Morphological, chemical and physical characteristics of cryosolic soils from Arctic Canada

Cryosols are permafrost-affected soils whose genesis is dominated by cryogenic processes, resulting in unique macromorphologies, micromorphologies, thermal characteristics, and physical and chemical properties. In addition, these soils are carbon sinks, storing high amounts of organic carbon collected for thousands of years. In the Canadian soil classification, the Cryosolic Order includes mineral and organic soils that have both cryogenic properties and permafrost within 1 or 2 m of the soil surface. This soil order is divided into Turbic, Static and Organic great groups on the basis of the soil materials (mineral or organic), cryogenic properties and depth to permafrost. The great groups are subdivided into subgroups on the basis of soil development and the resulting diagnostic soil horizons. Cryosols are commonly associated with the presence of ground ice in the subsoil. This causes serious problems when areas containing these soils are used for agriculture and construction projects (such as roads, town sites and airstrips). Therefore, where Cryosols have high ice content, it is especially important either to avoid these activities or to use farming and construction methods that maintain the negative thermal balance.

(Appendix) Bulk inorganic chemistry at DSDP Leg 77 Holes

Clay mineralogic and inorganic geochemical investigations of Cretaceous and Cenozoic sediments of the western Gulf of Mexico lead to the following main conclusions. (1) Transition of lowermost Cretaceous continental to marine sedimentation is marked by a clay evaporitic stage, north of the Campeche Escarpment. (2) Existence of combined mineralogic and geochemical stratigraphy allows us to propose correlations between Sites 535 and 540, especially for the Albian. (3) Predominance of detrital clay assemblages is indicative of hot and variably humid continental climate until the early late Cenozoic. (4) Tectonic destabilization of the margins of Gulf of Mexico occurred at different periods, especially until the middle Cretaceous, with a mixed erosion of rocks and soils and temporary oxidized conditions of deposition. (5) Successive developments of confined perimarine basins occurred from the earliest Cretaceous until the Miocene, chiefly in the Florida area. The sources of inorganic materials were chiefly situated on the east of the studied area until the late Tertiary and after that in the Mississippi River basin. (6) Occasionally, volcanic activity influenced the clay mineralogy and mainly the geochemistry, and possibly contributed to the rather strong magnesian character of the deposition until the late Paleogene. (7) The argillaceous diagenesis is weak; variability of the carbonate diagenesis is marked by the relation Sr = f(CaO) and chiefly depends on the depth of burial, the clay content, the porosity, and the geologic age.

40Ar-39Ar investigation of volcanic clasts in glaciogenic sediments at ODP Sites 1097 and 1103

Three selected diamictite samples recovered within sequence group S3 at Sites 1097 (Sample 178-1097A-27R-1, 35-58 cm) and 1103 (Samples 178-1103A-31R-2, 0-4 cm, and 36R-3, 4-8 cm) of Ocean Drilling Program Leg 178 have been investigated by scanning electron microscope, electron microprobe, and 40Ar-39Ar laser-heating techniques. They contain variable proportions of fragments of volcanic rock groundmass (mostly in the range of 100-150 µm) with textures ranging from microcrystalline to ipocrystalline. Their rounded shapes indicate mechanical reworking. Fresh groundmass glasses, recognized only in grains from samples of Site 1103, show mainly a subalkaline affinity on the basis of total alkali-silica variations. However, they are characterized by relatively high TiO2 and P2O5 contents (1.4-2.8 and 0.1-0.9 wt%, respectively). Because of the small size of homogeneous grains (100-150 µm), they were not suitable for single-grain total fusion 40Ar-39Ar analyses. The incremental laser-heating technique was applied to milligram-sized samples (only for Samples 178-1097A-27R-1, 35-58 cm, and 178-1103A-36R-3, 4-8 cm) and to various small fractions (each consisting of 10 grains for the sample from Site 1097 and 30 grains for samples from Site 1103). The latter approach resulted in more effective resolution of sample heterogeneity. Argon ages from the small fractions show significantly different ranges in the three samples: 75-173 Ma for Sample 178-1097A-27R-1, 35-58 cm, 18-57 Ma for Sample 178-1103A-31R-2, 0-4 cm, and 7.6-50 Ma for Sample 178-1103A-36R-3, 4-8 cm. Ca/K ratios derived from argon isotopes at Site 1103 suggest that the data mainly refer to outgassing of groundmass glass. At Site 1103, we observe an overall apparent age increase with decreasing sample depth. This is compatible with glacial erosion that affected with time deeper levels of a volcanic sequence previously deposited on the continent. The youngest apparent age of 7.6 ± 0.7 Ma detected close to the bottom of Hole 1103A (340 meters below seafloor [mbsf]) is compatible with the age range of the diatom Actinocyclus ingens v. ovalis Zone (6.3-8.0 Ma) determined for the interval 320-355 mbsf and with the maximum ages derived from strontium isotope composition of barnacle fragments obtained at 262-263 mbsf at the same site. Nevertheless, this age cannot be taken as the maximum youngest age of the volcanic sequence sampled by glacial erosion or as the maximum age for the deposition of the Sequence S3 at 340 mbsf unless validated by further research.