L’évolution des versants d’une partie de la colline de Québec

Dans cette étude portant sur une région plutôt restreinte en surface (moins de 10 km 2 ), nous avons essayé de déterminer la part relative des différents facteurs ayant influé sur le développement d'un modelé caractérisé par des versants raides tranchés par des surfaces quasi planes parfois surmontées de barres de grès. Les bancs de grès présentent un pendage médian de 52° et une épaisseur médiane de 1m. Une analyse portant sur 42 bancs a montré qu'il existe une corrélation positive entre l'épaisseur des bancs et leur granulométrie. Nous avons également montré que la diaclasation des bancs est fonction de leur épaisseur. C'est cette diaclasation qui conditionne le mode d'évolution des versants qui se fait surtout sous l'action de la gélifraction et de la gravité, sous forme d'éboulis. Elle détermine également la taille des produits de l'érosion.Si l'histoire géologique de la région est un facteur déterminant, il apparaît toutefois que le rôle des facteurs lithologiques et structuraux est le plus important : le relief est étroitement calqué sur le mode de sucession des strates et la position des bancs inclinés vers le fleuve facilite l'érosion par enlèvement de pans sucessifs, surtout en position littorale où le rôle du pied de glace est et a été très important.In this rather small region (less tran 10 km 2 ) where relief is characterized by steep slopes cut by almost level surfaces with sandstone hog's backs, we tried to determine the relative portion of each of the development factors. Sandstone beds have a 52° mean slope and 1 m mean thickness. The statistical analysis of 42 beds shows a positive correlation between their thickness and their granulometry, and that jointing is a function of bed-thickness. Jointing conditions the type of evolution of slopes which essentially results from frost shattering and gravity (rockfalls . . .) It also determines the debris size.Though the geological history of the region has a certain role, it appears that litho-logical and structural factors are the most determinant ; the relief is closely related to the succession of strata (shale and sandstone). The dipping of beds towards the river favors successive beds erosion, chiefly along the St. Lawrence River banks where the ice-foot action is and has been very important

Éléments de la morphologie cryogène du golfe de Richmond, Nouveau-Québec

Dans la région du Golfe de Richmond, Nouveau- Québec (56°15'N - 76°30'W), l'auteur a dressé un inventaire des manifestations périglaciaires et étudié les principales formes liées à la présence et à la dégradation du permafrost. Ceci lui a permis de jeter les bases d'une classification des formes cryogènes et thermokarstiques rencontrées dans cette région.In the Richmond Gulf Area, Northern Québec (56°'N -- 76°30'W), the author has made an inventory of periglacial phenomena and studied the major landforms resulting from the presence of permafrost and its degradation. This enables him to establish the basis for a classification of cryogenic and thermokarstic features of this region

Mineralogical and geochemical characterisation of warm water, shallow marine glaucony from the Tertiary of the London Basin

Glaucony is present in the Palaeocene sediments of the London Basin, from the Thanet Sand Formation to the gravel beds at the base of the Lower Mottled Beds of the Reading Formation. The Upnor Formation glaucony is a rare example of formation in warm, shallow brackish water and this, combined with the ready availability of fresh material from boreholes, make this study important in developing our understanding of this mineral. Glaucony comprises up to 50% of the Upnor Formation, a grey to green sandstone, of variable thickness and composition, that was deposited in a warm, shallow marine to estuarine environment, ~55.6-56.2 Ma. Using morphological criteria, X-ray diffraction data and K+ abundance, the Upnor glaucony may be defined as evolved. The underlying shallow marine Thanet Sand contains <5% of nascent to slightly evolved glaucony. The REE data for the Upnor Formation suggest more than one source for the sediment from which the Upnor glaucony formed, while the Thanet REE data are consistent with a high detrital clay component. In the Upnor Formation, the high proportion of glaucony that occurs as granule fragments rather than whole granules, and the high energy estuarine to shallow marine environment of deposition, are indicative of reworking. The Upnor glaucony is inferred to be intraformationally reworked, rather than derived from the Thanet Sand Formation. The glaucony may have formed in sediments deposited away from the main estuarine channel, and been subsequently reworked into higher energy sediments. Warm seas with freshwater mixing are more typically characteristic of verdine formation than of glaucony. The shallow, brackish environment of deposition suggests that there is not a clear distinction between the environmental requirements of verdine (or odinite) and glaucony (or glauconite), as is often proposed. The highly fractured, delicate nature of some granules indicates that they have experienced some maturation in situ, after reworking. The oxygen and hydrogen isotopic compositions of Upnor Formation shark teeth and glaucony point to formation in low salinity water at ~23±3°C, also consistent with formation in the Upnor Formation, rather than in a fully marine sediment and subsequent reworking. A higher than normal temperature of formation may have increased the rate of evolution of glaucony. Our multidisciplinary study considers many of the factors relating to depositional environment that must be considered when glaucony rich facies are encountered in comparable palaeoenvironmental settings elsewhere in the geological record