Granite‐related overpressure and volatile release in the mid crust: fluidized breccias from the Cloncurry District,Australia

The source and transport regions of fluidized (transported) breccias outcrop in the Cloncurry Fe‐oxide–Cu–Au district. Discordant dykes and pipes with rounded clasts of metasedimentary calc–silicate rocks and minor felsic and mafic intrusions extend several kilometres upwards and outwards from the contact aureole of the 1530 Ma Williams Batholith into overlying schists and amphibolites. We used analytical equations for particle transport to estimate clast velocities (≥20 m sec^?1), approaching volcanic ejecta rates. An abrupt release of overpressured magmatic‐hydrothermal fluid is suggested by the localization of the base of the breccias in intensely veined contact aureoles (at around 10 km, constrained by mineral equilibria), incorporation of juvenile magmatic clasts, the scale and discordancy of the bodies, and the wide range of pressure variation (up to 150 MPa) inferred from CO₂ fluid inclusion densities and related decrepitation textures. The abundance of clasts derived from depth, rather than from the adjacent wallrocks, suggests that the pressure in the pipes was sufficient to restrict the inwards spalling of fragments from breccia walls; that is, the breccias were explosive rather than implosive, and some may have vented to the surface. At these depths, such extreme behaviour may have been achieved by release of dissolved fluids from crystallizing magma, in combination with a strongly fractured and fluid‐laden carapace, sitting under a strong, low permeability barrier. The relationship of these breccias to the Ernest Henry iron‐oxide–Cu–Au deposit suggests they may have been sources of fluids or mechanical energy for ore genesis, or alternately provided permeable pathways for later ore fluids.     

Chlorine stable isotope ratios as tracer for pore‐water advection rates in a submarine gas‐hydrate field: implication for hydrate concentration

At Ocean Drilling Program Site 997 in Blake Ridge gas‐hydrate field in West Atlantic, pore‐water studies revealed a pronounced downward depletion of the heavy chlorine isotope to nearly ?4‰δ³⁷Cl at approximately 750 m below sea floor (mbsf) associated with a 10% downward chlorinity decrease. This is one of the stronger ³⁷Cl depletions hitherto reported for marine pore waters. Chlorinity reductions in hydrate‐bearing sediments commonly result from fresh‐water release by hydrate melting. However, in situ measurements at Site 997 suggest that >50% of the chlorinity reduction occurred prior to hydrate dissociation. Modeling the chlorinity profile shows that advection of a strongly ³⁷Cl‐depleted, low‐chlorinity water (506 mm ) from below the drilled sequence can explain the reduction prior to sampling. Fitting the model to the δ³⁷Cl curve yielded an advection rate of 0.18 mm year^?1. Diffusive mixing with near‐0‰‐δ³⁷Cl paleo‐seawater with maximum chlorinity at shallow subsurface depths (561 mm at approximately 20 mbsf) produced the smooth, steady trend. Separating that part of the freshening caused by advection and diffusion from that due to hydrate dissociation allowed estimation of average hydrate concentrations of 3.8% of the pore space (up to 24.5% in hydrate‐rich layers; near‐100% in rare massive hydrate layers). The deep‐seated source of the ³⁷Cl‐depleted, low‐chlorinity water remains unknown and might be located below the sedimentary section in the oceanic basement.     

Ultrastructure and DNA sequence analysis of single Concentricystis cells from Alta Val Tiberina Holocene sediment

We successfully combined ultrastructure and chloroplast DNA analysis for single specimens of Concentricystis isolated from Holocene sediment by a palynology method based on filtration, progressive sieving and percoll-gradient sedimentation to concentrate fossil cells. We compared our method with the traditional harsh chemical treatment commonly used to isolate fossil pollen and spores. With our method, the cytoplasm of Concentricystis was sufficiently preserved to distinguish several cell structures by light and electron microscopy. DNA analysis of Concentricystis involved PCR amplification using specific primers for a spacer region of the chloroplast genome. Significant homologies were found with the Angiosperm chloroplast genome by BLAST DNA search for PCR product sequences.     

A modified sampler for uncontaminated DNA cores from soft sediments

A piston-type mud sampler is described. It is a development of the Livingstone corer and was designed to extract cores for DNA analysis of sediments. Prevention of contamination was paramount. As the entire system is self-contained and the sample is retained in the corer, it was found ideal for extracting very soft sediments which could not be captured by existing corers.     

The Late Upper Paleolithic occupation of the northern Tibetan Plateau margin

The pre-Neolithic history of the Tibetan Plateau is virtually unknown. Test excavations of Late Paleolithic sites, described here, provide preliminary evidence that the initial occupation of the plateau's extreme environments was by small groups of foragers probably traveling from lower elevation plateau margins. These foragers occupied very short-term camps focused on the procurement and extensive processing of small-to-medium mammals. Five separate occupations date to 13–15,000 Cal yr BP, but limited survey data suggest mid-elevation locations may have been temporarily occupied as early as 25,000 years ago. Full-time, year-round occupation of the plateau probably did not take place until the early Neolithic advent of domesticated animals.