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    ABSTRACT: The South Atlantic has experienced periods of intense anoxia and black shale deposition that form an important hydrocarbon source. Here we have investigated the depositional environment during the initial opening phase of the South Atlantic during the Early Cretaceous. The period is crucial as it is characterized by extensive source rock deposition and because it sets the stage for subsequent periods of anoxia within the northern sub-basin of the South Atlantic. Within an Aptian sequence of organic-rich sediments (up to 40% total organic carbon, TOC) from Deep Sea Drilling Project (DSDP) Site 364, we found a distinct biomarker distribution, including the presence of isorenieratane and an array of thiophenic (S-containing) compounds. Our results indicate that, during the time of deposition, corresponding to the initial phase of opening of the South Atlantic, most of the water column in the Angola Basin was hypersaline (> 40‰) and euxinic, with euxinia episodically reaching the photic zone. The low relative abundance of marine biomarkers in the samples suggests that these extreme conditions were unfavourable for typical marine organisms. Stratigraphically up-section, the biomarker distribution changed as the TOC content gradually decreased (< 20 wt.%), isorenieratane and thiophenic compounds became less abundant and marine biomarkers became more abundant. We interpret the results to reflect a shift towards more open marine conditions, with less extensive euxinia/anoxia and normal marine salinity as the opening of the South Atlantic continued and the basin became less restricted. Our results demonstrate that the opening of the South Atlantic was the dominant control on the deposition of organic rich shales in the Angola Basin during the Aptian, highlighting the control of local basin geography on the depositional environment and formation of organic rich black shales during the Early Cretaceous.
    No preview · Article · Sep 2014 · Organic Geochemistry
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    ABSTRACT: Hypothesis: Silica nanoparticles can be dispersed in organic solvents (organosols) using surfactants, such as didodecyldimethylammonium bromide (DDAB). DDAB analogs prepared with lathanide tetrahalide counterions, either a high-magnetic moment ion (HoCl3Br, DDAH) or low-magnetic moment one (NdCl3Br, DDAN), are expected to produce charged particles, but only DDAH-stabilized dispersions are expected to be magnetically responsive. Experiments: Phase-analysis light scattering (PALS) measurements have been performed to determine the charge on DDAH- and DDAN-stabilized organosols. Magnetic sedimentation experiments have been performed to determine whether or not the silica dispersions are magnetically responsive. Sedimentation was monitored both by visual observations and UV-vis spectroscopy. Findings: Both DDAH and DDAN organosols are negatively charged, the same as DDAB-stabilized nanoparticles. The DDAH-stabilized nanoparticles are found to respond to a magnetic field, whereas the DDAN-stabilized nanoparticles do not. This opens up possibilities for creating nanoparticle dispersions in nonpolar solvents which can be tailored to respond to desired external stimuli.
    No preview · Article · Jul 2014 · Journal of Colloid and Interface Science
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    ABSTRACT: Pioneering work by Edler et al. has spawned a new sub-set of mesostructured materials. These are solid, self-supporting films comprising surfactant micelles encased within polymer hydrogel; composite polymer-surfactant films can be grown spontaneously at the air-liquid interface and have defined and controllable mesostructures. Addition of siliconalkoxide to polymer-surfactant mixtures allows for the growth of mesostructured hybrid polymer-surfactant silica films that retain film geometry after calcinations and exhibit superior mechanical properties to typically brittle inorganic films. Growing films at the air-liquid interface provides a rapid and simple means to prepare ordered solid inorganic films, and to date the only method for generating mesostructured films thick enough (up to several hundred microns) to be removed from the interface. Applications of these films could range from catalysis to encapsulation of hydrophobic species and drug delivery. Film properties and mesostructures are sensitive to surfactant structure, polymer properties and polymer-surfactant phase behaviour: herein it will be shown how film mesostructure can be tailored by directing these parameters, and some interesting analogies will be drawn with more familiar mesostructured silica materials.
    No preview · Article · Jul 2014 · Advances in Colloid and Interface Science
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