Goals

Using German Vocabulary aims to offer a comprehensive, thematically structured vocabulary textbook for all but the very beginning levels of undergraduate instruction in German. The individual units treat topics that expose students to a broad range of vocabulary dealing with the physical, social, cultural, economic and political world. Vocabulary is graded into three levels that reflect frequency, difficulty and degree of usefulness. Exercises and activities are provided to reinforce and aid acquisition. The range of topics covered and the levels of competence addressed allow the book to be integrated into the curriculum in a variety of courses at multiple stages of any undergraduate program.

Because first-year German textbooks typically include a list of vocabulary to learn in each chapter, the acquisition of vocabulary during the first year of college-level instruction in German is relatively straightforward. After the first year, however, it becomes more difficult for instructors and students alike to deal with vocabulary in a systematic manner. Instruction at the intermediate and advanced levels tends to centre around authentic texts in the target language. The vocabulary that students acquire at these levels is thus limited in large part to the vocabulary that occurs in these texts. Using German Vocabulary is a tool for dealing systematically with vocabulary acquisition beyond the first year of instruction.

The past decade has seen the publication of a number of German language textbooks that seek to address the issue of vocabulary acquisition beyond the beginning stages of language learning.

Introduction

This chapter commences with events of the Middle Ordovician, a somewhat arbitrary beginning point in terms of the standard geologic periods but one that makes sense with respect to marine transgressions and sequences of strata in the Southwest. It corresponds to a major unconformity at the end of the Sauk transgression, expressed over wide areas of the Colorado Plateau and indeed of much of the North American craton. In the Southwest, this unconformity and the strata immediately below and above are nowhere better observed than in the Grand Canyon, a classic section in North American geology. In other parts of the Southwest, such as western Utah, southern Arizona and New Mexico, and northern Mexico, this division is arbitrary because marine waters continued to inundate the continental margin even while more central areas became emergent.

This chapter encompasses a major tectonic change in the plate boundary along the western margin of Laurentia. Following the Late Proterozoic rifting and breakup of Rodinia, a passive margin formed along western Laurentia as the two continental fragments drifted slowly apart. Western Laurentia and Antarctica–Australia were separated by a growing ocean basin (Fig. 4.1), presumably fed by a mid-oceanic ridge system. Thus, the overall theme for the Southwest during the first approximately 100 Myr of time represented by this chapter was stability. Not until sometime in the Late Devonian did the first evidence for an active margin appear, i.e. a margin characterized by subduction and by compressional tectonics.

Active margin

Throughout the Cretaceous and into the Cenozoic Era, eastward subduction of the Farallon plate beneath continental crust of the North American plate proceeded seemingly unabated. Convergence resulted in the formation of an Andean-type margin, i.e. a subduction margin with a narrow magmatic arc developed directly on continental crust. Much of the Sierra Nevada and the Southern California/Baja batholiths, now the backbone of California and Baja California (Mexico), were emplaced at this time. These mountain ranges consist of numerous, overlapping plutons emplaced into the middle and upper crust beneath magmatic-arc volcanoes; most of the overlying volcanoes have long since been eroded away. The driving forces for orogenic pulses, characterized by crustal thickening and magmatism, were probably the result of coupling between the leading edge of the continent and east-subducting oceanic lithosphere of the Farallon plate. Docking and overthrusting of rafted terranes played only a minor role (Burchfiel et al., 1992).

Compressional deformation occurred continuously throughout the Cretaceous and into the early Tertiary, with formation of uplifts and of sedimentary basins. In the area of the present Great Basin, the style of deformation was ‘thin-skinned,’ beginning earlier (see below) compared with regions to the east. This deformation, named the Sevier orogeny for the Sevier desert of Utah, is recognized mainly in Utah and Nevada, but extends from Arizona to British Columbia and Alberta. On the craton to the east, deformation resulted in basement-cored uplifts, beginning later than deformation to the west.

Progress in deciphering the Precambrian

The geologic story of the Southwest begins far back in the Precambrian, that period of the Earth's history prior to 543 Ma. It was during the Precambrian that the underpinnings of the crust were formed from the underlying mantle by a variety of processes. Yet events of this great age in the Southwest, as in most other areas of the world, have been difficult to interpret. For more than a century geologists have recognized that Precambrian rocks record events of regional and global importance, but it was not possible until relatively recently to make significant progress in deciphering these events. Earth's Precambrian history remained obscure for several reasons. Over great regions of the continents, rocks of Precambrian age are covered by younger sedimentary rocks, hiding them from direct observation except in deep wells. Where exposed, much of the Precambrian is highly metamorphosed and/or deformed on all scales, destroying or obscuring features of the original rocks that aid in interpreting their genesis. Most importantly, though, rocks of Precambrian age, even where unmetamorphosed, are nearly devoid of the fossils that were essential for the relative age determinations and regional correlations upon which an understanding of geological events was based. Only in the Cambrian period beginning around 543 Ma did organisms suddenly develop the hard body parts that enabled their remains to be preserved well.

Introduction

During the late Paleozoic, the geological development of the Southwest was controlled by two major events. The first of these, one of the major global events of the Phanerozoic era, was the final assembly of the supercontinent Pangea, which profoundly affected the Southwest. In fact, the Southwest found itself in a great squeeze (Fig. 5.1). From the southeast came Gondwana, which when crunched together with Laurentia, completed the assembly of Pangea. From the west, riding on oceanic crust, came bits and pieces of island arcs and perhaps a microcontinent, to be accreted to the western margin of Pangea when the supercontinent entered the subduction zone. In addition, near the beginning of the Pennsylvanian Period, global sea level rose again, marking the Absaroka transgression. The wide range in topography that resulted from continental collision, coupled with the changing sea level as marine water inundated then retreated from the continental margin, created a wide range of paleogeographic environments over relatively short distances.

Ancestors of the Rockies

A profound tectonic event or combination of events, affecting the eastern and southern margins of North America from New England to the Yucatán region and much of the western interior of the United States, began in the Late Mississippian, reached its greatest intensity in the Middle Pennsylvanian, and ended in the Early Permian.

The geologic history of the American Southwest is both fascinating and important, not least because it is openly revealed to both the professional Earth scientist and casual observer alike. The exposures in this arid to semi-arid region are generally superb. This book, then, is intended to present a systematic and comprehensive picture of the geology of the Southwest since the formation of its earliest rocks in subduction zones, through the formation and fragmentation of at least two and possibly additional supercontinents. It will supplement other books, including the popular road guides, presenting more detailed pictures of the geology of the region.

But the real importance of geological studies of this region lies in their broad application to other areas of the Earth. Geological paradigms developed in the Southwest have global import. Thus, a secondary purpose is to highlight the numerous concepts that have grown out of study and research in the Southwest and West and that have bearing elsewhere in the world. Since the geographical and topographical surveys of the middle and latter part of the nineteenth century, the geology of the West has strongly influenced the development of the geological sciences. Examples derived from the American Southwest have been used in the professional training of geologists for over a hundred years. In part, this book will illustrate how concepts derived from study of modern rocks feed back into an understanding of rocks from earlier periods of Earth's history, and vice versa.

Setting

By the beginning of the Mesozoic, Pangea was nearly fully assembled. Only a few microcontinents, such as North and South China, remained yet to collide with the main Pangean landmass, which they did by the end of the Triassic (Rees, 2002). Stretching nearly from pole to pole, Pangea drifted slowly northward across the equator (Fig. 6.1). The western margin of the supercontinent and of present North America continued to be a collisional boundary during the Mesozoic era, with the Cordilleran miogeocline present along the continental margin. Great tracts of new continental crust – ‘exotic terranes’ – were accreted to the continent during the Mesozoic. Together with magmatic arcs and sediments of the adjoining trenches, these terranes formed what are now the States of California, Oregon, and Washington, and much of Nevada and Arizona. The Early Triassic also saw the beginning of the end of Pangea, as great continental blocks were carved from Pangea to form new plates. The demise of Pangea was not sudden, but rather was drawn out over the next 150 Myr, not to be completed until the early Tertiary (c. 45 Ma). However, the disassembly of Pangea did not affect the western part of Pangea, including the present Southwest.

The edge of the craton extended through central Utah and southern Nevada. To the west, in central Nevada, lay terrane accreted to the continent during the Antler orogeny, and the miogeocline. On the continental margin, shallow-marine sediments alternated with terrigenous deposits as the shoreline fluctuated.