The use of a portable fluxgate magnetometer for the estimation in the field of the direction and stability of remanent magnetization of rock specimens

Summary A portable magnetometer of the fluxgate type is described, which is capable of measuring in the field the direction and intensity of remanent magnetization of rock samples of 2 cm diameter with an accuracy of the order of 6° for intensities of 10^–3 emu/cc or more. The measurement and calculation can be carried out in less than five minutes, and a precision of the order of 2° can be obtained if more readings are taken so that ten minutes are required for a complete measurement. The chief limitation to the precision of measurement was found to be inhomogeneity of magnetization of the specimens. The instrument has been used to estimate stability of natural remanent magnetization where A.C. cleaning apparatus is not available, and the method of doing so is briefly described.Now with English Electric Computers.     

Effect of iron type on kinetics and carbon isotopic enrichment of chlorinated ethylenes during abiotic reduction on Fe(0)

Four samples of two commercially available iron brands used as substrate for iron permeable reactive barriers (PRBs) were tested for suitability for remediation of perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE) and vinyl chloride (VC). Kinetic studies indicate that rates of reaction are enhanced for cDCE and VC on Connelly iron (2.8 x 10(-4) to 6.9 x 10(-4) L/m2/hr and 2.0 x 10(-4) to 9.0 x 10(-4) L/m2/hr, for cDCE and VC, respectively) vs. Peerless iron (3.1 x 10(-5) to 4.6 x 10(-5) L/m2/hr and 2.4 x 10(-5) to 4.1 x 10(-5) L/m2/hr, for cDCE and VC, respectively). Carbon isotopic analyses of the residual chlorinated ethylene (CE) during degradation indicate significant fractionation occurs during reductive dechlorination, with, for example, up to 70% enrichment in carbon isotopic values observed when VC is more than 99% degraded. Comparison of fractionation factors (epsilon) indicates significant differences in carbon isotopic fractionation for different iron types and for different CEs. For the lower CEs (cDCE and VC) in particular, both slower reaction rates and larger fractionation are observed for degradation on Peerless vs. Connelly iron. This is the first study to establish a correlation between the rate of abiotic degradation on Fe(0) and the extent of isotopic fractionation, and the first to confirm consistent differences in these two parameters as a function of iron type. The possibility that these differences in kinetics and carbon isotopic fractionation for cDCE and VC are related to differences in branching ratios between competing hydrogenolysis and beta-elimination reactions during reductive dechlorination on the iron surfaces is discussed.     

Use of the Marine Prophage Induction Assay (MPIA) to detect environmental mutagens

The prophage induction assay provides a biologically based carcinogen-screening tool for environmental samples grounded in the parallel mechanisms of carcinogenesis and prophage induction. We developed an assay using a previously characterized marine bacterialPseudomonas aeruginosa isolate designated as P94-4S3 for the detection of potentially genotoxic contamination in marine and estuarine environments. To perform the assay, the lysogenic isolate was exposed to either a known genotoxic compound or an environmental sample of interest. The response was considered positive when a statistically significant amount of prophage induction occurred in comparison to negative controls. Initial development of the assay for enviromental samples included testing under a range of salinities and optimizing the method for the processing of water column and sediment samples. The assay has been field-tested over 2 yr in the Rookery Bay National Estuarine Research Reserve, Florida. The Marine Prophage Induction Assay (MPIA) was performed concurrently with laboratory toxicological analysis. There was good correspondence between positive MPIA results and detection of potentially toxic compounds by laboratory analysis. Five positive laboratory detections of known toxic compounds in natural samples occurred in conjunction with positive MPIA results. Two laboratory detections of compounds that are not genotoxic were accompanied by a negative MPIA response. Eight of the sediment samples contained detectable levels of arsenic. Four of these samples demonstrated a positive MPIA response, which may be due to the oxidation state of the arsenic within the sediment. One detection of a known toxic compound by the analytical laboratory was not accompanied by a positive induction response. Nine positive induction responses occurred without concurrent laboratory detection. This was possibly due to the limited range of compounds included in the laboratory testing performed, although false positive assay results cannot be ruled out.     

Petrology of a suite of sedimentary rocks associated with some cole-bearing basins in northwestern Thailand

A number of basins in northwestern Thailand contain thick sequences of Cenozoic sedimentary rocks. Oil shales and coals are prominent lithologies within these sequences and occur together in some basins. Most of the sequences are, however, dominated by either oil shales or coals. The major oil shale deposit is in the Mae Sot Basin but oil shales also occur in the Ban Huay Dua, Mae Moh, Ban Pa Ka Li, Mae Teep, Ban Na Hong and Jae Hom Basins.Drilling and detailed mapping, in the Mae Sot Basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite. Trace amounts of telalginite, liptodetrinite, bitumen/resinite and huminite/inertinite are also present in some of the rocks. The parts of the sequences rich in authigenic minerals are, in general, petrographically similar to Green River Formation lamosites. Where clay/silt-sized epiclastics are more abundant, similarities exist to Australian Tertiary lamosites. Vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity.Oil shales from the other basins are, petrographically similar to the Mae Sot lamosites, however some differences do exist. The Mae Sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths.     

Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau

We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian–Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian–Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type II material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in δ¹⁵N values between −5 and 1‰, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian–Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian.     

Clionid sponge surveys on the Florida Reef Tract suggest land-based nutrient inputs

Bioerosion by Cliona delitrix and Cliona lampa was assessed at 43 sites along the Florida Reef Tract, USA, in the summer of 2001. Sponge abundances were estimated using rapid visual assessment. Tissue samples of sponges were taken for analysis of delta15N. Comparison samples were taken from Belize. Annual trends in sponge abundance were estimated from archived videos covering the period from 1996 to 2001. Sites with the greatest boring sponge size and cover were in the Backcountry and Lower Keys, where total nitrogen, ammonium, and delta15N levels were highest. The sites with the largest relative increase of C. delitrix and C. lampa over the 5 year period were in the Upper Keys, where the greatest relative decline in stony coral cover has occurred. Florida sponge delta15N values were 5.2(+/-0.1)%, suggesting the influence of human waste; in comparison, offshore Belize samples were 2.1(+/-0.1)%. These results suggest sewage contamination of the Florida Reef Tract, shifting the carbonate balance from construction to destruction.     

Late Holocene radiocarbon and aspartic acid racemization dating of deep-sea octocorals

Primnoa resedaeformis is a deep-sea gorgonian coral with a two-part skeleton of calcite and gorgonin (a fibrillar protein), potentially containing long-term records of valuable paleo-environmental information. For various reasons, both radiocarbon and U/Th dating of these corals is problematic over the last few centuries. This paper explores aspartic acid racemization dating of the gorgonin fraction in modern and fossil specimens collected from the NW Atlantic Ocean. Radiocarbon dating of the fossil specimen indicates a lifespan of 700 ± 100 years, the longest yet documented for any octocoral. Gorgonin amino acid compositions were identical in the fossil and modern specimens, indicating resistance to organic diagenesis. Similar to bone collagen, the fibrillar protein of gorgonin may impose conformational constraints on the racemization of Asp at low temperatures. The rate of racemization of aspartic acid (d/l-Asp) was similar to previously published results from an 1800 year old anemone (Gerardia). The age equation was: age (years BP 2000 AD) = [(d/l − 0.020 (±.002))/.0011 (±.0001)]² (r² = 0.97, p < .001). The error in an age estimate calculated by d/l-Asp was marginally better than that for ¹⁴C dating over the most recent 50-200 years, although the dating error may be improved by inclusion of more samples over a broader time range. These results suggest that d/l-Asp dating may be useful in augmenting ¹⁴C dating in cases where ¹⁴C calibrations yield two or more intercept ages, or in screening samples for further ¹⁴C or U/Th dating.