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To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on oodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of nonmarine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single-storey, very ®ne-to ®ne-grained sandstone ribbons with W/T ratios <30, encased in ®ne-grained¯oodplain sediments are interpreted as anastomosed channels. Fine-to medium-grained, laterally accreted point-bar deposits forming multistorey sand bodies with individual W/T ratios >30 are interpreted as the deposits of meandering rivers ®lling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, oodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol pro®les and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Inter¯uve, sequencebounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identi®ed using a combination of (1) stratigraphic position; (2) ®eld observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Inter¯uve palaeosols are similar to modern Al®sols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high-frequency base level cycles (eustatic?) that are expressed as transgressive±regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modi®ed by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading¯oodplains primarily Present addresses: Sedimentology (1999) 46, 861±891 Ó 1999 International Association of Sedimentologists 861re¯ects local sediment supply and drainage. In contrast, well-developed inter¯uve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in¯oodplain palaeoenvironments and palaeosol types re¯ect changes in accommodation rate. The detailed micromorphological analysis of inter¯uve palaeosols represents a powerful application of an under-used technique for the recognition of key surfaces in the geological record. This has broad implications for non-marine sequence stra...

Stable oxygen isotope analysis of siderite and dinosaur tooth enamel phosphate from the Campanian–Maastrichtian Prince Creek Formation, Alaska, USA, are analysed to determine the palaeohydrology of the ancient Colville Basin north of the Ancestral Brooks Range. δ18O of freshwater siderites relative to V-PDB ranges between −14.86 and −16.21‰. Dinosaur tooth enamel δ18O from three different sites (Kikak–Tegoseak, Pediomys Point, Liscomb) range between +3.9‰ and +10.2.0‰. δ18Ometeoric water are calculated from δ18Osiderite that formed at seasonal temperatures ranging from −2 to 14.5 °C, with a mean annual temperature of 6.3 °C. At 6.3 °C, the δ18Ow calculated from siderite ranged between −22.23 and −20.89‰ V-SMOW. Ingested water compositions are estimated from dinosaur teeth assuming body temperatures of 37 °C and local relative humidity of 77.5%, resulting in values ranging from −28.7 to −20.4‰ V-SMOW, suggesting consumption of meteoric water and orographically depleted runoff from the Brooks Range. The ranges in calculated δ18Ometeoric water are compatible between the two proxies, and are mutually corroborating evidence of extremely 18O-depleted precipitation at high latitudes during the Late Cretaceous relative to those generated using general circulation models. This depletion is proposed to result from increased rainout effects from an intensified hydrological cycle, which probably played a role in sustaining polar warmth.Supplementary material:Parameters used for generation of equations compared to Kohn (1996) can be found at http://www.geolsoc.org.uk/SUP18642

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Little is understood about chemical weathering processes in Alaskan arctic soils, where moisture is generally not limited but acidity varies and the average soil temperature is close to or below freezing. Weathering reactions in soil convert primary minerals into secondary clay minerals. Silty loam textured soils from three sites in moist acidic tundra (MAT) and three sites in moist nonacidic tundra (MNT) in the northern Arctic Foothills, Alaska, were characterized with emphasis on the origin of the clay minerals. The MNT soils had a discontinuous and thinner organic layer, which leads to a deeper summer thaw and greater cryoturbation than the MAT soils. The MNT had higher cation exchange capacity and base saturation than MAT. These buffer against acidification and account for the pH differences of MAT and MNT. Other chemical characteristics including C and N content as well as Fe and Al were similar (by horizon) across the MAT/MNT boundary. X‐ray diffraction of coarse (0.0002–0.002 mm) and fine clay (<0.0002 mm) fractions indicate that illite, vermiculite, and kaolinite are the predominant clay minerals. Presumably, kaolinite is detrital and vermiculite is weathered from illite. The proportion of vermiculite to illite is higher in MAT and the illite to vermiculite proportion is higher in MNT. This shows that soil acidity does affect weathering processes despite the low soil temperature.