Porphyrin geochemistry of Atlantic Jurassic-Cretaceous black shales

Late Jurassic-early Cretaceous black shales and an overlying sequence of Albian-Campanian zeolitic claystones from the Falkland Plateau (DSDP/IPOD Leg 71, Site 511) were analyzed for tetrapyrrole pigment type and abundance. The “black shale” sequence was found to be rich in DPEP-series dominated free-base, nickel (Ni) and, to a lesser extent, vanadyl (V = 0) porphyrins. A low level of organic maturity (i.e. precatagenesis) is indicated for these strata as nickel chelation by free-base porphyrins is only 50–75% complete, proceeding down-hole to 627 meters sub-bottom. Electronic and mass spectral data reveal that the proposed benzo-DPEP (BD) and tetrahydrobenzo-DPEP (THBD) series are present in the free-base and Ni species, as well as the more usual occurrence in V = 0 porphyrin arrays. Highly reducing conditions are suggested by an abundance of the PAH perylene, substantial amounts of the THBD/BD series and a redox equilibrium between free-base DPEP and 7,8-dihydro-DPEP series, which exist in a 7:1 molar ratio. The Albian-Campanian claystone strata were found to be tetrapyrrolepoor, and those pigments present were typed as Cu/Ni highly dealkylated (C₂₆ max.) etioporphyrins, thought to be derived via redeposition and oxidation of terrestrial organic matter (OM). Results from the present study are correlated to our past analyses of Jurassic-Cretaceous sediments from Atlantic margins in an effort to relate tetrapyrrole quality and quantity to basin evolution and OM sources in the proto-Atlantic.     

Palaeoflood hydrology of the Salt river,Arizona

Geomorphic evidence along bedrock-confined reaches of the Salt River in east-central Arizona provides a record of the river's largest flood events. Fine-grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low-flow channel. Discharges associated with flow events responsible for the deposits were estimated by computer flow modelling. These estimates document flood magnitudes in excess of gauged historic streamflows. Relative and radiocarbon dating suggest that a flood record in excess of 600 y is preserved in the slackwater sequences. A prominent flood scar cut into grussy hillslope soils allows the extension of the prehistoric flood record to several thousand years. A maximum discharge estimate of 4600 m³s^?1 affixed to the flood scar represents the largest flood event in the record, and is given a minimum recurrence interval of 1000–2000 y. The 1952 flood is the largest historic flow event experienced along the study reach and is estimated at 2900 m³s^?1. Two palaeoflood events preserved in the slackwater stratigraphy exceed the 1952 event, and are given recurrence intervals of 300 and 600 y. The latter flood event had an estimated discharge of 3200 m³s^?1. It is apparent that discharge estimates affixed to these infrequent, large-magnitude flood events approach a maximum with decreased probabilities (large recurrence intervals). This suggests that a physical limit on discharge may exist within the Salt River drainage basin and is perhaps directly related to drainage basin size.     

Case studies in organic contaminant hydrogeology

The effective management of domestic solid waste and hazardous, toxic, and radioactive waste is a major problem in the area of environmental geology and water sciences over the world. This series of case studies of organic contaminants from both solid and hazardous waste disposal facilities provides examples of these problems. The facilities were investigated to determine risks and liabilities before acquisition, to determine the site hydrogeologic conditions for design of appropriate groundwater monitoring plans, and/or to determine the potential for groundwater contamination. The results of these studies and investigations by Waste Management Inc. (WMI) and its consultants have shown certain relationships in the distribution of organic pollutants to the different geologic and hydrogeologic charac teristics of each facility. In each of the case studies, all 129 priority pollutants were analyzed in private wells and/or monitoring wells at the request of regulatory agencies. The 31 volatile organic compounds (VOCs) of the priority pollutant list were the majority of the organic compounds detected and these data are evaluated in each case study. The case studies are on disposal facilities located in glacial tills, carbonaceous weathered clay soils, weathered shale, limestone bedrock, dolomite bedrock, and alluvial and sedimentary deposits. A brief discussion of groundwater quality impacts and remedial measures also is included.Presented at the Second Annual Canadian/American Conference on Hydrogeology: Hazardous Wastes in Ground Water—A Soluble Dilemma. Banff, Alberta, Canada, June 26, 1985.     

A New Digestion and Chemical Separation Technique for Rapid and Highly Reproducible Determination of Lu/Hf and Hf Isotope Ratios in Geological Materials by MC-ICP-MS

A new digestion procedure and chemical separation technique has been developed for measurement of Lu/Hf and Hf isotope ratios that does not require high‐pressure bombs or use of HF or HClO₄ acids. Samples are digested in dilute HCl or HNO₃ after flux‐fusion at 110 0 °C in the presence of lithium metaborate. High field strength elements (HFSE) and rare earth elements (REE) are separated from this solution by co‐precipitation with iron hydroxide. The dissolved precipitate (in 2 mol l^?1 HCl) is loaded directly onto a standard cation exchange column which separates remaining sample matrix from the heavy REE (Lu+Yb), and the middle‐light REE and HFSE (Hf). The middle‐light REE and individual HFSE are then separated (10.5, 9 and 6 mol l^?1 HCl) using a miniaturized column containing TEVA spec resin which provides a REE‐, Ti‐ and Zr‐free Hf cut. This chemical separation scheme can also be readily adapted for isotopic analysis of the Sm‐Nd system and/or the other HFSE (Ti, Zr). Total procedural blanks for this technique are < 10 0 pg and < 2 pg for Hf and Lu, respectively, even when digesting large (0.5 g) samples. We present data from replicate digestions of international rock reference materials which demonstrate this technique routinely reproduces Lu/Hf ratios to < 0.2% (2s) and ¹⁷⁶ Hf/¹⁷⁷ Hf isotope ratios to < 30 ppm (2s). Moreover, the technique is matrix‐independent and has been successfully applied to analysis of diverse materials including basalts, meteorites, komatiites, kimberlites and carbonatites. The relative simplicity of this technique, coupled with the ease of digestion (and sample‐spike equilibration) of large difficult‐to‐dissolve samples, and the speed (2 days) with which samples can be digested and processed through the chemical separation scheme makes it an attractive new method for preparing samples for Lu‐Hf isotopic investigation.     

Long-Term Ground Heat Flux and Heat Storage at a Mid-Latitude Site

We analyzed a long-term (37 year) record of monthly average below-ground temperatures, at depths ranging from the surface down to 12.8 m,to determine the ground heat flux. Temperatures at all depths have increased over the period, evidence of a non-zero mean ground heat flux. Analysis indicates an average downward flux out of the root zone (below 1.6m) over the period of approximately 1.1 MJ m^–2year^–1. The corresponding average flux through the bottomplane of measurement has been approximately 0.22 MJ m^–2year^–1, indicating that 20% of the heat storage duringthe period has been at depths greater than 12.8 m. Current representations of ground heat flux in global climate models are inadequate to realistically simulate these results. This warming, if it continues, could affect a range of biotic and abiotic below-ground processes.     

A Cromerian Complex stalagmite from the Mendip Hills,England

In order to provide a better chronological constraint on a British Middle Pleistocene interglacial, a large stalagmite boss from the Mendip Hills was selected for palaeoclimate data using pollen analysis. Dating analyses by thermal ionisation mass spectrometry (TIMS) of uranium–thorium ratios and by magnetostratigraphy constrain the age of the sample to 450–780 ka. The isotopic consistency of the TIMS analyses, plus the presence of luminescence laminations, suggest that the sample has been preserved under closed-system conditions. Pollen assemblages have been recovered from the speleothems, despite the fact that the pH of calcite deposition is usually greater than 7. Furthermore the evidence presented here indicates that the pollen was probably transported by the speleothem feedwater, rather than entering the cave aerially. The pollen record contained within the stalagmite is interpreted as early–mid-interglacial but does not have clear Cromerian affinity. © 1997 John Wiley & Sons, Ltd.     

Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

Data from HF-radars are used to make the first simultaneous conjugate measurements of the day-side reconnection electric field. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic field (IMF) was southward whilst the eastward component (By) was variable. The flow patterns derived from the radar data show the expected conjugate asymmetries associated with IMF |By| ≥ 0. High-time resolution data (50 and 100 s) enable the flow of plasma across the open/closed field line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical difference of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s⁻¹) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively fits that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be significantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat flow occurs is different in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric field values are largest when the radar’s meridian is in the throat flow or early afternoon flow regions. In the morning or afternoon convection cells, the reconnection electric field tends to zero away from the throat flow region. The reconnection electric field observed in the throat flow region is bursty in nature.