The geochemistry of exinites—1. Evaluation of spectral fluorescence of a series of modern resins and fossil resinites

A series of six fossil resins and four modern resins have been analysed using microscope-based spectral fluorescence methods, in addition to a preliminary study of the chemical composition of these samples using infrared spectroscopy and pyrolysis-gas chromatography. This study illustrates problems encountered during the measurement of spectral fluorescence of resins and resinite kerogens using conventional microscopy methods. Most notable, alteration of fluorescence significantly influences spectral measurements. Further, fossilized resins within rocks are complex mixtures of resinite and bitumen. Pre-extraction of resinites prior to petrographic analysis resulted in somewhat more uniform spectral fluorescence results.Spectral fluorescence of recent resins used in this study could be used to distinguish angiosperm from gymnosperm derived resinite kerogens. Distinction of plant class source of resinite kerogens, however, is more difficult using this method and is considered genarally unreliable.     

Molecular genetic markers and maturity indices in intermontane lacustrine facies: Kishenehn formation, Montana

Molecular markers have considerable promise as thermal maturation indicators in source rocks having a well-defined depositional environment. This occurs in the Kishenehn Formation (northwest Montana and southeast British Columbia), an Oligocene unit comprised of fluvial and lacustrine shales. Up to 3 km of these non-marine sediments were deposited in a 900 sq.km elongated half graben atop the Precambrian rocks of the Lewis Thrust sheet. Specific outcrops of the Coal Creek Member of the Kishenehn Formation are known to contain excellent potential source rocks, including extensive oil shales. The source rock potential and molecular marker geochemistry of most of the major Kishenehn outcrops have now been investigated, and regional results are presented in this paper.source rock analysis of a regional suite of Kishenehn samples indicates excellent petroleum potential (immature Type I kerogen) throughout the basin. Several classes of distinctive diagenetic molecular markers occur within the Coal Creek Member of the Kishenehn Formation, including diasterenes, spirosterenes, methylspirosterenes, B-ring monoaromatic anthrasteroids, ββ-hopanes and moretanes. Molecular markers indicative of non-marine deposition include dehydroabietane (conifer input) and an onocerane recently identified in leaf fossils of Miocene lacustrine beds in adjacent Idaho. Triterpane ratios are significantly more sensitive than vitrinite reflectance methods in assessing thermal maturation in the Kishenehn, and are successfully used in this study to order outcrop locations according to thermal maturity level. The systematic variation of specific markers with increasing thermal maturation suggests that molecular correlation is feasible, and could provide a method of assessing stratigraphic continuity in the basin.     

Water contents, temperatures and diversity of the magmas of the catastrophic eruption of Nevado del Ruiz, Colombia, November 13, 1985

The petrology of the highly phyric two-pyroxene andesitic to dacitic pyroclastic rocks of the November 13, 1985 eruption of Nevado del Ruiz, Colombia, reveals evidence of: (1) increasingly fractionated bulk compositions with time; (2) tapping of a small magma chamber marginally zoned in regard to H₂O contents (1 to 4%), temperature (960–1090°C), and amount of residual melt (35 to 65%); (3) partial melting and assimilation of degassed zones in the hotter less dense interior of the magma chamber; (4) probable heating, thermal disruption and mineralogic and compositional contamination of the magma body by basaltic magma “underplating”; and (5) crustal contamination of the magmas during ascent and within the magma chamber. Near-crater fall-back or “spill-over” emitted in the middle of the eruptive sequence produced a small pyroclastic flow that became welded in its central and basal portions because of ponding and thus heat conservation on the flat glaciated summit near the Arenas crater. The heterogeneity of Ruiz magmas may be related to the comparatively small volume (0.03 km³) of the eruption, nearly ten times less than the 0.2 km³ of the Plinian phase of Mount St. Helens, and probable steep thermal and P_H2O gradients of a small source magma chamber, estimated at 300 m long and 100 m wide for an assumed ellipsoidal shape.     

Uniform-hazard response spectra—An alternative approach

An alternative method is presented for generating uniform-hazard response spectra making use of a seismic hazard curve expressing annual probability of exceedance as a function of Peak Ground Acceleration (PGA), a set of normalized (PGA = 1g) mean response spectra, and a coefficient-of-variation function for the random normalized spectral values in terms of period T. The practice of using mean + 1σ normalized response spectra, scaled to specified PGA levels, is discussed and associated mean return periods are evaluated.     

U.S. Bank Failures and Regional Economic Structure*

U.S. commercial bank failures approached historically high levels in the 1980s. The collapse of such institutions can have severe impacts on local economies, disrupting the supply of available investment credit. This paper situates bank failures within the broader transformation of global capitalism in the late 20th century. Next, it reviews the causes of bank insolvency, including mismanagement, deregulation, the glutted commercial real estate market, and depressed agricultural and petroleum-dependent local economies. It then illustrates multiple aspects of the spatial distribution of bank failures. A pooled time-series regression analysis, using primary causal variables as well as location quotients of state output in four industrial sectors, indicates that with the vital exception of petroleum, and to a lesser extent services, regional economic structure is not strongly related to bank failures. This finding likely reflects the structural and spatial transformation of the industry as it adapted to the highly competitive conditions of the last decade.     

Employment Trends in Geography,Part 1: Enrollment and Degree Patterns*

This paper is the first in a series of three papers dealing with the current and future labor market for geographers. It is based on a report prepared by the Association of American Geographers' (AAG) Employment Forecasting Committee to the National Research Council's (NRC) Rediscovering Geography Committee. This report provides a data-based analysis of the past and future supply of geographers, the current labor market conditions in the field, and the factors likely to influence the future demand for geographers (faculty hiring, geographic education initiatives, trends in private-sector jobs, etc.). Each year some 4,000 individuals receive degrees in geography from America's institutions of higher education. They, or some portion of them, make up the new supply of geographers entering the labor market. In the near future (up to five years), the availability of new geographers is related to the number of geography students now in the educational pipeline. Their current specialties, and the specialties of the programs from which they come, tell us about the types of skills and the kinds of interests to be held by future labor force entrants. In the longer term (five to ten years), the number of new geographers will be influenced by geographic education initiatives at the precollegiate level. More and better geographic instruction in elementary and secondary schools will expose more students to geography as a field of study and as a potential career path. The purposes of this paper are to (1) review degree and enrollment trends in geography, (2) assess the “trickle-up” effects of geographic education initiatives at the precollegiate level, and (3) investigate the characteristics of future supply as evidenced by the types of occupations for which geography departments are now preparing students.     

Dynamics of polychlorinated biphenyls in striped bass from the Hudson River. III. Tissue disposition and routes for elimination

Striped bass were exposed to¹⁴C-polychlorinated biphenyls (PCB) in single-dose and multiple-dose experiments. Samples were analyzed to determine rate constants for PCB elimination from individual tissues, PCB concentration in tissues, the proportion of the PCB burden retained and the proportion of the cumulative dose retained by each tissue at various times after exposure. An experiment was also conducted to determine both the potential for secondary PCB uptake in dietary exposure studies and the relative tissue disposition of PCBs assimilated from dietary sources as compared to direct water uptake. PCBs were present in the tissues of striped bass within 6 h after administration of a single dose. Certain tissue compartments, such as the liver/gall bladder, accumulated PCBs over a period of 48 h even though the whole-body burden had decreased between 24 and 48 h. Except for the gills, elimination rate constants for all tissues were similar and were similar to the whole body elimination rate constant. Elimination during the first few hours following exposure to PCBs may be due to equilibrium partitioning from the gill to the environment. The multiple-dose study showed that PCB burdens in striped bass continued to increase with dosing. However, tissue-specific rate constants for PCB elimination led to an increased flux of PCB out of tissues, and an overall decline in the percent of the cumulative dose remaining in the body 48 h after administration of each dose. The most likely route for PCB elimination from striped bass was from tissues to the liver and thence to the intestine via the bile. There were no differences in the tissue disposition of PCB related to route of exposure.     

Assessment of trace element geochemistry of Hampton Roads harbor and lower Chesapeake Bay area sediments

Acid extractable Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb. and Zn were determined in sediments from the Inner Virginia Shelf, and from shipping channels in the lower Chesapeake Bay and Hampton Roads, Virginia, harbor system. Data were evaluated by a variety of techniques Levels of Cd, Cu, Pb, and Zn exceeded average crustal abundances for most of the study sites. Cumulative frequency curves suggested that there were two major populations for all metals and perhaps a third and smaller, one for Cd, Cr, and Mn Plots of metal vs Fe indicated no anthropogenic inputs of metals for shelf and Chesapeake Bay channel sites, but suggested anthropogenic influences for all metals in several of the inshore sites. Enrichment factor calculations showed enrichment of Cd, Pb, and Zn with respect to average crustal abundances for all sites and of Cu for the industrial harbor system. A recommendation of this study for evaluation of environmental geochemical metals data is to utilize mean concentrations, cumulative frequency plots, and metal vs Fe and/or enrichment factor calculations when evaluating the pollution status of sediments.