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《Bulletin of Mineralogy, Petrology and Geochemistry》
JOPC 2016 Vol.18 Number 4
2016, Vol.18 Num.4
Online: 2016-08-01
REVIEW
PALAEOGRAPHY AND MINERAL RESOURCES
LITHOFA CIES PALAEODEOGRAPHY AND SEDIMENTOLOGY
BIOPALAEOGEOGRAPHY AND PALAOECOLOGY
REVIEW
497
Wu Shenghe, Feng Wenjie, Yin Senlin, Yu Chen, Zhang Ke
Research advances in alluvial fan depositional architecture
Alluvial fan,which develops in the margin of the basin,is a significant sedimentary facies type. In recent two decades,great progress has been made in the controlling of distribution,internal architecture and reservoir characteristics of alluvial fans. Firstly,the controlling of fault activities,lithology of provenance,and the base-level cycles on alluvial fan depositional architecture were elaborated. Secondly,three depositional architecture models of alluvial fans and terminal fans were established,including the alluvial fan dominated by debris flow,alluvial fan co-dominated by debris flow and fluvial and fluvial fan. Thirdly,how depositional fabric and mechanism of alluvial fan control the reservoir quality was analyzed. Further research is required on the process of deposition,internal architecture and reservoir heterogeneity of alluvial fans through advanced technologies,such as advanced flume simulation experiment,numerical simulation of deposition,GPR and so on.
2016 Vol. 18 (4): 497-512 [
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513
Mei Mingxiang
Stratigraphical natures for the Hadean:An important clue for understanding of both evolutionary history and palaeogeographical background in forming and initial periods of the Earth
Within the current Precambrian geological time scale, it is an undefined base of the Archean Eon that it is roughly indicated at about 4000,Ma,which results in a use of Hadean is informal as it has not been defined. Two of key advances led to the revision of stratigraphical nature for the Hedean,which as follows: (1)The discovery of truly ancient zircon crystal in Archean conglomerates at Jack Hills in Western Australia,which extend back to 4404,Ma and contain a wealth of information about conditions on very early Earth; (2)The discovery of ca.4030,Ma Acasta Gneiss in northern Canada. These discoveries,together with age dating of the Moon and meteorites,have yielded a great deal of knowledge about the early history of our solar system that is just an important foundation to revise the stratigraphical nature of the Hadean. The knowledge includes the formation of the solar system and the Earth, the important changes and their physical records on very early Earth, the origin of life and its early evolution. This revised Hadean Eon that has been recognized as the earliest period of Earth history,extends from the age of formation of the solar system at T0=4567,Ma,to the age of Earth��s oldest dated rock from the Acasta Gneiss Complex,at 4030,Ma,and has further been subdivided into two eras:(1)the Chaotian Era(4567,Ma-4404±8,Ma);and(2)the Jack Hillsian Era or the Zirconian Era(4404±8,Ma-4030,Ma). Both the lower(4567,Ma)and upper(4030,Ma)age limits for the Hadean Eon would necessarily be defined as chronometric boundaries,as there is no preserved stratigraphy. A Hadean Eon that has been endowed with a definitely stratigraphical nature not only delegates an important advance of studies on Precambrian stratigraphy, but also provides lots of important ideas for the further understanding of the evolutionary history of the early Earth.
2016 Vol. 18 (4): 513-524 [
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745
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613KB] (
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PALAEOGRAPHY AND MINERAL RESOURCES
525
Liu Zhaojun, Sun Pingchang, Liu Rong, Meng Qingtao, Hu Fei
Genetic types and deposit features of oil shale in continental basin in China
Scholars at home and abroad have done some effective discussion on the genetic classification of oil shale,however,there is no uniform classification. Considering that most oil shale in China are continental deposits, starting with the sedimentary environment of oil shale,the conclusion that the content of aquatic organism was decreased in the oil shale while the value of terrestrial organic matter was increased from aphytal to semi￣deep lake to limnetic environments was drawn. Based on the above understanding,continental oil shale could be divided into three genetic types,namely aphytal sapropelic oil shale,semi-deep lake humic-sapropelic oil shale and limnetic sapropelic-humic oil shale. Characteristics of oil shale in 29 continental basins show that the ore of aphytal sapropelic oil shale is always distributed widely in the large to mid￣sized depression basins and characterized by wide stable lateral distribution and medium oil shale grade and thickness. In addition,aphytal sapropelic oil shale ore in small rift basins is characterized by huge thickness,good quality and small distribution scale and great differences in lateral thickness. Semi-deep lake humic-sapropelic oil shale is distributed in both depression and rift basins,with small distribution scale and significant differences in lateral and vertical quality and thickness. Limnetic sapropelic-humic oil shale are mainly deposited in rift basins characterized by limited distribution,small thickness and high quality.
2016 Vol. 18 (4): 525-534 [
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938
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535
Jin Zhenkui, Shi Liang, Yan Wei, Zhu Xiaoer, Peng Biao
Contribution of sedimentary and diagenetic factors to clastic reservoir quality: Quantitative determination by single factor comparison method
Quality of clastic reservoirs refers to permeability and porosity. Factors controlling reservoir quality are mainly sedimentary and diagenetic. Sedimentary factors include grain size,rounding,sorting and content of clay matrix. Diagenetic factors include compaction degree,content of dissolution pores,type and content of cements. The reservoir quality of a sandstone is commonly controlled by many factors,and the key to determine major controlling factors is to find out quantitative contribution of each factor. In this paper,a method to analyze quantitative contribution of sedimentary and diagenetic factors to reservoir quality—the single factor comparison method—is proposed out,and is applied to the sandstone reservoirs in the Dongying Formation of Paleogene in the Bozhong sag. There are two types of sandstones in the Dongying Formation,distributary channel sandstone and mouth bar sandstone of deltaic facies,and their permeability differs greatly. Quantitative contribution rate of each factor to the reservoir quality difference is calculated,and major controlling factor is determined:Contribution rate of clay matrix content is 78.5%,indicating clay matrix content is the major controlling factor;that of grain size is 2.7%,that of sorting coefficient is 1.5%;that of authigenic clay mineral content is 15.9%,that of carbonate cement content is 2.3%,that of dissolution pore content is 1.5%,that of compaction degree is 1.7%. Comprehensive contribution rate of sedimentary factors is the sum of each sedimentary factor��s contribution rate,
i.e.
, 82.7%;comprehensive contribution rate of diagenetic factors is the sum of each diagenetic factor’s contribution rate,
i.e.
, 18.4%(the rate of dissolution pore is -1.5% because of its reverse influence). Thus,sedimentary factors are major factors resulting in great difference in permeability between channel sandstone and mouth bar sandstone in this area.
2016 Vol. 18 (4): 535-544 [
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875
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545
Ji Hancheng, Fang Chao, Hua Nan, Xiao Jing, Li Haiquan, Li Xue, Li Chen, Ma Pengpeng, Mao Xiang
Characteristics and favorable controlling factors of karst reservoirs within the uppermost part of Ordovician in western Shandong-eastern Henan area
Based on observation of outcrops,cores and thin sections and analysis of logging data,combined with regional geological background,features,evolution,main controlling factors of the reservoir within the Fengfeng Formation and Majiagou Formation,the uppermost part of Ordovician in the western Shandong-eastern Henan(Dongpu) area were studied deeply. Subsequently,the distribution of favorable reservoirs was predicted. The study results revealed that grain limestone,dolomitic limestone,micrite limestone,silty-fine crystalline dolostone,gypsum-bearing dolostone and algae dolostone were the dominant rock types,and the main reservoir spaces were cracks and pores. The average porosity of dolomite reservoirs was 2.5%,and the average permeability was 7.43×10
-3
μm
2
. The average porosity of limestone reservoir was 2.2%,and the average permeability was 2.72×10
-3
μm
2
. The reservoirs had experienced four evolution stages,which are the period of penecontemporaneous pore formation(Cambrian-Middle Ordovician), weathering leaching period(Late Ordovician-Early Carboniferous), minerals filling period(Late Carboniferous-Late Cretaceous) and the period of pore dissolution reconstruction(Paleogene). Sedimentary facies,diagenesis and tectonic stress play a significant role in controlling the formation of favorable reservoirs. The study indicates that areas superimposed by the grain bank, tidal flat facies zone,fault belt,dolomitization area,penecontemporaneous karstification area,epigenic karstification area and buried karstification area are predicted as the most favorable reservoir zone. Areas superimposed by the grain bank, tidal flat facies zone,dolomitization area,penecontemporaneous karstification area,epigenic karstification area and areas superimposed by the fault belt,epigenic karstification area,buried karstification area are predicted as the secondary favorable reservoir zones. Areas superimposed by the grain bank, tidal flat facies zone,fault belt,dolomitization area,penecontemporaneous karstification area and buried karstification area are predicted as the general reservoir zone.
2016 Vol. 18 (4): 545-559 [
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830
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334
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560
Li Yuan, Cai Zhongxian
Division of karst platform architecture and cave levels correlation in the early Hercynian, Tahe Oilfield, Tarim Basin
Multi-levels of karst platforms are generally formed in karst regions due to multi-stage tectonic movements,and one phase of caves will be generated by a drainage base level corresponding to a karst platform,which are observed in modern karst geological surveys. A complex karst cave system,marked by multi-layer architecture in vertical and acted as an important exploration target,was created in early Hercynian,Tahe Oilfield, Tarim Basin. In order to better understand the mechanism of cave development,modern karst theories,3-D seismic data and three different methods,namely river terraces,flow concentration and onlap termination,were utilized to subdivide karst platform architecture. Moreover,cave levels correlation constrained by karst platform was carried out. This study result demonstrated that:(1)karst platforms in Tahe Oilfield can be subdivided into 4 levels,and platform I was first formed,while the area of platform Ⅲ was the maximum; (2)three cave levels were identified,distributing to be layered,and the scale of the cave level controlled by platform Ⅲ was the largest. Actually,this three cave levels are not overlapped in vertical except some part of the cave level controlled by platform Ⅲ extending to platform Ⅱ. This feature above proved that the cave level controlled by platform Ⅲ was resulted from a long stable tectonic stage,while the other two cave levels were created in a relatively restricted tectonic stage, and the headward￣erosion scale controlled by ground water level was limited.
2016 Vol. 18 (4): 560-568 [
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764
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4159KB] (
368
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569
Meng Yuanlin, Wang Zhixuan, Zhang Fenglian, Meng Fanjin, Jiao Jinhe, Shi Lidong
Characteristics and forming mechanism of tight sandstones in the Paleogene Shahejie Formation of southern West Sag,Liaohe Depression
Low-yield and commercial oil flows have been discovered in the Paleogene Shahejie Formation,southern West Sag,Liaohe Depression,Bohai Bay Basin. The reservoirs are typical tight sandstone reservoirs characterized by low-ultralow porosity,extra-low-ultralow permeability and low pressure. Based on data of thin sections,SEM,grain size,mercury pressure analysis and physical property,the micro-characteristics and formation mechanisms of tight sandstones were analysed. The results show that:The tight reservoirs(with porosity value lower than 10%)are mainly distributed in the sag area;The formation of tight reservoirs are not controlled by factors such as mineral composition,grain size,grain sorting and roundness;Pore types mainly consist of secondary pores and pore structures are characterized by medium pore diameter,tiny throat and heterogeneous throat sorting;The tight sandstones are mainly formed through compactions and cementations and are thus categorized as diagenetic tight sandstones.
2016 Vol. 18 (4): 569-580 [
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911
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6251KB] (
419
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581
Zhang Yaguan, Du Yuansheng, Chen Guoyong, Liu Jianzhong, Wang Zepeng, Xu Yuanyuan, Tan Daiwei, Li Lei, Wang Dafu, Wu Wenming
Sedimentary characteristics and mineralization model of high￣grade phosphorite in the Sinian Doushantuo Age of Kaiyang area, central Guizhou Province
There were thick and high-grade phosphorite beds in Kaiyang area of central Guizhou Province during the global phosphogenesis events in the Sinian Doushantuo Age. This paper used thin sections observation,stratigraphic comparison and subdivision and sedimentary facies analysis to study the sedimentary characteristics and mineralization model of phosphorite deposits in the Sinian Doushantuo Age in Kaiyang area,central Guizhou Province. The result showed that: (1)Kaiyang area was located in north margin of Central Guizhou Old Land which was a phosphorus beach during the Sinian Doushantuo Age. The high-grade phosphorite ore in Kaiyang area was mainly composed of sand clastic phosphate rocks which were formed in the process of sedimentation-diagenesis of phosphorus-rich deposits,during which they were erosion and broken,exposed and leached,accumulated and cemented repeatedly. (2)The palaeogeographic environment and unstable seawater condition controlled the deposition and enrichment of phosphorite in Kaiyang area. Shore face zone like Yangshui or Yongwen which were in a depositional condition with moderately-deep seawater in the Sinian Doushantuo Age was the advantageous metallogenetic zone. Foreshore zone with too shallow seawater and offshore zone with too deep seawater were unbeneficial for phosphorus aggregation and mineralization. (3)The dynamic mineralization model of phosphorite deposits in Kaiyang area showed that frequent transgression and regression during the Doushantuo Age made phosphate rocks which originally deposited in shore face zone experienced multi-stages erosion,exposure,leaching,cementing and redeposition. Physical winnowing action,weathering and leaching gathered phosphorus and ultimately led to the formation of high-grade phosphorite.
2016 Vol. 18 (4): 581-594 [
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791
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595
Heshan Formation in western Guangxi
Sedimentary environment of allites in the Permian
There exists a controversy about the sedimentary environment of the allites in the Permian Heshan Formation in western Guangxi: Land environment or marine environment? Based on the field investigation and geochemical data of samples from the Permian allites, we believed that the Permian allites in western Guangxi were deposited in the land environment. That the allites distributed continuously and widely on the isolated carbonate platforms in the Permian in western Guangxi indicated that the bausite ore beds were formed in an exposed carbonate platform environment. According to the contact between the allites and the carbonate substratum of the Maokou Formation, there existed carbonate gravels in the bottom of allites formation, and it could be seen that the allites filled the carbonate substratum in some sections, and this indicated that the bauxitization occured directly on the ancient karst surface. Additionally, the acient plant fossils in the bauxite ore beds also revealed the allites were formed in land environment. Combined with the V/Zr-Zr/Cu discriminant plot, the geochemical data of the allite samples, Boron contents lower than 10×10-6, Sr/Ba range of 0.291.61 with the mean of 0.92, Rb/K range of 0.00110.0025 with the mean of 0.0017, indicated that the allites in the Permian Heshan Formation in western Guangxi were formed in the land freshwater environment.
2016 Vol. 18 (4): 595-604 [
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1103
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605
Wang Yufang, Leng Jigao, Li Peng, Li Fei
Characteristics and its main enrichment controlling factors of shale gas of the Lower Cambrian Niutitang Formation in northeastern Guizhou Province
The shale gas resource is rich in northeastern Guizhou Province,and especially,the Lower Cambrian Niutitang Formation has great exploration potential. Based on the data of several drilling wells,combined with the data of outcrops and their geochemistry characteristics,we studied the characteristics and main enrichment controlling factors of the shale gas of the Lower Cambrian Niutitang Formation in northeastern Guizhou Province. The shale is characterized by great thickness,wide distribution,high content of organic carbon,higher thermal evolution degree and good reservoir conditions,etc. However,most wells met the phenomena of low gas content,low methane content and high nitrogen content. Upon the system analysis of main enrichment controlling factors,it is considered that the shale gas enrichment of the Niutitang Formation in study area has distinct characteristics of distribution zone controlled by sedimentary facies and reservoir controlled by fault.
2016 Vol. 18 (4): 605-614 [
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LITHOFA CIES PALAEODEOGRAPHY AND SEDIMENTOLOGY
615
Ji Youliang, Liu Junlong, Wang Tianyun, Liu Dawei, Cheng Tongran
Distributing pattern and mapping method of delta and beach￣bar composite sand-bodies in continental lacustrine basin
The continental lacustrine basin, which is different from marine environment, has the characteristics of shallow￣water, low￣energy, frequent progression and regression,
etc.
Based on key technologies of high-resolution sequence stratigraphy and seismic sedimentology, combined with the exploration practice, analysis of outcrops and investigation of modern sediments of the typical continental lacustrine basins in eastern and central￣western regions of China, we summarized the distribution pattern of delta and beach￣bar composite sand￣bodies in the continental lacustrine basin and proposed the geological mapping method of composite sand-bodies. The results show that: (1) The “lacustrine￣continental transitional sedimentary system” in continental lacustrine basins, not only has tributary channels, but also has channel mouth bars and longshore bars, sediments of tributary channels, channel￣mouth bars and longshore bars in different geological times were superimposed and preserved in ancient strata and modern sediments; (2) In the condition of flat￣terrain, shallow￣water and low￣energy wave regime, the fluvial process is predominated and channel sand￣bodies were formed; in the condition of steep￣terrain and high￣energy wave regime, the sand￣bodies of tributary channel were reformed and the beach￣bar sand￣bodies along the lake shore were formed; (3) In the background of high frequent lake level changes, the migration of sedimentary slop￣break was dominated by the migration of shoreline, and the special structure of composite delta and beach￣bar sand￣bodies, which were superposed by the multi￣period dendritic distributary channel sand￣bodies perpendicular to the coast, and the multi￣period banding beach￣bar sand￣bodies along the shore in continental lacustrine basin, was formed; (4) Based on the distribution pattern of composite sand-bodies, the geological mapping method of composite sand￣bodies is derived from traditional single factor method, and it mainly focused on the delta and beach￣bar sand￣bodies that developed in continental lacustrine basins with shallow water and low slope.
2016 Vol. 18 (4): 615-630 [
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634
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631
Li Hua, He Youbin, Huang Wei, Liu Zhuruizhi, Zhang Jin
Contourites of the Ordovician Pingliang Formation in southern margin of Ordos Basin
The contourites,gravity flow deposits and deep water autochthonous deposits, consisting of limestone,mudstone with sandstone with radiolarian chert and volcanic tuff interbeds, were developed in the Ordovician Pingliang Formation in the southern margin of Ordos Basin. Contourites were divided into calciruditic contourites,calcarenitic contourites,calcisiltitic contourites,calcilutitic contourites and silt-sandy contourites. Ripples and bioturbation were well shaped on top of calcisiltitic contourites. The ripples,with wave length 1-5,cm and wave height 0.2-0.5,cm,were asymmetric and showed migration direction obviously. The complete and incomplete sedimentary sequences were composed of superimposed calcarenitic contouritse,calcisiltitic contourites and calcilutitic contourites,and displayed upward fine-coarse-fine trend with thickness several millimeters to centimeters. The sequences consisted of not only superimposed multilayer,but also single layer,or appeared between two adjacent muddy layers or stylolites;and the thickness of the upward￣coarsening sequences and the upward￣fining ones were asymmetrical. Contour current moved from the east to the west with path subparallel to the slope. The deep water autochthonous deposits and gravity flow deposits were developed in the lower part of the Lower Pingliang Formation; by contrast,the deep water autochthonous deposits and contourites were favored in the upper part. The contourites were mainly influenced by tectonic movements,relative sea-level rise,current energy,palaeotopography and motion path.
2016 Vol. 18 (4): 631-642 [
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1013
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446
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643
Wang Jialin, Wu Chaodon Zhu Wen, Li Zhuang, Wu Jun, Chen Rong, Wang Jun
Tectonic-depositional environment and prototype basin evolution of the Permian-Triassic in southern Junggar Basin
The tectonic-depositional environment and prototype basin evolution of the Permian-Triassic in the southern Junggar Basin have long been debated. Detailed sedimentary environment,stratigraphic correlation and sedimentary evolution analyses,combined with collection and sorting out of relevant data, have been carried out on the Permian-Triassic strata. Hereby,we discussed a multicycle of compressional and extensional transformation in the Permian-Triassic,and proposed the prototype of the sedimentary basin. In the Late Carboniferous,the west segment of the southern Junggar Basin situated at the end of the North Tianshan Ocean crust subducted southward below the Yili Block,and dominated by littoral and neritic facies,showing the characteristic of a remnant ocean basin. However,the east segment of the southern Junggar Basin is mainly composed of bathyal carbonate deposits and a set of bimodal volcanic rocks,implying that it formed under an extensional environment. In the Early Permian,they both primarily contain fine grained clastic rocks of the littoral-shallow facies. Moreover,syn-depositional faults and collapse deformations can be observed,indicating an intracontinental rift basin. Later on,the deposition rates is faster and the thickness is thicker. Thus,the prototype basin has been transformed into the depression basin in the Middle Permian. Until the Late Permian,the depositional environments were characterized by the alluvial fan or fan delta deposits in the North Tianshan and Bogda area. Also,the Upper Permian Quanzijie Formation is in unconformity relation with the Middle Permian Hongyanchi Formation. Hence,it implied the rapid uplift of the North Tianshan, formed an intracontinental compressional basin. In the Early Triassic,because of the end of the uplift,the basin entered into a relatively stable stage,which formed a weak intracontinental compressional basin dominated by a series of fine grained sediments of coastal shallow-lake facies. In the Middle-Late Triassic,with the occurrence of continuously transgress of the basin,the North Tianshan have been eroded,which was consistent with the expansion of the lacustrine basin and the widespread fine-grained shallow-deep lacustrine sediments. Taken together,we suggested that the basin of the Late Carboniferous to Middle Permian belongs to post-collision extensional depression stage. Nevertheless,a short thrust stage happened in the Late Permian. In the Triassic,the plate squeezing action weakened and Junggar Basin gradually entered a depression-subsidence stage from the intense compressive stage. The Early Triassic is a weak compression and denudation stage,and the Middle-Late Triassic is a stable depression and peneplanation stage.
2016 Vol. 18 (4): 643-660 [
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514
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661
Huang Qingyu, Liu Wei, Zhang Yanqiu, Shi Shuyuan, Wang Kun
Geochemistry and evolution of dolomitizing fluids of the Upper Cambrian-Lower Ordovician dolostones in Central Uplift, Tarim Basin
Based on the detailed petrology study as well as isotope data (
δ
13
C,
δ
18
O and
87
Sr/
86
Sr),the evolution of dolomitizing fluids and genetic mechanism of the Upper Cambrian-Lower Ordovician dolostones are investigated in the Central Uplift,Tarim Basin.The results indicate that:The Upper Cambrian dolostones are composed of micritic dolostones,microbial dolostones and(relict)grainy dolostones with well-preserved precursor lithologic fabric. These dolostones have similar
δ
13
C values and
87
Sr/
86
Sr ratios to the coeval seawater and slightly higher
δ
18
O values,suggesting that the dolomitization occurred during the penecontemporaneous period and the dolomitizing fluid was associated with the slightly evaporitic seawater. The Lower Ordovician dolostones are mainly comprised of fine-crystalline,planar-euhedral to subhedral dolomites. Poor-preserved precursor texture,similar
δ
13
C values and
87
Sr/
86
Sr ratios to the coeval seawater as well as slightly depleted
δ
18
O values of the dolostone indicated the dolomitization occurred during shallow burial. Some of the dolostones formed in early stage could be altered to fine-coarse crystalline,nonplanar-anhedral dolostones and rift-cavity-filling saddle dolostone cements through recrystallization and tectonically controlled hydrothermal dolomitization during medium to deep burial. The dolomitizing fluids of the burial dolomitization were derived from remnant seawater preserved in the formations,deep mantle hydrothermal fluids and hot brine water in the underlying Middle Cambrian evaporate rocks. These dolostones formed during burial have wide range of
87
Sr/
86
Sr ratios and obviously more negative
δ
18
O values due to the combined impact of multi-stage and multi-source diagenetic fluids. Generally,these dolostones in the study area formed in multiple stages of dolomitization with the tendency of forming in early period(large scale replacement during near-surface and shallow burial),being mature in middle diagenetic stage (partly recrystallization during medium-deep burial)and modified in late diagenetic stage(partial adjustment of hydrothermal fluid).
2016 Vol. 18 (4): 661-676 [
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438
)
BIOPALAEOGEOGRAPHY AND PALAOECOLOGY
677
Yin Jian, Liu Chunlian, Wu Jie, Huang Yi, Wu Yueqin
Foraminiferal records and palaeoenvironmental changes since the Late Pleistocene in central Pearl River Delta
Late Quaternary sedimental records,especially Late Pleistocene transgressive records,are well preserved in Boreholes PRD20 and PRD17 drilled in central Pearl River Delta. Based on the comprehensive analysis of foraminifera and lithological characteristics of Boreholes PRD20 and PRD17,combining with previous researches,palaeoenvironmental changes since the Late Pleistocene have been reconstructed,with the Late Pleistocene transgression highlighted. Before 44500 cal a BP, a fluvial environment developed,indicated by coarse-grained sediments. Between 44,500 and 21300 cal a BP, a drowned valley estuary setting developed with the sea water intrusion into the study area,which was corresponding to the transgression of the Wurm Sub-Interglacial Stage. Two short-term transgression-regression circles can be recognized based on foraminiferal data. It can be deduced that Boreholes PRD20 and PRD17 were located in the fluvial-tidal interaction area of the drowned valley estuary during this period. A mottled clay layer in Borehole PRD17 and a conglomeratic sand layer in Borehole PRD20 ware sandwiched between Upper Pleistocene and Holocene sediments,which were most likely formed by subaerial oxidation of the underlying sediments during the last glacial maximum. The study area was influenced by postglacial sea level rise after around 8000 cal a BP, which was recorded by a peat layer in Borehole PRD20. The foraminferal and sedimental records of Borehole PRD20 suggest a bay head environment during 8000-5500cal a BP. Since then,a deltaic plain facies developed in the study area. As a result of the tectonic uplift,the core site of Borehole PRD17 showed a higher topography and did not accept sediments until 4700 cal a BP, which is much later than in other parts of the Pearl River Delta. During this time,the study area could be occasionally influenced by tidal water with sporadic foraminifera tests.
2016 Vol. 18 (4): 677-690 [
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870
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395
)
691
Peng Wei,Lin Xueru, Huang Xiaozhong, Liu Sisi ,Jia Wanna
Preliminary study on assemblages characteristics of waterborne pollen and accumulated pollen from the Yellow River at Lanzhou station
Twenty-four water samples were collected from the Yellow River at Lanzhou station from September in 2011 to June in 2012. Based on the pollen analysis, the temporal change characteristics and accumulated pollen features of the waterborne pollen were discussed. The result shows that pollen assemblages and pollen concentration have obvious changes over time:Ulmus,Populus,Salix and Betula are the major components of the pollen assemblages in the spring and summer;and Artemisia and Chenopodiaceae are main species in the autumn and winter. Pollen concentration has a positive correlation with waterborne sediment concentration. There are obvious differences between pollen assemblages of individual samples and the accumulated pollen assemblage,and pollen assemblages of individual samples cannot reflect regional plant communities. Accumulated pollen assemblage can basically represent the vegetation status of loess area from Liujiaxia reservoir to Lanzhou where it is suggested to be the main pollen and sediment source area in this study site.
2016 Vol. 18 (4): 691-704 [
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679
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