EXTENDING THE CLIMATIC PRECESSION CURVE BACK INTO THE LATE MIOCENE BYSIGNATURE TEMPLATE COMPARISON

The rhythm of sedimentary cycles reflecting the climatic precession si gnal (19 and 23 kyr components) from the upper Miocene of the Bou Regr eg section at Ain el Beida near Rabat, Morocco, had been analyzed to d etermine the age of the geomagnetic polarity reversals of Subchron 5N1 (C3An.1n). A new method of analysis of cycle ''signatures'' uses adju sted data series as represented by a signal obtained from grey-level t races through image-enhanced photographs of the sediment cycles. The m easured, ''timeless'' signal is reduced and geometrically transformed to a signature template in order to compare its pattern with similar t ime constrained segments of the target precession signal (retrodicted for 35 degrees N). Conventional statistical and spectral analysis test s are used to regress to the best possible fit. A date estimate of 5.9 4 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 b e in close agreement with independent approximations derived from extr apolation of sea floor spreading, radiometric dating, and younger Eart h-orbital tuning ages.