SPECMAP Chronology in 2011

The chronology methodology introduced by SPECMAP revolutionized Earth history research. Time calibration ("tuning") of paleoclimatic proxies to astronomical forcing models is now a major player in defining the Pleistocene geological time scale. There is additional information in the contributing data that bears on SPECMAP chronology that the original procedures did not emphasize. This was observed by Thomson (1990), who found that coherence in the obliquity band of the SPECMAP stack decays significantly back through time. Here we decompose the stack to identify the source(s) of this decay in an effort to quantify astronomically tuned chronology uncertainty. We focus on the phasing of precession signals in stratigraphy as a leading cause of uncertainty, and 'minimal tuning' procedures as a solution to the problem. [Reference: Thomson, D, 1990, Phil. Trans. R. Soc. Lond. A, 332(1627), 539-597.]