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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 17:57 |
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Conference: Bucharest University Faculty of Physics 2002 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
An astronomical timescale for the loess deposits of the Southeastern Romania
Authors:
Cristian Panaiotu, Cristina Panaiotu, Cristian Necula, Adrian Grama
Affiliation:
University of Bucharest, Paleomagnetism Laboratory
E-mail
Keywords:
Abstract:
Two loess¡Vpaleosol profiles at Mostistea and Costinesti in the Southeastern Romania were sampled at 5-cm intervals, in order to obtain a high resolution climatic record. All samples were measured for magnetic susceptibility, which is regarded as a good proxy for past Quaternary climatic changes. On the basis of the astronomical theory of Pleistocene climatic change, an age model of these loess¡Vpaleosol sequences was developed by tuning the magnetic susceptibility record to time-series of insolation changes (Laskar, 1990), to the orbitally tuned ODP677 N Ô18O records of Shackleton et al. (1990) and to Luochuan magnetic susceptibility (Heslop et al, 2000). The formulation of an orbitally tuned palaeoclimatic timescale, based on the assumptions that loess units correspond to regions of insolation minina/even numbered MIS and palaeosols to regions of insolation maxima/odd numbered MIS, provides a robust, high-resolution chronological solution for the Romanian loess sequences. We used two different algorithms that allows the analysis of unevenly spaced time series to test whether coherent orbital frequencies have been succesfuly introduced into the susceptibility time series during tuning procedure: SPECTRUM based on the Lomb-Scargle Fourier transform for unevenly space data and (Schultz and Stattengger, 1997) and MC-CLEAN based on a series of Monte Carlo simulations. Both procedures show that the obtained time series are dominated by the known orbital orbital periods of eccentricity (100 kyr ) and obliquity (41 kyr) at 0.95 significance level. However through the use of an Inverse Fourier Transform a signal based on the mean spectrum derived from the MC-CLEAN procedure was reconstructed in the time domain to give a (hopefully) noise free version of the input signal only if the orbital period of precession (23 kyr) is taken into account (0.8 significance level).
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