Composition of Black Sediments at Rhossili

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Composition of black beach sediments viewed under the microscope

Natural patterns on a sandy beachImages of patterns on the beach caused by wave action winnowing out lighter black sediments from the heavier yellow sand grains have been shown in earlier posts. Here are three microphotographs of the black sediments from a small sample that I scooped up on the shore at the time. Sorry there is no scale because I haven’t fathomed out how to include one in the images yet.

Natural patterns in black detritus on the strandline at Rhossili beachHopefully these shots are clear enough to show that the numerous black particles are small fragments of waterlogged wood; shiny hard pieces of coal (coal dust); a few large pale seeds not yet identified; minute fragmented seashells such as mussels; and many white slender organic objects which I think are small fish rib bones but could be or include heart urchin spines. It was these bones that gave the dried sample in the petri dish an almost fibrous appearance. I am going to see if I can find someone from the world of archaeology who would be familiar with the analysis of this type of material – to see if I can get some more specific information about these black sediments from the beach at Rhossili in Gower.

Composition of black beach sediments viewed under the microscope

Composition of black beach sediments viewed under the microscope

9 Replies to “Composition of Black Sediments at Rhossili”

  1. I first thought of plastic fibres (not uncommon in marine sediments nowadays), but I have not seen the original. What are the black grains. Is that pieces of basalt? Or augit?

  2. Hello Nannus. There was a text accompanying the photographs in the post saying “Hopefully these shots are clear enough to show that the numerous black particles are small fragments of waterlogged wood; shiny hard pieces of coal (coal dust); a few large pale seeds not yet identified; minute fragmented seashells such as mussels; and many white slender organic objects which I think are small fish rib bones but could be or include heart urchin spines. It was these bones that gave the dried sample in the petri dish an almost fibrous appearance. I am going to see if I can find someone from the world of archaeology who would be familiar with the analysis of this type of material – to see if I can get some more specific information about these black sediments from the beach at Rhossili in Gower.”

  3. I think this is great. I love that one can get so much interest by looking at different layers of detail – whether the seemingly abstract patterns on the surface or by looking at the constituent parts.
    I myself collected some fine shell wash at the high tide mark on a local beach some time back – and am still trying to identify everything it contained! – I must share on my blog too 🙂

  4. I look forward to seeing your post about the fine shell wash at high tide mark. I am not too bad at identifying shell fragments because of my research on marine molluscs as food remains in the past – lots of excavated samples are fragmentary, especially the sieved samples. I have a difficulty with seeds and other vegetable matter.

  5. Hi Jessica, great photos as ever. The pale wrinkly seed in the second photo looks like a Rubus (blackberry or possibly raspberry), and the black one to the right looks like a Chenopodium (goosefoot). Overall it really does look like an eroding archaeological deposit.

    Matt

  6. Hi Matt. Good to hear from you. Thank you very much for the seed identifications. That is very interesting. It is a small sample of the black sediment, just a couple of teaspoons’ worth. I’ll look through it again and separate out the other seeds to see if there is anything else recognisable. Could you recommend a book or paper that would help with seed identification?

  7. Hello, Matthew. Thank you very much for this information on seed identification. I will follow up both sources. It should be very useful.

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