Abstract

The term "Tethys" is entrenched in geologic literature as an ancient fossil ocean that more or less separated the northern continents from the southern continents during the Mesozoic Era. In ancient Greek religion, Tethys was wife of the Sea God, Oceanus, and mother of all the Oceanids. In geologic mythology also, Tethys was a sort of Mother of All Oceans prior to the Tertiary. A. E. M. Nairn (South Carolina University) and his coeditors Ricou and Vrielynck (CNRS, Paris) and Dercourt (Pierre et Marie Curie University, Paris), with the collaboration of more than 100 international experts over a five-year period, have synthesized the plate-tectonic history of Tethys, mapped Mesozoic paleogeographic reconstructions, and developed a series of syntheses of Tethyan resources and sedimentation. The part played by Tethyan evolution in the history of the northern Andes, in particular, is discussed. There are "spitters" and "lumpers" - those who devote careers to analyzing small items in excruciating detail vs. those who gaze over the universe and manage to fit all available facts and theories into one grand super- theory. This book's megathinking approach groups discussions of Israeli phosphates, California gold, worldwide distribution of bauxites, sedimentation rates of radiolarites, strike-slip fault trends, transgressive and regressive episodes, depositional environments, magmatic cycles, sutures, subductions, and salinities, and expresses all in terms of Tethyan history. Not surprisingly, some field observations fit theory better than others. Western Gondwana (South America and Africa) and Eastern Gondwana (India and Australia) tend to have separate kinds of interpretive problems, and the ways they are retrofitted together with the northern continents (Eurasia/Laurussia) are not always consistent among various contributors to the science. Unique solutions are not easy, even with all the voluminous polar wandering data and other data sets from all continents. When one is presented with (n + 1) solutions that are in conflict, it is tempting to suspect at least n solutions are in error. A number of grand notions are expressed, for instance the asymmetry of Tethys, with tectonic blocks drifting northward toward active margins and away from passive margins in the south. In general, each successive collision of a drifting continental block subducting beneath Eurasia led to a southward shift of the new southern margin of Eurasia, but when India accreted against Eurasia in the last 50 million years, no such shift took place. Instead, convergence was apparently accommodated by intracontinental deformation within Asia (p. 29). I am troubled by maps showing huge transit plates as big or bigger than the entire Pacific Ocean, across which such large continental blocks as India, Australia, and Antarctica presumably drifted. Huge areas of the reconstructed paleogeographic maps show these transit plates or bearing plates to have been at great depths in excess of calcite compensation depths (p. 193). One wonders how much of this is fact, based on observed data, and how much is really a model.

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