A SURVEY OF PALEOZOIC CYCLOSTRATIGRAPHY (Invited Presentation)

Milankovitch cycles identified in sedimentary successions are being used to formulate an "Astronomical Time Scale" (ATS) for the geologic record, with efforts well underway for the Cenozoic and Mesozoic eras. Back through time, however, ATS resolving power declines due to uncertainties in the orbital solutions and Earth precession model. Prior to 50 Ma, only the modeled 405-kyr orbital eccentricity cycle retains high accuracy, leading to the idea for a "405-kyr metronome" to define the ATS for all geologic time. Radioisotope geochronology now offers a 2 sigma dating precision of 0.1%, which for Paleozoic time equates to an uncertainty on the order of 0.3 to 0.5 myr, i.e., comparable to the 405-kyr metronome resolution. This parity of resolution provides strong motivation to search for Paleozoic Milankovitch cycles, together with high-precision geochronology "anchor" dates, to define an incremental geologic time scale for the Paleozoic. The responses of the paleoclimate system as it experienced multiple intense greenhouse states, two severe ice ages, rise of land plants and assembly of supercontinent Pangea are all recorded in the Paleozoic Milankovitch record. Earth's length-of-day (LOD) expected for Paleozoic times is sufficiently smaller from the present-day to be clearly discernible in the obliquity and precession frequencies. Finally, the evolution of planetary secular resonances may be recorded in low-frequency obliquity and precession cycle modulations. The current state of knowledge of Paleozoic-age Milankovitch cycles is reviewed by period, with emphasis on paleoclimate response, ATS, precession, LOD, and solar system resonance.