Sequence palaeogeography, lacustrine basin evolution, and coal accumulation in the Lower Cretaceous Fuxin continental faulted basin, China

Abstract

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.

Jurassic continental coal accumulation linked to changes in palaeoclimate and tectonics in a fault‐depression superimposed basin, Qaidam Basin, NW China

“…Coal accumulation based on sequence‐stratigraphic analysis has been broadly used (Bohacs & Suter, 1997; Diessel et al, 2000; Holz et al, 2002; Li et al, 2018; Xu et al, 2020). The peat‐forming environments were also discussed in sequence‐stratigraphic intervals (Petersen, Lindström, Therkelsen, & Pedersen, 2013).…”

“…The peat‐forming environments were also discussed in sequence‐stratigraphic intervals (Petersen, Lindström, Therkelsen, & Pedersen, 2013). Previous works can be summarized as ‘a coal seam would develop well when the increasing rate of accommodation kept balance with the production rate of peat, and the destruction of the balance will terminate the coal accumulation’ (e.g., Li et al, 2014, 2018; Xu et al, 2020). However, there are few studies on the quantitative analysis of palaeoclimate and provenance tectonic activity, and how they control accommodation creation rates and sediment supply rates.…”

“…However, there are few studies on the quantitative analysis of palaeoclimate and provenance tectonic activity, and how they control accommodation creation rates and sediment supply rates. Furthermore, most of the researches mainly focus on a single faulted basin or a depression basin (e.g., Wang et al, 2019; Xu et al, 2020), lacking the research on coal‐accumulating models in a fault‐depression superimposed basin. Based on the previous analysis of sequence stratigraphy, palaeogeography, palaeoclimate changes, and tectonic activity, two different coal‐accumulation models are summarized in Figures 15 and 16, respectively.…”

“…Bohacs and Suter (1997) and Holz, Kalkreuth, and Banerjee (2002) considered that peat can be preserved to form coal only when the overall rate in peat generation of accommodation approximately equals the accumulation rate of peat. Among them, the tectonic subsidence and base‐level change are the main controlling factors of accommodation variation; the supply of plant availability provides material for the accumulation of peat (Xu et al, 2020). In continental lacustrine basins, the primary driving factors of base‐level fluctuation include tectonic and climatic controls (Shanley & McCabe, 1994).…”

Continental chemical weathering during the Early Cretaceous Oceanic Anoxic Event (OAE1b): a case study from the Fuxin fluvio-lacustrine basin, Liaoning Province, NE China

“…According to previous studies, it can be inferred that the Fuxin Formation was deposited during the Albian. The Fuxin Formation was mainly formed in alluvial fan, fan delta and fluvial depositional systems (Xu et al 2020), while the underlying Shahai Formation represents a set of sedimentary strata mainly deposited in alluvial fan, fan delta and lacustrine depositional systems (Cai et al 2011). From the bottom to the top the Shahai Formation can be divided into the first, second, third and fourth members (Fig.…”