Abstract The preservation and accretion rates of fluvial meander-belt deposits appear to vary with the time over which they are evaluated, but the drivers of this effect are not fully understood. Using channel trajectories tracking the temporal evolution of meandering rivers, constrained with data on past river planforms, a numerical model is used to simulate planform evolutions of meander-belt reaches that underwent different types of meander transformation behaviours and bend cutoffs. Sediment preservation and bar accretion rates are quantified for three hierarchies of depositional products: (i) accretion stages reflecting intervals of bend migration by a certain meander-transformation style, (ii) meander-belt segments encompassing multiple stages but no bend cutoffs and (iii) meander-belt segments that experienced one or multiple cutoffs. Results show that distinct power-law relationships between the accretion rate and the time of sedimentation exist for river systems of different magnitudes in scale. Within each order of magnitude in river-system size, a single power-law relationship fails to effectively capture all depositional hierarchies. Sediment preservation varies with the time over which it is computed, but systematic variations in accretion rates with time primarily portray an apparent dependency of river migration rates on time: these variations largely reflect the temporal resolution and timespan of the modelled examples, highlighting an inherent issue affecting studies of river evolutions.

Abstract The collision of Siberia and the Kazakstan microplate with the eastern side of the Fennoscandia continent in the Permian amalgamated the last major continental fragments to produce the supercontinent Pangaea, which persisted into the Jurassic ( Fig. 13.1 ). During the last phases of this collision, during the latest Permian–Early Triassic, extrusion of massive amounts of flood basalts occurred in Siberia, to the east of the Urals ( Otto & Bailey 1995 ). Some have proposed this event as one of the key processes controlling the largest extinction in Earth’s history at the Permian–Triassic boundary ( Wignall 2001 a ; Benton & Twitchett 2003 ). During the Triassic, England and Wales lay beyond the western termination of the Tethys Ocean, which was divided into a northern part, the Palaeotethys, and a southern part, the Neotethys ( Fig. 13.1 ). Between these oceans occurred the Cimmerian terrains; several now widely separated continental fragments which had rifted from the northern fringe of Gondwana in the Permian ( Stampfli & Borel 2002 ). The Triassic witnessed the northward drift of these Cimmerian terrains, and the northward subduction of the Palaeotethys, which was mostly completed by the Late Triassic.

Abstract The term ‘Anthropocene’ has been proposed to indicate a geological interval characterized by global anthropogenic environmental change. This paper attempts to recognize a method by which the Anthropocene can be defined micropalaeontologically. In order to do this, microfloras and microfaunas (diatoms, macrophytes, dinoflagellate cysts, foraminifera and ostracods) from nearshore waters through to paralic and freshwater aquatic milieux are considered, and biotic variability with an anthropogenic causation identified. Microbiotic change can be related to anthropogenically induced extinctions, pollution-related mutation, environmentally influenced assemblage variability, geochemistry of carapaces/tests, floral change related to lacustrine acidification, faunal and floral correlation to industrial and agricultural signatures and introduction of exotic species via shipping. The influence of humanity on a local scale can be recognized in assemblages as far back as 5000 years BP. However, widespread anthropogenic change took place in Europe and America, particularly in the nineteenth and twentieth centuries, although in Asia (e.g. Japan) it cannot be observed prior to the twentieth century. Profound and global biotic change began in the mid-twentieth century and, if the Anthropocene is to be defined in this way, then the period 1940–1945 might encompass the biotic base of the interval.