« PreviousContinue »
Division will continue to place considerable emphasis on the maintenance of this basic research capability because of its importance, not only to the Division's other programs, but also to a large and growing user community.
Mineral Resource Surveys
In addition to the completion and publication of the results of the mineral resource appraisal of the Rolla, Missouri, quadrangle, which are described in a following article, the Geologic Division completed similar work in 11 other 2-degree quadrangles in the United States; maps and reports dealing with the results of these appraisals are either in press or in final compilation. Field investigations are underway in five additional quadrangles. The Division produced its first annual report under the Alaska National Interest Lands Conservation Act of 1980, approached completion of mineral resource assessments of Forest Service wilderness lands, and accelerated assessments of Bureau of Land Management wilderness lands. The Division completed a compendium of 48 mineral occurrence models while also continuing work on the use of space shuttle technology, described below, and other innovative approaches to mineral resource exploration.
Future long-term directions for the minerals programs include placing high priority on the identification of unconventional sources of strategic and critical minerals while continuing the systematic appraisal of the Nation's mineral resources through the Alaska Mineral Resource Appraisal Program and Conterminous United States Mineral Appraisal Program. The Division will also be challenged to address the short- to mid-term requirements of the Wilderness Programs of the Bureau of Land Management and the Forest Service.
qualitative assessments of the oil and gas potential of land units within oil and gas basins. The Division also moved closer to completion of a major study of the occurrence of uranium in the San Juan Basin, New Mexico, which contains the largest known uranium reserves and resources in the United States.
The Division completed an additional 10 coal folios at 1:100,000 scale in support of the Bureau of Land Management's land use planning requirements. Of the 110 quadrangles identified for the preparation of the folios, 14 are now completed, and an additional 22 will be completed in the near future based on efforts underway during fiscal year 1982.
Following the oil embargo of 1973 and the ensuing energy crisis, the Geologic Division recognized a rapidly evolving responsibility to provide a central repository for the vast amounts of data that were collected, not only by the Survey, but also by other Federal agencies, regarding the Nation's coal, oil and gas, oil shale, and uranium resources. To meet this responsibility, the Geologic Division began in 1974 to design and implement the National Coal Resources Data System, a computer-based capability to store and provide both quantity and quality analyses of the Nation's coal resources. During fiscal year 1982, an additional 30,000 drillholes were entered into the system bringing the total to 80,000, leaving an estimated 320,000 to be entered. This system, which is now operational, is available to support land use planning at the Federal, State, and local levels and has, in fact, been built with substantial participation by the coal-bearing States. Work will continue to complete data entry in the data system while other efforts are already underway to similarly address other energy commodities.
Offshore Geologic Surveys
Energy Resource Surveys
During fiscal year 1982, the Geologic Division successfully completed a prototype project in using digital cartographic techniques to produce both quantitative and
During fiscal year 1982, all functions in direct support of the Department of the Interior's Outer Continental Shelf Leasing Program were transferred from the Geologic Division to the newly created Minerals
Management Service. The Division continued its efforts in indirect support of the Outer Continental Shelf Leasing Program by providing resource appraisals of offshore basins where future Outer Continental Shelf lease sales may be held. These offshore resource appraisals were incorporated in revised estimates of the undiscovered recoverable petroleum resources in the United States, which was published in fiscal year 1982 as U.S. Geological Survey Circular 860. Compared to the 1975 assessment, Circular 860 confirms the same amount of oil remaining to be discovered but reflects a 22-percent increase in the amount of gas. The Secretarial Order clarified the Geologic Division's research mission to perform work similar to that which is described in the article entitled "Oceans and Oil." This type of basic research will provide the Nation with the capability to discover and assess new
areas of petroleum potential as conventional sources are depleted.
The refocusing of the Geologic Division's offshore mission provided impetus for new activities in areas of polymetallic sulfides in the Juan de Fuca and Gorda Ridges, which contain commercial amounts of zinc, sulfur, iron, copper, lead, cadmium, and silver; in the newly identified cobalt-rich manganese crusts off the coast of Hawaii and the Trust Territories; and in the planning for surveys offshore Antarctica in anticipation of the treaty renegotiation, which may occur in 1991.
In the following sections, highlights from some of the major programs are described.
The Evolution of the Pacific Coast of North America
New geological, geophysical, and paleontological data obtained during the past 10 years or so have dramatically changed our ideas concerning the geologic history of western North America. It has long been known that the stable central shield region of the continent is very old-some rocks are known to have formed at least 3.8 billion years ago. These ancient rocks do not extend continuously westward to the Pacific Coast, however, but end along a line running northward from about central Nevada. On the basis of the new data, we now believe this line, which can be defined both on geologic and geochemical bases, marks the edge of the North American Continent about 250 million years ago. Since that time, the western edge of the continent has grown through the addition of new material. We now recognize that a belt averaging over 370 miles in width and extending from Mexico north to Alaska - nearly 25 percent of the total land area - represents new crust that has been added to the continent through a process that involved collision between the continent itself and separate oceanic blocks.
This growth of new continental crust has been piecemeal, resulting in new crust that is highly variable in composition and character. Much effort has been expended lately in an attempt to identify these separate accreted blocks, now called terranes, and to determine the following: • Where they originated; • How much and by which path they
moved; • When they collided with North America;
and • What mechanical processes, such as fold
ing, faulting, and compositional
Nearly 200 terranes have now been identified in western North America, but sufficient information to permit answering all the above questions for all these terranes is not yet available. Despite this, we do know that some terranes have traveled a very long distance and can be realistically described as exotic elements because they are displaced from their place of origin. A good example of a far-traveled terrane is Wrangellia (see fig. 1), which extends from southern Alaska to eastern Oregon. Combined geologic and paleontologic data suggest that Wrangellia originated far to the south of its present position, perhaps near to the equator. This hypothesis has been substantiated by geophysical studies, such as paleomagnetism, that show that some rocks in Wrangellia did indeed form at low latitudes, near the equator, and probably in the Southern Hemisphere. Thus, Wrangellia has moved northward relative to North America by nearly 60 degrees of latitude, the equivalent of about 3,600 miles, or one-sixth of the circumference of the Earth. This terrane was added to the continental margin of North America about 100 million years ago, and, since then, its distribution has been further affected by younger lateral movement along faults that have dispersed fragments of Wrangellia along the Pacific Coast.
Geologic and geophysical research carried out by scientists of the U.S. Geological Survey has been critical to the development of this new concept of continental growth by accretion of exotic terranes. Because this new concept touches almost all areas of the earth sciences from paleontology to seismology, it has tended to draw together specialists from disciplines that hitherto had little in common into closely coordinated research teams. Only in this way can questions about the accretionary process be answered. And these answers are important.
For example, the crustal properties of
Figure 1.- This map shows
the original configuration of
Oceans and Oil
past, the continents were not in their present positions; for example, 200 million years ago, world geography was very different from that of today. This is why past circulation patterns must be modeled theoretically; simply superimposing modern circulation on past geography does not produce a valid model.
Once we know the worldwide patterns of ancient winds, we can predict the probable locations of ancient upwelling zones. The potential for source areas for oil can then be assessed. For example, U.S. Geological Survey geologists predicted that, from the viewpoint of ocean models, the source rock potential for Baltimore Canyon (located about 90 miles offshore from Atlantic City, New Jersey) was not favorable and that the potential for Georges Bank (located about 100 miles offshore from Nantucket Island, Massachusetts) was good. Since that time, dry holes have been drilled in Baltimore Canyon, and oil has been found on Georges Bank. Like any exploration technique, the ocean modeling studies do not guarantee oil discoveries, but, even in the early stages of their development, they have proved a valuable tool.
The traditional emphasis in the exploration for oil has been on reservoir rocks; that is, the rocks from which the oil is pumped. However, as the larger reservoirs are depleted and we have begun to search for smaller and smaller reservoirs, it has become important to understand the distribution of so-called "source rocks," the rocks in which the oil originates before it migrates to and pools in the reservoirs. Exploration for oil has also moved into “frontier” areas; that is, areas that have not been previously explored. Oil and gas research within the U.S. Geological Survey is designed to develop models and techniques that will guide industry to these new petroleum resources in a manner that gives maximum value for each exploration dollar.
One of the techniques being used at the U.S. Geological Survey for promoting the understanding of source-rock distribution involves modeling and producing maps of ancient ocean currents. The work aimed at producing the ocean models and predicting the locations of oil source rocks is exciting because it combines knowledge derived from a large number of scientific endeavors.
Most oil is composed of material originating from the bodies of single-celled marine plants that were deposited on the ocean floor. Vast numbers of these tiny plants are needed to create significant amounts of oil. Some environments are favorable for the preservation of any plants that fall to the sea bottom. In other environments, the plants are so numerous that, even though large numbers decay or are eaten, many are buried in the sediments, and they eventually create large amounts of oil. It is to these environments that ocean modeling studies are directed.
We know that certain ocean currents create the conditions favorable for the continued and rapid growth of marine plants. These currents, which are called upwelling zones, occupy less than 1 percent of the ocean surface. The currents are driven by strong winds that are part of very large scale wind patterns, the components of which cover areas as large as the Pacific Ocean north of the equator. The overall global pattern of circulation seen today is dependent on the present positions of the continents and seas. We know that, in the geologic