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Many continents have been claimed as having once existed in the Pacific before disappearing subsequently, but hardly any of these claims are true. Accounts of some of the undoubtedly mythical continents claimed to have existed in the Pacific are discussed in chapter 7; in this chapter I discuss two continents that have been suggested to have once existed in the Pacific. One has indeed become hidden; fragments of the other, if it ever really existed, may lie hidden beneath the ocean surface. The Paleozoic Continent in the Southeast Pacific The structure and composition of some of the oldest rocks found along the west coast of South America, particularly in northern Chile, Peru, and Bolivia, have long puzzled geologists . Some of these rocks, ancient sediments called turbidites, form on the steep slopes along the edge of a continent, where particles of terrestrial rocks accumulate in huge sediment aprons (or fans). No obvious surprise then that there should be turbidites along the high steep western margins of the South American continent. But what is surprising when you come to look closely at these turbidites is that they become thicker and coarser to the west, the complete opposite of what you would expect had they been washed off the continent of South America.1 It is not only the reversed turbidites that caught the attention of early geologists working along the west coast of South America but also the folded rocks in belts trending parallel to the coast and the truncation of what are today northwest-trending structures.2 The only mechanism that appeared credible to early geologists working in this area was that a huge landmass—un ancien continente Pacifique—had once existed off the west coast of the South American continent.3 It must have been large to produce enough sediments to Ancient Continents Hidden by Time 4 ancient continents hidden by time 63 create the thick turbidites off its east coast, and it must have occasionally collided with the modern continent of South America, causing some of the rocks there to be folded parallel to the coast. In addition, it must have moved sideways along the western border of the South American continent, causing some of the preexisting structures to be partly scraped off. Handicapped by working with fixist models of earth-surface behavior, early geologists could do little more than simply infer the existence of a Southeast Pacific continent. It is possible that they were encouraged in this radical interpretation by the widespread belief in the late nineteenth century that the Pacific was a site of a sunken continent.4 Reconstructing what the earth looked like during the Paleozoic era (590–250 million years ago) is understandably a major challenge because of the massive overprint from later processes and overlay of younger formations. Yet considerable advances in understanding the Paleozoic world have been made from examining those areas of the continents that have remained comparatively undisturbed since that time. The model of plate tectonics has helped this process immeasurably, by providing various options for reconfiguring the positions of existing continental fragments at various times in the past. One of its most successful applications has been the SouthWest US–East Antarctica (or SWEAT) hypothesis, championed by Ian Dalziel at the University of Texas, which involved the juxtaposition of the Pacific margin of North America (Laurentia) with East Antarctica–Australia during late Precambrian times (about 1,000–800 million years ago) when the supercontinent Rodinia existed (see Figure 2.2). At the end of the Precambrian period , after the opening of the first Pacific Ocean between these continents, Laurentia moved a short distance away from (what is now) the west coast of South America, and the turbidites were produced. But Laurentia came back again, colliding several times with South America, causing the folding noted earlier, and also producing, along the collision suture, a line of fold mountains that today comprise the Andes of South America and the Appalachians of eastern North America.5 The truncation of South American structures was caused by the northward movement of Laurentia along the west coast of South America. The identity of the Paleozoic Southeast Pacific continent and its current whereabouts have not been known for long. Mainly through the increasing recognition that the Andes and Appalachian mountain ranges formed at the same time as a result of the same processes , it now seems beyond doubt that this continent (Laurentia) is simply an ancestor of the modern continent of North America. From northern Canada to...

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Additional Information

ISBN
9780824865443
Related ISBN
9780824832193
MARC Record
OCLC
456566429
Launched on MUSE
2012-01-01
Language
English
Open Access
No
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