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An account of what happened on 13th July 2019.

A bright day in July saw 15 people arrive at Cantley Village Hall for the ‘Palaeolandscapes of the Broads’ day school. This event was part of ‘Water, Mills & Marshes’, and aimed to introduce participants to the ‘deep history’ of the Broads landscape, which has its geological roots over two million years ago in the early Pleistocene period.

The first presentation was by geologist Tim Holt-Wilson, who explained the succession of strata underlying the Broads, and showed how the area was at the crossroads of great landscaping forces: the fluctuating boundaries of the North Sea, the impact of two ice sheets and the passing of two now-vanished rivers. Evidence of these forces can be seen in local landforms and in the geology seen in pits and quarries, the plough-soil and even the rubble built into church walls.

Ecologist Andrea Kelly followed with a presentation on a theme of environmental change over the past 10,000 years, since the end of the last ice age. She focused on the evidence contained in the thick layers of peat and alluvium that underlie the wide valleys of the Broads. She explained how peat is able to store huge quantities of carbon dioxide, so helping mitigate climate change.

Then came a field excursion in shared cars, to economise on fuel and parking space. First stop was an old gravel pit at Buckenham Wood, Strumpshaw, where geologist Adrian Read explained how glacial sands and gravels provide information about a Middle Pleistocene ice sheet.

Adrian Read pointing out features of geological interest at Buckenham Wood Pit, Strumpshaw.

These glacial sands were probably laid down on an outwash plain in front of an ice sheet. They are overlain by a bed of coarse, chalk and flint-rich gravel which has distorted the underlying strata; the orientation of the cobbles suggests that it flowed in from the north-west.

The next stop was a mile away at the RSPB reserve, Strumpshaw Fen. Some group members rolled up their sleeves and braved the sticky, brown mud to collect samples of peat from the marshy floor of the Yare valley. Andrea Kelly introduced the group to the use of a metal corer with jointed rods which was able to reach down over six metres to recover a sediment sequence of mossy, peaty, silty and woody layers that are likely date back several thousand years. They showed the succession of wetland environments over time.

Andrea Kelly (left) directing recovery of the first core sample of peat at Strumpshaw Fen.

Later, we moved to a nearby sand pit near the valley side where Adrian Read demonstrated a sequence of sands, gravels, silts and clays belonging to the Norwich Crag formation.  Deposited in coastal or estuarine waters about 2 million years ago, they are evidence that the North Sea once covered the Broads area.

Adrian Read explaining the sedimentary sequence: the top of a unit of dipping sands, probably deposited in offshore sandbanks, has been truncated by a horizontal sequence of sands and silts, perhaps in a tidal flat or estuarine environment.

By this time lunch beckoned, so the group returned to Cantley for refreshments and further discussion.

The first excursion of the afternoon was to Wickhampton church about three miles away, to look at the geological materials built into its walls. This fine building is located right on the edge of the marshes, which were once tidal flats of the Great Estuary. Boats might once have been able to come up a saltmarsh creek and moor close to the church. An interestingly diverse stony rubble can be seen in the walls, with boulders of ship’s ballast and other imported materials as well as flints and other stone types sourced from local fields.

Wickhampton Church

Rubble from Wickhampton church. Top: a) boulders of basalt – most likely ship’s ballast; b) pink granite, perhaps ship’s ballast from Norway. Bottom: a) fragment of a circular lava quern imported from the Mayen area of Germany; b) a lump of grey chalk ‘clunch’, perhaps a glacial erratic from north-west Norfolk.

The final excursion was to nearby Halvergate church, which is sited on rising, sandy ground. The church has some interesting geology in the tower, where the buttresses are keyed in with dressed blocks of a distinctive, grey ‘silver carr’ quartzite. This stone is thought to have been shipped in from the demolition of a Roman fort at Brancaster in Norfolk, though originally quarried in the Castle Rising area. Halvergate is one of a group of churches in this part of the Broads which have ‘silver carr’ in their fabric, most notably Reedham. The tower is also notable for the variety of Mediaeval brick types – all made from local clays, whether from glacial deposits in the uplands or from alluvium in the marshes.

Halvergate Church

Rubble from Halvergate church. Top: a) a block of Roman ‘silver carr’; b) a red-brown sandstone, quite possibly imported as ship’s ballast from Scotland or north-east England. Bottom: a) a red-stained quartzite cobble, most likely originating in the Triassic pebble beds of the West Midlands and brought to the area by a now-vanished early Pleistocene river; b) a ‘black-hearted’ brick made of clay from the marshes, with a bubbly texture caused by inclusions of organic matter in the raw clay.

The Day School finished back at 16:30. Our thanks go to the Heritage Lottery Fund for making it all possible, to the ‘Water, Mills and Marshes’ team, particularly to Dr Andrew Tullett for his admin support, and to Cantley Village Hall for providing such a convenient venue.