Excursion to Warwickshire, Saturday 28th September 2002

The Section C party met up at the Warwickshire Museum in Warwick town centre at 10.30 am, to see the displays of local geology. Warwickshire’s ‘solid’ geology is similar in some respects to that of Leicestershire, ranging from late Precambrian to Middle Jurassic in age. Warwickshire’s highlights include a fossiliferous Cambrian succession, a Caledonian intrusive suite, well-developed Coal Measures, and Permo-Triassic, early Jurassic and Quaternary vertebrates.

Members spent some time looking at examples of local rocks and fossils, including amphibian and reptile material from the Permo-Triassic sandstones of Kenilworth and Warwick. Mounted skeletons also attracted attention, notably a plesiosaur from the local early Jurassic Wilmcote Limestone. One display concerns the Rev. Peter Bellinger Brodie, Warwickshire Museum’s honorary Keeper of Geology during the latter part of the nineteenth century. Brodie was an enthusiastic local collector and many of his specimens are featured in the display.

After about an hour in the museum, the group was led to nearby premises currently housing the Museum’s Field Services department. The basement is excavated in the early Triassic Bromsgrove Sandstone. This afforded the group an opportunity to view fresh faces of the local bedrock that display a range of sedimentary structures. The basement also houses a collection of cores from Judkins Quarry, northern Warwickshire, comprising fine to coarse-grained pyroclastic rocks of the late Precambrian Caldecote Volcanic Formation. These attracted some interest.

Following an early lunch, the party reassembled at Edgehill Quarry (SP 372468), on Edge Hill, 20 km south-east of Warwick. The Edge Hill escarpment is made up of a Pliensbachian (Lower Jurassic) marine succession, comprising (in ascending order) the Charmouth Mudstone, Dyrham Formation (formerly Middle Lias Silts and Clays) and Marlstone Rock Formation. The Marlstone is developed here as a fossiliferous chamosite-siderite oolite, weathering to limonite. It is quarried for building and ornamental stone (‘Hornton Stone’) and as a source of aggregate.

(Left) In Warwick looking at the Marlstone Rock Bed as used for building stone (Photo © 2002 Andrew Swift)

(Right) In an underground store used by Warwick Museum, cut into solid Bromsgrove Sandstone. (Photo © 2002 Andrew Swift)

(Left) Rough cut Marlstone Rock Bed showing a 'nest' of brachiopods. (Photo © 2002 Andrew Swift)

(Right) In Edge Hill Quarry. From L to R: unknown, Peter Appleton, Ray Fox, Dennis Gamble, Andrew Swift, Joanne Norris, Robert Tripp, Karen Stace, Mrs Latham, Mark Evans, Roger Latham, Jon Radley (leader), Helen Jones. (Photo © 2002 Andrew Swift)

The party entered the quarry and proceeded through a maze of abandoned workings and spoil tips. At the currently quarried south-western end, shallow pits revealed a belemnite-rich shelly mudstone (a good example of a ‘belemnite battlefield’) at the top of the Dyrham Formation. A little way above, the Marlstone’s basal pebble bed forms the main quarry floor. This attracted much attention. The ‘pebbles’ are actually cobbles and slabs of shelly sandstone and ironstone derived from the underlying Dyrham Formation. The matrix is richly fossiliferous and members soon discovered specimens of the bilobate oyster Gryphaea sportella. An example of Gryphaea gigantea was also found. Several large pectinids were excavated, including smooth-shelled Entolium liasianum. Many brachiopods were noted, including a few examples of Spiriferina.

Several metres of Marlstone are visible in the quarry faces. Here it is mainly limonitic, well jointed, and locally cross-bedded. Blue-green chamositic ‘cores’ were seen in places, as well as a few fossils including wood fragments. A dump of sawn Marlstone slabs on the quarry floor additionally revealed a variety of trace fossils.

The party dispersed at approximately 16.30, following a vote of thanks for the excursion leader, Dr Jon Radley, the curator of the Museum.

Jon Radley

Warwickshire Museum