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Stratigraphic terminology and descriptions are presented for Late Archean and Early Proterozoic rocks of the Sierra Madre and Medicine Bow Mountains, southern Wyoming.
This wide-ranging discussion of Precambrian rocks includes contributions from a diverse array of authors actively engaged in investigations of various aspects of U.S. Precambrian geology. Summary discussions by the editors of the five major chapters place these contributions in a logical regional framework.
The Early Proterozoic Michigamme Formation of northern Michigan was deposited in the southeastern part of the Animikie basin. The formation conformably overlies the Goodrich Quartzite and comprises three widespread members a lower member of thin-bedded shale, siltstone, and sandstone; the Bijiki Iron-formation Member; and an upper member of tur- biditic graywacke, siltstone, and mudstone and a few local members. The Goodrich Quartzite is interpreted as having been deposited in a tidally influenced shallow marine environ- ment. The lower member of the Michigamme is interpreted as having been deposited in a tidally influenced environment, the iron-formation member as having been deposited below wave base in somewhat deeper water, and the upper member as having been deposited in still deeper water with turbidity currents being a major depositional mechanism. Several lines of evidence including paleocurrents, paleo- geographic setting, and neodymium isotopes suggest that the graywacke of the southern part of the outcrop area was derived from the south (Early Proterozoic Wisconsin magmatic terranes, Archean miniplates, and older Early Proterozoic sedimentary units formed on the continental margin), and that the graywacke in the northern area was derived from an Archean terrane to the north. The tectonic model that best fits the available data is a northward-migrating foreland basin.
In this book the editors strive to cover all primary (i.e. non-applied) topics in Precambrian geology in a non-partisan way, by using a large team of international authors to present their datasets and highly divergent viewpoints. The chapters address: celestial origins of Earth and succeeding extraterrestrial impact events; generation of continental crust and the greenstone-granite debate; the interaction of mantle plumes and plate tectonics over Precambrian time; Precambrian volcanism, emphasising komatiite research; evolution and models for Earth's hydrosphere and atmosphere; evolution of life and its influence on Precambrian ocean chemistry and chemical sedimentation; sedimentation through Precambrian time; the application of sequence stratigraphy to the Precambrian rock record. Each topic is introduced and a non-partisan closing commentary provided at the end of each chapter. The final chapter blends the major geological events and rates at which important processes occurred into a synthesis, which postulates a number of "event clusters" in the Precambrian when significant changes occurred in many natural systems and geological environments. Also available in paperback, ISBN: 0-444-51509-7