Monday, October 11, 2010

Palaeoporn 19

Another holy grail


Ignore the cute baby buffalo. See that unprepossessing roadside quarry with the people sitting on a pile of rubble (click to enlarge)? Well that rubble is the type section for the Chengjiang fauna.

Yeah! Not so unprepossessing now, is it?!

The Chengjiang fauna occurs in the Maotianshan Shale, a member of the Lower Cambrian Chiungchussu formation. They are found about 5 km northwest of the Fuxian Lake, and 6 km northeast of Chengjiang, Yunnan, China.

The age of the fauna is between 525-520 million years old, significantly older than the Burgess Shale (at 505 million years ago), and the Emu Bay Shale (approx 515 million years old).

The Chengjiang fauna rivals that of the Burgess Shale in preservation and diversity. Although not in difficulty to get to. The Burgess Shale is a 3 hour hike. Here, you can drive right to the outcrop!


In this shot (click to enlarge) you can see the quarry from photo one in the middle distance. There is a bus parked next to it with some people in the road. The hill to the right is Maotian Mount (hence Maotianshan Shale)


In this photo (click to enlarge), I am right at the back in short sleeves and a broad-brimmed brown hat (I'm in the same position in the first photo). I'm there partly because it's in the shade, and partly because there were some nice fossils there (all went to Nanjing University for study).

The depositional environment was delta front prograding eastwards into an open sea. Most of the fossil layers appear to be episodic events onto the marine muds in front of the delta, possible storm induced deposition of clays and fine sand. There's not much evidence of transport, so most organisms were locals and were buried by a series of turbidity flows.


This is a smaller quarry close by (click to enlarge). The dark colour is the fresh colour of the Maotianshan Shale. It is black when fresh, but rapidly oxidises to a tan colour on exposure to air. This is near the top of the Maotianshan Shale. The pick axe handle in the middle of the shot is marking the topmost Maotianshan Shales. The very top of the handle is resting against the first influx of sands, which coarsen upward until they are topped by a large lenticular sandstone at the top of the sequence above my head. This represents the prograding delta as it moves out over the muds of the Maotianshan Shale - just like the sands of the Mississippi Delta are prograding out into the Gulf of Mexico.

7 comments:

  1. So can the Chengjiang fossils be readily distinguished in the field, or are you collecting promising-looking samples and preparing them in the lab?

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  2. The fossils are orange/brown and stand out well enough (Google Chengjiang fauna images to see). The problem is that, as they are entombed by turbidity currents, they do not lie nicely along the bedding, but are inside the beds. This means that when you crack the rock, it splits randomly, usually uncovering only a portion of the fossil. The rest has to be prepared out in the lab to expose the whole fossil.

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  3. Very nice! Congratulations on another tick on the palaeo bucket list. Are all the other people collection there just private collectors? If so, I'm guessing they may not be so nice as you and hand fossils over to the Uni.

    Rolf

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  4. It was a post-symposium field trip organised by Nanjing University.

    Everyone there was a geologist, and all the samples went back to the university.

    It is now a protected area and casual collecting is not allowed.

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  5. Stunning article, Chris.

    I am emigrating to China in a few weeks, and hope to make it out to the Maotianshan shales a few months after that.

    Hopefully, Nanjing Uni will need an extra pair of hands if they have any fieldwork on the calendar.

    I hope you enjoy(ed) yourself out there. Grab a few cha xiao bao for me!

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  6. Well, from what I know, the area having the same formation is much much bigger than ChengJiang. It spreads to even the west side of KunMing city. I did several collections at ChengJiang, even with Ms Zhou.
    I strongly recommend the book "The Dawn of Animal World" (in Chinese) by Chen JunYuan. To those who can not read Chinese, the color photos are excellent.

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  7. Jennifer,
    Yes you can use the image as long as it isn't for commercial purposes. I've disabled you comment because it links to a betting site.

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