ALBERT

Description: The intercalating growth of new silicate layers or metal hydroxide layers in the interlayer space of other clay minerals is known from various mixed-layer clay minerals such as illite-smectite (I-S), chlorite-vermiculite, and mica-vermiculite. In a recent study, the present authors proposed that smectite-group minerals can be synthesized from solution as new 2:1 silicate layers within the low-charge interlayers of rectorite. That study showed how oxalate catalyzes the crystallization of saponite from a silicate gel at low temperatures (60ºC) and ambient pressure. As an extension of this work the aim of the present study was to test the claim that new 2:1 silicate layers can be synthesized as new intercalating layers in the low-charge interlayers of rectorite and whether oxalate could promote such an intercalation synthesis. Two experiments were conducted at 60ºC and atmospheric pressure. First, disodium oxalate solution was added to a suspension of rectorite in order to investigate the effects that oxalate anions have on the structure of rectorite. In a second experiment, silicate gel of saponitic composition (calculated interlayer charge –0.33 eq/O 10 (OH) 2 ) was mixed with a suspension of rectorite and incubated in disodium oxalate solution. The synthesis products were extracted after 3 months and analyzed by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The treatment of ultrathin sections with octadecylammonium ( n C = 18) cations revealed the presence of 2:1 layer silicates with different interlayer charges that grew from the silicate gel. The oxalate-promoted nucleation of saponite and talc crystallites on the rectorite led to the alteration and ultimately to the destruction of the rectorite structure. The change was documented in HRTEM lattice-fringe images. The crystallization of new 2:1 layer silicates also occurred within the expandable interlayers of rectorite but not as new 2:1 silicate layers parallel to the previous 2:1 silicate layers. Instead, they grew independently of any orientation predetermined by the rectorite crystal substrate and their crystallization was responsible for the destruction of the rectorite structure.

Description: A bstract :  The Bohai Sea coastal zone of China faces the Pacific Ocean to the east and the Eurasian continent to the west; hence, this region is influenced by both the ocean and continental landmasses. The Bohai Sea coastal zone has significant monsoon climate characteristics and a strong sensitivity to climate change. The Miaodao stratigraphical section (MDS) contains historical information about climate features in the region, especially the high-frequency variations during the last interglacial, sea-level changes, and the evolution of the East Asian monsoon. By analyzing the ages of various sedimentary facies in combination with proxy paleoclimatic indices (i.e., grain 〈 63 µm fraction, average grain size (Mz), clay + silt/sand content (SC/D), magnetic susceptibility, and the ratios Na 2 O/Al 2 O 3 and (Al 2 O 3 + TOFe)/SiO 2 , in the fifth segments of the MDS from the last interglacial (MDS5), we conclude that subsections 5a, 5c, and 5e were controlled by summer monsoons, whereas subsections 5b and 5d were formed when winter monsoons prevailed. These results were similar to oxygen isotope analyses from previous studies including the Spectral Mapping Project (SPECMAP) and the North Greenland Ice Core Project (NorthGRIP). Five and a half comparable oscillations in proxy indices that were dated to ca. 116.1, 118.3, 121.2, 122.7, 125.9, and 128.7 ka occurred within the MDS 5e subsection when winter monsoon winds strengthened. This millennial-scale climate variability during the Eemian period may have reached up to ten and a half oscillations with a quasi-periodicity of approximately a 1,470 year cycle during the late glacial period. This rapid period of climate change has been recorded in northern and central Europe, central Asia, and in East Asia. The climate-influencing mechanism was probably initiated by changes in solar activity and driven by the East Asian monsoon and sea-level oscillations.

Description: Neoichnological experiments with vinegaroons (Arachnida: Thelyphonida: Thelyphonidae) were conducted to describe the trackway patterns, evaluate the preservation quality and potential of its trackways in different sediment textures and moisture conditions, and compare them to trackways found in the fossil record. Trackways were produced in nine experimentally controlled variations of sediment size (fine-, medium-, or coarse-grained sand) and moisture added to the sediment surface (0 mL, 5 mL, or 10 mL). Trackways were photographed and video recorded during trackway production, and cast in plaster. Individual tracks were oblong to linear, with the first and third foot on each side producing a track parallel to the direction of motion, and the second foot producing a track perpendicular to the direction of motion. Video evidence indicates that track associations form a triangular pattern with the track of the second foot furthest from the midline of the trackway, rather than a linear pattern as described for most other arthropod trackways. The morphology of vinegaroon trackways is indicative of hexapedal motion. Though similar to some fossil trackways attributed to eurypterids, vinegaroons are not good locomotion analogs for eurpyterids. No fossil trackway has been attributed to vinegaroons, so these trackways can serve as a model for assessment of fossil trackways. Trackway expression decreased as a function of increasing moisture content and grain size, with tracks becoming less oblong and more circular before ultimately becoming unexpressed on the surface. These trackways are more similar to the ichnogenus Hexapodichnus than to Lithographus . We propose a system to distinguish arthropod trackways based on the orientation of the triangular track series.

Description: Corals are important marine archives for high-resolution reconstructions of low-latitude climate variability in preinstrumental and historical periods. Herein, we present monthly-resolved records of 18 O and Sr/Ca for the 20th century (1917–2007) from a Porites lutea colony from the Maldives (northwestern Indian Ocean). Previous studies of annual mean extension rates of this coral revealed a distinct dependency of coral growth on variations of sea surface temperature (SST) and hydraulic energy, driven by El Niño-Southern Oscillation (ENSO) and southwestern Indian monsoon forcing. This enables the investigation of coral 18 O and Sr/Ca ratios from the Maldives as archives of historical ENSO and Indian monsoon variability. Unlike other locations in the Indian Ocean, correlation of 18 O and SST is weak (r = –0.42; p 〈 0.001), suggesting interferences of SST and seawater 18 O at the location. These interferences probably caused significantly weaker interannual ENSO signatures in 18 O as evident in the extension rates of our coral and in geochemical proxies measured at other sites in the northwestern Indian Ocean. Sr/Ca ratios show bias by nontemperature effects, and were not used to estimate seawater 18 O and salinity. Strong decadal variability (10–14 years) in 18 O, indicative of a Pacific ENSO signal, is not found in instrumental SST, and could be explained by variations in salinity. Interannual and decadal monsoon variability (6–7 yrs and 18–19 yrs), found in the extension rates, was not found in 18 O, suggesting, in agreement with other studies, that geochemical coral proxy records from the northwestern Indian Ocean do not capture temporal variations of the Indian monsoon strength.

Description: Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74–91±0.5–3.3 meq/100 g and exchangeable cation values of 22–61±1.2–3.9 meq/100 g Na + , 7–23±0.8–1.5 meq/100 g Mg 2+ , and 19–39±0.8–1.6 meq/100 g Ca 2+ . The precision was comparable to the standard Cu-trien method even for exchangeable Ca 2+ , although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep.CAN bentonite exchangeable Ca 2+ values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca 2+ values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na + , Mg 2+ , and Ca 2+ values.

Description: Clay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p'-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p'-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked with p,p'-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30{degrees}C. Results revealed a progressive decrease in p,p'-DDT and increase in p,p'-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

Description: Predatory drill holes in marine invertebrates are an important source of information on the nature of biotic interactions and are often used to explore the ecological and evolutionary roles of such interactions in deep time. Measures of drilling frequencies and drill-hole site stereotypy represent the raw data for inferring the intensity and selectivity of drilling predation. One potential source of bias explored in this study relates to the hydrodynamic properties of shells: presence of drill holes and/or drill-hole position may influence how shells behave when subjected to moving fluids. In a unidirectional flow-tank study with the bivalve Donax scortum Linnaeus, 1758, we found that the threshold current velocity for the entrainment of undrilled convex-up shells is significantly lower than for centrally drilled shells, which could be explained by Bernoulli's principle. The position of the drill hole on a shell also affects its hydrodynamic properties because umbonally drilled shells require a lower entrainment velocity than centrally drilled shells. This difference could potentially result in assemblages of different stereotypic patterns. We also demonstrate the extent of alteration of an assemblage by this process using a simulation parameterized with experimental results. The latter show that a dramatic change in inferred drilling intensity, size selectivity, and stereotypic patterns from the original population can be produced by hydrodynamic sorting. Our study indicates that such sorting can yield a sample significantly different from the original one in terms of drill-hole characteristics. Hence, the effect of such bias should be assessed before inferring the nature of biotic interaction of fossil assemblages.

Description: Occurrences of articulated, multi-element skeletons of edrioasteroids provide evidence of sudden burial and an opportunity for detailed paleoecologic analysis. This study examines two catastrophically buried communities of edrioasteroids from Florence, Kentucky and Sharonville, Ohio. In these two occurrences, the edrioasteroids Isorophus cincinnatiensis , Streptaster vorticellatus , and Carneyella pilea utilized brachiopod and mollusk shells as hard substrates for attachment. Age structure analysis for specimens of Isorophus cincinnatiensis on both pavements show right-skewed distributions that are attributed to high juvenile mortality. Thecae on the Florence pavement have slight bimodal preferential orientation, likely in response to current flow, whereas no preferential thecal orientation was noted for specimens on the Sharonville pavement. Spatial analysis of the Florence pavement indicates a clustered edrioasteroid distribution resulting from multiple edrioasteroids attached to single brachiopod shells. Edrioasteroid margin deformation, in response to inter- and intraspecific competition, provides evidence that edrioasteroids were unable to move once attached to the substrate. Spatial analysis for Isorophus cincinnatiensis on the Sharonville pavement shows few instances of multiple edrioasteroids attached to individual shells. Instead, this clustered distribution suggests enhanced encrustation in areas of enhanced survival (i.e., increased feeding opportunity). The high degree of thecal disarticulation on the Sharonville pavement suggests postmortem bloating and rupture.

Description: Surface locomotory trace fossils from the Mistaken Point Formation of Newfoundland, dated at ~ 565 Ma, suggest that organisms capable of controlled locomotion and possessing muscular tissue may have existed among Avalonian Ediacaran macrofossil assemblages. Here we describe the Mistaken Point trace-fossil assemblage in full, discuss its stratigraphic context within the Mistaken Point Formation, and explore the competing hypotheses for the formation of the traces. We find that the trace fossils, preserved within a turbidite succession in a deep-marine depositional environment, are not attributable to abiogenic structures, to Ediacaran tubular or filamentous body fossils, to rangeomorph stems, or to a host of late Ediacaran and early Phanerozoic ichnofossils. Specimens within the assemblage show some similarities to the ichnogenera Helminthoidichnites and Archaeonassa , but discrepancies in certain aspects of their structure mean that we do not formally attribute them to these ichnotaxa at this time. The Mistaken Point ichnofossils possess morphological characteristics indicative of formation by an organism with a round base. Comparison with traces formed by modern organisms of such character appears to rule out formation by protistan, echinoderm, or annelid styles of movement, but is consistent with organisms moving via muscular controlled locomotion in a similar way to some modern mollusks and actinian cnidarians. We suggest therefore that the Mistaken Point trace-fossil assemblage reveals the presence of muscular metazoans in late Ediacaran deep-marine ecosystems. Such organisms cannot yet be attributed to specific phyla, but their inferred locomotory mechanisms share closest similarities with those utilized by extant actinians.

Description: A bstract : Carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions. One concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital (lithogenic) marine calcite, thus compromising interpretations of stable-isotope compositions. To investigate the impact of lithogenic calcite on environmental interpretations using paleosols, we measured stable-isotope ratios in pedogenic carbonates and coexisting soil organic matter (SOM) in modern Vertisols (fine, smectitic, thermic, Udic Haplusterts) from Riesel, Texas (Heiden series) and Zabcikville, Texas (Houston Black series) forming on Cretaceous chalk deposits. The pedogenic and lithogenic components in the Heiden series soil at Riesel were identified using micromorphology and cathodoluminescence (CL), which showed incorporation of luminescent marine allochems (i.e., foraminifera, mollusks) into hard nodules and soft powdery pedogenic masses. Additionally, micromorphology showed evidence of meteoric recrystallization of the allochems. Despite the presence of these inherited carbonates into hard nodules and soft powdery masses, the stable-isotope compositions recorded a partial pedogenic signal. Recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils. This study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions. However, overprinting of marine allochems, if present, can be important and needs to be identified using micromorphology and cathodoluminescence, before using stable-isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions.