The Arenig Fawr area of North Wales constitutes the type area for the British Lower to Middle Ordovician Arenig Series and is complemented by sections in the Carmarthen and Whitland areas of South Wales. We describe chitinozoan assemblages from both areas in order to aid correlation of the Arenig Series in its type region with the global Ordovician series and stages. Chitinozoans recorded from Arenig Fawr provide permissive rather than conclusive evidence but suggest that the Henllan Ash Member correlates with the upper Floian Stage Slice Fl3 or lower Dapingian Stage Slice Dp1. Better results were obtained from South Wales where six chitinozoan assemblages are distinguished, ranging in age from late Tremadocian to middle Darriwilian (early Llanvirn). Most species are known from South China, Gondwana and/or Baltica where there are controls on ranges. They show that much of the lower Arenig (Moridunian) succession in South Wales correlates with the upper Floian Stage (Fl3). Correlatives of the lower and middle Floian Stage (Fl1, Fl2), if present, must be represented by the Ogof Hên Formation and lowest Carmarthen Formation. Chitinozoan assemblages from the upper Arenig Series (Fennian Stage) are more readily correlated with Gondwanan biozones and indicate correlation of the Fennian Stage with the Dapingian and lower Darriwilian (Dw1) stages. The middle Arenig Whitlandian Stage is constrained in South Wales to an interval from the uppermost Floian Stage to the basal Dapingian Stage, resulting in an inferred increased rate of sediment accumulation.

The fabric of a city represents a transformation of raw geological materials into a complex assemblage of new, human-made minerals and rocks such as steel, glass, plastics, concrete, brick, and ceramics. This activity has been considered in terms of an “urban metabolism,” with day-to-day inflows and outflows of people, food, water, and waste materials. Here we adopt a longer time-scale spanning years to millennia, related to geological time-scales but still meaningful for present and future generations of humans, and consider cities as sedimentary systems. In natural sedimentary systems, flows of materials are governed by natural forces such as climate and gravity, and leave physical records in, for instance, river-strata. In cities, the flows of geological materials needed for construction and reconstruction are directed by humans, and are largely powered by the fossil energy stored in hydrocarbons rather than by gravity or the sun. The resultant assemblages of anthropogenic rocks and minerals may be thought of as sedimentary (and/or trace-fossil) systems that can undergo fossilization and now exist on a planetary scale. Far more diverse than natural geological strata, they are also evolving much more rapidly, not least in terms of their growing waste products. Considering cities through such a perspective may become increasingly useful as they come to be influenced by, and need to adapt to, the changing conditions of the emerging Anthropocene epoch.