Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin, Tibetan Plateau

Global climate during the Jurassic has been commonly described as a uniform greenhouse climate for a long time.However,the climate scenario of a cool episode during the Callovian-Oxfordian transition following by a warming trend during the Oxfordian(163.53 to157.4 Ma)is documented in many localities of the western Tethys.It is still unclear if a correlatable climate scenario also occurred in the eastern Tethys during the same time interval.In this study,a detailed geochemical analysis on the 1060 m thick successions(the Xiali and Suowa formations)from the Yanshiping section of the Qiangtang Basin,located in the eastern Tethys margin during the Callovian-Oxfordian periods,was performed.To reveal the climate evolution of the basin,carbonate content and soluble salt concentrations(SO_(4)^(2-),Cl^(-))were chosen as climatic indices.The results show that the overall climate patterns during the deposition of the Xiali and Suowa formations can be divided into three stages:relatively humid(164.0 to 160.9 Ma),dry(160.9 to159.6 Ma),semi-dry(159.6 to 156.8 Ma).A similar warming climate scenario also occurred in eastern Tethys during the Callovian-Oxfordian transition(160.9 to159.6 Ma).Besides,we clarify that the Jurassic True polar wander(TPW),the motion of the lithosphere and mantle with respect to Earth’s spin axis,inducing climatic shifts were responsible for the aridification of the Qiangtang Basin during the Callovian-Oxfordian transition with a review of the paleolatitude of the Xiali formation(19.7+2.8/-2.6°N)and the Suowa formation(20.7+4.1/-3.7°N).It is because the TPW rotations shifted the East Asia blocks(the North and South China,Qiangtang,and Qaidam blocks)from the humid zone to the tropical/subtropical arid zone and triggered the remarkable aridification during the Middle-Late Jurassic(ca.165-155 Ma).

Finite-thickness effect of the fluids on bubbles and spikes in Richtmyer–Meshkov instability for arbitrary Atwood numbers

This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability(RMI) for arbitrary Atwood numbers by using the method of the small parameter expansion up to the second order. When the thickness of the two fluids tends to be infinity, our results can reproduce the classical results where RMI happens at the interface separating two semi-infinity-thickness fluids of different densities. It is found that the thickness has a large influence on the amplitude evolution of bubbles and spikes compared with those in classical RMI. Based on the thickness relationship of the two fluids, the thickness effect on bubbles and spikes for four cases is discussed. The thickness encourages(or reduces)the growth of bubbles or spikes, depending on not only Atwood number, but also the relationship of the thickness ratio of the heavy and light fluids, which is explicitly determined in this paper.