A lot of focus is often put on discovering fossils. But there’s another aspect that I enjoy about going out into the field and exploring: palaeoenviromental indicators. They tell us where and how fossil bones were deposited, as well as what the world was like at the time the plant or animal was alive. This information can sometimes be equally as important – if not more important – than the fossil itself.
In the Herschel bonebed, there are a whole host of really interesting palaeoenvironmental indicators:
Greyish green shale and sand.
The fact that some of the fossils are associated with greyish green shale indicates that they were deposited in a marine setting – however, the rock record here suggests that there were some fluctuations in the type of marine setting. There are marked changes in the colour and type of sediment we find throughout the bonebed. The knife in the above photo, demonstrating one of these changes, gives us a sense of scale.
Cobbles and clay pebbles.
There are also a few cobbles and clay pebbles associated with the sediment, which contrast with the very fine sands, muds and shales in the rest of the bed. In some cases, these stones may have been brought by storm events, and in others by the animals themselves as gastroliths (stomach stones). Some of the clay pebbles may have formed inorganically after the original depositional event.
Interestingly, there is also fossilized wood and amber in this marine. This material must have been washed into the sea at some point, suggesting that we can’t have been too far from the palaeocoastline - at least during one point of the bone bed deposition (the sea level may have risen and fallen over time).
Trace fossil Thalassinoides, found at Herschel. It could have been created by a ghost crab.
For me, one of the most exciting paleoenvironmental indicators we found are called trace fossils. Trace fossils (also called ‘ichnofossils’) are traces left by animal activities. In this case, we found animal burrows, likely made by invertebrates (e.g. crustaceans, worms) burrowing in the sediment, which were later filled in with sand and preserved as sandstone or ironstone ‘tubes’. Trace fossils can be highly indicative of the paleoenvironment, which is why we were excited to find them in the Herschel bone bed.
Trace fossil, Monocriterion, found at Herschel. It was probably created by a polychaete worm.