William C. Ward

Bio: William C. Ward is an academic researcher from Rice University. The author has contributed to research in topics: Eolianite & Micrite. The author has an hindex of 4, co-authored 7 publications receiving 5744 citations.

Brazos River bar [Texas]; a study in the significance of grain size parameters

Abstract: A bar on the Brazos River near Calvert, Texas, has been analyzed in order to determine the geologic meaning of certain grain size parameters and to study the behavior of the size fractions with transport. The bar consists of a strongly bimodal mixture of pebble gravel and medium to fine sand; there is a lack of material in the range of 0.5 to 2 mm, because the source does not supply particles of this size. The size distributions of the two modes, which were established in the parent deposits, are nearly invariant over the bar because the present environment of deposition only affects the relative proportions of the two modes, not the grain size properties of the modes themselves. Two proportions are most common; the sediment either contains no gravel or else contains about 60% gravel. Three sediment types with characteristic bedding features occur on the bar in constant stratigraphic order, with the coarsest at the base. Statistical analysis of the data is based on a series of grain size parameters modified from those of Inman (1952) to provide a more detailed coverage of non-normal size curves. Unimodal sediments have nearly normal curves as defined by their skewness and kurtosis. Non-normal kurtosis and skewness values are held to be the identifying characteristics of bimodal sediments even where such modes are not evident in frequency curves. The relative proportions of each mode define a systematic series of changes in numerical properties; mean size, standard deviation and skewness are shown to be linked in a helical trend, which is believed to be applicable to many other sedimentary suites. The equations of the helix may be characteristic of certain environments. Kurtosis values show rhythmic pulsations along the helix and are diagnostic of two-generation sediments.

Fault zone deformation and displacement partitioning in mechanically layered carbonates: The Hidden Valley fault, central Texas

Abstract: The Hidden Valley fault is exposed in Canyon Lake Gorge (central Texas) and cuts the Cretaceous Glen Rose Formation. This exposure provides an opportunity to explore the relationship between deformation mechanisms and fault displacement along 830 m (2723 ft) of a normal fault typical of those in carbonate reservoirs and aquifers around the world. The fault zone has five domains: gently deformed footwall damage zone, intensely deformed footwall damage zone, fault core, intensely deformed hanging-wall damage zone, and gently deformed hanging-wall damage zone. Footwall deformation is more intense and laterally extensive than hanging-wall deformation, and the intensely deformed hanging-wall damage zone is narrow and locally absent. The fault core contains thin clay-rich gouge or smear in most places but is locally represented by only a slickensided surface between limestone layers. The 55- to 63-m (180–207-ft) fault throw across a 43- to 98-m (141- to 322-ft)-wide fault zone is accommodated by slip along the fault core, layer tilting (synthetic dip development) in footwall and hanging-wall damage zones, and distributed faulting in footwall and hanging-wall damage zones. Total offset across the fault overestimates actual stratigraphic offset by 8 to 12 m (26–39 ft) or about 14 to 21%. In our interpretation, the Hidden Valley fault zone records both early extensional folding of the Glen Rose Formation and subsequent normal faulting that propagated downward from the overlying competent Edwards Group. The damage zone width is thus established before fault breakthrough.

Blackening of Eolianite and Caliche Adjacent to Saline Lakes, Isla Mujeres, Quintana Roo, Mexico

Abstract: A partly blackened limestone and caliche rubble has been produced in situ at the edge of hypersaline lakes on the island of Mujeres off the northeast coast of the Yucatan peninsula. The angular gravel along the quiet lake shores is formed by dissolution and desiccation-fracturing of dark and lighter-colored country rock and caliche crusts. Dark-colored constituents of this rubble gravel are of two types: 1) blackened Pleistocene (?) eolianite country rock and 2) black porous laminated "caliche-algal micrite" crusts. Pale to dark yellowbrown constituents, which make up 50 to 75% of the rubble, are fragments of caliche and eolianite. Chemical analyses of the dark and light-colored fragments of this deposit indicate that concentrations of Fe, Mn, and S in the black rocks are equal to or less than that in the brown rocks. HCl-insoluble organic C, however, is slightly higher in the darker rocks. The blackened calcarenite is infiltrated with finely-disseminated organic matter of algal origin. The black color is attributed to preservation of the organic matter. A secondary source of the dark color may be minor amounts of iron sulfide, produced in the presence of H2S derived from bacterial reduction of sulfates within the reducing environment of an algal "mat." Apparently dark-colored caliche-like crusts may be laid down in localities where caliche deposition is simultaneous with production of black algal matter. These conditions probably existed at several northeast Yucatan localities where black "caliche-algal micrite" fragments are found near hypersaline water. The environment necessary for the blackening of caliche or limestone is probably one in which the pH is high enough and the Eh low enough that the preservation of finely-disseminated organic material produced by algae can be accompanied by deposition of secondary calcite which includes and preserves the organic matter. In such a reducing environment associated with sulfate deposition, bacterial action may produce H2S. The black rocks of the northeast Yucatan hypersaline reas contain H2S. Blackened limestone in ancient carbonate sections may call attention to stratigraphic breaks. A few workers have recognized an association between blackened limestones and unconformities in certain Mesozoic and Paleozoic sections. The presence of layers of fragmented, dark-colored limestone may indicate subaerial exposure adjacent to hypersaline water. Black fragments in limestone strata, then, may be an aid in locating coastal areas in ancient carbonate provinces and the landward edge of evaporite deposits.

High-Energy Carbonates on the Inner Shelf, Northeastern Yucatan Peninsula, Mexico

Abstract: High-energy carbonate sands and gravels are accumulating on the inner margin of the eastern Yucatan shelf. Carbonate sands are deposited in large spillover lobes, submarine dunes, seagrass banks, beaches, spits, and eolian dunes. Major factors controlling dispersal and deposition of these Holocene carbonate sediments are: (1) the northward flowing Yucatan current, (2) pre-Holocene topography on the limestone shelf, (3) littoral drift, (4) hurricanes, (5) normal waves and wind, and (6) biota. Carbonate sediments on the inner Yucatan shelf are deposited in textural belts paralleling the strandline. Grain size generally decreases toward the mainland, with sand-size material concentrated in the nearshore-beach-coastal dune zone. Carbonate mud is deposited in lagoons landward of beach-dune barriers. The best-sorted sand is found along the landward margin of the sand belt in the beach-dune trend. A partly submarine, partly subaerial belt of oolitically coated sand parallels this coastline. Ooids are formed in the nearshore zone of two high-energy segments of the coast and are reworked from submerged outcrops of older oolitic limestone. The belt of oolitic sediment is thickest on its landward edge, where coastal dunes accumulate. The carbonate dune-beach deposits are rapidly lithified, enhancing their chance of preservation. Effective porosity in the Holocene dune limestones ranges from 26-36%. The oolitic sand passes seaward into uncoated bioclastic, pelletoid, and lithoclastic sand and gravel. Periodic storm waves wash ooids landward into the muddy lagoons behind the dune and beach-ridge barriers. Preservation of the carbonate facies deposited on the inner shelf of northeastern Yucatan would create stratigraphic traps in the most up-dip carbonate grainstones. Carbonate mudstones of the coastal lagoons would be both permeability barriers and source rocks for hydrocarbons.

Diagenesis and Secondary Porosity Evolution of Sarir Sandstone, Southeastern Sirte Basin, Libya: ABSTRACT

Abstract: Virtually all porosity is of secondary origin in the productive Lower Cretaceous Sarir Sandstones of the Calanscio area in the southeastern Sirte basin, Libya, where production is obtained from depths of about 8,000 to 13,000 ft (2,438 to 3,962 m). Principal reservoirs are fluvial sandstones now composed predominantly of quartz, but originally composed of up to 25% mud intraclasts, rock fragments, feldspars, and mica. Even though most of the original porosity was destroyed by compaction and cementation, deep-burial leaching of the non-quartz constituents created considerable porosity. Average porosity is 13%; the maximum is 31%. Most secondary pores are oversized molds of dissolved non-quartz grains. Skeletal feldspars and ragged metamorphic rock fragments are preserved i some layers. Commonly, feldspar and rock fragments are End_Page 889------------------------------ preferentially preserved in finer grained and muddy layers. However, even in some muddy sandstones, rock fragments, feldspars, and matrix were dissolved, creating secondary porosity. The probable paragenetic sequence of major diagenetic events was: (1) hematite-clay coatings (red-bed units only); (2) quartz-overgrowth; (3) local clay, carbonate, and sulfate cementation; (4) compaction (ductile grains deformed); (5) leaching of non-quartz grains, cement, and matrix; (6) crystallization of authigenic kaolinite and minor illite and halloysite in some secondary pores; (8) minor dolomite cementation and replacement. Hydrocarbons migrated after kaolinite had partly occluded some pores. The products of diagenesis vary according to original composition, porosity, and permeability. End_of_Article - Last_Page 890------------

GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments

Abstract: Grain size analysis is an essential tool for classifying sedimentary environments. The calculation of statistics for many samples can, however, be a laborious process. A computer program called GRADISTAT has been written for the rapid analysis of grain size statistics from any of the standard measuring techniques, such as sieving and laser granulometry. Mean, mode, sorting, skewness and other statistics are calculated arithmetically and geometrically (in metric units) and logarithmically (in phi units) using moment and Folk and Ward graphical methods. Method comparison has allowed Folk and Ward descriptive terms to be assigned to moments statistics. Results indicate that Folk and Ward measures, expressed in metric units, appear to provide the most robust basis for routine comparisons of compositionally variable sediments. The program runs within the Microsoft Excel spreadsheet package and is extremely versatile, accepting standard and non-standard size data, and producing a range of graphical outputs including frequency and ternary plots. Copyright © 2001 John Wiley & Sons, Ltd.

The Rock Physics Handbook: Tools for Seismic Analysis of Porous Media

Abstract: Preface 1. Basic tools 2. Elasticity and Hooke's law 3. Seismic wave propagation 4. Effective media 5. Granular media 6. Fluid effects on wave propagation 7. Empirical relations 8. Flow and diffusion 9. Electrical properties Appendices.

The Rock Physics Handbook

Abstract: Responding to the latest developments in rock physics research, this popular reference book has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results. It brings together the vast literature from the field to address the relationships between geophysical observations and the underlying physical properties of Earth materials - including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates. This third edition includes expanded coverage of topics such as effective medium models, viscoelasticity, attenuation, anisotropy, electrical-elastic cross relations, and highlights applications in unconventional reservoirs. Appendices have been enhanced with new materials and properties, while worked examples (supplemented by online datasets and MATLAB® codes) enable readers to implement the workflows and models in practice. This significantly revised edition will continue to be the go-to reference for students and researchers interested in rock physics, near-surface geophysics, seismology, and professionals in the oil and gas industries.

A review of the origin and characteristics of recent alluvial sediments

Abstract: SUMMARY Recent alluvial sediments are reviewed with respect to their geometrical, textural, structural and biological characteristics. These properties are related to the physiographic occurrence and hydraulic geometry of streams and to the dynamics of flowing water as controlling sediment transport-deposition and stream morphological activities. Based on this data, three-dimensional facies models are presented as an aid to the identification of ancient alluvial sediments, which are briefly reviewed also.

A review of grain‐size parameters

Abstract: SUMMARY This paper comprises a review of the many graphical and mathematical techniques that have been proposed for the statistical summary of grain-size data. Satellitic problems, such as laboratory techniques, choice of size scales, and interpretation, are only considered briefly.