Tag Archives: Uttlesford

Object of the Month – June 2020

June’s Object of the Month celebrates Volunteers’ Week. These fossils have been cleaned and recorded by two dedicated geology volunteers, helping to audit the thousands of fossils held in the Museum’s stores. The project is suspended at the moment, but we all look forward to getting back together when times are better.

These fossils are from the Red Crag layers, which are the reason Walton-on-the-Naze is famous for marine fossils. The sandy Red Crag rocks and fossils were laid down in the late Pliocene and early Pleistocene epochs between 3.3 and 2.5 million years ago, when a warm, shallow sea and bay covered most of Essex. The fossils have stained red-brown over time due to iron-rich water washing through the sandy rock.

The first fossil is a species of whelk, Neptunea contraria, which is still alive today (extant, rather than extinct). This species has an unusual left-spiral shell, hence the word contraria in its scientific name. Almost all species with a coiled shell have a right-hand spiral.

Neptunea contraria

Cardita senilis

Cardita senilis is a species of bivalve, a group which also includes oysters, mussels and scallops. These molluscs have a flattened body protected by two shells or valves joined by a hinge. A bulge near the hinge, called the umbo, is the oldest part of a growing shell, and is at the centre of the growth rings that can sometimes be seen on the surface.

Spinucella tetragona is an extinct species of predatory sea snail, in a group known as murex snails or rock snails. This species’ shells are highly ridged, but other extant species (such as Chicoreus aculeatus) have exaggerated and complicated patterns of spines on their shells, which makes them very popular with shell collectors.

Chicoreus a

Spinucella tetragona

Chicoreus aculeatus

Oyster: Ostrea species

Later Pleistocene fossils from Essex, such as the oyster, don’t really ‘belong’ here at all. They were brought south or churned up from older rocks by glaciers during the Pleistocene Ice Age, which lasted from 2.5 Mya to 12,000 years ago. They appear in glacial drift deposits left behind as the glaciers grew and shrank. This fossil of Chicoreus aculea is actually from the Jurassic period (201-145 Million years ago).

All images © Saffron Walden Museum, except C. aculeatus: H. Zell – Own work, CC BY-SA 3.0

Identification – flint, fossil sponge

Figure showing flint nodule from chalk

In Essex and south east England, almost every pebble on the beach and in gardens is flint. It’s a hard rock found in the Chalk, a soft, white, limestone layer that is up to 200m (600 ft) thick in north Essex and Cambridgeshire. In north west Essex, this chalk is between 90 million and 66 million years old and lies just below the soil, north of a line running from Stansted to Sudbury.

Diagram showing bedrock geology of Essex

Diagram showing the main bedrocks across a section of Essex. Chalk appears as the bedrock across northern Essex. Credit: reference 1.

Chalk started out as a thick mud on the floor of a tropical sea that covered most of Britain and north west Europe. This mud contained the remains of tiny sea creatures (plankton) which grew shells of calcium carbonate. When they died, these plankton and their shells fell to the sea floor to form a thick mud, which compacted into chalk over millions of years.

As it compacted, it squeezed out the seawater containing dissolved quartz, or silica (which comes from the skeletons of tiny sponges, a very simple animal).This silica was pushed out into gaps, cracks and burrows in the chalky mud to form nodules or layers of flint. These flints have a white outer layer (cortex), and are black inside. They can come in very complicated, bulging shapes, or with spikes, holes and cavities. Because of this, they can be easily confused with fossilised bones.

Figure showing flint nodule from chalk

An irregular flint nodule with a white cortex. Credit: reference 2.

Some flints do contain fossils, often urchins, or cockles or other small shellfish. Sometimes, the whole flint looks like fossil, and this may be because the silica that created it was forced into a hollow space in the hardening chalk which contained a sponge. Sponges are very simple animals which live on the sea floor. They still exist today, and the earliest known fossil sponges are  580 million years old.

The silica fills the gaps in the sponge’s skeleton and, over millions of years, the skeleton itself can dissolve away and be replaced by other minerals. This skeleton is a fossil, and the flint fills the spaces left by the soft parts of the animal after they rotted away.
Sponges are hollow tube or cone shapes and have no muscles, stomach, brain or nerves. They are filter feeders that catch bacteria and microscopic plants & animals from seawater that flows through tiny channels (pores) in their body.  Sponges are open at the top, and water currents flowing across the opening helps pull in water through the pores and remove it from the centre chamber, like wind blowing across a chimney.

Diagram showing water flow through a sponge's body

A simple diagram of a sponge’s body showing the pores in the sponge’s body, and the direction of water flow (blue arrows). Credit: reference 3.

Figure showing a living sponge

A living sponge, showing the typical hollow tube shape. Credit: reference 4.

The first sponge below is preserved in chalk and is a typical funnel shape. Some fossils may have a textured ring around the top, showing the rough pattern of the sponge’s surface and pores, like in the second photo.

Figure showing typical funnel shaped sponge

Fossil of a sponge (Ventriculites species) that lived in the Chalk sea. This sponge attached to the sediment with its branching roots. © SWM.

Figure showing rim imprint of a sponge's body in flint.

A flint nodule showing the imprint of the upper rim of a sponge’s body. Credit: reference 5

References

  1. Essex Bedrock, Essex Rock 1999. GeoEssex.org, retrieved 11:36, 24.4.2020
  2. © G Lucy. GeoEssex.org, retrieved 11:31, 24.4.2020
  3. Adapted from: Porifera_body_structures_01 By Philcha – Own work, CC BY-SA 3.0
  4. NOAA Photo Library reef3859 By Twilight Zone Expedition Team 2007, NOAA-OE. , Public Domain,
  5. Flint rim print. flint-paramoudra.com, retrieved 11:47, 24.4.2020

Object of the Month – October 2019

This case is arranged to show which butterflies live in the Saffron Walden area today (left), and which are extinct (right).

These butterflies died off mainly because of changing land use in the 19th & 20th centuries. Butterflies such as the Adonis blue (1) and chalk-hill blue (2) prefer large areas of chalk wildflower meadow, grazed by sheep and cattle. However, much of this land was converted to crop farming in the 1800s and these specialist insects died off. Other changes, such as the end of coppicing in woodlands, removed the open wooded habitat that butterflies such as the grizzled skipper (3) thrive in.

Species like the purple emperor (4) and white admiral (5) feed on the sugary waste products from aphids (honeydew). Pollution from coal burning may have contributed to these butterflies’ extinction as the toxins could dissolve into the honeydew on the leaf surface.

However, 2019 has been a very good year for some impressive larger butterflies too, with lots of painted ladies (6) arriving in Britain from the Mediterranean as they migrate north. Protected roadside verges in Uttlesford also provide good chalk grassland habitat for species such as the small copper (7).

There is also some very good news for three ‘extinct’ species (green boxes in main image). The purple emperor (4) returned to Uttlesford about two years ago and has been seen in Shadwell Wood and Rowney Wood, two local Essex Wildlife Trust nature reserves. The silver-washed fritillary (8) was first seen again about five years ago and is now known from Shadwell Wood, Rowney Wood and Hatfield Forest. The marbled white (9) has also been spotted at Harrison Sayer and Noakes Grove nature reserves and along some protected roadside verges over the last two years. The return of these three species in protected areas of countryside and special habitats show just how important effective conservation efforts are in supporting our native wildlife.

You can learn more about how humans have affected local environments and wildlife, for bad and for good, in the Take Away the Walls exhibition until 3 November.
Find out how you can help local wildlife groups on the Discovery Centre noticeboard next to the stick insects, and in the Take Away the Walls exhibition.

 

 

Hello to James

Hello! As I’ve been here since the end of April, it’s well-and-truly time to introduce myself. I’m James Lumbard, and I’m delighted to have been chosen to share the post of Natural Sciences Officer with Sarah Kenyon. I’ve really enjoyed my introduction to the job, the museum and the friendly staff and volunteers who make it such a pleasant place to work and visit. I’m originally from South Wales and moved to East Anglia two years ago. I’ve moved around a few times since then, moving to Tendring district at the start of this year, so it’s great to have the chance to explore Uttlesford and the lovely town of Saffron Walden.

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