Sedimentology of the Old Red Sandstone (Siluro-Devonian) in the Clee Hills area,Shropshire, England

The sequence of approximately 1300 m is divided by a major unconformity (Middle Devonian) into the thick Lower Old Red Sandstone (Siluro-Devonian), resting disconformably on Ludlovian (Silurian) marine strata, and the much thinner Upper Old Red Sandstone (Upper Devonian) overlain by the Carboniferous.The Lower Old Red Sandstone commences with littoral sediments (Downton Castle Formation) followed by tidal mud-flat deposits (Temeside Formation) formed after a brief marine transgression. The predominant remainder of the sequence (Ledbury Formation, Ditton Group, Abdon Group, Woodbank Group), characterized by fining-upwards cyclothems, records the establishment during a marine regression of extensive and persistent alluvial plains. Prior to Ditton Group times, detritus came from relatively distant regionally metamorphosed rocks lying to the north or west of the Clee Hills. Subsequently, apparently as the result of river-capture or drainage-reversal consequent on the commencement of the final (mid-Devonian) phase of Caledonian movement, high-level crustal rocks closer at hand (largely Wales) replaced the metamorphics as the sources of sediment, the earlier Lower Old Red Sandstone itself being recycled. To judge from the calcretes preserved in the alluvial formations, the area lay near the Equator and experienced a relatively dry hot climate.The Upper Old Red Sandstone likewise reveals fining-upwards cyclothems. The overlying Carboniferous rocks evidence the renewed marine transgression of the area, after the removal of the effects of the mid-Devonian movements.     

Suspended‐sediment sources in an urban watershed,Northeast Branch Anacostia River,Maryland

Fine sediment sources were characterized by chemical composition in an urban watershed, the Northeast Branch Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible land‐based sediment sources and suspended sediment collected from the water column at the watershed outlet during storm events. These tracer concentrations were used to determine the relative quantity of suspended sediment contributed by each source. Although this is an urbanized watershed, there was not a distinct urban signature that can be evaluated except for the contributions from road surfaces. We identified the sources of fine sediment by both physiographic province (Piedmont and Coastal Plain) and source locale (streambanks, upland and street residue) by using different sets of elemental tracers. The Piedmont contributed the majority of the fine sediment for seven of the eight measured storms. The streambanks contributed the greatest quantity of fine sediment when evaluated by source locale. Street residue contributed 13% of the total suspended sediment on average and was the source most concentrated in anthropogenically enriched elements. Combining results from the source locale and physiographic province analyses, most fine sediment in the Northeast Branch watershed is derived from streambanks that contain sediment eroded from the Piedmont physiographic province of the watershed. Sediment fingerprinting analyses are most useful when longer term evaluations of sediment erosion and storage are also available from streambank‐erosion measurements, sediment budget and other methods. Copyright © 2010 John Wiley & Sons, Ltd.     

Extension of a polar ionospheric current to the nightside equator

A detailed analysis of rapid-run magnetograms from Guam (geomagnetic latitude = 4.2°) revealed that there are two kinds of geomagnetic sudden commencement (SC) observed in nighttime. One is the ordinary SC consisting of a main impulse only which has a smooth rise of the H-component. The other is a superposition by a small positive impulse on the very beginning part of the smooth rise of the main impulse and consequently the SC starts with a small stepwise increase of the H-component. The latter type of SC occurs between 20 and 08 h L.T. and its occurrence rate takes the maximum value of about 50% around 03 h L.T. Corresponding magnetograms from a dayside equatorial station (Huancayo, geomagnetic latitude = ?0.7°) were examined and a good correlation was found between the stepwise SC at the nightside (Guam) and SC¹ with a preliminary reverse impulse (PRI) at the dayside (Huancayo). Since PRI observed at the dayside equator may be interpreted as an extension of an ionospheric current due to an dusk-to-dawn electric field impressed on the polar ionosphere, our results show that a polar originating ionospheric current can extend to the nightside equator and produce a small but observable magnetic effect in spite of much reduced nighttime ionospheric conductivity.     

Chaoborus (Diptera: Chaoboridae) mandibles—paleolimnological indicators of the historical status of fish populations in acid-sensitive lakes

Paleolimnological analyses of Chaoborus mandibles were used to assess the status of fish populations over the previous 150 to 300 years in five lakes from the Adirondack region of New York State. Windfall Pond (pH 6.5) has not acidified and currently has viable fish populations. Big Moose Lake (pH 5.0) has acidified in recent years, and the number of fish populations declined from 14 in the 1930's to seven in the early 1980's. The occurrence of only migratory Chaoborus (subgenus Sayomyia) in the cores indicated the long term presence of fish populations in Windfall Pond and Big Moose Lake. Brooktrout Lake (pH 5.0), Deep Lake (pH 4.7) and Upper Wallface Pond (pH 4.8) have all acidified in recent years, and all three are currently fishless. Chaoborus (Sayomyia) was present throughout the Brooktrout Lake core, but the entirely limnetic species, C. americanus, appeared in the topmost interval in the core. The appearance of C. americanus in the top of the core indicated a recent elimination of fish from Brooktrout Lake, probably during the 1970's. Elimination of fish by the 1940's was inferred for Deep Lake because C. americanus appeared above the 1930 level and replaced C. trivittatus as the dominant. Dominance of C. americanus throughout the Upper Wallface Pond core indicated that planktivorous fish were never present. These results strongly suggest that stratigraphic analyses of Chaoborus mandibles provide a useful assessment of the general status of historical fish populations in Adirondack lakes. The technique should be useful in other regions, as well as for applications other than those concerning lake acidification.This is the eleventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

ITERA: IDL tool for emission-line ratio analysis

We present a new software tool to enable astronomers to easily compare observations of emission-line ratios with those determined by photoionization and shock models, ITERA, the IDL Tool for Emission-line Ratio Analysis. This tool can plot ratios of emission lines predicted by models and allows for comparison of observed line ratios against grids of these models selected from model libraries associated with the tool. We provide details of the libraries of standard photoionization and shock models available with ITERA, and, in addition, present three example emission-line ratio diagrams covering a range of wavelengths to demonstrate the capabilities of ITERA. ITERA, and associated libraries, is available from http://www.brentgroves.net/itera.html.     

Evidence for pervasive mud volcanism in Acidalia Planitia, Mars

We have mapped 18,000+ circular mounds in a portion of southern Acidalia Planitia using their sizes, shapes, and responses in Nighttime IR. We estimate that 40,000+ of these features could occur in the area, with a distribution generally corresponding to the southern half of the proposed Acidalia impact basin. The mounds have average diameters of about 1 km and relief up to 180 m and most overlie units mapped as Early Amazonian.High resolution images of mound surfaces show relatively smooth veneers, apron-like extensions onto the plains, moats, and concentric circular crestal structures. Some images show lobate and flow-like features associated with the mounds. Albedo of the mounds is generally higher than that of the surrounding plains. Visible and near-infrared spectra suggest that the mounds and plains have subtle mineralogical differences, with the mounds having enhanced coatings or possibly greater quantities of crystalline ferric oxides.Multiple analogs for these structures were assessed in light of new orbital data and regional mapping. Mud volcanism is the closest terrestrial analogy, though the process in Acidalia would have had distinctly martian attributes. This interpretation is supported by the geologic setting of the Acidalia which sits at the distal end of the Chryse-Acidalia embayment into which large quantities of sediments were deposited through the Hesperian outflow channels. In its distal position, Acidalia would have been a depocenter for accumulation of mud and fluids from outflow sedimentation.Thus, the profusion of mounds in Acidalia is likely to be a consequence of this basin’s unique geologic setting. Basinwide mud eruption may be attributable to overpressure (developed in response to rapid outflow deposition) perhaps aided by regional triggers for fluid expulsion related to events such as tectonic or hydrothermal pulses, destabilization of clathrates, or sublimation of a frozen body of water. Significant release of gas may have been involved, and the extensive mud volcanism could have created long-lived conduits for upwelling groundwaters, providing potential habitats for an in situ microbiota.Mud volcanism transports minimally-altered materials from depth to the surface, and mud volcanoes in Acidalia, therefore, could provide access to samples from deep zones that would otherwise be inaccessible. Since the distal setting of Acidalia also would favor concentration and preservation of potentially-present organic materials, samples brought to the surface by mud volcanism could include biosignatures of possible past or even present life. Accordingly, the mounds of Acidalia may offer a new class of exploration target.     

Method for comparing fish growth curves

The method of comparing growth curves that is described in this paper consists of describing growth for the ith group by the equation Li(t) = ai + bi r^t, which is linear in the two parameters ai and bi, and subsequently using the analysis of variance to compare the curves. The advantages of the linear growth equation over the von Bertalanffy equation, l i (t) ⁼ ai + bi r^t i, are easier analysis and a much simpler interpretation of the differences in the parameters in terms of growth rate and maximum size. An example comparing the growth of male and female red gurnard Chelidonichthys kumu from four areas within the Hauraki Gulf is given.