Model chains for assessing the impacts of nitrogen on soils, waters and biodiversity: a review

[摘要] All the samples yielded relatively abundant palynofloras; allochthonous palynomorphs of Carboniferous, Jurassic, Cretaceous, ?Palaeogene and Quaternary age are present. The organic contents of these associations are similar, hence the succession studied is interpreted as belonging to the same genetic unit. Carboniferous spores are normally the predominant component. The most common Carboniferous spores are Densosporites spp. and Lycospora pusilla, but other forms were also recognised. The majority of these spores are consistent with input from the Namurian-Westphalian interval and this association of Namurian and Westphalian forms is typical of the Quaternary of the UK. These spores were most likely to be derived from the Pennines, north-east England or southern Scotland. Jurassic miospores and microplankton are also present in relatively large proportions throughout, with miospores being more abundant than microplankton. The presence of key pollen genera indicates the incorporation of Toarcian and Mid-Late Jurassic strata respectively. This configuration is mirrored by the microplankton, which is indicative of input from the late Pliensbachian-early Toarcian. The remainder of the Jurassic dinoflagellate cysts are indicative of input from the Kimmeridge Clay Formation. No late Kimmeridgian markers were observed, hence the majority of this input is probably from the Lower Kimmeridge Clay Formation. The source of this reworking is probably from the East Midlands Shelf and/or the Yorkshire Basin. Cretaceous palynomorphs were generally recorded in small numbers and most of these forms are relatively long-ranging dinoflagellate cysts. Some stratigraphically diagnostic dinoflagellate cysts were observed however, and these are indicative of the Hauterivian/Barremian interval. They are probably locally-derived from, for example, the Tealby Clay and/or the Tealby Limestone. Some of the longer ranging forms such as Odontochitina operculata may be from the Chalk Group. The previous discussion refers to the matrix of the till. Individual clasts of Chalk from four of the samples proved organically sparse. These associations are hence likely to be from the Lower and/or Middle Chalk Group. Low numbers of possible Palaeogene dinoflagellate cysts were recorded from samples 6 and 3 and these may represent the reworking of Palaeogene strata from the North Sea Basin. Typically Quaternary pollen is present and these elements were probably derived locally. Non age-diagnostic palynomorphs are also consistently present. The Welton Till yielded the lowest proportion of Carboniferous spores, generally high levels of Cretaceous dinoflagellate cysts and the highest proportions of non age-diagnostic palynomorphs. The Calcethorpe Till appears to have a low palynological productivity and the Marsh Till is dominated by Carboniferous and Jurassic miospores.

[发布机构] NERC/Centre for Ecology & Hydrology

[效力级别] Atmospheric Sciences