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Scientific Ocean Drilling (HUSOD) report entitled "Ocean Margin Drilling Program" and issued by the Interim Planning Committee, JOI Inc.,* March 1980. In October 1981, the ten petroleum companies of the partnership voted, for reasons not related to the scientific value of the program, not to support the program beyond the initial planning. Withdrawal of the petroleum companies turned the program focus away from the ocean margins and reopened the larger question of what sort of drilling program is justifiable over the next five to ten years. Program design was, of course, dependent on the technology and on the ships available. Consideration of these questions forms the main thrust of this report. THE CASE FOR FUTURE DRILLING There is no question about the success of NSF's DSDP/IPOD** program or of its contribution to geological sciences. DSDP has amassed an unmatched record of exploration into the least known parts of the earth's crust. The accumulated data and the consequent increased understanding of the earth's structure and dynamics will mold geologic thinking for many years to come. The willingness of other nations to participate in the scientific work and to help finance the operation is emphatic evidence of the high international regard in which the project has been held. The many accomplishments of DSDP have been well-documented, and we cite here only a few examples, such as verification of the sea-floor spreading model, demonstration of large-scale vertical movement and the discovery of past chemical, physical, and biological ocean environments different from those *Joint Oceanographic Institutions, Inc. **International Phase of Ocean Drilling
of the present. Hidden behind the more glamorous headlines is what may be DSDP's most enduring contributionâthe building of a reconnaissance geological section of the sediments that constitute the upper part of the oceanic crust. But this reconnaissance section, valuable as it is, is built upon only about 500 drill sites in the deep oceans, or one data point for each 275,000 square miles. Further investigation of this section, its variations, and its relation to continental crust hold promise of major advances in understanding earth history, composition, structure, and resources. Past success alone does not justify continuation. Starting with the FUSOD meeting in 1977 and culminating with a meeting in November 1981 of a group called the Committee on Scientific Ocean Drilling (COSOD), various interested groups have discussed the scientific merits and outlined the desirable content of a follow-on program. The several reports vary more in emphasis than in content, and all have two features in common. First, they are problem oriented. This is a logical and proper outgrowth of the DSDP program, which started as geologic reconnaissance and then identified specific important problems for attack. Second, although the proposed programs all require the drill as an essential testing tool, drilling is to be considered only as part of an integrated effort that uses all available toolsâgeophysical and geological surveys, follow-up analyses, syntheses, etc. This integrated attack upon chosen problems is a very important feature of the proposed program. The drill, albeit required for the tests, is also the most expensive of the various tools available, and it would be wasteful to use it without the guidance provided by the other techniques. The Committee notes favorably that the NSF plans adopt this rationale.
In our opinion, the several groups that have considered ocean drilling have made a very strong scientific case for a continued program. One of the best summary statements is in the introduction to the COSOD report, which we quote here with slight modification (indicated by italics): "The drilling of sediments and rocks of the ocean basins makes contributions to many branches of science. The continuous and detailed record of microfossils preserved in ocean sediments may give the best data for describing evolutionary changes and for understanding their causes. Sediments bear the imprint of ocean temperatures and currents, information critical to the reconstruction of oceanic circulation of the past, and hence to the reconstruction of ancient climates and ultimately to a better understanding of the nature of modern climate and of climatic change. Drilling provides access to the rocks of the oceanic crust, and thus is helping to unravel its structures and motions, information required to understand the phenomena of seafloor spreading and continental drift, and, more broadly, the structure of the earth as a planet. Deep sea sediments record the contributions of the rivers and winds of the past, and thus the history of the continents, records otherwise lost by erosion of the land. In addition to greatly increasing our knowledge of earth history in general, the scientific information gained by drilling is basic to the understanding needed to guide the search for mineral and petroleum resources both on land and beneath the seas. As the ocean is the last frontier for these resources, the importance of a thorough understanding of its geologic history and framework cannot be overstated. "Before the Glomar Challenger . . . set sail on her initial trials, JOIDES identified as primary objectives for the Deep Sea Drilling Program 'the determination of the age and processes of development of the ocean basins.'
Implicit in these objectives was the need to have long cores for 'biostratigraphy, physical stratigraphy, paleomagnetism . . . and for studies of the physical and chemical aspects of sediment dispersal, deposition, and the post-depositional changes in sediments.' The success of the program in achieving or progressing toward these goals is almost legendary. Indeed the results confirmed the concept of seafloor spreading, the relationship of crustal age to magnetic anomalies, the basaltic nature of the oceanic crustal rocks, and, through the systematic sampling afforded by the drill, initiated an entirely new field of study: paleoceanography. "This technology has taken geological sciences through more than a decade of unprecedented advancement and has been instrumental in bringing us to our present level of understanding of the origin and history of the ocean environment. That understanding stems primarily from reconnaissance drilling based on reconnaissance geophysical studies. We now need to advance our level of technical expertise in both drilling, . . . geophysical surveying, and in down-hole instrumentation. It is clear from the discussion and position papers presented at the Conference on Scientific Ocean Drilling that we are entering into a new era of ocean exploration utilizing the concepts of natural laboratories on the seafloor and carefully chosen arrays of drill sites to study general processes and global problems. In the past decade we have learned that the keys to geological processes and much of the history of the earth for the past 200 million years are recorded in the sediments and rocks of the ocean basins. We have only begun to read and to interpret the story that they hold." More detailed justifications follow different formats in the several reports. We will summarize them under the four headings used by FUSOD.
1. Paleoenvironment This is the subject area to which Challenger has devoted most effort. Therefore, many of the questions have been posed by the data already provided. The questions relate particularly to the history of ocean sedimentation, to chemical and physical environments, to biological evolution, to the thermal and circulation history of the oceans, to the responses of oceans to orbital and other geophysical variations, and to the response of the deep sea environment to sea level fluctuations. The hydraulic piston corer, recently developed by DSDP engineers, allows the taking of overlapping five-meter undistorted cores of soft sediments, aggregating several hundred meters. These remarkable samples studied with new highly sensitive magnetometers can lead to a refined global magnetic stratigraphy. With such a framework, all manner of paleoenvironmental studiesâbiological, chemical, and physicalâcan be integrated and correlated from ocean to ocean. Much of the paleoenvironment program could be carried out from Challenger, but some prime target areas include sediments too thick or latitudes too high for effective or safe Challenger operation. For a truly worldwide investigation of paleoenvironments, Explorer (without riser) would be the most effective vehicle. 2. Composition and evolution of the oceanic crust These problems relate to the generation, structure, and composition of igneous rocks below the ocean sediments. Of particular interest are hydrothermal processes associated with the spreading centers. These processes dominate the chemical control of the oceans and also generate metallic ores. As our mineral resources dwindle, the investigation of ore-forming processes becomes even more important. We need to know how the hydrothermal systems vary spatially away from the ridge crusts, how magma is generated below the spreading center, and how and at what rate the new Â». ast is formed.
8 Answers to such questions can lead to a better understanding of the composition of the crust and upper mantle and to progress in understanding the dynamics of the plate tectonics model. Some of this important work can be done by Challenger, but the deep penetration into fractured basalts that would be necessary could be most effectively handled by Explorer. In a few cases, a riser would be necessary so that heavy mud could be used to inhibit caving. 3. Studies of active margins Where two plates collide, one typically overrides the other, which is drawn down or subducted back into the mantle. The zone of collision is usually delineated by a deep-ocean trench. Where both the subducted and overriding plates are oceanic crust, plate borders are commonly marked by volcanic arcs (e.g., the trenches and arcs of the western Pacific). Where a continent rides the leading edge of the plate, the result is usually a long chain of coastal mountains, generally well-exposed and consisting partly of crumpled sediments and partly of volcanics (e.g., the South American Andes). Drilling along active plate boundaries will provide information which, added to geophysical and geological investigations, will allow better understanding of the dynamics of subduction. These integrated data will provide a more complete view of continental geology. An excellent start has been made by Challenger in investigating these dynamic regions of the earth's crust, but many important new targets require deep penetration into the seafloor and probably cannot be reached by Challenger. Such targets would require the greater capabilities of Explorer. 4. Passive margins Passive continental margins result from rifting, formation of spreading centers, and the generation and lateral movement of new crust. The rocks of
passive margins record a history of continental break-up and chemical transition between continent and ocean crust. Some of geology's most intriguing problems lie here, but they are also some of the most difficult to tackle. Atop the continental transition are thick wedges of sedimentâsome half of all the marine sediments deposited during the past 200 million years. Because of these enormous wedges of sediments, the passive margins have the potential of containing gas and oil, a potential that precludes deep penetration without a full riser and blowout prevention system. Marine drilling with a riser has been initiated by the petroleum industry, but only on the continental shelves, and only where the potential for hydrocarbons is greatest. Moreover, the data from that drilling are not always readily available to non-industry scientists. Drilling to study the continent-ocean basin transition will be out on the continental slope, in deeper water, and with advanced technology. It must await a vessel with Explorer's capacity. In summary, we believe that the various advocate groups have made a strong and convincing case for continuing scientific ocean drilling through the 1980's. The problems that can be addressed are among the most exciting facing the geological sciences, and their solution would make major contributions to our understanding of this planet. We urge that support of such a program be clearly recognized as a long-term commitment, without which there can be no effective planning or efficient execution. We urge also that support for ocean drilling (or indeed any other similar large projects) not detract from NSF's regular program of basic research support.