Surface structure characteristics of 1. quartz sand particles
By studying the surface structure of quartz sand particles, the genesis of sediments can be classified and the ancient environment can be reconstructed. Therefore, we must attach great importance to the relationship between particle morphology and conveying medium conditions. The surface structure characteristics of quartz sand particles formed by different transport media and power conditions should be different, but different media transport conditions and power often form similar surface morphology characteristics. This brings some difficulties to the research work, and also fully shows the complexity and commonality of nature. Things have similarities and differences, so studying their differences has become the main aspect of studying the surface structure of timely particles. Some surface features are completely similar in different environments, but their "probability" or "abundance" are different. Therefore, it is of great significance to study the "abundance" of surface characteristics of timely particles in a certain sedimentary environment. Previous studies have found that the most common features on the surface of timely particles are conchoidal fracture, flat cleavage plane, rolling on cleavage plane or crystal plane, pits, dish-shaped pits, scratches, dissolution and precipitation of SiO2 _ 2, mineral recrystallization, particle morphology and so on.
In order to facilitate research and comparison, the surface characteristics of chronotropic particles in sediments from different sources (Table 5- 1) obtained by predecessors were compared with those in sediments from Qinghai-Tibet Plateau to determine their genesis and corresponding sedimentary environment.
Table 5- 1 Surface Structure Characteristics of Quartz Sand Particles in Different Sedimentary Environments
2. Statistical analysis of surface characteristics of timely particles.
The surface morphology and structural characteristics of different genetic types of timely particles were compared and analyzed. Through comparison, it is found (Table 5- 1) that although the morphology and surface structure types of timely particles are influenced by various external forces and complex conditions, their combination characteristics largely reflect the internal relations and laws of the causes. As mentioned above, the surface characteristics of timely particles are significant for identifying their sedimentary environment, but we should not only emphasize an isolated sign, but also adopt quantitative analysis methods. This book uses the method of characteristic particle percentage for quantitative analysis.
1 14 quartz sand particles were observed under scanning electron microscope. According to Powell's principle of roundness classification, the surface morphology of timely particles is simply divided into four grades: sharp edge, subangular edge, subangular edge and spherical edge. Its main surface features include the following 2 1 types: siliceous scales, siliceous spheres, pits and grooves, scales peeling, V-shaped impact pits, dished impact pits, pitted surfaces, polished surfaces, semi-parallel or arc-shaped stepped fractures, conchoidal fracture, flat shear fractures, fracture with enlarged cracks, adhered small fragments, flat joint surfaces, polished surfaces, upturned flakes, pits and grindings. With the help of the above indicators, the characteristics and frequencies observed under the electron microscope are statistically analyzed as follows (Table 5-2):
Table 5-2 Particle frequency statistics of genetic types of surface structure of timely particles.
(1) cross-section of Yeniugou (P 1-5, P 1-7) (Figure 5-20).
The P 1-5 sample is collected from the south of maduo county, Qinghai Province, and its lithology is khaki gravelly sandstone. Coordinates: N3431'39.4 "; e97 59′56.9″； The altitude is 43 13m. The surface characteristics of P 1-5 samples are as follows: the particles are mainly angular (4 1.67%), 83.3% of the particles have adhered small particles, in addition, 25% of the particles have silica spheres, 25% of the particles have scaly aging, and 50% of the particles have pits and ditches, which reflects the time. These surface morphological characteristics indicate that the sediment source is relatively close or the hydrodynamic conditions are relatively strong. Combined with the environmental analysis of the study area, it is considered that the sediments were deposited in a short time in a strong hydrodynamic environment and were river products in the early stage of the formation of the source lake.
The P 1-7 sample is collected from the upper part of this profile, and the lithology is gray-black gravelly silty sand layer. The surface characteristics of P 1-7 are obviously different from those of P 1-5: the particles are mainly spherical (80%) and round. 33.33% of the particles were polished, and 86.7% of the particles were adhered with small particles. At the same time, pits and ditches, silicon balls and silicon scales representing high-energy chemical environment are also common. This combination shows that the sedimentary environment of P 1-7 is completely different from that of P 1-5, and the hydrodynamic environment is weak. The sediments are in turbulent water environment and belong to lake sediments.
(2) Great Yemaling section (P2T 1- 1, P2T4- 1, P2T7- 1) (Figure 5-2 1).
P2T 1- 1 The sample was collected from Dayaling, southern maduo county, located at the bottom of lacustrine terrace, with grayish brown silt layer and horizontal bedding. Coordinate: N34 40' 44.1"; e98 4′ 1.0″； At an altitude of 4220 m p2t1-1,the timely surface characteristics of the sample are as follows: 86.67% of the particles are mainly spherical, the rest are sub-circular, and 46.67% of the particles are polished, and there are no pits and ditches, silica spheres and silica scale particles representing high-energy chemical environment, but there are conchoidal fracture and stepped cracks caused by machinery. This combination shows that its sedimentary environment is almost the same as that of P 1-7, with weak hydrodynamic environment and low energy environment, and it belongs to lake deposition. The combination characteristics of samples P2T4- 1 and P2T7- 1 are basically the same as those of samples P2T 1- 1. While the sample P2T4- 1 has particles (14.29%) representing the high-energy chemical environment, which may represent the lake at that time.
Figure 5-20 See Table 5- 1
Fig. 5-2 1 dayaling section The surface characteristics represented by the frequency of appearance of surface morphological characteristics of timely particles are shown in Table 5- 1.
(3) Overview of Heihe Township (P3- 13, P3- 18) (Figure 5-22).
P3- 13 and P3- 18 samples were collected from the east of Heihe Township, maduo county, and the lithology was grayish yellow silty sand. Coordinates: N34 48.110'; +00'; e98 8. 133′； At an altitude of 4252m, P3- 13 and P3- 18 have similar surface characteristics, which are mainly spherical particles. The spherical particles of P3- 13 reach 85.7% and P3- 18 reach 73.3%, and the rest are sub-circular particles without subangular edges. Particle surface features are obvious, such as polished surface, flat joint surface, stepped fracture, conchoidal fracture, etc. The corresponding percentages of these characteristics are shown in Table 5-2. However, corrosion pits, corrosion grooves and silica spheres representing high chemical energy are not common, while disk-shaped impact pits representing high-energy mechanical impact are common in the two samples, reaching 42.8% and 33.3% respectively. The above comprehensive characteristics show that the sample was in a lake with low chemical energy at that time, but the kinetic energy of the lake was huge, and the surface of particles collided with each other to form disc-shaped pits. Compared with the stable lake water body corresponding to the Dayemaling profile sample, the lake water body corresponding to the two samples in Heihe Township profile is more turbulent.
(4) North Halatan section of Ering Lake (P6- 1) (Figure 5-23)
P6- 1 The sample was collected at a river scarp in Halatan, maduo county, with a section thickness of about 9m. The lithology is yellow-green medium-coarse grained gravelly coarse sand layer with wavy bedding. Coordinates: N3511.193'; e97 52.07 1′； The altitude is 4391m. The timely surface characteristics of P6- 1 sample are as follows: most of the particles have silica spheres, pits, ditches and scaly exfoliated particles representing high-energy chemical environment, with contents of 6.67%, 60.00% and13.33% respectively; The contents of conchoidal fracture and flat shear fracture representing mechanical collision are 26.67% and 53.33% respectively. In addition, most particles have the characteristics of adhering small chips and upturned sheets. Like the sample of Yeniugou P 1-5, the particles in this sample are mainly angular (86.7%). The combination characteristics of Halatan profile samples indicate that the samples were formed in a high-energy environment, and the surface morphological characteristics indicate that the sediments are from close sources or have strong hydrodynamic conditions. It can be considered that the sediments were deposited in a strong hydrodynamic environment for a short time, which is the product of river facies in the initial stage of lake formation in the source area. This is consistent with the conclusion drawn from Ye Niugou profile P 1-5. According to the surface characteristics of seasonal particles, the formation environment of Yeniugou profile and Halatan profile is basically similar, but the distribution areas are different.
Figure 5-22 See Table 5- 1
Figure 5-23 See Table 5- 1 for the surface features represented by the frequency number of timely particles in Halatan profile.