Patterns made by trace fossils at Lyme Regis

Natural patterns made by trace fossils in rock

Visitors to Lyme Regis are always amazed by the wonderful large ammonites embedded in the beach rocks and rock pavement, and are often frantic in their search for take-away fossils as mementos for their day out…. but they frequently overlook the less spectacular but nonetheless fascinating myriads of trace fossils underfoot. Trace fossils are also known as ichnofossils and they are the evidence, preserved in stone, for the activities of organisms rather than the petrified remains of the animals themselves. They tell us about the way animals behaved and interacted with their environment in the past.

The patterns in the rocks shown in these photographs are the traces of burrows and tunnels that were made in the sediments before they became rock. They were made by marine invertebrate creatures like crabs and worms. The intriguing natural patterns are found in the Blue Lias Limestone from the Jurassic Period. The Jurassic system is exposed along the Dorset coast between Lyme Regis and Swanage with very few breaks. Melville and Freshney (1982) say that trace fossils are abundant in rocks of this area and there are four common types:

Diplocraterion with U-shaped burrows at right angles to the bedding planes, measuring 21 by 4 cm with the diameter of the tubes up to 0.7 cm. These were the permanent domicile of worms or crustaceans that angled or swept for food suspended in water.

Chondrites with regularly branching, vertical to horizontal burrows spreading down like the roots of a tree, and 2mm or more in diameter. The work of sediment-eating animals, perhaps sipunculoid worms.

Thalassinoides Ramifying, Y-shaped branching networks of plain horizontal and vertical tubes, 1 to 5 cm in diameter. Feeding burrows of decapod crustaceans.

Rhizocorallium Horizontal to oblique U-tubes, each arm 1 cm or more in diameter with arms several centimetres apart with reworked sediment between them. Tubes short or long depending on whether the animal was in a suspension-feeding or deposit-feeding phase of activity.

The pictures show several burrow types intermingled.

REFERENCE

Melville R. V. and Freshney E, C. (1982) British Regional Geology: The Hampshire Basin and adjoining areas, Institute of Geological Sciences, NERC, HMSO, pp 7 – 8, ISBN 0 11 884203 X.

7 Replies to “Patterns made by trace fossils at Lyme Regis”

When I come across these in fragments of stone – or larger versions in rocks – I’m never sure whether I’m looking at a root or a tunnel.

LikeLike

I suppose it depends on what the rock is and where it has come from. I think burrows by animals are more commonly found than those made by roots on account of the sedimentary rocks round here mostly being formed in marine lagoonal types of environment. However, I do recall that preserved root systems are recorded in the more terrestrially-derived Triassic Otter Sandstone rocks at Budleigh Salterton (http://www.southampton.ac.uk/~imw/jpg-Budleigh-Salterton/11BST-Rhizoconcretions-Seafront.jpg).

LikeLike

That’s fascinating. There are rocks near me which come into this ‘is it a burrow or is it not?’ bracket. They’re a bit awkward to get at at present because the path has slipped. There’s another way round but only once the ground has dried out. When I can get there, I’ll take some photos and see what you think.

LikeLike

That would be great. Photos of the roots/burrows, and some of the wider setting in which they were found as well will give me an idea of the context. If you also tell me the exact location where you took the photographs, I can look up the geology maps and books to see what the likely rock type is and see which trace fossils have been recorded there.

LikeLike