Detailed Bathymetric Surveys in the Central Indian Basin

Over 420,000 line kilometers of echo-sounding data was collected in the Central Indian Basin. This data was digitized, merged with navigation data and a detailed bathymetric map of the Basin was prepared. The Basin can be broadly classified into three regions as high relief area, medium relief area and plain area represented by western, eastern and central portions of the Basin, respectively. The bathymetric map prepared from this survey is the first of its kind for this region and will in the future be used as a base by navigators and researchers

Multibeam echosounder pseudo sidescan images as a tool for manganese nodule exploration

Deep ocean floor is the storehouse of vast quantities of mineral resources and manganese nodules are one of the important resources. The method of semi quantitative evaluation of nodule resource estimation using the rms (root mean square) backscatter amplitude gain values from a multibean echosounding system is presented. Normally, the echosounding system provide information only about the water depths whereas the sidescan images can provide information on the large and small scale roughness and seafloor composition in terms of texture etc. Present day multibeam sonars can produce sidescan images of the surveyed region. The multibeam system- Hydrosweep on Indian Research ship ORV Sagar Kanya doesn't provide the sidescan images, but only gives the rms amplitude values for each of the 59 pre formed beams. In this report, the rms amplitude values are utilised to generate pseudo sidescan images of the seafloor. An area of about 6600 km sup(2) in the Central Indian Basin was mapped using the Hydrosweep system and depth contour and pseudo sidescan images of the area have been generated. A comparison of nodule abundance values with the sidescan image shows that, the light gray patches show high manganese abundance values (more than 10 kg/m sup(2)) where as the dark tones on the sidescan images correspond to low abundance values (up to 4 kg/m sup(2)). As multibeam mapping can be carried out at normal ship speeds, the pseudo sidescan images can be a useful and inexpensive tools for manganese nodule exploration

A note on the morphology of Kainan Maru Seamount, East Antarctica

Kainan Maru Seamount lies off the northern end of the Gunnerus Ridgealong the margin of East Antarctica. The seamount is separated from theGunnerus Ridge by only about 15 km. Detailed Hydrosweep multibeamsurveys of the seamount have shown that the seamount rises over3,500 m above the surrounding seafloor, has an oval shape about 60 kmwide and 120 km long, and has a gently sloping summit. The northernand eastern sides of the seamount are steeper than the southern andwestern sides. Many erosional channels cut the northern and easternflanks of the seamount, whereas the western side shows evidence oflarge sediment slides and is more gently sloping. The morphology of theseamount, as observed in the bathymetry and satellite gravity data,suggests that Kainan Maru Seamount may be a detached piece of theGunnerus Ridge that rotated clockwise away from the ridge during therifting of Gondwana in this area

Pseudo sidescan images from backscatter amplitude data of the Hydrosweep multibeam sonar system

278-282Using the rms (root mean square) backscatter amplitude values, a procedure was evolved to generate pseudo sidescan images. A comparison of the pseudo sidescan image with actual Hydsosweep sidescan image, from an area covering a pear shaped seamount in the southeast Pacific Ocean is presented. The two sidescan images are perfectly comparable. This result will enhance the utility of the Hydrosweep multibeam system so that, even in the absence of sidescan option, the offline pseudo sidescan images can be obtained using only the rms backscatter amplitude values

Two layers of Australasian impact ejecta in the Indian Ocean?

Only 2 Australasian tektites have been found in the Indian Ocean, and both are associated with surficial sediments. We collected cores from both locations where the tektites have been reported. The microtektites in these cores (and both the tektites, as reported earlier) have chemical compositions within the compositional range previously reported for Australasian tektites and microtektites. In both locations, while the tektites are occurring at the sediment/water interface, the microtektites are found buried in older horizons beneath the seafloor at stratigraphic levels, conforming to the radiometric age of the strewn field. Thus, at first glance, there appear to be 2 layers of Australasian impact ejecta in the Indian Ocean. However, the manganese nodules are associated with the tektites which, although millions of years old, are invariably resting on recent sediments. Therefore, the mechanism that retains nodules at the seafloor also seems to be operative on the tektites, thus leading to this apparent "age paradox" of tektite/microtektite distribution in the Indian Ocean, although they both belong to the same impact event.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202