Downstream changes of large-scale bedforms in turbidites around the Valencia channel mouth,north-west Mediterranean: implications for palaeoflow reconstruction

Side-scan sonar, seismic and core data are used to identify mega-flutes, transverse and ‘V’ shaped bedforms in turbidites around the Valencia channel mouth, north-west Mediterranean. Long-range side-scan sonar data reveal a broad, curved, asymmetric, channel, that widens and terminates downfan. The western channel bank near the channel mouth has been partly eroded by turbidity currents that spilled out of the channel. Transverse bedforms on the east of the channel floor are interpreted as antidunes and, if this interpretation is correct, they indicate that the flow was probably supercritical at least locally within the channel. Trains of mega-flutes, are incised into coarse-grained sediments of the channel floor near the channel mouth. The association of mega-flutes and antidunes is thought to be diagnostic of channel–lobe transitions on deep-sea fans. The mega-flutes pass downfan into an area of streaks that diverge at up to 45° and indicates flow expansion from the channel mouth. About 75 km downfan from the channel mouth, deep-towed side-scan data record transverse bedforms (interpreted as antidunes) passing downfan into an area covered by ‘V’ shaped bedforms with upflow pointing apices (named chevrons here). The chevrons are commonly c. 200 m from limb to limb and c. 2 m in amplitude with flow-parallel wavelengths of c. 400 m. We propose that chevrons were formed by a strong, probably supercritical (or near critical) turbidity current spreading from the channel mouth and flowing towards the Balearic Abyssal Plain. Thinning of the turbidity current, resulting from flow spreading would allow the Froude number to remain high up to 100 km from the channel mouth and could explain the observed reduction in antidune wavelength.     

Compositional diversity in insoluble organic matter in type 1, 2 and 3 chondrites as detected by infrared spectroscopy

Insoluble organic matter (IOM) isolated from 22 carbonaceous and ordinary chondrites spanning a wide range of groups and petrologic types were analyzed using Fourier transform infrared spectroscopy (FTIR). Based on common IR spectral features, it is observed that IOM falls into 4 molecularly distinct groups (designated here as A through D). Spectral group A includes type 1 and 2 chondrites and exhibits intense aliphatic C-H and carboxyl vibrational peaks. Spectral group B includes the least metamorphosed type 3 chondrites and Tagish Lake, and exhibits weaker aliphatic and carboxyl vibrational intensity. Spectral groups C and D include metamorphosed type ?3.1 chondrites and a heated CM chondrite. The carbonyl stretching features in spectral groups C and D differ from that in spectral groups A and B and from each other. In spectral group C, the carbonyl stretching is assigned to cyclic unsaturated lactones; in spectral group D carbonyl exists predominantly in the form of unsaturated ketone moieties. Both spectral groups C and D have a relatively narrow band structure around 1210 cm⁻¹ (assigned to aromatic skeletal modes) as compared with spectral groups A and B, which is consistent with the formation of more condensed aromatics by extensive thermal metamorphism. The differences in carbonyl structures in spectral groups C and D are not the result of different effective metamorphic temperatures, rather these differences likely result from variation in the activity of water and oxygen at different stages of parent body metamorphism. Such environmental variations must be local phenomena in the parent bodies as there is no correlation between spectral grouping and chondrite class or group.     

Structural controls on the pathways and sedimentary architecture of submarine channels: New constraints from the Niger Delta

In submarine settings, the growth of structurally influenced topography can play a decisive role in controlling the routing of sediments from shelf-edge to deep water, and can determine depositional architectures and sediment characteristics. Here we use well-constrained examples from the deep water Niger Delta, where gravity-driven deformation has resulted in the development of a large fold and thrust belt, to illustrate how spatial and temporal variations in the rate of deformation have controlled the nature and locus of contrasting depositional styles. Published work in the study area using 3D seismic data has quantified the growth history of the thrust-related folds at multiple locations using line-length-balancing, enabling cumulative strain for individual structures over time and along-strike to be obtained. We integrate this information with seismic interpretation and facies analysis, focusing on the interval of maximum deformation (15 to 3.7 Ma), where maximum strain rates reached 7%/Ma. Within this interval, we observe a vertical change in depositional architecture where: (1) leveed-confined and linear channels pass upward in to (2) ponded lobes with erosionally confined channels and finally (3) channelised sheets. Our analysis demonstrate that this change is tectonically induced and diachronous across the fault array, and we characterise the extent to which structural growth controls both the distribution and the architecture of the turbidite deposits in such settings. In particular, we show that leveed-confined channels exist when they can exploit strain minima between growing faults or at their lateral tips. Conversely, as a result of fault linkage and increased strain rates submarine channels become erosional and may be forced to cross folds at their strain maxima (crests), where their pathways are influenced by across-strike variations in shortening for individual structures. Our results enable us to propose new conceptual models of submarine channel deposition in structurally complex margins, and provide new insights into the magnitude of fault interaction needed to alter depositional style from leveed to erosionally confined channels, or to deflect seabed systems around growing structures.     

Pollution history of the savannah river estuary and comparisons with Baltic Sea pollution history

The sediment record, as revealed in sediment cores, can be used to reconstruct the history of contaminant input into estuaries. The basic assumptions are that contaminant inputs equilibrate relatively rapidly with sediment inputs and that the sediment column represents a continuous sequence of sediment and associated contaminant accumulation. With radiochemical chronologies, it is possible to date sediments over a period corresponding to about five half-lives (100 years for ²¹⁰Pb). In our study we reconstruct the pollution history of the Savannah Estuary, which is a typical estuary in the South Atlantic Bight. A series of cores were taken in the estuary, followed by the analysis of the cores for a variety of organic and inorganic contaminants. Ages were assigned to different depth intervals by the use of two radiotracers, ²¹⁰Pb and ¹³⁷Cs. The major pesticides found were an isomer of DDT and dieldrin. The peak in their concentrations (1967) correlated with peak use of these pesticides before their use was banned. Between 1959 and 1962, there was more input of anthropogenic PAHs than before and after this period. The metals which showed significant changes in the cores include mercury, lead and chromium. Chromium reached a maximum during the late 1950s, followed by a decrease in the late 1960s. This chromium peak coincided with the initial operation of a titanium dioxide pigment plant in the Savannah Estuary. An interesting aspect of the study, which has been noted by many pollution history studies, was the decrease in the concentration of anthropogenic chemicals during the past two decades, suggesting that pollution controls have been effective, even while industrial and population growth was taking place.Similar studies have been carried out to reconstruct the historical record of contamination in the Baltic Sea. Concentrations of metals were found to increase after 1880 (industrial revolution in northern Europe). PCBs peaked in concentration in the late 1960s and the early 1970s, while DDT peaked in the 1960s. The Baltic experienced a major input of nutrients (N and P) after 1965 resulting from heavy use of fertilizers in this region.     

Magnetic field at the core boundary in the nearly symmetric hydromagnetic dynamo z

Summary The behaviour of the poloidal and toroidal magnetic field at the core-mantle boundary is analysed in more detail, assuming that the conductive layer in the lowest mantle is thin. We can conclude that, in the case of the Z-model of the nearly symmetric hydromagnetic dynamo, the poloidal field may be considered potential everywhere in the mantle and that the azimuthal field depends on the geostrophic azimuthal velocity in the same manner as derived in[1] and[3].

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aau ¶rt;-amu n¶rt;nuu m n¶rt; amuu aauum n¶rt;u nu¶rt;a u mu¶rt;a n. am ¶rt;, m Z-¶rt;u nmu umuu¶rt;aum ¶rt;ua aum nu¶rt;a n umam nmua ¶rt; amuu a n¶rt;u . ¶rt;m¶rt;am na [1] u [3] auum auma aum n m auma mu.

     

Remobilization of authigenic uranium in marine sediments by bioturbation

Uranium behaves as a nearly conservative element in oxygenated seawater, but it is precipitated under chemically reducing conditions that occur in sediments underlying low-oxygen bottom water or in sediments receiving high fluxes of particulate organic carbon. Sites characterized by a range of bottom-water oxygen (BWO) and organic carbon flux (OCF) were studied to better understand the conditions that determine formation and preservation of authigenic U in marine sediments. Our study areas are located in the mid latitudes of the northeast Pacific and the northwest Atlantic Oceans, and all sites receive moderate (0.5 g/cm² kyr) to high (2.8 g/cm² kyr) OCF to the sediments. BWO concentrations vary substantially among the sites, ranging from <3 to ∼270 μM. A mass balance approach was used to evaluate authigenic U remobilization at each site. Within each region studied, the supply of particulate nonlithogenic U associated with sinking particles was evaluated by means of sediment traps. The diffusive flux of U into sediments was calculated from pore-water U concentration profiles. These combined sources were compared with the burial rate of authigenic U to assess the efficiency of its preservation. A large fraction (one-third to two-thirds) of the authigenic U precipitated in these sediments via diffusion supply is later regenerated, even under very low BWO concentrations (∼15 μM). Bioturbating organisms periodically mix authigenic U-containing sediment upward toward the sediment-water interface, where more oxidizing conditions lead to the remobilization of authigenic U and its loss to bottom waters.     

NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups

Solid-state ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake. These solid state NMR experiments reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by reductions in aliphatic (sp³) carbon moieties, e.g., “CH_x,” and “CH_x(O,N).” Oxidized sp² bonded carbon, e.g., carboxyls and ketones grouped as “CO,” are largely conservative across these meteorite groups. Single pulse (SP) ¹³C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds with an apparent concentration ranking in the IOM of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that, on average, the aromatic moieties in the IOM of all four meteoritic IOM fractions are highly substituted. Fast spinning SP ¹H MAS NMR spectral data combined with other NMR experimental data reveal that the average hydrogen content of sp³ bonded carbon functional groups is low, requiring a high degree of aliphatic chain branching in each IOM fraction. The variation in chemistry across the meteorite groups is consistent with alteration by low temperature chemical oxidation. It is concluded that such chemistry principally affected the aliphatic moieties whereas the aromatic moieties and nanodiamonds may have been largely unaffected.     

Tsunami awareness: a comparative assessment between Japan and the USA

Awareness about the threats posed by different types of coastal disasters has increased throughout the world, as people are exposed to the nature of these hazards through media reports on events in distant countries. This has resulted in coastal residents being aware about the destructive power of tsunamis, despite no such events having taken place in their country in recent times. Regardless of this increased awareness, it has been hypothesized that there is still need for local governments to enact adequate policies to raise the awareness of local residents, for example, by holding regular evacuation drills. The present research presents a comparative assessment of tsunami awareness in two tourist destinations in Japan and the USA, which was derived through structured questionnaire surveys of beach users in the city of Kamakura and various coastal cities in Florida. The results show how despite relatively high level of awareness tsunamis still pose a considerable risk to each of the communities, for example, due to shortcoming in evacuation knowledge and infrastructure.