Beisi Formation

Beisi Formation
Name	Beisi Formation
Type	Geological formation
Period	Early Cretaceous
Lithology	Sandstone, siltstone, conglomerate
Region	Jiangxi Province
Country	China
Thickness	Variable
Namedfor	Beisi (temple)

Beisi Formation The Beisi Formation is an Early Cretaceous terrestrial stratigraphic unit exposed in Jiangxi Province of southeastern China. It comprises fluvial to lacustrine clastic successions dominated by sandstones and siltstones, with intercalated conglomerates and paleosols that preserve vertebrate, invertebrate, and plant fossils. The formation has been the focus of regional mapping and paleontological investigations by Chinese universities and museums, contributing to understanding Early Cretaceous faunal assemblages in East Asia.

Geology

The Beisi Formation occurs within the broader tectonostratigraphic framework of the southeastern Yangtze Block and lies adjacent to Mesozoic basins influenced by the uplift of the Yanshanian Orogeny and subsidence related to the South China Sea region. Lithologies include medium- to coarse-grained sandstones, fine-grained siltstones, claystones, and episodic conglomerates, reflecting high-energy channel deposits and lower-energy overbank and lacustrine facies. Sedimentary structures such as cross-bedding, ripple marks, and mudcracks indicate cyclical fluvial dynamics influenced by monsoonal paleoclimates and regional paleogeography near the paleo-coastline of the Gondwana-derived terranes. Structural deformation is minor compared with Mesozoic units in neighboring provinces like Fujian and Hunan.

Stratigraphy

Regionally, the Beisi Formation overlies older Jurassic and Lower Cretaceous units and is overlain by younger Cretaceous formations that record continued basin evolution during the Mesozoic. Its internal stratigraphy is characterized by fining-upward sequences typical of braided and meandering river systems, with distinct channel conglomeratebeds capped by sandstone bars and siltstone floodplain deposits. Biostratigraphic ties have been drawn using plant macrofossils and vertebrate remains to correlate discrete members within the formation to contemporaneous units in Liaoning, Hebei, and Shandong provinces. Key marker horizons include persistent lateritic paleosols and volcanic ash layers that allow radiometric calibration in collaboration with laboratories at Peking University and the Chinese Academy of Sciences.

Paleontology

The Beisi Formation has yielded a diverse assemblage of fossils, contributing to knowledge of Early Cretaceous biodiversity in East Asia. Vertebrate remains include fragmentary dinosaur bones and teeth referred to theropod and ornithopod clades, isolated crocodilian osteoderms, and freshwater turtle shells resembling taxa described from Jehol Biota-age deposits. Plant fossils comprise leaves, trunks, and seed ferns comparable to assemblages documented by paleobotanists at Nanjing Institute of Geology and Palaeontology. Invertebrates and trace fossils—burrows, tracks, and insect remains—record terrestrial and marginal lacustrine ecosystems similar to those studied in the Yixian Formation and Tianchi Basin. Paleontological work has been published by teams affiliated with Sun Yat-sen University, China University of Geosciences, and provincial museums, with specimens curated in regional collections.

Age and Correlation

Biostratigraphic and limited radiometric data constrain the Beisi Formation to the Aptian–Albian stages of the Early Cretaceous, roughly coeval with portions of the Jehol Group and other Early Cretaceous successions across northeastern and southeastern China. Correlations have been made with contemporaneous fluvial-lacustrine units in Guangdong and Zhejiang based on shared plant taxa and vertebrate fossils, as well as with marine-influenced strata along the Yellow Sea margin where sequence stratigraphy records parallel eustatic trends. Ongoing isotopic dating of intercalated tuffs by teams at Nanjing University aims to refine absolute ages and improve correlation with global Aptian–Albian events such as the Aptian extinction pulses and oceanic anoxic episodes recognized in marine records.

Depositional Environment

Sedimentological evidence indicates deposition in a continental setting dominated by braided to meandering rivers, ephemeral lakes, and floodplain wetlands. Channel sandstones and conglomerates represent high-energy fluvial transport, whereas laminated siltstones and claystones mark overbank and lacustrine settling during lower energy phases. Paleosols and calcareous horizons reflect intervals of subaerial exposure and soil formation under subtropical to warm temperate climates, influenced by monsoonal precipitation patterns akin to those reconstructed for the Early Cretaceous in East Asia by regional climate modelers. Volcaniclastic layers suggest episodic ashfall from nearby volcanic centers linked to the broader Mesozoic magmatic activity affecting the South China Block.

Economic and Paleoclimatic Significance

The Beisi Formation holds economic interest for regional aggregate resources, with sand and gravel exploited for construction by local authorities and private firms. Its paleosols and organic-rich lacustrine shales offer potential as proxies for Early Cretaceous terrestrial carbon cycles, informing studies conducted by researchers at institutions like Fudan University and Tsinghua University using stable isotope and palynological analyses. The formation’s fossil assemblages contribute to reconstruction of paleoclimate and biogeographic patterns during a time of major plate reorganization and climatic perturbations, linking terrestrial records in China to global Aptian–Albian events investigated in publications from international collaborations with universities such as University of Cambridge and University of California, Berkeley.

Category:Geologic formations of China Category:Cretaceous paleontological sites