Architecture and recognition criteria of ancient shelf ridges; an example from Campanian Almond Formation in Hanna Basin,USA

Shelf ridges are sedimentary bodies formed on the continental shelf due to transgressive reworking (tidal or storm) of lowstand deposits. Common on modern shelves, they are under‐represented in the geological record due to a lack of recognition criteria and facies model. This article proposes a new facies and architectural model for shelf ridges, linked to their inception–evolution–abandonment cycle and the process regime of the basin. The model is mainly based on new outcrop data and interpretations from three sandstone bodies of the Almond Formation, an overall transgressive interval during the infill of the Campanian Western Interior Seaway. Building from the case study, and ancient and modern examples, six characteristics are proposed for the recognition of ancient shelf ridges. Shelf ridges: (i) are encased between thick marine mudstone intervals; (ii) have a basal unconformity that erodes into marine muds or into the remnants of a previous shoreline; (iii) have a non‐erosional upper boundary that transitions into marine muds; (iv) are characterized by clean and well‐sorted sandstones, often cross‐bedded; (v) contain fully marine ichnofauna; and (vi) present compound architectures with large accretion surfaces and lower order structures. Although shelf ridges have been described in previous studies as generated exclusively by either tidal or storm currents, it is clear, from modern examples and the case study, that these two processes can be recorded and preserved in a single shelf ridge. The stratigraphy of these sandstone bodies is therefore much more complex than previously recognized, bearing the signature of changing tidal and storm intensity through time. Because they are developed during transgressions, shelf ridges are commonly subject to strong changes in process regime as sea‐level changes can easily affect the oceanographic conditions and the morphology of the basin. For this reason, shelf ridges can provide the best record of shelf process variability during transgressions.     

A search for carbon stars in the AFGL Catalogue

A comparison between theGeneral Catalogue of Cool Carbon Stars (CCS) and theAFGL Catalogue has been performed.Eighty-five stars have been found in common between the two lists. Eighty-four stars which were present in Baumert's comparison between CCS and the 2 Sky Survey have no counterpart in the AFGL. Four new tentative identifications are given. The analysis of the two colours diagrams K-[4.2 ] vs. I-K and I-[4.2 ] vs. [4.2 ]-[11 ] led to the conclusion that all the infrared emission from the sources seems to come from a single circumstellar shell.     

A search for S stars in the IRC and AFGL Catalogues

There is a clear relation between the amplitude of the visual light curve, the period and the luminosity of the low amplitude Scuti stars.     

Effects of some representative petroleum refinery effluent compounds on photosynthesis and growth of natural marine phytoplankton assemblages: Part 1—cresols

The effects of cresols on the photosynthesis and growth of natural marine phytoplankton assemblages from the Scripps Pier at La Jolla, California, USA were measured. In two experiments, in which dinoflagellates were the dominant algae, photosynthesis (measured by ¹⁴C uptake) was inhibited at concentrations > 100 μg litre^?1 and the concentration giving half-maximal photosynthesis was 10,000 μg litre^?1. In a third experiment, in which diatoms were dominant, photosynthesis was not inhibited until levels > 10,000 μg litre^?1 were reached and the half-maximal concentration was 20,000 μg litre^?1. These experiments suggested that dinoflagellates were more sensitive to cresols than diatoms. However, the reverse was true in an experiment using cultures. In a long-term growth experiment (natural assemblages from the Scripps Pier), only a level of 88,000 μg litre^?1 completely inhibited growth. There was a two-day lag in growth at 8500 μg litre^?1, but the algae recovered and grew as well as the controls which contained no cresols. This experiment was started with a mixed diatom-dinoflagellate-microflagellate population but only the diatoms grew. High concentrations of cresols (> 900 μg litre^?1) resulted in a decrease in the diatom Skeletonema costatum, compared with the controls. Otherwise there was no selection for resistant species. In these experiments, cresols were measured by extraction with methylene chloride from seawater followed by measurement by UV absorption. In all experiments cresol levels decreased with time. This was attributed to uptake by phytoplankton and bacterial degradation.     

Disturbance and Community Pattern of Polychaetes Inhabiting Valle Magnavacca (Valli di Comacchio,Northern Adriatic Sea,Italy)

Abstract. Polychaete community structure in Valle Magnavacca, the largest basin of the Valli di Comacchio (Northern Adriatic Sea) lagoonal ecosystem, was analyzed in a three‐year study. Three shallow‐water stations were sampled at about 3‐month intervals. Univariate and multivariate analyses were utilized to investigate community structure changes in relation to natural and man‐induced disturbance. The polychaete community at station 3, in the central area of the lagoon, was the most disturbed, while that of station 2 was the most well structured. We hypothesize that polychaete community structure results from regular seasonal disturbances which lead to almost predictable fluctuations in species abundance. Superimposed on these regular cycles are acute disturbance events that further reduce species abundance or exclude species from the habitat.