Looking back on the research history of coal-bearing sedimentology, we can see that the development of coal-bearing sedimentology has gone through "cycle stage" and "delta migration mode stage" (Rahmni et al.,1984; Chen Zhonghui,1988; Riegel,1992; Zhang Pengfei et al., 1993).

At the beginning of the 20th century, when Uden (19 12) clearly pointed out that the transgression-regression cycle was the reason for the regular repetition of lithologic units of coal-bearing measures in Upper Carboniferous in North America, it immediately aroused geologists' extensive interest in the cyclic deposits of coal-bearing measures. Weller( 1930), Wanless and Weller( 1932) and Wanless and Shepard( 1936) further emphasized the extensive lateral continuity of these cycles and their practical value in stratigraphic correlation, and formally put forward the term "cycle", which was attributed to crustal movement. After Yugoslav mathematician Milankovic put forward the change period of earth orbit parameters, Weller and others further realized that "coal-bearing cycle" is related to the change of orbit parameters, and the ice-controlled sea level change caused by the change of earth orbit parameters is the main controlling factor of coal-bearing cycle, thus opening the prelude to the "cycle era" in the history of coal-bearing rock series research. Although many scholars later found that the composition of sedimentary units in the cycle layer of coal-bearing measures is different from the original "ideal cycle layer" of Weller( 1930) and Wanless and Weller( 1932), and found that these differences are mainly caused by the differences of regional tectonic background and sedimentary environment. However, the cycle concept of Weller( 1930) has been strongly influencing the sedimentology of coal-bearing series for decades, and has played an active role in searching for minable coal seams according to the lithologic combination characteristics of standard cycles.

In 1960s, Fisk( 1960) and his students applied the research results of modern Mississippi River Delta to the study of coal-bearing strata in Appalachia in Pennsylvania. After comparing the Carboniferous coal-bearing strata in Appalachia with the sediments in the Mississippi Delta, they think that the simple transgression and regression process in the Carboniferous cycle in Appalachia can be explained by the retrogradation and retrogradation process of delta blades similar to the modern Mississippi River Delta. So far, people have realized that episodic or periodic actions such as river burst, the swing of distributary channel and the migration of sand bar can also cause cyclic phenomena (Ferm and Coleman,1963; Ferm, 1974), since then began the historical stage of "delta migration model". Ferm( 1974) and Horne et al. (1978) divided the sedimentary facies of Carboniferous Allegheny Formation in Appalachia into alluvial plain, upper delta plain, lower delta plain, lagoon behind barrier, barrier island and other types, summarized the famous delta sedimentary model of Allegheny Formation, and put forward that the coal seam formed in the transitional zone between upper and lower delta plain has the following characteristics. So far, various coal-forming models have been proposed, including coastal barrier lagoon model (Young, 1955), river-delta model (Ferm and Horne, 1979), alluvial fan model (Heward, 1978) and sandy braided river model (Haszeldi). 1980), lake model (Ayers and Kaiser, 1984), aeolian sand dune model (Richardson, 1985) and carbonate platform model (Zhang Pengfei et al.,1983; Shao Longyi et al., 1998). These coal-forming models provide an explanatory basis for the characteristics of coal-forming environment, coal seam development and basic control mechanism. At this stage, although there is controversy about the spin cycle of the cycle layer and its cycle mechanism, both the cycle layer theory and the later sedimentary model theory have played a great role in promoting the development of coal-series sedimentology.

Sequence stratigraphy was born in the 1940s. Sloss put forward the "stratigraphic sequence" of North American platform divided by regional unconformity at the "Symposium on Sedimentary Facies and Geological History" of the annual meeting of the North American Geological Society from 65438 to 0948, which marked the germination of the concept of "sequence". In the late 1950s and early 1960s, sloss, krum Bin, Daples and others creatively divided the stratigraphic records of the North American stable craton from late Precambrian to Holocene into six sets of stratigraphic sequences based on regional unconformity, and defined the sequences as "lithostratigraphic units higher than the group and superior". The theory of systematic sequence stratigraphy was born in the late 1980s. 1988, the special issue of Comprehensive Analysis of Sea Level Change edited by C.K. Wilgus and the Literature of Sequence Stratigraphy published by Sangree, Van Wagoner and Mitchum marked the birth of sequence stratigraphy. Van Wagoner et al. (1988), Posamentier et al. (1988), Van Wagoner et al. (1990), Mitchum et al. (199 1) put forward the concept system of sequence stratigraphy, and put the spin. Under the influence of sequence stratigraphy, more and more coalfield geologists have noticed that the spin cycle mechanisms such as river crevasse and delta migration can only explain the local changes inconsistent with Weller's (1930) ideal cycle, that is, some sedimentary features with limited distribution, but can't explain the causes of a large number of sedimentary features or cycles in the whole basin or even in the whole world. Obviously, the latter can only be explained by basin dynamic mechanism or other different cyclic mechanisms. The sequence stratigraphic framework, cyclic sequence and sea level variation reflected by the combination of sequence stratigraphy and cyclic stratigraphy can provide reliable basis for chronostratigraphy, cyclicity and basin evolution of coal-bearing series, and further promote the development of coal accumulation theory. Therefore, it can also be said that the emergence of sequence stratigraphy has opened a new chapter for the sedimentology research of coal and coal-bearing rock series.