Sedimentary Processes and Depositional Characteristics of Coarse-grained Subaqueous Fans along Steep Slopes in a Lacustrine Rift Basin: A Case Study from the Dongying Depression, Bohai Bay Basin, China

Coarse-grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin, China. The insufficient understanding of their sedimentary processes, depositional patterns, and controlling factors restricts efficient exploration and development. Coarse-grained subaqueous fans in the Yong′an area, Dongying Depression, are investigated in this study. These fans include nearshore subaqueous fans, and sublacustrine fans, and their sedimentary processes, depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology. Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence. Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction. While the topography was gentle, sublacustrine fans did not develop. During the late weak tectonic activity stage, late sublacustrine fans developed with multiple stages superimposed. Frequent fault activity and related earthquakes steepened the basin margin, and the boundary fault slopes were 25.9°–34°. During the early–middle deposition stage, hyperpycnal flows triggered by outburst floods developed. During the late deposition stage, with weak tectonic activity, seasonal floods triggered hyperpycnal flows, and hybrid event beds developed distally.     

Holocene stratigraphy-of the Lower Ganges-Brahmaputra River delta in Bangladesh

Major part of the Holocene Ganges-Brahmaputra delta occupies the southern and southwestern part of Bangladesh with a smaller part extending beyond the international boundary in the west. Five facies assemblages are documented in the lower deltaic plain in five different depositional environments: levee or levee complex, bil or depression, abandoned meander belt, interdistributary plain and estuarine plain. The thickness of the Holocene sediments ranges from 30 m to 70 m in the deltaic plain, usually floored by the Pleistocene stiff clays, with the exception of the abandoned meander belt deposit where Holocene channel sand deposited directly on the Pleistocene sand. Radiocarbon dates indicate that low-rate sedimentation has occurred in the northern part, where 4-6 m thick sediments were deposited since the mid-Holocene, whereas 10-30 mthick sediments were deposited in the southern part during the same span of time. In addition, significant coastal subsidence (3 mm/a on average), added by sea-level rise (1.5 mm/a, conservative rate) occurs in the study area, which serves as a negative factor in degrading the coastal plain of Bangladesh in the future, while taking into consideration the weaker sedimentation in the area.     

Petroleum hydrocarbon distribution in continental shelf region of southeast coast of India

In the surface sediment samples collected from 7 transects in the continental shelf region off Karaikkal, Parangipettai, Cuddalore-SIPCOT, Cheyyur, Chennai, Tammenapatanam and Singarayakonda in the s...     

KRISP 85 — An international seismic investigation of the Kenya Rift

British, German, American and Kenyan seismologists undertook a preliminary crustal seismic programme in the Kenya Rift in the summer of 1985. Thirteen explosions, totalling 7 tonnes, were fired in lakes and boreholes, and were recorded by 42 three-component stations. Preliminary results show that the deep structure along the axis of the Rift is more complex than previous models have suggested.     

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers, NW Pakistan

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan. Two grids covering an area of 10x18 m2 and 8x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer. The anomalous zones obtained were plotted on contour maps, 2D and 3D magnetic intensity maps. Based on the magnetic anomalies, grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis. These zones contain gold concentrations, ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm. Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.     

Biodiverse rotifer assemblage(Rotifera: Eurotatoria) of floodplain lakes of the Brahmaputra basin of lower Assam,northeast India: composition and ecosystem diversity

The study aims to ascertain the hypothesis on the rich rotifer biodiversity of the floodplain lakes(beels) of the Brahmaputra river basin and to use these metazoans to assess trophic status or to characterize habitat variations of wetlands. The plankton samples collected from four beels of lower Assam revealed 160 Rotifera species belonging to 35 genera and 19 families. The richness is of biodiversity value as ~38.0% and ~57.0% of the rotifer species known till date from India and northeast India(NEI), respectively. One species each is new to the Oriental region and NEI, and three species are new to Assam; 23 species merit global biogeography interest and several exhibit distribution values in the Indian sub-region. The diverse Lecanidae Brachionidae Lepadellidae Trichocercidae and speciose littoral-periphytic L ecane Lepadella Trichocerca, and richness of Brachionus spp. following removal of aquatic macrophytes are noteworthy. Overall rotifer composition showed homogeneity amongst beels while lower monthly richness and community similarities affirmed heterogeneity within individual beels. We propose L/B quotient based on L ecane : Brachionus species ratios to characterize habitat variations of the sampled wetlands. Sláde?ek's B/T quotient based on B rachionus : T richocerca species ratios affirmed general 'meso-trophic' status of diff erent beels. Our results provided little insight on the influence of individual abiotic factors but the canonical correspondence analyses asserted higher cumulative influence of ten abiotic parameters on Rotifera richness in each beel.