Friday, October 28, 2016

Evidence of "El Nino" Like Cycles From the Siderian PaleoProterozoic Huronian Glaciations


Howe et al


The Gowganda Formation of the 2.45-2.2 Ga Huronian Supergroup contains glacially-induced, varve-like rhythmites that potentially preserve a detailed record of climatic conditions during the Paleoproterozoic Era. Four rhythmic couplet thickness records were measured at two outcrops near Wharncliffe, Ontario for the purpose of time-series analysis. The couplets, which range from 1 – 32 mm thick, are composed of alternating layers of siltstone and claystone. Time-series analysis of the couplet thickness records using the MTM Toolkit of Mann and Lees (1996) consistently revealed periodicities in the range of 2.2-2.9 couplets per cycle, which is consistent with climatic cycles such as the quasi-biennial oscillation (QBO) and the El Niño Southern Oscillation (ENSO) observed in modern times. This periodicity suggests that the rhythmic couplets represent annual deposits (i.e. varves). Evidence for the presence of cycles at 3.0-4.9 couplets, 6.6-6.9 couplets, 8.8-9.2 couplets, 22.8 couplets, and 30.1-31.0 couplets were also observed in some couplet thickness records; however, the presence of these longer term cycles was inconsistent from site to site.

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