A method for analyzing sedimentary facies based on microorganism rock types and fabric features

Abstract

The application provides a sedimentary facies analysis method based on microbial rock types and fabric features, which comprises the following steps: (1) sample collection and pretreatment; (2) microscopic fabric identification, i.e. preparing a cast body slice to identify microstructures through a polarizing microscope and a scanning electron microscope; (3) combining macroscopic morphology to divide structural scales; (4) sedimentary facies analysis and determination, i.e. comprehensively determining and analyzing sedimentary facies features according to microbial rock types, macroscopic morphology and microscopic features; and (5) constructing a sedimentary model, i.e. constructing a sedimentary model by comprehensively considering the vertical sequence and the planar distribution features of microbial rocks. The application has reasonable concept and simple process, can efficiently determine paleo-water depth, water energy and salinity, and provides technical support for oil and gas reservoir prediction and paleogeographic reconstruction.

Description

Technical Field

[0001] This invention relates to the field of microbial rock research technology, specifically to a sedimentary facies analysis method based on microbial rock type and fabric characteristics. Background Technology

[0002] Microbial rocks are carbonate sedimentary bodies formed by microbial communities through bonding, trapping, or inducing mineralization; their type and structure are controlled by the sedimentary environment. Current techniques for sedimentary facies analysis largely rely on geochemical or paleontological indicators, lacking a systematic application to the structural characteristics of microbial rocks. Systematic studies of microbial rocks have shown that their morphology, scale, and assemblage can clearly indicate water energy, salinity, and paleogeography, but standardized analytical methods have not yet been developed. Summary of the Invention

[0003] To address the technical problems existing in the background art, this invention proposes a sedimentary facies analysis method based on microbial rock type and fabric characteristics. The method is reasonable in concept and simple in process, and can efficiently determine paleowater depth, water energy and salinity, providing technical support for oil and gas reservoir prediction and paleogeographic reconstruction.

[0004] To address the aforementioned technical problems, this invention provides a sedimentary facies analysis method based on microbial rock type and fabric characteristics, which mainly includes the following steps:

[0005] (1) Sample collection and pretreatment;

[0006] (2) Microstructure identification

[0007] Microstructures were identified by fabricating thin sections of cast bodies using polarizing microscopy and scanning electron microscopy.

[0008] (3) Combining macroscopic morphology to construct scale

[0009] Based on the scale and macroscopic morphology of sedimentary formations, the microbial rock structures in the microbial rock units collected in step (1) above are classified into different levels; then, based on the characteristics of microbial rocks in the outcrops or cores of the research object, their morphological types are identified.

[0010] (4) Sedimentary facies analysis and determination

[0011] Based on the type of microbial rock, macroscopic morphology and microscopic characteristics, the sedimentary facies characteristics are comprehensively determined and analyzed.

[0012] (5) Constructing sedimentation models

[0013] A sedimentary model was established by integrating the vertical sequence and planar distribution characteristics of microbial rocks.

[0014] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein the specific process of sample collection and pretreatment in step (1) is as follows: systematic sampling is performed at key strata in outcrops or drill cores, with priority given to microbial rock units whose original structures are intact; hand specimens are ≥10cm in size. 3 To ensure the presence of complete microbial structures, directional sampling is required for areas with cracks and pores, and the top and bottom orientations must be marked. Rock specimens should be cut and polished in a direction perpendicular to or parallel to the bedding plane to create a smooth surface, which facilitates observation of the morphology and structural characteristics of microbial rocks.

[0015] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein: in step (1), the gypsum-salt rock interlayer samples in the sampled microbial rock unit are individually marked during sample collection to prevent the deliquescence of salt minerals from affecting microscopic observation;

[0016] Before sample collection and pretreatment, step (1) requires field observation and mapping to observe the macroscopic morphology, structure and tectonic features of in-situ microbial rocks on the field profile, make a preliminary judgment on the rock type, and map the macroscopic morphological features of microbial rocks.

[0017] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein the specific process of identifying microstructures by polarizing microscope and scanning electron microscope in step (2) is as follows: first, observe the microstructure of different types of microbial carbonate rocks and determine the microscopic characteristics of hydrodynamic conditions by polarizing microscope, and then observe the ultramicroscopic characteristics of microorganisms by scanning electron microscope; for the clotted structure of clotted rocks, observe the calcified sheath of filamentous cyanobacteria at the edge of dark clotted rocks; for the lamellar structure in stromatolites and lamellar rocks, record the ratio of light and dark lamellar thickness and ultrathin single lamellar; then, quantify the number of concentric layers of nucleoid rocks, and simultaneously carry out energy dispersive spectroscopy analysis to detect anhydrite spots or siliceous cement.

[0018] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein: in step (2) in the microfabrication identification, it is also necessary to map the main microstructure characteristics of microbial rocks, such as the thickness of bright and dark laminae, the number of concentric circles of nucleoids, and the structure of clots.

[0019] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein: step (3) specifically divides the microbial rock structure scale in the microbial rock unit collected in step (1) into four levels, specifically including large structures with a structure scale > 1m, medium structures with a structure scale of 0.5–1m, small structures with a structure scale of 1–50cm, and micro structures with a structure scale < 1cm.

[0020] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein: in step (3), the large structure includes microbial mounds and microbial flats, whose formation is controlled by paleogeography, dominated by low-energy environment, and intermittent high energy provides clastic particles;

[0021] The medium-sized structures include stromatolites developed in the moderately hydrodynamic region at the edge of the platform;

[0022] The small structures include wavy stromatolites and nodular clumps that reflect high-frequency water level fluctuations;

[0023] The microstructures include clot structures and filamentous cyanobacteria that reveal the mechanisms of microbial calcification.

[0024] The sedimentary facies analysis method based on microbial rock type and fabric characteristics includes: sedimentary facies characteristics in step (4) include textured rocks and mud mounds indicating basin-lower slope facies, clotted rocks indicating upper slope facies, columnar stromatolites representing shallow water areas at the edge of the platform, wavy stromatolites reflecting tidal flat facies, and microbial flats in gypsum-salt interlayers indicating saline lagoons.

[0025] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein the specific process of establishing the sedimentary model in step (5) is as follows:

[0026] (5.1) Identify different types of microbial rocks through field or hand specimen observation;

[0027] (5.2) Combine the sedimentary facies corresponding to different types of microbial rocks and the microfacies indicated by microstructure under a microscope to determine the sedimentary facies characteristics of different microbial rocks and strata in the study area;

[0028] (5.3) Reconstruct the overall sedimentary pattern of the strata in the study area.

[0029] The sedimentary facies analysis method based on microbial rock type and fabric characteristics, wherein the specific process of step (5.3) is as follows: when reconstructing the paleosedimentary model according to the sedimentary characteristics of microbial carbonate rocks, based on the differences in water energy zoning and microbial community response, the sedimentary environment is divided into four secondary units according to energy zoning based on storm wave base, normal wave base and mean low tide line, namely, the outer gentle slope basin unit under low energy and anoxic environment, the middle gentle slope unit under medium intermittent energy, the inner gentle slope unit under high frequency wave action and the tidal flat unit under tide dominance.

[0030] By adopting the above technical solution, the present invention has the following beneficial effects:

[0031] The sedimentary facies analysis method based on microbial rock type and structure characteristics is well-conceived and has a simple process. It can efficiently determine paleowater depth, water energy and salinity, providing technical support for oil and gas reservoir prediction and paleogeographic reconstruction.

[0032] The present invention also has the following advantages or features:

[0033] (1) Accurately indicating the paleoenvironment: for example, stolonite indicates a low-energy environment in the subtidal zone, while columnar stromatolites reflect a high-energy environment from the lower part of the intertidal zone to the upper part of the subtidal zone.

[0034] (2) Supporting oil and gas exploration: The combination of microbial mound reservoirs and microbial plateau caprocks can delineate favorable oil and gas areas;

[0035] (3) Improved efficiency: The sedimentary facies can be roughly determined by classifying the types and morphologies of microbial carbonate rocks through field surveys. Microfacies characteristics can be further observed under a microscope to comprehensively determine sedimentary microfacies. Compared with determining different sedimentary environments through a large number of geochemical tests, this method is more convenient and efficient, avoids reliance on expensive geochemical tests, and reduces exploration costs.

[0036] (4) Quantitative correlation of scale-morphology-environment: The first four-level tectonic scale and six types of sedimentary facies mapping model (i.e., different microbial rock types correspond to different sedimentary facies, and the mapping relationship between the two can be adjusted in terms of expression) solves the problem of scale separation in traditional schemes;

[0037] (5) Criteria for the specificity of gypsum-salt rocks: Clarify the facies significance of gypsum-microbial rocks → saline lagoons;

[0038] (6) Engineering application: A standardized process of “scale classification → microscopic identification → combined analysis” is formed to support the selection of reservoir target areas. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a collection of field feature maps of microbial rocks involved in the sedimentary facies analysis method based on microbial rock type and fabric characteristics in this invention. Figure 1 In the text, A refers to microbial flats, B to columnar stromatolites, C to layered stromatolites, D to tuffaceous rocks, E to nucleoids, and F to oolitic microbial rocks.

[0041] Figure 2This is a sedimentary facies diagram of microbial rocks involved in the sedimentary facies analysis method based on the type and structure characteristics of microbial rocks in this invention. Detailed Implementation

[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0043] The present invention will be further explained below with reference to specific embodiments.

[0044] This embodiment provides a sedimentary facies analysis method based on microbial rock type and fabric characteristics, which specifically includes the following steps:

[0045] S100, Sample Collection and Preprocessing

[0046] Systematic sampling should be conducted in key strata of outcrops or drill cores (such as areas with well-developed microbial mounds / plateaus), prioritizing microbial rock units with well-preserved primary structures. Hand specimens are recommended to be ≥10cm in size. 3 To ensure the presence of complete microbial structures (such as clot edges and lamellar continuity), directional sampling (perpendicular to bedding direction) is required for areas with fractures and pores, with top and bottom orientations marked. Rock specimens can be cut and polished perpendicular or parallel to bedding direction to create smooth surfaces, facilitating observation of the morphology and structural characteristics of the microbial rock. Gypsum-salt interlayer samples within the sampled microbial rock units should be individually marked to prevent the deliquescence of salt minerals from affecting microscopic observation. Prior to sample collection and preprocessing, field (or core) observation and mapping are necessary to observe the macroscopic morphology, structure, and tectonic features of the in-situ microbial rock on field profiles, preliminarily determine the rock type, and map the macroscopic morphological characteristics of the microbial rock.

[0047] S200, Microstructure Identification

[0048] Thin sections (30 μm thick) of the cast body were prepared, and microstructures were identified using a polarizing microscope (200×–400×) and a scanning electron microscope (SEM). First, the microstructure of different types of microbial carbonate rocks was observed using a polarizing microscope to determine the microscopic characteristics of hydrodynamic conditions. Then, the ultramicroscopic characteristics of microorganisms, such as bacterial types and pyrite morphology, were observed using an SEM. For the clotted structure of stolonite, the calcified sheaths of filamentous cyanobacteria (such as *Gnaphalium affine*) at the edges of dark clots were observed. For the lamellar structure in stromatolites and lamellar rocks, the ratio of light to dark lamellar thickness and ultrathin single lamellars were recorded. The number of concentric layers in nucleoids was quantified. Simultaneously, energy dispersive spectroscopy (EDS) analysis was performed to detect anhydrite spots or siliceous cements (mineral composition in different locations). In the microstructure identification, the main microstructural features of microbial rocks, such as lamellars and clots, also needed to be mapped, including the thickness of light and dark lamellars, the number of concentric layers in nucleoids, and the clotted structure.

[0049] S300, Combining macroscopic morphology to classify structural scale

[0050] Based on the scale and macroscopic morphology of sedimentary formations, the microbial rock structures in the microbial rock units collected in step (1) above are divided into four levels; specifically, based on the measured data of outcrops / core profiles of the research object ( Figure 1 Microbial mounds are classified into four scales: large (>1m), medium (0.5–1m), small (1–50cm), and micro (<1cm). It is important to map the geometric morphology of microbial mounds before sampling (e.g., a mound height / width ratio >0.5 indicates a high-energy platform edge) and statistically analyze the wavelengths of wavy stromatolites (reflecting moderate tidal energy), among other microbial rock characteristics, to identify their morphological types. The specific process is as follows:

[0051] S301, microbial mounds, macroscopically, appear as mound-shaped or lenticular elevations, ranging in size from several meters to tens of meters in thickness, extending laterally for hundreds of meters; internally, they exhibit cyclic stratification, commonly with upward-shrinking sequences, and the core of the mound develops framework pores and dissolution cavities, while the base is mainly composed of micritic dolomite; microscopic observation reveals a mixed distribution of clotted and lamellar structures, with blurred clot edges and inclusions of sandy debris; the pore types are diverse, with framework pores filled by multiple stages of dolomite cementation, and intercrystalline pores and dissolution cavities are well-developed.

[0052] S302, microbial flats, are macroscopically low-lying sheet-like or blanket-like sedimentary bodies, with lithology mainly consisting of micritic dolomite, containing bird's-eye structures and desiccation structures, and locally wavy textures; microscopically, they have a homogeneous micritic structure, containing dispersed microbial debris (such as calcified cyanobacterial fragments), well-developed micropores (mainly intercrystalline pores), and commonly bird's-eye pores filled with gypsum or calcite.

[0053] S303, agglomerates, macroscopically exhibit an irregular agglomerate structure without clear layers, and a mottled surface. Based on morphology, they can be classified as dispersed (isolated agglomerates), bedding (distributed along bedding planes), and framework (porous skeleton). Microscopically, the agglomerates are composed of dark micritic carbonate aggregates, with the edges cemented by bright crystals.

[0054] S304, a type of nucleoid, macroscopically consists of bean-shaped or ellipsoidal grains with concentric shells, the core being bioclastic or rock fragments; microscopically, the concentric layers alternate between dark organic matter layers and bright carbonate layers (showing alternating light and dark under single polarized light). Cyanobacterial fragments or cohesive microbial communities are visible in the core.

[0055] S305, stromatolites

[0056] S3051, columnar / conical stromatolites: Macroscopically, columnar or bifurcated conical morphology indicates a medium- to high-energy shallow water environment; Microscopic observation shows alternating dark layers (rich in organic matter) and bright layers (microcrystalline carbonates), with algal filaments distributed upright or horizontally, high lamellar continuity, and local silicification or dissolution.

[0057] S3052, wavy / layered stromatolites, macroscopically, have horizontal or wavy laminations, developed in low-energy environments of tidal flats; microscopically, the laminations are of uniform thickness (0.1–0.5 mm), the dark layers contain organic matter from bacteria and algae, and the bright layers are micritic or microcrystalline.

[0058] S306, Oolitic microbial rocks, macroscopically, the oolitic grains are regularly spherical (grain size <2mm), formed in high-energy shallow water environments, and often coexist with microbial-bonded particles; microscopic observation shows that the oolitic core is quartz or bioclastic, the concentric layers are composed of microcrystalline carbonate, and microbial bonding alters the oolitic boundaries in some areas.

[0059] S307, textured stone, macroscopically, has thin, alternating light and dark layers, smaller in scale than stromatolites, and is found in deep, still water environments; microscopic observation shows that the layers are formed by microbial mats capturing mud crystals or inducing carbonate precipitation, containing pyrite, with a layer thickness of <0.1mm, high continuity, and lack of hydrodynamic erosion traces.

[0060] Among them, large structures include microbial mounds and microbial flats, whose formation is controlled by paleogeography, with low-energy environments dominating construction and intermittent high-energy environments providing clastic particles; medium-sized structures include stromatolite mounds, which develop in medium-hydrodynamic areas at the edge of the platform; small structures include wavy stromatolites and nodular clotted rocks, reflecting high-frequency water level fluctuations (such as in the intertidal zone); and microstructures include clotted structures and filamentous cyanobacteria, which can reveal the mechanism of microbial calcification.

[0061] Table 1. Macroscopic classification of microbial rocks

[0062]

[0063] Based on the characteristics of microbial rocks in outcrops / cores, their morphological types are identified as: layered, mound-like, wavy, columnar, clump-like, and nucleoid.

[0064] The rules for determining sedimentary facies are as follows:

[0065] Systematic studies have shown that the formation of different types of microbial rocks is often closely related to their environment, such as water depth, hydrodynamic conditions, and microbial development characteristics, and has strong indicative significance for paleosedimentary facies (Table 2).

[0066] The clots were formed in a low-energy environment in the lower part of the subtidal zone below the normal wave base, and were locally affected by storm disturbances. The core evidence includes filamentous cyanobacteria developed at the edges of the clots, their association with horizontally laminated micritic dolomite, and the widespread distribution of anhydrite spots in the clots of the Ordos Basin, which together indicate intermittent salinization and weak hydrodynamic conditions.

[0067] Columnar / dome-shaped stromatolites develop in the shallow waters of the platform margins in medium to high-energy environments, forming in the high-energy intertidal zone or the upper part of the subtidal zone. The pore structure and foam layer structure reflect periodic exposure. The 4–5 cm columnar height in the Three Gorges area of ​​Hubei Province corroborates the control of tidal action, while the alternating layers of the Dengying Formation and oolitic shoals in central Sichuan further characterize the water turbulence.

[0068] Wave stromatolites are found in the intertidal zone in medium-energy environments and are subject to periodic waves or tides, resulting in a relatively fast deposition rate. Their oolitic / spheroidal enriched laminae (0.2–0.5 mm in diameter), ultrathin monolayer thickness of 0.05–0.1 mm, and the scour surface structure of the Ordos Basin constitute diagnostic markers of high-frequency water level fluctuations and the combined effects of waves and tides.

[0069] The core-shaped rock layer indicates intermittent high-energy events in the tidal flat facies. The symbiotic combination of ellipsoidal concentric lamellars, grape-like lace-like structures, and siliceous cementation in the Chengkou manganese ore comprehensively reflects the synergistic control of tidal channel migration and shallow-water oxidation interface.

[0070] The specific indications of the gypsum-microbial rocks pertain to the salinized lagoon environment of the platform, the complete filling of microbial framework pores with anhydrite, the alternating cycles of gypsum-salt rocks and microbial flats in the Mizhi Depression, and the gypsum-stromatolites of the Leikoupo Formation in western Sichuan together reveal the hypersalinity deposition mechanism dominated by the evaporation pump effect.

[0071] Table 2. Indicative significance of microbial rock types for sedimentary environments

[0072]

[0073] Combined sequence analysis:

[0074] (1) Vertical cycles: Microbial rock-gypsum-salt rock interbedded sequence directly responds to sea level fluctuations. For example, the Mawu Formation in the Ordos Basin presents a complete regressive sequence of “clotted microbial mounds → gypsum → wavy stromatolites”. The clotted structure of the microbial mounds (25m thick) transitions to the anhydrite filling of the gypsum, indicating a decrease in water energy and an increase in salinity. The cycle of “clotted rock → layered stromatolites → windowpane dolomite” in the Dengying Formation in the central Sichuan records the progradation process from the subtidal zone to the supratidal zone.

[0075] (2) Planar symbiosis: Microbial mounds + oolitic shoals constitute platform margin mound-shoal complexes (such as the ancient uplift of Uxin Banner). The framework pores (average porosity 9.02%) inside the mounds and the dissolution pores between the oolitic grains form high-quality reservoir space (porosity-permeability ratio 2-3 times higher than that of microbial flats). Microbial flats + gypsum-salt rocks define the boundary of saline lagoons (eastern part of Mizhi Depression). The microbial flats (nucleate stone particle size 2-6 cm) covered by gypsum-salt layers form an effective caprock.

[0076] S400, sedimentary facies analysis and determination

[0077] Based on the type of microbial rock, macroscopic morphology and microscopic characteristics, the sedimentary facies characteristics were comprehensively determined and analyzed (as shown in Table 2).

[0078] S500, Constructing a deposition model

[0079] A sedimentary model was established by integrating the vertical sequence and planar distribution characteristics of microbial rocks. Figure 2 The specific process is as follows:

[0080] S501. Different types of microbial rocks were identified through field observation or hand specimen observation;

[0081] S502. By combining the sedimentary facies corresponding to different types of microbial rocks and the microfacies indicated by microstructure under a microscope, the sedimentary facies characteristics of different microbial rocks and strata in the study area are determined.

[0082] S503. Then, the sedimentary model of the entire stratigraphy in the study area is restored. In the process of reconstructing the paleosedimentary model based on the characteristics of microbial carbonate rock sedimentation, the sedimentary environment can be divided into four sub-units according to the energy zoning of the water body and the differences in the response of the microbial community. These sub-units are based on the storm wave base (SWB), normal wave base (FWB), and mean low tide line (MLWL). Specifically, these include the outer gentle slope basin (below SWB) under low-energy and anoxic conditions, the middle gentle slope (between SWB and FWB) under moderate intermittent energy conditions, the inner gentle slope (between FWB and MLWL) under high-frequency wave action, and the tidal flat (above MLWL) under tidal dominance.

[0083] The aforementioned outer gentle slope-basin unit (below the storm surge base): This low-energy, oxygen-deficient environment is characterized by the development of large-scale laminated carbonate rocks and mud mound formations, generally containing siliceous nodules and banded sediments, reflecting slow chemical precipitation and microbial-induced mineralization under still water conditions. High sedimentary accommodation space promotes vertical accretion, forming biochemical sedimentary bodies with dense micro-bedding.

[0084] The aforementioned moderately sloping units (between the storm wave base and the normal wave base) are characterized by the periodic disturbances caused by storm events, primarily resulting in the development of tuffaceous carbonate rocks (typically 2–15 cm in size). The breccia formed by storm energy breaking up microbial mats is cemented and reconsolidated by extracellular polymers (EPS) from microorganisms, forming tuffaceous assemblages with a fragmented-healing structure. This environment has moderate sedimentary capacity, and microbial construction exhibits intermittent growth characteristics.

[0085] The aforementioned inner gentle slope unit (between the normal wave base and the mean low tide line) is dominated by high-frequency wave scouring, characterized by the development of small to medium-sized wavy stromatolites. Limited accommodation space restricts the vertical growth of microorganisms, prompting filamentous flora to form wavy / rippled macroscopic morphologies resistant to flow deformation. Thin layers of algal debris and oolitic carbonate interlayers are common, occasionally interspersed with micro to small tuffaceous rocks, reflecting the modification of sedimentary fabric by water energy fluctuations.

[0086] The aforementioned tidal flat units (above the mean low tide line) represent intermittent exposure environments controlled by tidal rhythms, primarily characterized by large to medium-sized sheet-like to mound-like microbial carbonate rock formations. Periodic wet-dry cycles promote lamellar mineralization of the microbial mats (alternating seasonal calcite crystallization and thin organic matter layers). The sedimentary assemblage commonly includes argillaceous carbonate rocks, algal sandstone layers, and terrigenous clastic interlayers (such as siltstone), revealing the influence of tidal channel migration and terrigenous input.

[0087] This invention has a reasonable concept and a simple process, and can efficiently determine paleowater depth, water energy and salinity, providing technical support for oil and gas reservoir prediction and paleogeographic reconstruction.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sedimentary facies analysis method based on microbial rock type and fabric characteristics, characterized in that, The main steps include: (1) Sample collection and pretreatment; (2) Microstructure identification The microstructures of the cast thin sections were identified using a polarizing microscope and a scanning electron microscope. The specific process was as follows: first, the microstructures of different types of microbial carbonate rocks were observed and the microscopic characteristics of hydrodynamic conditions were determined using a polarizing microscope; then, the ultramicroscopic characteristics of microorganisms were observed using a scanning electron microscope. For the clotted structure of clotted stone, observe the calcified sheaths of filamentous cyanobacteria at the edges of dark clotted stones; for the lamellar structure in stromatolites and lamellar stones, record the ratio of light to dark lamellar thickness and ultrathin single lamellar; then, quantify the number of concentric layers in nucleoid stones, and simultaneously conduct energy dispersive spectroscopy analysis to detect anhydrite spots or siliceous cement. (3) Divide the structural scale by combining macroscopic morphology Based on the scale and macroscopic morphology of the sedimentary formations, the microbial rock structures in the microbial rock units collected in step (1) above are classified into different levels. Then, based on the microbial rock characteristics of the outcrops or cores of the research object, its morphological type is identified; (4) Determination of sedimentary facies Based on the type of microbial rock, macroscopic morphology and microscopic characteristics, the sedimentary facies characteristics are comprehensively determined and analyzed. (5) Constructing sedimentation models A sedimentary model was established by integrating the vertical sequence and planar distribution characteristics of microbial rocks; the specific process of establishing the sedimentary model is as follows: (5.1) Identify different types of microbial rocks through field or hand specimen observation; (5.2) Combine the sedimentary facies corresponding to different types of microbial rocks and the microfacies under the microscope to determine the sedimentary facies characteristics of different microbial rocks and strata in the study area; (5.3) Reconstruct the sedimentary model of the strata in the study area as a whole; the specific process is as follows: when reconstructing the paleosedimentary model based on the characteristics of microbial carbonate rock sedimentation, according to the differences in water energy zoning and microbial community response, the sedimentary environment is divided into four sub-units according to energy zoning based on storm wave base, normal wave base and mean low tide line, namely the outer gentle slope basin unit under low energy and hypoxia, the middle gentle slope unit under medium intermittent energy, the inner gentle slope unit under high frequency wave action and the tidal flat unit under tide dominance; In the microstructure identification step (2), it is also necessary to map the main microstructure features of microbial rocks, such as the thickness of bright and dark laminae, the number of concentric circles of nucleoids, and the structure of clots. The specific step (3) is to divide the microbial rock structure scale in the microbial rock unit collected in step (1) into four levels, specifically including large structures with a structure scale > 1m, medium structures with a structure scale of 0.5–1m, small structures with a structure scale of 1–50cm, and micro structures with a structure scale < 1cm. The large structures encompass microbial mounds and microbial terraces, whose formation is controlled by paleogeography, dominated by low-energy environments, and intermittently provided by high-energy clastic particles. The medium-sized structures include stromatolites developed in the moderately hydrodynamic region at the edge of the platform; The small structures include wavy stromatolites and nodular clumps that reflect high-frequency water level fluctuations; The microstructures include clot structures and filamentous cyanobacteria that reveal the mechanisms of microbial calcification.

2. The sedimentary facies analysis method based on microbial rock type and fabric characteristics as described in claim 1, characterized in that... The specific process of sample collection and pretreatment in step (1) is as follows: systematic sampling is performed at key strata in outcrops or well cores, with priority given to microbial rock units whose original structures are intact; Hand specimens should be ≥10cm³ in size and ensure they contain complete microbial structures; directional sampling is required for areas with cracks and pores, and the top and bottom orientations should be marked. Rock specimens are cut and polished by selecting directions perpendicular or parallel to the bedding plane to create a smooth surface, which facilitates the observation of the morphology and structural characteristics of microbial rocks.

3. The sedimentary facies analysis method based on microbial rock type and fabric characteristics as described in claim 1, characterized in that: In step (1), the gypsum-salt rock interlayer samples in the microbial rock unit are individually marked during sample collection to prevent the deliquescence of salt minerals from affecting microscopic observation. Before sample collection and pretreatment, step (1) requires field observation and mapping to observe the macroscopic morphology, structure and tectonic features of in-situ microbial rocks on the field profile, make a preliminary judgment on the rock type, and map the macroscopic morphological features of microbial rocks.

4. The sedimentary facies analysis method based on microbial rock type and fabric characteristics as described in claim 1, characterized in that: The sedimentary facies features in step (4) include textured rocks and mud mounds indicating basin-low slope facies, clotted rocks indicating upper slope facies, columnar stromatolites representing shallow water areas at the edge of the platform, wavy stromatolites reflecting tidal flat facies, and microbial flats in gypsum-salt interlayers indicating saline lagoons.

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