1,2Masayuki Ikeda,2,3,4Ryuji Tada
Earth and Planetary Science Letters 537, 116168 Link to Article [https://doi.org/10.1016/j.epsl.2020.116168]
1Department of Geosciences, Graduate School of Science, Shizuoka University, Shizuoka, 790-8577, Japan
2Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan
3The Research Center for Earth System Science, Yunnan University, Chenggong District, Kunming, Yunnan Province 650500, China
4Institute for Geo-Cosmology, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
Astronomical solutions for planetary orbits beyond several tens of million years (Myr) ago have large uncertainties due to the chaotic nature of the Solar System, mainly Myr-scale cycles related with the Earth-Mars secular resonance. Our only accessible archive for unraveling the Earth’s orbital variations in the geologic past are sedimentological records, yet their reliability and uncertainties are still debated. Here, we describe Myr-scale orbital signals of early Mesozoic monsoon records from two different sedimentary settings (lake level records of the equatorial Pangea and biogenic silica burial flux of deep-sea Panthalassa), along with a marine carbon isotope compilation. Although most of the dominant multi-Myr cycles are not exactly of the same frequency, 1.8 Myr cycles during ∼216–210 Ma are detected from the two mutually-independent sedimentary settings, and differ from available astronomical solutions. This finding provides not only convincing evidence for the chaotic nature of the Solar System in the geological past, but also additional constraints on astronomical models. On the other hand, besides the orbital cycles, tectonic forcing and consequent climatic perturbations could also have affected the proxies on multi-Myr timescales during episodes of large igneous province emplacement, such as Siberian trap volcanism (252–245 Ma), Wrangellia (233–225 Ma), Central Atlantic Magmatic Province (202–200 Ma), and Karoo-Ferrar volcanism (184–180 Ma). If we can distinguish orbital signals from other effects, such as tectonic and volcanic processes, the multi-Myr cycles in geologic records have the potential to reconstruct the chaotic evolution of the Solar System.