EXTENDING THE CLIMATIC PRECESSION CURVE BACK INTO THE LATE MIOCENE BY SIGNATURE TEMPLATE COMPARISON

The rhythm of sedimentary cycles reflecting the climatic precession signal (19 and 23 kyr components) from the upper Miocene of the Bou Regreg section at Ain el Beida near Rabat, Morocco, had been analyzed to determine the age of the geomagnetic polarity reversals of Subchron 5N1 (C3An.1n). A new method of analysis of cycle ''signatures'' uses adjusted data series as represented by a signal obtained from grey-level traces through image-enhanced photographs of the sediment cycles. The measured, ''timeless'' signal is reduced and geometrically transformed to a signature template in order to compare its pattern with similar time constrained segments of the target precession signal (retrodicted for 35 degrees N). Conventional statistical and spectral analysis tests are used to regress to the best possible fit. A date estimate of 5.94 Ma for the Chron 5/Gilbert boundary (C3An.1n/C3r), which occurs near the times of the closure of the Rifian Corridor and the beginning of the ''drawdown'' phase of the Messinian Salinity Crisis, is found to be in close agreement with independent approximations derived from extrapolation of sea floor spreading, radiometric dating, and younger Earth-orbital tuning ages.