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Iowa'S Geological Past

Three Billion Years Of Change

Wayne I. Anderson

Publication Year: 1998

Iowa's rock record is the product of more than three billion years of geological processes. The state endured multiple episodes of continental glaciation during the Pleistocene Ice Age, and the last glacier retreated from Iowa a mere (geologically speaking) twelve thousand years ago. Prior to that, dozens of seas came and went, leaving behind limestone beds with rich fossil records. Lush coal swamps, salty lagoons, briny basins, enormous alluvial plains, ancient rifts, and rugged Precambrian mountain belts all left their mark. In Iowa's Geological Past, Wayne Anderson gives us an up-to-date and well-informed account of the state's vast geological history from the Precambrian through the end of the Great Ice Age.

Anderson takes us on a journey backward into time to explore Iowa's rock-and-sediment record. In the distant past, prehistoric Iowa was covered with shallow seas; coniferous forests flourished in areas beyond the continental glaciers; and a wide variety of animals existed, including mastodon, mammoth, musk ox, giant beaver, camel, and giant sloth.

The presence of humans can be traced back to the Paleo-Indian interval, 9,500 to 7,500 years ago. Iowa in Paleozoic time experienced numerous coastal plain and shallow marine environments. Early in the Precambrian, Iowa was part of ancient mountain belts in which granite and other rocks were formed well below the earth's surface.

The hills and valleys of the Hawkeye State are not everlasting when viewed from the perspective of geologic time. Overall, Iowa's geologic column records an extraordinary transformation over more than three billion years. Wayne Anderson's profusely illustrated volume provides a comprehensive and accessible survey of the state's remarkable geological past.

Published by: University of Iowa Press

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pp. xi-xii

This book is written for a varied audience - interested citizen, engineer, teacher, college student, and anyone who is curious about Iowa's geologic past. Although not written specifically for the professional geologist, I believe that geologists will find...

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1. The Geologic Setting of Iowa

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pp. 1-15

Iowa has a rich record of the geologic past, particularly in the form of sedimentary rocks. These strata represent deposits of scores of ancient seas that inundated the heartland of the North American continent. However, the state's rock record is not confined to marine deposits alone. The coal beds of southern Iowa are products ...

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2. Precambrian: The Oldest Rocks

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pp. 16-47

The lengthy interval of time between the formation of the Earth and the appearance of an abundant record of hard-shelled invertebrates about 545 million years ago is known as the Precambrian. In Iowa, Precambrian rocks are exposed only in the northwestern corner of the state (fig. 2.1). Rocks of Precambrian age occur over a large area in the heart of the North American continent (the craton) and are particularly ...

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3. Cambrian: Sandy Marine Shelves and Shorelines

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pp. 48-64

By the beginning of Paleozoic time, approximately 545 million years ago, Iowa and the rest of the North American craton were part of a low landmass undergoing weathering and erosion. Weathering and erosion continued in the area into Middle ...

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4. Ordovician: Warm, Shallow Seas

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pp. 65-105

Ordovician rocks are well exposed in northeastern Iowa (fig. 4.1) and indicate that the state was under the sea for much of Ordovician time. Marine deposition that started during Late Cambrian time continued largely uninterrupted into Early Ordovician time. Consequently, the paleogeographic setting of Iowa during Early ...

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5. Silurian: Dolomite and Carbonate Mounds

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pp. 106-135

Silurian strata form some ofIowa's most resistant bedrock units (fig. 5.1), and a conspicuous erosional escarpment marks the edge of the Silurian System in northeastern Iowa. Rocks of Silurian age contribute significantly to the landscape and scenery in state parks and lands such as Backbone, Bellevue, Brush Creek, Echo ...

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6. Devonian: A Variety of Marine Deposits

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pp. 136-179

The seas withdrew from the craton during the Late Silurian, approximately 415 million years ago, and did not return until the Middle Devonian, approximately 385 million years ago. Considerable warping affected the interior of the continent before its resubmergence in the Middle Devonian. This warping affected the ...

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7. Mississippian: Last of the Widespread Carbonate Seas

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pp. 180-226

Seas inundated the North American heartland several times during Mississippian time, approximately 360 to 320 million years ago. These were the last widespread carbonate-producing seas to invade Iowa. The Mississippian seas teemed with life, including ...

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8. Pennsylvanian: Coastal Swamps and Shallow Seas

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pp. 227-269

The great, shallow, carbonate-producing seas retreated from Iowa during Late Mississippian time some 325 million years ago, and the newly formed Mississippian rocks of the craton were subjected to warping, uplift, and erosion. During this time, erosion stripped Mississippian rocks from parts of the craton and removed ...

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9. Mesozoic: Evaporite Deposits and the Last of the Inland Seas

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pp. 270-302

The Mesozoic Era (245 to 65 million years ago) consists of the Triassic, Jurassic, and Cretaceous periods. Mesozoic means middle life, and at the time it was named it was thought to be the middle part of earth history. We now know the great age of the Earth...

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10. Cenozoic: Erosion Climaxed by the Great Ice Age

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pp. 303-352

The Cenozoic Era is divided into two periods, the Tertiary and the Quaternary. The Tertiary Period represents about 65 million years, and the Quaternary Period includes the last 1.65 million years. The Quaternary consists of the Pleistocene Epoch and the Holocene (Recent) Epoch. The Holocene represents the last 10,000 to 10,500 years, ...

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11. Geology and Humankind

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pp. 353-384

One of the meanings that is generally attributed to the Native American word "Iowa" is "the beautiful land." Although the translation may not be exact, the reference to beauty is certainly not misplaced. And it is logical to assume that Native Americans ...


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pp. 385-414


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pp. 415-424

E-ISBN-13: 9781587292675
E-ISBN-10: 158729267X
Print-ISBN-13: 9780877456407
Print-ISBN-10: 0877456402

Page Count: 440
Publication Year: 1998