Geological reconnaissance route and observation content

In order to successfully and comprehensively complete the field geological teaching task in Liangshan area and improve the teaching quality, we must pay enough attention to the geological exploration work in the whole area, and lay a solid foundation for the measured profile and mapping work.

According to the geological survey, internship schedule, geological mapping requirements and traffic conditions in the region, 5 ~ 6 geological exploration routes in Liangshan area are planned, with the main observation contents and teaching emphases as follows.

Figure 6- 14 Schematic Diagram of Modaoshigou Normal Fault

(1) Route from Wangxiangcun to Gongjiawan

1. Geological route

The starting point of the route is located at Shengoukou, about 300 meters south of Wangxiang Village (Wang Jiaxiang) in the eastern hilly area of the exploration area. Westbound along the deep ditch, Pan Liang is operated to Gongjiawan, with a total length of about 2.5km.

Observation content

The following main geological phenomena can be observed in turn along the route: ① rock types, interrelationships and fabric characteristics of the Hannan complex in the pre-Sinian system; ② The sedimentary unconformity contact relationship between pre-Sinian rock mass and Sinian sedimentary strata; (3) the stratigraphic characteristics of Sinian system and the contact relationship between the upper and lower parts of Sinian system and the staggered layers in sandstone; ④ Nature and evidence of Modaoshigou normal fault; ⑤ V-shaped law of Sinian strata and river flow direction in Modaoshigou; ⑥ Characteristics of dip anticline from Gongjiawan to Danangou.

3. Teaching priorities and requirements

Combining with the observation content, the following contents are emphasized: ① Combining with Hannan complex, the basic types of rocks, the field identification marks of magmatic rocks and sedimentary rocks, the interpenetration relationship of rocks and the determination method of age attribution are taught; ② Through the contact relationship between pre-Sinian system and Sinian system, the contact relationship and systematic classification of rock (body) layers (strata) and the performance of various relationships in this area are comprehensively introduced; ③ Analyze the paleogeographic environment and its changes by combining the stratigraphic sequence, lithologic characteristics and contact relationship from pre-Sinian to Cambrian; ④ Through the observation of Modaoshigou fault, the classification of field faults and the method of judging fault properties are summarized; ⑤ Analyze the characteristics of Gongjiawan anticline and its genetic relationship with Liangshan syncline on the north side.

(2) Danangou route

1. Geological route

The route starts from the watershed on the east side of the bottom of Danangou, west of Gongjiawan, and goes up along the ditch to Zhongliang Temple, with a total length of about 1.5km.

Observation content

The main observation contents include: ① the sedimentary integration contact relationship and fossil boundary between Sinian and Cambrian strata; ② Stratigraphic sequence and lithologic characteristics of Lower Cambrian; ③ Observe and practice collecting biological fossils; ④ the parallel unconformity contact relationship between CAMBRIAN and Ordovician and the characteristics of bottom conglomerate; ⑤ The nature of the oblique slip reverse fault in Zhongliangsi.

3. Teaching priorities and requirements

① Through the observation of Cambrian strata, the role of biological fossils in stratigraphic division and its relationship with lithostratigraphy are emphasized; (2) Recovering paleogeographic environment according to Cambrian lithology and paleontological characteristics; ③ Focus on analyzing the nature and evidence of Zhongliangsi fault.

(3) Xialiangshan Hougou Route

1. Geological route

This route starts from Hougoukou, Xialiangshan (town), goes south along the ditch, and reaches the Permian stratum on the southern margin of the tectonic site. The length of the route is about 1.0km.

Observation content

The main observation contents include: ① continue to observe the rock assemblage and paleontological characteristics of the lower CAMBRIAN strata, the parallel unconformity contact relationship between CAMBRIAN and Ordovician, and the Ordovician Zhaojiaba Formation (? ) bottom conglomerate; ② Division of Ordovician stratigraphic system and paleontological characteristics, characteristics and causes of cracks in Baota limestone turtle; ③ The overall contact relationship between Ordovician and Silurian, and the stratigraphic and rock characteristics of Lower Silurian; ④ The parallel unconformity between Lower Silurian and Lower Permian Liangshan Formation; ⑤ Observe and search for biological fossils in strata of different ages.

3. Teaching priorities and requirements

The main teaching contents include: ① the formation of basal conglomerate and its significance in stratigraphic division; ② Analysis of rock characteristics and sedimentary environment of Ordovician to Silurian strata, especially the discussion of Baota limestone and its formation environment; ③ Biofossil characteristics, stratigraphic division basis and division principles of Cambrian, Ordovician and Silurian; ④ The contact relationship between Permian and Silurian.

(4) Winnie Cave-Wujiaping Route

1. Geological route

The route starts from Weini Cave at the mouth of Zhangkouzi River on the south side of Liangshan, passes through Shuimoshang, Zhangjiakou Zi and Chenjiacun from south to north, changes from Chenjiacun to west, passes through Zhongwanzi to the west bank of Chenjiacun Reservoir, bypasses the south side of the reservoir, and crosses the ridge to Wujiaping. The route is long, about 5.5km, and the distance from Wujiaping to Shangliang Mountain via Tuziling is 3.5km, totaling about 9km. To complete the teaching task of this route. It is suggested to increase the number of vehicles (with simple roads) from the starting point of the route to Chenjiacun Township.

Observation content

The observation contents include: ① Zhangkouzi (Weimudong) oblique slip reverse fault; ② Lithological characteristics of upper and lower Permian strata; (3) Permian carbonate rocks and karst landforms; (4) The sedimentary integration contact boundary and discrimination of Permian and Triassic strata, and the characteristics of Triassic strata, lithology and paleontology; ⑤ The core of the west bank syncline of Chenjiacun Reservoir was squeezed and folded by Triassic strata, and the Liangshan syncline structure and its geomorphological characteristics were measured from the axis; ⑥ Observe and discuss the faults, characteristics, occurrence and properties of Wujiaping and Hegou villages.

3. Teaching priorities and requirements

The teaching emphases and requirements of this route are as follows: ① Emphasize the characteristics and mechanical mechanism of Zhangkouzi fault, and ask students to correctly distinguish fault plane, joint plane (tension, compression and torsion) and sedimentary plane, measure their occurrence and draw a schematic diagram of the fault; ② Analyze and summarize the stratigraphic and lithologic characteristics of Permian and Lower Triassic, and restore their sedimentary paleoenvironment and land-sea change history; ③ Based on the observation of the above four routes, the geometric characteristics and formation mechanism of syncline structure in this area are summarized around the folding phenomenon of Triassic strata in the core of syncline. Students are required to correctly distinguish the geological and geomorphological concepts such as basin, syncline basin and syncline structure, and further clarify the basic characteristics of asymmetric, short-axis and inclined syncline structure in Liangshan.

(5) Lion Mountain-Shangliangshan Huanglong Temple Route

1. Geological route

This route starts from Triassic strata on the east side of Lion Mountain in syncline basin, and passes through Lion Mountain, Hejiashan and Tuziling to Huanglong Temple in Shangliang Mountain. The total length of the route is about 4.5km. In order to observe the systematicness of the stratum (from old to new), the starting point of the route should be placed in Lion Mountain, or the starting point should be set in Huanglong Temple according to the specific situation, and it should be observed from north to south.

Observation content

The main observation contents are as follows: ① the contact relationship between Triassic and Paleogene, Neogene-Paleogene stratigraphic sequence and rock characteristics; ② Lithology and horizon of the Upper Permian Wangpo shale in the syncline east of Tudiling; ③ Tuziling oblique slip reverse fault; ④ Carbonaceous shale and white clay of Liangshan Formation of Lower Permian to the west of Tudiling fault; ⑤ Quaternary alluvium (alluvial fan), slope deposit and residual deposit near Huanglong Temple at the northern foot of Liangshan Mountain, and secondary terrace and floodplain of Hanjiang River.

3. Teaching priorities and requirements

The teaching focuses include: ① Through the observation of Paleogene strata and lithology, we can understand the sedimentary paleoenvironment, such as paleogeomorphology, paleoclimate and material sources, hydrodynamic conditions, etc. And the genetic relationship between Paleogene sedimentary process and syncline structure development; ② Formation conditions of Wangpo shale and carbonaceous shale of Liangshan Formation, and their paleogeographic environment and mineral significance; ③ By observing the fault plane, scratches and tectonic rocks of the Tuziling fault, students are required to master the method of determining the fault and its properties in the field and analyze the genetic relationship between the Tuziling fault and the syncline structure; ④ Briefly introduce the genetic types of Quaternary sediments, the age division of terrace sediments, and the important role of Himalayan movement and external dynamic geological processes since Paleogene in shaping modern landforms of Liangshan.

(6) Route from Shangliang Mountain to Zhongliang Mountain

1. Geological route

From Shangliangshan Lime Factory to Zhongliangshan (955 meters above sea level) at the syncline turning point via Tuziling. The route is about 2.5km long.

Observation content

Take a bird's eye view of the practice area from the commanding heights of Zhongliang Mountain, including landform types and zoning, basic framework and distribution law of geological structures (folds and faults), general situation of stratum development, genetic relationship between stratum and landform, etc.

3. Teaching priorities and requirements

The main teaching contents include: ① according to the local magnetic declination (west139') or coordinate magnetic declination (east13') given by the topographic map of Liangshan area, correct the magnetic declination and seating magnetic declination (west 2 40') on the spot, and complete the orientation of the topographic map with the corrected compass; (2) Briefly introduce (compared with the field) the natural geographical location, structural location, main geomorphological features and types of the practice area, the mutual restriction of internal and external dynamic geological processes in the formation of modern geomorphological pattern in Liangshan, and the geological basis for the development of different landforms; ③ Focus on understanding the general situation, distribution law, main structural forms and spatial distribution characteristics of strata in the area, so that students can understand the geological and geomorphological positions of the main exploration routes and measured geological sections in the area and lay a good foundation for the smooth development of the follow-up work; (4) Using the commanding heights and turning ends of syncline, the methods for determining the occurrence of strata and geological points (visual inspection, intercept, tangent, front and back intersection, etc.) are mastered repeatedly. ) in groups. Through the occurrence of turning end and systematic determination, students have a preliminary understanding of syncline structure.

The above six reconnaissance routes, observation contents and teaching points are for the reference of all training teams, and can be flexibly mastered according to the actual situation such as training time, weather conditions and traffic conditions, but there should be no less than four basic reconnaissance routes.