Deltas, with their economic, political and scientific importance, have long fascinated and attracted Man's attention. The term 'delta' was coined by Herodotus in approximately 450 Bc for the triangular-shaped sedimentary body at the mouth of the River Nile. Today, the concept of a delta, its morphology and its controlling processes, are almost as numerous as the people who work on such systems.
This volume, of 23 papers on many aspects of modern and ancient deltaic sedimentary systems, will be useful to researchers as well as teachers and students alike. The well-balanced content of the book should prove particularly attractive.to those who seek a detailed state-of-the-science overview of this large and ever-expanding subject area. <...>

We report here an investigation of the distribution of Au, As, Sb, Hg, carbonates, K-Al silicates, and pyrite in the Twin Creeks Carlin-type gold deposit. The main objective of the study was to determine the nature and degree of correlation among these variables and use them to identify the process(es) that deposited gold. The study focused on deposit-scale variations in these parameters and was based, in part, on data from two large geochemical databases that were prepared by mine staff.

Country rocks at Twin Creeks include Ordovician-age interlayered calcareous shales and mafic igneous rocks, the overlying Leviathan allochthon, and the Pennsylvanian-Permian Etchart Formation that was deposited unconformably over these rocks. Most gold values are found in calcareous shales in the Ordovician sequence and in limestones in the Etchart Formation, although not all layers contain the same amount of gold. Strongest gold mineralization is not adjacent to faults but its general form and distribution suggest that gold-bearing solutions gained access to favorable layers along the faults. In the Ordovician sequence, gold values are highest in shales that have undergone maximum dissolution of carbonate minerals. Petrographic study shows that some gold is associated with adularia, but deposit-scale comparisons do not show a consistent relation between K/Al ratios and gold values. The distribution of antimony is similar to that of gold, whereas mercury is more concentrated than gold, and arsenic is more widely dispersed than gold.

The relation between gold, iron, and sulfide sulfur values shows that mineralization is concentrated in rocks that have gained sulfur, but not iron, to form gold-bearing arsenian pyrite. Thus, these rocks have undergone sulfidation rather than pyritization. The iron that underwent sulfidation came largely from preore, diagenetic(P) ferroan dolomite and was released into solution by decarbonation, a common form of alteration associated with Carlin-type deposits. The results of this study suggest that wall-rock iron content and decarbonation processes which liberate this iron are the most important factors controlling formation of Carlin-type gold deposits. New deposits should be sought where stratigraphic units containing abundant ferroan dolomite are cut by favorable structures.

The ammonite fauna of the so-called ,bauhini horizon" is described in detail. The material comes from the Upper Danube valley and from the Lochen area (SW Germany). The bauhini horizon marks the youngest horizon of the Hauffianum Subzone (Late Oxfordian) of the Te-thyan chronozonation. The comparison of amoeboceratids permits a correlation of this horizon with the base of the Subboreal Kimmeridgian (Baylei Zone, densicostata horizon). Hence the bauhini horizon is demonstrated to be one of the most important levels for correlations. Three new ammonite species are described from the bauhini horizon: Metahaploceras muehl-heimense n. sp., Physodoceras wulfbachense n. sp., and Pictonia praeperisphinctoides n. sp. A brief survey is given of the ammonite faunal horizons below and above the bauhini horizon.

Der Begriff der Gewölbten Staumauern schließt eine große Formenreihe von Staumauertypen in sich (15.613), deren Gemeinsames es ist, daß ihre statische Funktion ganz oder vorwiegend auf Gewölbewirkung beruht. Die von Schnitter (1987 b) erstellte Talsperrenstatistik weist aus, daß in den Jahren 1950 bis 1959 der Anteil der Bogenmauern an den 100 bis 149 m hohen Talsperren 46%, an den 150 bis 199 m hohen Absperrbauwerken 75 % und an den über 200 m hohen Absperrbauwerken 100 % ausmachte. Die Prozentanteile sind jedoch in der Periode von 1980 bis 1989 auf 11 % bei den 100 bis 149 m hohen, auf 19% bei den 150 bis 199 m hohen und auf 36% bei den über 200 m hohen Talsperren abgesunken. In Ländern, in denen die Geländeformen, insbesondere die Querschnittform der Täler, diesem Staumauertyp entgegenkommen und welche zugleich über eine hochentwickelte Talsperrentechnik und Ingenieurgeologie verfügen, sind bis zu 50% aller Talsperren von mehr als 15 m Höhe Gewölbte Mauern. <...>