Geology and sedimentary environment of the Surma Group of rocks, Bandarban anticline, Bandarban, Bangladesh

The study illustrates the effect of tectonics, climate, and relative sea-level change on the depositional process of the Miocene Bhuban and Boka Bil Formation of Bengal Basin. Outcrop sediments of five transverse sections exposed along the axial zone of Bandarban anticline were studied. Twelve lithofacies such as Gm, Gms, Sm, ST, Sp, Sr, Sl, Sf, Sll, Fw, Fl and Fm have been identified within the successions and grouped into (i) turbidite generated, (ii) outer fan distal lobe basin plain and (iii) tide-influenced facies association. The analyses reveal that the Bhuban Formation was turbidite- generated that deposited below the continental shelf-slope environment. The Lower Bhuban Member consists of gray to brownish-gray calcareous sandstone with shale deposited under the channelized lobe of submarine fan. The Middle Bhuban Member dominated by black shale-siltstone deposited in distal turbidite lobe due to change the flow regime. The Upper Bhuban Member consists of yellow to yellowish gray, coarse to medium-grained sandstone-siltstone with black shale that deposited under channelized to nonchannelized lobes of submarine fan. The increasing sedimentation during the formation of the Upper Bhuban Member can be caused by increased the intensity of the Asian Monsoon that carried huge sediment from the Himalaya. The Boka Bil Formation was deposited under estuary to tidal flat environment. The area was uplifted during and/or after subduction of the Indian Plate beneath the Burmese Plate. The monsoonal intensity enhances sedimentation that moved prograding delta towards the south. These processes shifted depositional environment from continental shelf-slope to marginal shallow marine during deposition of the Boka Bil Formation. The continental slope aligned east-west direction and sediments likely derived from the Himalaya and Trans-Himalaya in the present geographical setup during deposition of the sediments.

Parametric Subharmonic Instability of the Semidiurnal Internal Tides at the East China Sea Shelf Slope

On the basis of measurements from an observing mooring system, the observational evidence of parametric subharmonic instability (PSI) that transfers energy from semidiurnal internal tides (ITs) to the subharmonic waves at the East China Sea continental shelf slope is presented for the first time. Although the mooring station is very close to the energetic semidiurnal IT generation site, about 76% of the observed shear variance is contained in the near-inertial band, which is found to have comparable upward- and downward-propagating energy components. Bispectra and bicoherence estimates further confirm the occurrence of PSI transferring energy from the low-mode M2 ITs (vertical wavelength of ~1000 m) to high-mode subharmonic waves (vertical wavelength of ~200 m). The calculated energy transfer rate reveals an averaged net value of ~5 × 10−9 W kg−1. Strong temporal variation of is found that is not exactly in phase with the semidiurnal energy flux. After looking into the local vorticity fields, it is strongly suggested that the varying background relative vorticity associated with the evolving Kuroshio has modified the efficiency of PSI at the mooring location through changing the local effective inertial frequency.

Map of Quaternary formations of Ukraine in scale 1:2,500,000

The article announces a new map of Quaternary formations on the territory of Ukraine on the scale 1:2,500,000. It considers the prerequisites for the preparation of this map and summarises more than a century of historical research and mapping of the Quaternary formations on the territory of Ukraine. Due to the continuity of scientific research, an extremely developed theoretical and methodological basis of both research and mapping of Quaternary formations has been formed in the country. This is also due to the extraordinary diversity of the geological structure of the Quaternary cover, due to the presence of two mountain systems, lowland areas (including within them several deflections and two crystalline foundations), as well as due to the presence of two seas (including the continental shelf, slope and deep-water zone). A very wide spectrum of facies and formations is also listed (including a thick loess-soil cover, facies of two glaciers of different ages, alluvia, estuary, marine shelf, deep-water and etc.). Attention is focused on two important problems of mapping Quaternary cover. The first is related to new views on the origin of the subaerial cover. The significance of the new (geo-eolian) factor is disclosed, which determined both the thickness and lithological properties of the strata of each paleogeographic stage (of climatoliths) of each separate section, and the stratigraphic structure of the loess-soil cover. Spatial patterns of the structure of the subaerial cover are briefly described, in particular, the mosaic division into areas with a homogeneous stratigraphic structure (type-sections), due to the corresponding geo-eolian mode (sequence). The second problem concerns the ways of visualization of the geological structure of Quaternary sediments on the map. Two principles of reflection of the Quaternary cover are considered, and the disadvantages and advantages of each of them are indicated. Promising ways to map the Quaternary subaerial cover on the basis of ideas about its mosaic structure are proposed. A solution to the problem of various principles of visualization of the Quaternary cover is recommended involving compilation of «multi-visual» maps based on their interactive reissuing (re-design) with modern geographic information systems in accordance with various principles of visualization of the structure of the Quaternary. It has been proposed to use the above scientific approaches in the mapping of the Quaternary deposits of Europe and the World, and also to take into account the geo-eolian factor in the studies of the subaerial cover.

Distribution of Iospilidae (Annelida) along the eastern Brazilian coast (from Bahia to Rio de Janeiro)

We present the spatial distribution and abundance of the holoplanktonic family Iospilidae (Annelida, Polychaeta), along part of the eastern Brazilian coast, and its relation to environmental variables in the region. Samples were obtained from two collections made in 1998 and 2000 between 13°-25°S, and 28°- 42°W, on the Brazilian coast, between the Bay of Todos os Santos (BA) to Cape São Tomé (RJ). 216 stations were selected, covering the continental shelf, slope and oceanic regions, where plankton samples were collected for water and nutrient analysis. We analyzed environmental variables: temperature, salinity, dissolved oxygen, pH, ammonia, nitrite, nitrate, phosphate, silicate and chlorophyll-a. 363 individuals were collected, identifying two species, viz., Phalacrophorus uniformis and Phalacrophorus pictus, the first being the most abundant, with 354 individuals, while only nine specimens of P. pictus were found. Both species are mainly distributed in the oceanic region stations. The distribution of P. uniformis was related to the concentration of phosphate and nitrate. Significant differences between samples and between sectors of the continental shelf and oceanic region were found.

Shelf–Basin interaction along the East Siberian Sea

Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180° E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140° E, while it appears in the Makarov Basin at 150° E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to ∼ 34.5, i.e. in the water classically named lower halocline. East of 170° E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of ∼ 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity ∼ 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.