The arid conditions of the late Carboniferous continued into the Permian period. The newly uplifted Malvern Hills were surrounded by a hot, arid desert similar to the present day Sahara desert. Weathering was extremely rapid and the older Precambrian and Silurian rocks were rapidly eroded. The debris was transported by flash floods and debris flows, accumulating to form large alluvial fans. These features are commonly found in modern day arid or semi-arid locations such as Death Valley, California (Box Five). The coarse, angular fan deposits are represented by the Haffield Breccia, which obscures much of the former Precambrian and Silurian land surface.
Box Five. Alluvial Fan
An alluvial fan is a cone shaped depositional landform. They are formed be the accumulation of sediment transported by sediment laden streams or rapid mass movements (debris flows). Deposition is caused by a reduction in velocity when the streams emerge from their confined mountainous courses. Energy is dissipated and the sediment accumulates to form large fan shaped features. In some cases the fans merge to form Bajadas.
Alluvial fans are widespread, and tend to occur in arid and mountainous areas. However, they are particularly common in tectonic environments where there is a marked contrast between the mountain front and the depositional area.
Towards the end of the Permian the environment became more arid and large sand dunes occupied the Malvern area, forming the Bridgnorth Sandstone Formation. The prevailing wind direction was from a north – easterly direction, suggesting that the Malvern Hills lay within the sub-tropical trade wind belt, 30o north of the Equator. The Permian strata lie at the northern and southern limits of the Hills and flank their eastern slopes. Both the Haffield Breccia and the Bridgnorth Sandstone are exposed at Bromsberrow Lane (SO748344 to SO748348). The Haffield Breccia forms the pronounced ridge which runs between the Vineyard (SO782344) and the Glynch Brook valley (SO73153480). The Bridgnorth Sandstone lies to the east of the Hills and produces a relatively subdued topography because it is easily eroded due to its soft and friable nature.
The compressive forces experienced during the late Carboniferous relaxed and the area started to rift apart towards the end of the Permian. A large block of the Worcester basin was displaced by approximately 2 km. Downward displacement occurred along two major faults forming a graben structure (Box Six).
Box Six. Formation of the Worcester Graben.