A method for quantitatively simulating a geological history period microbial dolomite deposition mechanism

Abstract

The application discloses a kind of geologic history period microbial dolomite deposition mechanism quantitative simulation calculation method, which comprises the following steps: accurately assess whether the signal of original depositional environment of sample is preserved during deposition period, calculate the concentration of pH value, total alkalinity, calcium ion and magnesium ion of paleoseawater during deposition period, reconstruct the attribute parameter of paleoseawater in geologic history period, quantitatively analyze the different influence of the difference of physical and chemical conditions of paleoseawater on the deposition process of microbial dolomite, simulate and calculate the microbial dolomite genesis mechanism and process in geologic history period.The application quantitatively and comprehensively studies the microbial dolomite genesis mechanism, and can provide new ideas for the genesis of similar dolomite in geologic history period and the comprehensive solution of the old mystery "dolomite problem".

Description

Technical Field

[0001] This invention belongs to the fields of sedimentology and unconventional isotope geochemistry, specifically relating to a quantitative simulation and calculation method for the sedimentary mechanism of microbial dolomite during geological history. Background Technology

[0002] The "dolomite problem" is a century-old enigma in sedimentology that has remained unsolved. At its core lies the contradiction between the apparent scarcity of dolomite in modern marine sedimentary environments and its relative abundance in geological history. The essence of this problem is: how, where, when, and under what physicochemical conditions did dolomite form at low temperatures?

[0003] Seawater, as the largest site and element reservoir for the precipitation of various carbonate minerals on Earth, is rich in elements such as magnesium and calcium, which are essential for carbonate mineral precipitation. The molar concentration of magnesium ions is approximately five times that of calcium ions, far exceeding the concentration of calcium. The saturation index (Ω) is used to characterize whether minerals can precipitate in aqueous solution within a sedimentary environment: Ω = log(IAP / K) sp ), where IAP is the ion activity product, K sp It is the solubility product constant. At equilibrium, Ω = 0. If IAP > K sp If the minerals are precipitated, the solution is saturated and minerals will precipitate; otherwise, the solution is unsaturated.

[0004] Arvidson and Mackenzie, through computational simulations, concluded that under standard conditions (i.e., T = 25℃; P = 1 atm), ordered dolomite K... sp Approximately 10 -17 According to the known amount of Ca in seawater 2+ Mg 2+ and CO3 2- The activity of these IAPs is approximately 10. -15.01 Order of magnitude, IAP > K sp However, under the conditions of the Earth's surface, dolomite does not precipitate in seawater. Land used different materials such as magnesium calcite, dolomite powder, red algae, bryozoans, and octocorals to design different experiments. Over the course of 32 years, he still failed to precipitate orderly dolomite at 25°C.

[0005] Under normal temperature and pressure, only with the addition of microbial factors can primary dolomite be directly precipitated from solution under microbial mediation (by Xue Lian et al., 2011, 2018; You et al., 2015). Current research shows that under anaerobic conditions, sulfate-reducing bacteria (SRB) can promote the precipitation of primary dolomite; methanogenic anaerobic bacteria also play an important role in promoting dolomite precipitation; even under normal seawater salinity conditions, the marine sulfate-reducing strain *D. mediterraneus* can precipitate primary dolomite at 21°C. In aerobic environments, moderately halophilic aerobic bacteria in some lagoons can precipitate ordered dolomite crystals, even under SO42---. 2- Concentration of 56 mM (SO4 in seawater) 2- Even at low temperatures (concentration of 28.2 mM), dolomite still precipitates.

[0006] The Ediacaran–Cambrian (E–C) period was a crucial time in Earth's history, marked by significant changes in the Earth's surface environment and biological systems. For example, the Early Cambrian, compared to the Precambrian, saw important evolutions in marine ecology (the arrival of metazoans and dung pellets) and geochemistry (an increase in sulfate concentration). The oceanic redox state during the Early Cambrian exhibited a dynamic and heterogeneous spatiotemporal structure. With the continuation of the Late Neoproterozoic Great Oxidation Event, the overall degree of marine oxidation during the Ediacaran–Cambrian transition generally intensified amidst fluctuations. From the Late Ediacaran to the Early Cambrian, widespread anoxic ferritic deposits (containing free Fe) developed in the deep ocean. 2+ Early Cambrian deep-sea waters were characterized by anoxic sulfidation (containing free H2S) or hypoxic sulfidation. By Stage 3 (~521 Ma), ocean oxygen levels may have approached present-day levels, with deep-sea oxidation gradually increasing and promoting metazoan radiation. However, recent research suggests that under low atmospheric oxygen levels (~10–40% PAL), the Early Cambrian deep sea was generally characterized by anoxic waters; widespread deep-sea oxidation may have begun in Stage 4. Anoxic sulfidation areas resembled the present-day oxygen minimum zone at the continental shelf margin, their scale controlled by sea-level fluctuations (marine transgression-regression), and factors such as low ocean sulfate concentrations and dynamic sulfate supply from rivers. On the other hand, Early Cambrian ocean sulfate concentrations increased significantly compared to the Precambrian (~<1 mM), but remained generally low compared to the present-day ocean (~28 mM). (Seawater sulfate δ) 34The sulfur (S) value gradually increased from a low level (15-20‰) in the Neoproterozoic before 750 Ma to a peak (nearly 40‰) in the Early Cambrian, and then gradually decreased to about 28‰ in the Middle Cambrian. Early studies based on sulfur isotope models showed that the marine sulfate concentration in the Early Cambrian increased significantly, possibly reaching ~10 mM or higher, due to enhanced sulfide reoxidation caused by biological disturbance of sediments. However, recent model reconstructions show that the marine sulfate concentration was low throughout the Cambrian, either less than ~2 mM or about 5–10 mM. Therefore, there is no consensus on the quantitative reconstruction of the Early Cambrian marine sulfate concentration, but it is generally shown that the marine sulfate concentration was low and may have significant spatiotemporal differences.

[0007] Modern sedimentary dolomite is rarely found in environments such as the subtidal environment of the Arabian Gulf (also known as the Persian Gulf), supratidal dolomite crusts of Lake Coorondale in South Australia and Andros Island in the Bahamas, Lake Lagoa Vermelha near Rio de Janeiro, Brazil, and Pleistocene dolomite found in organic-rich sediments in the deep-sea Gulf of California, on the edge of California, during the Deep Sea Drilling Project (DSDP).

[0008] The dolomite stratigraphic sequences from the E–C periods in the Yangtze and Tarim regions of my country are well-developed and widely distributed, yielding fruitful results in paleomarine environments and biological evolution. For example, the entire Tarim Basin is characterized by a thick Lower Paleozoic carbonate rock system. As an important oil and gas basin in my country, a number of oil and gas wells (fields) with dolomite as reservoirs have been discovered, including wells 1 and 162 in Tazhong, wells 2, 15, and 7 in Shashen in Tabei, and wells 2, 3, and 4 in the Bachu-Hetianhe gas field. Since the 1990s, Chinese geologists have conducted extensive and detailed research on the genesis and dolomitization models of dolomite in the Tarim Basin, proposing a series of mechanisms, including quasi-syngenetic dolomitization (evaporation-pumping and reflux permeation models), atmospheric freshwater / seawater mixed dolomitization, deep-buried dolomitization, and hydrothermal dolomitization. However, these studies all focus on metasomatic dolomite. Current technologies do not incorporate microbial factors to re-verify microbial dolomite from geological history, nor do they consider using big data and ion-associated water models to quantitatively reconstruct the property parameters of ancient seawater from geological history, thus failing to provide new ideas for solving the ancient mystery of the "dolomite problem."

[0009] Therefore, providing a quantitative simulation method for the depositional mechanism of microbial dolomite during geological history has become an urgent technical problem to be solved in this field. Summary of the Invention

[0010] To address the aforementioned shortcomings in the existing technology, the present invention aims to provide a quantitative simulation and calculation method for the depositional mechanism of microbial dolomite during geological history.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0012] A quantitative simulation method for the sedimentary mechanism of microbial dolomite during geological history is provided, which includes the following steps:

[0013] To accurately assess whether samples preserve signals of the original sedimentary environment during the depositional period, unconventional isotopic methods are used to calculate the pH, total alkalinity, and concentrations of calcium and magnesium ions in the paleoseawater during the depositional period. This allows for the reconstruction of the property parameters of the paleoseawater during geological history. The different physical and chemical conditions of the paleoseawater have a quantitative impact on the depositional process of microbial dolomite. Finally, the genetic mechanism and process of microbial dolomite formation during geological history are quantitatively simulated and calculated.

[0014] First, we can use different methods (petrology, petrography, isotope geochemistry, unconventional isotopes, etc.) to accurately assess whether microbial dolomite in geological history has preserved the original sedimentary environment signals of the depositional period and has rarely undergone diagenetic alteration.

[0015] Furthermore, the composition and evolution of strontium in marine carbonate rocks can determine the continental weathering rate by the ratio of two end-members, thus reconstructing the total alkalinity of ancient seawater.

[0016] Furthermore, by measuring the unconventional stable isotope boron isotope of marine carbonate rocks that can represent the original sedimentary environment during geological history, the pH value of ancient seawater during geological history can be quantitatively reconstructed.

[0017] Furthermore, by applying big data and ion-associated water models, and with the help of PHREEQC, we quantitatively calculated the influence and constraints of paleoseawater pH, total alkalinity, calcium ions, and magnesium ions on the types of minerals formed and the saturation index during the sedimentation period, and simulated the geochemical inversion process.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention reconstructs the unique properties of ancient seawater from geological history and quantitatively simulates the different impacts that variations in the physical and chemical conditions of ancient seawater may have on the depositional process of microbial dolomite. By incorporating microbial factors to re-verify microbial dolomite from geological history, and applying big data and ion-associated water models, the property parameters of ancient seawater from geological history are quantitatively reconstructed, providing new insights into solving the age-old mystery of the "dolomite problem." Detailed Implementation

[0020] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0021] Example

[0022] A quantitative simulation method for the sedimentary mechanism of microbial dolomite during geological history includes the following steps:

[0023] To accurately assess whether samples preserve signals of the original sedimentary environment during the depositional period, unconventional isotopic methods are used to calculate the pH, total alkalinity, calcium ion and magnesium ion concentrations of paleoseawater during the depositional period, reconstruct the property parameters of paleoseawater during geological history, quantitatively analyze the different effects of differences in the physical and chemical conditions of paleoseawater on the depositional process of microbial dolomite, and quantitatively simulate and calculate the genetic mechanism and process of microbial dolomite formation during geological history.

[0024] Specifically, it includes the following:

[0025] Non-marine environments 87 Sr / 86 Sr ratio and seawater 87 Sr / 86 The Sr ratio is highly identifiable for both river and lake water. 87 Sr / 86 Sr is not only higher than that of mantle-derived basaltic rocks 87 Sr / 86 Sr, and the range of variation is large (0.712–0.726), with the specific ratio clearly depending on the age of the basement rocks through which the rivers and lakes flow and their Rb / Sr ratios, especially for river and lake water supplying silicate rock areas. 87 Sr / 86 The Sr ratio is higher than that of seawater. Strontium has a long residence time in seawater, reaching up to 10. 6 Years, far greater than 10 times the sea level 3 The mixing time of strontium in seawater is 1000 times longer than the mixing time of seawater. Therefore, on a geological timescale of millions of years, strontium in seawater is thoroughly mixed and highly homogeneous. This means that the strontium isotopic composition of seawater globally remains consistent across any given era. Thus, the geological history of seawater... 87 Sr / 86The Sr ratio is only related to time; it is a function of time. In 1948, Swedish geologist Wickman hypothesized that the isotopic composition of elements in seawater might be very close to the average value of the Earth's crust, while that in the continental crust... 87 The decay of Rb makes seawater 87 Sr / 86 The Sr ratio increases rapidly, thus causing the seawater 87 Sr / 86 Sr becomes an effective timer. Furthermore, rubidium hardly enters the carbonates and sulfates precipitated in seawater, so these minerals... 87 Sr / 86 The variation in the Sr ratio depends on the seawater during sedimentation. 87 Sr / 86 Sr ratio.

[0026] The composition of strontium isotopes in seawater is mainly controlled by strontium from both crustal and mantle sources. In other words, seawater strontium is a product of the mixture of these two sources. Crust-derived strontium primarily comes from the weathering of ancient continental sialic rocks and is transported to the ocean via rivers. Because crustal materials are rich in rubidium, their decay processes contribute to the weathering of continental rocks. 87 Sr / 86 The Sr ratio is relatively high, consistently greater than that of strontium in seawater. The global average estimate for modern rivers is approximately 0.712 ± 0.001, with a flux of 3.3 × 10⁻⁶. 10 mol / a, global 87 Sr / 86 The average Sr value can reach 0.7119; mantle-derived strontium is mainly supplied by hydrothermal vents in mid-ocean ridges or fluid systems associated with magmatic activity. Seawater in the mid-ocean ridge region is drawn into the hydrothermal circulation system, and the lost strontium is replaced by strontium leached from the basalt of the mid-ocean ridge. 87 Sr / 86 The Sr ratio is close to 0.703, and the flux is 1.0 × 10⁻⁶. 10 mol / a, entering the seabed fluid 87 Sr / 86 The Sr ratio is determined by the ratio of strontium in basalt to residual strontium in seawater. Mantle-derived materials contain extremely low levels of Rb, far lower than those found in seawater. 87 Sr / 86 The Sr ratio indicates that the hydrothermal circulation at mid-ocean ridges reduces the seawater temperature. 87 Sr / 86 Sr ratio, global 87 Sr / 86 The average Sr value is only 0.7035.

[0027] Any geological event that could alter the two sources of strontium (i.e., the amount of strontium and its isotopic composition) can lead to changes in the strontium isotopic composition of seawater, thus affecting strontium in marine carbonate rocks. Global events such as global tectonic movements, weathering rates, oceanic crust accretion rates, changes in mid-ocean ridge hydrothermal systems, orogenic events, glacial activity, paleoclimate, global sea-level changes, and global catastrophic events can all alter the relative ratio of crustal and mantle-derived strontium in seawater in different ways, thus becoming the most important controlling factor in the composition and evolution of seawater strontium isotopes. Similarly, by applying the strontium composition and evolution of marine carbonate rocks that have not undergone diagenesis and alteration in geological history, the rate of continental weathering can be determined by the ratio of the two end-members, thereby reconstructing the total alkalinity of paleoseawater. Boron isotopes have special indicative significance for changes in the marine environment; currently, the method used to reconstruct the pH value of paleoseawater from geological history is to utilize boron isotopes from marine carbonate rocks. In the 1990s, many scholars used the boron isotope composition of marine biological carbonate rocks to reconstruct seawater pH values, calculate atmospheric CO2 content during the same period, and thus infer paleoclimate changes. The method of reconstructing paleosea pH values ​​using boron isotopes is based on the fact that dissolved boron in seawater mainly exists as B(OH)3 (boric acid; planar triangular structure) and B(OH). - 4. (Borate ion; tetrahedral structure) exists in two forms. Due to the ionization equilibrium of a weak acid, the relative abundance of both is controlled by the pH of seawater, i.e.:

[0028] pH = pK B –lg(B(OH)3 / B(OH) - 4)

[0029] pK B It is the apparent ionization constant of boric acid.

[0030] In B(OH)3 and B(OH) - Due to differences in isotopic partition functions, isotopic fractionation will occur between 4 boron isotopes, where α is the fractionation coefficient between borate and boric acid, usually denoted as:

[0031] α 硼酸根和硼酸 =1 / K=R 硼酸根 / R 硼酸

[0032] Where R represents the boron element in a certain phase. 11 B / 10 The ratio of B.

[0033] in 10 B is enriched only in B(OH). - In 4, B(OH)3 and B(OH) - δ of 4 11The boron (B) value is controlled by the pH of seawater. Experiments have shown that boron exists primarily or entirely as B(OH). - In the lattice of carbonate minerals involved in biological processes (4 forms), boron isotope fractionation is negligible or nonexistent. Aragonite and calcite synthesized using a solution at pH = 8 have essentially the same δ¹⁴ morphology. 11 The B value is located within the calculated δ. 11 B 硼酸根 On the curve. Experiments on inorganic carbonate synthesis from boron isotope fractionation and on the culture of live foraminifera show that the δ¹⁸O⁻ of carbonate deposition... 11 B 碳酸盐 The value increases with increasing pH of the mother liquor, paralleling the theoretically calculated B(OH) value for seawater. - δ of 4 11 B is basically parallel, but will be 2‰ to 3‰ lower than the theoretical value. Moreover, as long as the selected foraminifera species are consistent, this deviation is constant and correctable, and does not affect the use of boron isotopes as an indicator of pH. Even when the planktonic foraminifera Globigerinoides sacculifer is used, the same experiment is conducted at pH 7.6±0.05, 8.20±0.05, and 8.60±0.05, and the experimental results do not deviate from the calculated curve.

[0034] The pH value of seawater and the boron isotope content of carbonates deposited in the ocean have the following theoretical relationship:

[0035] pH = pK B -lg{(δ 11 B 海水 -δ 11 B 碳酸盐 ) / [α -1 δ 11 B 碳酸盐 -δ 11 B 海水 +10 3 (α -1 -1)]}

[0036] Where δ 11 B 碳酸盐 Based on the measured data, the factors that can affect the accuracy of pH estimation using theoretical calculation formulas are: boron as a component, either solely or primarily, B(OH). - 4. In the lattice of carbonate minerals involved in biological processes, boron isotope fractionation is negligible or non-existent; δ 11 B 海水 α value and pK B The reliability of the value.

[0037] Regarding the residence time of boron in the ocean, different scholars have used different methods to study δ at different time scales.11 B 海水 Characteristics of the changes. On a short timescale, the δ¹⁸O value of seawater... 11 B 海水 Significant changes are unlikely.

[0038] For example, in deep-sea drilling research (ODP), the determination of the boron isotope composition of foraminifera calculated that over the past 21 million years, δ¹²⁴ ... 11 B 海水 It remains relatively stable at approximately 39.5‰. Research by Pearson and Palmer (2000) indicates that over the past 60 million years, δ... 11 B 海水 The variation range is only 1.7‰, so it can be approximately considered that the δ¹⁸O of seawater since the Cenozoic Era has been... 11 B 海水 The pH values ​​are all very stable, remaining at 39.5‰. This leads to the estimation that 21 million years ago, the pH of surface seawater was only 7.4±0.2, increasing to 8.2±0.2 7.5 million years ago. If we synthesize measurements of boron isotope composition from major rivers worldwide and extrapolate to assume that the exchange of boron between terrestrial rivers and the ocean keeps boron in seawater in balance, then the retention time of boron in the ocean would be less than 20 million years, only 14 million years. Within this timescale, δ... 11 B 海水 The value remains stable at 39.5‰, and the δ of seawater is predicted. 11 B 海水 The boron isotope composition was relatively low in the Cenozoic Era and increased in the Cretaceous Era, with a rate of change of approximately 0.1‰ / Ma, and reaching a maximum of up to 6 times, or 0.6‰ / Ma. This is likely mainly due to the adsorption equilibrium caused by terrestrial recharge and low-temperature alteration of the seabed, with the change in terrestrial recharge being the primary driving force. The boron isotope composition of brachiopod fossils from the Silurian, Devonian, Carboniferous, and Permian periods was determined to be approximately 6.8‰–11.0‰, 7.3‰–14.9‰, 12.4‰–15.8‰, and 10.1‰–11.7‰, respectively. Using box modeling to simulate the evolution of boron isotope composition in Paleozoic seawater, the δ¹⁸O values ​​of Paleozoic seawater were obtained. 11 B 海水 Compared to the δ of modern seawater 11 B 海水 The boron concentration in the ocean is about 10‰ lower, which is presumably due to increased terrestrial boron input (Joachimski et al., 2005). Using the boron isotope composition of Cretaceous biogenic carbonates and serpentinites, the boron isotopes of Cretaceous seawater are found to be very close to those of present-day seawater. The concentration and isotopic values ​​of boron in seawater also remain stable, and the retention time of boron in the ocean can be up to 10 million years. However, considering changes in oceanic crust and the intensity of tectonic activity, the marine delta... 11 B海水 There will also be variations on a timescale of 10 million years, likely ranging from 30‰ to 50‰. So, what about the δ¹⁸O values ​​of the oceans during geological history? 11 B 海水 The detailed curves of change have not yet been accurately depicted. Ancient samples from geological history, especially those from the Early Paleozoic, are considered when selecting δ¹⁸ oz samples. 11 B 海水 The value 39.5‰ was not chosen; instead, the δ¹⁹ value was selected based on the boron isotope record in Neoproterozoic marine carbonates studied by Kasemann et al. (2010). 11 B 海水 Meanwhile, it also takes into account that the marine environment underwent significant changes during the Phanerozoic Eon, with the oscillation range of seawater acidity potentially reaching ±0.4 pH units, or even 0.6 pH units, especially since the Late Cambrian was an anomalous period of warm climate.

[0039] The fractionation coefficient α of boron isotopes is currently obtained mainly through theoretical calculations and experimental measurements. The earliest calculations used partition functions and spectral data, resulting in α = 0.9810 at 25℃. Zeebe recalculated the α value using the same method and obtained the same data, but he found that the calculated α value was highly dependent on the magnitude of the molecular vibrational frequencies used in the calculation and the theoretical method used to calculate intermolecular forces. Liu et al. (2007) and Xiao et al. (2010) summarized that the theoretical calculation of α mainly uses ion exchange, molecular orbital theory, and isotope exchange equilibrium methods, employing generalized valence force fields, Yuri-Bradley force fields, and ab initio molecular orbital theory to calculate intermolecular forces. The theoretically calculated fractionation coefficient typically ranges from 0.981 to 0.972. Determining the α value through thermodynamic principles requires experimental measurement of B(OH)₃ and B(OH). - The fractionation coefficient between 4 and 4 is not actually measured; instead, the value of α is obtained by fitting an equation based on experimental results. Klochko et al. (2006) studied the fractionation coefficients of boric acid B(OH)3 and borate B(OH)3 in seawater. - In the study of the chemical kinetics and thermodynamic isotope exchange reactions between four elements, a spectrophotometric method was proposed to determine the boron isotope equilibrium constant at 25°C. 11-10 K BThe value was 1.0272 ± 0.0006, thus determining the α value to be 0.974, which showed no direct dependence on temperature. Pagani et al. (2005) estimated the empirical fractionation coefficient for inorganic carbonate precipitation experiments at 22℃ to be 0.974, lower than α = 0.9810, but similar to the theoretical result (α = 0.975) of Oi (2000). Inorganic carbonate experiments and foraminifera culture experiments yielded fractionation coefficients α = 0.973 and α = 0.969, respectively, while the fractionation coefficient α value for marine clay adsorption experiments was 0.968. Currently, experimental methods give fractionation coefficient α values ​​for boron isotopes ranging from 0.952 to 0.976. However, when researchers are interested in using boron isotopes to determine pH values, the α value is mostly taken as 0.974, such as in the study of Holocene biogenic carbonate minerals. Therefore, the same α value was selected for the data calculated in this study.

[0040] The apparent ionization constant pK of boric acid B Most of these are theoretical estimates because it is difficult to quantitatively separate boric acid B(OH)3 and borate B(OH)3 from seawater. - 4. pK is obtained by the ionization of boric acid in different solution media at 25℃. B The value is 8.830; the ionization constant of synthesized seawater under different temperature and salinity conditions was designed, and the apparent ionization constant pK of boric acid under different salinity and temperature was obtained from the experimental data. B The value is 8.597, and pK B The value of is inversely correlated with temperature and salinity, increasing as temperature and salinity decrease. Roy used an average seawater salinity of 35‰ and designed a temperature range from 0 to 55℃, finding that the ionization constant of seawater was in excellent agreement with Dickson's (1990) results. Therefore, the apparent ionization constant pK of boric acid is... B The value of 8.597 is considered a reliable ionization constant in seawater environments and is widely used in calculations to reconstruct paleopH. This ionization constant pK was also used in the results of this calculation. B Other studies have focused on how different experimental conditions, such as ionic media, measurement methods, and pH ranges, affect the ionization constant pK. B The changes are significant, but under normal circumstances, seawater is a very stable system, especially in terms of temperature and salinity. For example, interannual temperature variations of 5°C are rare, and even if the temperature changes by 5°C, the ionization constant pK remains relatively constant. B The change is approximately 0.04, while the effect on restoring paleopH is 0.04 pH units, which is negligible for the ocean.

[0041] The constraints on the relationship between boron isotopes and seawater pH are that atmospheric carbon dioxide partial pressure, dissolved inorganic carbon concentration, and total carbonate alkalinity all affect seawater pH. However, these factors, in turn, affect the boron isotope composition of marine carbonates. Based on the known boron isotope composition of marine carbonates, atmospheric carbon dioxide partial pressure, and the reconstructed paleopH values ​​of Cambrian seawater, this study provides the saturation index of Cambrian seawater relative to different carbonate minerals, offering some clues for deciphering the properties of seawater during geological history and the historical distribution of carbonate minerals.

[0042] The boron isotope variation range of the Upper Cambrian stromatolites and dolomite rocks in the Tarim Basin is 5.4–8.7‰. Based on different assumed boron isotope values ​​for Cambrian seawater, the pH values ​​of Cambrian seawater were calculated. 11 B 海水 When the pH is 22.5‰ or 26.5‰, the pH of Cambrian seawater is 8.1–8.6, slightly higher than the current pH of seawater (7.5–8.4). When δ... 11 B 海水 =31‰, the pH value of Cambrian seawater will show more characteristics of seawater acidification.

[0043] The strontium isotope range of the same sample is 0.708783 to 0.709342, consistent with the strontium isotope composition of marine carbonate rocks. Variations in seawater strontium isotopes are controlled by both mantle-derived and crustal-derived strontium, which have different isotopic ranges. Therefore, the strontium isotope results in this study are closer to the crustal-derived strontium in the two endmembers, indicating a relatively large input of crustal-derived strontium. Furthermore, according to Hardie (1996), the molar concentration of magnesium ions in seawater throughout the Phanerozoic Eon varied from 10⁶ to 85 meq / L, while the molar concentration of calcium ions (20 to 90 meq / L) varied drastically due to changes in seafloor spreading. During the Early to Middle Cambrian, the molar concentrations of calcium and magnesium ions reached a ratio of approximately 1, mainly due to intense hydrothermal activity and the non-isoisolysis of clinopyroxene. According to Hardy (1996), the molar concentration of magnesium in Middle and Upper Cambrian seawater was approximately 45 mM, slightly lower than the 52.8 mM in modern seawater; while the molar concentration of calcium was approximately 35 mM. The molar concentration of calcium in Middle and Upper Cambrian seawater was slightly different from the 24.5 mM estimated by Stanley and Hardy (1998) and Wilkinson and Given (1986), but both were much higher than the 10.3 mM in modern seawater.

[0044] By applying big data and ion-associated water models, and with the help of PHREEQC, we quantitatively calculated the influence and constraints of paleoseawater pH, total alkalinity, calcium ions, and magnesium ions on the types of minerals formed and the saturation index during the sedimentation period, and simulated the geochemical inversion process.

[0045] The conditions input into PHREEQC 2.14.3 (US Geological Survey) are shown in Table 1. Simulations were performed on the types of 18 ions in different solutions, along with their molar concentrations and activities in aqueous solutions. The solution properties were described in detail (Table 2). Comparisons revealed that in solutions of the same type, such as modern seawater, changes in pH, along with changes in the molar concentrations and activities of hydrogen and hydroxide ions, significantly altered the saturation indices (SI) of bicarbonate and related ions, which are highly sensitive to the acid-base properties of the solution. This directly affected the SI of different carbonate isomorphous minerals such as aragonite and calcite, and more importantly, the SI of calcium-magnesium carbonate, i.e., dolomite, causing the SI to jump directly from 1.02 to 2.62 (Table 3). Similarly, when the calcium ion concentration in Cambrian seawater was fixed, similar changes in the SI of carbonate minerals occurred with pH changes (Tables 2 and 3).

[0046] Table 1 Initial Condition Input Table

[0047]

[0048] When using PHREEQC to simulate Cambrian seawater, with the same pH value but varying the calcium ion concentration, the saturation indices of different types of carbonate minerals, such as calcite and dolomite, increase with increasing calcium ion concentration. However, more significantly, the saturation indices of homogeneous carbonate minerals, such as aragonite and calcite, increase substantially with increasing calcium ion concentration (Tables 2 and 3).

[0049] Table 2. Solution properties of different solutions, including the types, molar concentrations, and activities of various ions.

[0050]

[0051] Table 3 Theoretical precipitation simulation of different minerals in carbonate rocks under different conditions

[0052]

[0053]

[0054] This embodiment utilizes geochemical signals from the original sedimentary environment of Cambrian stromatolites and dolomite in the Tarim Basin to calculate the paleopH and total alkalinity of Cambrian seawater. It also estimates the concentrations of calcium and magnesium ions in the Cambrian ocean. Using PHREEQC software, big data and ion-associated water models were applied to simulate and calculate different property parameters of the paleoseawater. The results show that different pH values ​​and calcium concentrations affect the saturation index of the paleoseawater relative to various carbonate minerals. pH value has a more significant impact on the variation of the saturation index between carbonate minerals with different elemental compositions (e.g., between calcite and dolomite), while calcium concentration has a greater impact on isomorphous carbonate minerals with the same elemental composition (e.g., between calcite and aragonite). Reconstructing the unique properties of paleoseawater during geological history and quantitatively simulating the different effects of varying physical and chemical conditions on the depositional process of microbially formed dolomite is a comprehensive study of the genetic mechanism of microbial dolomite. This study may provide new insights into the genesis of similar dolomite formations during geological history and a comprehensive solution to the ancient mystery of the "dolomite problem."

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A quantitative simulation and calculation method for the sedimentary mechanism of microorganisms in dolomite during geological history, characterized in that, Includes the following steps: Accurately assess whether the sample preserves the signal of the original sedimentary environment during the deposition period, calculate the pH value, total alkalinity, calcium ion and magnesium ion concentration of the paleoseawater during the deposition period, reconstruct the property parameters of the paleoseawater during geological history, quantitatively analyze the different effects of the differences in the physical and chemical conditions of the paleoseawater on the deposition process of microbial dolomite, and quantitatively simulate and calculate the genetic mechanism and process of microbial dolomite during geological history. By applying big data and ion-associated water models, and with the help of PHREEQC, we quantitatively calculated the constraints and influences of different paleosea pH values, total alkalinity, calcium ion and magnesium ion concentrations on the types and saturation indices of mineral formation during different sedimentary periods, and quantitatively simulated geochemical processes.

2. The quantitative simulation and calculation method for the sedimentary mechanism of microbial dolomite during geological history according to claim 1, characterized in that, Accurately assess whether microbial dolomite in geological history preserves signals of the original sedimentary environment during the depositional period through petrology, petrography, isotope geochemistry, and unconventional isotope methods, and whether it has rarely undergone diagenetic alteration.

3. The quantitative simulation and calculation method for the sedimentary mechanism of microbial dolomite during geological history according to claim 1, characterized in that, By applying the composition and evolution of strontium in marine carbonate rocks that have not undergone diagenesis and alteration in geological history, the rate of continental weathering can be determined by the ratio of two end-members, thereby reconstructing the total alkalinity of ancient seawater.

4. The quantitative simulation and calculation method for the sedimentary mechanism of microbial dolomite during geological history according to claim 1, characterized in that, Marine carbonate rocks that can preserve the original sedimentary environment during geological history were analyzed by measuring their unconventional stable isotope boron isotopes to quantitatively reconstruct the pH value of ancient seawater during geological history.

5. The quantitative simulation and calculation method for the sedimentary mechanism of microbial dolomite during geological history according to claim 1, characterized in that, Based on the property parameters of ancient seawater during geological history, the pH value and calcium ion concentration of different ancient seawater will affect the saturation index of seawater relative to various carbonate rock minerals. Among them, the pH value has a more significant impact on the changes in the saturation index between carbonate rock minerals composed of different elements, while the calcium concentration has a greater impact on the homogeneous minerals of carbonate rocks composed of the same element.

Images