EHRC ホ ー ム ペ ー ジ | 新 し い 種 目 | あ な た の 質 問

A colleague of mine who is a sedimentologist has spent his entire career studying the Green River Formation is amused when he hears people refer to the Green River shales as varved deposits, and is especially contemptuous toward the suggestion of grand cycles in these shales. He has counted varves in various parts of the basin between two ashfall tuff beds that are basin-wide and are recognized chronostratigraphic markers. In the center of the basin there are significantly fewer "varves" between the ashbeds than near the margins of the basin, thus invalidating the use of these laminae as varves, or at least making them unusable for cyclical studies. Furthermore a number of careful statistical studies have cast doubt on the use of the laminae as "varves".

The original publication on the cyclicity of the Green river laminae suggested the possibility of 5 and 11 year cycles (" judicious data selection...") in what they viewed mostly as noise at other scales. See Crowley, Duchon and Rhi (1986) in J. Geophys. Res. 91:8637-8647.

Ripepe, Roberts, and Fischer made astonishing claims for 11 and 5 year cycles (1991) in J. Sed. Pet. 61:1155-1163 and subsequently extended their claims in a second paper by Fischer and Roberts asserting Milankovitch type 20k, 100k cycles in the Green River Shales. (same year) J. Sed. Pet. 61: 1146-1154.

Neither of the latter appeared to be aware of the paper by Pittock, cited in Crowley: (1978) Reviews of Geophysics and Space Physics 16:400-420. The abstract of this paper, entitled "A Critical Look at the Long-term Sun-Weather Relationships", reads as follows:

"Many and varied claims have been made over many years for a relationship between weather or climate and solar variations, notably sunspot cycles. Those relating primarily to the single and double sunspot cycles (of about 11- and 22-year quasi-periodicities) are critically reviewed in the light of what is known about solar variations, the observed variability of weather and climate, and possible physical connections between the two. Various pitfalls in the application or lack of application of statistics to the problem are discussed and illustrated from the literature. Following a survey of the literature it is concluded that despite the great number of recent papers on the subject, little convincing evidence has yet been produced for real correlations between sunspot cycles and the weather/climate on the 11- and 22-year time scales, although evidence for correlations with solar events on time scales of days appears to exist. The state of the literature in this particularly controversial area must raise doubts as to the prevaling standards of objectivity and critical analysis in other areas of science as well. Clearly, in the case of sun-weather relationships, further research requires MUCH HIGHER STANDARDS OF OBJECTIVITY, with the rigorous and critical application of statistics, and step by step investigation of hypothetical mechanisms. This criticism is not addressed to the recent studies of apparently significant correlations between certain meterological indices and the passage of interplanetary magnetic sector boundaries; however, the relevance of such correlations to time scales of climatic interest has yet to be demonstrated."

A further complicating factor in the case of the Green River Shale is that the counting of laminae is particularly problematic, since they are often thin or fragmentary and may change dramatically over horizontal distance. It is almost impossible to get two counts of a section of laminae to come out the same because of the fractured nature of the laminae. In any case, my friend doesn't think they are varves for these and a number of other compelling reasons.


Ó 2010 Arthur V. Chadwick, Ph.D.