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To better understand Early Cretaceous climate variation in inland East Asia, the temporal variation in the chemical index of alteration (CIA) was reconstructed in black shale from an outcrop of the Fajiaying Formation in the Lower Cretaceous Laiyang Group at Lingshan Island, East China. As the formation height increased, the corresponding CIA increased. The obtained index of compositional variability values and an (Al2O3)–(CaO* + Na2O)–K2O ternary diagram demonstrate that the gathered samples had not evolved into K-metasomatism during diagenesis. Moreover, low Zr concentrations parallel to the magmatic trend in the Th/Sc-versus-Zr/Sc diagram reveal that the sediment sorting and recycling did not affect the paleoweathering proxies. The lack of correlation between the CIA and Al/Si or K/Si further suggests that the paleoweathering proxies were not affected by the sediment sorting. Accordingly, as the CIA and the chemical index of weathering increased, the corresponding chemical weathering increased slightly. This is consistent with the transition from a dry-hot climate to a warm-humid one proposed by paleoclimatic proxies such as Rb/Sr, Sr/Cu, Al2O3/MgO, and clay minerals. In this study, a near-ubiquitous correlation is proposed between the variations of paleoclimate and the CIA of shale, in which a rise in humidity significantly increased the chemical weathering. Meanwhile, it was found that under the dry-hot conditions of the Early Cretaceous, chemical weathering in inland areas far from the ocean was relatively weak and dependent on atmospheric humidity. This analysis validates the CIA, as part of the stratigraphic record, to be a robust proxy for terrestrial paleoclimatic variation during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Important geological events that influenced the global environment occurred during the mid‐Cretaceous period. Dramatically increasing temperatures not only triggered oceanic anoxic events (OAEs) but also led to the aridity of terrestrial environments in East Asia. This study provides evidence for the aridity of a terrestrial East Asian environment during the mid‐Cretaceous and provides an example of the influence of the Cretaceous greenhouse climate on a terrestrial lake system in correspondence with the OAE 1a event. Palaeosalinity indexes (B, B/Ga, Sr/Ba, and Couch's palaeosalinity) and palaeoclimate proxies (Sr/Cu, Rb/Sr, Al2O3/MgO, and clay mineral compositions) of shale and mudstone from the Laiyang Group of the Jiaolai Basin in Eastern China were analysed. The results demonstrate that the palaeoclimate in the Wawukuang Formation was relatively warm and humid but became extremely dry and hot in the Shuinan Formation during the OAE 1a event before becoming warm and humid again in the Longwangzhuang and Qugezhuang formations. As a result, the palaeosalinity of the Jiaolai Basin increased from 4% in the Wawukuang Formation to 30% in the Shuinan Formation before decreasing to 0.48% in the Longwangzhuang and Qugezhuang formations. The following conclusions are from combining the distributional characteristics of the saliferous strata and its palaeontology, the palaeogeographic background, and the aeolian sandstone in eastern China. (a) The East Asian continental margin was influenced by the Cretaceous greenhouse climate, which resulted in the salinization of the Jiaolai Basin. (b) The significant increase of the palaeosalinity in the Shuinan Formation was an effect of the OAE 1a event on the terrestrial lake system, which further suggests the OAE 1a event was global. (c) Influences of the hothouse climate on the continental lakes changed the palaeosalinity of the water bodies. [ABSTRACT FROM AUTHOR]

The early Aptian (~120 Ma) Oceanic Anoxic Event 1a (OAE 1a) was associated with marked changes in palaeoclimate linked to a perturbation of the global carbon cycle. While it is well-studied in the marine realm, OAE 1a is poorly known from continental records. Here, we fill that knowledge-gap by describing OAE 1a from lacustrine facies in the East Asia continental margin (Jiaolai Basin and Lingshan Island in eastern China). Specifically, we integrate data from bulk organic carbon-isotopes (δ13C org), total organic carbon (TOC), and redox-and productivity-sensitive trace elements, as well as existing records on depositional environments, clay mineral compositions, elemental geochemistry and the latest detrital zircon U Pb ages. We propose a conceptual model of the response of the lake system to OAE 1a through analysis of the palaeoenvironmental and palaeoclimatic context. During the initial stage, an extreme greenhouse climatic event resulted in an abrupt increase in palaeosalinity in the lake system. This led to anoxic conditions, resulting in a high preservation rate of TOC and the development of organic-rich black shale. Organic carbon isotopes documented in the organic-rich black shale show negative and then positive excursions, consistent with the carbon cycle disturbance found in marine OAE 1a records. In addition, the data show that this event may have been associated with a transition from an extreme greenhouse climate to a cooling phase. The framework presented here facilitates further research on the expression of OAE 1a in continental ecosystems and its fingerprint in lacustrine depositional systems. Unlabelled Image • Evidence of OAE1a was identified in lacustrine depositional systems. • Lacustrine black shale in East China preserves information on early Aptian C-cycle perturbation during OAE 1a. • Palaeosalinity and RSTE data indicate environmental instability of inland lakes in East China during OAE 1a. • Terrestrial records suggest an extreme greenhouse climate led to OAE 1a. • The OAE 1a itself may represent a period of transition from an extreme greenhouse climate to a cooling phase. [ABSTRACT FROM AUTHOR]