Lithostratigraphy, sedimentation and evolution of the Volta Basin in Ghana

We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the Pan-African Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3–4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group

Community composition of epibenthic megafauna on the West Greenland Shelf

Epibenthic organisms are a critical component of the marine environment, functioning as ecosystem engineers, habitat and food for other organisms. Our knowledge of the diversity, complexity and sensitivities of these habitats is limited, particularly at higher latitudes and greater depths. The West Coast of Greenland is the site of a commercially important shrimp trawl fishery, but there are few published records describing the benthic community structure of the region. Here we report results from benthic camera surveys conducted at 119 sites, over 3 years, spanning 1400 km of the West Greenland continental shelf (61–725 m depth). A total of 29 classes of epibenthic taxa were identified from the images. There are significant differences of composition and diversity in sites with hard and soft substrate. Hard-substrate communities are relatively diverse with higher abundances and are characterised by sessile, attached groups such as Hydrozoa, Anthozoa, Bryozoa and Porifera. Soft-sediment sites are less diverse and dominated by Polychaeta and have specialist Malacostraca such as the commercially exploited shrimp, Pandalus borealis. Distribution patterns and variation in epibenthic megafauna are related to substrate and the environmental parameters depth, temperature and current speed. This study represents the first quantitative characterisation of epibenthic megafaunal assemblages on the West Greenland continental shelf. These data constitute an important baseline, albeit in a region heavily impacted by trawl fisheries, and demonstrate the utility of benthic photography for examining and monitoring seabed diversity and change

Physiological function and catalytic versatility of bacterial multihaem cytochromescinvolved in nitrogen and sulfur cycling

Bacterial MCCs (multihaem cytochromes c) represent widespread respiratory electron-transfer proteins. In addition, some of them convert substrates such as nitrite, hydroxylamine, nitric oxide, hydrazine, sulfite, thiosulfate or hydrogen peroxide. In many cases, only a single function is assigned to a specific MCC in database entries despite the fact that an MCC may accept various substrates, thus making it a multifunctional catalyst that can play diverse physiological roles in bacterial respiration, detoxification and stress defence mechanisms. The present article briefly reviews the structure, function and biogenesis of selected MCCs that catalyse key reactions in the biogeochemical nitrogen and sulfur cycles

Ultracompact HII regions with extended emission: The complete view

\ua9 2019 The Author(s). In this paper, we present the results of a morphological study performed on a sample of 28 ultracompact HII (UC HII) regions located near extended free-free emission, using radio continuum (RC) observations at 3.6 cm with the C and D Very Large Array (VLA) configurations, with the aim of determining a direct connection between them. By using previously published observations in B and D VLA configurations, we compiled a final catalogue of 21 UC HII regions directly connected with the surrounding extended emission (EE). The observed morphology of most of the UC HII regions in RC emission is irregular (single- or multipeaked sources) and resembles a classical bubble structure in the Galactic plane with well-defined cometary arcs. RC images superimposed on colour composite Spitzer images reinforce the assignations of direct connection by the spatial coincidence between the UC components and regions of saturated 24 μm emission. We also find that the presence of EE may be crucial to understand the observed infrared excess because an underestimation of ionizing Lyman photons was considered in previous works (e.g. Wood & Churchwell; Kurtz, Churchwell & Wood)

Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment

The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory (OVRO), Atacama Large Millimetric Array (ALMA), and the infrared \textit{Spitzer} observatories, are powerful facilities to study massive star formation regions and related objects such as ultra--compact (UC) \hii regions, molecular clumps, and cores. We used these telescopes to study the \uchiir G43.89--0.78. The morphological study at arcminute scales using NVSS and \textit{Spitzer} data shows that this region is similar to those observed in the \textit{ bubble--like} structures revealed by \textit{Spitzer} observations. With this result, and including a physical characterization based on 3.6 cm data, we suggest G43.89--0.78 be classified as an \uchiir with Extended Emission because it meets the operational definition given in this paper comparing radio continuum data at 3.6 and 20~cm. For the ultra-compact component, we use VLA data to obtain physical parameters at 3.6~cm confirming this region as an \uchii region. Using ALMA observations, we detect the presence of a dense ($2.6\times10^7$ cm$^{-3}$) and small ($\sim$ 2.0\arcsec; 0.08 pc) molecular clump with a mass of 220 M$_{\odot}$ and average kinetic temperature of 21~K, located near to the \uchii region. In this clump, catalogued as G43.890--0.784, water masers also exist, possibly tracing a bipolar outflow. We discover in this vicinity two additional clumps which we label as G43.899--0.786 (T$_d$ = 50 K; M = 11 M$_{\odot}$), and G43.888--0.787 (T$_d$ = 50 K; M = 15 M$_{\odot}$).Comment: 13 pages, 8 figures, 2 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Society Main Journal (2020

Electrochemical titrations and reaction time courses monitored in situ by magnetic circular dichroism spectroscopy

Magnetic circular dichroism (MCD) spectra, at ultraviolet–visible or near-infrared wavelengths (185–2000 nm), contain the same transitions observed in conventional absorbance spectroscopy, but their bisignate nature and more stringent selection rules provide greatly enhanced resolution. Thus, they have proved to be invaluable in the study of many transition metal-containing proteins. For mainly technical reasons, MCD has been limited almost exclusively to the measurement of static samples. But the ability to employ the resolving power of MCD to follow changes at transition metal sites would be a potentially significant advance. We describe here the development of a cuvette holder that allows reagent injection and sample mixing within the 50-mm-diameter ambient temperature bore of an energized superconducting solenoid. This has allowed us, for the first time, to monitor time-resolved MCD resulting from in situ chemical manipulation of a metalloprotein sample. Furthermore, we report the parallel development of an electrochemical cell using a three-electrode configuration with physically separated working and counter electrodes, allowing true potentiometric titration to be performed within the bore of the MCD solenoid