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1840 Views 1 Reply Last post: Sep 19, 2012 11:57 AM by Florin - Museum ID team RSS
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Feb 2, 2012 2:28 PM

2012-0205 What is this (arrow-shaped) fossil please?



Found at the very top of the Lias in the East Midlands, just below (almost on) the Mid-Cimmerian unconformity. In this location (near Stamford) the top of the Lias has 'Thalassinoides' burrows and the basal conglomerate of the Northampton Sand Ironstone has pebbles up to about 10mm diameter, including black probably phosphatic ones. Some pebbles are bored. The Lias matrix in this specimen is rather sandy which I why I suspect that it came from that no-mans land close to the unconformity. The lithology of teh Northampton Sand ironstone is different; the sand is much coarser.


The Lias in this location is mapped as the Whitby beds and I have seen 'Dacryomya ovum' which in Whitby is associated with the Alum Shales.


I attach pictures of the unconformity, which is stunning.

  • Hello,

    Sorry to keep you waiting. I've found an old email with a reply from an expert:

    "The photo is a very nice example of Rosselia (Dahmer 1937).  It is a conical trace fossil with a central tube. The cone is often laminated with a muddy fill.  In the photograph you can see several vertically stacked burrows produced by escape followed by re-establishment on the new sediment surface.  This is a common feature of Rosselia colonisations.  I have recorded this trace fossil in marine sediments in shelfal storm beds, wave reworked tidal flats and within wave-generated lower shorefaces where the rate of sedimentation can be variable to high.


    Possible producers could be detrital-feeding worms using the cone to trap silt.  Alternatively they could in infaunal deposit feeding bivalves using the tube for refuge and the cone to feed in.  I prefer the later and have found bivalves in life position within the central tube.

    This looks most like the species Rosselia socialis (Nara 1997, Palaios, 12, 489-494) but is on the small side."

    I hope this helps.



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