Hull Geological Society visit to the Frodingham Ironstone quarries on 24th June 2006,

led by Steve Thompson of North Lincolnshire Museums.

The meeting started by looking at the display of ironstone fossils in the North Lincolnshire Museum in Scunthorpe.

We then visited one of the old ironstone quarries where we had access to, at the top of the sequence, the Marlstone Rock, below which was an outcrop of the Pecten Ironstone resting on Frodingham Ironstone. All these rocks are Lower Jurassic and very fossiliferous.

The most common fossil seen in the Marlstone Rock was the belemnite Nanobelus . Many of those on the surface were split longitudinally by frost. One complete specimen of the ammonite Arnioceras was found, together with several partials. The Pecten Bed was packed with Chlamys sp ., but these were difficult to remove whole.

Our next location was a dump of ironstone. Some 25 000 tonnes of the rock has been removed from the nearby quarry and is on land owned by the local council. These rocks are packed with fossils including: Nanobelus belemnites, Arnioceras ammonites, Pleurotomaria angelica gastropods, Cardinia and Tancredia ferrea bivalves, and pectinids (mainly Chlamys ) were found. However the most common fossil found was the oyster Gryphaea arcuata , frequently with both valves. The literature states that Cardinia outnumbers Gryphaea in the ironstone, but this did not seem to be the case in the rockpile.

A characteristic of some of the ammonites and Cardinia was a distinct green colouring. This was due to the presence of iron silicate (chamosite) formed in water lacking in oxygen.

T Rockett.

(c) Hull Geological Society 1999 + 2007