• B L K Somayajulu

      Articles written in Journal of Earth System Science

    • Susceptibility as a tool for studying magnetic stratigraphy of marine sediments

      B L K Somayajulu C Radhakrishnamurty T J Walsh

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      Eighty six gravity cores collected from the Pacific Ocean by the Scripps Institution of Oceanography have been logged for magnetic susceptibility using a simple and rapid technique. These logs fall into three types: Type 1 showing several highs and lows, Type 2 with a single-broad-hump, and Type 3 showing nearly constant susceptibility with depth.

      Type 1 cores are found to be mainly from sediment-trap (trenches) areas which are close to the active volcanoes and the high peaks probably correspond to a slump or deposition of volcanic material; these events occurred between 0·1 and 2·8 million years ago.

      Type 2 cores are by far the most common, (56 out of 86) and show a maximum deposition of magnetic material (i.e. crest region of the hump) in the range of 0·2 and 1·7 million years. The susceptibility during this period was about a factor of two higher for several cores compared to their respective values during the last 0·1 million years. Oceanwide deposition of volcanic material and/or the atmospherically transported dust rich in magnetic material (cosmic and/or terrestrial) by our planet can account for such an increase. A third possibility may be the change (decrease) in accumulation rates of the sediments during this period.

      In type 3 cores the susceptibility is almost constant with depth and these are randomly distributed (excluding the sediment trap areas) analogous to the case of type 2 cores. A high deposition rate in these areas can alter type 2 into type 3.

      It appears that the maximum of type 2 hump can act as a stratigraphic marker since type 2 cores are the most common ones and are widely distributed over the entire Pacific.

    • Annual fallout of32Si,210Pb,22Na,35S and7Be in rains in India

      D Lal V N Nijampurkar G Rajagopalan B L K Somayajulu

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      The concentration of radioisotopes7Be,35S were measured in Bombay since 1956 and22Na,210Pb,32Si since 1963. In Khandala and other stations such measurements have been made at irregular periods since 1961. In addition several measurements especially that of32Si were made in 1970. Data available todate from Indian stations is summarised and critically analysed.

      We conclude that appreciable amounts of35S,22Na and32Si, over and above their production by cosmic rays, were produced during the high yield Russian tests as evidenced by their fallout between 1962–66. Based on the bomb produced excess the half period for their removal from the stratosphere is deduced to be less than 1 year. The ‘excess’ contribution of32Si due to bombs is, however, small; about 1% of its inventory in the oceans.

      The present study shows that for stations where orogeny is the principal mechanism of precipitation, the annual fallout is independent of the annual rainfall.

    • Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin

      N Hussain N Bhandari K R Ramanathan B L K Somayajulu

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    • Particle accelerator measurements of10Be in marine accumulations: Intercomparison with beta counting method

      P Sharma B L K Somayajulu D Lal W Wolfli G Bonani Ch Stoller M Suter J Beer

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      Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to ∼6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at10Be levels of 109–1010 atoms/g agree within the absolute errors of the two methods. The detection limit for10Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.

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