Early Cretaceous black shale in the Fajiaying Formation (Lingshan Island, East China): Terrestrial record of hothouse climate

Abstract

The significance of Cretaceous hothouse climate in terrestrial systems is currently unclear, and its records in terrestrial strata are rarely reported. This study investigated the sedimentary environment of the Fajiaying Formation, characterised by abundant black shale and soft-sediment deformation structures. Five lithofacies have been identified for the Fajiaying Formation, e.g. Facies A: black shale with siltstone inter-bedding, Facies B: black and gray-black shale and siltstone alternations with minor sandstone, Facies C: black and gray-black shale interbedded with gray-black sandstone, Facies D: pebbly sandstone and Facies E: gray-black shale and siltstone. The average TOC content of the shales decreases from facies A (av. 1.32%) to facies E (av. 0.46%) through facies B (av. 0.57%) and facies C (av. 0.40%). The paleosalinity gradually decreases from lithofacies A to lithofacies E, corresponding to the change of paleoclimate. In addition, Bivariate Scatter Plot of SiO2 and Al2O3 + K2O + Na2O and the clay mineral assemblages suggest an arid climate. Combined with distribution characteristics and paleontology of saliferous strata in eastern China, we determine that hothouse climate influenced the salification of lakes located in eastern China during the Early Cretaceous. Furthermore, the Fajiaying Formation in Lingshan Island was deposited in a terrestrial salified lake. Salinization of the sedimentary water bodies of the Fajiaying Formation might be related to an oceanic anoxic event. The black shale developed extensively in the Fajiaying Formation and represents the terrestrial record of hothouse climate.