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《Bulletin of Mineralogy, Petrology and Geochemistry》
JOPC 2015 Vol.17 Number 3
2015, Vol.17 Num.3
Online: 2015-06-01
GENERAL
GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS
PALAEOGEOGRAPHY AND MINERAL RESOURCES
GENERAL
285
Zhong Dakang, Jiang Zhenchang, Guo Qiang, Sun Haitao
A review about research history, situation and prospects of hydrothermal sedimentation
Hydrothermal sedimentation has been studied for over 70 years since being discovered,and its related terminology has been preliminarily unified. It has been classified into the white smoker and the black smoker according to the mineral forming temperature and color,as well as some depositional models. The former deposits light-colored minerals such as silicates and sulfates under lower temperatures(100-320℃),while the latter deposits dark-colored minerals such as sulfides and oxides under relatively higher temperatures(320-400℃). There are some differences in temperature and physics-chemistry between terrestrial and marine hot fluids. The terrestrial thermal fluids are with lower and more various temperatures,higher and relatively fixed pH values,similar Na+K ionic concentrations,and higher and more various Ca and Cl ionic concentrations as to the marine thermal fluids. Some hydrothermal sedimentation models have been set up,such as seafloor thermal fluids convection,compaction brine convection,mixed magma thermal fluid from mid-oceanic ridge-sea water convection,and overflowing-spraying-overflowing. However,due to the specificity and limitation of the hydrothermal sedimentation and its product distribution,the research is not enough. The discussion about the chemical and thermodynamics process of hydrothermal sedimentation is deficient. The origin,source,differentiation of thermal fluids,and the depositional mechanism are not very clear. All of these above should be further studied.
2015 Vol. 17 (3): 285-296 [
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GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENTS
297
Wei Kai, Li Xubing, Liu An, Li Jitao, Bai Yunshan, Zhou Peng, Chen Xiaohong
Trace element characteristics of carbonate rocks from the Ediacaran Doushantuo Formation of Xikou section, Cili County, Hunan Province and its palaeoenvironmental significance
Trace element and rare earth element(REE)of 64 carbonate rock samples from the Ediacaran Doushantuo Formation of Xikou section,Cili County,Hunan Province are analyzed. Palaeoredox indicated by the combination of U/Th,Ce anomalies and Ca/Mg is in accordance with that by sequence stratigraphic studies,suggesting that the three proxies in carbonates are applicable in reconstructing palaeoredox environment of the Ediacaran. In the bottom and middle of Doushantuo Formation,the REE distributional pattern changes from typical fresh water to typical sea water,probably indicating the injecting of deglacial meltwater and thus being replaced by normal sea water during the post-Marinoan and post-Gaskier period. The strong Eu anomalies,relatively higher Eu value as well as the seismites discovered in Xikou section by previous research may suggest that the hydrothermal activity probably occurs during the whole Doushantuo Age,being strong in the early and then weakened in the late stage. The hydrothermal activity may be of great significance to the appearance and the bloom of Ediacaran biota because of the important phosphorus supply.
2015 Vol. 17 (3): 297-308 [
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309
Yu Xinya, Li Pingping, Zou Huayao, Wang Guangwei, Zhang Yi
Rare earth element geochemistry of dolostones and its indicative significance of the Permian Changxing Formation in Yuanba Gasfield,northern Sichuan Basin
Rare earth element(REE)and Yttrium(Y)concents were determined from 49 carbonate samples of the Permian Changxing Formation of Yuanba Gasfield in northern Sichuan Basin,and the results show that the total content of rare earth elements(REE)is generally low(average 1.50×10
-6
),which indicates that rock samples were almost without any terrigenous clastics,and not be affected by the deep hydrothermal fluids. Shale-normalized REE characteristics of dolostone including light rare earth element(LREE)depletion,positive La anomalies,negative Ce anomalies(0.49 to 1.08,average 0.75),positive Eu anomalies(0.89 to 46.00,average 4.68) of different degrees and the higher Y/Ho ratios(28.82 to 63.47,average 43.04) recorded seawater-like REE and Y signatures,which show that the dolomitization fluids is reductive seawater derived,and the dolomitization occurred in a burial environment. The brecciated or zebra typical structure of hydrothermal dolostones were not observed in the cores and petrographic thin sections. Flattened structure and the horizontal continuous distribution of dolomite reservoirs and the higher
δ
18
O value(-7.07‰ to-2.92‰,average -4.95‰)illustrate that no obvious hydrothermal activities occurred in the study area,and the higher degree of positive Eu anomalies have no relationship with the deep hydrothermal fluids. Many elemental sulfurs and sulfur-rich pyrobitumen originated from thermochemical sulfate reduction(TSR) can be observed by scanning electron microscope,which indicates that TSR created an extremely reducing environment of stratal seawater,and then caused the higher degree of positive Eu anomalies,which in turn explains that TSR had a certain dissolution on dolomite reservoirs.
2015 Vol. 17 (3): 309-320 [
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321
Shen Cheng, Tan Xiucheng, Li Ling, Shi Kailan, Su Chengpeng
Lian Chengbo, Li Hongwei, Xiao Di
Sedimentary characters of carbonate platform marginal slope of the Early Cambrian in northern Sichuan Basin and perspective of deformation structures
In this paper,a case study of the Lower Cambrian Xiannüdong Formation in Tangjiahe,Wangcang County of western Micang Mountain was conducted. On the basis of the observation and analysis with microscope,the bottom of Xiannüdong Formation is composed of six major rock types,such as bioclastic mudstone,silty mudstone,analogous-nodular limestone,rudstone,algal clot limestone and calcareous sandstone with bioclastic,and is characterized by rudstone,analogous-nodular limestone,algal clot limestone,slump deformation structure and slide structure. Further analysis shows that L-M association was mostly deposited in low-energy slope environment. The rudstone,as a part of the L′-R association,deposited by the collapse and slump from the mud mounds in upper slope. The other part,analogous-nodular limestone,deformed from L-M association,was supposed synthetical effects by the collapse and slump from mud mounds,the force of differential compaction and the pressure solution caused by the differences of the components. These effects can be used to break the limestone layer to be rudstone shape,even lead to generate some slightly displacement. As a result,L-M,also be called ribbon rocks,become littery deformation structures. Mb association can be considered a mud mounds environment in upper slope. S-M association was deposited in turbidity environment of upper slope. After establishing the sedimentary model and the four associations of slope,all of the evidences indicate that at least during the Early Cambrian Xiannüdong period,the platform marginal slope was developed in western Micang Mountain.
2015 Vol. 17 (3): 321-334 [
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335
Ren Ying, Zhong Dakang, Gao Chonglong, Dang Lurui
Peng Ping, Chen Weidong, Mao Yakun, Hu Xiaolin
Sedimentary facies of the Lower Cambrian Longwangmiao Formation in eastern Sichuan Basin and its adjacent areas
Based on outcrops,logging data,seismic data and regional survey reports, the main rocks of the Lower Cambrian Longwangmiao Formation in eastern Sichuan Basin and its adjacent areas carbonate rocks(
i.e.,
silt￣sized crystalline dolostone, grain dolostone, micritic limstone and grain limestone), and some locally-developed large sets of evaporites(gypsum rock and dolomitic gypsum rock)and mixed carbonate-clastic deposits can be seen. Four types of sedimentary facies are identified from northwest to southeast,
i.e.,
mixed platform,restricted platform,evaporitic platform and open platform,among which,the restricted platform is most widely developed. Generally,all the facies are distributed in a southwest-northeast trending. The mixed platform is mainly distributed in the northwestern study area,the evaporitic platform is mainly distributed on the eastern side of Huayingshan Fault in the western study area,and eastwards, the restricted platform and the open platform are developed respectively.
2015 Vol. 17 (3): 335-346 [
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347
Jin Mindong, Tan Xiucheng, Li Ling, Zeng Wei
Lian Chengbo, Luo Bing, Shan Shujiao, Zhou Tao
Characteristics and distribution of grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area, Sichuan Basin
In this paper,the authors focused on grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area,Sichuan Basin. Combined with abundant materials,such as drilling and logging data,cores and thin sections,the characteristics,distribution and its major controlling factors of grain bank in the Longwangmiao Formation were synthetically analyzed. There are two main rock types of grain bank in research area,one is grain dolostone with obvious granular structure,which is dominated by dolarenite and oolite dolostone,and the other is crystal grain dolostone with residual granular structure. Grain bank mainly has upward shallowing and granularity coarsening sequences,and could constitute sedimentary sequences of interact bank sea-grain bank and restricted lagoon-grain bank with lower fine-grained sediment in the vertical direction. In the lateral direction,grain bank has good continuity and is characterized by continuous distribution in a large area. On the plane,the development degree of grain bank increases gradually from northwest to southeast. Further analysis shows that the development characteristics and superimposed pattern of grain bank in the Longwangmiao Formation were determined by the relative sea-level change and sedimentary energy variation,the development horizon and degree of grain bank were formed by different grades of sea level fluctuation,and thepalaeogeomorphology finally determined the difference of planar distribution of grain bank during the depositional period of Longwangmiao Formation.
2015 Vol. 17 (3): 347-358 [
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359
Zhai Daxing, Zhang Yongsheng, Tian Shugang, Wu Feimeng, Xing Enyuan
Wang Meng, Shi Lizhi, Wang Zhuozhuo
Sedimentary environment and evolution of the Upper Permian Linxi Formation in Linxi area, Inner Mongolia
Sedimentary environment of the Upper Permian Linxi Formation in eastern Inner Mongolia has been in dispute for a long time. Herein, based on previous research data, the environment is discussed in this paper after detailed field and indoor study on palaeontology,sedimentary structure,lithofacies,geochemistry
etc
. Evidences from marine fossils(calcareous algae,bryozoans,and sponges),B/Ga value,carbon and oxygen isotopes,sedimentary structure,and other aspects show that the Linxi Formation is mainly of marine facies along with partial transitional facies. It is principally divided into delta front,littoral,shallow sea and semi￣deep sea. Reefs mainly include blue green algae bonding reefs and algal bonding framework reefs,suggesting a littoral and shallow sea environment. The depositional environment of Linxi Formation developed from littoral,semi￣deep sea,delta front,shallow sea to littoral,while the evolution of sedimentary basin was divided into five stages, including uplift,rift,rapid,filling, steady subsidence and stable filling stages.
2015 Vol. 17 (3): 359-370 [
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371
Chen Nenggui, Wang Yanqing, Xu Feng, Yang Tiyuan, Xia Zhiyuan
Palaeosalinity characteristics and its sedimentary response to the Cenozoic salt-water lacustrine deposition in Qaidam Basin
The salt￣water lacustrine deposition was developed during the Cenozoic in Qaidam Basin,but its salinity and sedimentary response have not been known. Based on boron and clay mineral data,palaeosalinities of the Cenozoic in Qaidam Basin were reconstructed by Couch formula,which testified that: (1) The Cenozoic sediments belonged to the salt￣water lacustrine deposition with the maximum salinity over 20‰. (2) The zones with different palaeosalinities had different sedimentary responses,that is,the palaeosalinity values of terrigenous clastics supplying areas were commonly less than 12‰,while those of shore-shallow lake ranged from 10‰ to 18‰,and those of semi-deep lake exceeded 18‰. Under the control of salt￣water with middle to high salinity, the salt water lacustrine deposition in Qaidam Basin has the following characteristics: single layer is thin usually with 1-3 m thickness, sand layer and mud layer are frequently interbedded, delta sedimentary facies belt is relatively narrow, fine grained sediments are distributed in a wide range, and typical lacustrine carbonate rocks, gypsum and terrestrial fine detritus are mixed.
2015 Vol. 17 (3): 371-380 [
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PALAEOGEOGRAPHY AND MINERAL RESOURCES
381
Yuan Yuan, Jiang Zhenxue, Li Zhuo, Zhao Ruotong, Li Peng, Chong Minghao
Reservoir characteristics of salt-water lacustrine shale of the Paleogene Xiaganchaigou Formation in western Qaidam Basin
Great breakthrough has been made in the exploration of lacustrine shale gas in China, but little research on reservoir of salt-water lacustrine shale was carried out. Organic geochemical analysis,mineral composition analysis and pore structure analysis of reservoir of the Palaeogene Xiaganchaigou Formation lacustrine shale in western Qaidam Basin has been done by the authors. (1)The organic content has intense heterogeneity in the 0.12％～1.35％ range,the content of chloroform bitumen “A”is high and the organic matter is mainly of type Ⅱ.(2)The content of carbonate is the highest with an average of 27.8％,and then clay minerals and quartz. There are 38.2％ of the samples have anhydrite,which reflects the typical salt￣water lacustrine environments. (3) The organic matter micro-pores observed in the SEM are less developed,the shape is irregular and pore size is large. Intergranular pores are mainly micronl￣sized in diameter, while micro-fractures are mainly less than 1μm in width. Mesopores have most of specific surface area and pore volume of shale pores,and are main places for gas adsorption and storage. The chloroform bitumen“A”influenced the pore structure of the samples. (4)The content of clay minerals is low and brittle minerals is high in research area,which is comparable with the series of gas-containing shales in U.S. and with the Lower Paleozoic shale in the Sichuan Basin,are conducive to creating cracks,and are easy for fracturing.
2015 Vol. 17 (3): 381-392 [
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393
Wang Shuai, Shao Longyi, Yan Zhiming, Sun Qinping, Wang Dongdong, Lu Jing, Sun Bin
Sequence stratigraphy and coal accumulation of the Lower Cretaceous Saihantala Formation in Jiergalangtu Sag of Erlian Basin
The Jiergalangtu Sag of Erlian Basin is a continental faulting coal basin and the Early Cretaceous Saihantala Formation is its main coal-bearing strata. In this paper,we studied lithofacies types,sedimentary facies,sequence stratigraphy and coal accumulation characteristics by means of core and drilling data. (1) The Saihantala Formation is mainly composed of sandy conglomerate,sandstone,siltstone,mudstone,carbonaceous mudstone and thick-bedded lignite. Three depositional systems were classified,including fan delta,braided fluvial delta and lake. The fan delta system consists of fan deltaic plain and fan deltaic front facies;the braided fluvial delta system is composed of braided fluvial deltaic plain and braided fluvial deltaic front facies;and the lacustrine system includes littoral lake and shallow lake. (2) Key stratigraphic surfaces,
i.e.,
the unconformity and the erosional base of incised valley filling sandstones,are recognized,and the target coal measures are subdivided into two third-order sequences. Seam thickness and coal accumulation increase from sequence Ⅰ to sequence Ⅱ. (3) The thick coal seams,which were developed from the coastal and shallow lacustrine environments,were mainly formed in the early transgressive systems tract,and the thick coal seams,which were developed from the fan delta or the braided delta environments,were mainly formed at the end of the transgressive systems tract. The thickest coal bed was distributed in the central zone of the sag,which thins out towards northwest and southeast of the basin. Coal accumulation was significantly controlled by basin subsidence,and the increasing rate of accommodation space was well balanced with the rate of peat accumulation,thus forming a regionally very thick coal seam.
2015 Vol. 17 (3): 393-404 [
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405
Zhao Ya′nan, Wang Zhanghua, Wu Xuxu, Li Lin, Zhan Qing, Chen Ting
Grain size distribution of modern tidal flat sediments at the Yangtze River mouth and its application to identification of sedimentary facies
This study takes detailed analyses on the sediment grain size for six cores from the modern tidal flats of Yangtze River mouth,to draw the diagnostic indexes for recognization of tidal flat facies in the study area. We also examined the grain size of a Holocene Borehole SL67 from the southern Yangtze delta plain so that to apply the sensitive indexes derived from modern sediments. Results demonstrate that the cohesive sediment(<8μm)and coarse silt(32～63μm)could be the sensitive indexes for distinguishing upper and middle tidal flats. Sand(＞63 μm) and fine silt(8～32μm)components differ obviously for the middle and lower tidal flats of open coast. Results also show that the parameter mode derived from grain size frequency curves is an effective index to help identify the upper,middle and lower tidal flat sediments. Above sensitive sediment components and mode were applied to identify the successions of tidal flat in Holocene Borehole SL67,which revealed the mechanism of sea level change and an acceleration of sea level rise around 7.5 cal ka BP.
2015 Vol. 17 (3): 405-416 [
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417
Wang Qing, Sun Hongyan, Ren Jianwu, Yi Xianjin, Cheng Jie
Climatic change during the late stage of Late Pleistocene at Muli area in south slope of Qilian Mountains
Based on the precise measurement of AMS
14
C ages in Late Pleistocene stratigraphic section at Muli area in the south slope of Qilian Mountains,and combined with the study of sedimentary grain size,magnetic susceptibility, and oxide(SiO
2
,Al
2
O
3
and Fe
2
O
3
)content,we reconstructed the climatic change of the study area during 44.8-35ka B.P. with 3 stages:(1)During 44.8-40.5ka B.P.,all the proxies show that the regional environment is warm and humid. The warm event around 41.9ka B.P. corresponds to IS12 in Dansgaard-Oeschger events;(2)During 40.5-35.5ka B.P.,the climate fluctuated frequently and tended to be cold. The three warm events of IS9-IS11,
i.e.,
35.8ka B.P.,37.5ka B.P.,and 39.7ka B.P.,respectively,and the H3 cold event of 35.5ka B.P.,were found during this period;(3)During 35.5-35ka B.P.,the climate fluctuated strongly and tended to get warm. These features of climatic fluctuation fit well with those of the late stage of MIS3. It indicates that the climate changes could spread globally but the precipitation situation varies in different areas.
2015 Vol. 17 (3): 417-426 [
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