Late Pleistocene history of turbidite sedimentation in a submarine canyon off the northern Great Barrier Reef, Australia

Cores from slopes east of the Great Barrier Reef (GBR) challenge traditional models for sedimentation on tropical mixed siliciclastic-carbonate margins. However, satisfactory explanations of sediment accumulation on this archetypal margin that include both hemipelagic and turbidite sedimentation remain elusive, as submarine canyons and their role in delivering coarse-grained turbidite deposits, are poorly understood. Towards addressing this problem we investigated the shelf and canyon system bordering the northern Ribbon Reefs and reconstructed the history of turbidite deposition since the Late Pleistocene. High-resolution bathymetric and seismic data show a large paleo-channel system that crosses the shelf before connecting with the canyons via the inter-reef passages between the Ribbon Reefs. High-resolution bathymetry of the canyon axis reveals a complex and active system of channels, sand waves, and local submarine landslides. Multi-proxy examination of three cores from down the axis of the canyon system reveals 18 turbidites and debrites, interlayered with hemipelagic muds, that are derived from a mix of shallow and deep sources. Twenty radiocarbon ages indicate that siliciclastic-dominated and mixed turbidites only occur prior to 31 ka during Marine Isotope Stage (MIS) 3, while carbonate-dominated turbidites are well established by 11 ka in MIS1 until as recently as 1.2 ka. The apparent lack of siliciclastic-dominated turbidites and presence of only a few carbonate-dominated turbidites during the MIS2 lowstand are not consistent with generic models of margin sedimentation but might also reflect a gap in the turbidite record. These data suggest that turbidite sedimentation in the Ribbon Reef canyons, probably reflects the complex relationship between the prolonged period (> 25 ka) of MIS3 millennial sea level changes and local factors such as the shelf, inter-reef passage depth, canyon morphology and different sediment sources. On this basis we predict that the spatial and temporal patterns of turbidite sedimentation could vary considerably along the length of the GBR margin.

Filling the gap: A 60 ky record of mixed carbonate-siliciclastic turbidite deposition from the Great Barrier Reef

Late Pleistocene to Holocene margin sedimentation on the Great Barrier Reef, a mixed carbonatesiliciclastic margin, has been explained by a transgressive shedding model. This model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment (i.e. carbonate vs. siliciclastic) deposited during sea-level oscillations. However, this model documents only hemipelagic sedimentation and the contribution of coarse-grained turbidite deposition, and the role of submarine canyons in this process, remain elusive on this archetypal margin. Here we present a new model of turbidite deposition for the last 60 ky in the north-eastern Australia margin. Using highresolution bathymetry, 58 new and existing radiometric ages, and the composition of 81 turbidites from 15 piston cores, we found that the spatial and temporal variation of turbidites is controlled by the relationship between sea-level change and the variable physiography along the margin. Siliciclastic and mixed carbonate-siliciclastic turbidites were linked to canyons indenting the shelf-break and the welldeveloped shelf-edge reef barriers that stored sediment behind them. Turbidite deposition was sustained while the sea-level position allowed the connection and sediment bypassing through the interreef passages and canyons. Carbonate turbidites dominated in regions with more open conditions at the outer-shelf and where slope-confined canyons dominated or where canyons are generally less abundant. The turn-on and maintenance of carbonate production during sea-level fluctuations also influenced the timing of carbonate turbidite deposition. We show that a fundamental understanding of the variable physiography inherent to mixed carbonate-siliciclastic margins is essential to accurately interpret deep-water, coarse-grained deposition within a sequence stratigraphic context. 

A sedimentologic and 14C dating study of five eastern Australian upper continental slope submarine landslides

Sedimentologic and AMS 14C age data are reported for calcareous hemipelagic mud samples taken from gravity cores collected at sites within, or adjacent to five submarine landslides identified with multibeam bathymetry data on the Nerrang Plateau segment and surrounding canyons of eastern Australia's continental slope (Bribie Bowl, Coolangatta-2, Coolangatta-1, Cudgen and Byron). Sediments are comprised of mixtures of calcareous and terrigenous clay (10-20%), silt (50-65%) and sand (15-40%) and are generally uniform in appearance. Their carbonate contents vary between and 17% and 22% by weight while organic carbon contents are less than 10% by weight. Dating of conformably deposited material identified in ten of the twelve cores indicates a range of sediment accumulation rates between 0.017mka-1 and 0.2 mka-1 which are consistent with previous estimates reported for this area. One slide-adjacent core, and four within-landslide cores present depositional hiatus surfaces located at depths of 0.8 to 2.2 meters below the present-day seafloor and identified by a sharp, colour-change boundary; discernable but small increases in sediment stiffness; and a slight increase in sediment bulk density of 0.1 gcm-3. Distinct gaps in AMS 14C age of at least 20ka are recorded across these boundary surfaces. Examination of sub-bottom profiler records of transects through three of the within-slide core-sites and their nearby landslide scarps available for the Coolangatta-1 and Cudgen slides indicate that: 1) the youngest identifiable sediment layer reflectors upslope of these slides, terminate on and are truncated by slide rupture surfaces; and 2) there is no obvious evidence in the sub-bottom profiles for a post-slide sediment layer draped over or otherwise burying slide ruptures or exposed slide detachment surfaces. This suggests that both these submarine landslides are geologically recent and suggests that the hiatus surfaces identified in Coolangatta-1's and Cudgen's within-slide cores are either: a) erosional features that developed after the occurrence of the landslide in which case the hiatus surface age provides a minimum age for landslide occurrence or b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding in which case the post-hiatus sediment dates indicates approximately when landsliding occurred. In either case, it is reasonable to suggest that these two spatially adjacent slides occurred penecontemporaneously approximately 20,000 years ago.

Fluorescent PET (Photoinduced Electron Transfer) Sensors with Targeting/Anchoring Modules as Molecular Versions of Submarine Periscopes for Mapping Membrane-Bounded Protons

The two families of fluorescent PET (photoinduced electron transfer) sensors (1-9) show that the effective proton density near the surface of several micelle membranes changes over 2-3 orders of magnitude as the microlocation of the sensor (with respect to the membrane) is altered via hydrophobic tuning.

Sedimentology, structure and age estimate of five continental slope submarine landslides, eastern Australia

Sedimentological and accelerator mass spectrometry (AMS) 14C data provide estimates of the structure and age of five submarine landslides (∼0.4–3 km3) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka–1 and 0.2 m ka–1, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm–3, and distinct gaps in AMS 14C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation.

Post-depositional modification of atmospheric dust on a granite building in central Rio de Janeiro: implications for surface induration and subsequent stone decay

Extensive contour scaling of a 200 year old granite church is associated with the breaching of an apparently iron-rich crust and the widespread deposition of atmospheric dust within the canyon-like streetscape of Rio de Janeiro. Contemporary dust, accumulated dust from within the a depression on the building surface, the surface crust and the underlying granite are examined by a combination of total element analysis and sequential extraction, X-ray diffraction and energy dispersive X-ray fluorescence. Results indicate an increase in total organic carbon and a marked decrease in pH within the accumulated dust, and a rapid mobilization of anions and cations from the water-soluble and carbonate phases. It is considered that the latter is linked to salt accumulation within and eventual salt weathering of the granite. Post-depositional alteration of the dust is also linked with the de-silicification of clay minerals (Illite to kaolinite) and the loss of silica from the amorphous Fe/Mn phase of the accumulated dust under the initially saline and progressively more acidic conditions experienced at the stone - atmosphere interface. This mobilization of silica is associated with the formation of what is, in effect, a thin silica-rich surface crust or glaze. Within the glaze, assessory amounts of extractable iron are concentrated within the amorphous and crystalline Fe/Mn phases at levels that are significantly elevated with respect to the underlying granite, but much lower than the equivalent phases of the accumulated dust from which it is principally assumed to derive. The protection afforded to the stone work by the crust is not, however, permanent and within the last 15 years it has been possible to observe a rapid increase in the surface delamination of the church close to street level.

Comparative seasonal acclimatization of food and energy consumption in adjacent populations of common spiny mice (Acomys cahirinus)

Animals inhabiting environments with low productivity and food availability commonly have reduced energy demands and increased digestive efficiencies. The dry matter intake (DMI), apparent digestible dry matter (ADDM), digestible efficiency (DE) and digestible energy intake (DEI) of two populations of common spiny mouse Acomys cahirinus were compared during both winter and summer under conditions of simulated water stress. Mice were captured from the north- and south-facing slopes (NFS and SFS) of the same canyon that represent mesic and xeric habitats, respectively. Measured variables were also compared between F-1 mice that had been born to either NFS or SFS mice, and raised in the laboratory. SFS mice were able to assimilate energy more efficiently than NFS mice during the summer. By comparison, NFS mice were able to assimilate more energy during the winter. During winter, NFS mice assimilated more energy at low levels of water stress, whereas SFS mice assimilated more energy at higher levels. Differences were also apparent in F-1 mice. It is therefore suggested that local climatic conditions can impose physiological adaptations that are retained in succeeding generations, creating unique meta-populations.

Differential osmoregulatory capabilities of common spiny mice (Acomys cahirinus) from adjacent microhabitats

The osmoregulatory function of common spiny mice Acomys cahirinus living on opposite slopes of the lower Nahal Oren ('Evolution Canyon') on mount Carmel, Israel, was investigated by increasing the salinity of the water source whilst maintaining a high-protein diet. The southern-facing slope (SFS) of this canyon differs from the northern-facing slope (NFS) as it receives considerably more solar radiation and consequently forms a more xeric, sparsely vegetated habitat. During the summer, mice living on the two opposite slopes significantly differed in their urine osmolality, which also increased significantly as dietary salinity increased. Offspring of wild-captured mice, born in captivity, and examined during the winter, continued to show a difference in osmoregulatory function depending on the slope of origin. However, they differed from wild-captured mice, as they did not respond to the increase in dietary salinity by increasing the concentration of their urine, but rather by increasing the volume of urine produced. This study shows that A. cahirinus occupying different microhabitats may exhibit differences in their ability to concentrate urine and thus in their ability to withstand xeric conditions. We suggest that they may also differ genetically, as offspring from the NFS and SFS retain physiological differences, but further studies will be needed to confirm this hypothesis.

Inventors:Marconi's Device for Dialling the Dear Departed, The Flying Fenian

Two short site-specific pieces performed with others at the Royal Ulster Agricultural Show for Kabosh Theatre Company, as part of their continuing effort to broaden theatre audiences. One, using the form of the Edwardian melodrama, tells of Marconi's efforts to create a device to communicate with the dead. The second tells the tale of the Christian Brother who invented the submarine, John Philip Holland.