The Earth Story

Original caption:

Two weeks of exploring, chilling and kiting in Sardinia wrapped up in two minutes.

Soundtrack: "Dolce Vita" by Ryan Paris Shot & edited by AIRUSHADDICT All shot with a GoPro Hero7 Black

Geology: Like Cluedo, but with less death and more rocks

The job of a geologist is to study the rocks around them (their clues) and then come up with a hypothesis as to how they all ended up in their current state and condition.The photo below shows a megaclast (larger than a boulder >4.1m) of Cambrian Gonessa Limestone within younger Ordovician Mt Argentu Schist that was observed in southwest Sardinia. But how did a huge isolated clast of limestone end up standing proud within a large outcrop of schist?

It is unlikely the clast was deposited by fluvial processes due to its anomalous size. Faulting was also disregarded due to the lack of field evidence (the contact is non-linear and not at a consistent orientation). After careful consideration of the tectonic history and depositional environments it was proposed that the megaclast represents an olistolith ( ‘a pebble to several kilometre sized clast foreign to the host rock in which it is emplaced’ Cieszkowki, et al., 2012) emplaced shortly after the Sardic Phase (Cambrian age collisional event) of deformation.

A likely hypothesis is that this outcrop originated as a Limestone cliff overhanging an alluvial fan. Due to weathering, erosion and an increase in pore fluid pressure, a large section of the cliff cleaved off and fell into the muddy sediment below. This piece of cliff was originally emplaced horizontally within the sediment, however it is now standing vertical (stromatolite fossil evidence confirms this).

So how did it go from horizontal to vertical? Well Sardinia has had a rough history, having undergone several orogenic (mountain building) events as well as its fair share of volcanism. During this time it is proposed that folding led to the clast being returned to vertical and that subsequent erosion of the more easily weathered schist left the clast standing tall (see my rather crude sketch below).

However, as with most things in geology this conclusion is not set in stone (badum dum tss). The evidence we have so far indicates that the most likely emplacement of this clast was an olistolith but if new evidence comes to light this could easily change.

Refrences: Paper Citation - Cieszkowki, M., Golonka, J., Ślączka, A. & Waśkowska, A., 2012. Role of the olistostromes and olistoliths in tectonostratigraphic evolution of the Silesian Basin in the Outer West Carpathians. Tectonophysics, pp. 248-265.

Further Reading: Paper Citation - Ślączka, A. et al., 2012. Sedimentary basins evolution and olistoliths formation: The case of Carpathian and Sicilian regions. Tectonophysics, pp. 306-319. http://www.sciencedirect.com/science/article/pii/0037073870900229

Image Credit: Watson Horrific Sketch Credit: Watson

Sea cliffs on Sardinia

Limestone coastline on Sardinia

Phosgenite A rare lead carbonate with chlorine added in, it shares with other lead minerals a heavy density (6.3 times denser than water) and a high lustre (surface reflectivity) nearly as bright as diamond's. While it is usually colourless yellow, brown, greenish or pink material has also turned up in various places. It was named in 1820 after phosgene subsequent to its first discovery in the lead mines of Derbyshire in England (it is also called Comfordite after its type location). It is brittle and soft (Mohs hardness of 3) and so almost never faceted. It forms in the oxidation zone of lead deposits where chlorine and carbonate rich waters (such as sea water or deep Earth brines) have altered the primary oxygen poor minerals into secondary ones. It exhibits the property of fluorescence in UV light, whereby electrons are excited by the energy and jump up a level before releasing the energy as they form back down as visible light. Other localities include Sardinia (whence hails this lovely gemmy 3.0 x 3.0 x 2.2 cm crystal and most of the larger specimens on the market), Greece, Poland, Siberia, the USA, Namibia and Tasmania. One intriguing locale has been in ancient Greek slag dumps from mine ore processing that were dumped into the sea. Loz Image credit: Rob Lavinsky/iRocks.com https://www.mindat.org/min-3195.html http://www.galleries.com/Phosgenite http://www.minerals.net/mineral/phosgenite.aspx http://bit.ly/2Ac32Ip http://bit.ly/2iThnSZ http://bit.ly/2C5MMdl

Bear rock We regularly share interesting shaped rock formations formed by erosion. This granite work of nature's art is located in Sardinia. The type of structure is called Tafoni, or honeycomb structure, and results from water leaching dissolved minerals to the rock surface. As it dries the minerals precipitate and flake off layers of rock in a process called cavernous weathering. The shape of the formation therefore reflects the movement of fluids through the granite. Loz Image credit: Martin Wintsch

Cosmonaut Sergey Ryazanskiy shared this timelapse video taken as the International Space Station flew over Italy, Sardinia, Sicily, the Mediterranean, and Africa. Really neat overflight of a lightning storm in the latter part.

Landscape, cliffs, and bay - Sardinia

Check out those limestone cliffs

Pygmy Mammoths, Cyclops and Greek Mythology

Many people have heard the tales of the terrible Cyclops; giants with a single eye that had a nasty tendency to kill, and sometimes eat, unsuspecting adventurers. However, conjuring up such fearsome beasts may not have been purely a feat of imagination; their origins may have been based on fact.

This story begins with the Mediterranean Islands during the Pleistocene, when low sea levels allowed land bridges to be exposed and for fauna to cross between land masses. Both elephants and mammoths roamed the Mediterranean with several species living side by side. However, at the end of the Ice Age, melting ice led to a sudden sea level rise, destroying any land bridges and isolating any individuals unfortunate to find themselves stuck on the island.

A lack of food led to an evolution bias in the elephant (Sardinia is the only island to have Mammoths) populations, with smaller individuals more successful as they required less food to survive. Over several generations this led to elephants/mammoths that could be as small as 1m at the shoulder.

So how do the cyclops come into this? Well, when the animals died they were stripped of all their soft tissue, but parts of their skeleton were preserved. The trunk of an elephant contains no bones and therefore is rarely found. This leaves the skull looking like the image below. Which oddly enough looks just like a huge skull with a single eye socket, especially if the specimen in question had lost its tusks.

Greeks coming to the island subsequently found these preserved skulls, often separated from any other bones or remains, and hypothesised to what they could be. They came to the conclusion these skulls had belonged to giant men with a single eye in the centre of their forehead and the myth of the cyclops was born.

Image Credit: Darren Copley

Reference: http://bit.ly/1PaBTr7

Further Reading: http://bit.ly/1DbTqHE