Cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences

Abstract

Over the past 25 yr, the science of stratigraphy has evolved to include time-correlative data from vastly disparate components of the Earth system. Not least of these is the global signal afforded by cyclostratigraphy, which has recorded the evolution of Earth’s astronomical (“Milankovitch”) forcing of insolation and the paleoclimate system. Fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies, geochemistry, mineralogy, rock magnetism, color, etc. In step with the documentation of astronomically forced paleoclimate from ever-older older geologic times, innovations in computational science have provided ever-longer high-accuracy astronomical model “targets” that can be used for time scale calibration. The Earth’s orbit is affected by motions of other planets, notably the orbital perihelia of Venus and Jupiter, which impose a dominant 405 k.y. eccentricity cycle on Earth’s orbital evolution. The large mass of Jupiter stabilizes this cycle over hundreds of millions of years. The cyclostratigraphic record of 405 k.y. cycles is therefore often used to correct chronologies affected by variable sedimentation. Earth’s shape and rotation rate are influenced by tidal dissipation and climate friction; these effects affect Earth’s precession rate through time. Thus, a record of Earth-Moon evolution is also embedded in cyclostratigraphy. The geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high-precision radioisotope dating, which today has the potential to define the ages of stratigraphic horizons with 2σ uncertainties at the scale of a precession cycle. Precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system. Cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca. 50 Ma limit of accurate astronomical solutions, and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion. Astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time. Finally, space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of Mars, with patterns suggestive of astronomical forcing analogous to Earth.