Secular oscillations in the stratigraphic record—an acute debate

Abstract

Work on secular oscillations of the ocean-atmosphere system has reached a particularly interesting stage, characterized by competing models that alternately invoke endogenic and celestial drivers. The most widely accepted concept is the icehouse-greenhouse cycle with an approximate length of 300 Ma. The concept holds that in the past 600 Ma the Earth has oscillated between a glacial mode and one of rather warm, equable climate; correlative changes in mineralogy of marine carbonates and evaporites as well as abundance of igneous intrusions point to an endogenic cause, most probably variations in the rates of plate motion and mantle convection that modulate sea level and the level of atmospheric CO₂ and thus climate. However, the 300-Ma icehouse-greenhouse cycle leaves important data unexplained. The history of glaciations as well as certain climate indicators, such as sea-surface temperatures derived from oxygen isotopes, indicate oscillations with wave lengths of 130–150 Ma. Such oscillations have been observed in the reconstructed cosmic-ray flux of the past 1000 Ma; they may modulate climate via low-level cloud cover. The debate about long-term climate oscillations poses several distinct questions for sedimentary geologists.