Ophiomorpha irregulaire, rare trace fossil in shallow marine sandstones, Cretaceous Atane Formation, West Greenland

Ophiomorpha irregulaire is a large and extremely rare trace fossil. The type section is in the Book Cliffs, Utah, USA. A second on-shore locality is reported here, in the Nuussuaq Basin of West Greenland. Both occurrences date from the Late Cretaceous. Other reports of O. irregulaire are restricted to two-dimensional sections in well cores and are mostly Jurassic in age. The West Greenland occurrence is in the Atane Formation in shallow marine clean sandstone. The two on-shore localities lie in the same biogeographical region, in connection with the Cretaceous Western Interior Seaway of North America. O. irregulaire is characterized by a sinuous, branched meander maze lying mostly within a single horizontal plane, probably not far beneath the seafloor. The burrow lining has remarkably elongate pellets that probably were emplaced by the burrower. In some cases, diagenetic compression may have deformed the lining pellets to produce their elongated shape. The muddy sediment comprising the lining is almost unrepresented in the clean sands of the substrate, and it was probably trapped from suspension during suspension-feeding activity.     

Response of a subtropical estuarine marsh to local climatic change in the southwestern Gulf of Mexico

We examined the contrasting, effects of floods and droughts produced by large changes in local climatology on vegetation patterns in Nueces marsh, a semi-arid subtropical salt marsh in south Texas from 1995 to 2005. Climate variations during the study included an initial 4-yr period of moderate conditions, followed by a 2-yr interval of drought, and a recent 4-yr wet period that included large-scale floods. Variation in freshwater inflow, rainfall, and potential evapotranspiration were used in conjunction with field measurements of salinity, inorganic nitrogen, and vegetation structure collected at sites located at varying distances from Nueces Bay. Tidal creek salinities varied with Nueces Bay salinity, with strength of effect inversely related to distance from the bay. Mean (±standard deviation) pore water salinities ranged from 59±54‰ at two high, marsh stations farthest from the bay (10.1 km distant) to 30±21‰ in soil at a low marsh site closest to the bay (0.5 km distant). Mean pore water ammonium was also higher at stations most distant from the bay; nitrate + nitrite did not exhibit a high marsh to low marsh gradient. Nueces Bay salinity decreased substantially when the 10-d cumulative mean daily Nueces River flows exceeded 10 m³ s⁻¹. During periods of low and moderate flood frequency (flows mostly below 10 m³ s⁻¹), vegetation assemblages were dominated by stress-tolerant clonal plants. A catastrophic flood, which immersed vegetation for several weeks between July and September 2002, resulted in extensive plant mortality, but within months, unvegetated areas were rapidly colonized by the obligate annualSalicornia bigelovii. With the end of major flooding by late 2004, plant community structure began a return to pre-drought assemblages at high and middle marsh stations by summer 2005. At the low marsh station, new conditions favored clonal dominants (Spartina alterniflora andBorrichia frutescens), with the latter replacingSalicornia virginica as the dominant species. Our results support the theory that the importance of competition and abiotic stress in determining community composition are inversely related.     

Aragonite cycles: diagenesis caught in the act

Organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession. A record from the Early Pliocene of the Maldives (Ocean Drilling Program, ODP Leg 115) is presented containing precession and eccentricity cycles expressed as variable aragonite content. Additional sub‐Milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval. Comparison with palaeo‐productivity indicators (nannofossils, chlorin, total organic carbon) suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity. The coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment. The observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on Milankovitch and sub‐Milankovitch scales. Diagenetically stable proxies for palaeo‐productivity, such as nannofossil assemblage data, were used to distinguish between palaeoclimate and diagenetic influences.     

Testing earthquake prediction methods: «The West Pacific short-term forecast of earthquakes with magnitude MwHRV ≥ 5.8»

Analyzing the tables and probability maps posted by Yan Y. Kagan and David D. Jackson in April 2002–September 2004 at http://scec.ess.ucla.edu/~ykagan/predictions_index.html and the catalog of earthquakes for the same period, the conclusion is drawn that the underlying method could be used for prediction of aftershocks, while it does not outscore random guessing when main shocks are considered.