Climatically Controlled Sediments, the Geomagnetic Field, and Trade Wind Belts in Phanerozoic Time

Abstract

On five Lambert equal-area maps and three Lambert equal-area "composites" of the world in Phanerozoic time are plotted distributions of evaporites, tillites, coal, eolian sands, and radiolarian cherts. The paleolatitude distributions of tillites and evaporites confirm the plausibility of the view that the Earth's magnetic field has approximated to a geocentric dipole whose axis paralleled the Earth's spin axis throughout Phanerozoic time. Coal formed in a wide range of latitudes. Paleolatitude distributions of oceanic cherts support those dynamic models of the atmosphere that require the later Mesozoic and Tertiary high-pressure subtropical belts to have been more or less stable features of atmospheric circulation. Paleolatitude distributions of eolian sands provide inconclusive evidence for the extent of these belts. Though rainfall and temperature have varied at a particular paleolatitude, marked equatorward shrinkage of the subtropical high-pressure belts during ice-sheet glaciations and marked poleward expansion during ice-free epochs is not evident from geological observations. There is a need for quantitative work on these problems and for an integration of the continental with the oceanic data.