The Geology of the Channel Coasts

I found this geologic map while randomly searching files the other day and I was impressed at how much of the geologic history of this area, home to two of Europe’s major cities, is displayed right here.

The rocks to the far northwest are heavily faulted, folded, and metamorphosed. These rocks are the last remnant of Pangaea; the continent that is today Europe collided with the continent that is today North America, thrusting up a number of great mountain ranges, including the Variscan mountains represented by these rocks.

When those plates pulled apart, this are switched from an active range that was building mountains to a passive margin at the edge of the ocean. Basins opened, bounded by normal faults, allowing waters of the ocean to pour in. Shallow ocean sediments were deposited throughout the area from the Triassic through the Cretaceous. These sediments make up some of the famous outcrops on the shores of the English Channel, such as the high cliffs in Normandy and the fossil bearing rocks on the Jurassic coast. The thickness of these sediments varies through the Channel area because each fault-bounded basin subsided by a distinct amount.

After the Cretaceous, far away the continent of Europe collided with the continent of Africa. Far to the south, that led to the growth of mountains, but here in this area some of the old normal faults were reactivated as thrust faults. One of these faults pushed up the sedimentary rocks into a fold, seen here as the Weald-Artois anticline. At the heart of that anticline, the older Cretaceous and Jurassic rocks are thrust upwards, exposing the chalk in the White Cliffs of Dover. Away from this anticline, sediments continued accumulating in the London and Paris basins.

Finally, about 450,000 years ago, ice sheets covered areas to the north of here. Rivers continued draining into what is today the North Sea, but the thick ice sheets blocked that water from escaping to the ocean. Eventually, the water poured over the top of the hill created by the Weald-Artois anticline, creating a waterfall that carved the modern English Channel path.

-JBB

Image credit: http://bit.ly/2Dmhbsl

References: http://onlinelibrary.wiley.com/doi/10.1002/jqs.744/full http://sp.lyellcollection.org/content/162/1/25.short https://www.nature.com/articles/nature06018 https://dx.doi.org/10.1038%2Fncomms15101_ _

At Land’s End

There are few places in the world where one can imagine the idea of infinite possibility. There are few places in the world where one feels that they are truly at land’s end; the very point where our scope of sight becomes limited by the natural elements of planet Earth. Here, at the very tip of Cornwall, England, land and sea meet at a threshold.

It can be humbling to stand at the barrier of a continent with nothing between you but the trickles of a tide and the sand between your toes. Face one direction: you are in front of thousands upon thousands of miles of open ocean water. Turn the opposite direction: you face the English Channel, and then miles upon miles of mountains, plains, desert, and land. Possibilities are endless on this planet where frontiers are unlike any others known in the universe. Possibilities are endless when planet Earth itself has become its own frontier.

--Pete D

Photo Credit: Krzysztof Nowakowski http://bit.ly/1hLHdkS

Durdle Door and Jurassic Coast

Seven Sisters Cliffs

In East Sussex, along the English Channel coastline, you will find these cliffs eroded into cretaceous age chalk. The chalk is the remnant of marine organisms, formed at a time when the world was warmer and sea levels were higher. The waters that buried this land were hundreds of meters deep and far from shore; ocean-going organisms flourished in these waters and their carbonate shells settled slowly to the ocean floor to create the chalk.

Today the waves of the Channel are gradually removing the remnants of those organisms. There are considered to be 8 hills separated by 7 gulleys that now drain over the cliff, and I think most if not all can be seen from this vantage point. Many layers of these cliffs contain larger fossil shells that are collectable; about half the area is contained in a park while the remainder is generally accessible to visitors. Authorities do warn that there have been collapses of the steep cliffs lately, so caution is advised for visitors.

-JBB

Image credit: https://flic.kr/p/HSBnP8

References: http://www.discoveringfossils.co.uk/sevensisters_fossils.htm http://bit.ly/1sA0HTo http://www.sevensisters.org.uk/

The cliffs of Étretat

The white cliffs of Dover are mirrored by these similar looking cliffs in upper Normandy, France. Along this 130 kilometer stretch of the so called Alabaster coast lies the small town of Étretat. Claude Monet and other Impressionists of the nineteenth century were attracted by the picturesque setting of the small village and famously painted the spectacular coastline.

Étretat is known for its three natural arches and white cliffs that tower high over the Atlantic Ocean. The Alabaster coast is actually made out of chalk and flint and not alabaster. It received its deceiving name due to the beautiful white color of the cliffs.

The Alabaster coast and the Cliffs of Dover have a similar geological history. The sedimentary remains of various marine microorganisms became accumulated over time and created these spectacular coastlines. In between the chalk are bands of flint which were derived from siliceous organisms.

The soft chalk is highly sensitive to erosion and under the effect of swell, frost, water seepage, wind and waves the cliffs are eroded about twenty centimeters a year. The chalk is rapidly dissolved in the sea whereas the flint forms the pebbles along the shore. The pebbles act as a natural barrier protecting the bottom of the cliffs against the waves. Furthermore, they are a valuable industrial resource which can be used in many ways.

Xandi

Image Credits: http://bit.ly/1MGSllu http://bit.ly/236hwCc Sources: http://bit.ly/1X2SccB http://bit.ly/1RC3eSL http://www.estrancitedelamer.fr/anglais/AFALAISE.htm