Geoconservation work at Gullet Quarry -- re-exposing the unconformity between Llandovery siltstones, limestones and shales of the Silurian and the Malverns Complex schists of the Precambrian


The Geopark can be summarised as consisting of a number of distinct structural areas;

1. The Lower Palaeozoic and Devonian outcrops forming the western and south-western areas of the Geopark underlain by Precambrian basement.

2. The Carboniferous strata and synclinal basins to the north with faulted margins.

3. The Worcester Basin to east with a graben filled with red beds and underlain by Precambrian volcanic debris and with the Lower Jurassic (Lias) cover gently dipping off the Triassic strata.

4. Running north-south through the area is the Malvern Axis which marks a Proterozoic zone of crustal weakness that has undergone repeated reactivation; Precambrian igneous rocks of the Malverns Complex are dominant which become progressively more sheared to the south.

5. The re-emergence of folded Silurian strata at May Hill to the south of the Geopark as a pericline inlier.



Left: Triassic sandstone -- 230 million years old. The caves were used as a hermitage until the middle of the last century

Using information taken mainly from the Memoirs listed above it is possible to give a precise account of the geology of the Geopark. It is one of the classic areas of British geology and parts are of international importance. Research has been undertaken in the area for over 150 years and has culminated in recent times with detailed geological mapping, geochemical basement studies, seismic reflection traverses, aeromagnetic and gravity analyses, geothermal assessments and the drilling of deep boreholes.

The complex geological history is summarised in the Preface to the Worcester Memoir: “The detailed lithostratigraphy and chronstratigraphy chronicle the district's geological history, from the Proterozoic accretion on the northern margins of the southern hemisphere continent of Gondwana, the rifting and northward drift of the East Avalonian plate through the Cambrian, Ordovician and Silurian, its collision and docking with the North American Laurentian and European (Baltica) plates during the Acadian Orogeny, tectonic inversion of the region during the Variscan Orogeny, and finally, Permo-Triassic rifting and the formation of the Worcester Basin. Superimposed on these tectonic events, global sea-level rises are documented by the transgressive marine deposits of Cambrian, late Llandovery, early Ludlow and Rhaetian age”.



Left: Guided geology trail around Bewdley town centre -- here looking at the tower of St. Anne's Church which was built using highley Sandstone from the Forest of Wyre Coalfield

The Carboniferous rocks to north in the Wyre Forest coalfield are represented by Coal Measures consisting of Productive Measures and the Etruria Marl and Highley Formations. All rest unconformably on Devonian Old Red Sandstone. The many outcrops reveal the palaeolgeography of forest swamps, river deltas, mud flats and changing environments. In the coalfield Clows Top reaches 231m and affords excellent views to the Abberley and Malvern Hills to the south. The Silurian ridges of the Abberley Hills rise to 281m at Abberley Hill and are composed of steeply dipping and overturned Wenlock and Ludlow Series rocks; all the result of the influence of the Malvern Axis. Here are some of the best fossiliferous outcrops and exposures of the Much Wenlock Limestone and Aymestry Limestone Formations in the Geopark with complex structural features including an eastern boundary fault. An overthrust of Permian breccia forms the top of Woodbury Hill, which rises to 275m. This high ground with views across the whole of the northern part of the Geopark gives way to the valley of the River Teme to the south and west and to the lower relief of the Permo-Triassic plain and River Severn to the south and east. The River Teme cuts through an impressive sequence of Lower Old Red Sandstone rocks with the junction between the Silurian and Devonian present in the western escarpment as well as the regionally famous tufa deposits associated with the Bishop's Frome Limestone.

The extensive plain of Triassic Sherwood Sandstone and Mercia Mudstone Groups forming the eastern areas of the Geopark represents a vast thickness of red beds. Our knowledge here has recently been greatly enhanced by the drilling of the deep Kempsey borehole, which proved 2300m of Permo-Triassic rocks lying over at least 700m of Precambrian volcaniclastic deposits. Geochemical evidence from the latter suggests an affinity with the Charnian magma of Leicestershire.

The Permian dune bedded Bridgnorth Sandstone Formation to the north-east of the area undererlies the flash flood deposits of the Kidderminster Formation. Moving southwards along the eastern flank of the Geopark these beds are overlain by the Mercia Mudstones, deposited in playa lakes, an arid environment that gave way to a pluvial period with the deposition of the Arden Sandstone Formation. The lower Severn valley is of moderate relief and in the south-eastern corner of the Geopark marine Jurassic formations dip gently to the south-east. The Lower Lias sediments of grey silty mudstones and argillaceous limestones are overlain by the Blue Lias exposed as outliers.

The Malvern Hills form a narrow ridge rising to 425m and some 13 km long and are composed of plutonic and extrusive igneous rocks about 680 million years old and are believed to have formed during subduction of oceanic lithosphere and accretion on to Gondwana. The Malverns Complex is a calc-alkaline magmatic suite that underwent at least one high-grade regional metamorphic event in the Proterozoic. The rocks are predominantly of diorite and tonalite (granite). A foliation is often present giving the rocks a schistose or gneissic appearance. Basaltic lavas of the Warren House Formation occur also.