Lake District

Abstract

The Lake District of north-west England consists of a major Lower Palaeozoic inlier (~2600 km²) surrounded by Upper Palaeozoic rocks. Three major stratigraphical divisions have been identified, which generally young from north-west to southeast (Figure 3.1):

• 1. The oldest rocks (Ordovician; Upper TremadocUpper Llanvirn) form the Skiddaw Group, a sequence, c. 4000 m thick, of mudstones, siltstones and turbiditic sandstone (Wadge, 1978a). These are overlain in the north and east by the Eycott Group (Lower Llanvirn) (Downie and Soper, 1972) consisting of tholeiitic volcanic rocks and interbedded volcanic and sedimentary sequences, c. 2500 m thick.

• 2. The Borrowdale Volcanic Group (Ordovician; mainly Caradoc Series) unconformably overlies the Skiddaw Group and shales correlated with the Eycott Group. This group comprises c. 6000 m of calc-alkaline lavas, sills, and pyroclastic deposits, believed to have been erupted under subaerial conditions.

• 3. The Borrowdale Volcanic Group is, in turn, unconformably overlain by the Upper Ordovician—Silurian (Ashgill—Pridoli) Windermere Group consisting of c. 4500 m of shallow-water clastic and carbonate sequences, graptolitic mudrocks, siliciclastic turbidites, and siltstones. These are post-dated by the molasse-type Mell Fell Conglomerate of probable Devonian age (Wadge, 1978b).