Sphenothallus-Like Fossils from the Martinsburg Formation (Upper Ordovician), Tennessee, USA

Tubular fossils, up to 2 mm in diameter and 60 mm in length, occur rarely in the upper Martinsburg Formation (Upper Ordovician), northeastern Tennessee Appalachians, U.S.A. The fossils are unbranched, straight or slightly bent, occasionally twisted and wrinkled, and not significantly tapered. Orientation of the fossils within shallow-marine tempestites suggests that they represent remains of organisms that were broken, transported, and deposited by storm waves and currents. The fossils are morphologically similar to many of the previously identified species belonging to the genus Sphenothallus, a relatively rare tube-dwelling Paleozoic marine invertebrate. Owing to the limited evidence for distal widening of the tubes, lack of holdfasts, and carbonaceous rather than phosphatic composition, the affinity of these fossils remains uncertain, and we refer to them as Sphenothallus-like

Geochemical investigation of weathering in a high arctic watershed and provenance of ssediments in Kongressvatnet, Svalbard, Norway

This study uses changes in the chemistry and mineralogy of lake and surface sediments in a small lake in Kongress Valley (Kongressdalen), to interpret Late Holocene climate change in Western Spitsbergen, Svalbard. Changes in clay mineralogy across an inactive outwash fan (Black Fan) in the valley reflect weathering since the fan\u27s formation during the Little Ice Age (LIA) (1550-1920). X-Ray Diffraction analysis of clay samples from the meltwater channels and the Kapp Starostin rocks that compose the fan reveal a strong 10 Å peak, unaffected by ethylene glycol solvation or heating to 375 °C and 550 °C, indicative of illite. However, samples collected from vegetated debris flows between the meltwater channels reveal a diminished 10 Å phase and a slightly expandable peak at approximately 14 Å, unaffected by magnesium and glycerol saturation (d 060 of 1.54 Å), indicative of vermiculite. The inverse relationship between these peaks reflects the weathering of illite to vermiculite, suggesting an early period of Kapp Starostin Fm. deposition subsequently eroded by meltwater from Kongressbreen (glacier) during the LIA. Changes in lake sediment chemistry should reflect changing sources of sediment inflow as meltwater from an advancing ice activated the Black Fan. X-Ray Fluorescence analysis of the White and Black Fan, which are the two principle sources of sediment inflow to the lake, reveals that the Black Fan sediments have greater concentrations of K2O, Fe2O3, Zr, and Cr, while the White Fan is characterized by higher concentrations of MgO, CaO, Sr, and U. However, analysis of sediment cores from the central part of the lake reveals a chemical composition that resembles only that of the White Fan sediment, indicating almost no Black Fan input into Kongressvatnet. The most likely hypothesis to explain this absence is that Kongressbreen was a cold-based glacier and therefore did not produce fine glacial flour from bedrock scour. Despite the dominant White Fan signature in the core sediments, ITRAX Scanning XRay Fluorescence analysis reveals significant variations in core chemistry with depth, which is likely due to changes in climate. Periodic, massive high calcium layers, lacking internal laminations, characterize the upper 200 mm of the core, which correlates using MS to cores dated to the LIA (Guilizzoni et al., 2006). Preliminary SEM analysis reveals the presence of euhedral, sharp-edged rhombohedra and fibrous needles of calcite, high-Mg calcite, and dolomite, suggesting the precipitation of carbonate. The current supersaturation of Kongressvatnet waters below the chemocline with respect to calcite further supports this hypothesis. Alternatively, periods of extended ice cover during which the formation of lake ice concentrates the calcium in the underlying lake water, and may result in the formation of cryogenic calcite. Anomalous peaks in iron and sulfur characterize the lower portion of the core (300-400 mm), which MS correlations indicate corresponds to the Medieval Warm Period (Guilizzoni et al., 2006). An increase in organic terriginous inflow or lake productivity during this period likely spurs the activity of sulfur reducing bacteria, resulting in reducing conditions and the precipitation of iron sulfides. This analysis suggests that although provenance cannot be used in Kongressvatnet to constrain the timing of the Little Ice Age, changes in climate are intimately associated with fluctuations in lake chemistry and the lake\u27s biogeochemical cycles, providing the opportunity to interpret past climate change from lake sediment chemistry

Sphenothallus

Tubular fossils, up to 2 mm in diameter and 60 mm in length, occur rarely in the upper Martinsburg Formation (Upper Ordovician), northeastern Tennessee Appalachians, U.S.A. The fossils are unbranched, straight or slightly bent, occasionally twisted and wrinkled, and not significantly tapered. Orientation of the fossils within shallow-marine tempestites suggests that they represent remains of organisms that were broken, transported, and deposited by storm waves and currents. The fossils are morphologically similar to many of the previously identified species belonging to the genus Sphenothallus, a relatively rare tube-dwelling Paleozoic marine invertebrate. Owing to the limited evidence for distal widening of the tubes, lack of holdfasts, and carbonaceous rather than phosphatic composition, the affinity of these fossils remains uncertain, and we refer to them as Sphenothallus-like

Synthesis of Molecular Tripods Based on a Rigid 9,9'-Spirobifluorene Scaffold

The efficient synthesis of a new tripodal platform based on a rigid 9,9′-spirobifluorene with three acetyl protected thiol groups in the positions 2, 3′ and 6′ for deposition on Au(111) surfaces is reported. The modular 9,9′-spirobifluorene platform provides both a vertical arrangement of the molecular rod in position 7 and its electronic coupling to the gold substrate. To demonstrate the validity of the molecular design, the model compound 24 exposing a para-cyanophenylethynyl rod is synthesized. Our synthetic approach is based on a metal–halogen exchange reaction of 2-iodobiphenyl derivative and his subsequent reaction with 2,7-disubstituted fluoren-9-one to afford the carbinol 16. Further electrophilic cyclization and separation of regioisomers provided the corresponding 2,7,3′,6′-tetrasubstituted 9,9′-spirobifluorene 17 as the key intermediate. The molecular structure of 17 was determined by single-crystal X-ray diffraction crystallography. The self-assembly features of the target compound 24 were analyzed in preliminary UHV-STM experiments. These results already demonstrated the promising potential of the concept of the tripodal structure to stabilize the molecule on a Au(111) surface in order to control the spatial arrangement of the molecular rod