Determination of Gold in Twenty Geochemical Reference Samples by Flameless Atomic Absorption Spectrometry

After acid digestion, gold is extracted with MIBK and determinated by flameless atomic absorption spectrometry. The results for six USGS reference samples and fourteen French geochemical standards are presented and discussed. The agreement with working values for these standards is in the range of pm 5%.     

GEOLOGY OF NORTHERN CHIHLI AND EASTERN MONGOLIA.

During the last spring (April-May 1924), we have, F. Licent and I crossed the Northern Chihli and the eastern part of the Inner Mongolia.     

LA CHINE EST-ELLE PLACEE ENTRE DEUX GRANDES FRACTURES DE LA CROUTE TERRESTRE ?

Hest bien clair que toute reponse a cette question, sera du plus haut interet pour les geologues de la Chine, vu que les resultats de la geodesie semblent bien indiquer que la croute terrestre est divisee en plusieurs blocs independants, juxtaposes et equilibres isostatiquement.     

Diagenetic K-feldspar pseudomorphs in the Triassic Buntsandstein sandstones of the Iberian Range, Spain

Early diagenetic K-feldspar in the Triassic Buntsandstein of the Iberian Range (Spain) occurs as pseudomorphs after detrital K-feldspar (Or<93) and plagioclase (Ab<96). These pseudomorphs are chemically pure (Or>99), untwinned, commonly heavily clouded by vacuoles and tiny inclusions, dark-luminescing and are composed of numerous fine euhedral crystals of K-feldspar. The latter property suggests that the pseudomorphs form via dissolution of detrital K-feldspar and plagioclase and precipitation of authigenic K-feldspar. X-ray diffraction analysis shows that the authigenic K-feldspar is intermediate microcline.     

Mass Spectrometric Isotope Dilution Analyses Of Barium in Geochemical Reference Samples

Twenty-four geochemical reference samples have been analysed far barium using the stable isotope dilution technique. These include five CRPG, ten ANRT, six Nimroc and two CCRMP samples together with the Tonalite from Tanzania, Duplicate analyses have been made in each case and our values for barium are believed to be accurate to approximately 3 %. In general, our results are in good agreement with the published data except for Nimroc samples where our data are consistently lower than the presently accepted values. No evidence of sample inhomogeneities was observed in the present work.     

A depositional model for a wave‐dominated open‐coast tidal flat,based on analyses of the Cambrian–Ordovician Lagarto and Palmares formations,north‐eastern Brazil

Open‐coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open‐coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north‐eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave‐dominated or tide‐dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic hummocky cross‐stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky cross‐stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair‐weather wave base. However, in this model of an open‐coast tidal flat, hummocky cross‐stratification beds were found in very shallow waters above the fair‐weather wave base. Indeed, this depositional environment was characterized by: (i) fair‐weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these hummocky cross‐stratification deposits.