Wednesday, June 26, 2013

THE BELT SUPERGROUP: Take a Walk on the Proterozoic Beachfront


The Belt Supergroup is a Precambrian sedimentary formation that crops out across a wide expanse of Idaho, Western Montana and SE British Columbia., and, due to the splitting and wandering of tectonic plates, it’s highly probable that parts of it are found in Siberia, China, and even Australia. 

Study of the Belt is integral in “uniting” the early super-continent of Rodinia, a Meso-Proterozoic Pangaean-like aggregation of nearly all of the earth’s landmasses. Back in the ‘70s when I collected rocks from the Belt, they were thought to be ~800 – 1.5 billion years. Since then, the entire group has been re-dated to ~1.4 to 1.45 billion years in age. The age of the development of the Rocky Mountains that contain the Belt rocks are ~80 million. Geology progresses…

The sediments are in an excellent state of preservation: for so old a formation, there are exposures that look as if they formed yesterday. Some surfaces show the imprints of rain drops and mud cracks left behind when drying from a gentle rainfall. The flow of water over sands and clays formed ripple marks, just as those seen in the shallow waters of today’s rivers and seas. The only fossils that the Belt rocks are famous for are stromatolites (http://tinyurl.com/jvskq22 ), primitive colonies of cyanobacteria that cemented sedimentary particles into accretionary forms. Some reports of other kinds of early life forms turn out to be pseudofossils, though others may be authentic. Walking on the sands of the Belt is, literally, to walk on the beach of the Meso-Proterozoic. A time machine…

Imagining a Proterozoic world, one with no life on the lands and only bacteria in the seas… where else can this sort of environment be envisioned? The similarities between the Proterozoic on the Earth and the early, water-rich and potentially life-bearing era on Mars shed light on the early histories of both planets.

Conveniently enough, some of the best exposures of this supergroup are found in Glacier National Park. If you have the chance, visit the Belt Supergroup – a trip in time and space.

“Here about the beach I wander'd, nourishing a youth sublime. With the fairy tales of science, and the long result of Time…” Tennyson


Photo: Logan Pass in Glacier National Park, Montana
Downloaded with thanks fromhttp://commons.wvc.edu/rdawes/virtualfieldsites/LoganPass/VFSLoganPs.html

More information:
http://formontana.net/slabs.html
http://www.nps.gov/glac/forteachers/geology.htm
http://www.sciencedirect.com/science/article/pii/S0024493711003811
http://www.agu.org/books/ft/v334/FT334p0007/FT334p0007.shtml

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