August 5. Tethys

Paleo-Tethys (early Permian, about 290 million years ago)

I’ve mentioned the Tethys Ocean a couple times, I think. This was the oceanic basin more or less between Gondwana to the south and Eurasia to the north. But technically, anything I called Tethys up until now should have been called the Paleo-Tethys Ocean, the ocean that preceded the Tethys. The Paleo-Tethys was a large, roughly triangular sea, really almost a huge bay, between the northern and eastern margin of Gondwana – Arabia, India, and Australia today – and the complex and poorly understood margin of central Eurasia, essentially Kazakhstan, parts of Central Asia, and North China today. The eastern side of the triangular sea was a spotty boundary that was probably made up of independent small continental blocks including what is now South China. 


The Paleo-Tethys was a rifting oceanic basin that had extended west between what is now North Africa and independent blocks that would become Iberia and other parts of Europe. That western section was at least partly closed when Gondwana collided with North America and western Europe, the Alleghenian-Ouachita Orogeny in North America and the Variscan Orogeny in Europe.

Paleo-Tethys + NeoTethys (late Permian, about 250 million years ago)

There’s even a Proto-Tethys Ocean which lay between some of the blocks that united in Silurian and Devonian and later time when Kazakhstan, North China, and other pieces came together. All this nomenclature is obviously confusing – Proto-Tethys, Paleo-Tethys, Tethys, but they really do represent different oceanic basins that opened and closed at different times.

From our Permian point of view, just think of a wide triangular bay pointing west toward the juncture of Africa and Eurasia, roughly where Tunisia and Iberia are today. This Paleo-Tethys in early Permian time was destined to last until about the end of the Permian, when a long narrow strip of the margin of Gondwana rifted off of Gondwana and began to move north. That closed the Paleo-Tethys Ocean but opened a new ocean, usually just called Tethys but sometimes called Neo-Tethys. Is this all confusing enough? This is a time when it might be useful to check the nice maps from a PhD thesis by Pierre Dèzes at the University of Lausanne. I’ve posted them here.

But Tethys in all its incarnations is a major element of the earth’s geography from the Precambrian right up to the present. The Mediterranean, Black, and south Caspian Seas are probably remnants of one or the other of these ancient ocean basins today. 

Tethys was an ancient Greek sea goddess.

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Today’s geological birthday is Warren Judson Mead. He was born August 5, 1883, at Plymouth, Wisconsin. He taught geology for 25 years at the University of Wisconsin where he pioneered the field of engineering geology, and 20 more years at MIT where he chaired the Geology Department for many years. He also served as a professional consultant and expert witness for many industrial issues relating to geology, including the disputes over ownership of underground veins here in Butte, Montana, where I live. One of his sons, Judson Mead, was my professor of geophysics at Indiana University and director of the Indiana University Geologic Field Station – two roles that shaped my own life extensively.

—Richard I. Gibson

Tethys globe views from PhD thesis of Pierre Dèzes (1999; Institut de Mineralogie et Petrographie, Université de Lausanne) from 
http://www-sst.unil.ch/research/plate_tecto/alp_tet.htm via Wikimedia commons