Method for analyzing deep-time El Nino-Southern oscillation cycle based on sea-lake facies sediment annual lamina

Abstract

The invention relates to the field of sedimentary stratigraphy, in particular to a method for analyzing a deep-time El Nino-Southern oscillation cycle based on a sea-lake facies sediment annual stripe layer. The method comprises the following steps: sampling and grinding a sheet, carrying out high-definition scanning, estimating a deposition rate, carrying out element plane distribution, carrying out principal component analysis on the content of each element, carrying out laser in-situ carbon and oxygen isotope test and time domain spectrum analysis on an annual stripe layer one by one, and finally analyzing the climatic change of the interannual scale in the geological historical period. According to the method, element data, the thickness of the annual lamina and the carbon and oxygen isotope of the annual lamina are analyzed and explained in a combined mode, relevance exists among the indexes, a new method is provided for identification and analysis of the deep-time El Nino-Southern oscillation cycle, a time scale with the year as the unit is established on the basis of the marine facies or lacustrine facies annual lamina, and the identification accuracy of the deep-time El Nino-Southern oscillation cycle is improved. And the climate fluctuation is subjected to high-precision analysis under the scale, so that the related technical blank is filled.

Description

Technical Field

[0001] The invention relates to the field of sedimentary stratigraphy, and in particular to a method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminae of marine and lake sediments. Technical Background

[0002] The El Nino-Southern Oscillation is an ocean-atmosphere interaction phenomenon that occurs in the tropical Pacific and Indian Oceans, characterized by fluctuations between abnormally warm conditions, El Niño, and cold conditions, La Niño. Modern climate research has found that the El Niño-Southern Oscillation has a cycle of 2 to 7 years and is one of the most important drivers of global climate fluctuations. However, the current identification of the El Niño-Southern Oscillation phenomenon is almost completely limited to the modern and Quaternary periods, and rarely involves the geological history before the Quaternary period. This is because there is currently a lack of methods to establish a high-precision time scale on an interannual scale in ancient sedimentary strata and analyze high-frequency climate fluctuations on this basis. Traditional radioisotope dating methods (such as U-Pb and Ar-Ar methods) have errors of up to millions of years; the smallest scale cycle that can be identified by cyclostratigraphy methods is the precession cycle, with a precession cycle of 20,000 years, which cannot meet the interannual time accuracy requirements required for identifying the El Niño-Southern Oscillation.

[0003] In the strata before the Quaternary, annual lacustrine deposits are widely distributed. Their characteristics are that under the seasonal changes of paleoclimate, there is a clear interface between the sediments of each year and the sediments of the previous year, and a single annual laminae represents the sedimentary time limit of one year. For example, the shale of the lower third section and the upper fourth section of the Eocene Shahejie Formation in the Jiyang Depression has developed typical annual laminae: in spring and summer, the algae in the lake flourish and light-colored calcite laminae are deposited; in autumn and winter, the algae die and the terrigenous input increases, and dark organic-rich clay silt laminae are deposited. The combination of the two is an annual laminae. Marine lacustrine sediments with annual laminae can provide a high-precision time scale and can serve as a good carrier for analyzing the deep-time El Niño-Southern Oscillation cycle.

[0004] The El Nino-Southern Oscillation can cause frequent extreme floods and droughts, global temperature and sea level fluctuations, and have important impacts on the biosphere, including humans. Studying the El Nino-Southern Oscillation cycle in geological history (especially the greenhouse period) can help us better prepare for the challenges of future climate change.

[0005] In summary, existing technologies have conducted some research on the modern and Quaternary El Niño-Southern Oscillation cycles, but there is still a lack of relevant identification and analysis technologies for ancient periods before the Quaternary. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for identifying the deep El Niño-Southern Oscillation cycle based on annual laminae of marine and lake sediments.

[0007] Figure 1 The specific technical scheme of the present invention is as follows: S1. Grind the sample into thin slices and perform high-definition scanning on the slices Select the core section of marine-lake sediments with developed annual laminae and grind them into thin sections with a thickness of 0.03 mm without cover glass; scan and photograph the thin sections under a microscope to obtain overall photos of the thin sections that can clearly identify the annual laminae; S2. Establish a time scale and estimate the deposition rate The annual layers in the thin sections were counted and their thickness was measured one by one. Since each annual layer represented a year of sedimentation, a time scale in years was established perpendicular to the direction of the annual layers and the sedimentation rate was estimated based on the thickness of the annual layers. S3. Analyze the element plane distribution Use a micro-area X-ray fluorescence scanner (XRF) to scan the thin section to obtain the planar distribution of elements such as Si, Ca, K, Al, Fe, Ti, and S; S4. Principal component analysis of each element content Draw a straight line segment along the direction perpendicular to the annual layer, and extract the content of Si, Ca, K, Al, Fe, Ti, S and other elements on the line segment. Perform principal component analysis on the extracted element content data, and select the principal component that can represent the data volatility; S5. Extracting climate change information on an interannual scale using carbon and oxygen isotope testing Along the line segments perpendicular to the annual strata, laser in-situ carbon and oxygen isotope tests are performed on the annual strata one by one to extract climate change information on the interannual scale; S6. Time domain spectrum analysis Based on the time scale established in step S2, the annual lamina thickness data, element principal component data, and carbon and oxygen isotope data are subjected to time domain spectrum analysis to identify the interannual scale climate change cycle associated with the El Niño-Southern Oscillation.

[0008] Preferably, in step S2, if an annual laminae is composed of two or more laminae units (such as a calcite laminae unit and a clay silt laminae unit together constitute an annual laminae), the thicknesses of different laminae units can be further measured based on the measurement of the thickness of the annual laminae.

[0009] Preferably, in S4, an electron probe line scanning method may be used to obtain the element content on a line segment perpendicular to the direction of the annual grain.

[0010] Preferably, climate change (fluctuations in temperature, precipitation, etc.) will lead to changes in the amount of terrigenous input received by the sedimentary basin, changes in evaporation, and the prosperity or extinction of organisms involved in element cycles (including bacteria and other microorganisms), which will eventually be reflected in the changes in the elements of the sediments. Therefore, it is necessary to select characteristic elements that can reflect climate change.

[0011] The present invention has the following beneficial effects: (1) The present invention shows that the annual laminar thickness, characteristic element content changes, carbon and oxygen isotopes of the annual laminar layers and other indicators can reflect the climate changes on an interannual scale during the geological history.

[0012] (2) The present invention combines element data, annual layer thickness and annual layer carbon and oxygen isotopes for analysis and interpretation, indicating that there is a correlation between the indicators. For example, the carbon and oxygen isotope values ​​and annual layer thickness have a strong correlation, which together indicate the interannual scale cyclical changes between the warm and dry climate state and the wet and cold climate state.

[0013] (3) The present invention provides a new method for the identification and analysis of the deep El Niño-Southern Oscillation cycle. It establishes a time scale in years based on marine or lacustrine annual laminae and conducts high-precision analysis of climate fluctuations at this scale, thus filling the gap in related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flow chart of a method provided by an embodiment of the present invention; Figure 2 It is the annual lamination count and thickness analysis diagram; Figure 3 It is the thin-section XRF element scanning diagram and the first principal component and second principal component result diagram; Figure 4 This is the principal component analysis diagram of thin section XRF elements; Figure 5 This is the result of in-situ laser carbon and oxygen isotope analysis of the annual laminae; Figure 6 This is a summary diagram of the time domain spectrum analysis results. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] This implementation method selects the well-developed annual laminations of the lower third section to the upper fourth section of the Eocene Shahejie Formation in the Jiyang Depression as the research object for detailed description.

[0017] like Figure 1 As shown, the method for identifying the deep El Nino-Southern Oscillation cycle based on annual laminar layers of marine and lake sediments provided by the embodiment of the present invention comprises the following steps: S1. Grind the sample into thin slices and perform high-definition scanning on the slices A sample of 3552.1 m from Well Niu 55 Incline 1 in Dongying Sag, Jiyang Depression was selected for thin section preparation, and a German Leica DM6M electron microscope was used to perform high-definition scanning of the thin section at 50 times.

[0018] S2. Establish a time scale and estimate the deposition rate The thin slice photographs scanned in step S1 were scanned layer by layer for annual laminae and thickness measurement. A total of 360 annual laminae were counted in the thin slice, each of which represented a year and contained a layer of bright calcite laminae and a layer of dark clay silt laminae. The thickness of each annual laminae and the calcite laminae therein was measured, as shown in FIG. Figure 2 The average thickness of the annual laminae is 105.5 μm, and the sedimentary thickness divided by the sedimentary time gives a sedimentary rate of 10.55 cm / m2.

[0019] S3. Analyze the element plane distribution The thin slice was scanned with high-precision XRF elements using a Bruker M4 Tornado micro-area X-ray fluorescence spectrometer. The thin slice sample was placed in the sample chamber and the sample level was ensured by a level gauge. The element scan was performed using a silicon drift detector, with an acceleration voltage of 50 keV and a beam current of 800 mA. Rhodium was selected as the target for X-ray irradiation, and the scanning rate was 5 milliseconds. The quantitative characteristics of elements such as Ca, Si, Na, K, Al, Mg, Fe, S, Ti, Mn, Sr, Ba, V, Cr, Cu, Ni, Co, and Mo in the sample were determined. The scanning time for each sample was greater than 6 hours, and the sampling point spacing was 10 microns. The element concentration was in wt.%, and different elements were rendered in different colors to obtain a two-dimensional distribution map of the elements, as shown in the figure. Figure 3 Then, draw a straight line in the direction perpendicular to the lamination, Figure 3 The middle dotted line uses the software system supporting the X-ray fluorescence spectrometer to quantitatively calculate the changes in the content of each element on this straight line.

[0020] S4. Principal component analysis of each element content The principal component analysis of Ca, Si, K, Fe, S and Ti contents of the XRF data of the thin sections was performed using the principal component analysis application of Originpro v.2023b software.

[0021] like Figure 4As shown in the figure, the first principal component PC1 and the second principal component PC2 contribute 62.3% and 17.96% to the data variance respectively, and the sum of the variance contribution rates of the first and second principal components can reach 80.26%, indicating that the first and second principal components can effectively reflect the changes in the content of each element; PC1 is significantly negatively correlated with the Ca content, and positively correlated with the Si, K, and Ti contents, indicating that PC1 is an indicator that can reflect the production of carbonate minerals: when PC1 is low, carbonate mineral production increases, which may be related to the prosperity of algae in a warm climate; when PC1 is high, carbonate minerals precipitated under biochemical action decrease, while the proportion of terrigenous debris (with Si, K, Ti, etc. as characteristic elements) increases. PC2 is significantly positively correlated with Fe and S contents, and has a lower correlation with Ca and Ti contents. Fe and S are components of pyrite (FeS2), and the enrichment of pyrite indicates that the water body is highly reductive, indicating that PC2 can be used as an indicator to reflect changes in redox conditions.

[0022] S5. Conduct laser in-situ carbon and oxygen isotope testing on each annual layer The Delta V Advantage stable gas isotope ratio mass spectrometer and FLASH EA elemental analyzer and ND: YAG (neodymium-doped yttrium aluminum garnet crystal) laser produced by Thermofisher, USA, were used to conduct in-situ carbon isotope (δ13C) and oxygen isotope (δ18O) tests on thin-section micrite calcite laminae. In-situ laser carbon and oxygen isotope testing requires special thin-section production requirements, that is, the thickness of the thin section is required to be 60-80 microns, single-sided polishing, no cover glass is required, and fir glue is used for bonding (avoid the use of other adhesives such as epoxy resin). The sample needs to be pretreated before testing to remove moisture and organic matter in the sample. During the test, each selected micrite calcite laminae was placed in the center of the field of view (observed under a microscope) to ensure that the bright calcite laminae were tested, rather than carbonate cements in the terrigenous clastic laminae. The coherent laser beam output by the laser is focused on the selected micro-area for heating, and the CO2 gas produced by decomposition is measured by a gas isotope ratio mass spectrometer to measure the carbon and oxygen isotope values ​​of the CO2 gas. The spatial resolution of the micro-area measurement is 20μm, and the carbon and oxygen isotope data are in VDPB units, such as Figure 5 shown.

[0023] S6. Time domain spectrum analysis The time domain spectrum analysis of the thin-section XRF element data, annual laminae thickness data, and annual laminae carbon and oxygen isotope data showed that the PC1, PC2, and annual laminae thickness analysis showed a significant high-frequency period of 2.1 to 4.5 years (more than 95% confidence level). The annual laminae carbon and oxygen isotope spectrum analysis results showed that it had a period of 3.5 to 8.7 years and a period of 2.6 to 3 years, such as Figure 6As shown, this is consistent with the El Nino-Southern Oscillation cycle. Further analysis found that the thickness of the calcite laminae in the annual laminae has a synchronous change trend with the carbon and oxygen isotope values ​​( Figure 5 In warm and dry climates, algae flourish, forming thicker calcite laminae, with positive carbon and oxygen isotope excursions; in cold and wet climates, algae growth is inhibited, calcite laminae thin, with negative carbon and oxygen isotope excursions, further indicating the regional climate effect of the El Niño-Southern Oscillation in the Jiyang Depression during the Eocene.

[0024] Those skilled in the art should understand that the discussion of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0025] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for analyzing deep El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments, characterized in that: The following steps are involved: S1. Grind the sample into thin slices and perform high-definition scanning on the slices Select the core section of marine-lake sediments with developed annual laminae and grind them into thin sections with a thickness of 0.03 mm without cover glass. Scan and photograph the thin sections under a microscope to obtain overall photos of the thin sections that can clearly identify the annual laminae. S2. Establish a time scale and estimate the deposition rate The annual layers in the thin sections were counted and their thickness was measured one by one. Since each annual layer represented a year of sedimentation, a time scale in years was established perpendicular to the direction of the annual layers and the sedimentation rate was estimated based on the thickness of the annual layers. S3. Analyze the element plane distribution The thin slice was scanned using a micro-area X-ray fluorescence scanner XRF to obtain the planar distribution of Si, Ca, K, Al, Fe, Ti, and S elements; S4. Principal component analysis of each element content A straight line segment was drawn along the direction perpendicular to the annual stratum, and the contents of Si, Ca, K, Al, Fe, Ti, and S on the line segment were extracted. The principal component analysis was performed on the extracted content data of each element, and the principal component that could represent the data volatility was selected. S5. Extracting climate change information on an interannual scale using carbon and oxygen isotope testing Along the line segments perpendicular to the annual strata, laser in-situ carbon and oxygen isotope tests are performed on the annual strata one by one to extract climate change information on the interannual scale; S6. Time domain spectrum analysis Based on the time scale established in step S2, the annual lamina thickness data, element principal component data, and carbon and oxygen isotope data are subjected to time domain spectrum analysis to identify the interannual scale climate change cycle associated with the El Niño-Southern Oscillation.

2. The method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments according to claim 1, characterized in that: In the step S1, a microscope is used to perform a high-definition scan of the thin slice at 50 times magnification.

3. The method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments according to claim 1, characterized in that: In the step S2, if an annual laminae is composed of a plurality of laminae units, the thicknesses of different laminae units may be further measured based on the measurement of the thickness of the annual laminae.

4. The method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminae of marine and lake sediments according to claim 1, characterized in that: In step S2, the deposition rate is calculated by counting the annual layers and measuring the thickness of each layer of the high-definition scanned thin-section photograph, and the deposition rate is obtained by dividing the deposition thickness by the deposition time.

5. The method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments according to claim 1, characterized in that: In step S3, when scanning the slices, the scanning time of each slice is greater than 6 hours, and the sampling point spacing is 10 microns.

6. The method for analyzing deep-time El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments according to claim 1, characterized in that: In the step S4, electron probe line scanning is used to obtain the element content on the straight line segment perpendicular to the direction of the annual layer.

7. The method for analyzing deep El Nino-Southern Oscillation cycles based on annual laminar lacustrine sediments according to claim 1, characterized in that: In step S5, during the in-situ laser carbon and oxygen isotope test, the slice is required to be 60-80 microns thick, single-sided polished, without a cover glass, and bonded with fir glue.

Images