Modern spectral climate patterns in rhythmically deposited argillites of the Gowganda Formation (Early Proterozoic), southern Ontario, Canada

Abstract

Rhythmically deposited argillites of the Gowganda Formation (ca. 2.0^2.5 Ga) probably formed in a glacial setting. Drop stones and layered sedimentary couplets in the rock presumably indicate formation in a lacustrine environment with repeating freeze^thaw cycles. It is plausible that temporal variations in the thickness of sedimentary layers are related to interannual climatic variability, e.g. average seasonal temperature could have influenced melting and the amount of sediment source material carried to the lake. A sequence of layer couplet thickness measurements was made from high-resolution digitized photographs taken at an outcrop in southern Ontario, Canada. The frequency spectrum of thickness measurements displays patterns that resemble some aspects of modern climate. Coherent periodic modes in the thickness spectrum appear at 9.9^10.7 layer couplets and at 14.3 layer couplets. It is unlikely that these coherent modes result from random processes. Modern instrument records of regional temperature and rainfall display similar spectral patterns, with some datasets showing significant modes near 14 yr in both parameters. Rainfall and temperature could have affected sedimentary layering in the Gowganda argillite sequence, and climate modulation of couplet thickness emerges as the most likely explanation of the observed layering pattern. If this interpretation is correct, the layer couplets represent predominantly annual accumulations of sediment (i.e. they are varves), and the thickness spectrum provides a glimpse of Early Proterozoic climatic variability. The presence of interannual climate patterns is not unanticipated, but field evidence presented here may be of some value in developing a climate theory for the Early Proterozoic.

Field evidence suggests that the Palaeoproterozoic Gowganda Formation in Canada is non-glacial in origin

“…A -The "varves" in the Gowganda Formation are commonly subdivided into many thin, repetitive "couplets" of very thin light layers with large grain size and thick dark layers with small grain size, displaying no evidence of periodic yearly variation; B -Close-up photograph showing laminae with two light grains marked; C -Near close-up photograph showing a light lamina with large grains and dark laminae above and below (Site 1, at Cobalt). Compare with illustrations inJackson (1965),Hughes et al (2003),Melezhik et al (2013),Williams et al (2016) and especially to turbidite rhythmites described byEyles & Januszczak (2007, fig. 13).…”

2470 million-year-old banded iron formation reveals a climatic oscillation consistent with the Gleissberg solar cycle

“…No convincing evidence for solar cycles older than 1500 myr has been reported before. Both Hughes et al 13 and Dmitriev et al 59 reported potential records of solar cycles based on the same part of argillite strata in mid-Paleoproterozoic Gowganda Formation. However, neither studies have considered red noise when analysing climatic time series, nor did they provide any depositional rate constraints to support their varve interpretation of the couplets.…”

“…It is well accepted that some of the Earth's climatic cycles are coupled to the solar cycles 6 . Such cyclic climatic variations are revealed in sedimentary archives of Cenozoic 7 , Mesozoic 8 , Paleozoic 9 , Neoproterozoic 10 , and Mesoproterozoic 11 , but no convincing evidence from older sediment records 12,13 . When did the Sun's magnetic field exhibit stabilized cycles?…”

Climatic catastrophes in Earth history: two great Proterozoic glacial episodes

“…It has been suggested by a number of workers (Jackson, 1965;Lindsey, 1969;Young, 2001;Hughes et al, 2003) that there are varved deposits in some northern outcrops of the Gowganda Formation. If this interpretation is correct, it suggests that seasonal differences were sufficiently strong to produce alternating freezing and thawing in pro-glacial lakes, the warm seasons permitting deposition of coarser material including ice-rafted cobbles and boulders.…”