It has been a pretty good past two or so weeks. My third and very sadly, last geology field trip (7 – 17 Apr 2014). I don’t think I ever got round to blogging any of my field trips here proper (just a bit on Arran here), but this being my last geology field trip, I thought I should do it some justice.
Geology – the study of solid Earth, the rocks from which it is composed and the processes by which they change – has been nothing short of fascinating and awesome. I can only wish that the Ministry of Education in Singapore would introduce some geology into the curriculum, in particular Earth history and palaeontology (heh). Over the past year and a bit, I have learnt so much more about the history of the Earth, the physical and biological processes that result in what we now know to be our current planet, the life on the planet past, and of course the minerals and rocks that I have always glossed over (though to be honest, in steel and concrete Singapore, there aren’t that many rocks/outcrops to observe). The Department of Earth Sciences being the most awesome department in the university is just the icing on the cake.
Some background before trip details proper: there are two geological sciences courses offered in second year, broadly speaking with A focusing more on surface processes (sedimentary rocks and fossils) and B focusing more on mantle/core processes (igneous/metamorphic rocks and minerals). I chose to do GSA (cos I don’t like minerals and petrography all that much), along with ecology and animal biology, but I still went for the whole field trip (which encompassed a GSA half and a GSB half).
The GSA half was located mostly in Dorset, along the Jurassic coast where we were looking at Mesozoic sediments and fossils, while the GSB half was mostly in Cornwall, looking at granites, volcanics, ophiolites and metamorphic rocks related to the Variscan orogeny during the late Palaeozoic.
Geology is quite related to the oil industry, and we all know we get oil and coal from long-dead-creatures. Wytch Farm is the only onshore oil field in the UK (and apparently western Europe), and still a fairly important one. The primary source for all that oil is from the Lower Lias formation, laid down during the lower Jurassic. For better or worse, we do spend quite a bit of time talking about source rocks, reservoir rocks and seals.
Most of the rocks are exposed on the coast, in the form of cliffs. So we spent lots of time walking on beaches, looking at different kinds of rocks and of course, for fossils.
The beef mentioned in the title, unfortunately, doesn’t refer to the protein that many enjoy seeing on their plates. Instead, it’s the name given to a form of fibrous calcite crystals often seen in organic-rich shales (El-Shahat and West, 1983).
Lyme Regis is well-known amongst fossil-hunters because of Mary Anning, a famous British fossil-collector and palaeontologist who found many awesome fossils (ichthyosaurs and plesiosaurs, for example!) in the Jurassic coast of Lyme Regis. I was really pleased that we went to Lyme Regis on my birthday(:
Not just marine stuff, but also some trees! Or what used to be trees anyway. Some sort of gymnosperm that lived close to sea level during the Upper Jurassic and unfortunately got drowned when sea levels rose.
The GSA portion of the trip was largely about looking at lots of rocks deposited during the Mesozoic, the (trace) fossils found in them, and then trying to piece together what on earth went on during that time period (on the piece of land that present-day-Britain was on at least, which was generally the supercontinent Pangea/subsequent rifting to form the continents we now recognise). All too soon though, all that fun had to end, and we spent our time instead, looking at spectacular structures in rocks and other pretty amazing rocks. Older rocks, emplaced during the Palaeozoic.
Peridotite forms much of the upper part of the Earth’s mantle, which is really deep down, at least about 7 km below oceanic crust, or 30km below continental crust (not sea level). It is thus relatively rare to see it in broad daylight just like this (excitement!), and only occurs when it accidentally gets emplaced onto continental crust instead of disappearing down into the depths again as it should, when oceanic crust collides with continental crust. When it appears on the surface, it’s known as an ophiolite, and studied with great joy by geologists. Anyway, this was part of the Lizard complex and was plonked on the surface in early Devonian times, when Armorica collided into Laurentia to give Laurussia.
One usually thinks of rocks as being really hard (though of course, chalk isn’t quite as hard…), so rocks folding have to come from really really major events. Such as continents colliding into each other, producing mountains (orogeny). The rocks here are interbedded sandstones and shales, deposited during late Carboniferous, but were folded quite sharply when Gondwana collided into Laurussia to form Pangaea (still short of Siberia at that point though, which crashed to form Pangaea proper a short geological while later).
During the early Permian, during the last bits of the Variscan orogeny, the heat from thick piles of continental crust results in its melting and the formation of granite intrusions. Associated with the granite intrusions were these dykes, the exact details aren’t really known still, but anyway, so the magma squeezes between cracks to form a dyke, with really large crystals (phenocrysts) such as those seen above. Not as exciting as fossils in my opinion, but nonetheless still fairly important in telling us about what went on in this planet before humans existed to record things in storytelling/writing…
And the reason why mush appears in my title, is once again, not about the food, but rather a reference to crystal mush, when a half-solidified dyke is still warm and contains crystal mush in the middle, allowing another dyke to intrude and form a composite dyke. Which is what happened to that dyke in the picture – it squeezed into the middle of another half-solidified dyke, which had no large crystals in it.
But although looking at rocks is really more fun than it sounds, and really interesting for all the Earth history that one can learn just from them, I really still do prefer my animals and plants alive than dead. So here’s a Black Oil Beetle (thanks to Facebook friends who helped with ID) that Madeline picked up while on the way to visit Mr Steve Etches’ Kemmeridge fossil collection and a native adder that we were fortunate to see.
All in all, I had a very nice last geology field trip, lovely weather with lots of sunshine almost everyday except the very first day. I am definitely going to miss geology, but given that while we were on the coast looking at rocks, I by default think of competition on rocky shores, barnacles and limpets and anemones and all sorts of other little marine critters, I think zoology over geology was the right choice… ?