A relation among geomagnetic reversals, seafloor spreading rate, paleoclimate, and black shales

Abstract

The Mesozoic‐Cenozoic histories of reversals in the earth's magnetic field and of periods of widespread anoxia in the ocean basins show a remarkable correlation (Figure 1); periods of black‐shale deposition (“anoxic events”) occur during lengthy periods without magnetic reversals (“quiet” periods). My assembly of published work indicates a remote connection between quiet periods and anoxic events and suggests its form: Magnetic quiet periods coincide with fast seafloor spreading. During these periods, buoyant spreading ridges displace seawater onto broad shelves, thus decreasing earth's albedo and causing global warming. Temperature gradients, and thus density gradients, from pole to equator decrease in surface waters, and the deep ocean currents of oxygenated polar waters wane. Oxygen minimum zones intensify and widen; anoxic conditions throughout entire basins are indicated by black shales deposited in the deep sea. These relations thus suggest that the earth's interior processes and its climate are related and their status recorded by both magnetic polarity and anoxic event chronologies of the earth. A test of the model for the Palezoic is proposed and some implications for mineral resources noted.