Pressured Shale and Related Sediment Deformation--Mechanism for Development of Regional Contemporaneous Faults: ABSTRACT; Diversity-Equitability Analysis as Paleoecologic Tool: ABSTRACT; Paleomagnetism of Late Pleistocene-Holocene Sediments, Gulf of... Association Round Table 1897 shore winds is moved into clay dune complexes and eventually carried downwind to develop loess sheets. This extensive up- wind deflation of the system is accompanied by windward accreting clay-sand ridges with nuclei composed of either beach-ridge remnants of a Pleistocene barrier-strandplain sys- tem or remnants of inter-blowout areas developed during early phases of the deflation of the coastward margin of the system. Principal source of sand and loess is, therefore, local, repre- senting reworking of underlying, older sands. A sand source resulting from longshore convergence and inland transport from Padre Island accounts for only the minor, local infllling of Laguna Madre in the land-cut area, and is not the principal source of eoUan sand throughout the system. Facies fabric within Pleistocene depositional systems provides principal con- trol of environments, sedimentary processes, and resulting fa- cies within the subsequent eolian system. BRUCE, C. H., Mobil Oil Corp., Corpus Christi, Tex. PRESSURED SHALE AND RELATED SEDIMENT DEFORMATION—MECHA- NISM FOR DEVELOPMENT OF REGIONAL CONTEMPORANEOUS FAULTS Regional contemporaneous faults of the Texas coastal area are formed on the seaward flanks of deeply buried Unear shale masses characterized by low bulk density and high fluid pres- sure. From seismic data these masses have been observed to range in size up to 25 mi wide and 10,000 ft vertically. These features, aligned subparallel with the coast are en echelon or branching in pattern, and represent residual masses of under- compacted sediment between sand-shale depoaxes in which greater compaction has occurred. Most regional contemporane- ous fault systems in the Texas coastal area were formed during times of shoreline regression when the duration of fault devel- opment extended over short periods of geologic time, and where comparatively simple down-to-the-basin fault patterns were developed. In cross-sectional view, faults in these systems flatten and converge at depth to planes related to fluid pressure, and form the seaward flanks of underlying shale masses. Data indicate that faults formed during time of shoreline regression were developed primarily through differential compaction of adjacent sedimentary masses. These faults die out at depth near the depoaxis of the sand-shale section. In areas where subsidence exceeded the rate of deposition, gravitational faults developed where basinward sea-floor incli- nation was estabUshed in the immediate area of deposition. Some of these faults became bedding plane type when the incUnation of basinward-dipping beds equaled the critical slope angle for gravitational slide. Fault patterns developed in this manner are comparatively complex and consist of numerous antithetic faults and related rotational blocks. Nondepositional (structural) faults are common on the land- ward flanks of deeply buried shale masses. Many of these faults dip seaward and intersect the underlying low-density shale at relatively steep angles. Conclusions derived from these observations support the concept of regional contemporaneous fault development through sedimentary processes where thick masses of shale are present and where deep-seated tectonic effects are minimal. BUTLER, E. A., and H. W. SIMPSON, Atlantic Richfield Co., Dallas, Tex. DlVERSnT-EqUITABILITY ANALYSIS AS P A L E O E C O L O O I C T O O L Diversity-equitability analysis of microfaunal data as used by Beerbower and Jordan shows promise of being a rapid and useful technique for mapping paleoenvironmental gradients. It may even provide a more satisfactory definition of environmen- tal boundaries than biofacies analysis based on taxonomic com- position. Faunal diversity is calculated as Shannon's information the- ory average uncertainty measure. Using this diversity measure, a few equally common taxa can yield as high a diversity index as many unequally common taxa. Lloyd and Ghelardi's equita- bility index may be used to separate these two diversity compo- nents and refine seemingly homogeneous data. Recent microfaunal data from Barnstable Harbor, Massa- chusetts, and the northern Gulf of Mexico have been subjected to diversity-equitabihty analysis. From Barnstiible Harbor, con- tours based on the equitability index can be related rather clearly to tidal action within the harbor. A diversity-equitability plot of published Holocene Gulf of Mexico data reveals that some environments may be characterized by a unique D / E range. Although these results must be considered preliminary, an analysis of parts of the lower Miocene sequence in Block 24 field, High Island area, oflshore Texas, shows that the techni- que merits further consideration and is potentially a very useful tool for both identifying and mapping ancient environments. CLARK, H. C , Dept. Geology, Rice Univ., Houston, Tex. PALEOMAGNETISM OF LATE PLEISTOCENE-HOLOCENE SEDIMENTS, GULF OF M E X I C O Detailed paleomagnetic studies have been made on 15 sedi- ment cores selected along north-south lines in the eastern and western Gulf of Mexico. The piston cores were sampled at 20- cm intervals immediately upon extrusion and measurements of natural remanent magnetization (NRM) were made using a 5hZ spinner magnetometer. Excursions of the geomagnetic field are recorded at 2 levels in many cores. Extrapolation of the ZY boundary in the western Gulf indicates that the younger feature is between 13.5 and 17.5 X 10' years BP, and is consistent with the age determination of the Laschamp event. Dates are not available for the eastern Gulf cores, but the depth of the paleo- magnetic feature correlates with the expected sedimentation rates. The older feature is less distinct and further extrapolation of the ZY boundary places it between 20.0 and 24.0 X \(fi years BP. This age is within the range of a geomagnetic feature that is not the Laschamp. These re ".ults show that with extreme care, paleomagnetic measureme its may be used as a stratigraphic tool in the Gulf of Mexico. Several points should bi considered. First, because of the high sedimentation rates, the 2 yotmg features described herein are the only ones expected in piston cores from this region. Second, direction scatter is quite pronounced in the upper 1/2 m and lower few centimeters of several cores. Corre- lations at these levels are difficult. Finally, as measurement of the geomagnetic features described lasted for only a short time and did not traverse a full 180°, dense sampling is recom- mended to assure their definition. CRANDALL, K. H., Consulting Geologist, Piedmont, CaUf ECONOMIC AND OTHER FACTORS AFFECTING PETROLEUM EXPLORATION There is today almost universal agreement that we are facing a potential energy crisis, both imminently in the U.S. and possibly worldwide after the turn of the century. All studies of energy supply and demand indicate such tremendous growth in demand tiiat conventional sources will be hard pressed to sup- ply it. The short-range aimual growth rate in domestic and free- world demand for petroleum is estimated at 5% and 7 1/2% respectively, resulting in 19 million and 57 million bbl/day total demand in 1975. By 1980 U.S. demand will be nearly 25 million bbl and free foreign need nearly 90 miUion bbl/day. The areas which will supply this demand, especially for fhe U.S., ark quite imcertain because of the bewildering variety of poUtical, legal, and environmental factors—as contrasted with purely economic ones—which will be of critical influence. Therefore, it is difficult to forecast the areas and the amounts and costs of exploration and development, as well as prices and earnings. One thing is certain, however, there will be a growing short- age of domestic crude and an increasing dependence on foreign suppUes. Both the cost and dependabiUty of the latter are questionable in view of political considerations and the policies and actions of OPEC.