Abstract The latest early Campanian archipelago deposits of the Kristianstad Basin, southern Sweden, yield one of the most diverse Cretaceous chondrichthyan faunas collected from a narrow stratigraphical interval. Building on previous descriptions of various selachians, squatiniform and synechodontiform sharks are added to the faunal list. Squatinidae is represented by Squatina ( Squatina ) lundegreni sp. nov. and Squatina ( Squatina ) fortemordeo sp. nov. The poorly preserved type specimens of the nominal Squatina hassei from the Maastrichtian of The Netherlands were recently regarded conspecific with better preserved Santonian–Maastrichtian teeth of Squatina ( Cretascyllium ) from the Anglo-Paris Basin. This appears to have been based largely on the assumption that the nominal S . hassei was the only Squatina present in NW Europe during the Santonian–Maastrichtian. The Swedish material indicates a greater diversity of squatinoids, and the nominal S . hassei is here regarded as a nomen dubium of uncertain subgeneric affinity. Two types of synechodontid teeth with a tall central cusp co-occur in the Campanian of the Kristianstad Basin. Based on articulated jaws of the markedly dignathic S . dubrisiensis from the Cenomanian of England, the two morphs are regarded as upper and lower anterior teeth of the single species S . filipi sp. nov.

Abstract This publication consists of papers based on oral presentations at a symposium of the same name co-sponsored by the United States Geological Survey and the American Association of Petroleum Geologists. A wide range of technical issues are covered, as well as regulatory and liability concerns. Documentation of two areas in Colorado where earthquakes had resulted from subsurface fluid injection set the stage for modern debates regarding possible similar results elsewhere. A wide range of fluid compositions are subject to subsurface waste disposal. The largest volumes are brines separated during the production of oil and gas wells, but acid-water and industrial wastes of all types can be disposed in significant quantities in local areas. Large hydraulic fracture treatments never recover all of the injected fluids, and the chemical additives in the fluid that remains underground can be a concern. The subsurface injection of radioactive waste is a topic for three of the papers. The possible need for sequestration of carbon dioxide was not a significant concern at the time and was not covered, but many of the papers provide insight into the issues related to modern proposals. When fluids are injected under pressure into subsurface aquifers, they interact in numerous ways. The fluids can potentially migrate for long distances and potentially interfere with other uses for the native aquifer fluids. If the aquifer cannot transport all of the fluids away, the buildup in pressure can cause fracturing of the rock. Differences in composition between the injected and native fluids can cause chemical reactions to occur; in some cases these can be desirable in that they can immobilize certain solutes in mineral form. The long-term environmental consequences are a common theme in many of the papers because of the recognition that the disposed fluids would become a permanent fixture in subsurface aquifers and could have long-term consequences for their future utilization.

Abstract I am delighted to open this symposium on underground waste management. It would be difficult at this juncture to count the number of projects undertaken cooperatively by the AAPG and the USGS, for they have been numerous, indeed, and have taken place over several decades. Whatever the number, both organizations can take pride in the way in which they have joined their efforts to advance geologic knowledge in the service of the nation. Speaking for the Geological Survey, I am eager to see this cooperation continue and expand, and I intend to offer some suggestions for additional cooperative projects. Now, however, I want both to commend and thank those in both organizations who were responsible for arranging this fine symposium on such a timely and important topic.

Abstract Liquid wastes in unprecedented quantities are expected to be injected below the land surface because of recent stringent controls on disposal to streams. Some of the possible consequences of waste injection are (1) groundwater pollution, (2) surface-water pollution, (3) changes in rock permeability, (4) subsidence, (5) earthquakes, and (6) mineral-resource pollution. Although much work has been done to predict some of the effects, the current state of knowledge is not adequate to estimate them accurately. Theory regarding (a) dispersion, (b) nonlinear relations between rock stress and strain, and (c) interrelations of hydraulics, heat, chemistry, and rock mechanics at macroscale is especially deficient for application to the waste problem. Advances in the chemical thermodynamics and kinetics of geochemistry may provide improved technology.

Abstract A few months ago, when I looked at the Symposium title, I wondered how I might isolate underground waste management from the overall problem of managing all waterborne wastes. Of course, I realized there is no way to detach one aspect of the problem from the larger environmental context within which the problem occurs. Underground disposal of wastes is only one alternative means of dealing with a potential environmental pollutant. However, improper design or mismanagement of such facilities can result in adverse economic and environmental effects.

Abstract You represent the newest technique of waste disposal and potential environmental pollution. I represent the newest federal agency in the pollution control field, the Environmental Protection Agency. You are very interested in EPA, and we are very interested in you. The gist of my message—from the Environmental Protection Agency to The American Association of Petroleum Geologists, and to everyone else who might use the injection-well method of liquid-waste disposal—can be summed up in six words: EPA, of necessity, is watching you!

Abstract More than 300,000 water-using industrial plants discharge three to four times as much oxygen-demanding wastes as all of the nonindustrial wastes discharged to sewerage in the United States. Many wastes discharged by industries are toxic to aquatic life and, perhaps indirectly, to man. The volume of industrial wastewater discharge in 1968 exceeded 14 trillion gal before treatment. Indications are that more than half of this wastewater volume comes from four major industrial groups: paper, organic chemicals, petroleum refining, and steel. Industrial pollution problems are created by oxygen-demanding wastewater constituents, organic and inorganic settleable solids, suspended solids, floatable materials, toxic metals or substances, nuisance-stimulafing nutrients, and waste heat. Treatment and control processes are now available for most industrial wastes; however, some pollutants, including complex chemicals, present difficult abatement problems. The magnitude of the national industrial-waste problem has remained relatively unknown. There has not been until very recently a detailed inventory of industrial wastes. The Environmental Protection Agency within the past year embarked upon a three-pronged program to inventory, study, and regulate this vast waste complex. A voluntary national-industrial-wastes inventory was begun in early August 1971, following a test mailing to refine the questionnaire and the instructions. A comprehensive questionnaire has been mailed to 10,000 of the major water-using industries in the United States. The inventory questionnaire was designed to collect infor-mation on quantity and quality of wastewater constituents and discharge methods. Data from the inventory will be computerized to facilitate their use, and they should prove extremely valuable in all governmental activities connected with the control of industrial wastes. The Environmental Protection Agency is in partnership with the Corps of Engineers in the administration of the River and Harbor Act of 1899. Under the provision of this Act, each industrial waste discharge to the nation's waters will be regulated by a permit issued by the Corps of Engineers. The EPA will make a review, evaluate compliance with water-quality standards, and recommend actions on the permit requests. Comprehensive studies on 20 major industrial categories have recently been completed. These studies define a feasible effluent level based on production units for an industrial category. They present the best and most comprehensive compilation of data now available on wastewater management from these industrial categories.

Abstract Abstract Bureau of Mines engineers have investigated the feasibility and limitations of the underground injection of industrial wastes by observing installations at industrial plants, cities, and oil fields, The chemical industry is using about 175 deep wells to inject approximately 30 million gal per day of waste solutions. The wastes are (1) inorganic salts, (2) mineral and organic acids, (3) basic solutions, (4) chlorinated and oxygenated hydrocarbons, and (5) municipal sewage. The wells, ranging from 1,000 to 8,000 ft (300-2,440 m) deep, are completed in three general types of formations: (1) unconsolidated sand, (2) consolidated sandstone, and (3) vugular carbonate rock. The chemical and physical characteristics of the formation and waste dic-tate the design of the injection system and govern its operation. Commonly, underground injection is the most economical method for disposal of liquid wastes that are not amenable to surface treatment. Operating costs are lower for pretreatment and subsurface disposal than for surface treatment systems, and plant area requirements are less. Chemical treatment is minimal, and generally the only physical treatment required for underground injection is filtration.

Abstract Today, industry is being forced to meet qualify standards for all water effluents discharged or proposed to be discharged to public waters. This national policy demands the removal of substances from water or the management of processing so that restricted materials do not reach the water environment. Generally these restricted materials have no value in their present form or place and are, therefore, wastes. The dilemma is this: having removed or isolated these materials at great cost, what do you do with them? Concentration of the materials may lessen cost of transportation and storage, but it does not solve the ultimate disposal problem. Millions of tons of industrial residues are being stored in open pits above ground. Carbonates, hydrates, silicates, sulfates, oils, tars, acids, and brines can be found stored in diked areas near industrial centers. Some of these stored materials contain small quantities of toxic substances. All of these materials are subject to leaching and thus can reenter the environment. Maintenance of these open pits to avoid pollution is a never-ending concern. The alternatives to pit storage have been ocean disposal, deep-well disposal, disposal by dilution during flood periods, and, in the case of organic materials, incineration. One by one these alternatives are being legislated or regulated out of existence. The Utopian philosophy of complete recycling is gaining popularity. The atomic-energy industry has for years isolated dangerous materials, immobilized them, and buried them on reservations far removed from processing sites. Treatment of the wafer may cost as much as $1/gal. Transportation and burial of residues are a large added cost. Processing industries generate some very complicated waste waters. The most difficult to dispose of are those which contain both organic and inorganic substances in true solution. The dilemma is cause for national concern, requiring study and resolution. The road to complete recycling—if there is such a thing—is long and costly. Politicians must be forced to look at both sides of the environmental-protection coin.

Abstract Land subsidence due to fluid withdrawal has been reported from many parts of the world. It has de-veloped most commonly in overdrawn groundwater basins, but subsidence of serious proportions also has occurred in several oil and gas fields. Subsidence due to groundwater overdraft occurs in many places in Japan, where it has caused dangerous environmental conditions in several heavily populated areas. For example, in Tokyo, 2 million people in an area of 80 sq km now live below mean high-tide level; subsidence is only partially controlled, and the difficulties of achieving full control are great. The San Joaquin Valley in California is the area of the most intensive land subsidence in the United States. Subsidence, which affects 4,200 sq mi (10,875 sq km), reached 28 ft (8 m) in 1969. The total volume of subsidence to 1970 was about 15.5 million acre-ft. Surface-water imports to subsiding areas have reduced groundwater extractions and raised the artesian head, causing subsidence rates to decrease. In the Santa Clara Valley at the south end of San Francisco Bay, excessive pumping of groundwater between 1917 and 1967 caused as much as 180 ft (50 m) of artesian-head decline and maximum land subsidence of 13 ft (4 m). A fourfold increase in surface-water imports in 5 years has achieved a dramatic rise of artesian head—70 ft (20 m) in 4 years. Subsidence rates have decreased from as much as 1 ft (0.3 m) per year in 1961 to a few hundredths of a foot in 1970. Wilmington oil field, in the harbor area of Los Angeles and Long Beach, California, is not only the oil field of maximum subsidence (29 ft or 9 m) in the United States, but also the outstanding example of subsidence control by injection and repressuring. Large-scale repres-suring was begun in 1958 by use of injection water obtained from shallow wells. Subsidence of some bench marks was stopped by 1960. By 1969, when 1.1 million bbl of water per day was being injected into the oil zones, the subsiding area had been reduced from 20 to 3 sq mi (52 to 8 sq km) and parts of the area had rebounded by as much as 1 ft (0.3 m). Methods employed to measure the change in thickness of sediments compacting or expanding in response to change in effective stress include (1) depth-benchmark and counterweighted-cable or “free”-pipe extenso-meters with amplifying and recording equipment; (2) casing-collar logs run periodically in a cased well; and (3) radioactive bullets emplaced in the formation behind the casings at known depths and resurveyed by radioactive detector systems at a later time. In evaluation of potential land subsidence due to fluid withdrawal, an essential parameter is the compressibility of compactible beds. When effective (grain-to-grain) stress exceeds maximum prior (preconsolidation) stress, the compaction is primarily inelastic and nonrecoverable, and the virgin compressibility may be 50–100 times as large as the elastic compressibility in the stress range less than preconsolidation stress. If fluid pressures in a compacting, confined system are increased sufficiently to eliminate excess pore pressures in the fine-grained sediments, subsidence will stop. If fluid pressures continue to increase, the system will expand elastically and the land surface will rise.

Abstract Two factors, safety and utility, are basic in the design of disposal wells. Every means must be taken to insure the safety of the installation so that the environment is protected against inadvertent pollution. Also, the well must be designed for maximum utility so that continued disposal of the waste is assured. Disposal wells are of two general types—those which are considered open-hole completions and those which are “normal” completions (casing is run to total depth). Open-hole completions are common in those areas, such as along the Gulf Coast, where the disposal zones are in slightly consolidated or unconsolidated sands. These wells utilize gravel-packed screen sections and are generally similar in design to large-capacity water wells. Other open-hole completions are made in those areas where the disposal zones are in competent rocks such as limestone, dolomite, and sandstone that do not require casing. In places where the disposal liquid may attcck the cement of a sandstone or adversely effect a limestone or dolomite, casing is required for the full depth of the hole. Casing may be of either plastic materials or some of the more cosily metals, such as stainless steel. Hastelloy, Carpenter 20, or zirconium. Tubing and packer requirements vary depending on the nature of the waste stream. Lined tubing is required in almost every case to avoid excessive corrosion. Tubing lining may be either sprayed-on plastic or thin-gage metallic alloys swedged to the base metal. Packers must be made of the same materials as the tubing to insure longevity. In some wells, hydraulic seals are used rather than packers. Such an installation is satisfactory if injection is always under pressure. In every case, safety of the injection-well installation is a paramount consideration.

Abstract Because of fhe magnitude of damage wrought to our natural resources, pollution control and environmental protection are a vital part of our everyday living. Pollution of air, land, and surface water has led to the use of subsurface disposal (storage) of waste effluents. The federal government and the individual states are continually passing new laws governing deep-well disposal. Feasibility studies are mandatory and must include an analysis of fhe disposal reservoirs and a detailed geologic study to determine the presence of faults or abandoned wells that could be a source of contamination of potable waters. Many of the cementing procedures used in the oil industry are also used in disposal wells; however, added precautions must be taken in the design of the casing and injection strings. These precautions include the use of materials that are resistant to chemical attack, such as special alloys and fiberglass. Oil-well cements may be used in wells where the effluent is organic—e.g., weak organic acids, sewage waste, ferric chloride, and chemically treated effluents having a pH of 6 or above. A formulation of cement and liquid resin will resist attack from dilute acid solutions. The latest development in resin compositions is a blend of epoxy resin and an inert filler. This resin system has shown considerable promise for use in cementing disposal wells. It is resistant to concentrated acidic and caustic effluents and provides excellent bonding properties to the tubular goods.

Abstract Increasing interest in the use of the deep subsurface for disposal of industrial waste requires that both the practitioner and the governmental regulatory body be assured that injection is not harming the environment. There are three principal areas of interest in monitoring subsurface injection systems: (1) the well, (2) the surface equipment, and (3) the subsurface. Minimum monitoring function for the well requires measurement of wellhead injection pressure and of injection tube-casing annulus pressure; definition of corrosive effects of the waste on the well materials; in some cases, bottomhole monitoring of injection pressure; and the location of a conducfor-insulator interface. Monitoring of the surface equipment should include records of the injection-pump discharge pressure, fhe rate and cumulative measurement of injected volume, injecta temperature and quality, and the corrosive-erosive effects of the injected stream upon the materials of construction. Because the real purpose of the monitoring process is to establish that the waste is going where it is intended to go—and remaining there—an examination of the subsurface takes on special importance. The requirements will vary depending on the geographic location, the properties of the waste, the subsurface geology, and the design and construction of the disposal well itself. An occasional monitoring requirement is the drilling of one or more wells to the disposal formation to obtain pressure data and, perhaps, fluid samples. Although there is some purpose for monitor wells of this type where relatively shallow formations are used for disposal, the use of such wells to obtain measurements in deep aquifers may not serve a purpose commensurate with the expense and possible hazards that may result.

Abstract To ensure success of a subsurface waste-disposal operation, surface pretreatment of the waste water is generally required. Pretreatment can be quite expensive, but it can make the difference between a successful operation and one subject to repeated difficulties and even failure. Reduction of formation permeabilities and porosity, face plugging, and precipitation and polymerization reactions will all lead to diminished acceptance rates and excessive backpressure levels. Injection compatibility is directly influenced by formation structure, in-terstitial-water properties, and waste characteristics, including particle size of solids, pH, corrosiveness, viscosity, bacterial content, dissolved gases, temperature, and specific gravity. Each disposal problem and its related solution must be evaluated separately. Basic pretreatment designs vary considerably and are usually tailored to the particular operation. Of basic importance is the minimizing of precipitate-producing reactions and the removal of suspended solids before injection into unconsolidated formations. The latter is less important in vugular or fractured hard-rock areas. Usually, a pretreatment operation will involve waste storage, separation of oil and/or suspended solids through flotation or gravity means, filtration through coarse sand or fine cartridge and diatomaceous earth, chemical fixation of pH, and treatment to correct for corrosiveness or biologic growths. These procedures are followed by additional storage and final pumping to fhe disposal well. A thorough chemical and physical analysis of the waste water and the receiving formation will result in an optimum design. Simplicity should be the aim. Although difficult, it may be possible to define and classify the various types of wastes that are deemed suitable for deep-well injection.

Abstract A mathematical-simulation model has been developed for predicting the operational and cost responses of disposal-well systems. Sensitivity analyses are used to assess which design parameters, operational characteristics, or formation properties have the most significant impact on the overall system response. Although the available operating and cost data are limited, the method may be useful to both operators and regulatory agencies. The true utility of this approach will be demonstrated as additional and reliable data become available.

Abstract Sand-control methods were first used in water wells, and modified methods later were applied to oil and gas wells. The most recent application for sand control is in waste-disposal wells. The increasing use of unconsolidated sands as disposal zones has created a need for better sand-control systems. We suggest that the primary causes of sand-control problems in disposal wells are (1) greater completion intervals, (2) intermittent operation of the well, and (3) chemical characteristics of the injected effluent. Therefore, in order to prevent sand production in disposal wells, consideration must be given to (1) formation characteristics, (2) completion fluid, (3) type of completion, and (4) completion method. Two universally used methods of sand exclusion, with suggested modifications for disposal wells, are the method of in-place sand consolidation with plastics and fhe use of gravel packs in conjunction with sand screens. Sand consolidation has limited application because of the large completion intervals normally used in disposal wells and because of possible chemical reactions with injected effluent. However, a gravel-pack sand-screen completion generally eliminates the three primary causes of sand production in disposal wells. Factors of prime importance are (1) the drilling and completion fluids, (2) formation grain size and composition, (3) size and amount of gravel, (4) pumping rate, (5) pressure, and (6) gravel concentration. Field and laboratory data show that the method of gravel-pack sand-screen completions can be used successfully over intervals as great as 585 ft (178 m) in unconsolidated Frio sands.

Abstract Insoluble solid wastes can be buried at shallow depths in locations where they are safe from exhumation. If any parts are soluble, the solution must be managed as with any similar liquid waste. Programs for the management of waste liquids must be tailored to the chemical and physical characteristics of the liquids. Geologic requisites for successful underground management of liquid wastes include: (1) porous and permeable reservoir rocks, in which the storage space may be caverns, intergranular pores, or fracture crevices; (2) impermeable seals to prevent escape of fluid wastes; (3) adequate understanding of hydrologie parameters and planning to prevent undesirable migration of fluids; (4) compatibility between waste materials and the reservoir rocks and their natural fluids. Layered sedimentary rocks, rather than igneous or metamorphic rocks, provide the most suitable reservoir space, for both geologic and hydrologie reasons. If the wastes are hazardous to the biosphere, objective reservoir formations must be deep enough to provide permanent protection to groundwater aquifers. The site must be reasonably stable seismically and not actively moving along, or broken by, faults. Choice of a suitable underground disposal site can be made only after a thorough investigation of available subsurface data, supplemented by drilling and various other processes of subsurface exploration if sufficient data are not already available. Preliminary investigations and later subsurface operations will be expensive, but they cannot be avoided. Public insistence on an end to pollution must be accompanied by public understanding that a clean environment can be purchased only by higher taxes, if government managed, or by higher prices for consumer goods, if industry managed, plus individual awareness and practices. As waste-management costs rise, it will become more economical to convert wastes into usable products, in effect eliminating, rather than managing, wastes.

Abstract The increasing tempo of ecologic crusades for the cleanup of lakes and streams is literally driving pollution underground. There is in prospect a veritable explosion in the use of sanitary landfills for disposal of solid wastes, in the use of spray irrigation for disposal of partly treated sewage effluent, and in the use of deep-well injection for disposal of certain industrial wastes. Citations of the astronomical volume of storage space within the earth's crust, the very small velocity of groundwater motion, the evidence of entrapment of hydrocarbons and brines, and the presence of very fine-grained confining rocks all intrigue proponents of subsurface storage with the potential for resolving our waste-disposal problems. What gives cause for concern is the recognition that groundwater reservoirs or aquifers are not static environments, but represent dynamic flow systems that undergo change whenever a new stress is imposed. Attendant upon the injection of fluid into an aquifer is a consequent increase in hydraulic head which ultimately influences the hydrologie regime throughout the entire flow system, however distant its boundaries may be. Disposal to shallow aquifers, which are generally sources of water supply, poses a threat not only to present and future well developments, but also to lakes and streams that are sustained by groundwater seepage. In deep-lying confined aquifers, where overburden pressures are large, the hydraulic transmis-sivity is generally small; consequently, the pressures required for significant rates of injection are large. In marked contrast to the very slow migration of the cylinder of injected waste, a transient increase is propagated outward in a confined aquifer with the velocity of sound in the medium. Thus, evaluation of the conse-quences of waste injection requires not only consideration of the effects of the advancing cylinder of waste, but also the far-recching effects of the cone-of-pressure increase.

Abstract Natural underground reservoirs capable of containing water, petroleum, and gases include sandstones, limestones, dolomites, and fractured rocks of various types. Comprehensive research and exploration efforts by the petroleum industry have revealed much about the character and distribution of carbonate rocks (limestones and do!omites) and sandstones. Porosity and per-meability of the deposits are criteria for determining their efficiency as reservoirs for fluids. Trends of certain sandstones are predictable. Furthermore, sandstone reservoirs have been less affected than carbonate reservoirs by postdepositional cementation and compaction. Fracture porosity has received less concentrated study; hence, we know less about this type of reservoir. The discussions in this paper are confined to sandstone reservoirs. The principal sandstone generating environments are (1) fluvial environments such as alluvial fans, braided streams, and meandering streams; (2) distributary-channel and delta-front environments of various types of deltas; (3) coastal barrier islands, tidal channels, end chenier plains; (4) desert and coastal eolian plains; end (5) deeper marine environments, where the sands are distributed by both normal and density currents. The alluvial-fan environment is characterized by flesh floods and mud flows or debris flows which deposit the coarsest and most irregular sand bodies. Braided streams have numerous shallow channels separated by broad sandbars; lateral channel migration results in the deposition of thin, lenticular sand bodies. Meandering streams migrate within belts 20 times the channel width end deposit two very common types of sand bodies. The processes of bank-caving and point-bar accretion result in lateral channel migration and the formation of sand bodies (point bars) within each meander loop. Natural cut-offs and channel diversions result in the abandonment of individual meanders and long channel segments, respectively. Rapidly abandoned channels are filled with some sand but predominantly with fine-grained sediments (clay plugs), whereas gradually abandoned channels are filled mainly with sands and silts. The most common sandstone reservoirs are of deltaic origin. They are laterally equivalent to fluvial sands and prodelta and marine clays, and they consist of two types: delta-front or fringe sands and abandoned distributary-channel sands. Fringe sands are sheetlike, and their landward margins are abrupt (against organic clays of the deltaic plain). Seaward, these sands grade into the finer prodelta and marine sediments. Distributary-channel sandstone bodies are narrow, they have abrupt basal contacts, and they decrease in grain size upward. They cut into, or completely through, the fringe sands, and also connect with the upstream fluvial sands or braided or meandering streams. Some of the more porous and permeable sandstone reservoirs are deposited in the coastal interdeltaic realm of sedimentation. They consist of well-sorted beach and shoreface sands associated with barrier islands and tidal channels which occur between barriers. Barrier sand bodies are long and narrow, are aligned parallel with the coastline, and are characterized by an upward increase in grain size. They are flanked on the landward side by lagoonal clays and on the opposite side by marine clays. Tidal-channel sand bodies have abrupt basal contacts and range in grain size from coarse at the base to fine at the top. Laterally, they merge with barrier sands and grade into the finer sediments of tidal deltas and mud flats. The most porous and permeable sandstone reservoirs are products of wind activity in coastal and desert regions. Wind-laid (eolian) sands are typically very well sorted and highly crossbedded, and they occur as extensive sheets. Marine sandstones are those associated with normal-marine processes of the continental shelf, slope, and deep and those due to density-current orign (turbidites). An importent type of normal-marine sand is formed during marine transgressions. Although these sands are extremely thin, they are very distinctive and widespread, have sharp updip limits, and grade seaward into marine shales. Delta-fringe and barrier-shoreface sands are two other types of shallow-marine sands. Turbidites have been interpreted to be associated with submarine canyons. These sands are transported from nearshore environments seaward through canyons and are deposited on submarine fans in deep marine basins. Other turbidites form as a result of slumping of deltaic facies at shelf edges. Turbidite sands are usually associated with thick marine shales.