Many of you will be familiar with the fact that the Yixian Formation of Liaoning is an Early Cretaceous a lagerstatt type deposit that has a great many fine layers of sediment and thus can preserve fossils in exquisite detail including things like feathers, claws and so on. It can though of as a book with a great many thin pages which can be turned over (or torn off) in the hope that the odd page has something printed on it (or more accurately a fossil squished between them). This was largely my impression of the formation and the few photos that I had seen (plus of course a great many specimens), but now having had a chance to see the stuff first hand I have a few observations that might be of interest about the structure of the rocks (or at least of the patch that I saw). Simply getting to grips with a few outcrops for a couple of hours can give you a rather different impression of the rocks at hand and how you think of them when viewing specimens and that is certainly true here.
First off, there is a lot of curvature in the layers – that is they are not all preserved in horizontal layers. They are parallel certainly, but all kinds of flexes are there and while this is certainly common in geological formations (I’m not *that* ignorant about geology) it is something I have rarely seen in Yixian specimens but seems to be very common. There are some odd nodules in places too that obviously distort layers around them and add to this pattern.
The layers are incredibly thin and fragile and are not bound together tightly. I usually see slabs that have been glued together or set in plaster to protect them so I had not realised how thin some of them were. I could pick them off with just a fingernail they were so free from each other (though this was helped by a little weathering) and held up to the sun you could even see *through* some of them at least a little. This stuff is incredibly fragile as you can see from the photo of the fragments that have accumulated after just a few months exposure.
Fossils are incredibly common. OK, so I only found some odd seed cases, woody fragments and conchostracans but in 30 minutes of just general faffing about I had a small collection going as well as a couple of possible bone fragments and my colleagues had some nice insect larvae. There are a *lot* of fossils here.
Finally, while there are of course more than just small flat birds and lizards in the Yixian (i.e. there are big pseudo 3-D specimens like the iguanodontid Jinzhousaurus) I was amazed at the number of fossil tree trunks there were. A number had been pulled out of the site we were at and more were lying around in fossil dealers in large numbers and in parks and gardens. There are loads of them, they are very big, and often in very good condition. Ok, so I work on dinosaurs and pterosaurs and papers on fossil trees tend to pass me by, but I was still surprised to see how many there were.
That’s it for now, I’m no geologist or taphonomist (as you probably noticed, apologies for non-technical terminology) but obviously I have more than a passing acquaintance with Yixian specimens and was therefore both surprised and pleased to learn so much about it from my brief trip. Hopefully a few things will be new to some readers and certainly some of what I have learned will have an impact on how I view material in the future so I imagine it will benefit a few readers too.
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