Uranium series dating of stalagmites from Blanchard Springs Caverns,U.S.A.

Because stalagmites are enriched in ²³⁴U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, ²³⁴U/²³⁸U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP.     

Strontium isotope composition of ophiolitic and related rocks,Drocea Mountains,Rumania

Strontium isotopic analyses are reported for ophiolitic and associated rocks of Mesozoic and Tertiary age from the Drocea Mountains. The samples and their average Sr⁸⁷/Sr⁸⁶ and Rb/Sr ratios, in order, include: (a) ultramafics (partly serpentinized or uralitized peridotite, peridotite-melagabbro). 0.7043, 0.106; (b) gabbros, dolerites and anemasites (including magnetite-bearing, quartz dolerite, hornblende and normal gabbros), 0.7032, 0.021; (c) basalts (amygdaloidal, hyalopyroclasite), 0.7030, 0.040; and (d) granophyric and albitic vein rocks, 0.7046, 0.058. Also analyzed were (e) basalt-spilites of a younger intrusive cycle 0.7042, 0.046 (f) banatites, 0.7064, 0.542. Two Quaternary volcanics were analyzed from outside the Drocea Mountains: (g) augite-hypersthene andesite from Mt. Gut?i, 0.7083, 0.247, and olivine basalt from Raco?, 0.7043, 0.056. The data for the ophiolite suite show highest Sr⁸⁷/Sr⁸⁶ and Rb/Sr ratios in the ultramafics which suggests a two-stage origin with the ultramafics derived from a more primitive mantle than the later gabbros and basalts. Initial Sr⁸⁷/Sr⁸⁶ ratios range from 0.7021 to 0.7045 in gabbro and basalt and 0.7035 to 0.7056 in peridotite which is well within the limits found in oceanic tholeiites and suggests an origin for the complex as a spreading oceanic ridge. Cross-cutting felsic granophyric and albititic rocks as well as the late-stage basalts (a) have relatively low Sr⁸⁷/Sr⁸⁶ and Rb/Sr ratios, (b) represent a small volume, and (c) are intimately related to the ophiolites. They appear to have developed largely by late-stage differentiation and fractional crystallization of a tholeiitic magma. The higher ratios for the banatites and andesite from Mt. Gut?i suggest that significant amounts of sialic crustal material were involved in their formation. The basalt from Raco? is from the vicinity of a deep fracture zone; its relatively low Sr⁸⁷/Sr⁸⁶ ratio suggests a direct link to a mantle source with little or no crustal contamination.     

Unbiased station grid for study of the kinetic energy balance of the atmosphere

Summary For the past several years observational studies of the northern hemisphere kinetic energy balance and related subjects have been performed by the Planetary Circulation Project of the Massachusetts Institute of Technology. Numerous integrals required were recently evaluated directly from a five-year period of observations using a network of nearly 800 stations. The stations, however, are concentrated primarily over temperate latitude continents, and the data from maritime and tropical areas were comparatively sparse. The question then arises whether the results are representative. The problem discussed in this paper is to select a subset of more uniformly spaced stations and to recompute the zonal kinetic energy balance. This is accomplished and the results are presented herewith.The research reported in this paper was sponsored by the U.S. National Science Foundation under Grant No. GA-1310X.     

Photochemistry of methane in the Earth's early atmosphere

A detailed model is presented of methane photochemistry in the primitive terrestrial atmosphere along with speculation about its interpretation. Steady-state CH₄ mixing ratios of 10⁻⁶–10⁻⁴ could have been maintained by a methane source of about 10¹¹ cm⁻² s⁻¹, which is comparable to the modern biogenic methane production rate. In the absence of a source, methane would have disappeared in <10⁴ years, being either oxidized, or polymerized into more complex hydrocarbons. The source strength needed to maintain a steady CH₄ mixing ratio and the degree to which methane could have polymerized to form higher hydrocarbons depend upon the amount of CO₂ present in the early atmosphere. The dependence on H₂ is much weaker. Infrared absorption by methane, and especially by other hydrocarbon species, may have supplemented the greenhouse warming due to carbon dioxide. A radiative model is needed to establish this effect quantitatively. The destruction of the methane greenhouse early in the Proterozoic may have triggered the Huronian glaciation.These calculations also suggest that atmospheres rich in both CO₂ and CH₄ may be photochemically unstable with respect to conversion to CO.     

Boninite primary magmas: Evidence from the Cape Vogel Peninsula,PNG

Boninites from Cape Vogel, PNG, are dominantly pyroxene-glass rocks, but many contain olivine, sometimes as refractory as Fo₉₄. We derive a parental magma for this suite (in equilibrium with Fo₉₄) which contains 20 wt.% MgO and is quartz-normative. This liquid is hydrous, and from petrographie evidence and whole rock H₂O⁺ values, we estimate it to contain 2–3 wt.% H₂O. These data suggest olivine fractionation and primary magmatic water are important in boninite genesis, but both are often obscured by later alteration. The derived parental magma has probably formed at 1,250–1,300° C and low pressures (< ?10kB) and is similar to those which gave rise to olivine-clinoenstatite phyric boninites from New Caledonia and from Howqua, Australia, and possibly to a proposed parental magma for the Bushveld Complex.     

Distribution and significance of chlorophyll derivatives and oxidation products during the spring phytoplankton bloom in the Celtic Sea April 2002

The abundances and distributions of chlorophyll a and its common transformation products have been profiled by high performance liquid chromatography during the disruption, re-establishment, growth and senescence of a phytoplankton bloom in the Celtic Sea during April 2002. Transformation products of chlorophyll a indicative of herbivory of the phytoplankton bloom have been identified using atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry and chlorophyll oxidation products, formed by autoxidation, are present in increasing abundance in samples collected during the later stages of bloom development. The formation of oxidation products during the earliest stages in the chlorophyll transformation pathway identifies water column processes as sources of these early intermediates in the formation of geologic aetioporphyrins and/or cycloalkanoporphyrins.