EarthRef.org Reference Database (ERR) -- Abdul Aziz et al. 2003

We present an astronomically tuned polarity timescale for the late middle Miocene based on a cyclic shallow lacustrine/mudflat succession exposed in the Orera Composite Section (OCS; Calatayud basin, NE Spain). Spectral analysis and band-pass filtering of high-resolution carbonate and color reflectance records in the depth domain reveal cyclic changes with different cycle lengths, which correspond to lithological alternations observed in the field. An initial age model was constructed by calibrating the OCS magnetostratigraphy to the geomagnetic polarity timescale of Cande and Kent <1995>. Subsequent spectral analysis of the proxy records in the time domain reveals periodicities close to 23, 41, and 400 kyr and, to a lesser extent, 100 kyr, supporting an astronomical origin for the sedimentary cyclicity in the OCS. We established a new age model based on the astronomical calibration of the OCS to the Laskar et al. <1993> (La93) solution by tuning the cycles to the astronomical target curves. Cross-spectral analysis results of the tuned time series followed by band-pass filtering reveal a remarkably good and in-phase relation with precession and with obliquity despite a presumed uncertainty of 20--40 kyr in the tuning in some short intervals. Our tuning provides astronomical ages for sedimentary cycles and subsequently for polarity reversals in the interval between 12.9 and 10.6 Ma. Comparison with Cande and Kent shows that the OCS polarity reversal ages are older by 80 kyr. This age discrepancy decreases with increasing age to 50--60 kyr. We present an astronomically tuned polarity timescale for the late middle Miocene based on a cyclic shallow lacustrine/mudflat succession exposed in the Orera Composite Section (OCS; Calatayud basin, NE Spain). Spectral analysis and band-pass filtering of high-resolution carbonate and color reflectance records in the depth domain reveal cyclic changes with different cycle lengths, which correspond to lithological alternations observed in the field. An initial age model was constructed by calibrating the OCS magnetostratigraphy to the geomagnetic polarity timescale of Cande and Kent <1995>. Subsequent spectral analysis of the proxy records in the time domain reveals periodicities close to 23, 41, and 400 kyr and, to a lesser extent, 100 kyr, supporting an astronomical origin for the sedimentary cyclicity in the OCS. We established a new age model based on the astronomical calibration of the OCS to the Laskar et al. <1993> (La93) solution by tuning the cycles to the astronomical target curves. Cross-spectral analysis results of the tuned time series followed by band-pass filtering reveal a remarkably good and in-phase relation with precession and with obliquity despite a presumed uncertainty of 20--40 kyr in the tuning in some short intervals. Our tuning provides astronomical ages for sedimentary cycles and subseque