Stop about here
Stop as you come out of the wooded area into the open area. The rock here is a sedimentary rock called the Clent Breccia, because it is full of angular fragments (breccia) and is named after the Clent Hills a few kilometres to the north-west, where there is a lot more if it. It is much covered by leaves and grass here, but the next picture shows what it looks like in places where it is well exposed.
Clent Breccia looks like a collection of broken up rock fragments surrounded by a red clay. It is called a Breccia, as against a conglomerate, because the fragments are angular. There was a rocky desert here when these fragments were deposited.
Range of fragments
The fragments are often just 3 – 5cm big here, but on the Clent Hills they are 10 – 20cm big and sometimes up to 60cm in size. The Clent Breccia is a product of the harsh Permian desert conditions, with flash floods pushing rock debris across a wide gravelly plain.
Extending eastward into Europe (no North Sea then), was a rock desert with scattered patches of sand and gravel and small sand dunes. A hot dry wind, full of fine grit, was probably often blowing strongly from the east.
In the desert
Around 290 million years ago in the Permian time, this place was just north of the equator in the midst of the giant continent of Panagea. To the south the great mountain chain of the Variscans blocked any rain; to the north, west and east lay barren desert. Your water supply level is now important! Check on how important oxygen levels will be for this time (around 290 million years ago).
Fans of debris
The rock fragments of the Clent Breccia were eroded from the mountains and carried down in flash floods, but when the floods emerged from the confinement of the upland valleys and reached the open plain, much of their load of shattered rock was dumped in fans at the foot of the hills. These fans of rock fragments are called fanglomerates.
Deserts don’t have rain? Yes they do, possibly not for years, but a violent rain storm can rapidly fill a narrow valley (called a Wadi) with raging torrents and then spread a sheet of water, full of stones and even large boulders, out over the desert plain. The picture shows a flash flood in the Libyan desert.
Flash floods can leave temporary lakes (called playas) on the desert floor. The gravelly plains are called Bajadas (also spelt Bahada). It is the material of these plains which forms the Clent Breccia.
Travelled a short distance
The variable size of the fragments in this area, together with their angular shape shows that they were carried only a short distance, with no time for the fragments to be sorted or smoothed in the tumultuous flow of flood water. In contrast, some rounded pebbles you will meet later on your Voyage (in the Triassic), have travelled a long distance, perhaps hundreds of kilometres, from the rocks they were originally broken from.
Origin of the fragments
The fragments of rock in the Clent Breccia, include the following.\n\nThe Ordovician Lickey Quartzite, bits of Ordovician volcanic rocks, some Carboniferous fragments, but mostly it is fragments of the very oldest rocks, from the Precambrian Period, set in the red clay of the Permian desert. The diagram shows the nearest sources of Precambrian and other old rocks to the Lickey Hills. These areas may have formed outcrops rising above the gravelly plain of the Permian desert. When you arrive at the next task site, you can see the range of the Malvern Hills, formed of hard Precambrian rocks, still significant in the landscape of today.
The breccia is also found lapping around the southern end of the Malvern Hills. It seems to have covered the Abberley and Suckley Hills as it forms a thick layer on the top of Woodbury Hill, just south of Great Witley. In this area, it is given another local name – the Haffield Breccia, after the hamlet of Haffield just east of Ledbury.
Task Site 6 Questions
In which part of this landscape (in the following picture) do you think the Clent Breccia was deposited?
a, b, c or d
If you look at the fragments of rock in the Clent Breccia, from which geological time period would they certainly NOT be from?
Using information in the app, what would be the minimum age of the Precambrian rocks of the Malverns?
a) 100 million years old
b) 500 million years old
c) 600 million years old
d) 1000 million years old