Method for adaptively setting ancient ocean hypoxia environment discrimination threshold value
Through adaptive setting the discrimination parameters and values of the ancient oxygen environment, the enrichment characteristics and correlation analysis of the trace element are used to solve the problem of the inaccurate identification of the ancient oxygen hypoxia environment in the existing technology, and the lack of lack of lack of disappearance is achieved. Oxygen environment accurate identification and reconstruction of sedimentation environment.
Patent Information
- Application Number
- CN202411432564.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-14
- Publication Date
- 2025-01-28
AI Technical Summary
The prior art has inaccuracies and contradictions in identifying paleo-oxia environments, and lacks an accurate identification method.
Through adaptive setting to study the hypoxia deposition environmental discrimination parameters and their values of the basin, use the differences of trace element differences to enrich the characteristics, establish relevant scattered dot diagrams and linear fitting relationships, and determine the data inflection point in the dual -segment change mode. Adapt to determining the dedication of the hypoxia environment.
The accurate identification of the hypoxic environment of the ancient ocean has been achieved, and the uncertainty and contradictions brought by the ratio of fixed parameters are avoided, and the accuracy of the reconstruction of the sedimentation environment of the sea phase shale is improved.
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Figure CN119380869A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of sedimentary geochemistry, and particularly to a method for adaptively setting a discrimination threshold for ancient marine anoxic environments. Background Art
[0002] Accurately analyzing the redox conditions during the formation period of marine shale not only helps to restore the ancient marine environment and reconstruct the paleogeography of the basin, but also helps to predict the formation and distribution of organic-rich shale.
[0003] Previous studies have shown that the solubility of trace elements (such as U, Mo, Ni, V, Cu, etc.) in shale in water is controlled by the redox conditions of the water body. As the sedimentary water body changes from an oxidizing environment to an anoxic environment, the solubility of these redox-sensitive elements gradually decreases and accumulates in the sediment, and there are also certain differences in the enrichment efficiency of different elements in different environments. Therefore, using the enrichment law of trace elements in marine mud shale to carry out redox condition analysis has become an important part of ancient marine environment analysis.
[0004] Currently, people have initially established a set of parameter indicators for identifying the redox conditions of shale sedimentary environments using these redox-sensitive elements. For example, it is considered that V / Cr > 4.5 represents an anoxic environment, 4.5 > V / Cr > 2.0 represents an oxygen-poor environment, and 2.0 > V / Cr represents an oxidizing environment; V / (V + Ni) > 0.6 represents an anoxic environment, 0.6 > V / (V + Ni) > 0.46 represents an oxygen-poor environment, and 0.46 > V / (V + Ni) represents an oxidizing environment; U / Th > 1.25 represents an anoxic environment, 0.75 < U / Th < 1.25 represents an oxygen-poor environment, and U / Th < 0.75 represents an oxidizing environment; Ni / Co > 7 represents an anoxic environment, 5 < Ni / Co < 7 represents an oxygen-poor environment, and Ni / Co < 5 represents an oxidizing environment; Mo(ppm) > 100 represents an anoxic environment, 25 < Mo(ppm) < 100 represents an oxygen-poor environment, and Mo(ppm) < 25 represents an oxidizing environment. These fixed parameter indicators have been widely used in the analysis of the ancient sedimentary environment of strata in the past.
[0005] However, the latest research points out that it is not appropriate to apply the above parameters and their fixed thresholds to the interpretation of redox environments in various sedimentary basins or strata. This method not only ignores the particularity of different sedimentary basins, but also does not take into account the differences in the sources and abundance of related elements in different basins. This results in inaccuracy in the interpretation of redox conditions using the above method, and even certain contradictions between the interpretation results of different parameters, especially for the interpretation of anoxic environments. As we all know, anoxic environments are favorable conditions for the formation of marine organic-rich shales. Accurately determining anoxic environments is of great value for restoring sedimentary paleoenvironments and predicting the distribution of organic-rich shales. As far as the inventors know, there is currently no set of technical methods for accurately identifying ancient marine anoxic environments. Therefore, for a marine sedimentary basin, how to establish effective redox condition discrimination parameters and determine the thresholds for discriminating anoxic environment parameters has become an important issue that needs to be urgently addressed in the restoration of the ancient marine environment. Summary of the invention
[0006] In view of the deficiencies of the prior art: the present invention provides a method for adaptively setting the parameters and thresholds for distinguishing the anoxic environment of the ancient ocean. The present invention is based on the characteristics of differential enrichment of trace elements to adaptively set the parameters and thresholds for distinguishing the anoxic sedimentary environment of the research basin. The method of the present invention has a simple process and strong applicability. It can set the parameters and thresholds for distinguishing the anoxic environment suitable for the research basin, avoiding the uncertainty and contradiction caused by the use of fixed parameter ratios for interpretation, which is of great significance for accurately reconstructing the marine shale sedimentary environment.
[0007] The technical solution of the present invention is: a method for adaptively setting a threshold for distinguishing anoxic environments in ancient oceans, characterized in that it comprises the following steps:
[0008] Step 1: Sample collection: Based on the color difference of shale, intensive collection of marine shale samples that may represent different redox conditions is carried out in the target strata of the study area.
[0009] Step 2: Sample processing: Divide each collected sample into two groups and grind them into powder with a particle size of 300 mesh. Each powder sample should not be less than 30g.
[0010] Step 3, determination of organic carbon content: Take one group of samples and use a carbon-sulfur analyzer to determine the TOC content in the powder sample.
[0011] Step 4: Element content analysis: XRF is used to determine the Al, U, Mo, Ni, V and other element contents of another group of shale powder samples.
[0012] Step 5: Data calculation and processing: Calculate the enrichment coefficients of U, Mo, Ni, and V. The calculation formula is:
[0013] X-EF=(X / Al) 样品 / (X / Al) paas
[0014] Where, X-EF represents the enrichment factor of element X, (X / Al) represents the content ratio of element X to element Al in the sample, (X / Al) PAAS It represents the content ratio of element X to element Al in the average Australian Post-Archaean shale.
[0015] Step 6, selection of redox sensitive parameters: The existing conventional analytical techniques believe that U, Mo, Ni, V, etc. are redox sensitive elements in the sedimentary water of any basin, and use a fixed ratio between them as the redox environment discrimination threshold. This method is obviously very rough and inaccurate. In the present invention, the applicant proposed a method for screening effective redox sensitive parameters in different basins or formations based on the rule that the TOC content of shale and the enrichment coefficient of redox sensitive elements usually have a good positive correlation from oxidizing environment to anoxic environment. The specific steps are as follows:
[0016] (1) First, a scatter plot of the correlation between the enrichment coefficient of the measured element and the TOC content of the shale was established.
[0017] (2) Then, the linear relationship fitting of the scatter plot was performed to calculate the correlation coefficient R between the enrichment coefficient of each element and the TOC content. 2 Numeric value;
[0018] (3) Based on the sensitivity of TOC content to the redox environment, the value of the correlation coefficient R2 between the element enrichment coefficient and the TOC content also represents the sensitivity of the element enrichment coefficient to the redox environment. In order to eliminate elements with weak correlation and select elements with strong sensitivity to redox conditions for anoxic environment analysis, R2 was selected. 2 The element enrichment factor > 0.5 was used as a sensitive parameter of redox conditions.
[0019] Step 7, determination of anoxic environment: Since the relative enrichment rate of different redox-sensitive elements will change from oxidizing to anoxic environment, such as Mo and Ni, they gradually enrich from oxidizing environment to anoxic environment, but the relative enrichment rate of Mo is faster under anoxic conditions, resulting in a significant change in the relative enrichment rate between the two elements as the deposition environment transitions from oxidizing environment to anoxic environment. Therefore, whether there is anoxic environment in the water body during shale deposition can be determined based on the change in the relative enrichment rate between redox-sensitive elements. The specific method is as follows:
[0020] (1) Establish a correlation scatter plot between effective redox sensitive element enrichment coefficients.
[0021] (2) Identify the correlation pattern between the enrichment coefficients of redox-sensitive elements to determine whether there is an anoxic environment. The correlation patterns between the enrichment coefficients of redox-sensitive elements are classified into two categories: single-segment covariation pattern and double-segment covariation pattern. The single-segment covariation pattern means that the ratio of the enrichment rates of two elements remains stable, showing that the slope of the linear fitting relationship is basically stable. That is, when the oxygen content in the sedimentary water gradually decreases, the difference in the relative enrichment rates of the two elements does not change significantly, indicating that this change pattern cannot respond to the change of redox conditions, so it is impossible to judge whether there is an anoxic environment based on this. The double-segment covariation pattern means that when the oxygen content in the sedimentary water gradually decreases to an anoxic environment, the relative enrichment rates (slopes) of the two elements change significantly, and the data points can be divided into two parts with different slopes, indicating that the relative enrichment rates of the two elements change significantly in the gradually anoxic environment. Therefore, this change pattern can be used to identify an anoxic environment.
[0022] Step 8: Determine the discrimination threshold for an anoxic environment. The existing discrimination thresholds for an anoxic environment are fixed ratios between different elements, and it is obviously inappropriate to apply them to the discrimination of the anoxic environment of water bodies in different geological historical periods and different sedimentary basins. In the present invention, the applicant proposes a method for determining the discrimination parameter threshold for an anoxic environment based on the differential enrichment rate of effective redox-sensitive parameters. The specific steps are as follows:
[0023] (1) Determine the data inflection point in the scatter plot of the double-segment change pattern. The data inflection point in the scatter plot of the double-segment change pattern is the position where the relative enrichment rate of the element or the data slope begins to change significantly. In the correlation diagram of the double-segment change pattern, first identify the numerical change interval of the X-axis parameter value (X min ~X max ). Assume the inflection point value as X n =X0+(n - 1)×k, and divide the data points into two parts in turn (where K is the numerical increase constant, determined according to the X-axis parameter region, n is the number of divisions, X0 is the initial value set at the first division, Xmin < X n < Xmax. To ensure the reliability of the fitting curve, the number of data points in each part is not less than 6), calculate the linear correlation coefficients of the two parts of data points respectively, and obtain their sum R 2 sum . When R 2 sum is the largest, it represents that X n divides the data points into two parts with the best linear correlation, that is, X n represents the position of the inflection point.
[0024] (2) Determination of the adaptive hypoxic environment discrimination threshold. The inflection point of the data indicates that the relative enrichment rate of the elements in the sample begins to differ. Based on the inflection point, the data is divided into two parts, and the linear correlation equation of the two parts of the data is fitted to obtain the element enrichment coefficient value corresponding to the intersection of the equation. The intersection value is the hypoxic environment discrimination threshold of the research object. It can be found that with the formation of the hypoxic environment, the relative enrichment rate (slope) of the elements on both sides of the intersection value shows obvious differences.
[0025] Step 9, analysis: According to the adaptive threshold value of the anoxic environment discrimination parameter, the changes in the redox conditions of the vertical sedimentary environment of the stratigraphic section are described, and the layer sections with parameter values greater than the adaptive threshold value are determined as anoxic sedimentary environments, and can be compared with traditional anoxic environment parameters to clarify the effectiveness of this method. At the same time, the threshold values of the adaptive anoxic environment discrimination parameters in different regions of the same ocean basin can also be compared to clarify the differences in the water body limitations of their environments.
[0026] The beneficial effects of the present invention are as follows: the method of the present invention for adaptively setting the parameters and thresholds for distinguishing the ancient marine anoxic environment in the research basin has a simple process and high analysis efficiency, and can quickly determine the anoxic environment distinguishing parameters applicable to the research area, accurately identify whether an anoxic environment exists, and establish anoxic environment distinguishing parameter thresholds. For different regions in the same sedimentary basin, the size of the anoxic environment distinguishing parameter threshold can also be used to analyze the differences in the limitations of sedimentary water bodies. Therefore, this method is of great significance for analyzing the ancient sedimentary environment of marine organic-rich shale and reconstructing the paleogeography of the basin. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 This study is to investigate the correlation characteristics between TOC content and trace element enrichment coefficient of Wufeng-Longmaxi shale samples.
[0028] Figure 2 is the covariance relationship between the enrichment coefficients of different redox sensitive elements.
[0029] Figure 3 The inflection point is divided into two parts with different slopes.
[0030] Figure 4 It is the linear fitting relationship and intersection value of the two parts of data divided based on the inflection point.
[0031] Figure 5 The hypoxic environment indicated by the discriminant parameter Mo-EF determined by the new method is compared with the hypoxic environment determined by traditional conventional parameters.
[0032] Figure 6 It is the sedimentary background of the Xiang-Yangzi Basin in the Late Ordovician-Early Silurian (there are obvious differences in the sedimentary water limitations between western Hunan and western Hubei).
[0033] Figure 7 The original sedimentary basin water body limitation discrimination chart based on the Mo and TOC ratio shows that there is no obvious difference in the sedimentary water body limitation of the two places. DETAILED DESCRIPTION
[0034] The technical solution of the present invention is further described below in conjunction with examples.
[0035] like Figures 1 to 7 As shown, the following implementation examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. A method for adaptively setting the threshold for distinguishing anoxic environments in the ancient ocean, the specific steps are as follows:
[0036] Step 1, sample collection: Based on the color difference of shale, intensively collect marine shale samples that may represent different redox conditions in the target strata of the study area. In this embodiment, the inventor collected 91 fresh shale samples of the Ordovician Wufeng Formation-Silurian Longmaxi Formation in the eastern Chongqing-western Hubei region, numbered from S1 to S91, and the samples covered all shale layers with colors ranging from black to gray-green.
[0037] Step 2: Sample processing: Divide each collected sample into two groups and grind them into powder with a particle size of 300 mesh. Each powder sample should not be less than 30g.
[0038] Step 3, determination of organic carbon content: Take one group of samples and use a carbon-sulfur analyzer to determine the TOC content in the powder sample.
[0039] Step 4: Element content analysis: XRF is used to determine the Al, U, Mo, Ni, V and other element contents of another group of shale powder samples.
[0040] Step 5: Data calculation and processing: Calculate the enrichment coefficients of U, Mo, Ni, and V. The calculation formula is:
[0041] X-EF=(X / Al) 样品 / (X / Al) paas
[0042] Where, X-EF represents the enrichment factor of element X, (X / Al) represents the content ratio of element X to element Al in the sample, (X / Al) PAAS The ratio of the content of element X to Al in the average Australian Post-Archaean shale (Mo / Al) pass The value is 1.19×10 -5 , (U / Al) pass value is 1.08×10 -5 , (V / Al)pass value is 1.66×10 -3, (Ni / Al) pass value is 7.14×10 -4 .
[0043] Step 6, selection of redox sensitive parameters: The existing conventional analytical techniques believe that U, Mo, Ni, V, etc. are redox sensitive elements in the sedimentary water of any basin, and use a fixed ratio between them as the redox environment discrimination threshold. This method is obviously very rough and inaccurate. In the present invention, the applicant proposed a method for screening effective redox sensitive parameters in different basins or formations based on the rule that the TOC content of shale and the enrichment coefficient of redox sensitive elements usually have a good positive correlation from oxidizing environment to anoxic environment. The specific method is as follows:
[0044] (1) First, establish a correlation scatter plot between the enrichment coefficient of the measured element and the TOC content of the shale. Figure 1 In this example, a correlation scatter plot between U-EF, Mo-EF, Ni-EF, V-EF and TOC content was established.
[0045] (2) Then, the linear relationship fitting of the scatter plot was performed to calculate the correlation coefficient R between the enrichment coefficient of each element and the TOC content. 2 Numeric value;
[0046] (3) Based on the sensitivity of TOC content to the redox environment, the correlation coefficient R between element enrichment coefficient and TOC content 2 The numerical value also represents the sensitivity of the element enrichment coefficient to the redox environment. In order to eliminate elements with weak correlation and select elements with strong sensitivity to redox conditions for anoxic environment analysis, R 2 The element enrichment factor > 0.5 is used as a sensitive parameter of redox condition. In this example, the correlation coefficient R between U-EF, Mo-EF, Ni-EF and TOC is 2 is significantly greater than 0.5, indicating that they are particularly sensitive to the redox environment and can be used as sensitive parameters for redox environment analysis. The correlation coefficient R 2 Less than 0.5 indicates that the element is not very sensitive to redox conditions and is not suitable as a redox environment analysis parameter.
[0047] Step 7, determination of anoxic environment: Since the relative enrichment rate of different redox-sensitive elements will change from oxidizing to anoxic environment, such as Mo and Ni, they gradually enrich from oxidizing environment to anoxic environment, but the relative enrichment rate of Mo is faster under anoxic conditions, resulting in a significant change in the relative enrichment rate between the two elements as the deposition environment transitions from oxidizing environment to anoxic environment. Therefore, whether there is anoxic environment in the water body during shale deposition can be determined based on the change in the relative enrichment rate between redox-sensitive elements. The specific method is as follows:
[0048] (1) Establish a correlation scatter plot between the enrichment coefficients of different redox sensitive elements. Figure 1 In this example, a correlation scatter plot between the enrichment coefficients of U-EF, Mo-EF, and Ni-EF was established.
[0049] (2) Clarify the correlation pattern between the enrichment coefficients of redox-sensitive elements to determine whether an anoxic environment exists. The correlation patterns between the enrichment coefficients of redox-sensitive elements are classified into two categories: single-stage covariation pattern and double-stage covariation pattern. The single-stage covariation pattern refers to the stability of the ratio of the enrichment rates of the two elements, which is manifested by the basic stability of the slope of the linear fitting relationship. That is, as the oxygen content of the sedimentary water gradually decreases, the difference in the relative enrichment rates of the two elements does not change significantly, indicating that this change pattern cannot respond to changes in redox conditions, and therefore cannot be used to determine whether an anoxic environment exists. The double-stage covariation pattern refers to the fact that as the oxygen content of the sedimentary water gradually decreases to an anoxic environment, the relative enrichment rate (slope) of the two elements changes significantly, and the data points can be divided into two groups with different slopes, indicating that the relative enrichment rate of the two elements changes significantly in a gradually anoxic environment. Therefore, this change pattern can be used to identify anoxic environments. In this example, Mo-EF and Ni-EF have an obvious two-stage variation pattern. The data distribution of the latter part is significantly flatter than that of the former part, indicating that the enrichment rate of Mo in the later period is significantly faster than that of Ni, which means that an anoxic environment existed during shale deposition. Therefore, this pattern can be used to identify anoxic environments. Mo-EF and Ni-EF are effective parameters for identifying anoxic environments in the study area. However, U-EF has a single-stage covariation pattern with Mo-EF and Ni-EF, which cannot be used to determine whether anoxic environments exist.
[0050] Step 8, determination of the threshold for distinguishing anoxic environment. The existing threshold for distinguishing anoxic environment is a fixed ratio between different elements. It is obviously inappropriate to apply it to distinguish anoxic environment in water bodies in different geological history periods and different sedimentary basins. In the present invention, the applicant proposes a method for determining the threshold for distinguishing anoxic environment parameters based on the differential enrichment rate of effective redox sensitive parameters. The specific method is as follows:
[0051] (1) Determine the data inflection points in the scatter plot of the double-segment change pattern. The data inflection points in the scatter plot of the double-segment change pattern are the positions where the relative enrichment rate of elements or the data slope starts to change significantly. In the correlation plot of the double-segment change pattern, when the numerical change interval of the X-axis parameter (X min ~X max ) first appears clearly, taking X n =X0+(n - 1)×k as the assumed inflection point value, the data points are divided into two parts in sequence (where K is the numerical increase constant, determined according to the X-axis parameter region, n is the number of divisions, X0 is the initial value set at the first division, Xmin < X n < Xmax. To ensure the reliability of the fitting curve, the number of data points in each part is not less than 6), and the sum R 2 sum of the linear correlation coefficients of the two parts of data points is calculated respectively. When R 2 sum is the largest, it represents that X n divides the data points into two parts with the best linear correlation, that is, X n represents the position of the inflection point. In this example, Mo-EF and Ni-EF have obvious double-segment covariation characteristics. Mo-EF corresponds to the X-axis. There are 6 samples with Mo-EF less than 3. Therefore, taking X0 = 3 as the initial value and the Mo-EF range between 0.2 - 175, K = 2 can be used as the numerical increase constant. Using X n to divide the data points into two parts in sequence, calculate the correlation coefficients of the partial data points and sum them respectively. It can be found that when X n =33, the sum of the correlation coefficients of the two parts of data is the largest, as shown in the following table, indicating that the inflection point position of the data is X n =33, as shown in Figure 3 .
[0052] Characteristics of the linear correlation coefficients of the two parts divided by different assumed inflection points in the research example
[0053]
[0054]
[0055] (2) Determination of the discriminant threshold for the adaptive anoxic environment. The data inflection point indicates that the relative enrichment rate of elements in the sample starts to show differences. Based on the inflection point, the data is divided into two parts, and the linear correlation equations of the two parts of data are fitted. The numerical value of the element enrichment coefficient corresponding to the intersection point of the equations is obtained. This intersection point value is the discriminant threshold for the anoxic environment of the research object. It can be found that with the formation of the anoxic environment, the relative enrichment rates (slopes) of the elements on both sides of the intersection point value show obvious differences. In this example, Mo-EF and Ni-EF have obvious double-segment covariation characteristics. X n=33 is the inflection point of the sample data, and the fitting equation of the data points of Mo-EF<33 is Y=0.0415X+0.6629(R 2 =0.6948), the fitting equation of the data points of Mo-EF>33 is Y=0.0175X+1.5838(R 2 =0.7089), Mo-EF at the intersection is 38.37, and Ni-EF is 2.26, which are the adaptive hypoxic environment discrimination thresholds of the target layer in the study area. Figure 4 , Mo-EF greater than 38.37 represents anoxic environment, and Ni-EF greater than 2.26 represents anoxic environment.
[0056] The method of adaptively setting the threshold value for distinguishing anoxic environment in the ancient ocean of the present invention also includes step 9: analysis step.
[0057] Step 9, analysis: Based on the adaptive threshold of the anoxic environment discrimination parameter, the changes in the redox conditions of the vertical sedimentary environment of the stratigraphic section are described, and the layer sections with parameter values greater than the adaptive threshold are determined as anoxic sedimentary environments. The research results of the Wufeng Formation-Longmaxi Formation in the Yangtze region show that the interpretation of the anoxic environment by conventional parameters is quite different, but the anoxic areas determined based on the element differential enrichment pattern all fall into the anoxic layer sections indicated by conventional redox parameters such as V / (V+Ni), U / Th, and V / Cr, and the corresponding layers are rich in organic matter, such as Figure 5 , indicating that this method can effectively analyze the redox conditions in different basins.
[0058] At the same time, the adaptive threshold value of the hypoxic environment discrimination parameter can also be used to analyze the differences in the limitations of sedimentary water bodies in different regions of the same basin. Based on the same ocean background, affected by paleo-tectonic landforms, the limitations of water bodies in different regions will be different. Generally speaking, the concentration of redox-sensitive elements in the same ocean is relatively stable, while the water flow circulation in the region with strong limitations is poor, which is easy to form an hypoxic environment. At the same time, it is impossible to obtain the supplement of related elements from the ocean, resulting in the enrichment coefficient of redox-sensitive elements in the region with strong limitations being lower than that in the open water environment. Therefore, by comparing the effective adaptive threshold values of different regions when the oxidizing environment changes to the hypoxic environment, the higher the value, the more enriched the related elements, the more open the water body is, and it is more difficult to form an hypoxic environment; the lower the value, the lower the enrichment, the more limited the water body, the less connected to the outside world, and the easier it is to form an hypoxic environment. In this example, the adaptive threshold value of the anoxic environment of the Wufeng Formation-Longmaxi Formation in western Hunan (Mo-EF=25.9) is significantly lower than that of the eastern and western Hubei regions (Mo-EF=38), indicating that in the Yangtze Basin during the Late Ordovician-Early Silurian, the degree of limitation of the sedimentary water in western Hunan was significantly stronger than that in the western Hubei-eastern Chongqing regions, resulting in the inability of the ocean's Mo element to be fully supplemented into the seawater in western Hunan. This understanding is also completely consistent with the paleogeographic environment at that time, such as Figure 6 As shown in the figure, the western Hunan region is confined by the Hunan-Hubei uplift, the Xuefeng uplift and the Cathaysia paleocontinent, and has stronger limitations, while the western Hubei and eastern Chongqing regions are connected to the Qinling Trough, and have weaker limitations. It can be seen that based on the adaptive threshold value, the strength of the sedimentary water body limitations in different regions of the same basin at the same time can be effectively distinguished, avoiding the problem that the previous parameter chart cannot effectively distinguish the differences in water body limitations in different regions of the same basin, such as Figure 7 As shown, the commonly used water localization map cannot identify the difference in the anoxic environment between the two sites (samples from both sites fell into the same area).
[0059] It can be seen that the invention provides a new method for identifying anoxic environments suitable for different sedimentary basins, and has achieved good application results in the analysis of redox conditions in the sedimentary environment of the Wufeng Formation-Longmaxi Formation black rock system in the Yangtze region, realizing the accurate division of anoxic environments. At the same time, the method also provides a new idea for analyzing the differences in sedimentary water body limitations in different regions of the same basin, and can effectively distinguish the differences in sedimentary water body limitations in different regions of the same basin. The application of this method will provide important support for the restoration of the paleoenvironment of marine shale and the reconstruction of paleogeography of sedimentary basins.
Claims
1. A method for adaptively setting a threshold for distinguishing anoxic environments in ancient oceans, characterized in that: The following steps are involved: Step 1: Sample collection: Based on the color difference of shale, intensively collect marine shale samples representing different redox conditions in the target strata of the study area; Step 2, sample processing: Divide each collected sample into two groups and grind them into powder; Step 3, determination of organic carbon content: Take one of the samples and use a carbon-sulfur analyzer to determine the TOC content in the powder sample; Step 4, element content analysis: XRF is used to determine the element content of another group of shale powder samples; Step 5: Data calculation and processing: Calculate the enrichment coefficients of U, Mo, Ni, and V. The calculation formula is: X-EF=(X / Al) 样品 / (X / Al) paas Where, X-EF represents the enrichment factor of element X, (X / Al) represents the content ratio of element X to element Al in the sample, (X / Al) PAAS It represents the content ratio of element X to Al in the average Australian Post-Archaean shale; Step 6: Selection of redox sensitive parameters. The specific process is as follows: (1) Establish a correlation scatter plot between the enrichment coefficient of the measured element and the TOC content of the shale; (2) Perform data linear relationship fitting on the scatter plot and calculate the correlation coefficient R between each element enrichment coefficient and TOC content. 2 Numeric value; (3) Select R 2 The element enrichment factor > 0.5 is used as a sensitive parameter of redox conditions; Step 7: Identification of hypoxic environment. The specific process is as follows: (1) Establish a correlation scatter plot between the enrichment coefficients of different redox-sensitive elements; (2) clarify the correlation pattern between the enrichment coefficients of redox-sensitive elements and determine whether there is an anoxic environment; Step 8: Determination of the hypoxic environment discrimination threshold. The specific process is as follows: (1) Determine the data inflection point in the scatter plot of the double-segment change pattern; (2) Determination of the adaptive hypoxic environment discrimination threshold. The specific process is: divide the data into two parts based on the inflection point, fit the linear correlation equation of the two parts of the data, and obtain the value of the element enrichment coefficient corresponding to the intersection of the equation. The intersection value is the hypoxic environment discrimination threshold of the corresponding parameter.
2. The method for adaptively setting the threshold for distinguishing anoxic environment in the ancient ocean according to claim 1, characterized in that: The method also includes step 9, an analysis phase: based on the adaptive threshold value of the anoxic environment discrimination parameter, the change of the redox condition of the vertical sedimentary environment of the stratigraphic section is characterized, and the layer section with a parameter value greater than the adaptive threshold value is determined as an anoxic sedimentary environment.
3. A method for adaptively setting a threshold for distinguishing anoxic environments in the ancient ocean according to claim 1 or 2, characterized in that: In step 2, each powder sample is not less than 30 g, and the powder particle size is 300 mesh.
4. A method for adaptively setting a threshold for distinguishing anoxic environments in the ancient ocean according to claim 1 or 2, characterized in that: Step 5 (Mo / Al) pass The value is 1.19×10 -5 , (U / Al) pass value is 1.08×10 -5 , (V / Al)pass value is 1.66×10 -3 , (Ni / Al) pass value is 7.14×10 -4 .
5. A method for adaptively setting a threshold for distinguishing anoxic environments in the ancient ocean according to claim 1 or 2, characterized in that: In step 7: the correlation patterns between the enrichment coefficients of redox sensitive elements are summarized into two categories: single-segment covariation pattern and double-segment covariation pattern. The double-segment covariation pattern is selected to identify the hypoxic environment.
6. A method for adaptively setting a threshold for distinguishing anoxic environments in the ancient ocean according to claim 1 or 2, characterized in that: The specific process of determining the data inflection point in the scatter plot of the double-segment change pattern in step 8 is as follows: In the correlation diagram of the double-segment change pattern, the first clear numerical change interval of the X-axis parameter value (X min ~X max ) is found. Taking X n = X0 + (n - 1) × k as the assumed inflection point value, the data points are sequentially divided into two parts; where k is the numerical increase constant, determined according to the X-axis parameter interval, n is the number of divisions, X0 is the initial value set at the first division, Xmin < X n < Xmax; then the sum of the linear correlation coefficients R 2 sum of the two parts of data points is calculated respectively. When R 2 sum is the largest, X n represents the position of the inflection point.
7. The method for adaptively setting the threshold for distinguishing anoxic environment in the ancient ocean according to claim 6, characterized in that: In step 8, when the data points in the correlation diagram of the dual-segment change pattern are divided into two parts, the number of data points in each part is no less than 6.
8. A method for adaptively setting a threshold for distinguishing anoxic environments in the ancient ocean according to claim 1 or 2, characterized in that: In step 4, the contents of Al, U, Mo, Ni, and V elements are determined.