Bureau of Sport Fisheries and Wildlife, Geological Survey, National Oceanic and Atmospheric Administration, and Environmental Protection Agency with observers appointed by the Governors of Mississippi, Alabama, and Florida.

5. Additional Study and Research Programs FY '75

Funds amounting to $9.7 million have been allocated to

conduct baseline environmental studies in five areas of the OCS

during FY '75. In addition to a continuation of the study effort offshore Mississippi, Alabama, and Florida, baseline environmental research studies will be initiated offshore South Texas, Southern California, on the Atlantic and Gulf of Alaska OCS. If CEQ's study of the environmental impact of oil and gas production on the Atlantic OCS and in the Gulf of Alaska determines that development in these areas can proceed in an environmentally satisfactory manner, lease sales in one or both areas will be scheduled for the earliest practicable time.

The kinds of data that will result from the environmental baseline

and monitoring studies in these frontier areas of the OCS will enable the Department to make tract selections based on better prediction of potential environmental impacts of oil and gas leasing and development over the short-term, will contribute to the design of long-term leasing plans and objectives, and will provide bases for changes in, or additions to, OCS operating orders and procedures.

The Gulf of Mexico occupies part of a large sedimentary basin in which there has been deposition of terrigenous clastics (interbedded sand, silt, and shale), carbonates, and evaporites since early Mesozoic times. The Gulf of Mexico is a large Mediterranean-type

sea which extends approximately 1,000 miles east-west and 800 miles north-south. The Gulf basin extends inland from the shoreline 300

miles up the east Texas and Rio Grande embayments and about 500 miles up the Mississippi embayment (Figure 1).

Stratigraphic studies show that the major sedimentary units in the northern part of the Gulf of Mexico geosyncline are arranged in belts parallel to the northern shoreline of the Gulf of Mexico. These sedimentary units have the general shape of flattened ellipses, with the thicker part of each sedimentary lens being the locus of deposition (depocenter) for a particular depositional epoch.

The Tertiary sediments of the central and western Gulf Coast are composed almost entirely of terrigenous clastics, and are characterized by intertonguing marine and non-marine strata. Some of the marine formations extend to the outcrop, but the shorelines of most of the formations are now deeply buried and the outcrop equivalents of these subsurface marine formations are mostly of continental origin.

The Continental Shelf is a gently sloping submarine plain of

varying width forming part of the border of the continent out to a water depth of approximately 600 feet, at which point the continental slope begins. The continental slope is a steeper slope extending from the continental shelf edge to oceanic depths and will be discussed later in this report. The Texas-Louisiana shelf between the Mississippi delta and the Rio Grande delta ranges in width from about 60 miles on the west to 160 miles off the Texas-Louisiana border. Figure 2 shows a generalized cross section through the shelf portion of the sale area and indicates the relationship between the various ages of sediments and depths of burial. The slope is not included in this cross section because of the speculative and inadequate data about the stratigraphy of this province.

3. Prospective Horizons within the Proposed Sale Area

The prospective horizons of the continental shelf are shown in Figure 3 and are of Miocene, Pliocene, and Pleistocene ages, and the U.S. Geological Survey has conducted intensive structural, stratigraphic, and paleontologic studies of these sedimentary units. These studies are the means by which favorable areas for oil and gas production are delineated. Conditions necessary for oil and gas generation and entrapment are reasonably well understood. Generally, sands deposited within and on the fringes of a deltaic environment are favorable, especially the subaqueous portion deposited in ancient nearshore shallow marine environments. Very porous thick sands