26282_Geo_Arizona.qxd 8/17/07 5:51 PM Page 1 ESSENTIAL QUESTIONS TO ASK Arizona.1 Introduction Ⅲ What role has plate tectonics played in creating Arizona’s landscape? Ⅲ What are the three physiographic provinces found in Arizona? Arizona.2 The Proterozoic Foundation of Arizona Ⅲ What primary process was involved in forming the land in Arizona’s early history? Ⅲ Where do we see Proterozoic rocks exposed in the state today? Arizona.3 Paleozoic Clastics and Carbonates Ⅲ What evidence do we have that several episodes of transgressions and regressions deposited thick sedimentary sequences? Ⅲ How extensive were the marine inundations that covered Arizona? Arizona.4 Transitions during the Mesozoic Era Ⅲ Why were there extensive sand and river deposits covering the northeastern portion of the state? Ⅲ Where were the sources for volcanic deposits in southern Arizona? Arizona.5 Laramide and Mid-Tertiary Upheaval Ⅲ What role did plate tectonics play in creating geologic features in Arizona? Arizona.6 Volcanic Activity Ⅲ What are the time span and spatial extent of volcanism? Ⅲ What types of volcanic features have been formed? Arizona.7 Formation of the Grand Canyon Ⅲ How did the Colorado River form the Grand Canyon? Ⅲ Where did all the eroded material go? Ⅲ How dynamic is the Grand Canyon in terms of changing in the future? Arizona.8 Economic Resources Ⅲ Why is Arizona home to some of the largest copper deposits in the world, and how have they contributed to the development of the state? Ⅲ What does the future hold for mining in the state? Arizona.9 Water Resources Ⅲ Where does Arizona get its water? Ⅲ What is the future of water in Arizona? Arizona.10 Environmental Concerns and Geologic Hazards Ⅲ Has Arizona experienced natural disasters in the past? Ⅲ How stable is the state in terms of future disasters? Sample Copy Only Not for Reproduction © 2008 Thomson Brooks/Cole, a part of the Thomson Corporation. Thomson, the Star logo, and Brooks/Cole are trademarks used herein under license. ALL RIGHTS RESERVED. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means—graphic, electronic, or mechanical, including photocopying, recording, taping, Web distribution or information storage and retrieval systems—without the written permission of the publisher. The Adaptable Courseware Program consists of products and additions to existing Brooks/Cole products that are produced from camera-ready copy. Peer review, class testing, and accuracy are primarily the responsibility of the author(s). Geology of Arizona/David M. Best - First Edition ISBN 1-426-62628-2. Printed in the United States of America. 26282_Geo_Arizona.qxd 8/17/07 7:56 PM Page 2 2 Arizona Geology of Arizona ᮣ Figure Arizona.1 Geologic time scale. The numbers indicate the Arizona.1 number of years before present, in millions of years. Introduction Eon Era Period Epoch Recent or As a student taking a geology course in Arizona, you will Holocene 0 want to learn how the concepts you become exposed to can Quaternary be applied to the rich and diverse geologic settings within Pleistocene 0.01 the state. The overview that follows takes you across the Pliocene 1.8 state in terms of its geology, addressing some of the major topographic differences as well as the wide variety of rock Miocene 5 types and the manner in which they were formed and sub- Oligocene 23 sequently exposed. Tertiary Many people think of Arizona as being covered only by Eocene 34 Paleogene Neogene desert, with the Grand Canyon somewhere within the state Paleocene 56 boundaries. Located in the American Southwest, Arizona has a wide range of rock types, including some that formed Cretaceous 66 almost 2 billion years ago (Ga). The northern and north- Jurassic 146 eastern portions of the state are covered by relatively hori- Triassic 200 zontal layers of sedimentary units, which formed near Phanerozoic continental margins, in shallow seas, or in desert conditions. Permian 251 Portions of the southern and southwestern regions are the result of tectonic activity that occurred between 30 and Pennsylvanian 299 80 million years ago (Ma). Throughout the state, igneous activity produced several dozen mountain ranges and areas Mississippian 318 Carboniferous of extrusive material. We will refer to various geologic Devonian times throughout our discussion, so the geologic time scale Paleozoic Mesozoic359 Cenozoic is provided to help you gain a temporal appreciation for when different events occurred (Figure Arizona.1). Silurian 416 The overarching concept of plate tectonics, a theory that Ordovician 444 has become well established in geology since the early 1960s, has been instrumental in explaining the way the state Cambrian 488 looks and in contributing to the makeup of the Southwest. 542 The effects of major incursions of oceans and the uplift of mountain ranges and the surrounding land, coupled with collisions between landmasses, have all left their mark. Arizona has moved across the globe through geologic time, 2500 Early bacteria which helps explain the formation of major rock units such as limestone and sandstone deposits associated with marine Archean Proterozoic Precambrian and desert environments, respectively. Collisions with other plates produced volcanic extrusions and igneous masses 3600 buried below the surface. During the Cambrian Period, Hadean Arizona was situated at about 10 degrees north of the equa- tor, where shallow marine environments created lime muds 4600 (Figure Arizona.2). Sample Copy Only The region then began to move to the south until the mid-Silurian Period, when it began its long journey north- Exposed outcrops display areas that were once located at ward. This steady movement has seen it shift from roughly the depositional terminus of major streams that eroded 20 degrees south latitude to Notas far north as 45for degrees, Reproduction nearby mountains, creating extensive deposits of mud- which lies along the present-day Montana-Wyoming border. stones, sandstones, and conglomerates. During this time the region experienced a wide range of geologic environments. Today Arizona is located at approx- imately 35 degrees north of the equator. The Geologic Map of Arizona and Keep in mind that most of the current topography has Physiographic Provinces been carved by weather and climate over a relatively short A physiographic province is a region in which all parts time span (several tens of millions of years) when measured display similar geologic structures and geomorphology. against the age of the oldest exposed rocks or even the age When the concept is applied to Arizona, there are three of the Earth itself, estimated at about 4.6 billion years. such provinces within the state (Figure Arizona.3). 26282_Geo_Arizona.qxd 8/17/07 10:14 PM Page 3 Arizona.1 Introduction 3 ᮣ Figure Arizona.2 The Southwest was covered by shallow The northern third of the state lies in the Colorado equatorial seas during the Middle Cambrian. Extensive shallow waters Plateau, a relatively circular area centered on the Four covered most of Arizona and regions to the north and west. Deeper Corners region (the only point in the United States where oceans are shown to the west and continental landmasses to the east. four states come together—Arizona, New Mexico, Colorado, and Utah). Rocks on the Colorado Plateau in Arizona are predominantly sedimentary units consisting of sandstones, mudstones, and limestones (Figures Arizona.4 and Arizona.5). Most of the rocks range in age from Permian to Triassic, with lesser amounts of Cretaceous ᮣ Figure Arizona.4 Sedimentary rocks are common in northern Arizona. The Moenkopi Formation formed in continental rivers and epicontinental seas. Image by Dr. Ronald C. Blakey, Northern Arizona University. Ronald C. Blakey, Image by Dr. ᮣ Figure Arizona.3 The physiographic regions of Arizona. COLORADO PLATEAU ᮣ Figure Arizona.5 The Kaibab Limestone, as seen from the Little Colorado River Scenic Overlook east of the Grand Canyon, displays layered strata that formed in a shallow, warm water sea that existed TRANSITION during the Permian Period. Sample Copy Only Not forZONE Reproduction BASIN AND RANGE 26282_Geo_Arizona.qxd 8/17/07 5:51 PM Page 4 4 Arizona Geology of Arizona sediments cropping out in localized areas that contain sand- stones interbedded with coal and shales. There are also Section Arizona.1 Summary some volcanic rocks that form small mountain ranges and ● Arizona has had a complex geologic history, which is isolated peaks. recorded in a diverse range of rock sequences and Moving to the south we encounter the Transition Zone, surface features. a region that serves as the dividing line between the rocks of the Colorado Plateau and those of the Basin and Range ● The state is divided into three physiographic regions, physiographic province to the south and west. Within the each having a distinct geologic history and appearance. Transition Zone lie many of the oldest exposed rocks found in the state. In general the oldest rocks are found in the northwest part of the Transition Zone. Some samples found north of Kingman are about 1.8 billion years old. These rocks are thought to have been part of a continental mass Arizona.2 associated with the earliest formation of the North The Proterozoic Foundation American continent, which contains the Wyoming Province, an area that extends to the north and east from of Arizona northern Arizona across Wyoming and the Dakotas. The central part of the North American craton is composed Collisions of these landmasses produced intrusive igneous of continental lithosphere that formed by the suturing of and metamorphic rocks that are common in the mountains several smaller continental masses more than 2 Ga. In the of northwest Arizona and southeastern Nevada. To the southwestern United States several episodes of accretion southeast there are exposures of granites and metamorphic occurred that added multiple terranes to the 2.5-billion-year- rocks that formed from about 1.6 to 1.4 Ga.