| Potash is a very important and scare resource for the protection of national economic stability and the strategic safety. The proven potash resource is inadequate, comparing to the 1.3 billion people. China mainland is made up with much small landmass and orogenic belt between them, which experienced more discrete, split tectonic cycle. The unstable tectonic settings determine the particularity and complexity to finding the salt and potash in ancient China evaporation basin. So it is difficult to research the genetic model of potassium salt. With the development of modern geology, it is necessary to introduce sequence stratigraphy, sedimentary geochemistry, salt geochemistry, stratigraphy and other new cycle of research methods and ideas into the research of the potash deposit.Sichuan Basin is a geomorphology basin with a three-dimensional space. It is a sedimentary basin with a four-dimensional space including the concept of time and sedimentary geological history. It is a composite type or laminated type basin developed in the Yangtze craton platform basin. The Lower Triassic which is a shallow water platform- platform evaporite deposition in the basin has been an important formation to find the potash. The Triassic salt layers have been researched more deeply on the evaporite forming models and mechanism, the ancient geographical environment, the distribution of salt basins, rock geochemistry, salt minerals, potassium-rich brine composition and genesis for a long time, which is due to the exploration and development of oil and gas, potassium-rich brine, gypsum, polyhalite and salt resources. But the solid-state potash deposits has not yet found. There are numerous biography which have different division system to the different blocks, different horizons. Meanwhile the object and purpose of the horizon is inconsistent, a salt of times is disordered. It remains controversial that if potassium-rich brine and miscellaneous carnallite can be as a potassium Triassic instructions and if there are marine-solid potash deposits.Based on the field exploration, sampling and analysis, a large indoor comparative finishing drilling data, geochemical and geophysical methods to the major salt structure in Sichuan Basin, following understandings are obtained:1. The target potash layers are divided and unified on the basis of a detailed study of Triassic backbone profiles(Hechuan Libixia Section, Qu Xian Nongle Section) and drilling profiles(Changping 3 well, Guangsen 2 well) on the re-organize. The Triassic of Sichuan Basin can be divided into six salt time:the second sub-paragraph of Jialing group(T1j2-2), second sub-paragraph of four sedimentary deposition of Jialing Group(T1j4- 2),second sub-paragraph of five sedimentary deposition of Jialing Group(T1j5-2)~the first sub-phase deposition of the Leikoupo first section(T2l1-1), the third sub-phase deposition of the Leikoupo first section(T2l1-3),the second sub-phase deposition of the Leikoupo third section(T2l3-2) and the second sub-phase deposition of the Leikoupo fourth section(T2l4-2), which can be divided into five salt-forming region, 19 sub-salt structures(salt basin) in the space. The salt basin showed gradual westward migration evolution which are affected by ancient land tectonic activity of Sichuan Basin and the periphery old land.2. The sedimentary facies identification and typical salt, potassium drilling sedimentary facies are established through field observations of typical cross-section of the Sichuan Basin, according to facies assemblages, sedimentary structures, interior thin section analysis and other studies. The Sichuan Basin in early to middle Triassic is a shallow-water carbonate- evaporite platform. According typical profile sedimentary structures, biometrics, lithological composition, the sedimentary can be divided into 18 kinds of genetic types, which are formed on the open platform-restricted platform phase- evaporation platform equal three major sedimentary facies, 6 and 13 kinds of subfacies sedimentary microfacies. Through the temporal and spatial distribution of the Sichuan salt layer, focusing on the subfacies in a salt-evaporation process, the palaeogeography maps of the major salt-forming period are made up, which show that the sedimentary facies distribution is like a ring. The salt lake microfacies is usually at the core, a "bull’s-eye" type features.3. This article will introduce the cyclostratigraphy into the Sichuan Basin salinity profiles in practicethe: recognition carbonate platform depositional cycle of high frequency and ancient relative sea-level change of reconstruction. Using the cycle response characteristics remaining in the natural gamma log data, the platform sedimentary cycles superimposed high-frequency pattern is simulated. Through the inversion of the trend of early Triassic ancient sea level in the Sichuan Basin, salinity profiles are discussed. Then it is proposed that salt will not form when the sea level rapid decline or early regressive. The environment of sustained oscillations water is often only form a small amount of dolomite, gypsum + combinations + rock salt layer.Only in the late regression when the platform environment is long-term low-level, salt + gypsum + potassium may form, with a potassium potential. And that evaporite platform potassium-rich salt profile retains certain intervals in the sedimentary record. To study the response mechanisms, you can quickly lock into favorable potassium salt, enriching the means of geophysical methods to find potassium.4. Potash salt formation of different conditions were evaluated based on the study of the space-time distribution of the salt layer structure in Sichuan Basin and the space law of evolution, combining the salt layer geochemical characteristics, geophysical characteristics, ancient geography, paleoclimate background. It is proposed that favorable potash forming periods have 3 periods, including Jia Four 2(T1j4-2), Jia Five 2~Lei One 1(T1j5-2 ~ T2l1-1) and Lei Four 2(T2l4-2). The favorable potash forming formations have 4 ones, including Changshou Shuanglong structure in Jia Four 2 period(T1j4-2), Xuanhan Huangjinkou structure in Jia Five 2 ~ Lei One 1 period(T1j5-2 ~ T2l1-1), Nanchong salt basin in Jia Five 2 ~ Lei One 1 period(T1j5-2 ~ T2l1-1),and Chengdu Pingluoba structure in Lei Four 2 period(T2l4-2). It is considered from a event a potassium view that: the four favorable potash forming formations above have appeared off the potash event conditions. |
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