A ~400 ka supra-Milankovitch cycle in the Na, Mg, Pb, Ni, and Co records of a ferromanganese crust from the Vityaz fracture zone, central Indian ridge.
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A approx. 400 ka (kilo years) supra-Milankovitch cycle, recorded in the sodium, magnesium, lead, nickel and cobalt contents of a 32mm thick ferromanganese crust from Vityaz fracture zone, central Indian ridge is reported here. To arrive at the geological ages, we used both sup(230)Th sub(execcs) and Co-chronometric datings. The correlation coefficient between the sup(230)Th sub(execcs) based dates and Co-chronometric dates for the top 0-8mm is very high (r=0.9734, at 99.9 percent significance). The cobalt chronometric age for the bottom most oxide layer of this crust is computed as 3.5 Ma. Red-fit and multi-taper spectral analyses of time series data revealed the existence of the significant approx 400 ka cycle, representing the changes in the hydrogeochemical conditions in the ocean due to the Earth's orbital eccentricity related summer insolation at the equator. This is the first report of such cycle from a hydrogenous ferromanganese crust from equatorial Indian ocean.
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