## 1 Introduction  
One of China's most significant oil and gas basins, the Tarim Basin, provides the gas for the West-to-East Gas Transmission Project [1, 2]. The Kuqa Depression is the main source of natural gas in the Tarim Basin [2]. The oil and gas potential of petroliferous basins depends on the existence of high-quality source rocks. The Kuqa Depression's source rocks were primarily formed in Jurassic and Triassic ages [3, 4]. From old to new, there are mainly six sets of Triassic- Jurassic source rocks, including the middle Upper Triassic Karamay Formation (T\({}_{2,3}\)k), Upper Triassic Huangshanjie Formation (T\({}_{3}\)h) and Taliqike Formation (T\({}_{3}\)t), Lower Jurassic Yangxia Formation (J\({}_{1}\)y), Middle Jurassic Kezilenur Formation (J\({}_{2}\)kz), and the Qaikemake Formation (J\({}_{2}\)q) [3, 4]. Lacustrine mudstone, coal-measure mudstone, carbonaceous mudstone, and coal make up the majority of source rock types. Lacustrine mudstone is the mudstone of a formation without coal, coal-measure mudstone is the mudstone of a coal bearing formation with TOC less than 6 wt.%, carbonaceous mudstone is the mudstone of a coal bearing formation with TOC between 6 wt.% and 40 wt.% and coal is the rock with TOC \(>\) 40 wt.% [5].  
The upper sections of the Karamay Formation (T\({}_{2\text{-}3}\)k) and Huangshanjie Formation (T\({}_{3}\)h) comprise mainly dark mudstone of deep and semi-deep lacustrine facies source rocks, and they are widely developed in the Kuqa Depression. The T\({}_{2\text{-}3}\)k and T\({}_{3}\)h source rocks are thick, and the thickest part reaches 434 m and 444 m, respectively [6]. The Taliqike Formation (T\({}_{3}\)t) of the Upper Triassic is formed mainly by lacustrine and swamp alternating facies coal-measure mudstone, carbonaceous mudstone, and coal rock, with a limited distribution area and a thickness of less than 100 m [6]. The Yangxia Formation (J\({}_{1}\)y) of the Lower Jurassic and the Kezilenur Formation (J\({}_{2}\)kz) of the Middle Jurassic develop gray-black mudstone, carbonaceous mudstone, and coal rock, with a large thickness and wide development of lacustrine-swamp facies, and the thickness of source rock is 400-550 m [6]. The Middle Jurassic Qiakemake Formation (J\({}_{2}\)q) is composed mainly of shallow and semi-deep lacustrine facies mudstone, shale, and oil shale, and the thickest part is 155 m [6].  
The Cretaceous layers of the middle and southern Kuqa Depression were the principal areas of early exploration and study. There was no drilling involved and very little core sampling because of the deep burial of Jurassic layers. Most of the Jurassic source rock samples were field outcrop samples. Numerous exploration wells have revealed the Jurassic strata and retrieved core samples of the Jurassic coal-measure source rocks as a result of the exploration and development of the northern structural belt. The importance of Jurassic coal-measure source rocks has been confirmed [7]. However, the depositional environment, source of organic matter and factors that control the development of coal-measure source rocks are different from deep and semi-deep lacustrine source rocks [8], which need to be further clarified. As a result, the research of coal-measure source rocks in the northern structural belt of the Kuqa Depression contributes positively to the enrichment of the theoretical framework for source rock development and oil-gas exploration.  
Utilizing total organic carbon and total sulfur analyses, rock pyrolysis data, geochemical properties and biomarker characteristics may reflect the depositional environment of the source rocks. In this study, the following issues are fully addressed using Rock Eval pyrolysis and molecular proxies: (1) geochemical features of coal-measure source rocks; (2) redox degree, organic matter source and depositional environment of coal-measure source rocks; (3) factors that control the development of coal-measure source rocks.