Lithium isotopes in the system Qz-Ms-fluid:An experimental study

The fractionation of lithium isotopes among quartz, muscovite, and a chloride-bearing aqueous fluid has been investigated experimentally at 400°-500°C and 50-100 MPa. Experiments were performed for 15-60 days in cold seal vessels with natural mineral specimens. Lithium was introduced primarily through the fluid, which also contained KCl and HCl. In most runs, the fluid was prepared with the L-SVEC standard (δ⁷Li = 0) and was 1 M in total chloride with K/Li/H = 100/10/1. In two experiments, a ⁶Li spike was employed. The experiments demonstrate that quartz and muscovite are susceptible to pronounced, rapid shifts in Li isotopic composition by diffusion through interaction with a Li-bearing fluid, particularly at 500°C. At 500°C, fractionation factors were determined to be Δ_{quartz-aqueous} ≅ +8 to + 12‰ and Δ_{muscovite-aqueous} ≅ +18 to + 20‰. An intermineral fractionation factor is given by Δ_{muscovite-quartz} ≈ +9‰. At 400°C, the results suggest Δ_{quartz-aqueous} ≈ +4 to + 6‰. The study provides evidence of systematic fractionation in lithium isotopes at the temperatures of some magmatic processes, such as those associated with porphyry-type ore systems and pegmatites.     

The Upper Pliocene Bowden shell beds,southeast Jamaica

The Neogene fossil record of the Antilles is particularly rich and can satisfy the interests of most collectors, from foraminifers to vertebrates. The molluscs are among the commonest and most diverse groups, being found in both terrestrial and marine deposits. The Pliocene Bowden shell beds of southeast Jamaica, best known for its hundreds of species of molluscs, also yields diverse members of other groups, the total exceeding 800 species from a mere 5 m of stratigraphical section.     

How preferential flow delivers pre‐event groundwater rapidly to streams

Groundwater often accounts for a substantial fraction of flood hydrographs, but the processes responsible for this have been unclear. However, many aquifers have preferential flow and this explains how aquifers can be so responsive. In bedrock aquifers, weathering enhances the connectivity and apertures along the most efficient flow paths and hence enhances the permeability. This results in celerities and velocities of the preferential flow in these dual‐porosity aquifers that are two to three orders of magnitude higher than if the aquifers behaved as single‐porosity media. The celerities have been determined from artificial and natural flood pulses, from tidal lags, and from pumping tests. Preferential‐flow velocities have been calculated from tests using applied tracers. Celerities in bedrock aquifers are typically one to two orders of magnitude faster than velocities. The ubiquitous preferential flow in aquifers provides an additional explanation, besides groundwater ridging, for the rapid release of groundwater to streams during storm events.     

Population structure of two deep sea tubeworms,Lamellibrachia luymesi and Seepiophila jonesi,from the hydrocarbon seeps of the Gulf of Mexico

Vestimentiferan tubeworms are a group of large sessile marine polychaete annelids (family Siboglinidae) found in the regions of hydrothermal venting or seepage of the reduced chemical hydrogen sulfide. Hydrocarbon seeps on the Louisiana Slope of the Gulf of Mexico support large communities of the co-occurring vestimentiferan species Lamellibrachia luymesi and Seepiophila jonesi. These sessile species have the opportunity to disperse between the patchy sites of active seepage on the seafloor during a planktonic larval stage. However, it is unclear whether dispersal occurs at a local or global scale. Four (L. luymesi) and seven (S. jonesi) microsatellite loci were used to test for population substructure among ten hydrocarbon seep sites on the Louisiana Slope. Both species showed high levels of allelic diversity, averaging 18.5 (L. luymesi) and 22 (S. jonesi) alleles/locus, respectively, and high observed heterozygosity at all microsatellite loci (0.71–0.9 in L. luymesi, 0.27–0.84 in S. jonesi). The two species showed a significant deficiency in heterozygotes compared to that predicted under the Hardy–Weinberg equilibrium. L. luymesi showed a small but significant amount of population structure, with a positive correlation between genetic and geographic distance among the sample sites spanning 540 km. S. jonesi, in contrast, showed no evidence for isolation by distance, but did show a significant genetic difference between aggregations of different ages. These results suggest that these two species differ in how larvae are able to colonize new seep sites through space (L. luymesi) and though time (S. jonesi).