Field geological observation records and sketches

First, the basic requirements and format of field records

The specifications of the field record book are unified. The part with cm grid on the left is used for section drawing and sketch drawing, and the part with horizontal grid on the right is used for text recording. Before writing, vertical lines of about 1cm should be drawn on the left and right sides of the writing surface, and the number, position, content and observation along the way should be recorded on the left, and the numbers of specimens, photos and samples should be recorded on the right.

Qinhuangdao geological understanding practice course

Second, the contents of the written record

(1) Route and number: refers to the main location and direction of field investigation, which should be written in the first item on the front page of daily work.

(2) Purpose or task: refers to the main purpose and task of this geological route survey.

(3) Points: the number of observation points in the practice area. The numbers should be unified, written in the middle of the line, and the dot should also be marked on the topographic map and the letter section.

(4) Point: refers to the position of the observation point. Point records can be recorded by azimuth, such as the intersection of 85 azimuth of Liangjiashan and Niubi Station156 azimuth; Or in the form of a combination of azimuth and linear distance, such as Liangjiashan 16 azimuth 250m; Special terrain features can also be used to record, for example, the elevation control points of Liangjiashan. If the country is engaged in conventional geological mapping, the recording format of points has strict requirements, that is, points must be determined by horizontal, vertical and elevation, which can be expressed by rectangular coordinates and elevation can be found from contour lines. At present, GPS instruments are directly used for reading.

(5) Meaning of point or point: The geological meaning or nature of pointing mainly includes geological boundary points, structural points, mineral points, fossil points and hydrological points.

(6) Content: It refers to the geological phenomena in this point and its surrounding area. The description of strata should be carried out in the order of old first and then new; The lithology: composition: structure: structure: secondary change: thickness and occurrence of strata in different periods should be carefully observed and recorded: After describing the strata on both sides of the boundary point, it is necessary to further describe the strata contact relationship in different periods.

For intrusive rocks, besides describing the color, texture, mineral composition and content, it is also necessary to describe the contact relationship with the surrounding, contact metamorphism, occurrence and scale of surrounding rocks, etc.

For the structure, in addition to the description of the phenomenon, we should also collect data for analysis and research. Such as two-wing posture, scratch posture, fault plane posture, joint posture, small structure posture and so on.

(7) Observation along the way: refers to the summary of geological phenomena seen between two geological observation points.

Written records should be focused and concise. The most important thing is to objectively and accurately reflect the actual situation of this point, be true and comprehensive, and never make it up at will. In practical work, mistakes in records can be crossed out with a pencil, and must not be erased and rewritten with an eraser.

Third, draw the outline of the letter hand.

Xinshou profile is a macroscopic profile (Figure 5- 18) reflecting the stratum, lithology and geological structure along the route, which is very useful for understanding the geological characteristics of a large-scale route. The geological route should be as perpendicular as possible to the direction of rock strike or structural line. The specific requirements for drawing such a map are as follows:

(1) When drawing, the drawing name, scale, orientation and legend shall be indicated.

(2) Distance measurement can be measured step by step or visually, and then drawn according to the scale.

(3) Pay attention to the coordination of horizontal and vertical dimensions. It's best to know the topographic features of the observation route from the topographic map before making this map.

(4) Attitude calibration can be drawn according to the actual situation seen in the profile. If the included angle between the profile line and the stratum strike is large, it should be drawn on the profile according to the calculation results.

(5) When drawing the Xinshou section, if the old and new strata are separated by angle unconformity, the angle unconformity line should be drawn first, and then the new and old strata should be drawn separately. Faults cut strata, first draw fault lines, and then draw two sets of strata.

(6) The layout of the drawings should be reasonable, symmetrical and beautiful, the line thickness should be uniform, and the use of lithologic patterns should comply with the regulations.

Figure 5- 18 Cross-sectional view of Shimenzhai-Wajiashan stratum route

Fourth, sketch painting

All kinds of important geological phenomena can be represented by sketches. It is an important raw material and an indispensable part of geological reports and articles. Sketch can be roughly divided into three categories: landscape sketch, profile sketch and photo sketch. No matter what kind of sketch, we should follow the principle of sketch and really highlight the key content; The selected scale should be appropriate and the proportion of each part should be accurate; At the same time, the map name, orientation, stratigraphic age and legend should be marked.

(1) Landscape sketch: It is often used to sketch some macroscopic landforms and structural phenomena. It should be drawn according to the principle of perspective. When sketching, the outline of the distant mountain is thin, the outline of the near mountain is thick, and the closer it is, the thicker it is; There are many details near the mountain, but few details in the distant mountain. The farther away, the less. There should be a clearing between the front mountain and the back mountain. At the same time, the relative position between the sketcher and the sketcher should be pointed out.

(2) Sketch of outcrop profile: it is a sketch of profile on outcrop in a small area. It is mainly used to describe the contact relationship between strata, the intrusion and interpenetration of magmatic rocks and various structural phenomena.

(3) Photography and photographic sketch: Geological phenomena, whether large-scale or outcrop, can be photographed on the spot for use in reports and articles. When taking photos of outcrop geological phenomena, it is best to use a hammer or compass as a ruler. Photographic sketch is to sketch out the main geological phenomena according to photos on the basis of photography.

Photos and sketches should be recorded in the notebook.

V field observation and description of sedimentary rocks

(1) Description of sedimentary rocks

Observation and description of field sedimentary rocks mainly include the following six aspects:

1. color

The color of sedimentary rocks is the most remarkable macroscopic feature of sedimentary rocks. When describing sedimentary rocks, color is often put at the front.

The causes of color are divided into primary colors (including genetic colors and autogenous colors) and secondary colors. Genetic color is the inherent color of matter, for example, feldspar sandstone is flesh red because feldspar debris of granite is red. Authigenic color is the color caused by primary minerals in sedimentary and diagenetic stages, such as green glauconite sandstone. Secondary color is the color of secondary minerals produced by secondary changes in sedimentary rocks, such as brownish red formed by common secondary minerals on weathered crust.

Autogenous color and genetic color are uniform and stable, widely distributed, consistent with bedding; The secondary color is generally uneven, spotted and not widely distributed, which is inconsistent with bedding.

There are two ways to describe colors in the field: one is physical description, such as brick red and egg white color; The other is the description method of using colors to describe tones, such as deep purple and light yellow-gray, in which front red and rear gray are the main colors, placed after the name, deep purple and light yellow are the secondary colors, and placed in front of the main colors as adjectives.

The above color refers to the color of the dry and fresh face of the rock, and both the fresh face and the weathered face should be described in the field.

2. Petrology

Mainly refers to the characteristics of sediment composition and mineral composition.

When observing and describing rocks in the field, we should use magnifying glass, hydrochloric acid, knife and other tools to qualitatively identify the composition and mineral composition of sedimentary rocks.

For clastic rocks, it is necessary to preliminarily identify the composition and percentage of clastic particles and cements. Clastic rocks are mainly composed of detritus, including quartz, feldspar, cuttings and heavy minerals. The so-called heavy minerals refer to minerals with a relative density greater than 2.06. Common ones are zircon, monazite, sphene and tourmaline. Although their content is small, their chemical properties are very stable. Debris is a mineral aggregate that retains the structure of the parent rock, that is, rock debris whose mineral particles have not been completely separated after the parent rock is broken. It is mostly produced in coarse-grained clastic rocks, and it is difficult to identify sandstone with naked eyes.

Cements of clastic sedimentary rocks are usually siliceous, iron, calcareous and argillaceous. Their general field characteristics are that there are many siliceous cements, which make rocks hard, iron ones are often reddish brown, calcium ones are foamed in dilute hydrochloric acid, and muddy ones are often loose and have low hardness.

Clay rock is mainly composed of clay minerals (more than 90%), with fine particles and fine structure, and there is no sand feeling with teeth. In the field, it is mainly identified by dyeing reagents.

The field identification of carbonate rocks mainly depends on dilute hydrochloric acid, which can be divided into four basic rock types in combination with other lithologic characteristics. Among them, the surface of limestone is strongly foamed with dilute hydrochloric acid, and noise can be heard; Dolomitic limestone bubbles quickly with dilute hydrochloric acid, but the noise is not big; Lime dolomite with dilute hydrochloric acid bubbles slightly; Dolomite added with dilute hydrochloric acid basically does not bubble or bubbles slowly and weakly.

The detailed naming of clay rocks and carbonate rocks depends on indoor research.

3. Structure

Structure is a commonly used descriptive factor of sedimentary rocks, involving particle size and distribution, particle morphology and surface characteristics, sedimentary fabric and so on.

(1) clastic rock structure. The structure of clastic rocks should focus on particle size and separation. If it is conglomerate, it is necessary to describe the shape, roundness and particle surface characteristics of gravel.

The size of debris particles is called particle size, which is usually divided into four categories according to the particle diameter (Table 5-2).

Clastic rocks seen in the field are rarely composed of only one particle size, but of many particle sizes. The degree of fragment size is called sorting. When the content of a certain particle size is greater than 75%, or the particle size is equal, it is called sorting; When the content is 75% to 50%, the ranking is medium; When the content of no particle size exceeds 50%, or when the particles are very different, it is considered that the separation is poor.

The shape of clastic particles is one of the most characteristic signs of clastic rocks. Mainly including roundness and shape. This is of great significance to the study of conglomerate.

Table 5-2 Structural Classification of Clastic Rocks

Roundness refers to the degree of wear and roundness of abrasive particles, which is generally divided into three grades by naked eye: angular, sub-circular and circular. The roundness of particles is directly related to the length of conveying distance, and of course it is also related to the hardness, density and size of particles.

(2) Structure of clay rock. Because the particles of clay rock are very fine, it is often difficult to identify its structure in the field, mostly under indoor microscope.

Clay (argillaceous) structure: almost all of them are composed of clay particles, with a content of not less than 95%. When you bite with your teeth or touch with your hands, you can't feel the existence of particles. When you cut with a knife, the section is very smooth.

Silty clay (argillaceous) structure: it has obvious graininess (sand) feeling when bitten or touched by hand, with uneven section and rough fracture. A gentle washing with water in the palm of your hand can wash away clay particles and leave silt. Silty sand particles can also be seen under a magnifying glass.

Sandy clay (argillaceous) structure: obvious particles can be seen by hand and sand particles can also be seen by naked eyes.

(3) Carbonate structure.

Gravel structure: the structure of weakly consolidated carbonate sediments, eroded by underflow, waves and tides, and redeposited in situ. For example, the Cambrian gravel limestone is such a structure.

Biological structure: the biological skeleton structure of biolimestone and reef limestone composed of in-situ fixed growth organisms.

Oolitic texture: refers to the carbonate rock structure composed of concentric oolites with a particle size less than 2mm, which can be calcareous, dolomite, iron or siliceous.

Crystal structure: Structure formed by chemical and biochemical deposition and recrystallization of limestone and dolomite. According to the size of crystal particles, it can be further divided into three types: obvious crystal (more than 0. 1mm), microcrystal (0. 1 ~ 0.0 1 mm) and cryptocrystal (less than 0.00 1mm).

4. Structure

Mainly refers to the primary structure of mechanical origin. Include bedding, bedding structure and deformation structure. Especially the first two are more important.

(1) Bedclothes. Because of its composition, color, structure and trend, it is a layered structure in the vertical direction. The basic units of bedding include fine layers, strata and stratigraphic groups. According to the morphology, bedding can be divided into three basic types: horizontal bedding, wavy bedding and oblique bedding, and their forming environments are different. Horizontal bedding is almost completely developed in relatively calm clay or chemical sedimentary rocks. Wave bedding is generally formed in the fluctuation of water body. Oblique bedding is mostly developed in river sediments, indicating that the water medium flows quickly and rapidly.

When observing bedding, we should pay attention to its fine structure such as shape, size and thickness, interface properties, fine layer dip angle and lithology, which can directly reflect hydrodynamic conditions.

(2) Hierarchical structure. Refers to the structure on the sedimentary rock level, including wave marks, mud cracks, rain and hail marks and scouring surfaces. The common wave marks in the field are mostly developed in sandstone or siltstone, which are formed by the oscillation or directional movement of water. Mud cracking mostly occurs in mudstone and shale, which is formed because unconsolidated clay deposits dry up and shrink when exposed to water.

5. Rhythm of sedimentary rocks

On the section perpendicular to the stratum, the phenomenon of periodic repetition in rocks of the same lithology is called sedimentary rhythm or sedimentary cycle. Its causes are complex, mainly due to the periodic changes of natural geographical environment caused by the periodic rise and fall of the crust. Rhythm changes from coarse to fine are common in the wild from bottom to top. For example, from conglomerate, sandstone, siltstone and shale to coal or limestone, the opposite situation can also occur, that is, from bottom to top, from fine to coarse.

Field observation to describe the rhythm should include the following contents:

(1) First, observe the general trend of prosodic changes and determine the prosodic type, whether it is continuous or intermittent, semi-prosodic or full prosodic, positive prosodic or anti-prosodic.

(2) Lithological characteristics such as rock type, composition, color, structure and structure that constitute the rhythm.

(3) Whether the contact relationship between adjacent rhythms is gradual or abrupt, and whether there is erosion or scouring.

(4) The thickness of rhythm and the proportion of each rock.

6. Formation thickness

Generally, it is made of blocks (over 2mm), thick layers (1 ~ 2mm), intermediate layers (0. 1 ~ 1~2mm) and thin layers (0.01~ 0./kloc-0./~ 0. For some particularly obvious marker beds and target beds with stable horizons, the single-layer thickness should be specially pointed out.

7. Strata contact relationship

The contact relationship between strata can be divided into conformity and unconformity, and the latter can be further divided into angular unconformity and parallel unconformity. Pay attention to the left and right tracking during field observation, and don't blindly draw conclusions when you see one point. Unconformity surface is often an important sign to determine the mapping unit to divide strata, such as paleontological discontinuity, sedimentary discontinuity, erosion surface, basement conglomerate, paleoweathering crust and so on.

8. Paleontological fossils

Paleontological fossils can not only determine the relative age of rock formation, but also infer the conditions of forming media at that time, such as water temperature, salinity and depth. During field observation, we should pay attention to its ecological characteristics, burial and preservation conditions, quantity, integrity and distribution, and preliminarily identify its species and genera.

It is the basis of rock work to observe and describe the outcrops in the field in a comprehensive and detailed way. Therefore, be careful and attentive when observing; The description should be comprehensive and targeted, detailed and not cumbersome, in a certain order to avoid omissions.

(2) Field naked eye identification of sedimentary rocks

According to the data listed in Table 2-3, Table 5-3 and Table 5-4, the field visual identification and classification of sedimentary rocks can be carried out.

Table 5-3 Classification Table of Sedimentary Rocks

Table 5-4 Classification Table of Mineral Composition of Carbonate Rock

Contents of geological structure observation of intransitive verbs

(1) Observation and research contents of fold structure

1. Field identification mark of fold structure

(1) The strata from the core to both sides are symmetrical and appear repeatedly. The new and old wings of the core layer are anticlinal structures; The core stratum is new and the two wings are old, which is a syncline structure.

(2) Occurrence sign: strata and radial structures are inclined in reverse, and strata and dorsal structures are inclined in reverse.

(3) Formation bending and turning.

(4) Landform marks: Single-sided mountain, rock stratum triangle and rock stratum have the characteristics of symmetry and repetition, which are often indirect identification marks of folds.

2. Observation and description of folds

(1) It is necessary to measure the attitude of each part of the fold in the field, and then determine the geometric characteristics of the fold according to the attitude, and finally determine the spatial shape.

(2) Observe the relationship between the new and old strata in the fold, and determine the type and nature of the fold according to the relationship between the new and old strata in the core and the two wings and the occurrence of the two wings.

(3) Observe and record the distribution characteristics of folds and folds in scale, plane and profile, analyze their relationship with minerals and other structures, and study their formation period.

(4) In the field, we should pay attention to observe and describe the small structural features in folds, such as small folds, small faults, joint occurrences and other features formed by interlayer sliding.

(2) Contents of joint observation and research

Identification of mechanical properties of 1. joint

Characteristics of general shear joints:

A. The occurrence is relatively stable, extending far and deep along the strike.

B the joint surface is flat and smooth, and sometimes scratches or mirrors are left due to shearing and sliding.

Shear joints formed in sandstone and conglomerate usually pass through gravel and cement.

Typical shear joints usually form a conjugate X-joint system, which is perpendicular to the conjugate joints plane. Generally, one group of X-joint systems is developed, while the other group is less developed, and the spacing is generally equal.

General characteristics of tensile joints:

A. The occurrence of tension joint is unstable and does not extend far, and a single joint is short and curved.

B the tension joint is rough and uneven without scratches.

Tensile joints in sandstone and conglomerate usually bypass coarse sand or gravel. If you cut through gravel, the joint surface is also uneven.

D. Tension joints have many openings, and cracks are often filled by later dikes.

E sometimes the joints are zigzag tensile joints, and sometimes they are radial or concentric combinations.

2. Segmentation and matching of joints

Staging of joints is mainly based on the intersection of joint groups, which mainly includes the following three types:

(1) staggered. Joints formed in the later stage often cut off the joints in the earlier stage. If the joints in the later stage belong to shear joints, it indicates that the marker points on both sides of the fault line are staggered accordingly (Figure 5- 19).

(2) restrictions. The sudden termination of one set of joints before extending to another set of joints is called restriction. The restricted joint group was formed late. As shown in Figure 5-20, the combined groups 3 and 4 are limited by 1 and 2, so the former formed late.

Fig. 5- 19 Staggered Relationship of Different Joints

Figure 5-20 Constraints of Different Joints in Limestone in Xiangxi, Hubei Province

(3) mutual cutting. If two sets of joints cross or cut each other, it means that two sets of joints are formed at the same time, sometimes in a conjugate relationship (Figure 5-2 1).

(4) Tracking, utilization and transformation. Late joints sometimes use early joints, follow early joints or change early joints. Therefore, some late joints are often more obvious and complete than early joints.

The various intersecting relationships of the above joints are often not obvious, so we should carefully observe and consider all kinds of signs in actual work and supplement other evidence as much as possible to distinguish them.

Fig. 5-2 1 mutual cutting of two groups of conjugate shear joints

The matching of joints is mainly based on the combination relationship of joints, supplemented by the general characteristics of joint development and related structural relations.

3. Observation and research on the relationship between joints and large structures

(l) Joints related to folds. When a group of horizontal rock strata are squeezed laterally in the horizontal direction, two groups of X-shaped shear joints are formed on the plane before the rock strata are folded, and the joint plane is perpendicular to the plane, which is called early plane X-shaped shear joints. It can also produce tensile joints parallel to the direction of extrusion pressure before rock bending. This kind of joint is often traced by two groups of early plane X-type shear joints, and the joints extend in a sawtooth shape (Figure 5-22a).

Figure 5-22 Schematic diagram of the relationship between joints and folds (according to Structural Geology, edited by Wuhan Institute of Geology and other four universities, 1979)

When the stratum bends to form folds under the horizontal lateral compression pressure, longitudinal joints parallel to the direction of fold hinge are produced at the top of anticline. Sometimes, it can trace plane X shear joints and extend zigzag (Figure 5-22b).

When the rock folds develop to a certain extent, X-shaped shear joints are also produced on the profile, which are cross-shaped in profile, and their intersection lines are parallel to the direction of the fold hinge, so they are called X-shaped shear joints on the profile.

When the folded hinge fluctuates to a certain extent, tensile stress will be generated along the hinge, and tensile joints perpendicular to the direction of the hinge can be generated, which are distributed in a fan shape (Figure 5-22c).

(2) Joints related to faults. A group of joints are often formed due to the derived force generated by the relative motion of two plates of a fault. There are mainly pinnate tensile joints and shear joints. The acute angle between the tensile joint plane and the fault plane points to the movement direction of the plate. There are two groups of shear joints (S 1, S2) (Figure 5-23), in which the acute angle between S2 and the fault is generally less than 15, and the acute angle points to the movement direction of this plate.

(3) Joints related to regional structure. This kind of joint is the result of regional tectonic movement, which is widely distributed, stable in nature and occurrence and regional. Generally, it has large scale, wide spacing and long extension, and can cross different strata.

4. Selection of joint observation points

When arranging the position of joint observation points, the following conditions should be considered:

A. the outcrop is good and easy to observe.

B. The structural features are clear and the joints are developed.

C the outcrop is generally not less than 10m2, which is convenient for systematic measurement.

D observation points should be selected in important parts of the structure and distributed in different structural layers, different rock series and lithologic layers and different structures.

5. Joint observation content

(1) geological background observation. Before observing joints, we must first understand the geological background of the observation area. That is, stratum, lithology, bedding and geological occurrence, occurrence of folds and faults, and structural position of observation points.

(2) Joint classification and stratigraphic division.

(3) Study on joint development degree. Describe the influence of rock stratum and thickness on joint development degree and joint development density.

(4) Observation of joint plane and profile combination.

(5) Matching joints in stages.

(6) observation of joint surface. Refers to the observation and study of joint surface shape, occurrence, structure, flatness and smoothness and filler.

6. Collation of joint measurement data

Joints are mainly analyzed by rose diagram, joint pole diagram and isodensity diagram.

Figure 5-23 Related Structures Near Faults

(3) observation and research contents of faults

1. Field identification mark of fault

(1) Discontinuity of geological body. The sudden interruption or dislocation of various contact surfaces of strata, dikes, rocks and ore bodies on the plane or profile can be used as a sign to judge whether the geological body is continuous or not.

(2) Repeated or missing strata. Strike faults often cause the repetition or absence of strata. Fold and unconformity can also cause repetition or loss of strata. Stratigraphic repetition caused by folds is often symmetrical, while stratigraphic repetition caused by faults is asymmetrical. Unconformity will cause formation loss, but unconformity often has the characteristics of erosive and erosive substances.

(3) Fault marks. Polished surfaces and scratches, steps and reverse steps on the fault plane and its surface; The existence of fault fracture zone and its tectonic rocks, and small structures related to faults, such as small faults, traction folds, joints, cleavage and schistosity. Dynamic metamorphism, etc.

(4) Discontinuous structure. Including folds, faults, schistosity and dislocation of unconformity.

(5) Landform signs. There are mainly cliffs, fault triangles, staggered ridges and valleys, beaded lakes, depressions, springs, straight valleys, straight boundaries between mountains and plains, etc.

(6) Signs of magmatic activity and mineralization. Fault fracture zone is a fragile zone, so it often becomes a channel and place for magmatic activity and mineralization.

2. Determination of relative motion direction of two fault plates.

The relative movement direction of the two plates is mainly determined by the repetition and absence of strata, the characteristics of fault planes and associated structures.

(1) two sets of strata. Strike faults or longitudinal faults, the old strata are generally exposed in the rising plate, and the new strata generally appear in the falling plate.

(2) Traction structure. The relative movement direction of faults can also be judged by using the traction structure formed by fault dislocation. The judgment method is to find out the acute angle between the traction structure and the fault plane, which points to the movement direction of the disk (Figure 5-24).

Figure 5-24 Traction Fold in Fracture and Its Indicating Direction of Two Disks' Movement

(3) Scratch and step. When you touch the scratch with your hand, the smooth direction indicates the moving direction of the optical disc. For nail scratches, the direction from thick to deep to thin to shallow represents the relative movement direction of the disc. The scarp direction under the positive step represents the moving direction of the disk, and the scarp direction under the reverse step represents the relative moving direction of the disk.

(4) Associated small folds and joints. The acute angle between the axial plane of the small fold and the fault plane points to the movement direction of the disk.

The acute angle between the pinnate tension joint plane and the fault plane points to the movement direction of the plate (Figure 5-23).

3. The main contents of field observation and fault description

(1) Observe and describe the features of fault plane, such as fault plane occurrence, scratch characteristics and occurrence, flatness of section, step development, etc.

(2) Characteristics of fracture zone, such as length and width of fracture zone, material composition, occurrence and dynamic metamorphism.

(3) Characteristics and occurrence of associated small structures, such as associated tension-shear joints, traction folds, schistosity, cleavage and small faults, and their relationship with main sections.

(4) Two sets of stratigraphic characteristics and occurrences.

(5) The scale, plane and profile changes of faults and their relationship with other structures.

(6) Topographic and hydrological signs.

(7) The observation and description of the characteristics of multiple faults, such as the superposition of scratches on the fault plane, reflects multiple faults.