Some new Publications:: Sem Petrography of Eastern Mediterranean Sapropels: Analogue Data For Assessing Organic Matter In Oil and Gas Shales Kitty L. Milliken, Lucy T. Ko, Maxwell Pommer and Kathleen M. Marsaglia Examination of organic-matter-hosted pore systems in unconventional reservoir rocks has drawn attention to the appearance of sedimentary organic matter (OM) as seen in high-resolution SEM images. Field-emission SEM imaging of eastern Mediterranean sapropels (Pliocene–Pleistocene age from Ocean Drilling Program drill sites) was performed on samples prepared by Ar-ion cross-section polishing. The immaturity of marine kerogen in these rocks allows inspection of petrographic textures without overprints related to thermal maturation (hydrocarbon generation). Kerogen in these samples includes discrete particles that in some cases contain primary intragranular pores. The most abundant organic matter is in the form of microns-thick flaky or stringy material, largely nonporous and internally amorphous, and lacking the well-defined shapes of discrete particles. This dominant OM has behaved in a highly ductile manner in compaction and is now highly pervaded into intergranular spaces between silt- and clay-size grains. A portion of the larger mineral-hosted pores remain open, unfilled by ductile OM. Minor nanometer-scale pores of uncertain origin occur in the dominant OM. Silt- and clay-size mineral crystals are distributed in organic matter of most types, and it is difficult to fully ascertain if the OM/mineral mixing has occurred during compaction versus during aggregation during gravity settling (marine-snow sedimentation) or through sediment accumulation in OM-rich microbial mats. Results indicate that sediments rich in marine kerogen are subject to substantial compactional porosity loss in early burial. These observations of marine detrital organic matter in its early diagenetic state provide a useful baseline for interpretation of petrographic features in more mature OM-rich mudrocks. It is clear that petrographic discrimination of diagenetically generated organic matter (bitumen and related OM types) from ductile dispersed amorphous detrital OM (kerogen) using SEM data will be challenging in the absence of compositional information. ________________________________________________ Calcareous nannofossil response to the Weissert episode (Early Cretaceous): Implications for palaeoecological and palaeoceanographic reconstructions Stéphanie Duchamp-Alphonse,, Silvia Gardin, Annachiara Bartolini The causal link between changes in calcareous nannofossil abundances, their size and the palaeoenvironmental conditions in the Tethyan Realm across the Valanginian Weissert episode was examined through high-resolution quantitative analyses of the genera Nannoconus and Micrantholithusfrom the Angles section (Vocontian Basin, SE France). A set of published mineralogical, micropalaeontological and geochemical data from numerous European localities (including nannofossil data from Italy, France and Romania) and from the Atlantic and Pacific Oceans, allows us to propose a coherent palaeoecological and palaeoceanographic model, and to discuss the possible forcing factors behind the palaeoenvironmental changes that occurred during the Valanginian. In the Vocontian Basin, the genus Nannoconus appears to be particularly sensitive to global fertility conditions and local continental input while Micrantholithus is clearly associated with salinity levels. During the first phase of the Weissert episode, a global increase in nutrients, together with a breakdown of the upper water column stratification explains the nannoconid decline. Elevated freshwater fluxes into the Vocontian Basin under warmer and more humid conditions account for pentalith decreases. Low-resolution data on pCO2 and ocean Ca2 +concentrations cannot highlight large-magnitude rapid fluctuations in pCO2 and oceanic Ca2 + if they exist. However, relatively low pCO2 levels and high oceanic Ca2 + concentrations probably helped the recovery ofNannoconus and Micrantholithus from the aftermath of the Weissert episode to the early Hauterivian. The long-term changes observed in the Valanginian nannolith distribution are consistent with increased hydrothermal activity that influenced fertility levels. Low- to mid-latitudinal monsoonal circulation probably contributed to their short-term changes by the way of rapid changes in the chemical weathering pattern that triggered significant fluctuations in turbidity, fertility, and salinity conditions. ________________________________________________ Solar UV Irradiances Modulate Effects of Ocean Acidification on the Coccolithophorid Emiliania huxleyi Kai Xu and Kunshan Gao Emiliania huxleyi, the most abundant coccolithophorid in the oceans, is naturally exposed to solar UV radiation (UVR, 280-400 nm) in addition to photosynthetically active radiation (PAR). We investigated the physiological responses of E. huxleyi to present-day and elevated CO2 (390 vs 1000 μatm; with pHNBS 8.20 vs 7.86) under indoor constant PAR and fluctuating solar radiation with or without UVR. Enrichment of CO2 stimulated the production rate of particulate organic carbon (POC) under constant PAR, but led to unchanged POC production under incident fluctuating solar radiation. The production rates of particulate inorganic carbon (PIC) as well as PIC/POC ratios were reduced under the elevated CO2, ocean acidification (OA) condition, regardless of PAR levels and the presence of UVR. However, moderate levels of UVR increased PIC production rates and PIC/POC ratios. OA treatment interacted with UVR to influence the algas physiological performance, leading to reduced specific growth rate in the presence of UVA (315-400 nm) and decreased quantum yield, along with enhanced non-photochemical quenching, with addition of UVB (280-315 nm). The results clearly indicate that UV radiation needs to be invoked as a key stressor when considering the impacts of ocean acidification on E. huxleyi. _____________________________________________________ The mid-Valanginian Weissert Event as recorded by calcareous nannoplankton in the Vocontian Basin Emanuela Mattioli, Bernard Pittet, Laurent Riquier, Vincent Grossi The mid-Valanginian Weissert Event represents one of the most significant paleoceanographic events of the Early Cretaceous and is characterized by a major perturbation of the carbon cycle testified by a positive carbon isotope shift, a crisis of both neritic and pelagic carbonate producers, and climatic fluctuations. Here we propose a paleoreconstruction of paleoenvironmental changes that occurred in the reference Vergol and La Charce sections (Vocontian Basin, SE France) during the Weissert Event based on the analysis of calcareous nannofossil absolute abundance and assemblages. These latter are compared to newly acquired and already published sedimentological and organic geochemical analyses. Our approach is novel for the time interval considered. Indeed, Principal Component Analysis was applied for the first time to the entire nannofossil assemblage to reconstruct environmental conditions, instead of using paleoecological preferences of single species. The comparison of calcareous nannofossils and biomarker analyses indicates that a phase of severe sea–water stratification occurred prior to the carbon positive excursion of the Weissert Event in the Vocontian Basin. This was followed by a raise in fertility of surface waters, as attested by increased nannofossil abundances, in particular, of meso–eutrophic taxa, and biomarkers likely produced by dinoflagellates. This increase in fertility was likely triggered by a humid climate and enhanced continental input of clays and nutrients to surface oceanic waters. Calcareous nannofossils also proved to react to sea-level changes that occurred in the Valanginian, as inferred by previous works. Species likely inhabiting proximal areas were recorded in higher proportions during a major sea-level drop in the Peregrinus Ammonite Zone, Late Valanginian. The results of this study also permit to revise previously proposed paleoecological affinities of some nannofossil species. We suggest that Watznaueria barnesiae, one of the most-widely used species in the literature, should be used cautiously because of its high plasticity with respect to environmental conditions. Also, nannoconids that are usually regrouped in papers with paleoceanographic purposes should be analyzed separately because they show distinct species-specific ecological preferences. __________________________________________________ Effects of ocean acidification and nutrient enrichment on growth of the planktonic coccolithophore Emiliania huxleyi Leah Hayden Ocean acidification and eutrophication are relevant anthropogenic-caused stressors that effect many marine organisms. Emiliania huxleyi is a unique model organism for its responses to these stressors. This experiment utilized a pulse chemostat microcosm design to measure the effect of elevated CO2 concentrations and nutrient enrichment on E. huxleyi growth. CO2 concentrations were manipulated to 150 µatm and 4000 µatm and nutrient concentrations were manipulated to 30 µM NO3-/1.9 µM PO43- and 300 µM NO3-/19 µM PO43- during a 12 day incubation period. Ocean acidification inhibited growth while nutrient enrichment increased growth. Together these stressors had a significantly increased effect on growth since nutrient enrichment ameliorated the effect of ocean acidification. E. huxleyi under low CO2 conditions retained their coccoliths after 12 days whereas those under high CO2 lost their coccoliths. This study demonstrates the importance of stressor interaction and the significant impact ocean acidification and eutrophication can have on our oceans.
Posted on: Mon, 03 Nov 2014 17:41:22 +0000
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