Astronomical Periodicity Signals from Lamina Growth Rhythm Records of Lacustrine Stromatolites

Key words: 
• Lacustrine environment

Abstract: The lacustrine stromatolite samples was collected from the Oligocene Yaxicuo Formation in northern Tibetan Plateau. The microtexture features of alternative dark organicrich lamination and light mineralrich lamination distinctly display on polished sections and under microscope observation. The lamination bands occur as wavy and column shapes with step growth episodes. The grayscale values to extract from digitized photographs can be used as a method of lamination couplet counts and thickness measurements. The lamination couplet thickness series are obtained from four sample segments. Individual lamination couplet is interpreted to correspond to annual growth patterns. The periodicities in lamination couplet thickness variations are detected by power spectral analysis. Its significant spectral peaks about 11 years periodicities are related to 11 years sunspot cycle. It is suggested that regular growth rhythms of lacustrine stromatolites may record climate and environmental oscillations forced by sunspot activity. 