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Neoichnology of an Arctic fluvial point bar, North Slope, Alaska (USA)

Martin A. J.

Geological Quarterly

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2009

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Vol. 53, No 4

383-396

EN

This study is the first to describe the neoichnology of an Arctic fluvial point bar (Colville River, Alaska, USA) and examine the sedimentological effects of tracemakers in this sedimentary setting. Seasonal extremes in discharge and sediment deposition in this system result in sandwaves, current ripples, gravel bars and mud veneers, with the latter forming extensive mudcracks. Organismal traces are abundantly represented in sandy mudflats on the downstream portion of the point bar and are characterized by: (1) abundant shallow horizontal invertebrate burrows and surface trails, directly comparable to Treptichnus, Cochlichnus and Aulichnites; (2) avian tracks and (3) large mammal tracks. Treptichnus-like burrows are attributed to dipteran larvae tracemakers, whereas Cochlichnus- and Helminthoidichnites-like trails were likely from nematodes or oligochaetes. Avian tracks are primarily from seagulls, geese, swans and plovers; mudcracks were connected directly to tracks, which developed as a result of in creased amounts of sunlight available during the polar summer. Mam mal tracks were dom i nated by those of caribou (Rangifer tarandus), but include grizzly bear (Ursos arctos) and other mammals. Caribou herds significantly impacted emergent and submergent mudflat surfaces through advection of saturated thixotropic muds and dry sand, while also fracturing mudcracked zones, and hence actively produced mud clasts. Vertebrates thus can cause considerable mixing, redistribution and erosion of sediments in Arctic point bars with only a few months of activity. Ichnodiversity was low but accompanied by high trace abundance, reflecting fa vorable hydrodynamic, solar and atmospheric conditions throughout a polar summer. In contrast, sedimentation and bioturbation are absent during winter months, when ice cover prevents organismal interactions with fluvial sediments. As a reult, the ichnocoenose does not fit easily into paradigms of previously defined continental ichnofacies (e.g., Mermia and Scoyenia) and is more like a composite ichnofacies. These findings can thus serve as a starting point for more detailed studies of circum polar point bars, while also adding new perspectives to the interpretation of trace fossils in circum polar fluvial environments.

2

An Energy-Based Cohesion Function for Cubic Equations of State

Figueira F., Rodríguez A., Stamateris B., Olivera-Fuentes C.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 1

81-97

EN

Acohesion function is derived for cubic equations of state of van derWaals type, based on the behaviour of the residual internal energy of pure fluids; it contains two fluid-specific constants and is therefore suitable for nonpolar and polar fluids. The characteristic constants are obtained for the van derWaals, Redlich-Kwong and Peng-Robinson equations for 846 fluids by fitting cohesion parameters computed from vapour pressures taken from the DIPPR database. Comparison with similar functions proposed in the literature shows that the new function is generally better. A corresponding states generalization is presented using the acentric and critical compressibility factors.

3

On reducibility of the intersection curve of two second-order surfaces

Bieliński A., Łapińska C.

Journal Biuletyn of Polish Society for Geometry and Engineering Graphics

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2004

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Vol. 14

5--9

EN

A generalization of the well known theorem about the division of the common curve of two quadrics in two parts which are tangent to a common sphere is given.

PL

W pracy przedstawiono dowód twierdzenia o rozpadzie linii przenikania dwóch powierzchni drugiego stopnia stycznych do wspólnej kwadryki wzdłuż stożkowych. Idea dowodu polega na ustaleniu kolineacji środkowych zachodzących pomiędzy płaszczyznami stożkowych styczności i dowolną płaszczyzną, a następnie, korzystając z kolineacji pomiędzy przekrojami przenikających się powierzchni odpowiednio dobraną płaszczyzną, pokazanie, że przekroje te jednoczą się, uzyskując w ten sposób wspólną stożkową obu powierzchni. Sformułowano i udowodniono analogiczne twierdzenie dla dwóch kwadryk wpisanych w ten sam stożek.