2018 Vol. 36, No. 6
Display Method:
2018, 36(6): 1059-1074.
doi: 10.14027/j.issn.1000-0550.2018.091
Abstract:
A series of branches of stratigraphy have formed since 1970's along with the development of multiple stratigraphic classification theory and the application of various testing methods and means, These stratigraphy branches have greatly extended their research fields, and made stratigraphic theories developed towards multi-laterals, multi-levels and multi-scales directions. However, the specific and simple research object has also made stratigraphy fragmented and narrowly-defined. Therefore, it is necessary to review the stratigraphic history and consider the different stratigraphic units based on independent characteristics and attributes as a whole. In this paper, from the philosophy of time and space, the incompleteness, cyclicity, punctuated equilibrium and irreversibility of stratigraphic records are systematically summarized and combed. It is found that although lithologic, biologic, physical and chemical changes are not strictly unified into temporal variations, the strata are distributed orderly and regularly in time and space. From the Steno's Laws stating that rocks laid down in vertical order with younger strata on the top of the older one to the Walther's Phase Law suggesting that the contiguous relation in space can be transformed into the chronological sequence in time, the stratigraphy not only expresses the concept of space by using concepts of top and bottom, left and right, but also reveals its time attribution. The unconformity, once supposed to be a tectonic-induced concept from the beginning, which represented its spatial incongruity caused by folds or orogeny, is now defined with the help of time attribute i.e. the prolonged absence of stratigraphic records. Similarly, the stratigraphic cycle, a term previously describing the repetition of strata, after the confirmation of the Quaternary Milankovitch cycle is redefined as the transgressive and regressive sequences bounded by unconformities in the stratagraphic record. The discovery and restoration of the spatial and temporal order in the complex stratigraphic record is therefore becoming the driving force in promoting the development and integration of all stratigraphy branches.
A series of branches of stratigraphy have formed since 1970's along with the development of multiple stratigraphic classification theory and the application of various testing methods and means, These stratigraphy branches have greatly extended their research fields, and made stratigraphic theories developed towards multi-laterals, multi-levels and multi-scales directions. However, the specific and simple research object has also made stratigraphy fragmented and narrowly-defined. Therefore, it is necessary to review the stratigraphic history and consider the different stratigraphic units based on independent characteristics and attributes as a whole. In this paper, from the philosophy of time and space, the incompleteness, cyclicity, punctuated equilibrium and irreversibility of stratigraphic records are systematically summarized and combed. It is found that although lithologic, biologic, physical and chemical changes are not strictly unified into temporal variations, the strata are distributed orderly and regularly in time and space. From the Steno's Laws stating that rocks laid down in vertical order with younger strata on the top of the older one to the Walther's Phase Law suggesting that the contiguous relation in space can be transformed into the chronological sequence in time, the stratigraphy not only expresses the concept of space by using concepts of top and bottom, left and right, but also reveals its time attribution. The unconformity, once supposed to be a tectonic-induced concept from the beginning, which represented its spatial incongruity caused by folds or orogeny, is now defined with the help of time attribute i.e. the prolonged absence of stratigraphic records. Similarly, the stratigraphic cycle, a term previously describing the repetition of strata, after the confirmation of the Quaternary Milankovitch cycle is redefined as the transgressive and regressive sequences bounded by unconformities in the stratagraphic record. The discovery and restoration of the spatial and temporal order in the complex stratigraphic record is therefore becoming the driving force in promoting the development and integration of all stratigraphy branches.
2018, 36(6): 1075-1090.
doi: 10.14027/j.issn.1000-0550.2018.089
Abstract:
Depositional processes in deep-water slopes have been an important research focus for marine geologists because they have significant implications for deep-water hydrocarbon exploration and deep-water geological hazard prevention. Due to multiple sedimentary types and lots of controlling factors, the sedimentary processes on the deep-water slope and these productions are very complex. Therefore, it is necessary to summarize and organize research advances of deep-water slope sedimentology to help more comprehensively and systematically study deep-water slope sedimentation. Based on sedimentary settings, this paper divides the slopes into three types:continental-shelf slope, carbonate slope, and volcanic slope. The sedimentology of different types of deep-water slopes were overviewed systematically. We expect it to have implications for the study of deep-water slope sedimentation and help improve deep-water hydrocarbon exploration in the South China Sea.
Depositional processes in deep-water slopes have been an important research focus for marine geologists because they have significant implications for deep-water hydrocarbon exploration and deep-water geological hazard prevention. Due to multiple sedimentary types and lots of controlling factors, the sedimentary processes on the deep-water slope and these productions are very complex. Therefore, it is necessary to summarize and organize research advances of deep-water slope sedimentology to help more comprehensively and systematically study deep-water slope sedimentation. Based on sedimentary settings, this paper divides the slopes into three types:continental-shelf slope, carbonate slope, and volcanic slope. The sedimentology of different types of deep-water slopes were overviewed systematically. We expect it to have implications for the study of deep-water slope sedimentation and help improve deep-water hydrocarbon exploration in the South China Sea.
2018, 36(6): 1091-1104.
doi: 10.14027/j.issn.1000-0550.2018.097
Abstract:
The correlation between compaction degree and porosity derived from the theoretical model of sedimentary compaction and the variation of soil volume, pore ratio and porosity of soil units before and after compression shows that the variation of the porosity of overlying sediments depends on the initial sedimentary porosity when compaction degree of underlying sediments does not change during sedimentation. The change of sedimentary environment results in the change of initial sedimentary porosity, which is not related to buried depth, and the underlying sediment porosity is greater than that of the overlying deposits. This is the performance of the underlying-sediment pore water which cannot be discharged and the sediments are under-compacted. When the porosity of the lower part of the soil column is greater than that of the upper part of the soil column, the lower part of the soil column must be under-compacted without any external disturbance besides sedimentation, which is an important sign to identify the under-compacted littoral facies sediments after the overlying sediments is formed. Comparing the porosity and distribution depth of the same named soil in 58 boreholes and 191 soil samples from 8 engineering sites along the coast of Guangdong Province and 208 soil samples from different sites in Guangdong and other related areas in China, the analysis shows that the littoral deposits within about 40 m or sediments since the middle and late Pleistocene are under-compacted vertically and laterally. This kind of under-compaction is ubiquitous in horizontal distribution. Therefore, we proposed that sedimentary compaction generally has three stages in sequence:1) the initial sedimentary compaction stage of the thin layer in the most surface layer under the influence of initial sedimentary porosity; 2) under-compaction stage; 3) re-compaction stage. The results show that the littoral deposits generally have poor permeability and drainage environment. Apart from the local sediments which are re-compacted due to deposition process, the compaction subsidence of littoral deposits within 40 m near the surface or since the middle and Late Pleistocene is not obvious. Therefore, when you conduct the study on Paleo-Sea level and coastal crustal movement in littoral deposits, it is not necessary to take into account the impact of sediment compaction.
The correlation between compaction degree and porosity derived from the theoretical model of sedimentary compaction and the variation of soil volume, pore ratio and porosity of soil units before and after compression shows that the variation of the porosity of overlying sediments depends on the initial sedimentary porosity when compaction degree of underlying sediments does not change during sedimentation. The change of sedimentary environment results in the change of initial sedimentary porosity, which is not related to buried depth, and the underlying sediment porosity is greater than that of the overlying deposits. This is the performance of the underlying-sediment pore water which cannot be discharged and the sediments are under-compacted. When the porosity of the lower part of the soil column is greater than that of the upper part of the soil column, the lower part of the soil column must be under-compacted without any external disturbance besides sedimentation, which is an important sign to identify the under-compacted littoral facies sediments after the overlying sediments is formed. Comparing the porosity and distribution depth of the same named soil in 58 boreholes and 191 soil samples from 8 engineering sites along the coast of Guangdong Province and 208 soil samples from different sites in Guangdong and other related areas in China, the analysis shows that the littoral deposits within about 40 m or sediments since the middle and late Pleistocene are under-compacted vertically and laterally. This kind of under-compaction is ubiquitous in horizontal distribution. Therefore, we proposed that sedimentary compaction generally has three stages in sequence:1) the initial sedimentary compaction stage of the thin layer in the most surface layer under the influence of initial sedimentary porosity; 2) under-compaction stage; 3) re-compaction stage. The results show that the littoral deposits generally have poor permeability and drainage environment. Apart from the local sediments which are re-compacted due to deposition process, the compaction subsidence of littoral deposits within 40 m near the surface or since the middle and Late Pleistocene is not obvious. Therefore, when you conduct the study on Paleo-Sea level and coastal crustal movement in littoral deposits, it is not necessary to take into account the impact of sediment compaction.
2018, 36(6): 1105-1118.
doi: 10.14027/j.issn.1000-0550.2018.085
Abstract:
Soft-sediment deformation structures (SSDS) are a series of structures formed due to transformation of plastic sediment under liquidization and various driving forces after deposition but before lithification. SSDS are often developed in the strata with different scales, shapes, periods and origins. No doubt that earthquake is one of the most common causes of deformation of soft sediments, however, it is not limited only to earthquakes. SSDS are not a diagnosis of any specific trigger mechanism. According to the classification scheme of induced events, it is much more applicable in the same event, but it is difficult to distinguish the real cause in "multi causes and even the same phenomenon" of deformation. Therefore, the classification based on origin is often limited. In fact, the driving forces are the most direct factors causing the deformation of soft sediments and directly control specific forms of deforming structures. In order to clarify their specific types and development, this study advocates the classification of SSDS according to different driving forces. Based on literature and field outcrop investigation, the Early Cretaceous gravity flows deposit in the Lingshan Island are developed very well with SSDS in multi scales, forms, layers, periods and genesises, which can be classified into three types:the SSDS driven by gravity acting on slopes; the SSDS driven by gravity due to a reverse density gradient; and the SSDS driven by upward shear due to pore fluid. In addition, considering the SSDS development in the interior of the lower Cretaceous slump in the Lingshan island, according to the types of stresses when the deformation structures were formed, SSDS driven by gravity acting on slopes are further divided into three subtypes:compression types, tension types and shear types. 3 categories of more than 10 kinds of SSDS are identified in the Lower Cretaceous in Lingshan Island:SSDS driven by gravity acting on slopes including compression types (synsedimentary reverse faults and disordered compression deformation structures etc.), tension types (synsedimentary boudins, step faults and domino structures etc.) and shear types(some folds and fractures caused by shear and soft double structures etc.); SSDS driven by gravity due to a reverse density gradient including load structures, flame structures and ball-and-pillow structures etc.; SSDS driven by upward shear due to pore fluid including liquefied diaper, water-escape structures, convolute lamination and sandstone dykes etc. According to the types, development and distributions of SSDS, Early Cretaceous seismic activity was very frequent in Lingshan Island. The driving forces directly act on the soft sediment. And their types, strength, modes of action and duration affect the types, shapes and scales of the SSDS. Classification of soft-sediment deformation structures based on driving forces of Lower Cretaceous in Lingshan Island can distinguish SSDS in the slump beds from the normal sedimentary layer, and can distinguish SSDS formed during the slump process from the earthquake process. This classification can clarifies the dynamic mechanism of the deformation of soft sediment. Hence it is scientific, applicative and feasible to divide SSDS based on the driving forces. Discussion on classification of SSDS is benefit to facilitate its field identification and genesis analysis, and to provide a theoretical basis for other similar geological researches.
Soft-sediment deformation structures (SSDS) are a series of structures formed due to transformation of plastic sediment under liquidization and various driving forces after deposition but before lithification. SSDS are often developed in the strata with different scales, shapes, periods and origins. No doubt that earthquake is one of the most common causes of deformation of soft sediments, however, it is not limited only to earthquakes. SSDS are not a diagnosis of any specific trigger mechanism. According to the classification scheme of induced events, it is much more applicable in the same event, but it is difficult to distinguish the real cause in "multi causes and even the same phenomenon" of deformation. Therefore, the classification based on origin is often limited. In fact, the driving forces are the most direct factors causing the deformation of soft sediments and directly control specific forms of deforming structures. In order to clarify their specific types and development, this study advocates the classification of SSDS according to different driving forces. Based on literature and field outcrop investigation, the Early Cretaceous gravity flows deposit in the Lingshan Island are developed very well with SSDS in multi scales, forms, layers, periods and genesises, which can be classified into three types:the SSDS driven by gravity acting on slopes; the SSDS driven by gravity due to a reverse density gradient; and the SSDS driven by upward shear due to pore fluid. In addition, considering the SSDS development in the interior of the lower Cretaceous slump in the Lingshan island, according to the types of stresses when the deformation structures were formed, SSDS driven by gravity acting on slopes are further divided into three subtypes:compression types, tension types and shear types. 3 categories of more than 10 kinds of SSDS are identified in the Lower Cretaceous in Lingshan Island:SSDS driven by gravity acting on slopes including compression types (synsedimentary reverse faults and disordered compression deformation structures etc.), tension types (synsedimentary boudins, step faults and domino structures etc.) and shear types(some folds and fractures caused by shear and soft double structures etc.); SSDS driven by gravity due to a reverse density gradient including load structures, flame structures and ball-and-pillow structures etc.; SSDS driven by upward shear due to pore fluid including liquefied diaper, water-escape structures, convolute lamination and sandstone dykes etc. According to the types, development and distributions of SSDS, Early Cretaceous seismic activity was very frequent in Lingshan Island. The driving forces directly act on the soft sediment. And their types, strength, modes of action and duration affect the types, shapes and scales of the SSDS. Classification of soft-sediment deformation structures based on driving forces of Lower Cretaceous in Lingshan Island can distinguish SSDS in the slump beds from the normal sedimentary layer, and can distinguish SSDS formed during the slump process from the earthquake process. This classification can clarifies the dynamic mechanism of the deformation of soft sediment. Hence it is scientific, applicative and feasible to divide SSDS based on the driving forces. Discussion on classification of SSDS is benefit to facilitate its field identification and genesis analysis, and to provide a theoretical basis for other similar geological researches.
2018, 36(6): 1119-1130.
doi: 10.14027/j.issn.1000-0550.2018.117
Abstract:
Salt precipitation simulation experiments help enhance our understanding of salt-forming models; however, the premise of using forward modeling is that the experimental model is similar to the sedimentary mechanism of the salt lake prototype. Based on the field geological survey of modern salt lakes, this paper makes an analogy analysis of salt precipitation models and modern salt lakes, in terms of sediment texture, spatial distribution characteristics, and similarity of sedimentation mechanism. The results show that it is mainly the air-brine interface salt and salt formation through evaporation in the smaller depth of the flume; and for the deeper water and large-scale modern salt lake, the two kinds of salt-forming methods are mainly distributed in the shallow waters of the lake basin. The slopes and depressions with larger water depth are mainly brine-lake sediments interfaced with salt precipitation, which reflect the shallow water of the flume cannot reproduce lake basin bottom and sediment distribution characteristics of the ancient salt lake. Modern sediments show that in the closed inland salt lake basin, the rock salt is mainly formed in the lake retreat period-low period, and its depositional thickness gradually increases from the edge of the lake basin to the depression center, i.e. the deposition center of the rock salt and the depression center are consistent. The texture of rock salt is closely related to the sedimentary environment. The rock salt in the edge of the basin mostly coexists with the sandstone, and the grain size is small, while the depression is mainly composed of coarse-grained salt rock, single-layer thickness and is large, often with dark mudstone interbeds. The relationship between the center of the rock salt deposition and the center of the depression is of great theoretical and practical significance for the restoration of paleogeomorphology and sedimentary body of the lake basin.
Salt precipitation simulation experiments help enhance our understanding of salt-forming models; however, the premise of using forward modeling is that the experimental model is similar to the sedimentary mechanism of the salt lake prototype. Based on the field geological survey of modern salt lakes, this paper makes an analogy analysis of salt precipitation models and modern salt lakes, in terms of sediment texture, spatial distribution characteristics, and similarity of sedimentation mechanism. The results show that it is mainly the air-brine interface salt and salt formation through evaporation in the smaller depth of the flume; and for the deeper water and large-scale modern salt lake, the two kinds of salt-forming methods are mainly distributed in the shallow waters of the lake basin. The slopes and depressions with larger water depth are mainly brine-lake sediments interfaced with salt precipitation, which reflect the shallow water of the flume cannot reproduce lake basin bottom and sediment distribution characteristics of the ancient salt lake. Modern sediments show that in the closed inland salt lake basin, the rock salt is mainly formed in the lake retreat period-low period, and its depositional thickness gradually increases from the edge of the lake basin to the depression center, i.e. the deposition center of the rock salt and the depression center are consistent. The texture of rock salt is closely related to the sedimentary environment. The rock salt in the edge of the basin mostly coexists with the sandstone, and the grain size is small, while the depression is mainly composed of coarse-grained salt rock, single-layer thickness and is large, often with dark mudstone interbeds. The relationship between the center of the rock salt deposition and the center of the depression is of great theoretical and practical significance for the restoration of paleogeomorphology and sedimentary body of the lake basin.
2018, 36(6): 1131-1138.
doi: 10.14027/j.issn.1000-0550.2018.111
Abstract:
Holocene calcareous root tubes occur widely across the hinterland of the Alashan Desert and have been used for paleoenvironmental reconstructions. However, a clear and common understanding of their formation mechanism is still lacking, which limits their application to paleoenvironmental reconstructions. In addition, whether calcareous root tubes have any specific environmental significance needs to be investigated further. In this study, 32 calcareous root tube samples from the Alashan Desert were analyzed by scanning electron microscope to observe the calcite crystal mats or calcified filaments that characterize their absolute biogenic origin. Results showed that these structural features existed within all 32 calcareous root tube samples, which indicated that plant roots and rhizosphere microorganisms participated in the formation of the calcareous root tubes. Under a pronounced seasonal soil moisture regime, dissolved bicarbonates precipitate around the roots because of water evaporation in the rhizosphere and then cement loose sediments or sands, resulting in formation of calcareous root tubes. Recrystallization of groundwater could not explain the formation of such tubes. Calcareous root tube formation was found to be affected by soil moisture content and evaporation, which demonstrated that these tubes have explicit environmental significance. Furthermore, paleoenvironmental signals can be obtained from them to reconstruct changes in paleovegetation and paleo-effective moisture. This study could provide new valuable archives of paleoclimatic changes in desert hinterlands and develop research into paleoenvironmental evolution in arid regions.
Holocene calcareous root tubes occur widely across the hinterland of the Alashan Desert and have been used for paleoenvironmental reconstructions. However, a clear and common understanding of their formation mechanism is still lacking, which limits their application to paleoenvironmental reconstructions. In addition, whether calcareous root tubes have any specific environmental significance needs to be investigated further. In this study, 32 calcareous root tube samples from the Alashan Desert were analyzed by scanning electron microscope to observe the calcite crystal mats or calcified filaments that characterize their absolute biogenic origin. Results showed that these structural features existed within all 32 calcareous root tube samples, which indicated that plant roots and rhizosphere microorganisms participated in the formation of the calcareous root tubes. Under a pronounced seasonal soil moisture regime, dissolved bicarbonates precipitate around the roots because of water evaporation in the rhizosphere and then cement loose sediments or sands, resulting in formation of calcareous root tubes. Recrystallization of groundwater could not explain the formation of such tubes. Calcareous root tube formation was found to be affected by soil moisture content and evaporation, which demonstrated that these tubes have explicit environmental significance. Furthermore, paleoenvironmental signals can be obtained from them to reconstruct changes in paleovegetation and paleo-effective moisture. This study could provide new valuable archives of paleoclimatic changes in desert hinterlands and develop research into paleoenvironmental evolution in arid regions.
2018, 36(6): 1139-1147.
doi: 10.14027/j.issn.1000-0550.2018.143
Abstract:
The Last Glacial Maximum (LGM), which was the last and largest glacial period in the history of the Earth's climate, has long been a hot issue in paleoclimate research. The Heinrich2 abrupt event (H2 event) was a typical ice raft debris event formed in the LGM, which occurred about 25-24 kyr B.P. During the H2 event, ice raft debris extended southward, and large amounts of cold and fresh water were integrated into the North Atlantic. This led to the reduction of the Atlantic Meridional Overturning Circulation (AMOC), cooling of the Northern Hemisphere, and weakening of the East Asian Summer Monsoon (EASM) as a result of the southward shift of the Inter-tropical Convergence Zone (ITCZ). Although the H2 event is recorded in global records, there are still some discrepancies about the beginning and ending times of the H2 event due to the accuracy of dating and sample resolution. The NGRIP δ18O record with layer-counting time scales is not significant at the H2 event. The age of the H2 event can be calibrated in stalagmite records of high-precision 230Th ages in the Asian monsoon region, but the time and structure still need to be further investigated.
Xianyun Cave (116°59'E, 25°33'N, 970 m a.s.l) is located in Laiyuan Town, Liancheng County, Fujian Province, Southeast China. The cave is approximately 970 m in altitude and overlain by 30-50 m of Permian limestone bedrock. Annual average temperature in the region is 19.3℃, and the mean precipitation is 1 500-1 700 mm. The cave temperature is about 17.5℃. The relative humidity inside is close to 100%. The precipitation of δ18O in Xianyun Cave area is strongly influenced by the EASM:when the summer monsoon is strong, the δ18O value of precipitation is negatively biased, and vice versa.
This paper presents a high-resolution stalagmite isotope record (XYⅢ-28) from Xianyun Cave in western Fujian Province to reveal the detailed precipitation history of the EASM from 26.33 to 22.98 kyr B.P., based on nine high-precision 230Th ages and 301 oxygen isotope data points and yielding an average resolution of 11 years. The high-resolution stalagmite δ18O record is characterized by a positive shift process during the interval 24.09-23.39 kyr B.P. with an amplitude of 0.7‰, which demonstrates this remarkable H2 event from the North Atlantic. According to the midpoint of the main transition process, the beginning and ending times of the H2 event can be dated as 24.09±0.06 kyr B.P. and 23.39±0.07 kyr B.P., respectively. The duration of the H2 event was 0.69±0.06 kyr. The H2 event recorded by XYⅢ-28 shows a very obvious centenary-decade scale "double-positive" sub-cycle feature structure. This feature, which was recorded in the XYⅢ-28, also existed in the H1 event, the Younger Dryas event, and the Little Ice Age, illustrating that the internal structure of these extreme cooling events is unstable and that their driving mechanisms may be similar. Compared with paleoclimate records for high and low latitudes, XYⅢ-28 shows an anti-phase relationship between the Northern and Southern Hemispheres, namely the "see-saw" model.
The Last Glacial Maximum (LGM), which was the last and largest glacial period in the history of the Earth's climate, has long been a hot issue in paleoclimate research. The Heinrich2 abrupt event (H2 event) was a typical ice raft debris event formed in the LGM, which occurred about 25-24 kyr B.P. During the H2 event, ice raft debris extended southward, and large amounts of cold and fresh water were integrated into the North Atlantic. This led to the reduction of the Atlantic Meridional Overturning Circulation (AMOC), cooling of the Northern Hemisphere, and weakening of the East Asian Summer Monsoon (EASM) as a result of the southward shift of the Inter-tropical Convergence Zone (ITCZ). Although the H2 event is recorded in global records, there are still some discrepancies about the beginning and ending times of the H2 event due to the accuracy of dating and sample resolution. The NGRIP δ18O record with layer-counting time scales is not significant at the H2 event. The age of the H2 event can be calibrated in stalagmite records of high-precision 230Th ages in the Asian monsoon region, but the time and structure still need to be further investigated.
Xianyun Cave (116°59'E, 25°33'N, 970 m a.s.l) is located in Laiyuan Town, Liancheng County, Fujian Province, Southeast China. The cave is approximately 970 m in altitude and overlain by 30-50 m of Permian limestone bedrock. Annual average temperature in the region is 19.3℃, and the mean precipitation is 1 500-1 700 mm. The cave temperature is about 17.5℃. The relative humidity inside is close to 100%. The precipitation of δ18O in Xianyun Cave area is strongly influenced by the EASM:when the summer monsoon is strong, the δ18O value of precipitation is negatively biased, and vice versa.
This paper presents a high-resolution stalagmite isotope record (XYⅢ-28) from Xianyun Cave in western Fujian Province to reveal the detailed precipitation history of the EASM from 26.33 to 22.98 kyr B.P., based on nine high-precision 230Th ages and 301 oxygen isotope data points and yielding an average resolution of 11 years. The high-resolution stalagmite δ18O record is characterized by a positive shift process during the interval 24.09-23.39 kyr B.P. with an amplitude of 0.7‰, which demonstrates this remarkable H2 event from the North Atlantic. According to the midpoint of the main transition process, the beginning and ending times of the H2 event can be dated as 24.09±0.06 kyr B.P. and 23.39±0.07 kyr B.P., respectively. The duration of the H2 event was 0.69±0.06 kyr. The H2 event recorded by XYⅢ-28 shows a very obvious centenary-decade scale "double-positive" sub-cycle feature structure. This feature, which was recorded in the XYⅢ-28, also existed in the H1 event, the Younger Dryas event, and the Little Ice Age, illustrating that the internal structure of these extreme cooling events is unstable and that their driving mechanisms may be similar. Compared with paleoclimate records for high and low latitudes, XYⅢ-28 shows an anti-phase relationship between the Northern and Southern Hemispheres, namely the "see-saw" model.
2018, 36(6): 1148-1156.
doi: 10.14027/j.issn.1000-0550.2018.087
Abstract:
Grain size as an important proxy that reflects sedimentary provenance, transport, and deposition processeshas been widely used to reconstruct paleoclimatein loess, lacustrine, and marine sediments. There are two methods to present the result of grain size analysis:the parametric method, which analyzes grain size parameters, and the graphical method, which analyzes the frequency curve. Conceptually, the observed grain size distribution can be regarded as a mixing process of a finite number of end members, which in turn leads to a complex spectrum, commonly with a multimodal and asymmetrical form. Therefore, a method to decompose the different fractions becomes necessary. Although different methods of decomposing grain-size fractions have been successfully applied in the Chinese loess plateau, central Asia loess, which is under the control of westerlies, Siberian high pressure, and the Polar Front, may record complex dynamic processes. This study has analyzed the grain size of the XEBLK section in the Ili Basin, Xinjiang. Using the Bayesian end-member modeling analysis (BEMMA) and graded standard deviation (GSD) methods, the sensitive fractions of grain size and their significance for dust source have been examined. The results of the GSD method distinguish three fractions:0.4-31.7 μm (fine), 31.7-282.5 μm (middle), and 282.5-709.6 μm (coarse). Linearregressions indicate that the content of the middle fraction has a higher coefficient with mean grain size. This fraction implies that dust disperses into different high-altitude atmospheric layers downwind. The middle fraction reflects the component that becomes suspended a few hundred meters above the surface during dust storms and is carried over a distance of roughly 1 000 km. Therefore, the middle fraction is a particularly sensitive paleoclimate proxy. The coarse fraction may indicate the frequency of strong dust storms. The results from BEMMA distinguish three fractions:End Member(EM)1, EM2, and EM3. EM1(modal grain size:21.22 μm)may represent fine dust in the air background that reflects information on high-level atmospheric circulation. EM2 (modal grain size:75.29 μm) representsthe proximal fraction from river sedimentation. EM3 (modal grain size:47.5 μm) also represents a suspended fraction from nearby proximal sources, but this fraction was probably produced during an aeolian abrasion process. By analyzing the relationship between the fractions and the median grain size of bulk samples, EM2 was found to have the highest correlation coefficient. Therefore, EM2 is probably a more sensitive paleoclimate proxy than the other two fractions. EM2 not only records climatic rapid fluctuation since Marine Isotope Stage (MIS)2, but also provides evidence that Xinjiang loess has recorded the Heinrich, Younger Dryas, 8.2 ka, and 4.2 ka events. In summary, the BEMMA and GSD grain-size analysis methods can be used to trace the dust source of loess and to perform paleoclimate reconstruction in the Ili Basin. This paper provides new insights into dust sources and paleoclimate in Central Asia.
Grain size as an important proxy that reflects sedimentary provenance, transport, and deposition processeshas been widely used to reconstruct paleoclimatein loess, lacustrine, and marine sediments. There are two methods to present the result of grain size analysis:the parametric method, which analyzes grain size parameters, and the graphical method, which analyzes the frequency curve. Conceptually, the observed grain size distribution can be regarded as a mixing process of a finite number of end members, which in turn leads to a complex spectrum, commonly with a multimodal and asymmetrical form. Therefore, a method to decompose the different fractions becomes necessary. Although different methods of decomposing grain-size fractions have been successfully applied in the Chinese loess plateau, central Asia loess, which is under the control of westerlies, Siberian high pressure, and the Polar Front, may record complex dynamic processes. This study has analyzed the grain size of the XEBLK section in the Ili Basin, Xinjiang. Using the Bayesian end-member modeling analysis (BEMMA) and graded standard deviation (GSD) methods, the sensitive fractions of grain size and their significance for dust source have been examined. The results of the GSD method distinguish three fractions:0.4-31.7 μm (fine), 31.7-282.5 μm (middle), and 282.5-709.6 μm (coarse). Linearregressions indicate that the content of the middle fraction has a higher coefficient with mean grain size. This fraction implies that dust disperses into different high-altitude atmospheric layers downwind. The middle fraction reflects the component that becomes suspended a few hundred meters above the surface during dust storms and is carried over a distance of roughly 1 000 km. Therefore, the middle fraction is a particularly sensitive paleoclimate proxy. The coarse fraction may indicate the frequency of strong dust storms. The results from BEMMA distinguish three fractions:End Member(EM)1, EM2, and EM3. EM1(modal grain size:21.22 μm)may represent fine dust in the air background that reflects information on high-level atmospheric circulation. EM2 (modal grain size:75.29 μm) representsthe proximal fraction from river sedimentation. EM3 (modal grain size:47.5 μm) also represents a suspended fraction from nearby proximal sources, but this fraction was probably produced during an aeolian abrasion process. By analyzing the relationship between the fractions and the median grain size of bulk samples, EM2 was found to have the highest correlation coefficient. Therefore, EM2 is probably a more sensitive paleoclimate proxy than the other two fractions. EM2 not only records climatic rapid fluctuation since Marine Isotope Stage (MIS)2, but also provides evidence that Xinjiang loess has recorded the Heinrich, Younger Dryas, 8.2 ka, and 4.2 ka events. In summary, the BEMMA and GSD grain-size analysis methods can be used to trace the dust source of loess and to perform paleoclimate reconstruction in the Ili Basin. This paper provides new insights into dust sources and paleoclimate in Central Asia.
2018, 36(6): 1157-1168.
doi: 10.14027/j.issn.1000-0550.2018.102
Abstract:
Based on an AMS14C age framework, clay mineral analysis of Core OKT12 from the Middle Okinawa Tough was conducted to determine sediment provenance and its response to Holocene climate change. A remarkable change took place at 10 ka with an increase of illite and chlorite, and a decrease of kaolinite and smectite, indicating that sediment provenance changed from Changjiang and the ECS shelf to Taiwan after 10 ka. With a rise in sea level the distance between the Changjiang estuary and the Okinawa Trough increased. The Kuroshio Current was strengthened following the evolution of the East Asia summer monsoon since the LGM. The Kuroshio Current was able to transport sediment from Taiwan to OT and to obstruct the cross-helf transport of Changjiang sediment, resulting in an increase in Taiwan material and a decrease in Changjing material. Kaolinite/(illite+chloite) and chlorite/(illite+smectite) ratios have increased since 4 ka, indicating sediment provenance erosion change during the Holocene. By comparing the clay mineral compositions from the main rivers in Taiwan, it was determined that sediment provenance changed from northeastern to southeastern Taiwan Rivers since 4 ka. Holocene sediment provenance change was probably a result of erosion difference induced by a typhoon precipitation distribution discrepancy due to the southern shift of ITCZ and the strengthening of ENSO.
Based on an AMS14C age framework, clay mineral analysis of Core OKT12 from the Middle Okinawa Tough was conducted to determine sediment provenance and its response to Holocene climate change. A remarkable change took place at 10 ka with an increase of illite and chlorite, and a decrease of kaolinite and smectite, indicating that sediment provenance changed from Changjiang and the ECS shelf to Taiwan after 10 ka. With a rise in sea level the distance between the Changjiang estuary and the Okinawa Trough increased. The Kuroshio Current was strengthened following the evolution of the East Asia summer monsoon since the LGM. The Kuroshio Current was able to transport sediment from Taiwan to OT and to obstruct the cross-helf transport of Changjiang sediment, resulting in an increase in Taiwan material and a decrease in Changjing material. Kaolinite/(illite+chloite) and chlorite/(illite+smectite) ratios have increased since 4 ka, indicating sediment provenance erosion change during the Holocene. By comparing the clay mineral compositions from the main rivers in Taiwan, it was determined that sediment provenance changed from northeastern to southeastern Taiwan Rivers since 4 ka. Holocene sediment provenance change was probably a result of erosion difference induced by a typhoon precipitation distribution discrepancy due to the southern shift of ITCZ and the strengthening of ENSO.
2018, 36(6): 1169-1176.
doi: 10.14027/j.issn.1000-0550.2018.107
Abstract:
Based on the analyses of lithofacies and cathodo luminescence(CL) images, we measured the carbon and oxygen isotopic ratios of pedogenic calcretes from the Late Cretaceous Daijiaping Formationin Chaling Basin, Hunan province and estimated the paleoprecipitation-oxygen isotopes. Results show that the Daijiaping Formation is characterized by calcisols with in paraconglomerates, which were deposited in an alluvial fan environment along the mountain foot.Calcretes mainly consist of a reddish-brown calcite matrix and light-red calcite vein, corresponding to dull reddish-orange CL or non-luminescence and bright orange CL, respectively.δ18O values range from -7.96‰, VPDB to -11.35‰,VPDB, and δ13C values from -7.30‰, VPDB to -8.24‰,VPDB. The integration of calcite composition, CL, and oxygen isotopes indicates two stages of calcite precipitation have ever been experienced by the calcretes.From the oxygen isotope data, two meteoric calcite lines (MCLs) of δ18O values are recognized as(-9.04±0.18)‰, VPDB and(-8.0±0.11)‰, VPDB from the sample CL-11C4. Subsequently, the δ18Ow values of the Late Cretaceous paleoprecipitation are estimated from -5.76‰, VSMOW to -6.80‰, VSMOW at low paleolatitude (~17.4°N) for the Chaling Basin, consistent with those from the similar latitude in North America and providing basic reference data for the Cretaceous greenhouse hydrologic cycle model and paleoatmospheric circulation simulation.
Based on the analyses of lithofacies and cathodo luminescence(CL) images, we measured the carbon and oxygen isotopic ratios of pedogenic calcretes from the Late Cretaceous Daijiaping Formationin Chaling Basin, Hunan province and estimated the paleoprecipitation-oxygen isotopes. Results show that the Daijiaping Formation is characterized by calcisols with in paraconglomerates, which were deposited in an alluvial fan environment along the mountain foot.Calcretes mainly consist of a reddish-brown calcite matrix and light-red calcite vein, corresponding to dull reddish-orange CL or non-luminescence and bright orange CL, respectively.δ18O values range from -7.96‰, VPDB to -11.35‰,VPDB, and δ13C values from -7.30‰, VPDB to -8.24‰,VPDB. The integration of calcite composition, CL, and oxygen isotopes indicates two stages of calcite precipitation have ever been experienced by the calcretes.From the oxygen isotope data, two meteoric calcite lines (MCLs) of δ18O values are recognized as(-9.04±0.18)‰, VPDB and(-8.0±0.11)‰, VPDB from the sample CL-11C4. Subsequently, the δ18Ow values of the Late Cretaceous paleoprecipitation are estimated from -5.76‰, VSMOW to -6.80‰, VSMOW at low paleolatitude (~17.4°N) for the Chaling Basin, consistent with those from the similar latitude in North America and providing basic reference data for the Cretaceous greenhouse hydrologic cycle model and paleoatmospheric circulation simulation.
2018, 36(6): 1177-1189.
doi: 10.14027/j.issn.1000-0550.2018.120
Abstract:
Structural diagenesis, which is a cross-discipline of structural geology and sedimentology, is a frontier research field; it mainly studies the interaction between the tectonic action and its deformation structure and effect and the diagenesis of the sediments (rock). Deformation structures and processes have an important influence on the diagenesis heterogeneity through influencing the diagenetic fluid flow; the diagenesis research related to the deformation structure can provide people with diagenetic evolution, fluid flow, and period, stage and rate of structure development. Structural diagenesis provides a new idea for researching the reservoir evolution under the structure-diagenetic framework. It should be noted in practical work that this idea should be considered in research including genesis and prediction, densification mechanism of the reservoir, and evolution of sedimentary basins. The new classification system for deformation bands that include carbonates needs to be established urgently; the research related to deformation bands in carbonate rock started relatively late and is relatively weak. Therefore, research in this area should be strengthened in the future. The degree of research between different deformation structures is not balanced. Deformation bands and fractures constitute the main body of diagenesis research; diagenesis research related to deformation structures, such as soft sediment deformation structure and sandstone veins, needs further strengthening. The research concerning spatial distribution prediction of deformation structures and their influence on the fluid flow should be conducted by integration of various data and methods, such as cores, outcrops, and numerical simulations. Domestic scholars have carried out research on the impact of tectonic activity on physical changes of reservoirs in the Midwest Basin and made important progress; the influence of tectonism on reservoir chemical change has started. The dynamic mechanism and process of reservoir evolution and distribution should be explored by using structural diagenesis in the future in order to promote studies of reservoir diagenesis dynamics and sedimentary basin dynamics.
Structural diagenesis, which is a cross-discipline of structural geology and sedimentology, is a frontier research field; it mainly studies the interaction between the tectonic action and its deformation structure and effect and the diagenesis of the sediments (rock). Deformation structures and processes have an important influence on the diagenesis heterogeneity through influencing the diagenetic fluid flow; the diagenesis research related to the deformation structure can provide people with diagenetic evolution, fluid flow, and period, stage and rate of structure development. Structural diagenesis provides a new idea for researching the reservoir evolution under the structure-diagenetic framework. It should be noted in practical work that this idea should be considered in research including genesis and prediction, densification mechanism of the reservoir, and evolution of sedimentary basins. The new classification system for deformation bands that include carbonates needs to be established urgently; the research related to deformation bands in carbonate rock started relatively late and is relatively weak. Therefore, research in this area should be strengthened in the future. The degree of research between different deformation structures is not balanced. Deformation bands and fractures constitute the main body of diagenesis research; diagenesis research related to deformation structures, such as soft sediment deformation structure and sandstone veins, needs further strengthening. The research concerning spatial distribution prediction of deformation structures and their influence on the fluid flow should be conducted by integration of various data and methods, such as cores, outcrops, and numerical simulations. Domestic scholars have carried out research on the impact of tectonic activity on physical changes of reservoirs in the Midwest Basin and made important progress; the influence of tectonism on reservoir chemical change has started. The dynamic mechanism and process of reservoir evolution and distribution should be explored by using structural diagenesis in the future in order to promote studies of reservoir diagenesis dynamics and sedimentary basin dynamics.
2018, 36(6): 1190-1205.
doi: 10.14027/j.issn.1000-0550.2018.068
Abstract:
There are four types of reservoirs in the carbonate rocks confirmed by the practices of oil and gas exploration and production, namely reef and shoal reservoirs, dolomite reservoirs, erosion(karst) reservoirs, and fracture reservoirs. Therefore, the control factors of the reservoirs play a very important role in the practices. Six main outcrop profiles, 2 main well sections, and 81 various information points are analyzed using the methodology of "rapid sedimentary facies analysis of the shoal and flat assemblage", as well as rock slices and scanning electron microscopy (SEM) in the laboratory.On this basis, a large number of single factor maps, comprehensive sedimentary model maps, reservoir distribution prediction maps, and other maps have been completed, and finally summed up by the "Shoal,Dolomitization Shoal, Dolomitization and erosional shoal" (with fractures);the reservoir physical properties gradually improve.Therefore, it is considered that:1) the Longwangmiao Formation carbonates formed under arid climate conditions and were frequently influenced by storm activities. The carbonate reservoirs are controlled by various factors, including transgression or regression, shoal and tidal flat over or below the water, dolomitization, and dissolution. 2) Because of the benefitof primary porosity systems and their evolution, the erosions and dolomitizations during the contemporaneous period, penecontemporaneous period, and the early period following the contemporaneous are extremely important. The surface karsts not only improve the reservoir properties, but also increase the reservoir spaces. 3) Influenced by sea level and palaeogeomorphology, a combination of grain banks and dolomite flats or a combination of grain banks and limestone flats are widely distributed. The methodology of rapid sedimentary facies analysis of the shoal and flat assemblage in a carbonate platform can be applied to the unusual periods and conditions in the Yangtze Platform:the smooth bottom,steep slope, and the deep basin in the Longwangmiao Formation of the Early Cambrian. The method takes the shoal as the base point, giving there lative paleowater deptha value of 10 m (optimal interval value 5-15 m); giving the shoal and belt(limestones or dolostones) assemblage 20 m; and the shoal and lamina(laminatedcontemporaneous dolomites) assemblage 0 m. Thus, the curve of sea level changes can be drawn quickly, and the sequences and system tracts also can be recognized. Finally, a new sedimentary model of "shoal-to-shoal on the platform" and "Shoal flat assemblage" is identified in the study area, which provides a reliable geological foundation for the study of reservoir genesis and distribution.
There are four types of reservoirs in the carbonate rocks confirmed by the practices of oil and gas exploration and production, namely reef and shoal reservoirs, dolomite reservoirs, erosion(karst) reservoirs, and fracture reservoirs. Therefore, the control factors of the reservoirs play a very important role in the practices. Six main outcrop profiles, 2 main well sections, and 81 various information points are analyzed using the methodology of "rapid sedimentary facies analysis of the shoal and flat assemblage", as well as rock slices and scanning electron microscopy (SEM) in the laboratory.On this basis, a large number of single factor maps, comprehensive sedimentary model maps, reservoir distribution prediction maps, and other maps have been completed, and finally summed up by the "Shoal,Dolomitization Shoal, Dolomitization and erosional shoal" (with fractures);the reservoir physical properties gradually improve.Therefore, it is considered that:1) the Longwangmiao Formation carbonates formed under arid climate conditions and were frequently influenced by storm activities. The carbonate reservoirs are controlled by various factors, including transgression or regression, shoal and tidal flat over or below the water, dolomitization, and dissolution. 2) Because of the benefitof primary porosity systems and their evolution, the erosions and dolomitizations during the contemporaneous period, penecontemporaneous period, and the early period following the contemporaneous are extremely important. The surface karsts not only improve the reservoir properties, but also increase the reservoir spaces. 3) Influenced by sea level and palaeogeomorphology, a combination of grain banks and dolomite flats or a combination of grain banks and limestone flats are widely distributed. The methodology of rapid sedimentary facies analysis of the shoal and flat assemblage in a carbonate platform can be applied to the unusual periods and conditions in the Yangtze Platform:the smooth bottom,steep slope, and the deep basin in the Longwangmiao Formation of the Early Cambrian. The method takes the shoal as the base point, giving there lative paleowater deptha value of 10 m (optimal interval value 5-15 m); giving the shoal and belt(limestones or dolostones) assemblage 20 m; and the shoal and lamina(laminatedcontemporaneous dolomites) assemblage 0 m. Thus, the curve of sea level changes can be drawn quickly, and the sequences and system tracts also can be recognized. Finally, a new sedimentary model of "shoal-to-shoal on the platform" and "Shoal flat assemblage" is identified in the study area, which provides a reliable geological foundation for the study of reservoir genesis and distribution.
2018, 36(6): 1206-1217.
doi: 10.14027/j.issn.1000-0550.2018.092
Abstract:
Several wells drilled in the Shunnan area of the Tarim Basin revealed the enrichment and accumulation of natural gas in the dolomite reservoirs, but the genesis of those reservoirs is still controversial. Dolomite reservoirs cored from the lower Yingshan Formation in Well SN501 open a window to understanding the genesis of dolomite reservoirs in this area. Detailed core investigation, micropetrography, diagenesis event sequence, pore image analysis of casting thin section, computed tomography, backscattered imaging, and trace element Fe/Mn quantification of electron probes and fluid inclusions were carried out to study the characteristics and genesis of the dolomite reservoirs. The dolomite reservoir is the fracture-pores type, and the main reservoir space consists of intercrystalline pores and solution pores together with fractures and expansion fractures. There is a positive correlation between the occurrence of pores and fractures. Fluorite and calcite, as symbiotic hydrothermal minerals, filled in fractures and pores. The dolomites, dolomite ring edge, and calcite coexisted with fluorite near fractures, and pores show high contents of FeO and MnO. Groups of colorless transparent fluid inclusions in fluorites have 165℃-175℃ of homogenization and 15.5-17.5 wt.%NaCl salinity equivalent. Hydrothermal fluid activities should result in the enrichment of Fe2+ and Mn2+ in calcites and dolomites within the surrounding rock, and at the same time, provide the F- needed for fluorite crystallization. On the one hand, hydrothermal fluid reconstructs the dolomite to form the reservoir. On the other hand, the hydrothermal minerals acting as cements, represented by the fluorites and calcites, filled in fractures and pores. Thus, the generation of dolomite reservoir spaces should be related to tectonic-hydrothermal fluid activity. This understanding of the dolomite reservoir in well SN501 is of great significance to the establishment of a dolomite reservoir formation model and further exploration in this area.
Several wells drilled in the Shunnan area of the Tarim Basin revealed the enrichment and accumulation of natural gas in the dolomite reservoirs, but the genesis of those reservoirs is still controversial. Dolomite reservoirs cored from the lower Yingshan Formation in Well SN501 open a window to understanding the genesis of dolomite reservoirs in this area. Detailed core investigation, micropetrography, diagenesis event sequence, pore image analysis of casting thin section, computed tomography, backscattered imaging, and trace element Fe/Mn quantification of electron probes and fluid inclusions were carried out to study the characteristics and genesis of the dolomite reservoirs. The dolomite reservoir is the fracture-pores type, and the main reservoir space consists of intercrystalline pores and solution pores together with fractures and expansion fractures. There is a positive correlation between the occurrence of pores and fractures. Fluorite and calcite, as symbiotic hydrothermal minerals, filled in fractures and pores. The dolomites, dolomite ring edge, and calcite coexisted with fluorite near fractures, and pores show high contents of FeO and MnO. Groups of colorless transparent fluid inclusions in fluorites have 165℃-175℃ of homogenization and 15.5-17.5 wt.%NaCl salinity equivalent. Hydrothermal fluid activities should result in the enrichment of Fe2+ and Mn2+ in calcites and dolomites within the surrounding rock, and at the same time, provide the F- needed for fluorite crystallization. On the one hand, hydrothermal fluid reconstructs the dolomite to form the reservoir. On the other hand, the hydrothermal minerals acting as cements, represented by the fluorites and calcites, filled in fractures and pores. Thus, the generation of dolomite reservoir spaces should be related to tectonic-hydrothermal fluid activity. This understanding of the dolomite reservoir in well SN501 is of great significance to the establishment of a dolomite reservoir formation model and further exploration in this area.
2018, 36(6): 1218-1232.
doi: 10.14027/j.issn.1000-0550.2018.084
Abstract:
Microbial carbonate reservoirs are important research field of oil and gas geology, especially for oil-gas reservoirs. Regarding to the debate of excellent reservoirs of ancient and deep buried Xiaoerbulak microbial carbonate rocks in the Tarim Basin and their genesis, the Xiaoerbulak microbial carbonate rocks in the Kalpin area were investigated and studied systematically through field outcrops observation, section measurement, dense sampling, property test, thin section analysis and CT scanning in this paper. The results showed that the thrombolite with bright crystalline clotted texture was the excellent microbial carbonate reservoir of the Xiaoerbulak Formation with the max porosity about 9.35%. The proportion of porosity between 2.69% and 9.35% was 70.3%, the mean porosity was 5.07%, and there was an excellent positive linear correlation between the porosity and permeability of the rocks, suggesting the thrombolite as the excellent porous microbial carbonate reservoir of the Xiaoerbulak Formation. The excellent reservoir was composed of 6 types of reservoir spaces including intergranular pore, intercrystalline pore, intergranular dissolution pore, intercrystalline dissolution pore, extensive dissolution pore and dissolution vuge. The bright crystalline clotted texture formed in the high energy primary sedimentary environments of the upper subtidal zone provided the precondition for the thrombolite to form excellent microbial carbonate reservoir. Hydrothermal dissolution forming abundant large aperture fabric non-selective extensive dissolution pores and dissolution vuges were vital diagenesis process during the formation process of excellent reservoir, largely developing the porosity of thrombolite. This study can not only deepen the understanding of the type and genesis of the excellent Xiaoerbulak microbial carbonate reservoirs, but also provide sedimentary accordance for the effective selection of fair target in the future exploration.
Microbial carbonate reservoirs are important research field of oil and gas geology, especially for oil-gas reservoirs. Regarding to the debate of excellent reservoirs of ancient and deep buried Xiaoerbulak microbial carbonate rocks in the Tarim Basin and their genesis, the Xiaoerbulak microbial carbonate rocks in the Kalpin area were investigated and studied systematically through field outcrops observation, section measurement, dense sampling, property test, thin section analysis and CT scanning in this paper. The results showed that the thrombolite with bright crystalline clotted texture was the excellent microbial carbonate reservoir of the Xiaoerbulak Formation with the max porosity about 9.35%. The proportion of porosity between 2.69% and 9.35% was 70.3%, the mean porosity was 5.07%, and there was an excellent positive linear correlation between the porosity and permeability of the rocks, suggesting the thrombolite as the excellent porous microbial carbonate reservoir of the Xiaoerbulak Formation. The excellent reservoir was composed of 6 types of reservoir spaces including intergranular pore, intercrystalline pore, intergranular dissolution pore, intercrystalline dissolution pore, extensive dissolution pore and dissolution vuge. The bright crystalline clotted texture formed in the high energy primary sedimentary environments of the upper subtidal zone provided the precondition for the thrombolite to form excellent microbial carbonate reservoir. Hydrothermal dissolution forming abundant large aperture fabric non-selective extensive dissolution pores and dissolution vuges were vital diagenesis process during the formation process of excellent reservoir, largely developing the porosity of thrombolite. This study can not only deepen the understanding of the type and genesis of the excellent Xiaoerbulak microbial carbonate reservoirs, but also provide sedimentary accordance for the effective selection of fair target in the future exploration.
2018, 36(6): 1233-1242.
doi: 10.14027/j.issn.1000-0550.2018.088
Abstract:
The reservoirs of the Yingshan Formation are epikarst related, of which the short-term exposure between the above Upper Ordovician Lianglitage Formation and the beneath Lower-Middle Ordovician Yingshan Formation resulted in weak dissolution of surface rocks and undeveloped channels along the unconformity above the Yingshan Formation. Two sets of paleo-carbonate channels were discovered in the Yingshan Formation in Tazhong area by using strata slice and 3D visualization. Based on paleogeomorphology and patterns of distribution, the channels could be divided into two types, the surface ones and the underground ones. The channels fillings were identified by logging and lithology information. Based on the research mentioned above, the reservoirs were comprehensive accessed. The reservoirs relate to surface channels were mostly filled by shale during the process of exposure and thus not favorable for good reservoirs development. The reservoirs relate to underground channels were mostly preserved well with completed assemblage of reservoir-cap rocks, which were also confirmed as favorable reservoirs combined with drilling results. The discovery of channels do not only give new explanation for the genesis of paleo-karst carbonate reservoirs but also provide potential direction for further exploration and development of carbonate reservoirs in the Tazhong area.
The reservoirs of the Yingshan Formation are epikarst related, of which the short-term exposure between the above Upper Ordovician Lianglitage Formation and the beneath Lower-Middle Ordovician Yingshan Formation resulted in weak dissolution of surface rocks and undeveloped channels along the unconformity above the Yingshan Formation. Two sets of paleo-carbonate channels were discovered in the Yingshan Formation in Tazhong area by using strata slice and 3D visualization. Based on paleogeomorphology and patterns of distribution, the channels could be divided into two types, the surface ones and the underground ones. The channels fillings were identified by logging and lithology information. Based on the research mentioned above, the reservoirs were comprehensive accessed. The reservoirs relate to surface channels were mostly filled by shale during the process of exposure and thus not favorable for good reservoirs development. The reservoirs relate to underground channels were mostly preserved well with completed assemblage of reservoir-cap rocks, which were also confirmed as favorable reservoirs combined with drilling results. The discovery of channels do not only give new explanation for the genesis of paleo-karst carbonate reservoirs but also provide potential direction for further exploration and development of carbonate reservoirs in the Tazhong area.
2018, 36(6): 1243-1255.
doi: 10.14027/j.issn.1000-0550.2018.163
Abstract:
The Upper Ordovician Wufeng Formation-the Lower Silurian Longmaxi Formation is a set of black organic Marine shale. The high GR interval at the bottom of the Longmaxi Formation is the main gas producing section, which studies the sediment genesis of the GR peak and provides reference for shale gas exploration. Based on the data of well logs, rock cores, petrographic thin sections, trace elements, and mineral composition, the sedimentary stages of the GR peak interval were accurately divided (including upper shale section A of the Wufeng Formation,the top Guanyinqiao shale section B of the Wufeng Formation,section C of the lower GR peak of the Longmaxi Formation, and subpeak section D of the Longmaxi Formation), and characteristics of sedimentary changes for each stage were analyzed. The research shows that, by analyzing the correlation between U, TH, K, and GR, we find that the occurrence of the GR peak is mainly caused by the enrichment of uranium elements. Analysis of the sedimentary environment, organic matter, clay minerals, iron and phosphorous minerals, and their effects on uranium enrichment caused by a variety of geological events at various sedimentary stages were performed, highlighting that the emergence of the high GR peak is a geological response to a collective geological event. It is caused by the comprehensive influence of rapid transgression, stratification of seawater, terrestrial volcanic eruptions, and submarine magmatic hydrothermal events at the end of an ice age. According to the sedimentary facies characteristics of the Guanyinqiao at the top of the Wufeng Formation, the genesis of the Guanyinqiao ice age conforms to the "glacial catastrophe" and "snowball hypothesis" and has a great effect on the formation of the high GR peak.
The Upper Ordovician Wufeng Formation-the Lower Silurian Longmaxi Formation is a set of black organic Marine shale. The high GR interval at the bottom of the Longmaxi Formation is the main gas producing section, which studies the sediment genesis of the GR peak and provides reference for shale gas exploration. Based on the data of well logs, rock cores, petrographic thin sections, trace elements, and mineral composition, the sedimentary stages of the GR peak interval were accurately divided (including upper shale section A of the Wufeng Formation,the top Guanyinqiao shale section B of the Wufeng Formation,section C of the lower GR peak of the Longmaxi Formation, and subpeak section D of the Longmaxi Formation), and characteristics of sedimentary changes for each stage were analyzed. The research shows that, by analyzing the correlation between U, TH, K, and GR, we find that the occurrence of the GR peak is mainly caused by the enrichment of uranium elements. Analysis of the sedimentary environment, organic matter, clay minerals, iron and phosphorous minerals, and their effects on uranium enrichment caused by a variety of geological events at various sedimentary stages were performed, highlighting that the emergence of the high GR peak is a geological response to a collective geological event. It is caused by the comprehensive influence of rapid transgression, stratification of seawater, terrestrial volcanic eruptions, and submarine magmatic hydrothermal events at the end of an ice age. According to the sedimentary facies characteristics of the Guanyinqiao at the top of the Wufeng Formation, the genesis of the Guanyinqiao ice age conforms to the "glacial catastrophe" and "snowball hypothesis" and has a great effect on the formation of the high GR peak.
2018, 36(6): 1256-1266.
doi: 10.14027/j.issn.1000-0550.2018.096
Abstract:
According to various test methods, including Rock-Eval, GC-MS, ICP-MS, XRF and others, the abundance and type of organic matter, the major/trace elements, and the biomarker characteristics of the mudstone from the second and third beds of the third member of the Hetaoyuan Formation from the Biyang depression of the Nanxiang Basin were investigated. Based on this analysis, the geochemical characteristics and sedimentary environment of the lacustrine organic-rich mudstone have been discussed, and the deposition mode of the organic-rich mudstone has been definitively established. The results show that, during the depositional period of the second bed, the TOC values of the mudstone were relatively lower, and the organic matter of the lacustrine basin consisted of aquatic organisms and terrigenous organic matter. The kerogen types of the second-bed source rocks ranged from I to Ⅲ. The water column caused by high-salinity water and a reducing environment provided excellent preservation conditions for organic matter enrichment. However, high-salinity water conditions tend to lead to reduced primary productivity in lakes. In addition, the relatively higher terrigenous detrital matter input decreased lake productivity and was not conducive to organic matter accumulation. In contrast, during the sedimentary period of the third bed, the TOC values of the mudstone were relatively higher. The kerogen types of third-bed source rocks were mainly I and Ⅱ1. The lacustrine salinity decreased dramatically, and the water column was not obvious, meaning that the anoxic bottom water environment was responsible for organic matter preservation. Under such circumstances, high productivity is the controlling factor for organic matter accumulation in third-bed mudstone.
According to various test methods, including Rock-Eval, GC-MS, ICP-MS, XRF and others, the abundance and type of organic matter, the major/trace elements, and the biomarker characteristics of the mudstone from the second and third beds of the third member of the Hetaoyuan Formation from the Biyang depression of the Nanxiang Basin were investigated. Based on this analysis, the geochemical characteristics and sedimentary environment of the lacustrine organic-rich mudstone have been discussed, and the deposition mode of the organic-rich mudstone has been definitively established. The results show that, during the depositional period of the second bed, the TOC values of the mudstone were relatively lower, and the organic matter of the lacustrine basin consisted of aquatic organisms and terrigenous organic matter. The kerogen types of the second-bed source rocks ranged from I to Ⅲ. The water column caused by high-salinity water and a reducing environment provided excellent preservation conditions for organic matter enrichment. However, high-salinity water conditions tend to lead to reduced primary productivity in lakes. In addition, the relatively higher terrigenous detrital matter input decreased lake productivity and was not conducive to organic matter accumulation. In contrast, during the sedimentary period of the third bed, the TOC values of the mudstone were relatively higher. The kerogen types of third-bed source rocks were mainly I and Ⅱ1. The lacustrine salinity decreased dramatically, and the water column was not obvious, meaning that the anoxic bottom water environment was responsible for organic matter preservation. Under such circumstances, high productivity is the controlling factor for organic matter accumulation in third-bed mudstone.
2018, 36(6): 1267-1276.
doi: 10.14027/j.issn.1000-0550.2018.095
Abstract:
During the sedimentary period of Dainan Formation of Gaoyou sag, some ancient earthquake events were fiercely developed under the influence of Meso-Cenozoic tectonic movement. A series of quasi contemporaneous deformation structures related to earthquakes occurred in the strata, such as liquefaction extrusion deformation structure of liquefied rock veins, liquefied breccia, pillow beds, lamina circularis, seismo-folds and so on. Brittle deformation structure of step fault, shatter breccias, Self-broken breccia, internal debris breccia were also visible in the strata. In addition, these earthquake actions and deformation tectonic layers can be found on the cores to be always generated with turbidite stratum under earthquake action. The vertical sequence of earthquake rocks was described on the basis via summarizing single well and united wells sequences. Combined with hydrocarbon accumulation characteristics in the,study area, the significance of earthquake events was discussed in petroleum geology from three aspects, hydrocarbons transportation, accumulation and plugging. This research provided a new exploration direction, broken the previous exploration methods of "searching for oil around sags", and consider the deep sag belt sand bodies to be also equivalent in exploration value.
During the sedimentary period of Dainan Formation of Gaoyou sag, some ancient earthquake events were fiercely developed under the influence of Meso-Cenozoic tectonic movement. A series of quasi contemporaneous deformation structures related to earthquakes occurred in the strata, such as liquefaction extrusion deformation structure of liquefied rock veins, liquefied breccia, pillow beds, lamina circularis, seismo-folds and so on. Brittle deformation structure of step fault, shatter breccias, Self-broken breccia, internal debris breccia were also visible in the strata. In addition, these earthquake actions and deformation tectonic layers can be found on the cores to be always generated with turbidite stratum under earthquake action. The vertical sequence of earthquake rocks was described on the basis via summarizing single well and united wells sequences. Combined with hydrocarbon accumulation characteristics in the,study area, the significance of earthquake events was discussed in petroleum geology from three aspects, hydrocarbons transportation, accumulation and plugging. This research provided a new exploration direction, broken the previous exploration methods of "searching for oil around sags", and consider the deep sag belt sand bodies to be also equivalent in exploration value.
