Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Sandmidj on 03/11/2018 14:36:21

Title: What is this ridged fossil found in Somerset?
Post by: Sandmidj on 03/11/2018 14:36:21

I found this as it broke off from a larger piece that was embedded in a grey rock on the shore at Doniford Bay, Somerset.
Can anyone tell me what it is please?
I brought it home as I thought it looked like a fossilised shell.

fossil 3.jpg (178.11 kB . 1000x726 - viewed 10612 times)

fossil 2.jpg (239.15 kB . 1000x831 - viewed 6013 times)

fossil 9.jpg (179.13 kB . 562x1000 - viewed 5998 times)

fossil 5.jpg (181.22 kB . 1000x787 - viewed 5872 times)

Title: Re: What is this ridged fossil found in Somerset?
Post by: chris on 03/11/2018 15:59:03

Interesting how the ridged profile is symmetrical on both sides of the specimen.

This needs @Bass to make a diagnosis. It's above my paygrade.

Title: Re: What is this ridged fossil found in Somerset?
Post by: RD on 03/11/2018 18:04:19

Quote from: Sandmidj on 03/11/2018 14:36:21

(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=75256.0;attach=28202;image)

Fossilized sand-ripples look like that ...

(https://jurassiccoast.org/fossilfinder/wp-content/themes/fossilfinder/images/fossils-database/Rock_and_pseudofossil/SID.G146.2009-lowres.jpg)

https://jurassiccoast.org/fossilfinder/846-ripple-marks/

Title: Re: What is this ridged fossil found in Somerset?
Post by: Sandmidj on 03/11/2018 21:18:11

RD the ripples on my sample seem symmetrical and are on both upper and lower surfaces: could this really be sand ripples?

Title: Re: What is this ridged fossil found in Somerset?
Post by: chris on 03/11/2018 22:29:22

The first thing I thought about were fossilised ripples, but, as I pointed out, there are ridges on both sides, which made me question my original instinct. I've seen quite a lot of examples of ripple patterns, especially in the rocks in NW Australia where I spent a bit of time, but none had ripples on both sides.

Title: Re: What is this ridged fossil found in Somerset?
Post by: Colin2B on 03/11/2018 22:45:36

Is it possible that these ripples formed over another bed of ripples. They certainly appear laid down.

Title: Re: What is this ridged fossil found in Somerset?
Post by: chris on 04/11/2018 10:38:07

Quote from: Colin2B on 03/11/2018 22:45:36

Is it possible that these ripples formed over another bed of ripples. They certainly appear laid down.

Good point.

Title: Re: What is this ridged fossil found in Somerset?
Post by: Bass on 04/11/2018 17:58:03

These appear at first glance to be symmetrical ripples, but there are other possibilities. The Fossil2 photo seems to  show ripples disrupted by some sort of later channel.
I'm intrigued by the green in photo Fossil9- is that mineral? or organic (like lichen)? If it's mineral, then I suspect the rock is carbonate. Can you tell if the rock is sandstone (will feel like sandpaper)? If it's carbonate (limestone), it should bubble if you drop acid (10% HCl or equivilent), especially on the unweathered edges.

Title: Re: What is this ridged fossil found in Somerset?
Post by: Sandmidj on 04/11/2018 22:53:50

the green bits are lichen. I found it protruding from a rock on the edge of a rockpool at low tide.
I don't think it is sandstone, it doesn't feel like sandpaper.
what do you think of this pattern which is on several areas of one surface?

20181103_102347 (2).jpg (545.32 kB . 1264x2457 - viewed 5481 times)

Title: Re: What is this ridged fossil found in Somerset?
Post by: chris on 05/11/2018 08:09:27

Could be bits of fossilised marine algae. I found some nice fossilised wood pieces in Teignmouth, Devon, a few years back; the appearance is quite similar.

Title: Re: What is this ridged fossil found in Somerset?
Post by: chris on 05/11/2018 08:11:31

PS @Sandmidj - I modified your post to insert the image into the body text so it's immediately visible. To do this yourself, if you need to, you go to "attachments" below the text box (where you uploaded the image in the first place) and click on the "insert" link next to the image name. You can do this at the time of uploading, no need to modify later. I think it helps because the image is presented at full size and people have less work to do to review the picture. chris

Title: Re: What is this ridged fossil found in Somerset?
Post by: Bill S on 05/11/2018 18:25:43

The nearest fossilised ripple marks I have seen to these were on Arran. One of our group found a double-sided specimen, but only one side was as well defined as this. 

Could the photo at #8 show cracks, infilled with a secondary mineral?