Magnetisation history of lower old red sandstones from the Gamrie Outlier,Scotland

Red beds in the Lower Old Red Sandstone Gamrie Outlier on the southern margin of the Orcadian Basin originated through the diagenetic breakdown of iron silicates. The magnetic evidence indicates that haematite pigment was produced over a long time period because both normal and reversed components of magnetisation are present in individual specimens. A part of the magnetisation in these rocks is carried by coarse particle specularite but there is no evidence that this is DRM or PDRM. The composite nature of the magnetisation and its acquisition over a relatively long time period is also indicated by the fact that all sample/site mean directions are of the same polarity (reversed) but originated over a period when normal and reversed polarities were common. There is evidence that the production of early diagenetic pigment was necessary for the preservation of Devonian magnetisations in these sandstones.Another group of sandstones acquired their magnetisation in Permo-Carboniferous times and these occur in intimate association with those which retain the original composite Devonian direction. The stable NRM of these rocks is carried by specularite and they are thought to have been remagnetised because they originally contained a greater proportion of magnetite than those sandstones which retain the original magnetisation and also an unstable pigment magnetisation. In-situ oxidation of magnetite in Permo-Carboniferous times is thus thought to be responsible for the remagnetisation of these rocks.     

Polycyclic aromatic hydrocarbons in Recent lake sediments—I. Compounds having anthropogenic origins

Polycyclic aromatic hydrocarbons (PAH) in sediment cores from Lake Lucerne, Lake Zürich, and Greifensee, Switzerland, and Lake Washington, northwest U.S.A., have been isolated, identified and quantified by glass capillary gas chromatography and gas chromatography/mass spectrometry. Surface sediment layers are greatly enriched in PAH—up to 40 times—compared to deeper layers. In addition, concentration increases in upper sediments generally correspond to increasing industrialization and urbanization in the catchment basins of the lakes. Few PAH could be detected in pre-industrial revolution sediments, indicating that background levels for most PAH in aquatic sediments are extremely low.These results are consistent with an anthropogenic source for most of the aromatic hydrocarbons present in the modern sediments. A comparison of PAH distributions in the sediments and in possible source materials shows that urban runoff of street dust may be the most important PAH input to these lacustrine sediments. There is evidence that a significant contribution to the PAH content of street dust comes from material associated with asphalt.     

PCBs in the Hudson River

Hydrocarbon distribution in sediments from three lakes are related to the level of human activity in the respective drainage basins. Petroleum hydrocarbon contamination is found in surface sediments of a lake surrounded by a major city, compared to no detectable contamination in a lake located in a National Park.