November 29, 2021
The Proterozoic Eon, the Mesoproterozoic Era
Figure 1 – Proterozoic Timeline
Credit: Modified from original
by Julisa Cummins,
Creative
CommonsCC0 1.0 Universal Public Domain Dedication
This week we'll continue our look at the Proterozoic Eon with a look at the Mesoproterozoic Era which lasted from 1600 million years ago (Mya) to 1200 Mya. The is generally divided into the Calymnian, Ectasian and Stenian Periods, as in Figure 1.
The Mesoproterozoic Era encompasses the period of time called the Boring Billion. Also called the Barren Billion, the Dullest Time in Earth's History, and Earth's Middle Ages. The Boring Billion is the time period between 1800 and 800 Mya and it was characterized by fairly stable tectonics, climate and biology. Although eukaryote organisms had evolved, prokaryote organisms dominated. Also, although there was free oxygen in the atmosphere, the oxygen concentrations were much less than today. However, oxygen concentrations rose steadily throughout the Boring Billion.
Let's look at the individual Periods of the Mesoproterozoic Era.
Calymnian Period
Lasting from 1600 Mya to 1400 Mya, the Calymnian Period was marked by the beginning of the breakup of the supercontinent Columbia, 1600 Mya, into the fragments shown in Figure 2.
Figure 2 -
Supercontinent Columbia
Credit: Celiayangyy, Creative Commons Attribution-Share
Alike 4.0 International license
The beginning of the Calymnian Period was also marked by completion of the deposition of the Athabasca Basin, a group of quartzite and conglomerate formations deposited between 1760 Ma and 1500 Mya in what is now Northern Saskatchewan. The Athabasca Basin hosts major uranium deposits. Another group of group of quartzite and conglomerate formations deposited during the Calymnian Period was the Jotnian Group deposited in the Baltic region of Europe 1600–1260 Mya.
Ectasian Period
Figure 3 - The World 1260 Mya
Credit: Bjoertvedt, Creative Commons
Attribution-Share Alike 3.0 Unported license
The Ectasian Period (also spelled Ecstasian) lasted from 1400 Mya ago to 1200 Mya and was marked by the further breakup of the Supercontinent Columbia. An interesting feature of the sediments from the Ectasian Period is the first fossil evidence for sexual reproduction in microfossils of Bangiomorpha pubescens (a eukaryote red algae) from the Hunting Formation on Somerset Island, Canada.
Stenian Period
Figure 4 -
Supercontinent Rodinia
Credit: John Goodge, public
domain
The final period in the Mesoproterozoic, the Stenian Period lasted from 1200 Mya to 1000 Mya. The major event of the Stenian was the accretion of the Supercontinent Rodinia. In North America, the assembly of Rodinia was marked by the Grenville Orogeny, on the east coast of the continent. Another major geological event of the Stenian was the creation of the Midcontinent Rift System in what is now the centre of North America. The Sleeping Giant near Thunder Bay is part of the Midcontinent Rift System.
Figure 5 -
Sleeping Giant, Thunder Bay ON
Credit: D. Gordon E. Robertson, Creative Commons
Attribution-Share Alike 3.0 Unported license
Was it Really that Boring?
Although part of the Boring Billion (see the YouTube video), the Mesoproterozoic wasn't really that boring, in my opinion. Yes, the biology and tectonics appear to progress at a sedate pace, but things did change. One supercontinent, Columbia, broke up under tectonic stresses and another, Rodinia came together, under those same tectonic forces.
Our view of the biological changes is constrained by the poor fossil record. Except for the stromatolites, almost all the organisms living at the time were soft bodied and any fossil preservation had to be extraordinary. Further research into the Boring Billion can only uncover more interesting facts.
Standard Caveat
The purpose of my weblog postings is to spark people's curiosity in geology. Don't entirely believe me until you've done your own research and checked the evidence. If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here. If you want to, go out into the field and examine some rocks on your own with the help of a good field guide. Follow the evidence and make up your own mind.
In science, the only authority is the evidence.