Sequence stratigraphy and process sedimentology of the Cambrian of SW Wales

Rees, Andrew James (2005). Sequence stratigraphy and process sedimentology of the Cambrian of SW Wales. University of Birmingham. Ph.D.

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Abstract

Avalonian-Cadomian and related terranes of the circum-North Atlantic constitute portions of an accretionary orogen that developed on an active Gondwanan margin at the periphery of the Neoproterozoic supercontinent Vendia. These peri-Gondwanan terranes are defined by their Neoproterozoic evolution on an active continental margin, and by the peri-Gondwanan “Acado-Baltic” fauna of their Cambrian-Ordovician overstep sequence. Unlike most recent studies on the early evolution of Avalonia, this contribution focuses on the Cambrian overstep sequence (the Dyfed Supergroup) exposed in SW Wales (East Avalonia).
High-resolution sequence-stratigraphic techniques are applied to the Dyfed Supergroup across southern Britain to facilitate the integration of a revised lithostratigraphy into a unified Avalonian chronostratigraphy based on successions in Atlantic Canada (West Avalonia). The relative ease of integration reflects the shared epeirogenic history, sediment sources and accumulation history of a microcontinent unified by the Early Cambrian. The occurrence of lithologically similar and coeval depositional sequences may be relied upon to determine the limits of the Avalonian Superterrane in the Acadian-Caledonian orogen.
A broad subdivision of Cambrian stratigraphy into tectonically active and passive phases of sedimentation is recognized. Megasequence 1, which constitutes all of the Lower Cambrian and most of the Middle Cambrian, records transform termination of Avalonian subduction following oblique convergence, and the accretion of island arcs to the northern periphery of Gondwana. Under transpressional regimes, late Precambrian arc-related basins were inverted and recycled into Lower and Middle Cambrian pullapart successor basins dominated, at their margins, by alluvial fan and fan-delta depositional systems. Megasequence 2 (Upper Cambrian to Lower Ordovician) reflects passive margin sedimentation, with Avalonia acting as a sediment sink to vast quantities of fine-grained sediment transferred off Gondwana by large, mature fluvial systems. This marked the culmination of the Avalonian-Cadomian orogenic cycle.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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