environments of the sediments are assigned different paleoecological zone numbers and are ranked 1 through 6, with zone No. 1 being nearest shore in the shelf area, and the ascending zone numbers indicating the zones farther from shore and in progressively deeper water until zone 6 is reached, which is found in the abyssal plain in water deeper than 6,000 feet. In the Gulf Coast Region, most of the hydrocarbons occur from (or within) paleoecological zone 4, and to a lesser degree, from zones 3 The Pliocene and Pleistocene sediments in the proposed sale area have been deposited in paleoecological zones 2, 3, 4, and 5. and 5. Some of the proposed sale acreage is located on an established productive (predominantly gas) Miocene trend with the expected thickness of the Miocene sediments being about 7,000 feet. If production were developed on these tracts, transmission of the oil and (or) gas could be directed through already established pipelines. This would reduce the need for additional platform-to-shore pipelines, thereby avoiding possible damage to the marine and coastal environments. 5. Flower Garden Banks Two unique areas, the East and West Flower Garden Banks, have received a number of nominations by oil and gas companies, but until this proposed sale, they have not been offered for leasing because they were the sites of biological research projects. The Flower Garden Banks, located approximately 110 miles SSE of Galveston Texas, are the most prominent of a series of topographic highs in the northwestern Gulf of Mexico, and have been noted and studied for a number of years. These features result from salt uplift, and many are capped by biohermal reef development, (thriving or ancient). The continental slope of the northern Gulf of Mexico represents the seaward part, or the growing margin, of the Gulf Coast geosyncline. The continental slope off Texas and Louisiana consists of two parts, a relatively steep lower slope which breaks off abruptly along the Sigsbee Scarp and the upper slope (with 1-2° dip) which is characterized by a hummocky topography which is made up of small hills (seaknolls) and depressions. This upper slope occurs at about the 600 foot or 200m bathymetric contour which delineates the Outer Continental Shelf - upper slope hinge line. The structural grain and the topography of the slope are controlled primarily by salt tectonics and the hummocky or hilly nature of the upper slope is due to diapiric salt structures. The top of the salt surface is identified on seismic and sparker records as a strong reflector or an envelope of diffraction patterns. Seismic reflection profiles across the continental margin of Louisiana and Texas suggest that all the topographic "highs" on the upper continental slope probably represent salt intrusions. Seismic records across the shelf edge commonly show one or several zones of active down-to-the-south faults. Some of them form small escarpments on the sea floor; however, usually the displacement is leveled by sedimentation and slumping. This process results in a thicker or expanded sedimentary sequence on the downthrown side causing "growth" faults which go through one or several periods of strong deformation. Sparker records indicate that active growth faults are present across the continental shelf from Galveston Bay into the upper slope. The escarpments on the sea floor formed by many of the faults are caused by relatively small and late movements along the fault planes. Coring along the shelf edge shows regressive wedges of shallowmarine clastic material and consists of interbedded sand and mud and containing deltaic, prodeltaic, inner-neritic, and outerneritic foraminiferal faunas. The synclinal areas on the continental slope are filled primarily with slump material and turbidities, most of which are mud. Some turbidite sands have been penetrated in core holes and cores and sparker data indicate that submarine slides, mudflows, and turbidity currents contribure significantly to the basin fills on the continental slope. The prospective horizons of the upper slope of offshore Texas should consist of a veneer of Miocene and Pliocene with thicker intervals of Pleistocene. The Pleistocene sediments are considered the most prospective reservoir beds and the thickness of these deposits on the slope in variable but at least 10,000 feet of sediment, predominantly clay, is estimated to be present in several synclines on the continental slope. 7. Seismic Hazards The area of eastern Texas and the western Gulf of Mexico is rather unique in its lack of seismicity (see Algermissen, 1969). No earthquakes of any noteable intensity have been recorded for this area and only two earthquakes of noteable intensity have occurred in the Gulf near this area; one north of Vera Cruz, Mexico and one southeast of the leasing area in over 600 meters of water near 93°W and 27 1/2°N. Neither of these earthquakes produced damaging tsunamis and neither were considered as a risk or were considered well located events. Complete assurance that a damaging earthquake will not occur in this area can never be made due to the fact that accurate locations and measurements of earthquakes is a fairly recent ability of the science. Three areas of zero seismic risk, i.e., southern Florida, western Florida, southern Alabama and Mississippi, and eastern Texas are shown on the NOAA Seismic Risk Map of the United States. Eastern Texas and the adjoining part of the Gulf of Mexico appear to be the most seismically quiet area of the three zones. B. The Climate of Coastal Texas and Louisiana, and Adjacent Gulf 1. General Climatology and Seasonal Weather Patterns The following air masses either influence or control the weather in the northwestern Gulf of Mexico. Tropical Maritime (Tm): This air mass enters South Texas from the south and southeast, as a result of the circulation around the Azores-Bermuda high pressure cell. During the period March through October, Tm air predominates at low levels across all of South Texas and the adjacent Gulf. From May through September, Tm air dominates the area almost completely. Overrunning of polar air by tropical maritime in the winter This situation almost always results in season is a common occurrence. stratus clouds with accompanying low ceilings and visibilities. Polar Continental (Pc): This air mass rarely pushes into the northwestern Gulf before October or after April, but is frequent during the winter and early spring months. It undergoes rapid modification in When this air mass pushes out over the Gulf of Mexico, the return flow of modified Pc and Tm air almost always produces low stratus clouds over adjacent land areas. the area. Polar Maritime (Pm): This air mass is most frequent during the fall and during spring. It is rapidly modified, and the return flow of Pm 1/ Information sources: Leipper (1954a), Louisiana Wildlife and Fisheries Commission (1971), and Orton (1964). |