An Intraformational Conglomerate by Mixed Sedimentation in the Upper Cretaceous of the Roc-de-Chère, Autochthonous Chains of High Savoy, France

The glauconitic and sandy limestone sequence, which in most places represents the Upper Cretaceous transgression throughout the High Calcareous Alps of the High Savoy, gives way in the Roc-de-Chère region to a 3- to 4-feet bed of conglomerate containing curiously shaped pebbles of fine-grained limestone scattered in a glauconitic matrix. Three distinct limestone types may be distinguished in the conglomerate on the basis of shape, dimension, and induced flow structures (from base to top): (1) contorted streaks, (2) larger irregular pebbles with highly deformed matrix inclusions, and (3) still larger subrectangular chunks with slightly deformed matrix inclusions. Well-developed flow structures are shown by the orientation of quartz grains and by the arrangement of deformed Globotruncana tests in both the pebbles and the matrix. A tentative explanation might suggest a mixed sedimentation in which beds of plastic calcareous muds and glauconitic sands were alternately deposited. Reworking phenomena intensively stretched and mixed the freshly deposited beds. However, intensity of deformation decreases upward as depth of water increased during transgression. Such a sediment may be classified as a special type of intraformational conglomerate formed under wave action when beds were still plastic

Recent Calcite-Cemented Sandstone Generated by the Equatorial Tree Iroko (Chlorophora Excelsa), Daloa, Ivory Coast

In the region of Daloa, Ivory Coast, several Iroko trees (Chlorophora excelsa, family of the Moraceae), a frequent species of the equatorial rain forest known for its calcareous excretions always related to wounds kept unhealed by insect activity, show an unusual lithogenetic aspect of this process. Between severely damaged roots, large-scale bleeding of the sap, after unsuccessful attempts to build crusts of fibrous carbonate over the wounds, has penetrated into the interstitial spaces of the adjacent granitic residual sand and cemented it by precipitation of calcium carbonate into large blocks of hard and massive calcite-cemented pure-quartz sandstone. The quartz and rare feldspar grains displayed a high amount of marginal corrosion by the cryptocrystalline calcite cement. The agents responsible for the severe damage to the trees cannot be determined with certainty but are assumed to be elephants, wild boars or jungle buffaloes. This recent sandstone demonstrates processes of intense corrosion of detrital quartz and feldspar grains and of general cementation both by calcite which have taken place at or near the surface before any decay, burial, overburden or compaction could occur and which, therefore, should be considered as geologically instantaneous

Distorted oolites and pseudoolites

Distorted oolites and pseudoolites are relatively rare occurrences in the geological column. They have been described in oolitic iron ores, phosphorites, limestones, argillaceous, and sideritic deposits. The shapes created by the distortion processes are very characteristic and independent from the mineralogical composition. They illustrate a complete gradation from plastic deformation to the rupture of rigid bodies. The distortion, which is localized in pockets or affects only isolated individuals, has always preceded the deposition of the cement and compaction wherever the latter has been active. The conclusion is reached that the distortion was generated during sedimentation in agitated conditions and resulted from the reciprocal impacts among oolites or pseudoolites at different stages of diagenetic induration