CN113295849B - Method for determining ancient wind direction of continental lake basin through distribution pattern of deposition system - Google Patents

Abstract

The invention provides a method for determining the ancient wind direction of a continental lake basin through a distribution pattern of a deposition system, which comprises the following steps: (1) defining a region and a horizon to be restored; (2) determining and analyzing a deposition system of the area to be recovered; (3) Summarizing the distribution rule of a deposition system and summarizing the combination of different positions; (4) And determining the ancient wind direction of the area to be recovered by using a sedimentology method. The invention mainly analyzes the stratum and the horizon, the sedimentary facies and the sedimentary subphase in the area to be restored; summarizing the deposition phase combination, dividing the deposition phase combination into different orientations, and summarizing main deposition phases in different orientations; and analyzing the hydrodynamic force and the energy level in different directions in the area based on the theory of sedimentology, thereby recovering the ancient wind direction.

Description

A method to determine the paleowind direction of continental lacustrine basins based on the distribution patterns of sedimentary systems

technical field

The invention relates to the technical field of geological research, in particular to a method for determining the paleowind direction of continental lake basins through the distribution patterns of sedimentary systems.

Background technique

Global climate change is a hot topic in scientific research today. Restoring paleoclimate and paleoenvironmental change information is the basis for studying future climate and environmental evolution. Tertiary terrestrial faulted lake basins in eastern China, such as the Bohai Bay Basin, are similar to Qinghai Lake in both the geological structure of the faulted lake basin and the saline-brackish water environment. In modern times, domestic and foreign scholars proposed to use the "source-sink" system as a research idea to analyze the dynamic process of surface sedimentation. Taking the determination of the paleowind direction of the lake basin of Qinghai Lake as an example, the study of the modern sedimentary system of Qinghai Lake can provide an example for the study of the sedimentary system of ancient continental faulted basins, which is conducive to the study of sand bodies in continental faulted lake basins in eastern China The planar distribution law of the basins in eastern China will further guide oil and gas exploration in continental faulted lake basins in eastern China. At present, most foreign scholars, such as Moore, Anthony, Somme, etc., apply this research idea to modern ocean or ancient marine strata. Domestic scholars, such as Xu Changgui, Lin Changsong, Wu Dong and others, also applied this research idea to ancient continental faulted lake basins.

Existing technology 1: Jiang Zaixing and Zhang Yuanfu (2019) provided a method and device for predicting reservoir sand bodies based on wind field, provenance, and basin system; wherein, the method includes: obtaining geological data of the area to be predicted; among them, Geological data include at least core data, paleontological data, logging data and seismic data; input geological data into the preset wind field, provenance, and basin system models to generate beach-bar sand bodies in the area to be predicted Formation process data; among them, the wind field, provenance, and basin system models include at least a variety of paleosource restoration tools, paleowind force restoration tools, paleowind direction restoration tools, paleogeomorphology restoration tools, and paleowater depth restoration tools; according to beach bar Sand body formation process data, using geological and geophysical methods to predict the specific distribution of beach bar sand bodies in the area to be predicted. Disadvantage of prior art 1: This solution is mainly aimed at beach-bar sedimentary bodies, and is not applicable to other sedimentary systems.

Existing technology 2: Jiang Zaixing et al. (2015) provided a paleowind measurement method and device based on a quantitative method for the thickness of coastal sandbars. The method includes: determining the wave breaking water depth at the crest of the coastal sand bar according to the pre-acquired base slope of the coastal sand bar and the original thickness of the coastal sand bar; The effective wave height in the deep water area is determined by the breaking wave height and the known wave statistical characteristics; the wind pressure coefficient is calculated according to the ancient wind distance and the effective wave height in the deep water area, combined with the wave prediction formula of the water body in the limited wind area; the wind pressure coefficient is calculated according to the wind pressure coefficient and the known wind pressure The relationship between the coefficient and the wind speed is used to determine the paleowind force and wind speed. The invention determines the paleowind force according to the thickness of the sand bar along the coast, and can quantitatively restore the paleowind force more accurately.

Disadvantage of prior art 2: This research method is suitable for measuring paleowind force, and has little significance for the restoration of paleowind direction.

Contents of the invention

The present invention provides a method for determining the paleowind direction of continental lacustrine basins through the distribution pattern of the sedimentary system. This patent starts with the distribution pattern of the sedimentary system in the area to be measured, analyzes the laws of the distribution pattern of the sedimentary system in different areas, and summarizes and summarizes the facies of the area to be measured. Combined features provide guidance for the analysis of paleoatmospheric circulation.

In order to achieve the above purpose, the present invention provides a method for determining the paleowind direction of continental lake basins through the distribution pattern of the sedimentary system, comprising the following steps:

S1: Define the area and layer to be restored;

S2: Determine and analyze the sedimentary system in the area to be restored;

S3: Summarize the distribution laws of sedimentary systems and summarize the facies combinations in different regions;

S4: Use sedimentological methods to determine the paleowind direction of the area to be restored.

Further, the step S1 includes the following sub-steps:

S11: Investigation work and data collection of the geological characteristics of the area to be restored;

S12: Field investigation in the area to be restored.

Further, the step S11 specifically includes: research work on the geographic location of the area to be restored, the regional geological background, the development of structures, and the distribution characteristics of strata in the area.

Further, the step S2 specifically includes: determining the sedimentary facies and sedimentary subfacies according to the facies markers appearing in the area to be restored, and describing the characteristics of the sedimentary facies and subfacies; wherein, identifying the facies markers can be based on lithological features, structural markers, sedimentary facies Analysis of five aspects: structural marks, color marks, and biofossil marks.

Further, the lithological characteristics include the color, composition, structure, structure, rock type and combinations thereof; the structural signs include maturity, grain size, sorting degree, roundness and the shape of the rock mass section; The sedimentary structure signs include bedding structure and shape structure, and the shape structure is divided into parallel, staggered, massive, horizontal, graded bedding, deformation structure, exposed structure, and filling structure; the color mark includes whether the color of the sediment appears or not. Oxidized colors such as red, yellow, and brown-red; the biofossil signs include plankton, plants, and their residual sediments and wrecks.

Further, the step S3 specifically includes: counting the distribution law of the deposition in the area to be restored, and after comprehensively analyzing the depositional system, determining the law of the depositional system; combining the literature data and the regular distribution characteristics of the area to be restored, and obtaining the distribution of the area to be restored. Sedimentary differentiation law: the distribution law of the sedimentary system is divided into different regions according to certain sedimentary facies combinations.

Further, the step S3 includes the following sub-steps:

S31: Establish a two-dimensional coordinate system with the center of the area to be restored as the origin;

S32: Divide into eight regions according to the natural orientation;

S33: The sedimentary facies and sedimentary subfacies determined according to step S2 are converted into percentages according to the ratio in each orientation, and drawn in a two-dimensional coordinate system in the form of a disc;

S34: Sedimentary facies or subfacies with larger specific gravity are used as the dominant sedimentary facies or subfacies in this orientation.

Further, the eight areas are respectively north, north east, east, southeast, south, south west, west, and northwest areas.

Further, the step S4 specifically includes: using sedimentological methods to analyze the hydrodynamic high-energy bands and low-energy bands, so as to obtain the hydrodynamic energy levels of sedimentary facies or sub-facies in different orientations in the area to be restored, so as to determine the basin Based on the windward and leeward positions of the windward side, the paleowind direction of the area to be measured can be obtained.

Compared with related technologies, the method for determining the paleowind direction of continental lake basins provided by the present invention through the distribution patterns of sedimentary systems has the following beneficial effects:

(1) Understand the energy relationship of the lake basin through the characteristics of hydrodynamic zoning, and judge the ancient wind direction of the continental lake basin; The distribution of energy and minerals in ancient wind farms is of great significance.

(2) The present invention determines the paleowind direction of the continental lake basin through the sedimentary system, and the mineral resources of the continental lake basin and the oil and gas exploration to the continental lake basin can be found through the law of the sedimentary system; by restoring the paleowind direction, the ancient sedimentary model is understood, and for the lake edge sedimentary system Generally speaking, the paleowind direction of continental lacustrine basins is from low-energy environment to high-energy environment. Using paleowind direction to distinguish high-energy environment is a means of predicting beach bar oil and gas reservoirs, which is beneficial to oil and gas exploration in the field.

Description of drawings

Fig. 1 is a schematic flow chart of a method for determining the paleowind direction of continental lake basins through the distribution patterns of sedimentary systems provided by the present invention;

Figure 2 is a landform map of Qinghai Lake and its surrounding areas;

Figure 3 is a pie chart of sedimentary facies and subfacies in different orientations;

Figure 4 is a diagram of the dominant sedimentary facies in different orientations.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The definitions of key words in this application are as follows:

Sedimentary system: A set of three-dimensional sedimentary facies assemblies formed during genetically related depositional environments and interrelated depositional processes.

Fan delta: A wedge-shaped sedimentary body mainly developed underwater or completely underwater, provided by an alluvial fan.

Delta: Refers to the estuary area where a river flows into a sea (lake) basin. Due to the slowing down of the slope, the diffusion velocity of the water flow is reduced, and the mud and sand carried are deposited here, forming a triangular sedimentary body close to the apex towards the land.

Drift deposits: also known as sheet flow deposits, mainly refer to sheet sand, silt and gravel deposits deposited by braided rivers.

Meandering river: a single channel with a sinuosity index greater than 1.5, relatively stable channel, and a ratio of width to depth less than 40. The slope of the channel is relatively gentle, the flow is stable, the sediments transported are fine, and there is obvious lateral erosion and accretion, and side banks are developed.

Braided river: It develops many channels, forks many times and converges into a braided river. The river channel is wide and shallow, with small curvature, the ratio of width to depth is greater than 40, and the curvature index is less than 1.5. The slope of the river course is large, the sediment transport volume is large, the grains are coarse, unstable, and the channel is developed, and there are many middle and upper reaches.

Braided River Delta: A sand and gravel-rich delta formed by a braided river foredecum into a stagnant body of water.

Braided river delta plain: The plain subfacies is composed of braided river channels and alluvial plains, with river swamps developing. The terrain has low relief, the channel has a large width-to-depth ratio, sedimentary glutenite, and flat sand bodies. The alluvial plain is formed by the migration and swing of braided channels, with a wide range and mainly gravel deposits. Fluvial swamp deposits can develop under humid climate conditions. There are tan mudstone, coal and gravel, and sandstone alternately, and the scour-fill structure and parallel bedding are developed.

Braided river delta front: underwater distributary channel, mouth bar, far bar, sheet sand and underwater distributary channel deposits developed. The underwater extension of the braided channel is relatively fine-grained; there are large cross-beddings and parallel beddings. Multiple channels superimposed-positive rhythm, underwater distributary channels are the main deposits of braided river deltas. Light gray powder and fine sandstone are developed, with cross bedding and lenticular bedding.

Pre-braided river delta: mainly muddy deposits, when the deposits are unstable, gravity flow deposits can develop. Pure quality, dark mudstone with horizontal bedding is developed, and even thin-bedded siltstone is developed.

Previous studies did not determine the paleowind direction of continental lake basins through sedimentary systems. In order to find mineral resources and oil and gas exploration in continental lake basins, it is necessary to restore the paleowind direction of continental lake basins. The invention starts with the distribution pattern of the sedimentary system in the area to be restored, analyzes the law of the distribution pattern of the sedimentary system in the area to be restored, summarizes and induces the characteristics of facies combination, and provides guiding significance for the analysis of paleo-atmospheric circulation.

As shown in Figure 1, a method for determining the paleowind direction of continental lacustrine basins through the distribution pattern of sedimentary systems includes the following steps:

Step 1: Identify the area and horizon to be restored, which specifically includes: 1. Investigation and data collection of the geological characteristics of the area to be restored: investigation of the geographical location of the area to be restored, regional geological background, structural development, and stratum distribution characteristics in the area 2. Field investigation in the area to be restored.

Step 2: Determine and analyze the sedimentary system in the area to be restored; determine the sedimentary facies and sedimentary subfacies according to the facies signs in the area to be restored, and describe the characteristics of the sedimentary facies and subfacies; Analysis of five aspects: sedimentary structure marks, color marks, and biofossil marks.

Lithological characteristics include rock color, composition, structure, structure, rock type and their combination; structural signs include maturity, grain size, sorting degree, degree of roundness and shape of rock mass section, etc.; sedimentary structural signs include bedding structure and shape structure, the bedding structure is divided into parallel, staggered, blocky, horizontal, graded bedding, deformation structure, exposed structure, filling structure; color marks include red, yellow, brown red and other oxidized colors of sediments ; Biological fossil signs include plankton, plants and their residual sediments, wreckage and so on.

Step 3: Summarize the distribution law of the sedimentary system and summarize the facies combinations at different locations. Statistical distribution rules of sedimentation in different locations, after a comprehensive analysis of the sedimentary system, determine the law of the sedimentary system; comprehensive literature data and regular distribution characteristics of the area to be restored, to obtain the sedimentary differentiation law of the area to be restored; the distribution law of the depositional system Classified according to certain sedimentary facies combination.

Specific steps: 1. Establish a two-dimensional coordinate system with the center of the area to be restored as the origin; 2. Divide it into eight areas according to the natural orientation: north, north east, east, southeast, south, south west, west, northwest; 3. According to The sedimentary facies and sedimentary subfacies determined in step 2 are converted into percentages according to the ratio of each orientation, and drawn in a two-dimensional coordinate system in the form of a round pie; 4. The sedimentary facies or sedimentary subfacies with larger specific gravity are used as The dominant sedimentary facies or subfacies of this orientation.

Step 4: Restore the paleowind direction of the area to be restored; use sedimentological methods to analyze the hydrodynamic high-energy bands and low-energy bands, so as to obtain the hydrodynamic energy levels of sedimentary facies or sub-facies in different orientations in the area to be restored, and determine the basin Based on the windward and leeward positions of the windward side, the paleowind direction of the area to be measured can be obtained.

The present invention mainly summarizes and analyzes the strata and layers, sedimentary facies, and sedimentary subfacies in the area to be restored; summarizes the combination of sedimentary facies, divides them into different orientations, and summarizes the dominant sedimentary facies in different orientations; and then analyzes the sedimentary facies in the area based on sedimentology theory. The hydrodynamic force and energy levels in different directions restore the ancient wind direction.

Example

Taking Qinghai Lake and surrounding areas as an example to illustrate

Step 1: Determine the horizon of the area to be restored in the Qinghai Lake area. Literature research and data collection include (1) research on the geographical location, geological background, structural development, and stratum distribution characteristics of Qinghai Lake; (2) field research study.

Step 2: Determine and analyze the sedimentary system around Qinghai Lake. The sedimentary facies and sedimentary subfacies around Qinghai Lake are determined according to the facies markers. Fluvial facies, deltas, alluvial fans, fan deltas, coastal zones, eolian dunes and beach bars appear around Qinghai Lake, and the sedimentary facies and subfacies are statistically described Characteristics.

Determination of sedimentary facies and sedimentary subfacies around Qinghai Lake:

1. Alluvial fan:

In the Gangcha sand mining field near Gangcha County, sediments composed of gravel and sand were found. Sedimentary structure, trough-shaped cross-bedding is concave in shape, and has a erosion-erosion contact relationship with the flank sediments. The top and bottom gravel layers of the plate-shaped cross-bedding are arranged in parallel, and the middle part of the gravel layer is connected with the top and bottom gravel layers. Oblique structure, which can be judged as channel deposits on alluvial fan; cross-bedding or parallel bedding often appear inside, which can be judged as flood deposit of alluvial fan; muddy sediments are mostly red, yellow, brown-red and other oxidized Color, organic matter content is very little, almost no fossils; the same sedimentary structure developed in Jiangjuntai, the front of Longbaoshan Mountain, the front of Tuanbao Mountain and Daban Mountain.

2. Fan Delta:

The terrigenous clastic sediments of the Gangcha alluvial fan towards the lake are relatively coarse, mostly coarse sand and pebble-bearing sand, with high shale content, poor sorting and roundness, and low maturity. The gravel layer has inconspicuous parallel bedding or cross bedding, which can be judged to be a fan delta plain; in the transition zone, there is a steeper foreset facies, and the traction current structure is well developed. Large and medium-sized cross bedding is seen, which is the fan delta front. Similar sedimentary facies can be seen on the southeast side of the Heima River.

3. River-dominated deltas:

Sandy deposits are found in the lower reaches of the Buha River and at Tiebuga, tapering upwards and showing a positive rhythm. The profile of the sand body is lenticular. It has trough-shaped, plate-shaped, and wavy cross-bedding. The number of forks in the channel is small, the channel is almost straight, and there are residual sediments such as mud gravel and plant stems, which can be determined as the distributary channel subfacies of the delta plain; At the narrowing and thinning place of the river channel on both sides, silt and silty clay are found, with horizontal texture and wavy cross-bedding development, rain marks, dry cracks, and water flow ripples can be seen. There are plant debris, Plant stems, roots and burrows, etc., calcareous and carbonate nodule fossils, can be determined as the natural dyke subfacies of the delta plain; dark organic mudstone, peat or lignite deposits are found on the side near the lake, often interbedded with thin layers of powder Sandstone, with uniform bedding and horizontal texture, has fossil structures such as plant debris, charcoal, roots, ostracods, gastropods, and siderite, which can be determined as the swamp subfacies of the delta plain.

At the delta front, a multi-layered small-rhythm sandstone was found superimposed on the underwater sand body. The vertical flow section is lens-shaped, and the lateral direction becomes fine-grained sediments. It can be determined as an underwater distributary channel at the delta front. Subfacies: very fine sand and silt are found in the narrowing part of the channel, and plant fragments can be seen. The whole is a wavy bedding formed by flowing water, and there is a complex cross bedding formed by the interaction of flowing water and waves locally, which can be judged as delta pre-delta There are two triangular dam bodies at the mouth of the Buha River, with sand and silt, sorted sediments appear, and sheet sand on the flanks, showing wedge-shaped cross-bedding or "S "Foreset texture and horizontal texture are developed, the long axis direction of the plane is the same as the direction of the river, the cross section is lenticular, and the fossil content is scarce, which can be determined as the mouth bar of the delta front.

On the side near Qinghai Lake, dark gray silty clay was found, showing horizontal texture and massive bedding, with bioturbation structures and burrows, which can be determined as prodelta subfacies.

In summary, it can be concluded that the Buha River delta developed in the lower reaches of the Buha River and Tiebujia, and similar sedimentary facies developed in the south of the Shaliu River 4 km south of the Qinghai-Tibet Railway.

4. River phase:

The source of the Buha River was found near the Amuniku Mountain, and the catchment section where the intermountain rivers converge is the initial stage of the river formation process; this phenomenon also exists in the upper reaches of other rivers in Qinghai Lake, such as the Shaliu River and the Hargai River. But not as obvious as the Buha River; the lithology of the river erosion is mostly granite, and the sediments are mainly gravel, with less sediment.

Downstream from the Buha River, the terrain of the river valley widens, the channel is wide and shallow, the curvature is small, the ratio of width to depth is small, and the curvature index is less than 1.5. The sediments are mostly gravel, with obvious characteristics of braided rivers. The characteristics of braided river sediments can also be seen in the upper reaches of the Hargai River. In the upper reaches of the Hargai River, mainly coarse-grained sediments, mostly gravel, developed obvious erosion-filling structures, and few imbricated structures; It is lenticular and sheet-like on the top; it appears at the bottom of the river deposits vertically. It can be judged as channel bed subfacies; the centripetal sediments are mainly sand and gravel, with little muddy accretion, medium-poor sorting, more rolling components, and large plate-like cross-bedding.

On the plane: the upstream sediments are thicker and eroded, and the downstream sediments are finer; vertically: the grain sequence is not obvious upward; horizontally: a single lens, mostly connected with each other by washing, forming "sand-wrapped mud", which can It was judged as cardiac subphase.

The Buha River near the Qinghai Lake Highway becomes a single channel with a curvature of 1.6, while the Tiebujia River still maintains a single curved channel shape, which is a meandering river. The lateral erosion effect of the mainstream channel on the valleys on both sides is very strong, and the embankments on both sides of the river bank are mostly sandy and muddy sediments. The channel of the Tiebuga River is narrow and the water depth is relatively large. The sediments are mainly sandy and muddy, and there are gravels at the bottom of the channel. The north and south branches of the Hargai River have an obvious "L" shape, with a curvature of 1.5-1.7. The sediments in the curved channel are mainly sand, with low maturity, medium sorting, and many jumping components; large and medium-sized trough-shaped and plate-shaped cross-beddings and parallel beddings are developed; the sediments become finer upwards, and the layers The physical scale becomes smaller; it is plate-shaped and lenticular in the horizontal direction and band-shaped in the plane, and there is no vegetation cover on the surface, so it can be judged as the subfacies of the side beach.

5. Gu Binan phase:

The area between the Ganzihe sandy area on the east bank of Qinghai Lake and Tuanbao Mountain develops trough cross bedding, low-angle oblique bedding, wavy bedding, horizontal bedding, etc. Coarse gravel and sandy sediments appear, which can be determined It is the prime minister of Gu Binan.

The sediments at the top of the foreshore are mainly gravel and sandy, the surface layer is covered by aeolian sand, containing a large amount of mica, occasionally gravels are arranged in a directional manner, and the convex side faces upwards, showing trough-shaped cross-bedding and parallel bedding, Low-angle oblique bedding can be judged as foreshore subfacies.

The sediments in the breaking wave zone are mainly pure coarse sand, and the grain size becomes finer in the depressions. The sedimentary structures are mainly wave-forming sand-ripe bedding and parallel bedding; coastal sand bars and troughs are often developed, which can be judged as the coastal subfacies. The sediments in the transition zone are relatively complex, ranging from fine sand to gravel, in the form of trough-shaped cross bedding and low-angle oblique bedding, which can also be seen in Yilangjian and Erlangjian in Nanshan, Qinghai.

6. Beach and dam phase:

A series of large north-south dams appeared near the Erhai Lake on the southeast coast of Qinghai Lake. Three types of lithofacies can be seen on the profile, namely massive gravel sandstone facies, massive conglomerate facies and graded glutenite facies, which can be judged as beach bar facies; beach bar facies can be divided into 6 facies belts, namely semi-deep lake Facies belt, outer wave facies belt, breaking wave facies belt, flushing facies belt, transshore facies belt, lagoon facies belt; similar sedimentary facies and sedimentary subfacies can be seen along the southeast highway, Erlangjian, and the middle of the south bank.

The sediments are mainly silt and mud, with horizontal bedding, hilly cross-bedding and other sedimentary structures; they are in sudden contact with the overlying sand and conglomerate strata, but are flat and without erosion, and bioturbation structures and biofossils can be seen , can be judged as a semi-deep lacustrine facies zone, where the water body is relatively deep and below the normal wave base, and normal waves cannot affect the bottom sediments.

The sediments are medium-coarse sand with pebbles, the gravels are mostly flat, lying flat and scattered in the sand, the sediments are poorly sorted, and the hydrodynamic force is not strong, so it can be judged as an outer wave facies zone.

The sediments are composed of well-sorted fine gravel, without corrugation or bedding structure, and are densely packed in massive form. It can be judged as the wave-breaking facies belt, which is an obviously raised step towards the lake side and slopes towards the lake.

The distribution of the sediments shows obvious gradation, and the updip direction is composed of gradually finer fine gravel and medium fine sand. After being broken, it turns into a facies belt where flushing flow spreads to land, and the facies width is mostly 40-80cm.

The sediments at beach bars with higher uplift and lagoons are slightly thicker than normal beach bar sediments, and plate-shaped cross-bedding or parallel bedding inclined to the land is developed, which can be judged as transshore facies belt; Under wave conditions, the lake water crosses the top of the beach bar and spreads on the top of the beach bar and on the landward side.

Mainly muddy sediments, in the closed or semi-closed shallow water area blocked by the beach bar, located on the landward side of the beach bar, it can be judged as a lagoon facies belt, the wave action of this facies belt is very weak, and it is a low-energy environment .

7. Feng Chengxiang:

The lakeside eolian sedimentary environment can be seen in the southwestern margin of Tuanbao Mountain, with wind as the main geological force and eolian facies, which can be divided into two sub-environments: dunes and inter-dunes.

Most of the sand dunes are small in scale. The plane shape of the dunes is crescent-shaped, with two animal horns pointing to the downwind direction. The windward slope (facing east) is convex and gentle; the leeward slope (facing west) is a concave and steep slope. The grain size of the sand grains is finer than that on the windward slope, so it can be judged as a barchan dune; the height of a single barchan dune is generally small, rarely exceeding 10m; the wind direction indicated by all barchan dunes is from the land to the lake .

In the center of the eolian sandy area, barchan dune chains develop; there is basically no vegetation coverage between the barchan dunes in the Ganzi River sandy area, and large areas of seabuckthorns can often be seen between the barchan dunes in the eastern lake sandy area. vegetation.

On the edge of the sandy area near the foot of the mountain, there are multiple facets, the base of the dune is relatively gentle, the top of the dune is very sharp, with obvious ridges; the bottom of the dune is parallel bedding, which is conical in macroscopic shape, With their sharp tops and narrow ridges, they can be identified as pyramidal dunes.

Step 3: Make a two-dimensional coordinate system with the center of the satellite image of Qinghai Lake and its surrounding areas as the origin; The depositional system is divided into six regions, namely the North, Northeast, East, Southeast, South, Northwest, West and Southwest regions, as shown in Figure 2.

The sedimentary facies that appeared in the six areas were summarized into six sedimentary systems; the northern area is the Datongshan alluvial fan, fan delta, braided river, and meandering river sedimentary system; the northeastern area is the Hargai River, Ganzi River, Gubinan , delta sedimentary system; the eastern area is the Tuanbaoshan-Dabanshan-alluvial fan, paleoshore, and eolian facies sedimentary system; the southeastern area is the Riyue Mountain-Bison Mountain-alluvial fan, beach bar, Daotanghe sedimentary system; the southern area It is the sedimentary system of Nanshan, alluvial fan, beach bar, fan delta and paleo-shore facies in Qinghai; the northwest area is the sedimentary system of Buha River delta. The proportions of sedimentary facies in the six regions are shown in Table 1.

Table 1. Combination and proportion of sedimentary facies in different regions

The proportion of sedimentary facies and sedimentary subfacies in each orientation is plotted in the coordinate system with a pie chart, as shown in Figure 3;

The sedimentary facies and subfacies with the largest proportion in each orientation are regarded as the dominant sedimentary facies of this orientation, as shown in Figure 4.

Step four:

From the analysis of Step 3, it can be seen that the northwest of Qinghai Lake is a low-energy environment, because the delta facies is the main sedimentary facies, and it is mainly constructive, and the area of eolian facies deposition is almost invisible, so it can be deduced that the northwest area is the leeward side; The area is a higher energy area, because there is enough power in the high energy area to move the sand particles near the water further to the shore, forming a large area of destructive delta, and forming a large area of beach bar along the coast, so it can be inferred that the south For the sedimentary system at the edge of the lake, since the paleowind direction is from the leeward side to the windward side, the paleowind direction of Qinghai Lake is from northwest to south, that is, northwest wind.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process conversion made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (2)

1. A method for determining the paleowind direction of continental lacustrine basins by sedimentary system distribution patterns, characterized in that it comprises the following steps: S1: Define the area and layer to be restored; S11: Investigation work and data collection of geological characteristics of the area to be restored; investigation work on the geographical location of the area to be restored, regional geological background, structural development, and stratum distribution characteristics in the area; S12: Conduct field investigations in the area to be restored; S2: Determine and analyze the sedimentary system; determine the sedimentary facies and sedimentary subfacies that appear according to the facies markers in the area to be restored, and describe the characteristics of the sedimentary facies and subfacies; among them, the facies markers can be identified from lithological characteristics, structural markers, sedimentary Structural markers, color markers, and biofossil markers are analyzed from five aspects; the lithological features include rock color, composition, structure, structure, rock type and their combination; the structural markers include maturity, grain size, sorting degree, The degree of roundness and the shape of the rock mass section; the sedimentary structure signs include bedding structure and shape style, and the bedding structure is divided into parallel, staggered, massive, horizontal, graded bedding, deformation structure, exposed structure, and filling structure ; Color signs include whether red, yellow, or brownish red appear in the color of the sediment; the biological fossil signs include plankton, plants and their residual sediments and wrecks; S3: Summarize the distribution law of the sedimentary system and summarize the facies combinations at different locations; count the distribution law of the sedimentation in the area to be restored, and determine the law of the sedimentary system after comprehensive analysis of the sedimentary system; comprehensively integrate literature data and regular distribution characteristics of the area to be restored, The sedimentary differentiation law of the area to be restored is obtained; the distribution law of the sedimentary system is divided into different areas according to the following sedimentary facies combinations; S31: Establish a two-dimensional coordinate system with the center of the area to be restored as the origin; S32: Divide into eight regions according to the natural orientation; S33: According to the sedimentary facies and sedimentary subfacies determined in step S2, convert them into percentages according to the ratio in each orientation, and draw them in a two-dimensional coordinate system in the form of a pie; S34: Sedimentary facies with larger specific gravity as the dominant sedimentary facies in this orientation, and sedimentary subfacies with larger specific gravity as the dominant sedimentary subfacies in this orientation; S4: Use sedimentological methods to determine the paleowind direction of the restored research area; use sedimentological methods to analyze and study the hydrodynamic high-energy and low-energy bands, so as to obtain the hydrodynamic energy levels of sedimentary facies or sub-facies in different orientations in the area to be restored , to determine the positions of the windward side and the leeward side of the basin, and obtain the paleowind direction of the area to be measured. 2. A method for determining the paleowind direction of continental lake basins according to claim 1, wherein the eight regions are respectively north, north east, east, southeast, south, south west, west, Northwest region.

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