Fossils from Avon Gorge

Jikes, it was a long time since we went to Avon Gorge, but I first now got down to taking pictures of the fossils (and other rocks) I brought back home. I will not make an extensive post of this either, I'm afraid. I need to prepare for the large fieldtrip we are facing in the end of this week!

These tiny blobs are not fossils, but some odd form of carbonate balls. They could be peloids – fossilised pellets of invertebrate faeces (bug poo) – or maybe ooids, a strange type of round balls with onion-like layers of carbonate around a usually empty core; no one really knows how they are formed, though there have been several guesses, the most accepted to date being that they form as bug mucus coats around some small object and traps carbonate particles around it, slowly forming a round, layered coating of limestone.

Limestone is basically any sedimentary rock with plenty of calcium carbonate (CaCO₃). The mineral (i.e. crystalline) form  of calcium carbonate is calcite, of which I found a rather large, (fairly) pure example. 

Calcite looks a lot like quartz (and a few other grey translucent minerals), but there is a (fun) way of making sure it is calcite. CaCO₃ reacts with hydrochloric acid (HCl) to form water (H₂O), a salt (CaCl₂, which is dissolved in the water, so you can't see it) and gas (hydrogen gas H₂ and carbon dioxide CO₂) which escapes from the water as bubbles. So, if you pour a drop hydrochloric acid on the rock and it fizzles, there is surely carbonate in it. 

 As for the fossils, a few are less spectacular, such as the two brachiopods below (the second might be har do see from that angle, but to be honest, it is hard to see from any angle!). 

I tend to find crinoids in large, disorganised masses, perhaps because they have been thrown around by strong currents. 

It is a shame, because I find them rather adorable from time to time (even though I always only find bits of stalks...). Albeit not remarkably interesting anatomically, these buggers have their charm.

More to my current interests, I found a few rugose corals.

Where is the little coral there? Actually, I just noticed it when I was taking the picture. Let me zoom in for you.

Look at the part where it has been broken in two. The inward-facing groovey thingies are tell-tale signs that it is a rugose coral.

And here are finally some nice brachiopods.

The end.

Please understand why I cannot make too many elaborate posts. I would be happy to, but time needs to be budgeted, and so on.

However, for the mammoth field trip to the island of Arran in Scotland, I promise you an interesting story, if anything about surviving in a God-forsaken island that has recently sufferet from a long, heavy power-cutting snow storm, where the visitors were stranded because the ferries were cancelled. That of course does not stop hard-core geologists...

Avon Gorge fieldtrip

Monday the 11th of March we had another one-day fieldtrip with the first-year geology group, this time to a site within Bristol: the Avon Gorge.

As scary as the name sounds (I have no idea of what it means, but the words sound ominous), the only frightening thing was the size of it.

(And that bit continues below!)

(We went to a few other sites, but this exposure was the main part, and where all fossils were found, so I will only retell our adventures here.)

I have been very unproductive in terms of blogging of late, simply because I really need to do more schoolwork now than ever before, plus search for and arrange accomodation for next year, prepare for the one-week field session we are having during the break, and begin to plan my summer (work, rehabilitation exercise for my bad knees, and I want to bring some friends from Bristol over), and do not forget the scientific method post I am working on (which seems like it will be massive, so I am considering cutting it into pieces and publishing them one at a time instead of the whole thing when it is all finished...)!

(However, I am intending to resurge my blogging soon, and especially include more discussions around material from our classes. I have a few ideas that could be of interest! Hopefully, it will bring a new dimension to this blog. I will also try to resume the PalQuizes.)

So, for this fieldtrip, I will actually dismember the narrative to focus on the fossils only. (Really, they were the only fascinating bit: the rest fell pale, especially since, typically, that day was like the coldest day of the year!)

Some fossils were large and clearly visible from far away.

There are some clear echinoderms – starfish, to be precise – and a few indeterminate worm-like creatures I have never seen before, so it was quite fun to see something new.

We found plenty of crinoids in the exposure wall (though the first one could perhaps be a rugose coral...). 

A really nice impression of a stalk plate: 

Another impression, this time of the side of the stalk, showing the contours of several plates: 

There were also plenty of rugose corals.

 

The last one is adorable! I think it was Nigel who found it. He finds all the nice ones, so it probably was. *grumble*





However, I did made one rather amazing find. We were told that there would basically only be crinoids and rugose corals here, and indeed, it seemed so...

*TAH-DAM-DAM-DAAAM*

... until I saw this:

Some form of shelled creature, most likely a brachiopod impression from the side. The top part would be its dorsal shell (upper shell) and the bottom its ventral shell (bottom shell), which is larger. In life, it would sit on the seabed on a fleshy stalk sticking out from the tip you can see on top right there, and it would sit upside down – i.e. with its ventral shell upward – and stick out a tentacly tongue-like structure from its other end (bottom left) to filter food particles from the water.

Brachiopods are one of my favourite invertebrate fossil groups, and this is one of the finest specimens I have seen in the field. A really successful day after all!

We also found plenty of fossils to bring back home, and I will show them in another post.