2022 Vol. 40, No. 2
Display Method:
2022, 40(2): 281-291.
doi: 10.14027/j.issn.1000-0550.2021.155
Abstract:
Sedimentology and basin dynamics have become the main disciplines in geology in China， and have strong social needs. This study summarizes the applications and funding records of the National Natural Science Foundation （NSFC） generally in China， and youth projects in sedimentology and basin dynamics， from 1987 to 2020， and provides a reference for future research. The analysis shows that during the period from the “Eighth Five-Year Plan” to the “Twelfth Five-Year Plan”， the number of declared projects in this field was relatively large， and the total number of approved projects increased rapidly. It also indicates that the “Eighth Five-Year Plan” to the “Twelfth Five-Year Plan” period was a significant time for the development of sedimentology and basin dynamics in China， and the training of young scientific and technological talents in this field has achieved certain development. Applications for funding mainly fall within three categories： Basic sedimentology and basin geodynamics； Applied sedimentology and basin geodynamics； and Cross-over between sedimentology and basin geodynamics. During the “Fourteenth Five-Year Plan” period： （1） Basic sedimentology and basin geodynamics are paying more attention to studies of paleoenvironment and paleoclimate； （2） Applied sedimentology and basin geodynamics research will continue to occupy a pace in the field of tectono-sedimentology， and it will continue to develop and increase its interests in sedimentary mineralization； （3） Applications in the cross-over between sedimentology and basin geodynamics focus more on carbonate sedimentation and biological sedimentation. In addition， the application of computer simulation technology in sedimentology may also become an important direction and field in the future.
2022, 40(2): 292-318.
doi: 10.14027/j.issn.1000-0550.2021.108
Abstract:
Sequence stratigraphy is a research focus in geosciences. It is widely used in the analysis of sedimentary basins and for hydrocarbon exploration and development. Sequence stratigraphic theory and methodology based on marine basins has been established through hydrocarbon exploration on passive continental margins， and has a development history of about 50 years. In this study the three main evolutionary stages and major advances in deepwater siliciclastic sequence stratigraphy were reviewed： 1970⁃2000 （classical marine siliciclastic sequence stratigraphy）； 2000⁃2010 （sequence stratigraphy of shelf margins）； and 2010⁃2020 （the standardization of sequence stratigraphy）， exploring frontier areas and controversial topics in current research on deepwater siliciclastic sequence stratigraphy.
2022, 40(2): 319-334.
doi: 10.14027/j.issn.1000-0550.2021.137
Abstract:
The study of ooids has a long history， and there is not yet a consensus as to their origin. The “inorganic process” that has been accepted by most sedimentologists has recently been challenged by the accumulating evidence of microbially-mediated mineralization within modern and ancient ooids. For microbial mechanisms involved in the genesis of ooids， photosynthetic microorganisms （e.g.， cyanobacteria） use light energy to produce organic carbon and to create alkaline microenvironments during metabolism that induce ambient carbonate nucleation. The organic matter that they produce may feed heterotrophic microorganisms， and some of these heterotrophs （e.g.， sulfate-reducing bacteria） are capable of increasing neighboring alkalinity and facilitating carbonate precipitation during their metabolic activities. It is possible that physicochemical conditions rearrange pre-precipitated nanograins produced by biologically-induced and -influenced mineralization processes， and promote the genesis of modern ooids with delicate tangential fabrics （Diaz’s model）. In addition， some types of ancient ooids （e.g.， alternating dark- and light-colored laminar ooids， and cerebroid ooids） with natural organic matter-rich laminae， closely resemble so-called “regularly laminational stromatolites” or “hybrid stromatolites”， implying their similar origins. The microbial accretion mechanism of such ooids resembles the growth model of laminar stromatolites，i.e.， combined biologically-induced （mainly photosynthetic microorganisms and sulfate-reducing bacteria） and biologically-influenced （providing templates for carbonate nucleation） mineralization. Organic matter-rich， laminar （or banded） fabric ooids are rare in modern marine settings but not uncommon in ancient records. Further work focusing on this kind of ooids may provide a new perspective to understand the organomineralization process in the genesis of ooids.
2022, 40(2): 335-349.
doi: 10.14027/j.issn.1000-0550.2020.119
Abstract:
The formation mechanism of dolomite has always been the focus of geologists. The microbial dolomite model is an important supplement to the "dolomite problem". Microbial processes can not only provide nucleation sites， but also significantly improve the chemical conditions of adjacent water columns， thus forming a microenvironment that favours dolomite precipitation. However， for ancient strata， due to the lack of convincing evidence， it is difficult to determine whether dolomite is of microbial origin. In particular， the special microscopic morphologies of minerals should be carefully used to evaluate the origin of dolomite. A great deal of evidence indicates that hydrochemical and hydrologic conditions are the key factors for dolomite precipitation. Although the distribution and forming environment of modern dolomite cannot be compared with the geologic historical period， the scale and optimal environment for microbial dolomite may be much more extensive in the Precambrian period. However， to date， the contribution of microbial processes to ancient dolomites is still difficult to effectively evaluate， so there are still many challenges in explaining the formation of large-scale dolomites in geological history with this model. It is worth noting that microbial activity is still beneficial to the formation of dolomite to some extent since the potential intermediates， such as very high magnesium， calcite， and proto-dolomite， can be widely promoted.
2022, 40(2): 350-359.
doi: 10.14027/j.issn.1000-0550.2020.135
Abstract:
Many mechanisms have been suggested in previous studies as to the genesis of dolomite， but many of them are unconvincing and lack strong evidence. Studies in recent years have shown that dolomite is deposited at room temperature with the help of microorganisms to form microbial dolomite. Simulations have reinforced this view. The discovery of microbial dolomite indicates that primary dolomite does exist in nature， and is therefore of considerable scientific interest. Experiments have shown that dolomite is formed in the presence of many forms of microorganism. This paper describes the formation mechanism of four kinds of microbial dolomites that have been found in nature and for which abundant data is available. These are： anaerobic sulfate-reducing bacteria dolomite； methane-oxidizing bacteria dolomite； anaerobic methane-forming （methanogenic） bacteria dolomite； and aerobic （halophilic） bacteria dolomite. The basic principle and key data for each mechanism are described in detail， to enable readers to grasp the core content and information without the need to refer to the original text. In particular， the identification markers of all microbial dolomite types are summarized， and some problems posed by their formation mechanism are pointed out.
2022, 40(2): 360-379.
doi: 10.14027/j.issn.1000-0550.2021.011
Abstract:
Dating sedimentary rocks and reconstructing the diagenetic process continue to be urgent scientific problems in the field of chronology. This study introduces traditional long-lived radioisotope systems suitable for sedimentary rocks and systematically reviews the key problems of dating glauconite， illite， K-feldspar and calcite which widely occur in sedimentary rocks. This is accompanied by a discussion of the applicability of these authigenic minerals for dating sediments， recovering heat flow events， indirectly dating ore deposits， reconstructing the history of hydrocarbon injection， dating fault activity and determining remagnetization events. The study predicts the development direction of isotopic chronology of sedimentary rocks， in the promotion of sedimentary chronological development in our country.
2022, 40(2): 380-395.
doi: 10.14027/j.issn.1000-0550.2020.129
Abstract:
Time series analysis has been widely employed in the study of Milankovitch cycles in recent years. It uses mathematical transformation to quantitatively analyze the stratigraphic data series， so as to identify the astronomically forcing cycle signals in geological records， which can provide an important basis for time calibration， stratigraphic division， paleoclimate research， etc. According to the main steps of the time series analysis method in the study of Milankovitch cycles， the basic principles of the existing methods were expounded upon from three aspects of the data types of stratigraphic sequence， astronomical testing， and astronomical tuning， and their advantages and limitations were summarized. In the study of Milankovitch cycles based on time series analysis， responses of different stratigraphic sequences to astronomical forcing and non-astronomical noise are different. The comprehensive utilization of geological information contained in various data proxies can help reduce the uncertainty in cyclostratigraphic analysis； various newly emerged approaches for astronomical testing and tuning have greatly promoted the quantitative development of Milankovitch cycle analysis， but further verification and improvement of these new methods are still of great concern. In the future work， quantitative evaluation of different stratigraphic data series and the information optimization of multiple data types are still worthy of in-depth study； more attention could be paid to the effective integration of existing time series analysis methods， as well as the introduction of novel methods and ideas.
2022, 40(2): 396-409.
doi: 10.14027/j.issn.1000-0550.2021.031
Abstract:
Conodonts are phosphatic fossils widely distributed in Cambrian to Triassic marine strata. Due to the advantage of well preservation， the oxygen isotope values of conodont apatite have been used to constrain coeval seawater temperature. In this context， we make a review of the development of oxygen isotope palaeothermometry， including the aspects of biological features， geochemical fundamentals， and oxygen isotope measuring methods of conodont apatite. We further summarize the three main factors that are critical for a quantitatively accurate reconstruction of the paleotemperature in deep time， including the life habit of conodont animals， diagenetic alteration of oxygen isotopes， and empirical formulas for paleotemperature value calculation based on phosphate oxygen isotopes. Presently， oxygen isotope palaeothermometry of conodont apatite has been widely and successfully applied in reconstructions of the paleo-oceanic temperature， living habit of conodont animals， and paleogeographic configurations， which have significantly enhanced our understanding of deep-time paleoenvironmental and life evolution. In the future， the development and application of this paleothermometer would be favored for more deep studies on the oxygen isotope fractionation mechanism between conodont and coeval seawater， the ecology of key conodont animal species， evaluation of diagenetic alteration， and full consideration of the paleogeographic background. Undoubtedly， oxygen isotope palaeothermometry of conodont apatite will play an indispensable role in paleo-oceanic， paleo-environmental， and paleontological studies.
2022, 40(2): 410-421.
doi: 10.14027/j.issn.1000-0550.2020.124
Abstract:
Based on the sandstone physical property test data of 10 wells in the western Yuanba area， northeastern Sichuan， this paper analyzes the characteristics and physical control factors of tight sandstone reservoirs by means of casting thin sections， scanning electron microscopy， cathodoluminescence， X-ray diffraction analysis， and mercury intrusion testing. The study shows that the sandstone of the Xu-2 Member in the western Yuanba area is a low-porosity and low-permeability reservoir with a porosity of 0.99%⁃10.53% and a permeability of 0.003 6 ×10-3 μm2 - 1.41 ×10-3 μm2. The porosity-permeability relationship is characterized by “stratification”. According to the porosity-permeability relationship， three types of reservoirs can be classified： low-porosity and infiltration reservoirs， low-porosity and low-permeability reservoirs， and ultra-low-porosity and low-permeability reservoirs. The physical properties for the different types of sandstone reservoirs are controlled by sedimentary conditions and diagenesis. The sedimentary conditions determine the petrological characteristics of the sandstone， which in turn has an important impact on diagenesis. The heterogeneity of diagenesis ultimately determines the difference in the reservoir physical properties. Different types of reservoir sandstones show strong diagenetic heterogeneity in the vertical direction and the diagenetic combination sequence of the developed lithic dissolution section （chlorite film cementation section） - silica cementation section - calcite cementation section. The best reservoir quality is mainly distributed in the middle-grained lithic sandstone in the middle of the sand body where the strong dissolution is developed. The results of this study can better predict the deep tight sandstone desserts and guide the deep tight sandstone gas exploration in the Sichuan Basin.
2022, 40(2): 422-434.
doi: 10.14027/j.issn.1000-0550.2021.027
Abstract:
Tight sandstones are well developed in the Upper Paleozoic in the Ordos Basin. Burial diagenesis in the reservoirs of the Hangjinqi area and Daniudi gas field are quite different. Their comparative study is helpful in understanding the formation process of the reservoir in tight sandstone. Their diagenesis and pore development characteristics are revealed by the observation of casting thin sections and scanning electronic microscopy. The study shows they are in Stage A1 and B of Middle Diagenesis as a result of different burial depths， fracturing， and later uplift. Kaolinite cementation developed extensively in the reservoir of the Hangjinqi area where in the north of the Boerjianghaizi Fault， and the feldspar content is 10%. Within the feldspar， dissolution， moldic， and intergranular dissolution pores are the dominant types. With the connection of tension fissure， reservoir porosity is quite high， and its forming mechanism is “feldspar dissolution to improve porosity and tension fissure connection in the uplift area”. The reservoir of the Hangjinqi area north of the Boerjianghaizi Fault is similar to the Daniudi gas field. The reservoir in the Daniudi gas field is characterized by deep burial， a high degree of diagenetic evolution， and complete dissolution of feldspar. Reservoir porosity is low and rock fragment dissolution pores and micropores are dominant. Its forming mechanism is “rock fragment dissolution to improve porosity in the slope area”.
2022, 40(2): 435-449.
doi: 10.14027/j.issn.1000-0550.2021.144
Abstract:
A submarine fan is a body of sediment on the sea floor deposited by sedimentary gravity flows. Taxonomy and facies models indicate that submarine fans mainly comprise submarine channel， overbank and lobe depositional elements. However， previous case studies on ancient and modern submarine fans show that they cannot be interpreted by one single facies model. Facies models based on different grain sizes contain a wide range of information， and are relatively straightforward and applicable. The triggering mechanisms of submarine fans include seafloor sediment failures， flood-related hyperpycnal flows， dynamic oceanographic processes， and several combinations of these. The predominant types of gravity flow （debris flow and turbidite flow）， submarine geomorphology （confined and unconfined） and oceanographic condition （e.g.， bottom current） strongly control sedimentary processes， planar geometry and spatial association. Briefly， these may be subdivided into three categories. （i） Turbidite-dominated submarine fans have a fan- or finger shape in unconfined submarine settings. These shapes are then largely modified by confined basin geomorphology. （ii） Debrites-dominated submarine fans are tongue-shaped and fringe-shaped due to freezing en masse. （iii） Hybrid （turbidite-contourite） submarine fans may be deflected laterally by bottom currents， with parts sometimes being reworked into isolated drift mounds. Submarine fan sediments record both source-to-sink propagation and degree of preservation， which are useful indicators of tectonic deformation and paleoclimate change. Modern submarine fans in the Anthropocene have also been found to be the major repository of microplastics and terrestrial organic carbon in deep-sea settings. Quantification of their content sheds a strong light on environmental evaluation， contamination treatment and management， as well as the global carbon cycle.
2022, 40(2): 450-464.
doi: 10.14027/j.issn.1000-0550.2021.035
Abstract:
Many siliceous rocks are located at key stratigraphic intervals and can provide critical information regarding the formation of sedimentary basins， tectonic orogens， and climatic settings. Previous studies have mainly focused on the siliceous rocks that developed within marine strata in China. However， in continental strata of China， siliceous rocks also have a wide distribution. Affected by the rich experience in studying marine siliceous rocks， most previous work of continental siliceous rocks was mainly based on geochemical analysis and has attributed continental siliceous rocks to biological and hydrothermal origins. Since the occurrences of continental siliceous rocks and their host rocks are much different from those hosted in marine deposits， the application of marine chert formation models to continental siliceous rocks will lead to the bias of some important conclusions on climate， tectonics， and environments.We review the genesis of continental siliceous rocks， and three types of continental siliceous rocks are introduced： penecontemporaneous cherts， burial diagenetic cherts， and meteoric diagenetic silcretes. Based on silica precursors and formation settings， three penecontemporaneous cherts are identified： Magadi-type cherts， Coorong-type cherts， and Bogoria-type cherts. Magadi-type cherts are commonly associated with saline， alkaline lakes and may be bedded lake-wide or localized in nodular deposits， forming from a sodium silicate precursor such as magadiite （NaSi7Oi3［OH］3•3H2O）. Coorong-type cherts are deposited by direct Opal-crystobalite precipitation due to seasonal water pH variation and are also associated with saline， alkaline lakes. Bogoria-type cherts form from a siliceous， probably gelatinous precursor that precipitated around submerged hot springs during high lake level. Burial diagenetic cherts are formed during burial by replacing other minerals， mostly carbonates. Most of the silicification processes encountered in continental carbonates are interpreted as having occurred during the early burial diagenesis of lacustrine or palustrine sediments. Meteoric diagenetic silcretes or siliceous duricrusts are defined as the indurated products of surficial and penesurficial silica accumulation and are formed by cementation and/or low-temperature replacements of all types of rocks and sediments. Silcretes are further divided into pedogenic and groundwater silcretes.When studying continental silica rocks， petrological and mineralogical analysis are the first and foremost means for determining type. Bedded （>1 mm） and laminated （<1 mm） cherts are mostly formed during penecontemporaneous periods and are transformed from hydrous precursors， but the possibility of the total replacement of bedded carbonated by silica cannot be excluded. Slumping， soft-sediment deformation， V-shaped shrinkage， and brecciation can further verify penecontemporaneous cherts. Characteristics of Magadi-type cherts that differ from Coorong-type cherts are （1） a groundmass mosaic of fine quartz crystals that vary in orientation from random to rectilinear； （2） finely disseminated inclusions of silicate clays， zeolites， and/or carbonates （predominantly calcite）； （3） large crystal molds （probably after trona） concentrated near sample margins； and （4） inward-directed shrinkage cracks and/or more irregular internal voids filled with chalcedony， silicate clays， zeolites， and/or carbonates （predominantly calcite）. Nodular cherts are mainly diagenetic products. Based on the mold shapes and mineral remains in cherts， the replacement precursors of silica can be identified and the paragenesis between silica and other minerals can be rebuilt. Cauliflower cherts are generally lacustrine silcretes. Pedogenetic and groundwater silcretes mainly appear in the form of cements， filling voids and replacing the matrix between skeleton particles.The origins of continental cherts are quite varied. If water pH increases higher than 9， many materials in lakes can release dissolved silica into the water， like detrital quartz， silicates， and tuff materials. A pH of 9 is a key point for silica precipitation， above which silica solubility can increase exponentially. Temperature variation is not an important condition for increasing silica concentrations in continental settings， as water temperatures are generally lower than 100 ℃ in continental settings and not sufficient to greatly enhance silica solubility. In this regard， continental cherts are mainly associated with evaporative alkaline waters. Evaporation and pH variations are the main drivers inducing the dissolution， precipitation， and replacement of silica in continental conditions. In most cases， continental silica rocks can be regarded as a special evaporite.
2022, 40(2): 465-472.
doi: 10.14027/j.issn.1000-0550.2021.043
Abstract:
Unconsolidated sand bodies are prone to liquefaction due to external forces， forming sedimentary structures such as sand volcanoes and liquefied sandstone veins. Earthquakes are the most common triggers of liquefaction. A large number of sand volcanic structures were discovered in modern river bed sediments. Although their generation is affected by human activities， their formation conditions occur in particular structural parts of sedimentary basins. Analysis of their characteristics， evolution and dynamics provides references for the study of seismites and soft-sediment deformation in other types of formation. This study found sand volcanoes of different scale and characteristics at different evolutionary stages. Small-scale sand volcanoes have a small crater and no overflow channel， and turbid water is ejected from the crater during the growth stage. The presence of clear water and the generation of overflow channels in a sand volcano indicate that it has entered its extinction stage. The volume of a sand volcano gradually increases after it is produced， the outflow water becomes clear and overflow channels are generated. This increases its size， and re-deposition then takes place after reworking. It is suggested that sand volcanic structures are formed when earthquake or fault activity produces sufficient pressure difference between the parent base rock and the surface to fracture weak zones in the overlying strata. Sand volcanoes formed by low pressure differences may be more universal.
2022, 40(2): 473-483.
doi: 10.14027/j.issn.1000-0550.2020.103
Abstract:
The Triassic-Jurassic transition （~201 Ma） was a critical period in the Earth’s history. The rapid emplacement and eruption of the Central Atlantic Magmatic Province （CAMP） put huge environmental pressure on the global surface ecosystem. One example was the synchronous wildfire events reported widely. However， previous reports have commonly focused on the area directly influenced by the CAMP. It is debatable whether the wildfire events were a global or a regional phenomenon. This study systematically collected samples across the Triassic⁃Jurassic boundary （TJB） in the Haojiagou section at the southern margin of the Junggar Basin， Xinjiang. Abnormally high values of combustive-derived polycyclic aromatic hydrocarbons （PAHs） were found around the TJB. The anomalies correspond well with the Hg/TOC peaks， indicating the CAMP emplacement or eruptions. This is the first report on wildfire records across the Triassic⁃Jurassic transition in high-latitude terrestrial strata outside the CAMP region. It is concluded from integrated global TJB correlations that the sharply rising wildfire frequency was triggered by the CAMP effect， but CAMP volcanism itself was not the direct igniting source. Increased wildfire frequency is inferred as a global event beyond the regions of CAMP activity， and similar wildfire records across the TJB could be observed on a global scale.
2022, 40(2): 484-493.
doi: 10.14027/j.issn.1000-0550.2021.033
Abstract:
Affected by the tropical monsoon climate and the land inputs， the Gulf of Thailand （GOT） is characterized by extensive land-ocean interaction， making it an ideal region for studying the relationship between organic carbon burial in sediments and the land-based input， marine primary productivity， and variation of the marine environment. Based on the highly resolution chronology constrained by the excess of lead isotopes （210Pb， 210Pbex）， the geochemical characteristics of organic carbon and its burial records during the past century were reconstructed by analyzing the total organic carbon （TOC）， total nitrogen （TN）， stable carbon isotope （δ13C）， and sediment grain size of core sediments （T43） in the GOT. The results showed that the sedimentary organic matter originated from mixed terrestrial and marine origins and mainly from marine organic matter （OM） contributions. TOC showed a coupled variation with that of TN and δ13C， indicating a consistency of provenance towards organic carbon and nitrogen. Both C/N and δ13C showed that the OM at the lower sections was mainly derived from marine primary productivity， followed by a gradual increase in terrestrial OM. The mass accumulation rate and the burial flux of TOC in the core showed a general decrease after the 1960s， which may be related to the decline of sediment transport caused by the dam construction in the drainage basin. However， since the 1980s， δ13C has shown an obvious depletion with increased terrestrial OM， which may be related to the enhanced heavy rainfall and coastal erosion associated with tropical cyclones over the last 30 years.
2022, 40(2): 494-507.
doi: 10.14027/j.issn.1000-0550.2020.099
Abstract:
Aggradated red earth is a typical eolian deposit in the mid-subtropical zone， where it is characterized by simultaneous deposition and weathering. The complete stratigraphy includes four soil units （upwards from the base）： a reticular gravel unit， a reticular red soil unit， a homogeneous red soil unit and a yellowish-brown soil unit. Previous studies have shown that the degree of reddening and reticulation has clearly been weakened since 0.4 Ma， when the climate tended to be dry and cool. There are still some disputes on provenance， such as proximal source， distal source and mixed source. To determine it， we analyzed 22 heavy mineral samples and two detrital zircon U-Pb age spectra of the yellowish-brown soil deposit in the JL section （29° 42′ N， 116° 02′ E） at the northern piedmont of Lushan Mountain， which is 1 846 cm thick. Moreover， chronological studies of this section by others indicate that the slightly reticular yellowish-brown soil and yellowish-brown soil was formed in the middle and late Pleistocene since 0.44 Ma. The following conclusions are drawn： （1） There are 19 kinds of heavy minerals in the yellowish-brown soil and reticular yellowish-brown soil， predominantly opaque minerals （more than 50%）. Common minerals include zircon， rutile， anatase， tourmaline， epidote， pyroxene， etc. （2） The content of extremely stable and stable minerals， and the values of ZTR （zircon-tourmaline-rutile） reflecting mineral maturity and GZi （garnet：zircon index） of these soils are respectively 52.49% and 52.88%， 32.22% and 41.49%， 47.53 and 72.73， 0.10 and 0.06， which are significantly different from the northern loess values （17.77%， 19.21%， 8.42， 0.47）. However， they are more closely similar to the values for eolian sand samples along the Yangtze River （55.93%， 20.15%， 43.65， 0.02 ）. These results show that the PI values of the yellowish-brown and reticular yellowish-brown soils are 0.73 and 0.70 respectively， which are inclined to a Yangtze River source. The similarity index （cosθ） of these two types of soil and the eolian sand samples along the Yangtze River （0.76 and 0.74） also support the conclusion of a Yangtze River source. （3） The analysis of detrital zircon U-Pb geochronology showed numerous and widely distributed age peaks for typical samples. The age peaks of 70⁃130， 200⁃300， 390⁃570， 680⁃870 and 870⁃3 013 Ma are consistent with the age peaks of Yangtze River sediments， while those of <65 Ma and 150⁃200 Ma in the yellowish-brown soil samples are related to the Qinling orogenic belt， but the contribution is not significant. Proximal sources are predominant in the aggradated red earth in the JL profile since 0.44 Ma， and the dust has mainly come from the exposed floodplain of the Yangtze valley. （4） There is not complete consistency with the geochemical source tracing results of particle size stable elements in the JL profile （supporting the mixed-source conclusion）， which may indicate that the provenance of the red earth aggradation was affected by grain size. The grain size of the heavy minerals and detrital zircons is usually more than 20 μm， and the contribution from the north loess is enriched in the 4⁃20 μm components.
2022, 40(2): 508-524.
doi: 10.14027/j.issn.1000-0550.2020.091
Abstract:
Measurement of magnetic susceptibility anisotropy and paleomagnetic analysis of the core C-P19 in the Parece Vela Basin of the western Pacific Ocean established the age framework of the magnetostratigraphy. Grain size and clay minerals analysis determined provenance and paleoclimate. The paleomagnetic results show that the sedimentary sequence has a lower limit age younger than 1.072 Ma， which includes the deposition since the early Pleistocene. The sedimentation process was divided into two stages： one with a sedimentation rate of 4.0 mm/kyr during ca. 1⁃0.78 Ma， and the other at 3.6 mm/kyr since 0.78 Ma. The grain size and clay mineral analyses showed that the predominant sediment types in the study area are silty and sandy silt， with a small clayey silt component. The average content of illite + chlorite in the clay mineral composition is as high as 70%. A principal component analysis of the granularity parameters by SPSS software indicates that the source of coarse-grained material in the study area is mainly volcanic island arc clastic material in and around the Parece Vela Basin， and the fine-grained component is mainly from Asian dust. The percentage content of the 2⁃4 μm grain size component and the ratio of （illite + chlorite + kaolinite） / smectite corresponds closely with fluctuations in the contribution of Asian dust in the study area. These were used as an alternative indicator to reveal both the dryness or wetness of the paleoclimate in the source area and the evolution process of East Asian winter monsoon intensity since 1 Ma.
2022, 40(2): 525-533.
doi: 10.14027/j.issn.1000-0550.2020.083
Abstract:
The sedimentary record of organic carbon from the East China Sea inner shelf was explored by determining the lignin in core T06. The transport mechanism of organic matter in different historical environments along the Zhejiang⁃Fujian coast was also investigated for the period since 8.8 ka B.P. by the indicator function of lignin on the paleoenvironment and paleoclimate. The results revealed that hydrodynamic transport driven by the East Asian winter monsoon in the East China Sea inner shelf played an important role in the variation of the content and its related parameters of lignin phenols in the sediments. Vise verse， the lignin content and its related parameters in the mud areas along the Zhejiang⁃Fujian coast indicate the influence of variation in the East Asian winter monsoon in the study area to some extent. Therefore， these are reliable indicators for reconstructing East Asian winter monsoonal climate change. The current study also revealed a “50 years” period during which dramatic data fluctuations were observed. The period might have been due to climate change and continuous flooding in the Yangtze River Basin. This led to the transport of a large amount of non-woody angiosperm residue and surface soil to the study area， which were finally deposited and buried in the sediment core， via hydrodynamic transport and ocean currents.
2022, 40(2): 534-546.
doi: 10.14027/j.issn.1000-0550.2020.076
Abstract:
The sedimentary strata of Chang-8 section in Huanxi-Pengyang south section of Ordos Basin are dominated by braided river delta plain and their reservoir quality is obviously controlled by sedimentary microfacies. Based on core observation， slice observation， mercury injection and conventional logging data analysis， the chang-8 section in the study area was divided into 5 small layers， and the sedimentary reservoir characteristics of the braided river delta plain were studied in detail. The results show that there are three microfacies in the study area： distributary channel， overbank deposit and interdistributary bay. Distributary channel constitutes the main sand body framework， which is distributed from south west to north east. The distributary channel sand body has the best physical property， the overbank deposit property is second， and the interdistributary bay has the worst physical property. Correspondingly， the reservoirs in the study area can be divided into four types： I， II， III and IV. The type I with the best reservoir quality is mainly located in the middle of the channel， while the type IV with the worst reservoir quality corresponds to the interdistributary bay. The oil test data also further confirmed the difference of reservoir quality in the study area of sedimentary microfacies control. Plane distribution based on sedimentary microfacies can be used to predict the plane distribution of reservoir. The research results can lay a foundation for the follow-up fine evaluation of sedimentary reservoirs and even the comprehensive study of oil and gas exploration and development.
2022, 40(2): 547-556.
doi: 10.14027/j.issn.1000-0550.2021.145
Abstract:
Molecular markers play an increasingly important role in the study of early life evolution and paleoenvironment of the Precambrian ocean. Typical molecular markers have been detected in the black shale of the Mesoproterozoic Xiamaling Formation in the Xuanlong Depression， the North China Craton， which are characterized by a notably higher base level of the unresolved complex mixture， high abundances of methyl branched alkanes， C24 tetracyclic terpane， C19-C2013β（H），14α（H）-tricyclic terpanes， 13α（n-alkyl）-tricyclic terpanes and four types of rearranged hopanes， and the absence of steroids. Their distribution characteristics and geological significance are different from the Phanerozoic sediments. Because the lack of steroids may be the result of heterotrophic microbial transformation and degradation， we cannot exclude that eukaryotic algae may have flourished locally in the paleo-ocean 1.4 billion years ago， but the primary biological community is still dominated by prokaryotes.
2022, 40(2): 557-572.
doi: 10.14027/j.issn.1000-0550.2020.136
Abstract:
In recent years， a significant amount of oil and gas reservoirs have been discovered in the Hari sag of the Yingen-Ejinaqi Basin， which proves that the area is a good prospect for oil and gas exploration. However， due to the complex geological conditions， in particular， the lack of understanding of the symbiotic characteristics and hydrocarbon accumulation mechanism of multi-type reservoirs， the scientific prediction of oil and gas distribution is severely limited， which restricts the process of oil and gas exploration in this area. Based on the analysis of various types of oil and gas reservoirs， this paper discusses the symbiotic characteristics and accumulation mechanism of multi-type oil and gas reservoirs， predicts the distribution of oil and gas， and analyzes the exploration direction， providing the basis for exploration decision-making and deployment in the study area. The study shows that there are many types of oil and gas reservoirs， such as dolomitic mudstone biogas reservoir， limestone mudstone gas reservoir， limestone mudstone oil reservoir， sandstone oil reservoir， and volcanic rock gas reservoir， for which the K1y， K1b2， and K1b1 source rocks are the main source rocks， and their oil and gas accumulation has “near source and within source” characteristics. The reservoirs are characterized by the coexistence of oil and gas reservoirs， conventional and unconventional reservoirs， and structural and lithologic reservoirs. The study of the oil and gas accumulation mechanism shows that the lack of an effective migration pathway is the main reason for “near source accumulation and in source accumulation”， the difference of thermal evolution degree of the main source rocks in different structural positions makes the oil and gas exhibit the distribution characteristic of “up oil and down gas”， and the development of a multi-type effective reservoir leads to the situation of “multi-type oil and gas reservoir symbiosis”. We predict that the cumulative oil and gas bearing area of various reservoirs in the study area is 381 km2. The calcareous mudstone gas reservoir， as the actual field of discovered reserves， is the main direction for future exploration， the sandstone reservoir is a potential field of expanding exploration results， making it the secondary direction， and the volcanic gas and calcareous mudstone oil reservoirs， as a beneficial supplement to the joint exploration of multiple types of oil and gas reservoirs， are the third potential direction.
