Orbital pacing and secular evolution of lake-level changes reconstructed by sedimentary noise modeling during the Early Jurassic icehouses-(super)greenhouses

Lake-level changes can significantly affect paleoenvironmental evolution,resource occurrence,terrestrial carbon budget,and biodiversity in continental basins.Climate is one of the most critical factors controlling lake-level changes.Paleoclimate of the Early Jurassic has been evidenced by oscillating icehouses to(super)greenhouses with interrupted intermittent extreme climatic events(hyperthermal and cooling),e.g.,the Toarcian oceanic anoxic event(~183 Ma)and the late Pliensbachian cooling event(~185 Ma).Lake-level evolution and hydrologic cycling on Earth’s surface during the Early Jurassic icehouses-to-(super)greenhouses are thus far poorly understood due to a lack of continuous high-resolution nonmarine evidence.Here we present a super-long nonmarine lake level record for this pivotal interval from the early Pliensbachian to Toarcian by sedimentary noise modeling,and construct a 16.7-Myr-long astronomical time scale(174.2 Ma to 190.9 Ma)based on cyclostratigraphy analysis of rock color datasets(CIE b*)of the Qaidam Basin.Our results document lake-level oscillations on a 5-to 10-million-year(Myr)scale which shows a pronounced correlation with long-term climate variation and extreme climatic events,and 1-to 2.5-Myr-scale lake-level changes that are prominently paced by the 2.4-Myr long-eccentricity forcing and the 1.2-Myr obliquity forcing.At the Pliensbachian Stage,the 1.2-Myr-scale lake-level changes are in phase with the coeval sealevel variations.Orbitally forced growth and decay of the ephemeral or permanent ice sheets in polar regions are interpreted to control the synchronous ups-and-downs of continental lake level and global sea level.However,during the Toarcian ice-free greenhouses to(super)greenhouses,the 1.2-Myr-scale lake-level variations show an anti-phase relationship with global sea level,indicating a‘seesaw’interaction between continental reservoirs(lakes and groundwater)and global oceans.The 2.4-Myr longeccentricity cycles mainly regulate variations of lake level and sea level by controlling the growth and decay of small-scale continental ice sheets,which is especially notable during the Pliensbachian Stage.These findings indicate a remarkable transition of hydrological cycling pattern during the Pliensbachian-Toarcian icehouses to(super)greenhouses,which provides new perspectives and evidence for investigating the hypothesis of global sea-level changes(e.g.,glacio-eustasy and aquifer-eustasy)and long-period astronomical forcing in nonmarine stratigraphy.

Forced motions around triangular libration points by solar radiation pressure in a binary asteroid system

By using two tri-axial ellipsoids to approximate the two asteroids,forced orbits around triangular libration points of the binary asteroid system(BAS)induced by solar radiation pressure are studied.The work is firstly carried out in the doubly synchronous binary asteroid system(DSBAS).The results show that the amplitude of the forced periodic orbit can be large,even for small to moderate surface area-to-mass ratios of the spacecraft.The position,amplitude,and stability of these forced periodic orbits are influenced by the asteroids'non-spherical terms.Also,the stability of them may be different,depending on the Sun's motion direction w.r.t.to the BAS's orbit motion direction.This study is then generalized to the asynchronous and synchronous BAS(ABAS and SBAS,respectively).The forced orbits in the complete system are quasi-periodic orbits around the forced periodic orbit of the averaged system.