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Introduction

Sedimentary basins are places where subsidence of Earth's crust has allowed sediment to accumulate on top of a basement of igneous and metamorphic rocks. Over geologic time these sediments and associated fluids are chemically and mechanically transformed through the compaction and heating associated with basin subsidence. The buried materials constitute the sedimentary stratigraphic record and contain both unique natural resources and information regarding the history of tectonic, biologic, oceanographic, and climatic events during Earth's evolution. Sedimentary basins and sedimentary materials cover most of Earth's surface. Understanding the evolution of sedimentary basins, and the reasons for their existence in particular places at specific times, can provide fundamental insights into a wide range of Earth processes. The imprint of geologic events left on the materials of sedimentary basins is the most detailed record of the history of Earth's outer shell, the lithosphere.

Basins come in many shapes and sizes and form in response to a variety of processes that influence the elevation of Earth's surface. Some are filled with strata deposited entirely in terrestrial environments, others with strata deposited below sea level in marine environments; many basins include both kinds of sediment. Sedimentary basins also develop in many different geodynamic settings, and their geohistories are diverse. To define the nature of basin-forming events, it is essential to understand



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--> 1 Introduction Sedimentary basins are places where subsidence of Earth's crust has allowed sediment to accumulate on top of a basement of igneous and metamorphic rocks. Over geologic time these sediments and associated fluids are chemically and mechanically transformed through the compaction and heating associated with basin subsidence. The buried materials constitute the sedimentary stratigraphic record and contain both unique natural resources and information regarding the history of tectonic, biologic, oceanographic, and climatic events during Earth's evolution. Sedimentary basins and sedimentary materials cover most of Earth's surface. Understanding the evolution of sedimentary basins, and the reasons for their existence in particular places at specific times, can provide fundamental insights into a wide range of Earth processes. The imprint of geologic events left on the materials of sedimentary basins is the most detailed record of the history of Earth's outer shell, the lithosphere. Basins come in many shapes and sizes and form in response to a variety of processes that influence the elevation of Earth's surface. Some are filled with strata deposited entirely in terrestrial environments, others with strata deposited below sea level in marine environments; many basins include both kinds of sediment. Sedimentary basins also develop in many different geodynamic settings, and their geohistories are diverse. To define the nature of basin-forming events, it is essential to understand

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--> how and where sedimentary strata have been deposited and preserved during Earth history. The formation of sedimentary basins is ultimately controlled by topography that defines the surface depressions that receive the sediments, the elevated regions that provide sediment sources, and the topographic and bathymetric gradients that transport sediments from source to basin. Topography is ultimately governed by lateral variations in the thickness and density of crustal rocks coupled with global-scale flows in Earth's mantle. Through these geodynamic links to regional topography and sediment transport, research on basins overlaps almost the entire spectrum of earth sciences and thereby provides a unifying focus for research efforts in a wide range of subdisciplines. Basin Fill The rock sequences that fill sedimentary basins can be viewed as a structural framework for exchange reactions among sediments, organic matter, and fluids, mainly water. These transformations yield the energy resources of petroleum, natural gas, coal, geothermal energy, and uranium and they lead to the precipitation of a wide range of ores for important metals such as copper, lead, zinc, iron, and mercury. The rock sequences are also the framework for aquifers, the most porous and permeable geologic units in the crust and the major reservoir for fresh water on Earth. Increasingly, these deposits are subjected to anthropogenic impacts because basins are the predominant repository for wastes from resource development and industrial production. Because the characteristics and settings of basins are varied, research on sedimentary basins cuts across a wide range of scientific and engineering disciplines. Amidst these differences, however, two central themes emerge. First, the historic record of sedimentary basins has wide application for fundamental studies across the full span of the earth sciences. In recognition of the importance of basin data, there has been considerable effort to develop new technologies for measuring and interpreting the geochemical, tectonic, climatic, and biologic record of Earth history as preserved in basin fill. Second, sedimentary basins host many key natural resources, including fossil fuels, ground water, industrial minerals, and metallic ores. Consequently, there has been great interest in developing new multidisciplinary approaches for studying the generation and evolution of these resources in fluid-rock systems.

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--> For as long as fossil fuels continue to be the main energy source for the world, knowledge of the modes of occurrence and distribution of hydrocarbon resources in sedimentary basins will remain key background information for public policy in both the domestic and international arenas. The fruits of this facet of basin research are critical now that imported petroleum accounts for roughly half of domestic consumption. The time is long past when the United States could meet domestic petroleum demand by simply expanding production from internal sources. Future Research With diverse areas of focused interest, the opportunities for research on sedimentary basins are currently at a watershed. Decades of disciplinary research across earth sciences and engineering have amassed a vast data set of basin properties and settings. Worldwide campaigns of drilling, seismic imaging, and fieldwork have elucidated global patterns of basin fill and history. Over the same period, the development of plate tectonics has created a theoretical framework that integrates basin studies into the broad spectrum of earth sciences. With this perspective, and utilizing these data, there are now great opportunities for multidisciplinary research on basins to address fundamental problems in earth sciences. These include the relationship between plate tectonics and deep mantle convection, the causes and consequences of global climate change, the scale of fluid flow and chemical transport through the continental crust, and the distribution of mineral and fossil-fuel resources through the stratigraphic record. These opportunities unfortunately come at a time of intense financial pressure on funding sources for research on sedimentary basins. Historically, research on basins has been financed primarily by the petroleum industry and secondarily by the federal government. Since 1985, however, falling oil prices and corporate restructuring have resulted in significant reductions in the work force and research expenditures by international and domestic oil companies. Between 1989 and 1993, for example, research expenditures by the 15 largest oil companies decreased from $2.3 billion to $1.9 billion (in current dollars) (Oil and Gas Journal, 1995), and this continuing decline in research investment was superposed on a level of expenditure already reduced from its peak of 10 to 15 years ago. Over the past 10 years employment in the petroleum industry has decreased by more than 400,000 jobs (Oil and Gas Journal, 1995). For

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--> the past five years the major oil companies have devoted approximately 0.5 percent of their revenues to research expenses. By comparison, oilfield service companies invest a larger fraction of their relatively smaller revenues (about 5 percent), while the research expenditures of environmental remediation companies appear to be significantly lower, although estimates are not available. The implications of these funding cuts on the broader scientific community have been severe. For example, membership in the American Association of Petroleum Geologists has decreased by approximately 30 percent since its peak in the early 1980s. Industry support for university research programs also has declined significantly. Consequently, several university programs related to sedimentary basins have broadened their emphasis beyond the traditional focus of petroleum geology. Widening research perspectives is a potentially valuable strategy but cannot alone compensate for reduced funding without better coordination of continuing efforts. Throughout the research community, changing research arrangements have sparked considerable interest in preserving and disseminating the results from a half century of proprietary research on sedimentary basins that was carried out by petroleum companies. Charge to the Panel At this budgetary and intellectual transition, there is a need to evaluate opportunities for multidisciplinary research on sedimentary basins. Given the continuing challenges of tight budgets and a shrinking scientific work force, effective strategies are critical to allow continued advances in basin research. To this end, this report by a panel of the National Research Council's U.S. Geodynamics Committee (USGC) assesses the status of multidisciplinary research on the formation and evolution of sedimentary basins. In carrying out this study, the National Research Council appointed a study panel of 14 members with expertise across the broad range of basin studies representing academia and industry. For this work the panel's charge was to identify scientifically important research problems that can be addressed by multidisciplinary studies of sedimentary basins, identify new techniques and/or data sets that can be brought to bear on these problems, and

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--> identify the cross-disciplinary ties that are essential to addressing these problems. This report summarizes the panel's deliberations on these questions. It presents a brief summary of important topics in basin research and a description of the critical issues and requirements for developing a unified process model for basin initiation and evolution. Finally, conclusions and recommendations are presented.

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