Abstract: The Carboniferous strata in the northwestern margin of the Junggar Basin represent an important target for deep hydrocarbon exploration, with the characteristics and formation background of source rocks attracting significant attention. This study focuses on the dark mudstones of the Carboniferous strata in Well MH55, utilizing systematic sampling and organic-inorganic geochemical analyses to investigate their hydrocarbon potential, paleo-depositional environment, and organic matter enrichment mechanisms. The results reveal that the organic matter content in the dark mudstones of Well MH55 is moderate, dominated by Type Ⅲ kerogen. The source rocks exhibit a high degree of thermal maturity with significant fluctuations, likely influenced by frictional heating associated with fault activity, and are overall classified as poor-to-moderate source rocks. The mudstones were deposited in a brackish-to-saline transitional environment characterized by dysoxic water conditions and oscillating climatic shifts between warm-humid and cold-arid periods. Organic matter enrichment was primarily controlled by terrigenous input and dysoxic conditions. Terrigenous input provided the primary source of organic matter, while dysoxic conditions effectively reduced organic matter oxidation and decomposition rates. In contrast, the contribution of paleo-productivity was relatively limited, which may be attributed to insufficient nutrient availability in the water column and dilution effects from terrigenous material input during deposition.