Dr Geoff Lloyd - Current Activities

Structural Geology of SW England

Micro-to-macro scale mapping in the Upper Carboniferous Culm measures of NW. Devon and N. Cornwall has led to new understanding of the behaviour of multilayer sequences during deformation. Detailed stratigraphic logging has revealed the existence of several regional scale ‘bedding-parallel’ thrust sheets which developed prior to the classic chevron fold trains caused by horizontal shortening. Subsequent backthrust-related shear deformation has both refolded and ‘unfolded’ the chevron structures. The progressive nature of the flexural slip accommodated deformations, including the ‘tectonic shuffling’ of sedimentary sequences, is expected to be typical of multilayer sequences.
SW England - deformation

A microcosm (compare with regional section in figure below) of the progressive deformation affecting the Upper Carboniferous Bude Formation during the Variscan Orogeny. Initial northerly (to the left) directed thrusting (red) produced an antiformal imbricate stack and ramp-related folds (purple axes). Continued layer parallel shortening resulted in upright chevron folds (light blue axes), subsequently overturned to the south (right) by southerly directed (backthrust related?) simple shear, which also produced subhorizontal modification folds (dark blue axes) on the contracting (southerly dipping) limbs of the main folds.
3d section from Bude to Duckpool

Three dimensional section from Bude to Duckpool based on detailed structural and sedimentary mapping (Fig. 5) showing the effects of northerly thrusting, chevron folding and southerly shear due to back thrusting on the wavecut platform and cliff profile outcrop patterns. The geology is markedly non-cylindrical, even over a structural strike length of ~100m. This cross-section shows 6 major thrust sheets, including at least one back thrust sheet. The combination of the thrust sheets and broad folds explains why older rocks occur in the cores of synclines and younger rocks occur in the cores of anticlines.
Research page