Strong inclination pacing of climate in Late Triassic low latitudes revealed by the Earth-Saturn tilt cycle

Abstract

The solar system is chaotic, and over long timescales small differences in the initial conditions of numerical models of solar system dynamics lead to vastly different outcomes that are difficult or impossible to predict using calculated solutions (Laskar, 1999) prior to 50 Myr before the present (Hinnov, 2018). But the gravitational interactions of the sun, planets, moons, and other masses produce climate changes through deformations of Earth’s orbit and axial orientation that are recorded in the geological record, allowing the actual history of these gravitational interactions to be recovered. For example, carbon isotope excursions in the marine carbon cycle of the Late Triassic to Early Jurassic are paced by long-eccentricity cycles (Storm et al., 2020). Environmental changes of orbital origin also influence patterns of evolution and extinction (Li et al., 2016), such as those of Late Triassic fish (Whiteside et al., 2011b), and influence speciation by sorting species into distinct provinces (Whiteside et al., 2011a). The most famous example of orbital pacing of climate is the Pleistocene Ice Ages, paced by orbital eccentricity, precession, and obliquity of Earth’s axis (Hays et al., 1976). The Newark Basin, currently in eastern North America, was located in the tropics to subtropics during the Triassic and Early Jurassic. Sequences in this region from 201–221 Ma represent a low-latitude record of the Late Triassic, a period with no ice sheets, testing CO2 control of hydrology. In particular, very low CO2 levels likely caused muted cyclicity in the top of the section, potentially allowing evidence of inclination control of climate to appear more easily. The Newark Basin Coring Project (NBCP) data consists of proxies of lake depth, which itself can be used as a climate proxy: astronomical cycles drive variations in solar insolation and hence paleoclimate trends. The lake depth proxies consist of sedimentary structures and fabrics, color, natural gamma radioactivity, and sonic velocity (Olsen & Kent, 1996), but geochemical data or any other measurable features that vary with lake depth could be used. Olsen et al. (2019) used Late Triassic cores of lake sediments from the NBCP and Colorado Plateau Coring Project (CPCP) to calculate the values of the secular precession of perihelion (the change in the point on a planet’s orbit closest to the sun as the shape of the orbit changes) of the inner planets (g values, g1, g2, g3, g4), and to demonstrate that the Earth-Mars eccentricity cycle (g3-g4; the ABSTRACT Gravitational interactions among masses in the solar system are recorded in Earth’s paleoclimate history because variations in the geometry of Earth’s orbit and axial orientation modulate insolation. However, astronomical models are unreliable before ~50 Ma due to the chaotic nature of the solar system and therefore must be constrained using geological observations. Here, we use environmental proxies from paleo-tropical Late Triassic lake deposits of the Newark Rift Basin to identify and tune to previously undescribed strong variations in orbital inclination. Tuning to the 173 kyr Earth-Saturn inclination cycle, theoretically stable due to the high mass of Saturn, reveals both other predicted inclination cycles and previously reported eccentricity cycles. Slight, complementary offsets in the eccentricity and inclination cycles shown by the Earth-Saturn (s3-s6) and Venus-Jupiter (g2-g5) tunings may be due to chaotic variations of the secular fundamental frequencies in Earth’s nodal and Venus’s perihelion orbital precessions. The strength of the inclination cycles suggests that the Earth system modulates orbital pacing of climate and provides a mechanism to further constrain astronomical solutions for solar system dynamics beyond the ~50 Ma limit of predictability. Strong inclination pacing of climate in Late Triassic low latitudes revealed by the Earth-Saturn tilt cycle