Characterization of kerogens and study of their evolution by infrared spectroscopy: carbonyl and carboxyl groups

Measurements of the absorption coefficient of the band around 1710cm^?1, combined with adequate chemical treatments, allow an evaluation of the importance of carbonyl, carboxylic acid and ester groups in various series of kerogens. The concentration of carbonyl and acid groups, the concentration of oxygenated functions other than carbonyl or carboxyl, and the total oxygen content are higher in shallow kerogens originating from higher plants than in those containing an important algal contribution; however the concentration of ester groups varies in the opposite direction.The carboxylic acid groups are the most sensitive to catagenetic evolution or pyrolysis. The carbonyl groups are removed progressively as evolution proceeds but a fraction of them is retained up to advanced degrees of evolution.Study of the band at 1630cm^?1 has shown that, besides the bending vibration of molecular water, there is some contribution of bridged quinones and unsaturated hydrocarbons. However at least 50% of the absorption coefficient is due to polyaromatic structures. This band is generally much more intense for kerogens originating from higher plants.     

Sediment budget controls on foredune height: Comparing simulation model results with field data

The form, height and volume of coastal foredunes reflects the long‐term interaction of a suite of nearshore and aeolian processes that control the amount of sand delivered to the foredune from the beach versus the amount removed or carried inland. In this paper, the morphological evolution of more than six decades is used to inform the development of a simple computer model that simulates foredune growth. The suggestion by others that increased steepness of the seaward slope will retard sediment supply from the beach to the foredune due to development of a flow stagnation zone in front of the foredune, hence limiting foredune growth, was examined. Our long‐term data demonstrate that sediment can be transferred from the beach to the foredune, even with a steep foredune stoss slope, primarily because much of the sediment transfer takes place under oblique rather than onshore winds. During such conditions, the apparent aspect ratio of the dune to the oncoming flow is less steep and conditions are not as favourable for the formation of a stagnation zone. The model shows that the rate of growth in foredune height varies as a function of sediment input from the beach and erosion due to storm events, as expected, but it also demonstrates that the rate of growth in foredune height per unit volume increase will decrease over time, which gives the perception of an equilibrium height having been reached asymptotically. As the foredune grows in size, an increasing volume of sediment is needed to yield a unit increase in height, therefore the apparent growth rate appears to slow. Copyright © 2018 John Wiley & Sons, Ltd.     

ANALYSIS OF COUNT DATA USING POISSON REGRESSION*

In geographical research the data of interest are often in the form of counts. Standard regression analysis is inappropriate for such data, but if certain assumptions are met, a form of regression based on the Poisson distribution can be used. This paper illustrates the use of Poisson regression in the computer package GLIM with an example from historical geography. Apprentice migration to Edinburgh is regressed on a combination of categorical, count, and continuous explanatory variables.     

Impacts of environmental degradation on rivers,with some examples from the Hawkesbury‐Nepean system

Environmental degradation is a widespread contemporary problem. It will be exacerbated by Greenhouse. The alteration of the land surface by humans is examined in terms of on-site impacts as well as off-site effects in other storages, notably rivers. Examples of bank erosion in the Hawkesbury-Nepean system are related to regime shifts, dams and dredging. Examples of environmental pollution by different forms of sewage disposal are given for Wollondilly Shire. It is suggested that much more relevant information is required to effect total catchment management.     

Separation of He and CH4 signals on the Mid-Atlantic Ridge at 5°N and 51°N

Abiogenic methane may be produced in submarine hydrothermal systems by degassing of basalts or serpentinization of ultramafic outcrops. The latter process presumably releases little primordial helium and is therefore implicated by high CH₄/³He ratios in vent fluids from the ultramafic-hosted Rainbow field and in methane plumes near ultramafic outcrops. In two segments of the Mid-Atlantic Ridge, at 5.4°N and 51°N, we have observed depth-separated CH₄ and ³He plumes. In both cases, the helium plume was deeper, near the valley floor. It may be that the plumes issue from separate vents, where the helium is discharged near the volcanic axis and the methane is generated by serpentinization on the valley wall. However, at the present time the locations of the vents that produce these plumes are not known. Using a one-pass model, we investigated whether separate venting could arise from heat conduction from a primary, helium-carrying, hydrothermal circulation to a second, shallower fracture loop intersecting ultramafic rock. The model results indicate that the flow rate through the secondary loop would have to be relatively low in order for it to stay warm enough for serpentinization to proceed. In this case, some of the exothermic heat production is lost by conduction, and the temperature increase in the circulating fluid is only a fraction of that expected from a water/rock ratio of 1:1.     

Integrating Cavity Absorption Meter measurements of dissolved substances and suspended particles in ocean water

We have developed a new device to measure the separate contributions to the spectral absorption coefficient due to a pure liquid, due to the particles suspended in it, and due to the substances dissolved in it. This device, the Integrating Cavity Absorption Meter (ICAM), is essentially independent of scattering effects in the sample. In April 1993, a prototype of the ICAM was field tested on board the research vessel USNS Bartlett. A major part of the cruise track included criss-crossing the area where the Mississippi flows into the Gulf of Mexico at various ranges from the mouth of the river; thus samples were collected from areas of blue, green, and brown/black water. We evaluated 35 seawater samples collected with 5-l Niskin bottles from 22 locations to determine absorption spectra (380–700 nm) of suspended particles and dissolved substances (gelbstoff). Results validate the ICAM as a viable tool for marine optical absorption research. Gelbstoff absorption at 432.5 nm ranged from 0.024 to 0.603 m⁻¹. Over the spectral region 380→560 nm, gelbstoff absorption by each of the samples could be accurately fit to a decaying exponential. The particle absorption spectra are generally characteristic of those of phytoplankton and exhibit a local maximum at 430–440 nm. Absorption values at 432.5 nm ranged from zero to 1.0 m⁻¹. Some samples with moderate particulate absorption, however, did not show the characteristic local maximum of phytoplankton in the blue and instead resembled the characteristic decaying exponential of detritus with a shape similar to that observed in the gelbstoff. The ratio of gelbstoff to particulate absorption at 432.5 nm ranged from 0.46 to 152.