Study of the fauna inhabiting the holdfasts of Laminaria hyperborea (gunn.) fosl. along some environmental and geographical gradients

A survey of the holdfast fauna of Laminaria hyperborea was carried out at thirty-five sites around the UK, mostly along the North Sea and south coasts.Data from different age classes of holdfast from a polluted and unpolluted site indicate that volume of holdfast space is a most important measurement of sample size, a minimum size of sample being one litre and, preferably, three.Gradients of increased heavy metals were defined down the North Sea and west coasts and, by utilising measurements of kelp penetration, water clarity gradients were determined as increasing northwards on the west coast and both north and southwards on the North Sea coast from a point near Tyne and Wear county. Analysis of holdfast fauna showed numerous gradients of total numbers, species and diversity which correlate closely with the heavy metal and water clarity gradients, or with undetermined parameters analogous to latitude and longitude. Where there were increases of heavy metals or decreases of water clarity, various reciprocal relationships between suspension feeders and all other trophic groups were commonly observed. In the North Sea numbers of suspension feeders increased while numbers of all other trophic groups declined. On the west coast a heavy metal increase correlated with a decreasing species richness of all trophic categories except suspension feeders, while with total numbers only suspension feeders showed an increase. On the south coast transect neither gradient existed, and only here did all trophic categories covary, except at one very polluted site where the same reciprocal relationship was again indicated.In terms of species similarity the North Sea showed a greater pool of common species than occurred between sites of other regions and between North Sea sites with other regions, despite the widest range of heavy metal levels and wate clarity that existed there. Between-site similarity appeared to be much more dependent on geographical proximity than on the two measured environmental factors. It is suggested that effects of clarity-reduction can be measured by trophic analysis more successfully than by species presence or absence, and that changes of holdfast fauna along the North Sea coast are due largely to pollution.     

The Malines Cambrian carbonate-shale-hosted Pb-Zn deposit,France: Thermometric and isotopic (H,O) evidence for pulsating hydrothermal mineralization

Microthermometric, stable isotope (D/H, ¹⁸O/¹⁶O), and Raman spectroscopic data are given for four different mineralization events located beneath a Triassic unconformity. These events include the Pb-Zn-bearing K_II mineralization which fills geodes and fractures in the main karstic mineralization K_I and the F mineralization which fills fractures in the Cambrian carbonates and shales. Post-K_I, pre-K_II, and F mineralization fluids were hot (150°C), moderately saline (10 equiv. wt% NaCl), and precipitated red dolomite. Subsequently, equally hot but more saline (20 equiv. wt% NaCl) fluids deposited white dolomite and then sphalerite of the F mineralization; they were followed by another generation of dolomite at about 70°C from fluids with about 15 equiv. wt% NaCl and, even later, barites (165°C, 10 equiv. wt% NaCl). Variation in the homogenization temperature with salinity for the different dolomite generations suggests that the hot saline fluids were repeatedly diluted by a cooler, less-saline fluid. The fluids are interpreted to be of formation-water origin having possibly developed in the deep levels of the Rhone basins to the southeast, which was at least 3 km thick at the time of mineralization (post-Hetangian). The inferred metal-bearing hot brines were probably episodically expulsed during the dewatering of the basin, depositing their mineralization in the more permeable fault and karstic zones associated with the uplift of the St. Bresson horst. Cold surface waters probably invaded the mineralized zones between the pulses of hydrothermal solutions. This hydrothermal model with the introduction of sulfides can account for the precipitation and dissolution textures associated with the hydrothermal mineralizations.     

The age of glacier peak tephra in west-central Montana

At Sheep Mountain Bog, near Missoula, Montana, a late-glacial tephra, that probably fell in late summer, is preserved as an 8-mm-thick graded bed overlain by another 8 mm of redeposited ash mixed with lake deposits. Sediment surrounding the ash was ¹⁴C dated to about 11,200 yr B.P. Electron-microprobe analyses of the volcanic glass and hornblende phenocrysts from this ash layer indicate that they are similar in major-element chemistry to those of Glacier Peak layer G previously considered to be about 12,000 yr old or older.     

Late Hercynian U-vein mineralization in the Alps: fluid inclusion and C,O, H isotopic evidence for mixing between two externally derived fluids

Late Hercynian U-bearing carbonate veins within the metamorphic complex of La Lauzière are characterized by two parageneses. The first is dominated by dolomite or ankerite and the second by calcite and pitchblende. Fluids trapped in the dolomites and ankerites at 350–400° C are saline waters (20 to 15 wt % eq. NaCl) with D –34 to –49. In the calcite they are less saline (17 to 8 wt % eq. NaCl) and trapped at 300–350° C with D –50 to –65. All fluids contain trace N₂, CO₂ and probably CH₄. The carbonates have ¹³C –8 to –14. and derived their carbon from organic matter. Evolution of the physico-chemical conditions from dolomite (ankerite) to calcite deposition was progressive.H and O-isotope studies indicate the involvement of two externally derived fluids during vein development. A D-rich ( –35) low fO₂, saline fluid is interpreted to have come from underlying sediments and entered the hotter overlying metamorphic slab and mixed with more oxidizing and less saline U bearing meteoric waters during regional uplift. This evidence for a sedimentary formation water source for the deep fluid implies that the metamorphic complex overthrusted sedimentary formations during the Late-Hercynian.     

Contrasting climatic histories for the Snake River Plain, Idaho, resulting from multiple thermal maxima

Ten sites near the Snake River Plain have consistent differences in their climatic histories. Sites at low elevation reflect the “early Holocene xerothermic” of the Pacific Northwest, whereas most climatic chronologies at high elevation indicate maximum warmth or aridity somewhat later, ca. 6000 yr ago. This elevational contrast in climatic histories is duplicated at three sites from the central Snake River Plain. For sites in such close proximity, the different chronologies cannot be explained by changes in atmospheric circulation during the late Quaternary. Rather, the differences are best explained by the autecology of the plants involved and the changing seasonal climate. The seasonal climatic sequence predicted by multiple thermal maxima explains the high- and low-elevation chronologies. During the early Holocene, maximum insolation and intensified summer drought in July forced low-elevation vegetation upward. However, moisture was not a limiting factor at high elevation, where vegetation moved upward in response to increased length of growing season coincident with maximum September insolation 6000 yr ago.     

The main issues affecting coasts of the Indian and western Pacific Oceans: a meta-analysis from Seas at the Millennium

A review of the world oceans in three volumes by 365 scientists, provides scope for several ‘meta-analyses' of the main problems affecting over 100 areas in the year 2000. This article summarises the main issues affecting a sub-set of the reviewed areas, covering Asian, African and Arabian countries dealt with in Volume 2, which included over 50 articles. From all issues raised, assessment is made of the nature of the major ones, including evaluation of reasons why so many of them remain important issues after so much attention to them. These include long standing problems, several problems more newly flagged as becoming particularly important, the issue of global warming and no less than three related issues connected with fishing and over exploitation. One or two issues such as industrial pollution and sewage, previously considered of almost universal concern, almost traditional pollution issues even, continue to feature strongly for some countries, but while these were almost always referred to in Seas chapters, by and large these categories appear not to be the most pressing of issues today, except in localized areas (albeit areas where huge numbers of people live). Perhaps other issues have simply taken over. They are excluded from this article.     

Barium- and LREE-rich, olivine-mica-lamprophyres with affinities to lamproites, Mt. Bundey, Northern Territory, Australia

Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 ± 6 Ma, intrude lower greenschist facies rocks of the Early Proterozoic Pine Creek Inlier, of northern Australia. They are spatially, temporally and probably genetically associated with a post-tectonic composite granite-syenite pluton (Mt. Bundey pluton). The dykes have unusually high contents of large-ion-lithophile (LILE) and LREE elements (e.g. Ba up to 10,000 ppm, Ce up to 550 ppm, K₂O up to 7.5 wt. %) that resemble the concentrations found in the West Kimberley olivine and leucite lamproites. However, mineralogically the Mt. Bundey lamprophyres resemble shoshonitic lamprophyres and lack any minerals diagnostic of lamproites; leucite or leucite-pseudomorphs are absent. Mineral compositions are also unlike those in lamproites: micas contain higher Al₂O₃ than lamproitic mica; amphiboles are secondary actinolites after diopside; and oxides consist of zincian-chromian magnetite and groundmass magnetite. Heavy mineral concentrates contain mantle-derived xenocrysts of magnesiochromite, pyrope, Cr-diopside and rutile indicating a depth of sampling > 70 km. The Mt. Bundey lamprophyres are non-peralkaline to borderline peralkaline (molar (K + Na)/Al = 0.8 − 1.0) and potassic rather than ultrapotassic (molar K/Na < 2.5). They have distinctive major element compositions (≈46−49 wt. % SiO₂, ≈1.5−2 wt. % MgO, ≈7 wt. % CaO), and element ratios (e.g. molar Al/Ti ≈10, K/Na ≈2) that indicate they are best classified amongst transitional lamproites, i.e. potassic rocks such as cocites, jumillites and Navajominettes, that have geochemical characteristics transitional between Groups I and III. (Foley et al., 1987). The Mt. Bundey lamprophyres have LILE enrichment patterns that resemble the W. Kimberley pamproites but have moderate negative Ta---Nb---Ti anomalies and HREE abundances that are closely similar to the jumillites of southeastern Spain and Mediterranean-type lamproites. Single-stage modelling of Rb---Sr data is consistent with enrichment of the source-region of the Mt. Bundey lamprophyres ≈ 120–170 Ma before partial melting; i.e. at 1.95–2.10 Ga. Source enrichment does not appear to be associated with subduction processes, but may instead relate to incipient rifting of the Archaean basement. Negative Ta---Nb---Ti anomalies in the Mt. Bundey dykes may, therefore, relate to stability of residual titanate minerals in an oxidized subcontinental mantle source. This view is supported by high Fe³⁺/ΣFe ratios of mantle-derived magnesiochromite xenocrysts which indicate oxidized mantle conditions (ƒ_o2 ≈ FMQ + 1 long units), and by the presence of xenocrystic Cr-bearing rutile. Although the Mt. Bundey dykes have sampled upper mantle material, the oxidized nature of the magma source-region, and of the magma itself, suggests that conditions may not be favourable for diamond survival at depth nor for diamond transport in transitional lamproite magmas of this kind.