Environmentalists consider invasions by exotic species of plants and animals to be one of the most serious environmental problems we face today, as well as one of the leading causes of biodiversity loss. We argue that in order to develop and enact sensible policies, it is crucial to consider two philosophical questions: (1) What exactly makes a species native or exotic, and (2) What values are at stake? We focus on the first of these two questions, and offer some preliminary suggestions with regard to the second. Through a series of case studies, we show that it is not always clear whether a species is native or exotic. We identify five possible criteria that could be used for distinguishing natives from exotics. Rather than identifying one of these criteria as the 'correct' one, we suggest that the concepts of 'native' and 'exotic' function more like what some philosophers have called cluster concepts. That is, there are several characteristics that are typical of native species, and a corresponding set of characteristics that are typical of exotic species. None of these characteristics is either necessary or sufficient for identifying a species as either native or exotic. We then identify several of the values that are at stake in dealing with exotic species, and we suggest that policies need to avoid being overly simplistic.

A rationalized lithostratigraphy for the Great Scar Limestone Group of the southeast Askrigg Block is established. The basal Chapel House Limestone Formation, assessed from boreholes, comprises shallow-marine to supratidal carbonates that thin rapidly northwards across the Craven Fault System, onlapping a palaeotopographical high of Lower Palaeozoic strata. The formation is of late Arundian age in the Silverdale Borehole, its northernmost development. The overlying Kilnsey Formation represents a southward-thickening and upward-shoaling carbonate development on a south-facing carbonate ramp. Foraminiferal/algal assemblages suggest a late Holkerian and early Asbian age, respectively, for the uppermost parts of the lower Scaleber Force Limestone and upper Scaleber Quarry Limestone members, significantly younger than previously interpreted. The succeeding Malham Formation comprises the lower Cove Limestone and upper Gordale Limestone members. Foraminiferal/ algal assemblages indicate a late Asbian age for the formation, contrasting with the Holkerian age previously attributed to the Cove Limestone. The members reflect a change from a partially shallow-water lagoon (Cove Limestone) to more open-marine shelf (Gordale Limestone), coincident with the onset of marked sea-level fluctuations and formation of palaeokarstic surfaces with palaeosoils in the latter. Facies variations along the southern flank of the Askrigg Block, including an absence of fenestral lime-mudstone in the upper part of the Cove Limestone and presence of dark grey cherty grainstone/packstone in the upper part the Gordale Limestone are related to enhanced subsidence during late Asbian movement on the Craven Fault System. This accounts for the marked thickening of both members towards the Greenhow Inlier.

The Steptoean Positive Carbon Isotope Excursion (SPICE) of earliest late Cambrian (Furongian) age is identified in England. The excursion is found within a ca 145 m thick siliciclastic succession within the middle and higher part of the Outwoods Shale Formation of Warwickshire, and reaches a maximum δ 13 C org amplitude of 4.1‰ at values of -25.6‰. Biostratigraphical data show that the excursion occupies the greater part of the Olenus trilobite biozone, an equivalent of the Glyptagnostus reticulatus biozone that marks the base of the Furongian and coeval base of the Steptoean in North America. The amplitude of the excursion approaches that recorded in limestonedominated Laurentian successions, and is greater than that recently documented for organic-rich mudstones of palaeocontinental Baltica in southern Sweden. A minor positive excursion above the SPICE may equate with a similar excursion recognised in Siberia. The SPICE in the Outwoods Shale Formation seems closely linked to the widely recognised early Furongian eustatic sea level rise. There is no evidence in the English succession for slightly later regression, elsewhere considered coincident with the peak of the excursion and pivotal to some previous models explaining the SPICE.Keywords: Cambrian, Furongian, carbon isotope excursion, England, Avalonia Late Cambrian (Furongian) carbonate successions in many parts of the world (North America, Argentina, Siberia, Kazakhstan, China, Australia) contain an interval of markedly positive δ 13 C carb values, peaking at +5‰ (Saltzman et al., 2000;Kouchinsky et al., 2008). More recently, the same positive Carbon Isotope Excursion (CIE) has been identified in organic-rich mudstones of the Alum Shale Formation in southern Sweden, where δ 13 C org peak values are around -28‰ (with a maximum amplitude of around 2‰) (Ahlberg et al., 2009). This CIE, first recognised in the late Cambrian of North America by Brasier (1993) and confirmed as a global CIE by Saltzman et al. (1995), is termed the Steptoean Positive Carbon Isotope Excursion (SPICE) (Saltzman et al., 1998). We report here the occurrence of the SPICE in the Cambrian of central England, the first record in an Avalonian succession. The palaeogeographic setting of these mid-shelf clastic deposits contrasts with 1 areas where the SPICE has previously been identified (e.g. shallow carbonate shelf in North America; shallow, dysoxic-anoxic shelf in southern Sweden). This contrasting setting provides an opportunity to critically assess the likely driving mechanism(s) that created this global isotopic excursion.The SPICE is believed to have had a duration of about 4 Ma (Saltzman et al., 1998), although 3 Ma is probably a better estimate based on dates recently published by Peng and Babcock (2008). In common with other positive CIEs in the geological record, one interpretation of the SPICE is attributed to increased burial of organic carbon, that is enriched in isotopically light 12 C thus increasing the 13 C pool in the oceans. However, terrestrial weathering impacts relate...

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Discoveries of Late Triassic alatoform bivalves (family Wallowaconchidae) in Alaska and in south Asia and Arabia reveal a broad distribution for these tropical bivalves, overturning the concept of these bivalves being endemics of offshore island arc terranes in eastern Panthalassa. They occupied an area extending from central Tethys to the eastern Pacific margin of Panthalassa. The Tethyan wallowaconchids occur in nearshore environments on the north margin of Gondwana, indicating an environmental tolerance for continental shelf settings in addition to their primary occurrence on isolated oceanic islands. The new sites reveal a taxonomic diversity among wallowaconchids. Wallowaconchids present in India are conspecific with Wallowaconcha raylenea, the type species of Wallowaconcha, whereas wallowaconchids in Arabia are an undescribed taxon and wallowaconchids in south‐central Alaska are small in size and a different undescribed taxon. All known wallowaconchids are of Norian age and they appear to be a wide‐ranging component of Late Triassic tropical biotas.

Abstract:The southern margin of the Askrigg Block around Cracoe, North Yorkshire, shows

have been demonstrated to affect coeval strata in parts of the eastern Weald, these may not be the dominant control on the Devizes succession, which seems to be more strongly influenced by its palaeogeographical setting with respect to sediment source areas, and the effect this had on the volume and timing of sediment infill.Palaeogeography may also be indirectly responsible for the absence of cherts in the INTRODUCTIONThe Upper Greensand of the Devizes district is famed for its abundant fossils, with several significant collections amassed in the latter part of the 19th century now residing in major British museums. It was Jukes-Browne's (1892) work in the Devizes area that established our current understanding of the Gault and Upper Greensand formations as contemporaneous deposits (now unified in the SelborneGroup of Hopson et al., 2008). However, relatively little has been published on the M. A. Woods et al.3 succession since this work (Jukes-Browne, 1892, 1905Jukes-Browne & Hill, 1900) more than a century ago. Thus, the new geological survey of the Devizes district(1:50 000 geological sheet 282), commenced by the British Geological Survey (BGS) in 2004 and completed in Spring 2005, presented an opportunity to re-evaluate the earlier work in the context of modern stratigraphy. Although the combined effects of landslipping and poorly and impersistently developed topographical features prevented member subdivisions from being defined on the new geological map, the data from sections and cored boreholes ( Fig. 1) did provide ample evidence of stratigraphical changes that could be used to correlate between successions locally and further afield. These observations form the basis for a revised subdivision of the Devizes Upper Greensand, supported by macrofossil, microfossil and thin-section data. Significantly, the current work has identified the Potterne Rock of Jukes-Browne & Hill (1900) as a well-developed marker-bed at several localities, and provides the first description of this horizon in more than 100 years.The stratigraphy of the Upper Greensand of the Devizes district is summarised on Figure 2. The Late Albian biozonal scheme used in this work follows Owen (1975Owen ( , 1984, but the relationship to the recently revised scheme of Owen & Mutterlose PREVIOUS RESEARCHThe most detailed historical accounts of the Upper Greensand of the Devizes district were made in the late 19th and early 20th centuries by Jukes-Browne (1892, 1905 and Jukes-Browne & Hill (1900). The historical nomenclature for the succession is confusing and explained below (Fig. 2).The earliest account of the district (Jukes-Browne, 1892) appears to describe two broad subdivisions of the Upper Greensand, comprising 'Malmstone' overlain by 'Grey and green sands'. 'Malmstone' consisted of grey or buff sandstone with common sponge spicules and globules of silica derived from the spicules, and a macrofauna dominated by the small, partly coiled annelid Rotularia. However, Malmstone only accounted for the lower part of the succession found b...

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