A carbonate island barrier from the Great Oolite (Middle Jurassic) of central England

Over part of south-central England the widespread shallow-water carbonate sedimentation represented by the White Limestone Formation (Great Oolite Group: Middle Jurassic), culminated locally with the formation of a sun-cracked, stromatolitic micrite indicating a supratidal environment. The emergent area can be mapped as a broad strip running at an angle to, and offshore from, the coast-line of the ancient Anglo-Belgian landmass. As a result of the emergence of this carbonate area a polarization of environments occurred. To the north-east a series of clay-rich sediments containing lignite and a brackish and fresh-water fauna were laid down: a lagoonal environment is indicated. To the south-west fully marine shelf carbonates continued to be deposited. We suggest that isolation of the northerly area of reduced salinity from the open sea was due directly to emergence of this carbonate area, which can thus be specifically interpreted as an island barrier or spit.     

Implications of iodine-xenon studies for the timing and location of secondary alteration

Abstract— Iodine-xenon ages (based on 15.7 Ma ¹²⁹I) of meteoritic samples are highly susceptible to secondary alteration processes, so they have the potential to determine both the timing, and in some cases the location, of those secondary processes. Iodine-xenon studies can determine the location in two cases. First, if the length of time required is greater than the lifetime of the nebula, then the process must have occurred on a parent body. Ages from sodalite in Allende, dark inclusions in Efremovka (CV3), and some samples from CM chondrites all suggest durations of several million years, in some cases marginally longer than the predicted duration of the nebula. Second, in some cases the evolution of the ¹²⁹Xe/¹³²Xe ratio can be used to determine the I/Xe elemental ratio of the reservoir in which the evolution occurred. For chondrules from the unequilibrated ordinary chondrites Chainpur and Tieschitz, the isotopic evolution is quantitatively consistent with evolution in a chondritic (parent body), rather than nebular, reservoir.     

Martian “microfossils” in lunar meteorites?

Abstract— One of the five lines of evidence used by McKay et al. (1996) for relic life in the Martian meteorite Allan Hills (ALH) 84001 was the presence of objects thought to be microfossils. These ovoid and elongated forms are similar to structures found in terrestrial rocks and described as “nanobacteria” (Folk, 1993; McBride et al, 1994). Using the same procedures and apparatus as McKay et al. (1996), we have found structures on internal fracture surfaces of lunar meteorites that cannot be distinguished from the objects described on similar surfaces in ALH 84001. The lunar surface is currently a sterile environment and probably always has been. However, the lunar and Martian meteorites share a common terrestrial history, which includes many thousands of years of exposure to Antarctic weathering. Although we do not know the origin of these ovoid and elongated forms, we suggest that their presence on lunar meteorites indicates that the objects described by McKay et al. (1996) are not of Martian biological origin.     

Palaeoclimate of the Late Jurassic of Portugal: comparison with the Western United States

Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal and comparison with published palaeoclimate reconstructions of the Upper Jurassic Morrison Formation in western North America provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish. Geochemical analyses and observations of palaeosol morphology in the informally named Upper Jurassic Lourinhã formation of western Portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns. Palaeosol profiles are dominated by carbonate accumulations and abundant shrink‐swell (vertic) features that are both indicative of seasonal variation in moisture availability. The δ¹⁸O_SMOW and δD_SMOW values of phyllosilicates sampled from palaeosol profiles range from +22·4‰ to +22·7‰ and ?53·0‰ to ?37·3‰, respectively. These isotope values correspond to temperatures of formation between 32°C and 39°C ± 3°, with an average of 36°C, which suggest surface temperatures between 27°C and 34°C (average 31°C). On average, these surface temperature estimates are 1°C higher than the highest summer temperatures modelled for Late Jurassic Iberia using general circulation models. Elemental analysis of matrix material from palaeosol B‐horizons provides proxy (chemical index of alteration minus potassium) estimates of mean annual precipitation ranging from 766 to 1394 mm/year, with an average of approximately 1100 mm/year. Palaeoclimatic conditions during deposition of the Lourinhã formation are broadly similar to those inferred for the Morrison Formation, except somewhat wetter. Seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas. The similar climate between these two Late Jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas.     

New Zealand and Environmentalism: An Outsider's View

Abstract. This paper is a personal perspective on how New Zealand appears to have changed in its approach to environmental management in the twenty years since 1 first came to know and love the country.     

Fossil charcoal: a plant-fossil record preserved by fire

Small pieces of black organic material are common in many post-Devonian sequences, both sedimentary and volcanic. While many of these are coalified plant fragments, others are fossil charcoal, also known as fusain. Charcoalification preserves exquisite detail of the plant ultra-structure and is best viewed by scanning electron microscopy.     

The Quantitative Mineralogical Composition and Variation of the Lacorne, La Motte, and Preissac Granitic Complex, Quebec, Canada

Variation of quartz percentage, colour index, potash feldspar/plagioclaseratio, feldspar percentage, and specific gravity within theLacorne, La Motte, and Preissac granitic complex is studiedby means of trend surface analyses based on 198 specimens. Markedpatterns of variation emerge; the more clear-cut patterns relateto massifs with mafic- and potash feldspar-rich centres, andquartzose peripheries. The trend components suggest that theLacorne massif is a composite body, and re-evaluation of thefield evidence supports this prediction. These results are usedto demonstrate a quantitative technique and its applicationto geographically distributed data of granitic complexes; aplea is made for the collection of areally distributed quantitativedata of all types.