The U.S. Exclusive Economic Zone; a summary of its geology, exploration, and resource potential

Publlo Inquiries O:f':f'ice

~ -·. s . . Geological Survey

JAMES G. WATT, Secretary

THE WHITE HOUSE Office of the Press Secretary

March 10, 1983 Embargoed for release at 4:00 pm EST

EXCLUSIVE ECONOMIC ZONE OF THE UNITED STATES OF AMERICA

A PROCLAMATION BY THE PRESIDENT OF THE UNITED STATES OF AMERICA

On March 10, 1983, President Ronald Reagan signed a proclamation establishing the Exclusive Economic Zone (EEZ), an area contiguous to the territorial sea of the United States, the Commonwealth of Puerto Rico, the Commonwealth of the Northern Mariana Islands, and the U.S. overseas territories and possessions. The EEZ area is approximately 3. 9 billion acres. In comparison to the 2.3 billion acres of related onshore area, the EEZ proclamation brings within the national domain an enormous new frontier area in which the types of energy and mineral resources present are fairly well known but which are still largely unassessed in terms of the abundance and recoverability. The purpose of this report is to (1) summarize the geology of the EEZ sea floor, (2) specify the known geologic resources of the EEZ, and (3) describe geophysical and sampling techniques which can be used to map the EEZ and estimate its resource potential. Figure 1 outlines the extent of the EEZ, and figure 2 shows a schematic diagram of the boundaries.

The motivation and guidance for this report were provided by A. F. Holser. Reviews by N. T. Edgar and T. W. Offield significantly improved the text. Throughout the development of this report, we benefited from the aid and advice of S. B. Griscom, G. D. Hardin, T. A. Landry, and W. C. Schwab.

The legal basis for U.S. offshore jurisdiction was set in the Presidential Proclamation of September 28, 1945, which recognized that "the continental shelf may be regarded as an extension of the land-mass of a coastal nation and thus naturally appurtenant to it" (Proclamation No. 2667, 59 Stat. 884). At that time an offshore depth of 600 feet was assumed to be the outer limit of technology for resource exploitation. Later, the Outer Continental Shelf Lands Act of 1953 recognized the Outer Continental Shelf as "all submerged lands lying seaward of [state waters] . . . which are subject to [United States] jurisdiction and control," without defining the outer limit of U.S. jurisdiction. The 1958 United Nations Convention on the Continental Shelf defined the outer limit as "a depth of 200 metres or beyond that limit to where the depth of the superjacent waters admits exploitation of the natural resources." This convention became effective for the U.S. in 1964. Thus the seaward extent of the U.S. has never been clearly defined either in a geologic or in a legal sense, although since 1945 the concept of an extension of the land mass has been in place. The term continental shelf has been used domestically and internationally at the Third United Nations Conference on the Law of the Sea (UNCLOS) to include continental and insular shelves, slopes, rises, and other features such as continental borderlands (see fig. 3). International law also recognizes that the continental shelf usually extends a minimum of 200 nautical miles, regardless of geology.

The March lOth announcement did not specifically designate the geographic coordinates of the outer extent of the EEZ, but a general indication of its extent is the U.S. fisheries conservation zone, since the operational language of the EEZ proclamation generally follows the language of the Fisheries Conservation and Management Act. The limits of the fisheries zone were set forth in the Federal Register on March 7, 1977, and successive notices issued in 1977, 1978, and 1979 have corrected errors and made modifications to the original notice. An official depiction of these boundaries can be found on the National Ocean Survey's marine boundary charts and maps listed in the Nationa! Oceanic and Atmospheric Administrations's Map and Chart Catalogue 5.

Also relevant in the definition of the EEZ outer limit is the fact that in some places the natural geologic prolongation of an undersea land mass can be more than 200 nautical miles from the shoreline. Article 76 of the UNCLOS treaty (Appendix C) addressed this issue, and the merits of this article have been widely discussed (see Hedberg 1979, 1983; McKelvey, 1983). In any event, the EEZ is a vast new frontier to study and understand. It also is an immense region with potential resources of possibly economic importance.

Geologic features and processes, as we study them, do not stop at the ocean's edge, but extend offshore into the area known as the continental margin, which constitutes much of the EEZ. For the U.S. this margin area includes the edge of the North American continent as it extends out under the Atlantic, Pacific, and Arctic Oceans, the Gulf of Mexico, and the Caribbean and Bering Seas and is very diverse in its geologic history. Geologists have been conducting studi~s here because it affords an opportunity to learn more about the processes and forces responsible for shaping our continent and controlling the distribution of resources.

The continental margin can be divided into a series of provinces called the continental shelf, continental slope, and continental rise, which occur in progressively deeper water (fig. 3). As the water depth increases, the complexity of studying each province-and developing its resources-also increases. A brief discussion of the geologic history of the North American continent, and its place on the Earth's surface, will provide an example of how continental margins are formed.

The Earth's crust is made up of gigantic plates of continental crust and oceanic crust. Most continental plates extend far out under the covering ocean and eventually meet a neighboring plate of oceanic crust or (in areas of narrow seas) an adjacent continental plate. According to the widely accepted plate-tectonic theory, crustal plates are in motion relative to each other; from time to time over hundreds of millions of years they are broken along rift zones, and the huge fragments then spread away from the rift as though borne on conveyor belts in the underlying Earth's mantle. As each fragment moves, its leading edge may collide with another plate. Depending on the kinds of plates and the nature of their collision, this process may result in the building of a mountain range (such as the Rocky Mountains) or an oceanic island arc (such as the Mariana Islands or Aleutian Is-

(collision)

SOUTHERN CALIFORNIA BORDERLAND: (extentional)

FIGURE 3.-Idealized physiography of a continental margin and some common margin types.

SOUTH PACIFIC: (volcanic arcs trenches, and carbonate reefs)

lands), or a fault zone (such as the San Andreas). The collision, or subduction, zones as well as the rift zones are sites of volcanism and seismicity. In this process of plate collision, rocks formed in the oceans, even whole marine basins, can be emplaced onto continents, where erosion may later expose them so that they may be studied. Also in this process, broad reaches of continental crust can subside and be invaded by the sea; subsequent uplift then presents to geologists the resulting record of marine deposition and erosion over that part of the continental plate. Similarly, mineral deposits that form on the ocean floor and petroleum deposits within marine sedimentary basins may end up on the dry land of a continent.

Two hundred million years ago the supercontinent called Pangea, composed of North and South America, Africa, and Europe, began to break up, with North America moving to the west-northwest. As North America moves on the Earth's surface, the Pacific coast-the leading edge-overrides the sea floor of the Pacific Ocean. Because this continental-oceanic plate interaction involves plate collision, characterized by tectonic and volcanic activity, the Pacific coast of North America is termed an active continental margin. The Atlantic coast is the trailing edge and is called a passive margin.

Although the ocean severely limits the observations a geologist can make of the seabed, it does provide an excellent laboratory for studying ancient as well as modern marine sedimentary or mineral deposits. In addition, observations of active processes of marine deposition and erosion can be directly applicable in understanding our onshore geologic surroundings, and in the search for resources. Conversely, studies of former marine settings, now on land, together with offshore geophysical data and drillhole or surface samples, can provide an understanding of today's sea floor geology-the setting and makeup of the continental shelves, slopes, and rises, as well as the deep ocean floor. It is these studies that have already led to a vastly improved understanding of the processes shaping the Earth and moreover to the discovery of significant resources.

Major deposits of oil and gas and potentially important deposits of minerals, including strategic commodities, occur in the EEZ. However, because of its extreme size, resource estimates are based on spotty data coverage requiring extrapolation of findings into unsurveyed and unsampled areas. Future exploration, technological developments, and economic conditions will determine which of these resources will be developable and when. Here, we present a general assessment of the hydrocarbon and mineral potential of the EEZ, as far as present understanding of the environments and processes will allow, and outline· techniques for improving this preliminary appraisal.

Of offshore resources worldwide, oil and gas are the most extensively developed; accordingly, more reliable estimates of their abundance are available than for any other resources in the EEZ. The appraisal by Dolton and others (1981) of conventionally producible crude oil and natural gas on a portion of the U.S. outer continental shelf was used as the basis for our discussion of U.S. estimates. We use the commonly accepted terminology which defines "reserves" as proved and economically recoverable accumulations and "resources" as both reserves and undiscovered potential resources based on geologic knowledge of an area (fig. 4). The estimates presented below for the four major U.S. offshore regions (figs. 5, 8) are for undiscovered recoverable resources and are given as statistical mean values determined from data of Dolton and others (1981).

The major geologic factors related to hydrocarbon occurrence and exploration are: (1) an adequate thickness of sedimentary rocks; (2) source beds containing considerable dispersed organic matter; (3) a suitable environment for the maturation of organic matter; (4) porous and permeable reservoir beds; (5) hydrodynamic conditions favorable for both early migration and ultimate entrapment of oil and gas; (6) a favorable thermal history; (7) adequate trapping mechanisms; and (8) suitable timing of hydrocarbon generation and migration in relation to the development of traps. Many other features can indicate favorability, for example, the presence of oil and gas seeps, a varied sequence of rock types, some organically rich marine sediments as source beds for the generation of oil and associated gas, nonmarine organically rich sediments for genesis of nonassociated gas, structural features that show progressive growth through geologic time, unconformities, and the presence of evaporite deposits.

FIGURE 4.-0il and gas resources classification. (Modified from U.S. Bureau of Mines and U.S. Geological Survey, 1980.)

z

z en<{ en<{

z JURASSIC I CRETACEOUS REEF TREND

FIGURE 5.-Location of basins with oil and gas potential within the EEZ. Dashed lines indicate the boundary location discussed in Appendix C.

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After Pangea broke up and North America began drifting northwest, the Atlantic Ocean started to form. In its early days, the Atlantic must have been a narrow, shallow, highly saline sea, with much evaporation; these features are recorded by numerous layers of salt along the continental margin. Salt was also being deposited in the Gulf of Mexico at this time. As the Atlantic widened, sediments pouring in were deposited on top of the salt, which in places flowed plastically due to the weight of the sediments and intruded upward into the overlying sediment layers as fingerlike masses called diapirs. In areas where conditions were right for oil and gas formation, hydrocarbons often accumulated in structural traps around such diapirs. As the ocean continued to widen, oceanographic conditions became favorable for the development of a major reef system which can be traced, through the use of seismic reflection equipment, for hundreds of miles from the Gulf coast around Florida and along the Atlantic coast (fig. 6). Between this reef and the coast were deposited sediments carried by rivers, filling in a series of basins which formed as North America split away from Africa (fig. 7). Today rocks sampled in deep oil-test wells drilled on the continental shelf show a succession of deep-water deposits, due to the many times sea level has risen and fallen during the evolution of the margin.

The Atlantic region includes a series of basins-Georges Bank Basin, Baltimore Canyon Trough, several southeast Atlantic sedimentary basins, and the Blake Plateau Basin (fig. 5}--which are filled with sediments and sedimentary rocks sometimes reaching a thickness of 43,000 feet. In addition, the continental slope and rise are underlain by a great wedge of sediments. The deep basins and the continental rise are all targets for petroleum exploration. Another potential resource is the offshore buried reef (fig. 6), noted in the previous paragraph; depending on the porosity of the reef rock and the thermal history of the nearby slope and shelf, this ancient reef might serve as a hydrocarbon reservoir. Because of the depth of water in which they are located, these areas are just beginning to be evaluated for their resource potential.

Much detailed marine geophysical work and rock coring from deep wells remain to be done to show what the Atlantic region's hydrocarbon potential really is. However, oil and gas resources have been estimated for Georges Bank, the Baltimore Canyon Trough, and three sedimentary basins in the southeast Atlantic. The total estimate as of 1981 is 5.4 billion barrels (bbl) of oil and 23.5 trillion cubic feet (tcf) of gas.

As for the Atlantic region, the early history of the Gulf of Mexico region was characterized by the deposition of a thick low-density salt layer. Later, the Mississippi River flowing into the Gulf deposited a thick accumulation of sediment, eroded from the central United States. This accumulation has built a large delta, the weight of which on top of the salt has resulted in extensive plastic flow of the salt upward into the sediments to form diapirs as well as deforming the sediments and shaping the morphology of the sea floor into ridges, troughs, and hills. The Gulf is bounded on the east and south by the large carbonate platforms of Florida and the Yucatan Peninsula, which were constructed by marine organisms; in fact coral reefs can be found growing today on the tops of ridges or hills underlain by salt diapirs in the shallow waters. Over millions of years, abundant organic material generated by these marine organisms in the warm, nutrient-rich water and a high rate of sedimentation have served to provide conditions favorable for the generation of oil and gas, and it is the vertical walls of the diapirs that provide numerous structural traps in which the oil and gas can accumulate.

The Mississippi River, its delta, and deep-water fan afford geologists a view of a modern active river delta system and its associated hydrocarbon reservoirs. On land in buried basins, oil and gas are often found in ancient river deltas and fans. Therefore, by studying the dynamic processes active today in the Mississippi River system, scientists can understand and more efficiently exploit both modern and ancient delta and fan reservoirs.

The Gulf of Mexico shelf area has been extensively and successfully developed; however, the area more than 200 meters deep has not. This deeper area has been separated into eastern and western slope zones for the purpose of resource assessment (fig. 5). Study of the eastern zone suggests that there is little potential for oil and gas reserves as indicated by resource estimates of 0.2 bbl of oil and 0.5 tcf of gas. The western zone is much more favorable, containing a complex pattern of salt intrusions and thick sediments; resource estimates for that area are 2. 4 bbl oil and 26.1 tcf gas. No resource estimates are available for the deep abyssal plain within the EEZ, but it is also covered with thick sediments containing large structures capable of trapping large amounts of oil and gas.

The Pacific region constitutes the leading edge of the North American continent and is an active margin in which the continental plate of North America is in collision with the sea-floor plate of the Pacific Ocean. This active margin has, as most all generally have, a much narrower continental shelf, slope, and rise than a passive margin. Flanking the narrow margin to seaward is a broad continental borderland composed of numerous islands, banks, and basins, some of the basins which are over 6,000 feet deep, where sediments transported by ocean currents or eroded from surrounding ridges have accumulated (fig. 3). Several basins close to the coast contain old deep-water fan deposits and have proven oil reservoirs, such as those in the Santa Barbara Channel.

The Pacific region has been split into three areas for purposes of resource assessment: the southern California borderland, the northern and central California margins, and the Oregon-Washington basins (fig. 5). No assessment of oil and gas potential has been made by the U.S. Geological Survey seaward of the 2,500-meter depths of the slope, though the possibility for economically exploitable hydrocarbon deposits may exist in the area of the enormous Monterey deep-sea fan off central California (Wilde and others, 1976) (fig. 5). The resource estimates for the Santa Barbara Channel are 1.3 bbl of oil and 2.5 tcf gas; for the more southerly borderland basins the estimates are 1.1 bbl and 1.4 tcf, for a total of 2.4 bbl of oil and 3. 9 tcf of gas. The northern and central California margins have been subject to large-scale faulting which formed a series of five sediment-filled basins. Test wells have generally had negative results in the basins, despite promising source rocks and structures. Total resource estimates are 1.0 bbl of oil in three basins, with individual basins containing from 0.1 to 0. 7 bbl; gas estimates are

1. 7 and 0.2 tcf in only two of the basins. The Ore-

gon-Washington basins represent a single, large sedimentary trough separated into structural basins; however, there appear to be few rocks with

USSR

organic deposits, and moreover the thermal history is believed to be unfavorable for hydrocarbon development. The area resource estimates are 0.3 bbl of oil and 1.5 tcf of gas.

The Alaska region is an enormous area comprising diverse geologic elements. Whereas southern Alaska is a complex of small connected plates that extend offshore into the Gulf of Alaska (fig. 8), the Aleutian Islands represent a full-fledged active margin forming a volcanic arc which is flanked on the seaward side by a deep basin, or trench. Along this trench, the sea floor of the Pacific Ocean is being pushed down, or subducted, under the continental margin; over 5,000 linear miles of ocean crust have been consumed along this trench.

ALASKA

As this crust is pushed down deep within the Earth, it melts and then rises to form the volcanic rocks of the Aleutian Islands. Minerals originally deposited within the rocks of the sea floor are also subducted beneath and redeposited within the Aleutian arc. Geologists are particularly interested in island-arc regions because they include deep sedimentary basins, which if conditions are right, can contain oil and gas. In front of the arc, between the arc and the trench, is the forearc basin, where compressional forces can deform the sediments eroded from land, erupted by volcanoes, or composed of organisms settling out of the water column and deposited in the basin. Cook Inlet and several other basins located near shore in this forearc region are being evaluated for their hydrocarbon potential. Behind the arc are backarc basins, formed by tensional forces caused by the downgoing sea-floor slab, that, if conditions are right, may contain hydrocarbon deposits.

The northern coast of the Alaska region is a passive type margin with thick accumulations of sediments, diapirs, and other features similar to the Atlantic margin. The giant oil field onshore at Prudhoe Bay suggests that the continental margin, under the shelf, slope, and rise, also may have important hydrocarbon reserves.

The vastness of the region and the hostile climatic conditions make exploration for resources difficult. When resources are found, the winter storms and ice make it difficult to build permanent recovery stations. In some areas, ice extends all the way down to the sea floor in the waters overlying the shelf, and so ice movement leaves large gouges in the sediment. Under these conditions, drilling for oil or production itself are extremely difficult. For the sake of brevity, the Alaskan region is divided into three sections (fig. 8), despite inhomogeneities, and described only briefly: (1) the Gulf of Alaska area, south of the Aleutians, (2) the Bering Sea area between the Aleutians and the Bering Strait, and (3) the area north of the Bering Strait.

South of the Aleutians the resource estimates are as follows: The thermal and structural history of these three basins suggests that gas rather than oil was generated. The western Gulf of Alaska area has thick sediments (up to 5 km) and abundant structures capable of containing hydrocarbons, but drilling results have been poor, apparently due to lack of suitable reservoir rocks. The same is true for the Cook Inlet area. The eastern Gulf of Alaska area is most promising, with excellent source rocks and fair trap potential, though the reservoir potential is questionable.

Resource estimates for Bering Sea and environs are as follows:

The basins in the Bering Sea area vary widely in geologic origin. Bristol Bay Basin is a single, broad structural depression with a sediment thickness as much as 7 km; St. George Basin is a 10-km deep, sediment-filled, fault-bounded basin; Navarin Basin is actually three elongate basins with a sediment thickness of as much as 15 km; and Norton Basin is broken by faults into sections with sediment thicknesses as much as 7 km. Only Bristol Bay has been drilled, showing some oil and gas in its southern reaches. Resource potential estimates for the other basins are based on seismic information and surface sampling.

For the area north of Bering Strait, the resource estimates are as follows:

The Hope Basin has a sediment thickness of only 3 km, barely enough for hydrocarbon generation. The Chukchi Basin is more than twice as thick and has structural features providing potential hydrocarbon traps. By far the most promising basin of the three for hydrocarbon production, is the Beaufort Basin, where the onshore producing oil fields are within 10 km of the coastline; here, petroliferous onshore deposits are thought to extend offshore, and sediments at least 6 km thick occur all the way to the edge of the broad shelf. It is critical to point out that the continental shelf in the vicinity of the Chukchi and Beaufort Seas extends well beyond 200 nautical miles from shore (fig. 8). Thus if the "natural prolongation" criterion discussed in the section "Description and History of the EEZ" is applied, this extended portion could fall within U.S. jurisdiction.

Besides the U.S. part of the North American continent, the EEZ also includes waters and subsea lands adjacent to Puerto Rico and the Virgin Islands in the Caribbean Sea, and the Hawaiian Islands, Northern Mariana Islands, and numerous other islands in the Pacific Ocean. Puerto Rico, the Virgin Islands, and the Northern Mariana Islands, like the Aleutian Islands, are parts of island arcs.

The potential for oil and gas resources within the EEZ of the U.S. Pacific possessions has not yet been evaluated. Most island areas were not until recently believed to have any potential for hydrocarbon resources. However, the facts and models relating to the geologic history of this region are changing rapidly as a result of U.S. Geological Survey-United Nations hydrocarbon resource studies in the southwest Pacific (Greene and Wong, 1983) (fig. 9). Current information indicates that the most promising area for oil and gas is the region west of Guam and the Marianas, which should be surveyed geophysically to locate sedimentary basins.

FIGURE 9.-Ship tracklines from U.S. Geological Survey-United Nations hydrocarbon resource study (Greene and Wong, 1983).

Nearly all known hard-mineral resources of the U.S. continental margin are located on the continental shelf (fig. 10), owing, in part, simply to the paucity of information on the deeper, slope regions. Until recent plans for leasing polymetallic sulfides in the Gorda Ridge area (figs. 5, 11) were announced, no hard-minerals leasing in Federal waters had occurred since 1968. The lifting of this defacto moratorium is expected to encourage the exploration for hard minerals.

Near-shore shelf resources usually include sand and gravel, salt, phosphorite, and placer deposits (Manheim and Hess, 1981). Sand and gravel deposits are reasonably well known and have attracted commercial interest where dictated by local need. Salt deposits of the Gulf of Mexico may contain evaporite minerals enriched in potassium, bromine, or other economic commodities. Phosphorite, necessary for agriculture, is known to be present off southern California and the southeast Atlantic margin. Other surveys have revealed the presence of phosphorite and of pavement-like deposits and nodules of manganese covering the Blake Plateau, off the Carolina coast (fig. 10).

Glaciers and rivers disgorge large quantities of sediments onto the continental shelf, including minerals of economic interest. Ocean currents and storm-driven currents rework these sediments, often concentrating mineral deposits as placers, of titanium, platinum, rare-earth elements, and gold. Several such deposits are known offshore of Alaska, California, Oregon, and Washington, and others are likely buried within the continental margin.

Development of salt and evaporite, phosphorite, and placer deposits is presently not economically feasible, but advanced technologies and increases in prices might make them profitable. These deposits, therefore, warrant study. The two other possibly economic hard-mineral resources located farther offshore but still within the EEZ are polymetallic sulfides and cobalt-rich manganese crusts.

Spreading oceanic rift zones are sites where molten rock rises from the Earth's interior and is injected along the axis of the rift (fig. 11). The rock then cools and creates new sea floor. Sea water is believed to percolate deep into cracks near the rift

spreading

OX IS

allic sulfides

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and react with the rocks of the ridge to form mineral-rich hydrothermal solutions that rise to the sea floor, where minerals precipitate as sulfiderich deposits. They take on a variety of forms, including flows, columnar edifices around vents, encrustations on slopes, and small cones built on sediment (figs. 12, 13). The deposits are relatively rich in zinc, iron, and copper, with lesser quantities of silver, cadmium, molybdenum, lead, vanadium, chromium, barium, strontium, gold, and platinum.

Deposits of polymetallic sulfides were first discovered in the axis of the East Pacific Rise at 21°N. latitude in 1978 (Francheteau and others, 1979). They have since been found along the rift zones and spreading centers, as well as in the axis, of the Juan de Fuca Ridge, off the coast of Washington (figs. 5, 11); this ridge is partly within the U.S. EEZ but also extends northward into waters off Canada. Another active spreading center nearby and closer to shore is the Gorda Ridge, also judged to be a possible location for sulfide deposits. Because spreading-center deposits are considered to be modern counterparts of on-land copper-iron-zinc sulfide ores, they have been compared with the southwest U.S. land-based deposits, which suggests that the thickness, continuity, and grade of ore is probably not uniform within, and between, spreading centers. Ore-deposit thicknesses of up to 40 m occur on land, but currently no subsurface coring has been done to assess the thickness of marine mineral deposits. A joint U.S.-Canadian program was scheduled to drill shallow cores in the Juan de Fuca area in September 1983. This program of surveying, sampling, and analysis of the U.S. Geological Survey was to determine the resource potential of polymetallic sulfide deposits at this ocean ridge. Core, surface, and fluid samples, as well as suspended-sediment samples downcurrent from vents, are expected to be collected in a grid large enough to show spatial variability.

Not all the islands in the Pacific are at the edge of a plate capping an island arc. Some, like the Hawaiian and Midway Islands, occur within the Pacific plate. They form over what geologists call hot spots, places where plumes of molten rock are rising from deep within the Earth. These plumes are fixed in location, and as the crustal plate of the Pacific moves over them, a line of volcanoes or seamounts-volcanoes that do not reach above the sea surface--is formed. The island of Hawaii today is over a hot spot which is causing volcanic activity. The trend of the chain of islands from Midway to Hawaii shows the northwesterly direction that the Pacific plate is moving. Each island was originally over the hot spot where Hawaii is today. Although no deep basins filled with sediment are associated with this type of island, minerals accumulating on the volcanic edifice may be important. Polymetallic sulfides may be deposited at, or just beneath, the sea floor in the vicinity of the hot spot where volcanic activity is occurring.

Geologists have only just begun to study the geology and resources of these hot spot islands. The underwater flanks of the volcanoes are relatively steep and the water is over 12,000 feet deep in places, which makes their study difficult. The very basic question of their particular types of resources and distribution still needs to be answered.

Recent work by the U.S. Geological Survey suggests that cobalt-rich manganese crusts on the flanks of seamounts and oceanic islands in the central Pacific could represent a significant mineral resource. The crusts appear to average 2 em in thickness and are fairly uniformly distributed at depths of 1,000-2,600 m (Geotimes, 1982). They are known to be present on many of the islands which are U.S. territories and possessions in the Pacific, and there are over 200 such islands and seamounts within the U.S. EEZ boundaries in the Pacific.

The crusts generally contain 1. 0 percent or more cobalt, 0.5 percent nickel, and 15-25 percent manganese. Though the concentrations vary, they may represent an economic resource. Crusts at depths shallower and deeper than 1,000-2,500 m are generally not as rich in cobalt. Deep-sea manganese nodules, believed to be forming by processes similar to those which produce the crusts, have a mean cobalt content for high-grade samples in the Pacific of 0.27 percent (McKelvey and others, 1983). The crusts thus apparently contain significantly more cobalt than the nodules, which have received so much attention in recent years. However, preliminary analysis of a sample collected on the top of Horizon Guyot, a seamount southeast of Hawaii, yielded a cobalt content of 0. 74 percent. As a result the economic potential of shallow-water nodules is being reevaluated. If the seamounts prove to be covered with the crusts or nodules, a single seamount could yield enough ore for a commercial mining operation. The importance of this is highlighted by the fact that the U.S. has no domestic sources of cobalt, depending largely on Mrica for its supplies of this strategic mineral.

The resource assessments in this report are tentative, for they are based, in most cases, on extrapolation of the data available from uneven geographical coverage of the vast area of the EEZ. Conclusions, especially for the cobalt crusts and nodules and the polymetallic sulfides, have been drawn without a complete understanding of the spatial extent of the resources or variability in composition.

A variety of geophysical and sampling techniques is available for identifying resources and assessing their potential in the EEZ. Some employ traditional seismic reflection and sampling equipment; their capabilities and limitations for resource assessment are well documented and thus are only briefly mentioned here. Newer techniques, for mapping broad swaths of the sea floor, are especially well suited to surveys of the large areas of the EEZ, and three such systems are described here.

Seismic reflection techniques are useful for identifying the physiography of the sea floor and the character of the underlying strata (fig. 14). Interpretation of such seismic records is the basic source for regional assessment of oil and gas resources. For resources which are surficial, seismic reflection techniques are less useful, since no idea of the lateral extent of a feature can be extracted without a lengthy survey. The combination of seismic profiling with a swath-mapping system, as those mentioned below, dramatically increases the information value of an oceanographic trackline.

Side-scan sonar is a process in which a swath of the sea floor is ensonified with acoustic signals; variations in the topography of the ocean floor alter the energy in the signal bounced back to the receiver, and these irregularities are used to produce an acoustic picture of the ocean floor. The signals are sensitive to changes in shape as well as bottom composition, and thus side-scan systems are able to map bedforms in addition to such deposits as sand and gravel deposits on the continental shelf. With the development of the GLORIA (Geological Long Range Inclined Asdic) system in 1970, this technique became available for the deep ocean as well (fig. 15).

The GLORIA system consists of a 2-ton, 8-m long transducer towed 50 m below the sea surface at speeds of up to 10 knots. The swath width can be set at 14, 30, or 60 km, and resolution of features on the scale of tens of meters is possible. The record produced by the newest systems is digitally recorded on magnetic tape and can be processed to account for variation in the ship's speed and corrected for the slant range distance to the sea floor. Additional corrections account for water-density variation, particularly those due to the thermal structure of the water column.

The GLORIA system is particularly useful for reconnaissance of frontier regions, for it can determine the orientation and extent of large linear features such as ridges, bedforms, and channels. In a survey of the continental slope off the mid-Atlantic states, for example, canyons 20 km long cutting across the slope can be traced on the GLORIA sonographs, and tributaries as closely spaced as a few hundred meters can be also distinguished (fig. 16). In this case, and others, GLORIA has made clear for the first time the intricate patterns of meandering gullies and channels of oceanic canyon and fan systems (Twichell and Roberts, 1982; Damuth and others, 1983).

The Seabeam wide-angle multibeam profiling system produces a bathymetric map in real time from a swath of the ocean floor beneath a ship's track. The contoured strip covers a 43° arc beneath the ship so that the width of coverage varies from about 150 m on the outer shelf to 4 km in the deep ocean. The contour interval can be set as low as 2 m. The hull-mounted transducer system is presently available, or in the process of installation, on three U.S. university ships, on Surveyor (operated by the National Oceanic and Atmospheric Administration), and on several French and German research vessels.

The Seabeam system can be used simultaneously with seismic reflection equipment, so that the lateral extent of a surface feature can be related to its vertical structure. This combination is valuable for delineating the surface expression and lithologic character of structural traps for hydrocarbons, such as salt domes and diapirs.

One of the resident ships for the Seabeam system is the Atlantis II, of the Woods Hole Oceanographic Institution; it also is the mother ship for the deep-sea research submersible vehicle Alvin. With this dual operation, the exact nature of bottom features can be observed and sampled from Alvin at the same time their extent is being mapped by the Atlantis II. This type of survey will be especially valuable for identifying and assessing surface res_gurces such as cobalt crusts.

The Sea MARC I* side-scan sonar, was developed for Lamont-Doherty Geological Observatory, records, like GLORIA, differences in acoustic reflectivity of the sea floor. Unlike

GLORIA, it is towed 100-300 m above the bottom, avoiding the distortions introduced by the water column, particularly temperature variation. This system provides for greater resolution of sea-floor features than the GLORIA system but at a reduced swath width (compare figs. 16, 17). The swath width can be set at either 1 km or 5 km, with horizontal resolution in centimeters or meters, respectively. The former, for example, might distinguish nodule-sized features; the latter could trace the fronts oflava flows.

A recent version, the Sea MARC II, operated by the Hawaii Institute of Geophysics, is towed higher in the water column than the Sea MARC I, allowing for higher speeds. A major innovation, one also available on later versions of the deeptowed Sea MARC I, is a bathymetry system with a theoretical resolution of 6 m for the entire 5-km swath (fig. 18), though this resolution has not yet been verified. Once verified this system will give clearer images of smaller scale features than GLORIA, providing the capability for even more useful geologic investigations.

The primary value of GLORIA, Seabeam, and Sea MARC is the detailed information obtainable over extended areas. The huge expanse of the EEZ, combined with the current minimal coverage in the nonshelf areas, makes this equipment important for initial surveys in order to determine regional geology. Follow-up multichannel seismic surveys will be necessary for locating deep basins which could serve as hydrocarbon traps, and sampling programs will be necessary for resource assessment, as well as the initial geologic mapping.

Although the EEZ has high potential for significant recoverable energy and mineral resources, further information is necessary before the extent of that potential can be reliably estimated. The values in this report are mostly hypothetical, based on the best available data. Moreover, they do not take into account the technical or economic feasibility of the mineral recovery. The exploration section is intended as an introduction to the equip-

KM/Cl

ment and methods available for making relatively rapid, reasonably accurate assessments of geologic environments. This advancing technology is extending our scientific reach, so that surveys are increasingly improving our knowledge of the geologic processes and the presence and distribution of resources in the EEZ.

APPENDIXE'S A-C

Office of the Press Secretary

March 10, 1983 Embargoed for release at 4:00 pm est

STATEMENT BY THE PRESIDENT APPENDIX 8

Office of the Press Secretary

March 10, 1983 Embargoed for releast at 4:00 pm est

UNITED STATES OCEANS POLICY FACT SHEET APPENDIX C

PART VI, CONTINENTAL SHELF

Article 76, Definition of the continental shelf

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