Book reviews

Natural Resources Research -     

Zipf’s Law: A Viable Geological Paradigm?

Zipfs Law originally was proposed as a guide to a statistical distribution in social studies. The law describes a relationship between size and rank of discrete phenomena. It is a variant of Paretos 1927 Law known as the 80/20 rule and is similar to Bodes Law in concept. The relationship described by Zipfs Law is a succession of order data with the largest followed by half the size for the next largest, which in turn, the next is half that size, and so on. In geology, it has been used with moderate success in resource assessment of mining and petroleum. In essence, it predicts how many entities of a certain size may be left in a sequence of decreasing size assuming the largest has been ascertained. Examples of applications would be plotting the rank and size of ore deposits or oil fields to determine how many deposits remained undiscovered and their size. After a flurry of papers in the 1970s and 1980s, application of the law apparently either was successful and thus not reported in way the literature or was determined to be ineffectual and its use discontinued, but either way the law lapsed into obscurity. Examples of oil- and gas-field size in Kansas, the occurrence of historic earthquakes that affected the state, and size of anticlines (plains-type folds) are presented to illustrate application and limits of Zipfs Law.     

Characteristics of Water-Well Yields in Part of the Blue Ridge Geologic Province in Loudoun County,Virginia

Loudoun County, Virginia, which is located about 50 km to the west of Washington, DC, was the site of intensive suburban development during the 1980s and 1990s. In the western half of the county, the source of water for domestic use has been from wells drilled into the fractured crystalline bedrock of the Blue Ridge Geologic Province. A comprehensive digital database that contains information on initial yield, location, depth, elevation, and other data for 3651 wells drilled in this 825.5-km² area was combined with a digital geologic map to form the basis for a study of geologic and temporal controls on water-well yields. Statistical modeling procedures were used to determine that mean yields for the wells were significantly different as a function of structural setting, genetic rock type, and geologic map unit. The Bonferroni procedure then was used to determine which paired comparisons contributed to these significant differences. The data were divided into 15 temporal drilling increments to determine if the time-dependent trends that exist for the Loudoun County data are similar to those discovered in a previous study of water-well yields in the Pinardville 7.5-min quadrangle, New Hampshire. In both regions, trends, which include increasing proportions of very low yield wells and increasing well depths through time, and the counterintuitive result of increasing mean well yields through time, were similar. In addition, a yield-to-depth curve similar tothat discovered in the Pinardville quadrangle was recognized in this study. Thus, the temporal model with a feed-forward-loop mechanism to explain the temporal trends in well characteristics proposed for the New Hampshire study appears to apply to western Loudoun County.     

Hydrogeologic Significance of the Association Between Well-Yield Variography and Bedrock Geologic Structures,Pinardville Quadrangle,New Hampshire

The spatial continuity of water-well yields is associated with the fracture properties of the crystalline basement rocks in the Pinardville quadrangle, New Hampshire. The analysis reported in this paper expands upon previous work of a study of 939 wells in the quadrangle. This expanded analysis was performed on updated and new geologic map data, new fracture-set data and analyses, and a set of water-well yields that was expanded by 752 newly located wells. Variogram mapping of the water-well yields formed the basis for the synthesis of the spatial continuity in well yield with the geological data. A variety of associations were determined that directly relate the spatial properties of well yields to the characteristics and structure of the crystalline bedrocks in the quadrangle.     

The evolved B[e] star HD 87643: observations and a radiation-driven disc wind model for B[e] stars

New high-resolution spectroscopic and medium-resolution spectropolarimetric data of the B[e] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km s⁻¹ is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Hα. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disc structure. A hydrodynamical model is then presented, the results of which are consistent with the original two-wind concept for B[e] stars, and which exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disc. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disc wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region.     

Photosynthesis, Respiration and other Factors Influencing the Growth of Laminar/a ochroleuca PYL below 50 Metres in the Straits of Messina

Abstract. The population of Laminaria ochroleuca in the current swept Straits of Messina was investigated regarding its age structure and photosynthesis. Age structure appears to be determined by sporadic recruitment and the limitation of growth due to peak currents decapitating older plants, which is corroborated by drag force resistance calculations. The calculation of a carbon budget from measurements of photosynthesis and dark respiration both in the laboratory and in situ shows that L. ochroleuca cannot satisfy its carbon demands for growth and respiration at 50 m depth and no satisfactory explanation can be given for its rapid growth between 50 and 100 m.     

Analysis of the rate of wildcat drilling and deposit discovery

The rate at which petroleum deposits were discovered during a 16-yr period (1957–72) was examined in relation to changes in a suite of economic and physical variables. The study area encompasses 11,000 mi² and is located on the eastern flank of the Powder River Basin. A two-stage multiple-regression model was used as a basis for this analysis. The variables employed in this model were: (1) the yearly wildcat drilling rate, (2) a measure of the extent of the physical exhaustion of the resource base of the region, (3) a proxy for the discovery expectation of the exploration operators active in the region, (4) an exploration price/cost ratio, and (5) the expected depths of the exploration targets sought. The rate at which wildcat wells were drilled was strongly correlated with the discovery expectation of the exploration operators. Small additional variations in the wildcat drilling rate were explained by the price/cost ratio and target-depth variables. The number of deposits discovered each year was highly dependent on the wildcat drilling rate, but the aggregate quantity of petroleum discovered each year was independent of the wildcat drilling rate. The independence between these last two variables is a consequence of the cyclical behavior of the exploration play mechanism. Although the discovery success ratio declined sharply during the initial phases of the two exploration plays which developed in the study area, a learning effect occurred whereby the discovery success ratio improved steadily with the passage of time during both exploration plays.