The Pre Quaternary Period Geology of Suffolk
The first rocks laid down beneath Suffolk occured during the Silurian Period (443.7 416 Million Years bp) of the Paleozoic Era. These can be found at a depth of 500 to 490 metres and are made up of metamorphosed mudstones (hardened clay), siltstones (a sedimentary rock that is finer than sandstone) and Carstone (Green sandstone that is used as a building material). No layers are present from the Triassic and Jurassic Periods as these were eroded by the Cretaceous Period layers that followed.
The next geological layers to be laid down beneath Suffolk come from the Cretaceous Period (145.5 to 65.5 Million Years bp) of the Mesozoic Era. These were rocks from the Lower Cretaceous Period (145.5 to 99.6 million years bp), which are found at an approx depth of 490 to 460metres and made up of mainly Gault (a formation of stiff blue clay deposited in a calm, fairly deep water marine environment) and Carstone (Green sandstone, used as a building material). And chalk Upper Cretaceous (99.6 to 65.5 Million Years bp) which is found at an approx depth of 460 to 170 metres which is made up of White Micritic Limestone with layers of flint nodules (sedimentary crytochystalline form of mineral quartz, categorized as a variety of chert). These Calcareous rocks formed from the silica of sponges and microscopic marine creatures as during the Upper Cretaceous sea levels were probably at an all time high as there was no polar ice. Britain was therefore under water and at a similar global position than today.
In the following Cenozoic Era clays were deposited during the Paleogene Period (65.5 to 23.1 Million Years bp) at an approx depth of 160 to 60 metres. This occurred during the early part of this period but ceased around 40 Million Years bp probably do to the land rising above sea level due to volcanic and seismic activity caused by the continents drifting away and the Atlantic Ocean forming. Traces of volcanic ash is present in the London Clay in the south east part of Suffolk.
Towards the end of the Neogene Period (23.1 to 2.59 Million years ago) the east side of Britain submerged back into the sea.
The Quaternary Period- 2.59 Million Years bp to the Present Day
The submergence of Britain towards the end of the Neogene Period led to The Crags (shelly sands which are the youngest layer of solid geology in Britain) being deposited between 2 to 3 million years bp (from the Pliocene Epoch at the end of the Neogene Period to the Pleistocene Epoch at the beginning of the current Quaternary Period) at an approx depth 75 metres to actually breaking the surface. The presence of fossil shells of species similar to the present indicates that environmental conditions were close to those of modern-day England. It likely that these deposits (such as the Red Crag at Bawdsey Cliffs) were deposited in a shallow sea.
The Westleton Beds
The earliest exposed geological layer on The Millennium Green can be found in The Folly. The top part of Folly Meadow also appears to have very similar layers present but these are further below the surface than those in The Folly. This is the layer known as The Westleton Beds (a photo of an exposed section of this layer, caused by quarrying in The Folly, is shown above). The Westleton Beds are thought to have been deposited between 1.8 to 1.3 Million years bp, part of the shelly sands known as The Crags (see above) they are described as a group of lenticular flint gravels that are present within a formation of the Crag Group known as the Norwich Crag.
From now on the geology is that of drift deposits and we skip ahead some 2 million years for the next layer that was deposited on what is now The Millennium Green, this is the glacial wash known as Head and was deposited in the middle of Devensian glaciation some 40000 to 70000 years bp. The makeup of this layer is mainly stony sandy clays and clayey sands. A band of Head runs through the centre of Folly Meadow. The climate at this time would have been cool with tundra being the dominant landscape.
The dominate and most recent layer is the Alluvium, this is undifferentiated: mainly sand and silt deposits laid down during the last few thousand years of the current Holocene epoch via the flow and flooding of rivers. This can be found at the bottom of Folly Meadow and in Angel Meadow, Chestnut Meadow, Lester’s Piece, Two Acres and Blyth Meadow.
Geological Survey of The Millennium Green
In the summer of 2011 the task of trying to make sense of the geology of The Green was begun. A map of the simplifield geology and soils that were indentified during the intitial survey is shown below.
The next stage of our research was to acquire a more detailed picture of the geology of Folly Meadow. This was done via the digging of a series of exploiratory trial pits, the location of which is shown on the map below.