A method for marine biological fossil U-Pb dating based on LA-ICP-MS

Abstract

The application discloses a marine organism fossil U-Pb dating method based on LA-ICP-MS, and comprises the following steps: S1, according to stratigraphic division, marine organism fossils and iron manganese oxides of each layer are selected from a deep sea sediment column, and the rest is taken as a sediment residue; S2, the marine organism fossils are cleaned, and marine organism fossil target samples are prepared; S3, a laser ablation inductively coupled plasma mass spectrometer is used to perform laser ablation, point marking, sequencing and testing on the marine organism fossil target samples, and uranium lead isotope data is obtained; S4, baseline deduction and mapping are performed on the uranium lead isotope data, the lead isotope ratio of the sediment residue is anchored as an initial value to perform ordinary lead correction, and the age data of the marine organism fossils is obtained; the laser ablation mode is a line scanning mode. The marine organism fossil U-Pb dating method realizes dating test of marine organism fossils, and has high determination accuracy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical analysis, and particularly relates to a marine biological fossil U-Pb dating method based on LA-ICP-MS. BACKGROUND

[0002] Biological fossils are a cryptocrystalline apatite that constitutes the skeleton of vertebrates, and the U content thereof is low. During the fossilization process after the death of vertebrates, biological apatite is converted from hydroxyapatite to fluorapatite, and is accompanied by the crystal coarsening and cementation of pores, the content of trace elements (U, etc.) in the fossils is enriched, and the process is considered to be completed on the scale of thousands to tens of thousands of years. Therefore, determining the age of biological fossils has important significance for studying the chronology of strata, the distribution and evolution of paleoclimate environment in time and space.

[0003] Isotope dating, especially uranium-lead isotope dating (U-Pb dating), has wide applicability, and the testing techniques for U-Pb dating currently mainly have two kinds, one is secondary ion probe (SIMS), and the other is laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The secondary ion probe technology has the characteristics of micro-area originality, small sample consumption, and high precision (the external precision of uranium-lead dating can reach 1%), but its analysis speed is slow, and one point needs 15 minutes, so its use is less; and the laser ablation inductively coupled plasma mass spectrometer has the advantages of micro-area originality, fast analysis speed (2 minutes for one analysis point), simple sample preparation, and relatively high precision (the external precision of uranium-lead dating can reach 2-3 %), and is more widely used in the fields of geology, materials, biology, etc. So far, the U-Pb dating method based on LA-ICP-MS has been widely used in the dating test of terrestrial sedimentary strata, and not only realizes the dating test of titanite, garnet and zircon, but also successfully performs the dating test of terrestrial biological fossils, because the measured age is consistent with the data of paleomagnetism and biological chronology. However, due to the fact that the complexity of marine biological fossils is much higher than that of terrestrial biological fossils, the existing U-Pb dating method of terrestrial biological fossils based on LA-ICP-MS cannot accurately determine the age of marine biological fossils in the dating test.

[0004] Therefore, it is of great significance to develop a marine biological fossil U-Pb dating method based on LA-ICP-MS to accurately determine the age of marine biological fossils. SUMMARY

[0005] The purpose of the present application is to solve the problem that the existing U-Pb dating method of terrestrial biological fossils based on LA-ICP-MS cannot accurately determine the age of marine biological fossils, and to provide a marine biological fossil U-Pb dating method based on LA-ICP-MS.

[0006] In order to achieve the above object, the application adopts the following technical scheme:

[0007] A marine organism fossil U-Pb dating method based on LA-ICP-MS comprises the following steps:

[0008] S1. According to stratigraphic division, marine organism fossils and iron-manganese oxides of each layer are selected from a deep-sea sediment column, and the remaining ones are used as sediment residues;

[0009] S2. The marine organism fossils are cleaned and made into marine organism fossil target samples;

[0010] S3. Laser ablation, spot marking, sequencing and testing are performed on the marine organism fossil target samples by using a laser ablation inductively coupled plasma mass spectrometer to obtain uranium-lead isotope raw data;

[0011] S4. Baseline deduction and mapping are performed on the uranium-lead isotope raw data, ordinary lead correction is performed by anchoring the lead isotope ratio of the sediment residues as the initial value, and linear fitting is performed to obtain the age data of the marine organism fossils;

[0012] The laser ablation mode is a line scanning mode.

[0013] The lead isotope ratio of the application refers to 207 Pb / 206 Pb, and the uranium-lead isotope raw data is obtained by LA-ICP-MS.

[0014] The marine organism fossil U-Pb dating method based on LA-ICP-MS developed by the application by jointly selecting the line scanning mode and the ordinary lead correction by anchoring the lead isotope ratio of the sediment residues as the initial value realizes the dating test of the marine organism fossils, and has high determination accuracy.

[0015] Specifically, when the uranium-lead isotope data of the marine organism fossils is mapped, if ordinary lead correction is not performed, the horizontal coordinates of all test points in the Tera-Wasserburg diagram will be 238 U / 206The Pb values are similar, and the lower intersection age (representing the age of marine biological fossils in the application) cannot be obtained by linear fitting due to the concentration of all test points. For this reason, terrestrial biological fossils often use the crustal lead isotope evolution model for ordinary lead correction, but this method is not suitable for marine biological fossils, and the age determination of marine biological fossils may be inaccurate. The application corrects the ordinary lead by anchoring the lead isotope ratio of the sediment residue to the initial value, avoids the concentration of all test points in the Tera-Wasserburg diagram, successfully detects the lower intersection age, and accurately determines the age of marine biological fossils.

[0016] Compared with ordinary apatite, marine biological fossils are easy to burn under single-point laser ablation due to their unique structure and shape, resulting in a larger ablation surface and a deeper ablation depth, thereby affecting the signal stability and persistence of LA-ICP-MS, losing continuous and stable signals or shortening the stable signals, which seriously affects the dating test of marine biological fossils and loses the accuracy of the dating test or even cannot detect the age of marine biological fossils. When the application selects the line scanning mode instead of the single-point mode, the above problems are overcome, and the age of marine biological fossils is successfully and accurately determined.

[0017] Preferably, the step S1 is specifically: under a binocular stereomicroscope, marine biological fossils and iron-manganese oxides of each layer are selected from the deep-sea sediment column by tweezers according to stratigraphic division, and the remaining is used as a sediment residue.

[0018] Preferably, the marine biological fossils are one or both of fish teeth and fish bones.

[0019] Further preferably, the fish teeth are one or both of complete fish teeth and broken fish teeth.

[0020] In the application, the complete fish teeth refer to fish teeth containing complete enamel and dentin, i.e., the dentin is covered with enamel on both sides and has a cusp; and the broken fish teeth do not have complete enamel and dentin, i.e., the dentin is covered with enamel on one side or has no cusp.

[0021] Preferably, the diameter of the marine biological fossils is > 30 μm.

[0022] Preferably, the step S2 is specifically: the marine biological fossils are ultrasonically cleaned with an ethanol and hydrogen peroxide mixed solution, then placed at the bottom of a standard circular target mold, poured with resin and a curing agent and vacuumized, polished with diamond suspension after polishing to expose the surface of the marine biological fossils, and then polished with diamond suspension to obtain a marine biological fossil target sample.

[0023] Since marine fossils are generally covered with iron and manganese oxides, this invention uses a mixed solution of ethanol and hydrogen peroxide to ultrasonically clean the marine fossils to remove the iron and manganese oxides from their surface. This avoids interference and influence of iron and manganese oxides on uranium-lead isotope data and the age data of marine fossils, improves the accuracy of the dating method, and enables more accurate determination of the age of marine fossils.

[0024] More preferably, the ethanol and hydrogen peroxide mixed solution is prepared by mixing anhydrous ethanol solution and 30% hydrogen peroxide solution at a volume ratio of (1~4):1.

[0025] More preferably, the mass ratio of the resin to the curing agent is (1~2):1.

[0026] The resins and curing agents used in this invention are commonly used resins and curing agents in the art. Specifically, the resin is one or more of phenolic resin, epoxy resin, urea-formaldehyde resin, melamine-formaldehyde resin, furan resin, silicone resin, polyester resin, polyamide resin, acrylic resin, polyurethane, vinyl resin, hydrocarbon resin, or polyether resin; the curing agent is one or two of amine curing agents or acid anhydride curing agents; the amine curing agent is one or more of polyamide curing agents, aliphatic amine curing agents, aromatic amine curing agents, alicyclic amine curing agents, polyether amine curing agents, or imidazole curing agents.

[0027] Preferably, step S3 specifically involves: turning on the laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), tuning it, performing laser ablation in a line scan mode, setting the laser ablation parameters, and selecting the element to be measured as... 238 U、 204 Pb, 206 Pb and 207 By setting the integration time for Pb and U, as well as the total collection time, the marine fossil target sample was marked with selected points. Then, the test points selected from the marine fossil target sample, the international standard apatite Durango, and the international standard apatite Madagascar were subjected to a sorting experiment to obtain the raw uranium-lead isotope data of the selected test points, the international standard apatite Durango, and the international standard apatite Madagascar on the marine fossil target sample.

[0028] More preferably, the tuning solution is a nitric acid solution containing Li, Mg, Y, Ce, Tl and Co.

[0029] More preferably, the laser ablation parameters are: the diameter of the laser ablation beam spot is 32~60μm, the frequency is 4~10Hz, the line scanning speed is 2~4μm / s, and the laser ablation time is ≥30s.

[0030] The present application controls the line scanning speed and the laser ablation time, so that the ablation length of the laser ablation is greater than or equal to 60 microns.

[0031] Further preferably, the integration time of the Pb and U is 0.02-0.04 s and 0.006-0.02 s, respectively.

[0032] Further preferably, the total collection time is 85-95 s.

[0033] Further preferably, the sorting experiment is: sorting all the test points selected from the marine fossil target sample, inserting the international standard apatite Durango and the international standard apatite Madagascar twice every 6-10 test points selected from the marine fossil target sample, and inserting the international standard apatite Durango and the international standard apatite Madagascar twice at the beginning and the end of all the test points selected from the marine fossil target sample.

[0034] In the present application, the international standard apatite Durango and the international standard apatite Madagascar are used to monitor the signal drift and the background signal of the LA-ICP-MS.

[0035] In the sorting experiment of the present application, if the signal of the LA-ICP-MS appears a signal peak when testing a test point selected from the marine fossil target sample, the test point needs to be abandoned, and other test points are selected to retest.

[0036] Preferably, the step S4 is specifically: using the Iolite software to perform baseline subtraction on the uranium-lead isotope raw data of the test points selected from the marine fossil target sample, the international standard apatite Durango and the international standard apatite Madagascar, and then using the IsoplotR software (isotope online processing software) to perform Wetherill and Tera-Wasserburg concordia diagram plotting, anchoring the lead isotope ratio of the sedimentary residue as the initial value to perform common lead correction, and linear fitting to obtain the age data of the marine fossil.

[0037] Preferably, the test method of the lead isotope ratio of the sedimentary residue in the step S4 is:

[0038] The deposition residue is dried in a freeze dryer, and then digested in a high-pressure PTFE gas cylinder using a mixed solution of perchloric acid, hydrofluoric acid and nitric acid, placed in an oven at 200 DEG C for 72 hours, and then evaporated to near dryness in an electric furnace, and redissolved in a solution of hydrobromic acid and nitric acid before ion exchange purification; Pb is separated out using a Biorad AG-X8 anion exchange column, and then washed with a solution of hydrobromic acid and nitric acid, and eluted with Mill-Q water; the Pb fraction is not pure at this time, and needs to be further purified using a second anion exchange column, and the anion resin is discarded after each separation; finally, the eluent containing Pb is evaporated to dryness, redissolved in nitric acid, and spiked with Tl. 205 Tl / 203 Tl=2.3885, and the Pb isotope ratio is measured using a multi-receiver inductively coupled plasma mass spectrometer.

[0039] Further preferably, the hydrofluoric acid in the mixed solution of perchloric acid, hydrofluoric acid and nitric acid is 40wt% hydrofluoric acid, the nitric acid is 60wt% nitric acid, and the perchloric acid is 50wt% perchloric acid.

[0040] Further preferably, the volume ratio of perchloric acid, hydrofluoric acid and nitric acid in the mixed solution of perchloric acid, hydrofluoric acid and nitric acid is (1-2):(2-4):(1-2).

[0041] Compared with the prior art, the beneficial effects of the present application are:

[0042] The marine biological fossil U-Pb dating method based on LA-ICP-MS developed by the present application through the joint selection of the line scanning mode and the anchoring of the initial value of the Pb isotope ratio of the deposition residue for ordinary Pb correction realizes the dating test of marine biological fossils, and has high determination accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 For the line scanning mode of the laser ablation inductively coupled plasma mass spectrometer in Example 1, 238 U, 206 Pb and 207 Pb signal intensity-time curves.

[0044] Figure 2 For marine biological fossils 238 U signal intensity-time curves under different laser ablation modes; Figure 2a is the marine biological fossils when taking single point method in comparative example 1 238 a signal intensity of U over time, Figure 2 b is the marine biological fossils when taking line scanning method in example 1 238 a signal intensity of U over time.

[0045] Figure 3 a marine biological fossils age data graph of example 1; Figure 3 a Tera-Wasserburg graph of marine biological fossils of example 1, Figure 3 b Wetherill graph of marine biological fossils of example 1.

[0046] Figure 4 Wetherill graph of marine biological fossils of comparative example 2. DETAILED DESCRIPTION

[0047] The application will be further described in conjunction with the examples. These examples are only used to illustrate the application and are not used to limit the scope of the application. The experimental methods in the following example are not specified, which are usually according to the conventional conditions or according to the conditions suggested by the manufacturer; the raw materials, reagents, etc. used, if not specifically stated, are all raw materials and reagents that can be obtained commercially from conventional markets. Any non-essential changes and substitutions made by those skilled in the art on the basis of the application shall fall within the scope of the application.

[0048] Example 1

[0049] The present embodiment provides a marine biological fossil U-Pb dating method based on LA-ICP-MS, comprising the following steps:

[0050] S1. Under the binocular stereomicroscope, marine biological fossils and iron-manganese oxides of each layer are selected from the deep-sea sediment column according to stratigraphic division with tweezers, and the remaining is used as sediment residue;

[0051] S2. The marine biological fossils are ultrasonically cleaned with a mixed solution of ethanol and hydrogen peroxide, then placed at the bottom of a standard circular target mold with a diameter of 2.54 cm, poured with resin and curing agent and vacuumized, after curing, polished with diamond suspension to obtain a marine biological fossil target sample;

[0052] S3. Turn on the laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) and tune it, take line scanning method for laser ablation, and set the laser ablation parameters, select the elements to be measured as 238 U, 204 Pb, 206 Pb and 207Pb was used to select and mark points on marine fossil target samples, and then the test points selected from the marine fossil target samples, the international standard apatite Durango, and the international standard apatite Madagascar were used to conduct an ordination experiment to obtain the uranium-lead isotope data of the test points selected from the marine fossil target samples, the international standard apatite Durango, and the international standard apatite Madagascar.

[0053] S4. Using Iolite software, baseline subtraction was performed on the raw uranium-lead isotope data of the selected test points on the marine fossil target sample, as well as the international standard apatite Durango and international standard apatite Madagascar. Then, IsoplotR software (online isotope processing software) was used to plot the Wetherill and Tera-Wasserburg concordance diagrams. The lead isotope ratio of the sedimentary residue was used as the initial value for ordinary lead correction, and linear fitting was performed to obtain the age data of the marine fossils.

[0054] in:

[0055] The marine fossils in step S1 are complete fish teeth, broken fish teeth, and fish bones with a diameter >30μm;

[0056] The ethanol and hydrogen peroxide mixed solution in step S2 is prepared by mixing anhydrous ethanol solution and 30% hydrogen peroxide solution at a volume ratio of 2:1; the mass ratio of resin to curing agent is 2:1, the resin is epoxy resin, and the curing agent is polyamide curing agent;

[0057] The tuning solution in step S3 is a 2% nitric acid solution containing 1 µg / L Li, Mg, Y, Ce, Tl, and Co; the laser ablation parameters are: laser ablation beam spot diameter of 32~60 μm, frequency of 5 Hz, line scan speed of 2 μm / s, laser ablation time ≥30s, and laser ablation length ≥60 μm; the integration times of Pb and U are 0.02s and 0.006s, respectively; the total collection time is 90s; the sorting experiment is as follows: all test points (60 in total) selected from the marine fossil target sample are sorted, and every 10 test points selected from the marine fossil target sample are inserted twice with international standard apatite Durango and twice with international standard apatite Madagascar, and at the beginning and end of all test points selected from the marine fossil target sample, two insertions of international standard apatite Durango and two insertions of international standard apatite Madagascar are made.

[0058] The method for testing the lead isotope ratio of the sediment residue in step S4 is as follows:

[0059] The deposition residue was dried in a freeze-drier for 24 hours, then digested in a high pressure PTFE bomb with a 1:2:1 volume ratio of 50 wt% perchloric acid, 40 wt% hydrofluoric acid and 60 wt% nitric acid mixture, left in a 200°C oven for 72 hours, then evaporated to near dryness on a hot plate and re-dissolved in hydrobromic and nitric acid solutions before ion exchange purification; Pb was first separated using a Biorad AG-X8 anion exchange column, then washed with 0.2N hydrobromic and 0.5N nitric acid solutions, and eluted with Mill-Q water; the Pb fraction was not pure at this point and required a second anion exchange column for further purification, with the anion resin discarded after each separation; finally, the Pb containing eluate was evaporated to dryness and re-dissolved in 1.0 ml of 2 wt% nitric acid with 10 ppb Tl added. The raw data for the Pb isotope ratios were internally corrected for mass fractionation using the exponential law normalisation to 205Tl / 203Tl = 2.3885, and the Pb isotope ratios of the deposition residue solution were measured using a multi-collector inductively coupled plasma mass spectrometer.

[0060] Example 2

[0061] This example provides a LA-ICP-MS based U-Pb dating method for marine biological fossils, which differs from example 1 in that the marine biological fossils in step S1 are fish bones with a diameter > 30 μm, and the rest are consistent with example 1.

[0062] Example 3

[0063] This example provides a LA-ICP-MS based U-Pb dating method for marine biological fossils, which differs from example 1 in that the marine biological fossils in step S1 are complete fish teeth and broken fish teeth with a diameter > 30 μm, and the rest are consistent with example 1.

[0064] Example 4

[0065] This example provides a LA-ICP-MS based U-Pb dating method for marine biological fossils, which differs from example 1 in that the marine biological fossils in step S1 are complete fish teeth with a diameter > 30 μm, and the rest are consistent with example 1.

[0066] Example 5

[0067] The embodiment provides a LA-ICP-MS-based marine biological fossil U-Pb dating method, which is different from the embodiment 1 in that the marine biological fossil in the step S1 is a broken fish tooth with a diameter of >30 mu, and the rest is the same as the embodiment 1.

[0068] Comparative example 1

[0069] The comparative example provides a LA-ICP-MS-based marine biological fossil U-Pb dating method, which is different from the embodiment 1 in that the step S3 is replaced by a single-point mode instead of a line scanning mode, and the rest is the same as the embodiment 1.

[0070] Comparative example 2

[0071] The comparative example provides a LA-ICP-MS-based marine biological fossil U-Pb dating method, which is different from the embodiment 1 in that the step S4 is not anchored to the lead isotope ratio of the sediment residue, and the rest is the same as the embodiment 1.

[0072] Sample characterization

[0073] Figure 1 For the embodiment 1, when the laser ablation inductively coupled plasma mass spectrometer adopts a line scanning mode, 238 U, 206 Pb and 207 Pb signal intensity changes with time. From Figure 1 It can be known that the line scanning mode adopted by the application can maintain the signal stability and persistence of LA-ICP-MS, the signal is continuous and smooth, the collection time of the smooth signal can reach 40s, and the signal data error is small, which is beneficial to accurately determine the age of the marine biological fossil.

[0074] Figure 2 For marine biological fossils 238 U signal intensity changes with time under different laser ablation modes; Figure 2 a is the marine biological fossil 238 U signal intensity changes with time when the single-point mode is adopted in the comparative example 1, Figure 2 b is the marine biological fossil 238 U signal intensity changes with time when the line scanning mode is adopted in the embodiment 1. From Figure 2 It can be known that when the line scanning mode is adopted, the marine biological fossil 238 U signal is continuous and smooth, and the collection time of the smooth signal can reach 40s, which can be used for dating test of the marine biological fossil, because the marine biological fossil U-Pb dating method of the application requires that the laser ablation time is greater than or equal to 30s; when the single-point mode is adopted, the marine biological fossil 238The signal stability and persistence of U is poor, and the effective signal is only 10s, which does not meet the requirements of the marine biological fossil U-Pb dating method of the application, and cannot be used for dating test of the marine biological fossil.

[0075] Figure 3 is a marine biological fossil age data graph of Example 1; Figure 3 a is a Tera-Wasserburg graph of the marine biological fossil of Example 1, Figure 3 b is a Wetherill graph of the marine biological fossil of Example 1. Figure 4 is a Wetherill graph of the marine biological fossil of Comparative Example 2. Figure 3 and Figure 4 It can be seen that when the lead isotope ratio of the anchoring sediment residue is corrected as the initial value, the Lower intercept = 4981.26 ± 2.62Ma (n = 100) is the initial setting value, which indicates that the marine biological fossil age of Comparative Example 2 cannot be detected; and the application corrects the lead isotope ratio of the anchoring sediment residue as the initial value, avoids the concentration of all test points in the Tera-Wasserburg graph, obtains a good linear fitting effect, successfully detects the lower intersection age Age = 18.88 ± 3.16Ma (n = 100) of the marine biological fossil, and has high determination accuracy, and the weighted mean square deviation MSWD = 0.97.

[0076] In addition, the marine biological fossil age data graphs of Examples 2-5 are similar to the marine biological fossil age data graph of Example 1. Figure 3 It can be seen that when the lead isotope ratio of the anchoring sediment residue is corrected as the initial value, the Lower intercept = 4981.26 ± 2.62Ma (n = 100) is the initial setting value, which indicates that the marine biological fossil age of Comparative Example 2 cannot be detected; and the application corrects the lead isotope ratio of the anchoring sediment residue as the initial value, avoids the concentration of all test points in the Tera-Wasserburg graph, obtains a good linear fitting effect, successfully detects the lower intersection age Age = 18.88 ± 3.16Ma (n = 100) of the marine biological fossil, and has high determination accuracy, and the weighted mean square deviation MSWD = 0.97.

[0077] Obviously, the above examples of the application are only examples for clearly illustrating the application, and are not intended to limit the embodiments of the application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all embodiments are not required to be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the claims of the application.

Claims

1. A U-Pb dating method for marine biological fossils based on LA-ICP-MS, characterized in that, Includes the following steps: S1. Based on stratigraphy, marine fossils and iron-manganese oxides from each layer of the deep-sea sediment column are selected, while the rest are treated as sedimentary residues. S2. Clean the marine fossils and prepare marine fossil target samples; S3. Laser ablation inductively coupled plasma mass spectrometry was used to perform laser ablation, site selection, sorting and testing on marine biological fossil target samples to obtain raw uranium-lead isotope data; S4. Baseline subtraction and mapping are performed on the raw uranium-lead isotope data. The lead isotope ratio of the anchored sediment residue is used as the initial value for ordinary lead correction. Linear fitting yields the age data of marine fossils. The laser ablation method is a line scanning method; The marine fossils are one or both of fish teeth or fish bones; The laser ablation time in step S3 is ≥30s; The method for testing the lead isotope ratio of the sedimentary residue in step S4 is as follows: The deposited residue was dried in a freeze dryer, then digested in a high-pressure PTFE cylinder with a mixture of perchloric acid, hydrofluoric acid, and nitric acid. The residue was then placed in a 200°C oven for 72 hours. The digested sample was then heated in an electric furnace to near dryness and reconstituted in hydrobromic acid and nitric acid before ion exchange purification. Pb was first separated using a Biorad AG-X8 anion exchange column, then washed with hydrobromic acid and nitric acid, followed by elution with Mill-Q water. The Pb fraction was impure at this point and required further purification using a second anion exchange column; the anion exchange resin was discarded after each separation. Finally, the Pb-containing eluent was evaporated to dryness, redissolved in nitric acid, and incorporated with Tl. NIST SRM 981 was used as the instrument drift calibration standard, and USGS BCR-2, BHVO-2, AGV-2, and RGM-2 were used as quality control reference materials. The raw Pb isotope ratio data were normalized to Pb using the exponential law. 205 Tl / 203 Internal calibration was performed for mass fractionation at Tl=2.3885, and the lead isotope ratio of the deposited residue solution was measured using a multi-receiver inductively coupled plasma mass spectrometer.

2. The U-Pb dating method for marine fossils according to claim 1, characterized in that, Step S2 specifically involves ultrasonically cleaning marine fossils using a mixed solution of ethanol and hydrogen peroxide.

3. The U-Pb dating method for marine fossils according to claim 2, characterized in that, The ethanol and hydrogen peroxide mixed solution was prepared by mixing anhydrous ethanol solution and 30% hydrogen peroxide solution at a volume ratio of (1~4):

1.

4. The U-Pb dating method for marine fossils according to claim 1, characterized in that, Step S3 specifically involves: turning on the laser ablation inductively coupled plasma mass spectrometer, tuning it, performing laser ablation in a line scan mode, setting the laser ablation parameters, and selecting the element to be measured. 238 U、 204 Pb, 206 Pb and 207 By setting the integration time for Pb and U, as well as the total collection time, the marine fossil target sample was marked with selected points. Then, the test points selected from the marine fossil target sample, the international standard apatite Durango, and the international standard apatite Madagascar were subjected to a sorting experiment to obtain the uranium-lead isotope data of the selected test points, the international standard apatite Durango, and the international standard apatite Madagascar.

5. The U-Pb dating method for marine fossils according to claim 4, characterized in that, The laser ablation parameters are: line scan speed of 2~4μm / s.

6. The U-Pb dating method for marine fossils according to claim 4 or 5, characterized in that, The laser ablation parameters are as follows: the diameter of the laser ablation beam spot is 32~60μm, and the frequency is 4~10Hz.

7. The U-Pb dating method for marine fossils according to claim 4, characterized in that, The integration times for Pb and U are 0.02~0.04s and 0.006~0.02s, respectively.

8. The U-Pb dating method for marine fossils according to claim 4, characterized in that, The sorting experiment was conducted as follows: all test points selected from marine fossil target samples were sorted, and every 6 to 10 test points selected from marine fossil target samples were inserted twice for international standard apatite Durango and twice for international standard apatite Madagascar. Furthermore, at the beginning and end of all test points selected from marine fossil target samples, two international standard apatite Durango and two international standard apatite Madagascar were inserted.

9. The U-Pb dating method for marine fossils according to claim 1, characterized in that, Step S4 specifically involves: using Iolite software to perform baseline subtraction on the uranium-lead isotope data of the selected test points on the marine fossil target sample, the international standard apatite Durango, and the international standard apatite Madagascar; then using IsoplotR software to plot the Wetherill and Tera-Wasserburg concordia diagrams; and using the lead isotope ratio of the anchored sedimentary residue as the initial value for ordinary lead correction to obtain the age data of the marine fossils.

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