Marine phosphorites, the principal raw material for phosphatic fertilizers, do not occur uniformly through time and space. The origin of these unusual sedimentary rocks appears to be related mainly to marine biological productivity, often associated with upwelling currents during certain intervals of geological time. This book examines the environmental setting and resulting phosphorites which formed during the Miocene, one of the major and most recent phosphogenic periods throughout the geologic record. In addition, an oceanographic perspective is given by investigations of modern oceanic environments where phosphorites are presently forming. Together, the geologic and marine approaches provide a complete outlook on this important mineral resource. This book is the third of four reference volumes which together cover the achievements of the International Geological Correlation Programme Project 156 (Phosphorites) during the ten years of the project's existence.

This unique survey describes the world's ancient phosphorite deposits on a scale never previously attempted. The International Geological Correlation Programme started Project 156, on world phosphate resources, in 1977. An international team of forty-six researchers describes in twenty-five chapters almost 100 Precambrian or Cambrian deposits of phosphate rock, extending through all continents except Antarctica. The total resources are large, but only a small fraction is minable at present. The data presented give a good understanding of the distribution, nature and origin of phosphate deposits. The book is an important contribution to the scientific understanding of phosphate deposits, as well as a valuable aid to the search for an exploitation of phosphates in many parts of the world.

The book presents a new and comprehensive model for the development of phosphate sediments. Starting with geochemistry and including new methods in sedimentology (sequence stratigraphy), it results in an interdisciplinary approach to a resource system covering all fields of phosphate geology. For researchers, teachers and students alike the book offers a complete overview of the whole field including case studies of major deposits.

This Proceedings volume contains 14 papers from the symposium ''Siliceous, Phosphatic and Glauconitic Sediments of the Tertiary and Mesozoic'', which was held during the 29th International Geological Congress, Kyoto, Japan, 24 August--3 September, 1992. The first part of this volume consists of papers dealing with Tertiary biosiliceous sediments of the Pacific Rim, starting in the northwest. The second part of the volume is composed of papers dealing with Tertiary and Mesozoic phosphatic rocks and phosphatebearing sequences, in particular of the eastern Pacific Rim and the Middle East. The articles serve to emphasize the similarities and differences between the Pacific Neogene successions and the Tethyan Mesozoic sequences of the Middle East.

Phosphatic concretions occur within diatomite in the upper part of the Miocene Monterey Formation near Lompoc, Calif. Absence of disruption of fine laminar bedding in the associated sediment by the concretions shows that they formed after complete compaction of the enclosing sediment.The concretions exhibit a strongly concentric color, chemical, and mineralogic zonation. Many of them are composed of a nucleus in which vivianite is the dominant mineral. Amorphous ferric phosphate, mitridatite, and francolite are the dominant phosphatic phases in successive layers toward the surface of the concretions. Cd and As contents increase tenfold from the nucleus outward, reaching a maximum of 2,000 ppm, whereas Ni content, with a maximum of 720 ppm, and Co content show the opposite trend. This mineralogy and elemental composition favor accretion under conditions of continuously increasing Eh and pH, during uplift into the fresh-ground-water zone of the terrestrial environment. Shale-normalized rare-earth-element patterns, however, suggest a marine source for the elements biogenic debris consisting of opal-A, organic matter, and carbonates of the enclosing sediment.