The depositional environments and structures of the Borrowdale Volcanic Group and the Windermere Supergroup in the Southern Lake District, England

Abstract

Field studies have been undertaken on the Borrowdale Volcanic Group (BVG) and the Windermere super group (WS) in the southern Lake District. This study has been conducted to provide further work towards the understanding of the BVG’s emplacement and the depositional environments of the WS. Formal unit descriptions and stratigraphic columns are compiled from field data and accompanied by stereonet, cross section, and thin section analysis. Numerous depositional features, including asymmetric ripples and aligned clasts, found within the BVG are supportive of a sub aerial and lacustrine setting for emplacement. Bow tie fiamme and rheomorphic flow structures also hold similar implications, by the necessity of heat input, to the environment of emplacement. An unconformable contact between the WS and the BVG is concluded by observations of parasitic folds passing below the WS at High Pike Haw. This is further supported by bedding anomalies uncovered by stereonet analysis. Four transgressions are linked with the deposition of the WS and show correlation with eustasy fluctuations and global cooling events, including the Hirnantian glaciation. Southward verging, open folds through Low Long Beck predate WS deposition and hold similarities with pre-Bala folding. A D2 folding event occurred post deposition to produce isoclinal folding along Dow Crag and a slatey cleavage throughout both units.