The Fuxin Basin is one of the major coal‐bearing basins in northeastern China with the coal seams mainly preserved in the Lower Cretaceous Fuxin Formation. The sequence stratigraphy, palaeogeography, basin evolution, and coal accumulation of the lacustrine coal‐bearing sequences in the Fuxin Formation were analysed based on borehole cores, well logs, and outcrop sections. Fifteen distinct lithofacies types were recognized with lithologies ranging from conglomerates, sandstones, siltstones, and mudstones to coals. Lithofacies are arranged into five facies associations representing alluvial fan, braided fluvial, meandering fluvial, fan delta, and lacustrine depositional systems. These facies associations collectively revealed a continental faulted basin setting. Based on the regional unconformities, basal scour surfaces of the incised valley fills sandstones, paleosols, or seat earths of coal seam on interfluves, and surfaces that mark abrupt depositional facies shifts, the Fuxin Formation was subdivided in two third‐order sequences. Palaeogeographic maps of each sequence have been reconstructed based on the contours of lithological parameters. The palaeogeographic units include alluvial fan, alluvial plain, channel (braided and meandering fluvial), fan delta, and lake. Preferred coal‐forming environments were mainly developed in the fan delta plain and fluvial back‐swamp. Compared with Sequence 1, the activity of basin‐margin faults and basement subsidence of the Sequence 2 gradually decreased, resulting in the lower rate of potential accommodation and less favourable conditions for peat accumulation. This background provided a basic understanding for the lacustrine basin evolution and coal accumulation. A six‐phase evolution model was proposed, which includes lowstand systems tract, early transgressive systems tract, late transgressive systems tract, early highstand systems tract, late highstand systems tract, and falling stage systems tract. The early and late TST of Sequence 1 and Sequence 2 were relatively beneficial stages for peat accumulation and coal development in the Fuxin Basin.

This study focuses on Early Cretaceous mudstones from the Shahai and Fuxin formations in the Fuxin continental basin. We analyse chemical weathering, land surface temperatures and palaeoclimates based on chemical weathering indices, and emphasize the implications of continental chemical weathering on nutrient fluxes into lakes and oceans. According to Cr and Ni abundance, Al 2 O 3-TiO 2 , La/Sc-Th/Co and V-Ni-Th×10 plots, as well as rare earth element (REE) analysis, mudstone samples from the Shahai and Fuxin formations were derived from the same type of provenance comprising mainly felsic igneous rocks. Chemical weathering trends reflected by the Chemical Index of Alteration (CIA), Weathering Index of Parker (WIP) and the Mafic Index of Alteration for Oxidative weathering environments (MIA (O)) are consistent with each other and allow the geological succession to be divided into four stages. Land surface temperatures of the Shahai and Fuxin formations are estimated based on the linear relationship of CIA to temperature, and also can be divided into four stages consistent with those determined from chemical weathering trends. During Stage A (early part of the late Aptian) chemical weathering and land surface temperatures were relatively low and showed characteristic high fluctuations, while Stage B (latest Aptian) represented a transitional period where weathering rates and temperatures increased, and high amplitude fluctuations continued. Conditions changed markedly in Stage C (early Albian) with very high and stable weathering, and warm, humid climates, while in Stage D (middle and late Albian) conditions returned to low chemical weathering and land surface temperatures. These stages of chemical weathering and land surface temperature fluctuations represent responses to global climate fluctuations during the Early Cretaceous, with the early Albian high weathering intensities and warm, humid climates combining to create high nutrient levels that would have flushed through rivers into lakes and ultimately oceans. This correlates stratigraphically with the development of Early Cretaceous black shales during Ocean Anoxic Event 1b, showing the importance of continental weathering regimes as a causal mechanism for lake and ocean anoxia.

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