Andalucia: a history of stuff

Andalucia is a province in Spain, at the far south west of Europe. Its long and varied human history has seen it linked to the middle East, north Africa and the Americas. The creation of these links brought new foods, metals, diseases: new stuff into Andalucia. Sometimes the impact of arrival created ripples that reached out far across the world.

Geological history

Some 200 million years ago Andalucia was within a massive continent called Pangea, close to both Africa and North America. Slowly Pangea broke into pieces, a new ocean basin – the Atlantic – filling the gap as the Americas drifted away. Some 50 million years ago, Africa was pushed north in Europe creating a long mountain range. Andalucia was part of this. Mountains form when the crust is thickened, pushing rock into the sky. A similar process at the base of the lithosphere 1 also forms a thick balancing ‘root’. Under Andalucia, this thick root ‘fell off’2 and sank into the hot convecting mantle beneath.

Mountain belts are surprisingly fragile. The sudden removal of the heavy root caused the over-thickened crust to collapse, flowing sideways and bringing deeply buried rocks up to the surface3. Fragments of mantle called peridotite, not often seen at the surface, form brown mountains around the town of Ronda. The collapse of the mountain belt went so far that its centre is now the very western part of the Mediterranean, the Alboran Sea. The mountain became a great hole in the ground.

Most of Andalucia is made up of sedimentary or metamorphic rocks folded and twisted by these dramatic changes. An exception is the basin of the Guadalquivir river. Here the weight of the collapsing rocks pushed down the rocks to the north, making a depression that has filled with recent sediments – a feature called a foreland basin. The edge of this flat basin makes a clear line that is easily visible from satellite views of Southern Spain.

From Wikimedia

Andalucia from Space. Image from Wikimedia 


People, at first hominins such as Neanderthals, have lived in Spain for over a million years. The little we know of prehistoric humans comes from their use of materials. First their gradually more sophisticated use of stone tools, then from about 5000 years ago the smelting of metals: first copper, then bronze (copper plus tin) and then iron. Mines in Andalucia have been been involved since the start, notably the Rio Tinto area. Here a Carboniferous massive sulphide deposit has yielded silver, gold and copper and spawned a global mining company.

Image of Rio Tinto mines, Andalucia. Image from David Domingo on Flickr under CC

Rio Tinto mines, Andalucia. Image from David Domingo on Flickr under CC

Around 3000 years ago (1100BC) the Phoenicians reached Andalucia, founding the town of Cadiz. A culture that reached across the Mediterranean they were also involved in trade with the British Isles. Tin from Cornwall in England was smelted with Spanish copper and the resulting bronze traded on. The olive tree reached Spain at this time, brought from the eastern Mediterranean.

A mere thousand years later, the Romans took control – their province of Hispania Baetica covers much of modern-day Andalucia. They introduced deep mining to the Rio Tinto, using the characteristically Roman combination of slaves and very big wheels to pump water up from the depths. Andalucia was a renowned source of many products for the wider Roman Empire, including silver, olives, emperors, philosophers, dancing girls, and garum, a sauce formed from fermented fish guts rich in umami flavours.

Yet Moor invaders

After the slow collapse of the Roman Empire, the next major influx of change in Andalucia was the Moorish invasions. The Islamic Moorish army4 conquered most of Spain between 711 and 718 AD, in time creating a kingdom of Al-Andalus with its capital in Cordoba. Once more Andalucia was part of a multi-national empire with good trade links. Valuable crops from further east, such as figs, citrus and pomegranate were introduced for the first time, as were sophisticated irrigation systems, some of which are still in use. By the 10th century, Cordoba was the most civilised city in Europe, it’s Grand Mosque was one of the wonders of the Muslim world.

Cordoba Grand Mosque

The site of the Grand Mosque was originally a Christian cathedral (before that, a Roman temple). Built over 200 years and funded in part by mining proceeds, the Mosque was built with local stone and brick, but also recycled Roman stone columns. Some of these were found locally, but others were brought in from much further afield, from the rest of Spain and perhaps wider.

The Columbian exchange

Eventually Moorish Spain came to an end as Christian rulers conquered the Muslim lands. The final Moorish kingdom of Granada fell to Ferdinand and Isabella in 1492, the same year that they sponsored Christopher Columbus to mount an exhibition across the Atlantic. As  the Spanish kingdoms turned into a global Spanish empire, lots of incredible things started flowing back into Andalucia. First Seville and later Cadiz were the main ports for the Atlantic trade. Gold and silver beyond imagining passed through Andalucia – enough to create a century of inflation across Europe. Some of this stuff ended up in the the Grand Mosque in Cordoba, which is now a cathedral again. Sitting within the vast pillared area of the mosque is a Christian church full of beautiful things made of American gold and silver. The choir stalls are made of American mahogany – lots of plant material crossed the Atlantic too.

Ingot of South American silver as brought over by Spanish treasure ships. Cadiz Museum.

Ingot of South American silver as brought over by Spanish treasure ships. Cadiz Museum.

A popular Spanish dish is called ‘patatas bravas’ and consists of potato, tomato and chili – all foodstuffs that spread across the world following the ‘discovery’ of the Americas. Andalucia was the first stop for many of these vegetable treasures. Botanical gardens turned seeds into plants, to be studied and propagated. A fine building in Seville is the old tobacco factory, dedicated to processing another new crop. The setting of Bizet’s opera Carmen, its walls are mottled with yellow and brown, like a smoker’s fingers. More immediately bad for the health, syphilis was first recognised in Europe in 1494, most likely brought back by Columbus’ sailors.

The British dimension

As an Englishman who likes history, I often visit other countries in an apologetic mood. A dimly remembered story about Francis Drake daringly ‘singeing the king of Spain’s beard’  is rather less jolly when you are sitting in Cadiz, the town that was attacked. Drake was engaged in warfare on behalf of his Queen, but also behaving like a pirate, raiding Spanish treasure ships. Still, no one seems to mind any more; it was in 1587 after all.

The British drink everything and anything. Not content with home-grown beer, gin and whisky we also crave grape-based booze. When Francis Drake returned from attacking Cadiz, he brought 2,900 barrels of sherry, a type of wine made only near Jerez in Andalucia. This went down rather well – we’ve been drinking it ever since, even getting involved in its manufacture.

Tonic water is sweet fizzy water flavoured with quinine, best taken with gin. Quinine, an extract from a South American tree was for centuries the only effective way of countering the effects of malaria. First popularised by Spaniards returning from Peru it was introduced to gin by the British in India. In the early 18th century the Royal Navy had a number of bases on Spanish soil, including in Andalucia, and passed the habit on. It remains popular in Spain to this day.

Image from Amanda Slater on Flickr under cc

Image from Amanda Slater on Flickr under cc

A final anglo-Spanish connection is marmalade. Seville is full of orange trees, of a particular kind, bitter and rich in pectin. They are pretty inedible raw, but for some reason 5A Scottish tradition and industry grew up of preserving them as jam, with pieces of the skin floating in jars of pungent and yielding orange delight. Paddington Bear, James Bond and Alice in Wonderland all eat marmalade, along with many real people, such as me. The bitterness gives it a very grown-up feel, with some of the grimy delight of cigarettes and whisky, but in a healthy breakfast-friendly form.

The future

What of the future? Recent research suggests that soon6The oceanic crust beneath the Atlantic will start to plunge down under Spain into the earth’s mantle. The collapse of the mountain belt I mentioned at the beginning left a tear in the crust and this may grow and extend into a full-blown subduction zone. This will bringing volcanoes to fertilise the soil with ash and earthquakes to shake the buildings (if any remain). As slowly as finger-nails grown the Atlantic will vanish and Spain and the Americas will be reunited once again.

Categories: History, mountains, subduction, tectonics

Deep time and dead things in the wall

Here in Cadiz, I’m surrounded by death and I don’t mind at all.

It’s the geologist in me thinking this – in every other way this is a lovely life-affirming holiday. It’s just that every surface seems to be filled with the remains of long-dead animals.

The floor and one wall of the hotel room in which I’m sitting is covered in a fine white limestone packed with the remains of fossils – mostly bivalves. There are thick finely layered oyster shells and finely ribbed shells that remind me of scallops. The stone has mostly been cut perpendicular to bedding so the shells are seen in cross-section. These elegant fine grey lines are within a lighter matrix that – on closer inspection – is made up of smaller pieces of something-that-once-was-alive-and-now-is-not.


This is of course a wonderful thing. To be surrounded by traces of an ancient sea-bed, as productive and vibrant as any modern tropical sea and to live in a time that fully understands that significant of these little grey squiggles is indeed a privilege. But they are still dead.

Leaving the room doesn’t help. The city of Cadiz seems largely built from the local rock. This is basically a pile of shells bound together with ground up shell and maybe a little brown sand.

20140126_160603Cadiz is great for seafood, there were men with buckets of sea urchins and big knives wandering around earlier. Imagine a seafood restaurant kitchen at the end of the evening: there’s a pile of shells somewhere – big chunky oyster shells, purple fragments of bust-open sea urchins, maybe a few spiny sea snails. If you laid them out in a layer they’d cover a few tables maybe, not more. If an eccentric restaurant owner made a pile in his garden, after a year it would be pretty big (and very smelly). Archaeologists call similar features shell middens and given thousands of years, greedy people can make piles that are kilometers long and meters thick and wide. The layer of stone that old buildings in Cadiz are made from covers a much wider area – it’s not just a strip along the coast – so it must be thousands of times the volume.

This is where deep time comes in. My simple thought experiment suggests that the stone that Cadiz is made of took millions of years to form. Similar thinking by 19th Century geologists revealed the unsettling scale of geological time and set the scene for Charles Darwin to formulate his theories. Over these timescales tiny steps can make enormous changes, just as piles of small animals can be used to build a city.

Deep time can be unsettling: what will the remorseless grinding of the years do to us and our achievements? Will everything and everybody you know be reduced to a few odd layers and a puzzling mass extinction? Maybe. Nobody knows. But my life is enriched by knowing my place within the wider framework just as my walk to the restaurant this evening will be enlivened by spotting the oyster shells in the wall.

Categories: sediments

Winds of change

There’s a fabulous new site that shows wind patterns - it gives you a whole new perspective on the globe. One of the most striking things is the regular patterns across the oceans. Until quite recently long-distance travel was dependent on sailing boats, at the mercy of the wind and regular patterns of wind were needed to support regular sailing routes. The goods and people moved by these winds in turn drove dramatic historical changes that still resonate. Let’s look at a few, illustrated by the Earth Wind Map.

Turn of the sea

In the early 15th Century, Portuguese sailors began exploring the Atlantic ocean. Initial footholds were made on groups of volcanic islands: the Azores and the Canaries. Regular travel between these islands and Portugal taught sailors an odd trick: the best route back home was not a straight line but instead a big loop. This ‘volta do mar’ or ‘turn of the sea’ relied on working with the prevailing winds and ocean currents.

Atlantic winds (green), currents (blue) and approximate Portuguese sailing routes (red). Image from Wikipedia.

Atlantic winds (green), currents (blue) and approximate Portuguese sailing routes (red). Image from Wikipedia.

Here’s how the Earth Wind map looked for this area recently: the same pattern can be seen even in this snapshot of actual conditions.

Image captured from Earth Wind Map. With permission.

Image captured from Earth Wind Map. With permission.

Later sailors showed this pattern to be of global significance. It stretches across the entire Atlantic – Columbus used it on his return from the Americas. Eventually Spanish sailors correctly guessed that it applies to the Pacific, allowing the Spanish empire to connect Central America and the Philippines.

These patterns are caused by global circulation of the atmosphere. Warm air rises at the Equator and flows up and towards the poles. At around 30° latitude (north or south) it descends again into a region of high pressure called the Horse latitudes. Further north a different circulation cell is found, forever whirling in a different direction. These flows of air, on a spinning globe, create patterns of prevailing winds: ‘trade winds’. These patterns are fundamental features of the earth and have been recognised in ancient climates.


The Portuguese weren’t the first people to sail long distances, of course. Trade across the Indian Ocean between Africa, the Middle East and India was established long before; it supplied the Romans with spices as well as lions and tigers for their circuses.

The northern Indian, like the Atlantic at the same latitude, has trade winds that move towards the south west. This is convenient if you want to speed your cargo of hungry tigers from India over into the Red Sea and via Egypt to Rome. But how do you get a cargo of gold coins to India to buy the animals in the first place? Unlike the Atlantic, the horse latitudes are on-land: there is no turn of the sea to get you east.

Indian Ocean2

The winter pattern of winds, away from India

In the Indian Ocean something remarkable happens. The billion year old trade winds are switched, flipped completely round every year. From May until October winds blow from the south and west, towards India. This pattern allows repeat journeys and supports trade. In later centuries these winds sculpted a maritime ‘Dhow culture’ that stretched from the East African coast via Arabia into India.

What has the power to overturn a global pattern of wind? The Himalayas and the Tibetan Plateau do. This massive area of high altitude land was formed and is kept aloft by the ongoing collision between Indian and Asia. During the summer, heating of the high land lowers air pressure, drawing in air from the ocean. This reverses the pattern of winds and brings massive rainfall to India, feeding crops that feed millions.

Sugar, gold and blood

European exploration of the Atlantic of course led to the ‘discovery’ of the Americas, a new land full of Silver and Gold and indigenous civilisations collapsing under the onslaught of vicious diseases to which they had no immunity.

For many, the question was: how to make money from this new land? For the Spanish in central and south America, silver and gold was the obvious answer.  The Portuguese in Brazil and the English and others in North America and the Caribbean turned to farming, preferably of addictive substances.

Sugar, cotton and tobacco could all be grown in the Americas and shipped west to newly addicted populations in Europe. But who was going to grow the stuff? Shamefully, the answer was slaves from Africa, sold in exchange for rum or textiles made in Europe (from ingredients grown in the Americas).  Part of the reason this system worked was to do with the winds. The ‘turn of the sea’ was scaled up into the ‘triangular trade’ that took ships from Europe, to Africa, to America and back again.

triangular trade

In time Europeans realised the full horror of this system. The world’s first consumer boycott was of sugar, first organised in Britain in 1792. They realised that not a cask of this slave-grown sugar came into Europe “to which blood is not sticking”.


What the British mostly did with sugar was put it in their tea. Until the mid-19th Century, drinking unboiled water in a British city was a good way to die young. The traditional solution to this was to drink beer or gin – both sterile, if not completely healthy. In time, powered by growing commercial power in Asia, tea replaced booze as the British drink of choice (at least during working hours). This thirst drove the last great flowering of commercial sailing ships: the tea clippers.

Tea is a seasonal crop and the best tea is fresh tea. For these reasons fabulous beautiful ships were built to speed it across the world. The great tea race of 1866 saw four sailing ships race from China to Britain packed with tea. The first ship to arrive would command the best prices. The route they followed was the fastest possible, drawing on hundreds of years of knowledge of the trade winds. Let’s trace their winding route on a windy globe.

From China, down the South China Sea through the Sunda Straight

From China, down the South China Sea through the Sunda Straight

Across the Indian Ocean and round the Cape

Across the Indian Ocean and round the Cape

Back to Blighty, past St Helena and the Azores

Back to Blighty, past St Helena and the Azores

Categories: History, not geology

New Scottish Oil field discovered (470 million years too late)

Scottish oil is topical. Most of Britain’s oil and gas deposits sit under the seabed around Scotland but the revenues are shared with the whole of the United Kingdom.  If Scotland decides to become an independent state (there’s a vote in 2014) then that wealth will be all theirs. So I was very interested to read about a new Scottish oil field that has been discovered. There’s only one reason you’ve not read about this in the papers: all the oil was boiled off 470 million years ago.

easdale slate bgs

Easdale Slate sample. From British Geological Survey, sample P519560

Oil deposits form from dead critters – buried organic matter. Bury this carbonaceous material deep enough (often in black mud) and it heats up and enters the ‘oil window’. These ‘source rocks’ then produce oil which seeps away. In ideal conditions it enters a rock rich in holes (the reservoir) and is prevented from rising further by impermeable rock layers above (the seal).

Most oil deposits are found in more recent rocks, from the last 541 million years where traces of life are everywhere (the Phanerozoic). We know from rare fossils and geochemical evidence that life was abundant before this time, it was just mostly microscopic bacteria or algae. The ‘Cambrian explosion’ is rightly celebrated for the creation of new lifeforms, but its impact is partly due to innovations like hard shells and burrowing in sediment that made ancient life much more visible. It doesn’t necessarily represent a step-change in the raw *volume* of life. Before the Cambrian, there was lots of carbon being ‘fixed’ and sinking into sediment - many oil deposits are found from the next oldest period, the NeoProterozoic (1,000  to 542 million years ago).

Scotland contains sediments of this age: the Dalradian Supergroup. Some clever chaps from the University of Aberdeen thought to look in them for evidence of oil. In their recent paper Timothy Bata and John Parnell focus on rocks from the Argyll Group – the Easdale Slate and the Scarba Conglomerate.

Figure 1 from Bata & Parnell 2013

Figure 1 from Bata & Parnell 2013

The Easdale slate is a dark rock that even today contains up to 6.3% organic carbon by weight -it was a good candidate for a source rock. The Easdale sediments formed in deep water and the Scarba Conglomerate was the equivalent shallow water deposit. As a coarse pebbly sandstone it would have contained many small holes, up to 11% by volume, and so was a good candidate for a reservoir rock. Today it is strikingly dark in colour because it  contains abundant solid hydrocarbon residue – it is a fossil oil reservoir. The residue is found within pore spaces and is associated with pyrite crystals which they interpret as forming from Precambrian bacteria attacking/eating the oil.

These rocks are found across Scotland and Ireland – our authors estimate they could have contained over 6 billion barrels of oil. This find isn’t going to affect the vote for Scottish independence in September though. The Iapetus ocean these sediments were deposited on the edge of is long gone and so is the oil. It wasn’t extracted by cunning trilobites but was destroyed along with the ocean. Around 470 million years ago the sediments were buried and heated to high temperatures – the Easdale source rocks were converted from muds into slates useful in roofing. Only useless degraded hydrocarbons remain, the rest would have been returned to the surface as gas.

Rocks equivalent to the Dalradian might be expected to have similar deposits and these are found from Greenland to North America. Other Precambrian fossil oil reservoirs are there to be found – if you live on lightly metamorphosed Neoproterozoic sediments in eastern North America or in Norway, you might be sitting on the ghost of an oil-field.

Bata T. & Parnell J. (2014). A Neoproterozoic petroleum system in the Dalradian Supergroup, Scottish Caledonides, Journal of the Geological Society, DOI:

Categories: Scotland, sediments