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《Bulletin of Mineralogy, Petrology and Geochemistry》
JOPC 2009 Vol.11 Number 5
2009, Vol.11 Num.5
Online: 2009-10-01
SEQUENCE STRATIGRAPHY AND PALAEOGEOGRAPHY
PALAEOGEOGRAPHY AND MINERAL RESOURCES
LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY
PALAEOBIOGEOGRAPHY AND PALAEOECOLOGY
NEW TECHNIQUES AND NEW METHODS
SEQUENCE STRATIGRAPHY AND PALAEOGEOGRAPHY
471
Deng Hongwen
Discussion on problems of applying high resolution sequence stratigraphy
High resolution sequence stratigraphy has been accepted by most geologists and widely applied to oil and gas exploration and development since it was introduced into China due to its wide applicability， feasibility， high accuracy and predicability. It has played an important role in oil and gas exploration and development in China. In its application, there still exists some deviation to the concepts of sequence stratigraphy, thus deep discussion needs to be carried out. The author discussed some problems occurring in high resolution sequence stratigraphy application in reservoir-scale， including the differentiation between base-level cycle and paraseqence， the orders of base-level cycles， the identification and correlation of base-level and so on， in order to provide a reflection and acquire a common understanding on the principles and methods of high resolution sequence stratigraphy.
2009 Vol. 11 (5): 471-480 [
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1864
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PALAEOGEOGRAPHY AND MINERAL RESOURCES
481
Zhang Xia, Lin Chunming, Ling Hongfei, Jiang Shaoyong, Li Yanli, Gao Likun, Yao Yulai, Liu Xiao
Nodular limestone and its genesis from the Ordovician Yanwashan Formation in western Zhejiang Province
In this paper，we discussed the genesis of the nodular limestones from the Ordovician Yanwashan Formation in the Huangnitang section(the first GSSP)，Changshan，Zhejiang Province on the basis of mineral component，texture，structure，chemical composition，and particularly the stable C-O isotopic composition of both the nodule and matrix. The research results indicate that there is an apparent difference between the nodule and matrix of the nodular limestones. The nodules are mainly composed of micritic calcite(70％～98％)，while the primary component of the matrix is clay mineral(40％～78％)with only 20％～58％ calcite. The
δ
13
C
VPDB
values of calcite of the nodule and matrix are 0.5‰ to 1.4‰(average 0.9‰)and -0.4‰ to 1.1‰(average 0.2‰)，respectively. The
δ
18
O
VPDB
values of calcite of the nodule and matrix are -12.8‰ to -8.0‰(average -10.6‰)and -11.7‰ to -9.0‰(average -10.3‰)，respectively. The nodule always shows higher
δ
13
C value and formation temperature than those of the matrix for the same sample. All features imply that the nodular limestones from the studied section are formed due to a combined processes of the periodical dissolution of bottom current during the sedimentary period and the differential compaction and pressure solution during the diagenesis. There are three existing types of the nodular limestones: banded nodular limestone，discontinuous nodular limestone and random nodular limestone. The occurrence mode of the nodular limestone is determined by the insoluble residue content of country rock of nodules and the pressure solution intensity.
2009 Vol. 11 (5): 481-490 [
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2398
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561
Liao Yuantao, Wang Hua, Wang Jiahao, Xiao Dunqing, Huang Chuanyan, Xia Cunyin, Liu Yanbo
The Paleogene Dongying Formation in central area of Huanghua Depression: Depositional characteristics and prediction of favorable exploration area
The characteristics of depositional systems of the Dongying Formation in the central area of the Huanghua Depression were analyzed based on analyses of sequence stratigraphy and modern sedimentology combined with core，well and seismic data. The Dongying Formation was formed in the transitional period of tectonic evolution from rifting to sagging stages. Mainly lacustrine deltaic and lacustrine systems were developed. Fan delta and turbidite systems were only distributed sporadically. Time-spatial distribution and evolution of the depositional systems were controlled by tectonic setting and sequence configuration. Three typical depositional models were established and they include gentle slope， fault-controlled steep slope， and multi-level step-fault. In details， lowstand and highstand systems tracts deltas were mainly developed in the SQE
d
3. Lowstand systems tract delta in local areas such as Banqiao Subsag and highstand systems tract delta with a large range were mainly developed in the SQE
d
2 and SQE
d
1x. Lowstand and highstand systems tract deltas were developed in the Qinan and Qibei Subsags in the SQE
d
1s. Based on the analysis of depositional systems， five types of traps were identified. They are subtle traps near the slope break， onlap pinchout traps across the sag center， structural-lithologic traps， and subtle traps including lowstand systems tract turbidites， highstand systems tract turbidites and incised valley. Six favorable exploration areas were predicted according to the characteristics of traps.
2009 Vol. 11 (5): 561-572 [
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2165
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573
Wang Youzhi, Zhang Weihai
Characteristics of fault accommodation structure-slope break zone and its control on reservoir distribution in southern subsag of Uliastai Sag，Erlian Basin
Based on restoration of the Early Cretaceous palaeogeomorphology of southern subsag of Uliastai Sag，researches have been carried out on the relationship between characteristics of fault accommodation structure-slope break zone， depositional systems， and reservoir distribution.The analyses show that the compound structural assemblage controls the shape of sandbody and reservoir distribution.There are accommodation structure-upper slope break， middle slope break and lower slope break spreading in NNE direction in southern subsag in the study area during the Early Cretaceous.The accommodation structure-slope break zone controls the formation of depositional systems. There are large-scaled fan delta—sublacustrine fan depositional system；The accommodation structure-slope break zone controls shapes of sandbodies，mainly seven small-scaled sublacustrine fan sandbodies were distributed in a tongue-like shape.Multistage slope breaks provide spaces for sediments deposition. The accommodation structure also controls provenance and drainage system，the major reservoir types are fan delta front and sublacustrine fan sandbodies controlled by the accommodation structure-slope break zone in southern subsag of the Uliastai Sag.The compound structure with different orders lead to the differences of reservoir types and their petrophysical property.
2009 Vol. 11 (5): 573-580 [
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1857
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1355KB] (
620
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LITHOFACIES PALAEOGEOGRAPHY AND SEDIMENTOLOGY
491
Gao Zhiyong, Han Guomeng, Zhu Rukai, Guo Hongli, Wang Daochuan, Li Benliang
Depositional setting and evolution of the Paleogene—Neogene foreland basin of southern margin of Junggar Basin
Good ways are found in studying clastic deposits of the Paleogene and Neogene in southern margin of Junggar Basin. The ways are ① Lithofacies and sedimentary facies are distinguished by outcrop analyses and core and thin section description, ② The boundaries of deposits are identified by recognition of shoreline evolution according to different characteristics of seismic facies and different locations of facies change and ③ The main and minor provenances are distinguished by characteristics of heavy mineral assemblages and isopach maps of sandstones. Characteristics of sedimentary facies have been studied by this comprehensive method. The depositional framework and evolution of the southern margin of Junggar Basin were analyzed on this basis. The results indicate that during the deposition of the Paleogene Ziniquanzi Formation， 4 large scale fan delta deposits were developed in thrust belt of the Tianshan Mountains and the lake level was lower. During the deposition of the Anjihaihe Formation， 3 fan delta deposits with decreasing sizes were developed in front of the Tianshan Mountains due to the lake level rising and the fan delta retrogration. Fan delta was not developed in Huoerguosi area. During the deposition of the Early Neogene Shawan Formation， fan deltas with larger scales were developed in front of the Mountains， the topography differences were large， the slope was steep and the climate was arid due to lake level quick falling. There are 2 main sedimentary provenances and 2 minor ones from the Paleogene to Neogene in southern margin of Junggar Basin. The main provenances are the Dongwan-Tugulu-Manas anticline in central area， the Xihu-Dushanzi anticline in western area. The minor sedimentary provenances are respectively the Hutubi anticline in eastern area and the Huoerguosi anticline in central western area. These four provenances are distributed in south-north direction. There is a very important provenance in Kayindike area which is from the foreland uplifting area.
2009 Vol. 11 (5): 491-502 [
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503
Li Hua, Ma Xueping, Wei Longming
Sedimentary facies and sea-level change across the Middle-Upper Devonian boundary at Caiziyan section， Guangxi: The mid-Givetian regression and its timing in South China
The Caiziyan section was located in a platform margin zone， with relatively abundant benthic and common-rare pelagic fossils， which may be regarded as a quite suitable reference section for stratigraphic correlation and division. On the basis of lithofacies and biofacies characteristics， sea-level change history is reconstructed for the interval from the Givetian to the Early Frasnian times. The Early Givetian Donggangling Formation of the study area may represent deposits under a persistent transgressive phase， probably with a slight sea-level fall at the end of the Lower
varcus
Zone. The lower part of the “Gubi” Formation is complex in lithology， probably resulting from extensive sea-level changes， including a significant transgressive event at the initial period of the Lower
hermanni-cristatus
Zone and the long-recognized mid-Givetian regression， whose timing has been precisely determined to be the Upper
varcus
Zone for the first time. The Late Givetian deposits host abundant tabulate corals and reef-associated bioclasts， including stromatoporoids， crinoid stems
etc
.， implying that the study area was probably located on the upper slope in front of a reef complex. The upper part of the “Gubi” Formation(conodont
falsiovalis
to lower
transitans
zones)is characterized by alternating medium-thin and thick bedded limestones(mainly with bioclasts of level-bottom organisms)， which indicates a change from fore-reef to fore-shoal environments， probably with little overall sea-level change across the Middle-Upper Devonian boundary. The Rongxian Formation(basal part)is characterized by grayish to gray-white thin-bedded to massive limestones， which may represent a significant sea-level rise in the Middle
transitans
Zone in South China. The finely-medium crystalline dolostone layer at Caiziyan is within the Upper
varcus
Zone， with normal marine fossils including corals and conodonts. The proposed interpretation for this dolostone layer is that a substantial sea-level fall event happened in the Upper
varcus
Zone in the Guangxi area， based on temporal and spatial correlation of the dolomitized layers and evidence of sea-level fall in other sections.
2009 Vol. 11 (5): 503-512 [
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1937
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727
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513
Li Xiangdong, He Youbin, Wang Dan, Gao Zhenzhong, Zheng Zhaochang
Internal-wave and internal-tide deposits of the Middle Ordovician Xiangshan Group Xujiajuan Formation， Ningxia
The Xiangshan Group of the Middle Ordovician in Ningxia is dominated by deep water turbidity current deposits which are mainly a set of lightly metamorphic terrigenous clastic rocks with lower content of carbonate rocks and chert interbeds. The Xujiajuan Formation of the Lower Xiangshan Group is composed of grayish green， yellowish green， fine- to medium-grained lightly metamorphic sandstone， calcareous sandstone， siltstone and shale(slate)， and thin bedded limestone at the top. Cross laminations including bi-directional cross bedding with abundant shapes and clear lamina and unidirectional ones with dipping up-slope or large angle between them are found in thin- to medium-bedded and very fine- to fine-grained sandstones， silty micrite and silty shale. Those lamina of bi-directional cross bedding are also inclined bi-directionally up- and down-slope. These cross beddings in deep water environment may not be formed by contour currents or turbidity currents， but be formed by alternating up- and down-slope currents produced by internal waves and internal tides. This paper has made detailed researches on the internal-wave and internal-tide deposits in the Xujiajuan Formation from sedimentary background， sedimentary structures and paleocurrents. A deep-water slope environment was suggested for the internal-wave and internal-tide deposits and an interpretation was made for the deletion of flaser bedding， wavy bedding and lenticular bedding in this case.
2009 Vol. 11 (5): 513-523 [
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2009
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551
Chen Zhonghong, Wang Li, Yang Yong, Zha Ming
Response of formation water chemical fields to evolution of lacustrine basin of the Paleogene in Zhanhua Sag of Jiyang Depression and its hydrocarbon significance
On the basis of calculation and analyses of 1160 testing data including salinity， formation water types， content of ions and physical properties of crude oil， the Paleogene formation water chemical field in Zhanhua Sag was investigated. The results show that the formation water chemical field has a good response to the evolution of lacustrine basin， the average salinity and content of ions decreased with the lake level deepening and desalinating from the initial faulted stage to the peak stage of fault development(the Member 4 to Member 3 of Shahejie Formation);The average salinity and content of ions increased with lake level shoaling in lake basin withering period(the Member 2 of Shahejie Formation to the Dongying Formation). Typical characteristics of an opening faulted lacustrine basin were displayed by the low content of total salinity and ions(total salinity averaged by 10 g/L)， NaHCO
3
formation water being the dominant type(with a proportion of 80％)， and the high values of
r
Na
+
/
r
Cl
-
and［
r
HCO
-
3
+
r
CO
2-
3
］/
r
Cl
-
(the average values respectively higher than 1.0 and 50)， which indicated the stronger metamorphic process and alternation of the formation water. Influenced by the opening formation water chemical fields， the viscous crude oil was widespread and the widespread secondary heavy crude oil was the result of water-flush， oxidization and biodegradation in the course of oil migration， accumulation and preservation in opening formation water chemical fields. The samples with NaHCO
3
type were mainly distributed in the formation water with a lower salinity（<15 g/L）， which indicated the opening hydrogeology and unfavorable preservation conditions for hydrocarbon. The formation water of NaHCO
3
type with a higher salinity（>15 g/L）was mainly distributed in the Bonan subsag and the Yidong faulted zone. Its origin was relative with oil and gas fields and a high content of CO
2
from mantle by the connection of faults， and correspondingly the density of crude oil was lower than 0.9 g/mL generally， which indicated favorable conditions for hydrocarbon preservation.
2009 Vol. 11 (5): 551-560 [
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2086
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1981KB] (
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PALAEOBIOGEOGRAPHY AND PALAEOECOLOGY
524
Tang Feng, Gao Linzhi, Wang Ziqiang,
Palaeogeography and palaeoecology of the Ediacaran(Sinian) macrofossil biota in South China
Ediacaran(635-542Ma)is the important geological period between the last global glaciation(Marinoan)and the Cambrian “explosion of life”. As a result of the tremendous changes of Neoproterozoic climate and environment， rapid evolution and diversity of many eukaryotic lives， including multicellular organisms arise to adapt significant radiation. The Sinian Doushantuo and Dengying Formations in South China and their coeval strata represent the deposition of this special geological time. The complete stratigraphic record，diverse depositional environments and abundant micro- and macrofossils make South China to be one of the ideal areas for further studies on the Ediacaran(Sinian)stratigraphic division and global correlation， and to explore the early origin and radiation of multicellular organisms of the areas of radiation. In particular， the more abundant macrofossils occurring in the Ediacaran(Sinian)strata in the Yangtze platform marginal facies， contain the more distinct assemblages with significant diversity. The recent researches indicate that the Sinian macrofossil assemblages in South China also include a couple of typical fossils of the Ediacaran Biota in Australia and the White Sea biota in Russian. We synthesize in this paper the previous researches in recent years on the Sinian lithofacies and Palaeogeography in South China; mainly displays some newly collections of the “Wenghui Biota” from Jiangkou， Guizhou and the “Jiangchuan Biota” from Jiangchuan， Yunnan; briefly describe the palaeogeographic locations and several Sinian macrofossil assemblages including “Miaohe Biota”. And hereby we conclude that a variety of Sinian macrofossil assemblages in South China were living and buried in the transitional/slope zone of carbonate rocks and clastic rocks at the margin of the Yangtze platform， the characteristics of each macrofossil assemblage were constrained by its sedimentary microfacies and went on changes regularly. The macrofossil records suggest that in this period， accompanied by significant climatic and environmental changes， a series of important evolution events took place， many macroalgae and metazoan generally appeared a diverse developments and laid an ecological foundation for the huge Cambrian radiation of early animal; and in the southern China， a brand new neritic ecosystem had been formed， the dominant planktonic and benthic eukaryotic algae were very prosperous to be the marine primary producers， especially the abundant multicellular macroscopic algae might be main plants of hydrocarbon generation in the transitional period of Precambrian-Cambrian.
2009 Vol. 11 (5): 524-533 [
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2064
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534
Ji Zhongkui, Liu Hongyan
Shifting of vertical vegetation zones in Manas River drainage on northern slope of Tianshan Mountains since the Late Glacier
The statistical relationships between climate indexes(moisture index and warmth index)and typical pollen taxa were established with linear regression method on the Manas River drainage on the northern slope of the Tianshan Mountains. Climate and vegetation developments in this region were reconstructed based on the different pollen taxa content of a previously published sediment sequence from the Manas Lake， a desiccated end lake of the Manas River， as well as modern climate， vegetation and landform relationships. Since 13000 a BP， the palaeoclimate change in this area has experienced several important stages: warm-dry， cold-moist， warm-dry， cold-moist， warm-dry， cold-moist and warm-dry， in correspondance with the climate change， ancient vertical vegetation change around the area has experienced a series of succession processes: desert， desert steppe(to develop lowland meadow and stepped locally)， extreme arid desert， desert steppe， desert， desert steppe， desert. When the climate in the Manas River drainage changed from warm-dry to cold-moist， all vegetation boundaries in the area moved downward， hence the area of desert and forest was enlarged and the lower limit of conifer may get to current steppe. When the palaeoclimate changed from cold-moist to warm-dry， all vegetation boundaries moved upward， the area of desert was enlarged， while the area of steppe and forest was decreased， and the lower limit of conifer may get to current alpine and sub alpine meadow.
2009 Vol. 11 (5): 534-541 [
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1717
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542
Ma Yanling, Xu Qinghai, Huang Xiaozhong, Zhou Gang, Zhang Liyan, Tao Shichen, Sun Huiling
Pollen assemblage characters of human disturbed vegetation in arid area in northwestern China
Assessment of human impact on modern vegetation has become a key issue in explaining the past human activities and their environmental effects. Studies on 40 surface pollen assemblages of farmlands and wildlands in arid northwestern area of China show that the pollen concentration of farmlands is lower than that of wildlands， which are 7227 grains/g and 32704 grains/g respectively. The percentages of agricultural pollen types from farmlands are larger than those of wildlands， while the agricultural pollen types are not dominant in both of the assemblages. The pollen assemblages in farmlands reflect not only local plant compositions of the lands but also regional vegetation information. The percentages of shrubs pollen of farmlands are lower than that of wildlands， and weed pollens are more abundant. Chenopodiaceae，
Artemisia
and
Ephedra
pollen widely present in all the samples. The percentages of different agricultural pollens indicate different vegetation in local and regional areas. The results of cluster analysis furthermore indicate a consistency of pollen assemblages between farmlands and wildlands. The percentages of vitaceae pollen are dominant and pollen assemblages are consisted well in grape lands， while not present in other vegetation types. The percentages of malvaceae pollen are quite low and other species are the main pollen types， with poor consistency to the local vegetation cover. If the farmlands and wildlands are close and the percentages of agricultural pollen of farmlands are low， pollen assemblages of the two land types are similar.
2009 Vol. 11 (5): 542-550 [
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1623
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755KB] (
551
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NEW TECHNIQUES AND NEW METHODS
581
Wen Junjun, Liu Jianbo
Quantitative study of bioclastic grains in carbonate rocks: Theoretical analysis and application of point-counting method
The abundance of bioclastic grains in carbonate rocks is of great value in researches of fossil diversity and reconstruction of paleoecological environment. It can be easily valued with point-counting method， which is more suitable for carbonate rock than the other two quantitative approaches-visual estimation and image analysis. However， few studies have been attempted to determine how many points should be counted to yield adequate and precise results， which made the point-counting procedure time-consuming. By comparative analysis of the comparison charts for visual percentage estimation and microphotographs of the Ordovician carbonate rocks， this study focuses on how these attributes influence the precision of point-counting method， and discusses a moderate number of points which facilitates the method. As a result， a number of 500 points or so is appropriately enough for precise measure of the abundance of the referred component in most of carbonate thin sections with an error of ±2.5％， and should be adjusted with abundance， grain size， sorting as well as biodiversity of bioclasts in thin sections.
2009 Vol. 11 (5): 581-592 [
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1899
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680
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