Geological background of Wendan origin

(1) Landform characteristics

The main production area of ??Yuhuan Wendan is mainly distributed in the coastal plains and hilly areas of Yuhuan County. The main production area faces the sea on three sides, and is connected to mountains in the north, with the highest peak The main peak of Daleitou Mountain is 446m above sea level. The main landform types include hills, alluvial plains and marine plains, which can be further subdivided into slopes, terraces, alluvial fans, coastal plains and coastal plains (Table 5-11).

Table 5-11 Landform types and characteristics of the main Wendan production area in Yuhuan, Zhejiang

The hilly slopes in the area are distributed in the central part in a north-south direction, with an elevation greater than 5m, and a large difference in steep and gentle slopes; The terraces are distributed at the bottom of hilly gullies, with an elevation of 30 to 40m, and a slope of less than 5°. There are alluvial fans distributed at the mouths of hilly gullies, with an elevation of 5 to 30m, and a slope of generally about 5°. Outside the hills are coastal plains and coastal plains, with an elevation of Less than 5m, the slope is less than 3°.

(2) Stratigraphy and lithology

The stratigraphy and lithology of the Yuhuan Wendan planting area are mainly composed of Quaternary loose sediments, Late Jurassic volcanic rocks and late Yanshanian intrusive rock masses composition.

The exposed strata in the hilly area include the Upper Jurassic Xishantou Formation (J3x) and Gaowu Formation (J3g), which are a set of extremely thick volcaniclastic rocks and volcaniclastic sedimentary rocks. The main lithology It is glass chip (sintered) tuff, crystal chip glass chip fused tuff, etc.

The Quaternary loose sediments in the plain area can be divided into the Holocene Zhenhai Formation (Q4zh), Yinjiangqiao Formation (Q4y), Upper Pleistocene Lianhua Formation (Q3l), and Middle Pleistocene Zhijiang Formation ( Q2z). Among them, the lithology of the Zhenhai Formation is marine phase silt loamy clay, clay, and silt soil, forming the coastal plain; the lithology of the Yinjiangqiao Formation is alluvial phase gravelly subsand soil and loam clay, and the lithology of the Lianhua Formation is The alluvial facies contains gravelly sand, sub-sand, and gravel, which form the alluvial plain; the Zhijiang Formation is distributed on the terraces at the bottom of hilly gullies, and the lithology is slope diluvial facies containing clay, sand, gravel, and loam.

Medium-acidic intrusive rock bodies are small in scale and scattered in hilly areas. The lithology includes syenite porphyry, potassium feldspar granite, granite porphyry, granodiorite, and quartz diorite. wait.

(3) Soil and soil-forming parent material

The soil types in the Yuhuan Wendan planting area mainly include yellow soil, sub-yellow clay, alluvial mud sand, light clay, and salty clay , coated clay, etc. (Table 5-12), different soil types are distributed from mountains to coated lands.

Table 5-12 Soil classification in the Wendan planting area of ??Yuhuan, Zhejiang

Yellow soil: mainly distributed in hilly areas, and the parent material is Jurassic Xishantou Formation and Gaowu Formation volcanic rocks. The texture is medium loam and the soil thickness is thin to medium. Yuhuan Wendan is planted more often and has better quality.

Yellow tendon mud: distributed on terraces, mainly in Shadi Tang and Nanshan areas. The parent material is the loose sediments of the Quaternary Zhijiang Formation. The texture is sticky, heavy loam, and the soil layer is thick. Yuhuan Wendan is less planted and of poor quality.

Alluvial mud and sand: distributed in piedmont alluvial fans, the parent material is the loose sediments of the Quaternary Lianhua Formation and Yinjiangqiao Formation. The texture is medium loam and the soil layer is thick. Yuhuan Wendan is widely planted and of good quality.

Light coating: distributed in the coastal plain, and the parent material is loose marine sediments of the Quaternary Zhenhai Formation. The texture is clay and the soil layer is thick. Yuhuan Wendan has little planting and is a rice planting area.

Salty clay: distributed in the coastal plain, and the parent material is also loose marine sediments of the Quaternary Zhenhai Formation. The texture is clay and the soil layer is thick. Yuhuan Wendan is widely planted and of good quality.

Coated clay: Distributed on the outer coating of the coastal plain, the parent material is loose marine sediments of the Quaternary Zhenhai Formation. The texture is clay and the soil layer is thick. No Yuhuan Wendan planting.

(4) The influence of geological background on the distribution of Yuhuan Wendan production areas

Yuhuan Wendan has two obvious areas in terms of distribution, one is the slope platform with an altitude of 5 to 50m; The soil type of the alluvial terraces at the mouth of the valley is mainly red soil, and the soil types include red soil, red clay, yellow mud sand, and fluvo-aquic ancient mud sand and valley mouth mud sand. The second is the "Tangdi" located on the coast. "The soil type is mainly coastal saline soil. The soil types include light and medium salty clay, and some are light-coated clay types of fluvo-aquic soil. Currently, Yuhuan Wendan is the most planted in this area.

Table 5-13 lists the distribution of Yuhuan Wendan under different geological background conditions. The origin and quality of Yuhuan Wendan are selective to the formation (lithology). In the background, growth and quality vary. According to the survey, Yuhuan Wendan is mainly produced in the hilly slopes distributed in the central part of the region in a north-south direction, with an elevation greater than 5m and a large difference in steep and gentle slopes. The hilly slopes are composed of volcanic rocks of the Jurassic Xishantou Formation and Gaowu Formation, on which loess soil and Yuhuan Wendan are developed, and the fruit quality is good; the alluvial fans distributed at the mouth of the hills and valleys have an elevation of 5 to 30m, and the slope is generally between At about 5°, it is composed of loose sediments of the Quaternary Yinjiangqiao Formation and Lianhua Formation, with alluvial mud and sand developed on it. Yuhuan Wendan is the most planted, and the fruit quality is good.

Table 5-13 The distribution and quality of rocks (strata) in the main Wendan production area in Yuhuan, Zhejiang

The terraces are distributed at the bottom of hilly gullies, with an elevation of 30 to 40m and a slope of less than 5°. The slopes of the Quaternary Zhijiang Formation are composed of alluvial red loose sediments, with sub-yellow veined mud developed on them. Although Yuhuan Wendan is planted more, the quality of the fruit is relatively poor; outside the hills is the coastal plain, with an elevation generally less than 5m, and a steep slope Less than 3°, it is composed of loose marine sediments of the Quaternary Zhenhai Formation, with light clay developed on it. Yuhuan Wendan is less planted, and the distribution of salty clay developed from the loose marine sediments of the Quaternary Zhenhai Formation In this area, Yuhuan Wendan is planted more and the quality is better.

Research shows that the soil conditions suitable for planting Yuhuan Wendan are that the soil layer should be deep, the thickness of the topsoil layer and the core soil layer should generally be greater than 70cm, the semi-weathered parent material layer should be about 1m, and the soil should have good The permeability of the soil should be between 1.5 and 2m, the soil texture should be medium loam to heavy loam, the soil pH should be slightly acidic to neutral, and the organic matter content should be 2% to 3%. Wendan production can be developed by improving coastal salt soil, but the salt content of the entire soil should be strictly controlled within 0.2%.