River sediment tracing method with multiple spatial and temporal scales

Abstract

The invention provides a multi-temporal-spatial-scale river sediment tracing method, and relates to the field of geomorphology and river dynamics. According to the method, light release light (OLS) samples of terraces and floodplains and zircon sand samples of corresponding layers are collected on the sections of a source (branch) and a sink (main stream), and different age sequences are divided in combination with contemporary zircon sand samples of a tender beach; the contribution rate of a source to a sink is directly calculated by using a zircon age spectrum matrix, and a quality contribution rate algorithm is optimized in combination with a zircon mass percentage. According to the method, contemporary and historical multi-time-scale sediment traceability is realized, the traditional fitting simulation process is simplified, the calculation efficiency and accuracy are improved, and the method is suitable for sediment source analysis in areas poor in data.

Description

Technical Field

[0001] This invention relates to the fields of geomorphology and river dynamics, specifically a method for tracing the source of river sediment at multiple spatiotemporal scales. Background Technology

[0002] Sediment, or sediment, is the result of various forces on the Earth's surface, such as glacial erosion, slope erosion, wind erosion, and river flow erosion or transportation. This erosion and transportation process realizes the journey of sediment from its source to its sink. Studying the source-sink process of sediment is a major category in geomorphology and river dynamics, that is, answering the source-tracing question: "Where does the sediment come from, and how much of it came from?" Sediment source tracing can explain the mechanism of river sediment transport, clarify regional evolution processes, and also distinguish the sources of pollutants or biogenic substances carried by sediment, facilitating source control.

[0003] There have been five main techniques for sediment source dating in the past: whole-sandstone facies dating, heavy mineral dating, clay mineral dating, single-mineral element isotopic dating, and whole-sand element isotopic dating. Among these, single-mineral element isotopic dating has become a popular method in recent years. Compared with the previous three methods, it has a wider range of applications, higher accuracy, and relatively simpler sampling. It is also significantly less expensive than the whole-sand element method, making it a method that is currently recommended by the industry, especially the zircon U-Pb dating method in single-mineral elements: by accurately measuring the isotopic ratio of zircon, the formation age spectrum of zircon is obtained, and the origin of sediments can be analyzed. Zircon is one of the most common accessory minerals in nature, widely found in igneous, metamorphic, and sedimentary rocks. Zircon is a mineral with strong resistance to physical and chemical weathering, and its U-Pb isotopic system has a high closure temperature. The Pb diffusion closure temperature in zircon can reach as high as 900℃ (Lee et al., 1997), thus it can exist stably in the surface environment. With advancements in zircon U-Pb geochronology micro-area testing techniques, its role in tracing source regions of basin sediments has become increasingly important, making zircon a crucial carrier for the study of source-to-sink processes. Its advantages include: uniqueness and extreme stability across different source regions, providing clear source identification; no need for large-scale sampling and analysis of the study area; and zircon being one of the most stable minerals in surface environments, its migration process unaffected by anthropogenic or natural changes, giving it advantages over large areas and geological depths, and making it particularly effective in complex geological environments.

[0004] However, it has the following shortcomings:

[0005] 1. The quantitative analysis process is complex: Traditional zircon tracing requires fitting the cumulative distribution function of the age spectrum and Monte Carlo simulation to calculate the contribution rate of the source to the sink. The process is cumbersome and prone to introducing fitting errors, making it difficult to meet the needs of rapid analysis in areas with scarce data.

[0006] 2. Limited time scale: Existing methods mostly focus on tracing the source of sediment in the current stratigraphic layer, without making full use of the stability of zircon to invert the source of sediment in historical periods (such as terrace and floodplain deposits), thus failing to reveal the long-term evolution of the watershed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to provide a simplified quantitative calculation and integrated sediment source tracing technology that integrates multiple time scales, thereby improving analysis efficiency and spatiotemporal coverage.

[0008] A method for tracing river sediment sources across multiple spatiotemporal scales includes the following steps:

[0009] (1) Sampling point selection: Select cross sections containing terraces, floodplains and shoals in the tributaries and main streams of the river as sampling points;

[0010] (2) Sample collection: Optically stimulated luminescence (OLS) samples were collected from the terraces and floodplains at the sampling points, and zircon sand samples from the corresponding layers and contemporary zircon sand samples from the tender beach were collected simultaneously.

[0011] (3) Chronological sequence division: The OLS samples are subjected to chronological testing. Based on the test results, zircon sand samples of the same age are divided into at least one chronological sequence A, where each sequence A corresponds to a historical period.

[0012] (4) Zircon sand sample numbering and pretreatment: In each chronological sequence A, the zircon sand samples from each tributary are numbered sequentially as follows: Where n is the number of tributaries, and the sand and gravel samples from the main stream are numbered S. D and weigh them separately;

[0013] (5) Zircon mass percentage test: Test the zircon sand samples from each tributary. Zircon mass percentage and the zircon mass percentage of the dry sand sample D. ;

[0014] (6) Zircon age spectrum analysis: testing each tributary sample The age spectrum is The age spectrum matrix P is obtained as follows:

[0015] ,

[0016] Where i=n, ​​j=m, m is the number of characteristic age intervals, and the age spectrum of the main stream sand and gravel sample D. The age spectrum row matrix P is obtained. D Where j = m;

[0017] (7) Zircon contribution rate calculation: Based on the age spectrum matrix P and age spectrum row matrix P obtained in step (6) by the data processing unit. D Calculate the zircon contribution rate of each tributary to the main stream. ;

[0018] (8) Quality contribution rate calculation: Based on the result obtained in step (5) by the data processing unit. C D And obtained in step (7) Calculate the quality contribution rate of each tributary to the main stream. ;

[0019] (9) Multiple timescale tracing: the multiple chronological sequences divided in step (3) ,in To determine the number of historical periods, repeat steps (4) to (8) to obtain the sediment source tracing results for different historical periods.

[0020] Furthermore, in step (3), the division of the chronological sequence A satisfies the following: zircon sand samples in the same sequence A come from the same strata in the source-sink area.

[0021] Furthermore, in step (7), the matrix P is an n×m matrix, where rows represent tributary numbers and columns represent characteristic age intervals; the age spectrum row matrix P D It is a 1×m matrix, and its columns correspond one-to-one with the characteristic age ranges of matrix P.

[0022] Furthermore, in step (7), according to the formula Calculate the zircon contribution rate of each tributary to the main stream. .

[0023] Furthermore, in step (8), according to the formula Calculate the quality contribution rate of each tributary to the main stream. .

[0024] This invention combines zircon provenance tracing with optically stimulated luminescence (OLS) sediment dating and optimizes the source-sink contribution rate calculation method to obtain a sediment source tracing method that can reflect multiple time scales, with the following beneficial effects:

[0025] (1) Simplify the calculation process of zircon contribution rate: avoid intermediate steps such as cumulative distribution function fitting and Monte Carlo simulation in traditional methods, and directly calculate the sink age spectrum based on the source zircon age spectrum matrix through the optimized algorithm, thereby reducing errors and improving efficiency;

[0026] (1) Achieve source tracing across multiple time scales: By combining optically stimulated luminescence (OLS) sediment dating with zircon provenance tracing, the source of sediment in contemporary (nen shoal) and historical (terraces, floodplains) conditions can be analyzed simultaneously, breaking through the limitations of a single time scale.

[0027] (3) Improve applicability in areas with scarce data: By unifying sampling standards (such as testing the percentage of zircon mass in samples of the same weight) and simplifying algorithms, the dependence on large-scale sampling and complex data processing is reduced, making it suitable for watershed scenarios with scarce data. Attached Figure Description

[0028] Figure 1 This is a flowchart of the multi-temporal and spatial scale river sediment source tracing method of the present invention.

[0029] Figure 2 This is a sample point distribution diagram of an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Please see Figure 1 This invention provides a method for tracing the source of river sediment at multiple spatiotemporal scales, comprising the following steps:

[0032] (1) Select sampling points. Select cross sections with terraces, floodplains and new siltation at each source (tributary) and confluence (main stream) as sampling points.

[0033] (2) Optically stimulated luminescence (OLS) sample collection. OLS sediment samples were collected from terraces and floodplains at each source-sink cross section for dating. Zircon sand samples from the same strata as the OLS samples, as well as tidal sand samples, were collected simultaneously, the latter representing contemporary sediment.

[0034] (3) OLS sample dating and determination of the historical period to be traced. OLS samples from different strata at each source and sink were dated. Zircon sand samples of the same age from each source and sink area were grouped together. Each age's zircon sand sample set was defined as one sequence A, and sets from multiple ages were designated as [sequence A]. K represents the number of historical periods (eras) that need to be traced.

[0035] (4) Zircon sand sample numbering. In each chronological sequence A, the zircon sediment samples from each source (tributary) and sink (main stream) are uniformly numbered: the tributary numbers are 1, 2, 3...n, where n is the number of tributaries, and the main stream number is D.

[0036] (5) Weigh each zircon sand sample and select samples of the same weight to test the zircon mass percentage. The tributary sand samples are as follows: ( ),Right now( ), the dry flow sand sample is S D Sand samples of equal weight were taken and the mass percentage of zircon in each sample was determined using elemental geochemistry. The results are as follows: ( ),Right now( ) and C D .

[0037] (6) Measure the age spectrum of zircon from each sample. The number of tributary samples is n, and the number of characteristic age spectrum intervals for each sample is m. Then the age spectrum of each tributary is ( The writing matrix is... The main stream is ( ), that is, row matrix ( ).

[0038] (7) Construct the age spectrum matrix and solve for the zircon contribution rate. Calculate the contribution rate of zircons from each source (tributary) to the zircons in the sink (mainstream). As above, λ i It is a 1×n row matrix. For an n×m matrix, Given a 1×m row matrix, the solution matrix is ​​as follows:

[0039] (1)

[0040] (8) Calculate the mass contribution rate of each source. Considering that the zircon mass percentages of samples from different tributaries are different, the zircon contribution rate cannot be directly used as the mass contribution rate of each tributary to the sediment in the main stream. The zircon mass percentage of each sample must be substituted to calculate the contribution rate of each tributary to the sediment in the main stream. The weighted contribution rate of the tributaries is then... Assuming the sum of the contribution rates of all tributaries is 1, the formula for calculating the contribution rate of each tributary to the sediment inflow into the main stream is as follows:

[0041] (2)

[0042] (9) Calculate the contribution rate of each source at different times. By performing steps (4)-(8) on zircon sand samples from different times, the sediment source tracing results at multiple time scales can be obtained.

[0043] The following example illustrates this point:

[0044] Sediment source tracing was conducted at multiple sources in the Yangtze River source area. Six sources—Yagequ, Keqianqu, Chumar River, Beilu River, the upper reaches of the Tongtian River, and Moqu—were identified as M1, M2, S9, S10, S17, and S18, which converge into the lower reaches of the Tongtian River at S7. Sampling points are shown below. Figure 2 Historical sediments are not considered at this time; 1000g of surface sand was collected from each sampling point. The percentage zircon content from the six sources was measured in the laboratory to be 78, 178, 177, 117, 199, and 179 ppm, respectively.

[0045] The selected zircons were subjected to age spectral analysis, with an age range of 0–1800 Ma, evenly divided into 6 intervals. The age spectra of each source sample and the main stream sample S7 are as follows:

[0046] M1 (77,20,2,10,5,5), M2 (75,21,4,15,1,3), S9 (61,22,15,9,7,5), S10 (70,29,2 ,10,3,5), S17 (74,20,5,12,2,6), S18 (62,18,10,18,3,8), S7 (68,22,8,12,4,5)

[0047] Substituting the above age spectrum into formula (1), calculate λ. i This represents the zircon contribution rate of each source sample to the main stream:

[0048]

[0049] Then λ i Substitute the calculated results and zircon mass percentages (78, 178, 177, 117, 199, 179) into formula (2).

[0050] The contribution rate of M1, M2, S9, S10, S17, and S18 to S7 is:

[0051]

[0052] This invention has the following features and effects:

[0053] 1. Achieving multi-timescale source tracing: By combining optically stimulated luminescence (OLS) dating with zircon provenance tracing, zircon sand samples from different strata are divided into sequences according to age, reflecting both the current (nen shoal) sediment source and the historical (terraces, floodplain) sediment source, breaking through the limitations of traditional single timescales and providing multi-time period data support for watershed evolution research.

[0054] 2. Simplified contribution rate calculation process: The source-sink contribution rate algorithm is optimized, and the sink age spectrum is directly calculated from the source zircon age spectrum matrix. This avoids intermediate steps such as cumulative distribution function fitting and Monte Carlo simulation in traditional methods, reduces calculation errors, improves efficiency, and is suitable for rapid analysis in areas with scarce data.

[0055] 3. Improve the accuracy and applicability of traceability: Zircon's weather resistance ensures stable source signals, combined with a unified sampling standard (testing the percentage of zircon mass of the same weight) and

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for tracing the source of river sediment at multiple spatiotemporal scales, characterized in that, Includes the following steps: (1) Sampling point selection: Select cross sections containing terraces, floodplains and shoals in the tributaries and main streams of the river as sampling points; (2) Sample collection: Optically stimulated luminescence (OLS) samples were collected from the terraces and floodplains at the sampling points, and zircon sand samples from the corresponding layers and contemporary zircon sand samples from the tender beach were collected simultaneously. (3) Chronological sequence division: The OLS samples are subjected to chronological testing. Based on the test results, zircon sand samples of the same age are divided into at least one chronological sequence A, where each sequence A corresponds to a historical period. (4) Zircon sand sample numbering and pretreatment: In each chronological sequence A, the zircon sand samples from each tributary are numbered sequentially as follows: Where n is the number of tributaries, and the sand and gravel samples from the main stream are numbered S. D and weigh them separately; (5) Zircon mass percentage test: Test the zircon sand samples from each tributary. Zircon mass percentage and the zircon mass percentage of the dry sand sample D. ; (6) Zircon age spectrum analysis: testing each tributary sample The age spectrum is The age spectrum matrix P is obtained as follows: ， Where i=n, ​​j=m, m is the number of characteristic age intervals, and the age spectrum of the main stream sand and gravel sample D. The age spectrum row matrix P is obtained. D Where j = m; (7) Zircon contribution rate calculation: Based on the age spectrum matrix P and age spectrum row matrix P obtained in step (6) by the data processing unit. D Calculate the zircon contribution rate of each tributary to the main stream. ; (8) Quality contribution rate calculation: Based on the result obtained in step (5) by the data processing unit. C D And obtained in step (7) Calculate the quality contribution rate of each tributary to the main stream. ; (9) Multiple timescale tracing: the multiple chronological sequences divided in step (3) ,in To determine the number of historical periods, repeat steps (4) to (8) to obtain the sediment source tracing results for different historical periods.

2. The method according to claim 1, characterized in that, In step (3), the division of the chronological sequence A satisfies the following: zircon sand samples in the same sequence A come from the same strata in the source-sink area.

3. The method according to claim 1, characterized in that, In step (7), the matrix P is an n×m matrix, where rows represent tributary numbers and columns represent characteristic age intervals; the age spectrum row matrix P D It is a 1×m matrix, and its columns correspond one-to-one with the characteristic age ranges of matrix P.

4. The method according to claim 1, characterized in that, In step (7), according to the formula Calculate the zircon contribution rate of each tributary to the main stream. .

5. The method according to claim 1, characterized in that, In step (8), follow the formula Calculate the quality contribution rate of each tributary to the main stream. .

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