There is however a strong correspondence between AA and the development of open field systems in the mediaeval period, with 53% of AA units in the UK formed within the last 1000 years (Fig. 2). In Fig. 3 AA units are plotted by UK regions, with the first appearance of AA in southeast, central, southwest and northeast England, and in central and south Wales at c. 4400–4300 cal.
BP. AA in southeast, southwest, central England AG-014699 ic50 as well as in Wales is associated with prehistoric farming. In southwest England and Wales there was significant AA formation during the mediaeval and post-mediaeval periods. AA in southern Scotland and northwest and northern England appears to be associated with mediaeval land-use change. In Fig. 4 AA units
are sub-divided according to catchment size where study sites are located. Most dated AA units fall either in catchments of <1 km2 learn more or are found in ones with drainage areas that are >100–1000 km2. The smallest catchments (<1 km2) have no dated AA units before c. 2500 cal. BP and most occur after c.1000 cal. BP. It is also perhaps surprising how few 14C-dated anthropogenic colluvial deposits there are in the UK, making it difficult to reconstruct whole-catchment sediment budgets. AA units from the larger catchments (>100 km2) show a greater range of dates with the earliest units dating to c. 4400 cal. BP. Fig. 5 plots AA units according to sedimentary environment. Channel beds (Fig. 5A) record earlier-dated AA, whereas AA units in palaeochannels (Fig. 5B), on floodplains (Fig. 5C) and in floodbasins
(Fig. 5D) increase in frequency from c.4000 cal. BP, and especially in the mediaeval period. One possible explanation for the early channel bed AA units is that channel erosion Tolmetin or gullying was contributing more sediment than erosion of soil, and that this was a reflection of a hydrological rather than a sediment-supply response to human activities (cf. Robinson and Lambrick, 1984). The earliest coarse AA unit in the UK uplands is dated to c. 2600 cal. BP (Fig. 6) with 73% of gravel-rich AA formed in the last 1000 years, and a prominent peak at c. 800–900 cal. BP. Fine-grained AA units in upland catchments have a similar age distribution to their coarser counterparts, and 80% date to the last 1300 years. By contrast, AA units in lowland UK catchments, outside of the last glacial limits, are entirely fine-grained and were predominantly (69%) formed before 2000 cal. BP, especially in the Early Bronze Age and during the Late Bronze Age/Early Iron Age transition c. 2700–2900 cal. BP. Fig. 7 plots relative probability of UK AA classified according to their association with deforestation, cultivation and mining. The age distributions of AA units attributed to deforestation and cultivation are similar with peaks in the later Iron Age (c.2200 cal. BP).