A few notes on the preservation of the Yixian Formation

IMGP3418Many 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.

IMGP3414First 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.

IMGP3415The 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.

IMGP3474Finally, 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.

IMGP3421That’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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6 Responses to “A few notes on the preservation of the Yixian Formation”

  1. 1 Alan Kellogg 02/08/2009 at 8:58 am

    After reading your post I’m thinking swamp. Swamp because of the type of sediment present, and the great number of trees. Not just a swamp, but one with slow moving, at times stagnant water. Possibly a rainforst. What’s the thinking among local paleontologists?

  2. 2 David Hone 02/08/2009 at 9:49 am

    I think most people think that the Yixian is lacustrine (i.e. a lake) which fits with the pattern of slow deposition of very fine sediments (perhaps seasonal or annual) which leads to the various layers being deposited. As for the big trees I just don’t know having not read anything on their preservation (and I didn’t think to ask anyone while I was out there). They seem to be mixed in with the other specimens though which makes me think that they simply have not decayed or been crushed rather than they were in a different environment.

    • 3 khoby Rowe 10/05/2012 at 4:58 am

      Hi There, I’m interested in some more info about your trip and Yixian in general could you please email me personally.

      Look forward to hearing from you soon


  3. 4 Bea 01/07/2013 at 1:58 am

    I was read from several sources that China does not allow the export of fossils. There have however, in recent years been the Chinese replication of fossils, even those of arachnids and possibly therefore insects. Also I am having a difficult time tracking down much documentation on the Yixian Formation from quotable sources. Can you give me some feedback on this problem? Also please if you are aware of documentation on the Yixian from a quotable source it would be of great help to me.

    • 5 David Hone 02/07/2013 at 8:03 am

      Hi Bea,

      I’m afraid I really don’t know what you mean by ‘quotable sources’, are you looking for researchers’s comments, or just papers / books on the subject? In the case of the latter, well, there’s endless amounts, in the case of the former, you really need to speak to the Chinese researchers who have seen this first hand, but I’m not sure there is much written about this – everyone knows about the problem, but I’m not sure much is in print.

      Can you be more specific?

  1. 1 The Sino-German Fossil & Geology Park « Dave Hone’s Archosaur Musings Trackback on 02/08/2009 at 1:46 pm
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