonic activity summarized from the dynamic mechanism of sedimentation are the best markers of environmental events for stratigraphic correlation. Based on the analysis and recognition of some significant environmental events at the typical stratigraphic sequences from various paleogeographic sedimentary facies and combined with the consideration of the variations in expressed form and strength of the events among different paleogeographic gradients and sedimentary facies, the stratigraphic sequences from different sedimentary facies can be easily correlated directly. Furthermore, the evolutionary history of the whole sedimentary basin can be clearly established.

Coupling within Fluvial Geomorphic Systems: Spatial and Temporal Implications
Adrian M Harvey
2000, 11(1): 9-27.

Coupling within fluvial systems relates to the connectivity between the various components of the system. It can be viewed at several scales from local scales of hillslope-to-channel and reach-to-reach coupling, to larger scales of zonal coupling between the major functional zones of the fluvial system, and to the scale of regional coupling. Coupling influences how the system responds to environmental change and how the effects of environmental change are propagated through the system. This paper provides a review, based largely on previously published work, of the coupling concept, and how the effective temporal scales vary with the spatial scale of coupling. Local scale coupling is considered through the hillslope-to-channel coupling in the Howgill Fells, northwest England, observed over a 30-year monitoring period, together with examples from badlands in Spain, and reach-to-reach coupling on the River Dane, northwest England. At the zonal scale the relative influence of climatic and base-level change on coupling through dry-region alluvial fans is considered on fan systems in Spain, Nevada, and UAE/Oman. For large scale regional coupling, the response of the Tabernas basin, southeast Spain to tectonic uplift, is examined. The factors influencing coupling mechanisms vary with temporal and spatial scales. At the hillslope-to-channel scale the significant factors are the magnitude and frequency characteristics of sediment generation and removal mechanisms within the context of progressive morphological change. Effective timescales range from the individual event to decadal timescales. At the zonal scale, that of alluvial fans, the significant factors are climatic change, and particularly in the appropriate morphological setting, base-level change. Effective timescales are of the order of hundreds to thousands of years. At the regional scale, the response to tectonic uplift may take >100 ka to be transmitted through the drainage basin.

Contrasting on Hydrocarbon Generation Model and Characteristics of Pyrolysis of Modern Aquatic Plant (Gloeocapsa) vs Marine Animal (Mantis Shrimp)
Dameng Liu, Kuili Jin
2000, 11(1): 28-36.

A hydrocarbon model of the modern aquatic plant Gloeocapsa and the aquatic animal mantis shrimp was found in thermal simulating experiment. The results show that the modern aquatic plant Gloeocapsa is characterized by late generation, late termination and a long duration of oil generation, while the aquatic animal mantis shrimp is characterized by early generation, early termination and a short duration of oil generation. The n-alkanes from Gloeocapsa and mantis shrimp are characterized by peak carbon C15-C17. With increasing thermal simulating temperature, the peak carbon changes from C17 to C15, and the odd-even predominance of n-alkanes becomes less clear. The products from Gloeocapsa contain abundant phenanthrene and naphthalene compounds, and even a little retene, while those from mantis shrimp are dominated by naphthalene compounds, and are poor in phenanthrene compounds. Gloeocapsa and mantis shrimp are rich in C27 sterane, relatively rich in tricyclic terpanes (C19-C29) and hopanes (C27-C35), poor in 5α, 14β, 17β sterane, and coprostane does not disappear until 450℃. The tricyclic terpanes in Gloeocapsa are characterized by peak carbon C23 and C23 > C21, and in mantis shrimp by C21 and C21 > C23. The content of pregnanes is very low at low temperature of thermal simulation, while above 360℃, high levels of pregnane series compounds and even degraded C25 and C26 steranes occur in thermal simulation products.

Study on Basin-Filling and Reservoir Sedimentology of Zhu Ⅲ Depression of Pearl River Mouth Basin, South China Sea
Fengjun Nie, Sitian Li, Xinong Xie, Hua Wang, Weilin Zhu, Keqiang Wu
2000, 11(1): 37-46.

Through basin-filling analysis, one coarsening-upward and two fining-upward sequences have been identified in Zhu Ⅲ depression. In accondance with the general model proposed by Ravnas and Steel (1998), the basin-filling has two large cycles—rift (sediment-balanced and -overfilled) and postrift (sedimentunderfilled and starved). During the rifting process, the rifted lake developed through three stages: early, climax and late. The sedimentary characteristics of reservoir rocks show that barrier bar, lagoon and tidal channel facies well developed in Zhuhai Formation; offshore, tidal and barrier bar well developed in Zhujiang Formation. Neighborly, Shenhu, Wenchang and Enping formations deposited in rifted lakes during Paleogene time; Zhujiang Formation deposited in bay, lagoon and shoreface in late Paleogene. Zhujiang and other formations deposited in offshore and open shallow sea to shelf.

Fluid Flow History in Lower Triassic Bulgo Sandstone, Central Sydney Basin, Australia
Guoping Bai, B Keene John
2000, 11(1): 47-55.

The fluid flow history during diagenesis of the Lower Triassic Bulgo sandstone has been investigated through integrated analyses of petrography, stable isotope and fluid inclusion. Combined application of these techniques was intended to constrain the temperature, timing, chemistry and source of pore fluids during diagenetic cementation events in the Lower Triassic Bulgo sandstone. The diagenesis proceeded in two different flow regimes: early dynamic fluid flow regime and late slow static fluid flow regime. The former was characterized by a slight increase of δ(18O) of pore waters form estimated -15×10-3 to -14×10-3 with the temperature increasing from ~10 ℃ to ~75 ℃. During early diagenesis, early clays and pore filling carbonates precipitated from the pore waters. The late slow flow/static fluid regime was characterized by a rapid18Oenrichment process. δ(18O) of pore waters increased from -14×10-3 to -5×10-3 with the temperature increasing from 75 ℃ to 110 ℃. During the late diagenesis, kaolin (generation Ⅱ), quartz and illite crystallized. Oil migrated to the sandstones of the Bulgo sandstone during quartz cementation.

Characteristics of Paleoproterozoic Subduction System in Western Margin of Yangtze Plate
Hongxiang Zhang, Congqiang Liu, Zhifang Xu, Zhilong Huang
2000, 11(1): 56-65.

Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.

Lead Isotopic Steep-Dipping Zone and Mineralization—An Example from Mineral Deposits Concentrated Area in East Qinling, China
Zhengwei Zhang, Bingquan Zhu, Keqin Cai, Jun Deng, Wei Wang, Lizhi Qiang
2000, 11(1): 66-73.

Lead isotopic geochemical steep-dipping zone usually exists on inhomogeneous boundaries of earth blocks. Its crossing with the geophysical gradient zone often convergently occurs at giant deposits. Deep structures or concealed structural planes obviously have the coupling relationship with the convergent area of mineral deposits. The geochemical steep-dipping zone is usually distributed along the boundary of ancient continental blocks. Its crossing effect with geophysical gradient zone is usually presented as depression or swell of Moho discontinuity on the crossing direction with the ancient continental margin, which would lead to form deep fractures of earth crust at block margins or lead to adjustment of earth crust texture. The deep hydrothermal liquid would rise up along the structural planes to form the convergent areas of mineral deposits. For example, Luonan- Luanchuan area in east Qinling is a typical crossed area of the geochemical steepdipping zone and geophysical gradient zone. The mineral deposit belt extends along EW direction. It was controlled by the geochemical steepdipping zone equidistantly distributed along NE direction like a string of beads controlled by a gravity gradient zone in NE direction and a mantle depression slope. Along a plunging mantle syncline on EW plunging direction, from the east to the west, checkform was distributed which controls synergic crustmantle granoporphyry rocks. Therefore, a convergent mineralization area of Mo, W, Zn and Au giant deposits occurred.

Grade and Tonnage Model of Contact Metasomatic Copper Deposit in China
Xueping Wang, Min Wei, Lipei Yang, Jingman Zhao
2000, 11(1): 74-78.

Grade-tonnage model is one of the research frontiers of systematical exploration theory. Based on the "Reserve Database of Mineral Resources in China (1997) ", this paper establishes the geological model, grade model, tonnage model, grade-tonnage model and tonnage-sequence model of contact metasomatic copper deposits in China. The mathematical properties of these models are described in detail.

Dynamic Analysis of Yinggehai Basin through Analogue Modeling
Zhen Sun, Di Zhou, Zuoxun Zeng, Zhihong Zhong, Wei Tian
2000, 11(1): 79-83.

The Yinggehai basin lies in the northwestern shelf of the South China Sea. The maximum depth of the Cenozoic sediments is 17 km. Present gas exploration was mainly in the Neogene strata. But it is estimated that the Paleocene sediments (~8 km in thickness) has productive potential. So research on the Paleogene rifting structure will greatly enlarge the exploration area. 3D scaled sandbox is the analogue model for the Yinggehai basin. Comparing modeling with the basin by the positions and movement of depocenters, the geometric similarity, we aim to summarize the dynamic situation of Yinggehai basin during the rifting stage and to cast an objective prediction on the structures in the areas without data.

Lagging and Its Kinetic Mechanism of Hydrocarbon Re-generation from Organic Matters in Coals
Yong Qin, Yousheng Zhang, Yanming Zhu, Bingheng Fan, Bo Jiang, Tianzhong Li
2000, 11(1): 84-88.

Based on the composite analysis of the coal sample series with natural and artificial maturation, the lagging and its kinetic mechanism of the hydrocarbon re-generation from the organic matters in coals were studied using the Rock-Eval gas chromatogram (Py-GC) method. The results show that the maturation at the hydrocarbon re-generation peak shifts regularly forward with increasing the starting maturation and the deadline of the hydrocarbon re-generation lies about at 4.0% Ro. The difference value between the peak and starting maturation of the hydrocarbon re-generation develops in a parabola-like pattern with increasing the starting maturation, and the resolute and relative laggings evolve in stage, from which the lagging depth could be predicted. The peak half-width of the hydrocarbon re-generation curve develops as the starting maturation increases, which might indicate that the hydrocarbon-derived rocks with the starting maturation lied about at oil-generated peak might be relatively high in the hydrocarbon-regenerated amount. In the meantime, the mean reactivated energy of the coal samples with starting maturation develops in four stages that are highly consistent with those of the hydrocarbon-regenerated amount and lagging, which indicated that the hydrocarbon re-generation is strictly controlled by the geochemical mechanism of the reactive kinetics.

Application of Wavelet Analysis to Interference Elimination for Geochemical Hydrocarbon Exploration
Liuping Zhang, Tianjian Ruan
2000, 11(1): 89-91.

Interference in the data of geochemical hydrocarbon exploration is a large obstacle for anomaly recognition. The multiresolution analysis of wavelet analysis can extract the information at different scales so as to provide a powerful tool for information analysis and processing. Based on the analysis of the geometric nature of hydrocarbon anomalies and background, Mallat wavelet and symmetric border treatment are selected and data pre-processing (logarithm-normalization) is established. This approach provide good results in Shandong and Inner Mongolia, China. It is demonstrated that this approach overcome the disadvantage of backgound variation in the window (interference in window), used in moving average, frame filtering and spatial and scaling modeling methods.

Gravel Image Segmentation in Noisy Background Based on Partial Entropy Method
Guangjun Wang, Jinwen Tian, Zhenyu Chen, Jian Liu, Guoping Wu
2000, 11(1): 92-94.

Because of wide variation in gray levels and particle dimensions and the presence of many small gravel objects in the background, as well as corrupting the image by noise, it is difficult to segment gravel objects. In this paper, we develop a partial entropy method and succeed to realize gravel objects segmentation. We give entropy principles and fast calculation methods. Moreover, we use minimum entropy error automaticly to select a threshold to segment image. We introduce the filter method using mathematical morphology. The segment experiments are performed by using different window dimensions for a group of gravel image and demonstrates that this method has high segmentation rate and low noise sensitivity.