Ordovician Revisited: Reconstructing a unique period in Earth History.

ACEÑOLAZA, GUILLERMO F. (ED.)

Instituto Jaume Almera

Lugar: Barcelona; Año: 2005 p. 409

The Ordovician is a remarkable period in Earth history. It began almost 500 million years ago, lasted 46 million years (488.3 +/- 1.7 to 443.7 +/-1.5), and has long been recognized for its intriguing geology. Extensive spreading of epicontinental seas over land, associated with strong episodes of volcanism and a clear global climatic zonation, triggered the second largest biodiversification in life history. Significantly lower oxygen levels in the ocean/atmosphere system, a greenhouse state, and distinct patterns of oceanic circulation represented the environmental background in which the Cambrian Evolutionary fauna was replaced by the Paleozoic Evolutionary fauna, with more than a three fold increase in diversity. However, marine life then suffered a great mass extinction to close out the period. Ordovician carbonate strata are widespread and extensively used for cement. In addition, Ordovician rocks are the host of many economically significant mineral deposits, including oil shales, extensive petroleum deposits, gold mineralizations, and porphyry coppers. Of special note, much of Jolmolungma Mountain (Mount Everest), the highest mountain in the world, is composed of Ordovician strata. The current monographic volume of Geologica Acta "Ordovician revisited: reconstructing the puzzle of a unique period in the earth history", represents a compilation of a team of Ordovician specialists that contributed with new data and synthesis of different biostratigraphical, chronostratigraphical and palaeontological aspects of the Ordovician System. Contributions are by 19 authors from 8 different countries of the international geological community, addressing issues that are currently being focus of attention in the Ordovician System: carbon isotope stratigraphy, paleogeography, paleontology and biostratigraphy of the western margin of Gondwana, and bringing additional data to the Ordovician forum. After the foreword presentation, an invited introduction by Stanley Finney (former Chair of the Subcommission on Ordovician Stratigraphy) highlights the current situation on global Chronostratigraphy of the Ordovician System. Berry and Ripperdan provide insights on the carbon isotope stratigraphy from the Upper Ordovician carbonate succession in the Carnic Alps, while Khun and Barnes present a detailed description of Ordovician conodonts from the Georgina basin of Australia. Following the last paper, a challenging view related to the origin of the Argentine Precordillera is presented by Finney, Peralta, Gehrels and Marsaglia, on the basis of new isotopic data that brings additional elements to discus in the para-autochthony / allochthony dilemma. Albanesi and Ortega presents a broad overview of the Argentine Tremadocian conodont/graptolite biostratigraphy, referring it within the Gondwanan framework. The next paper by Budil and Buthansová describes and analyzes the moulting process of the nicely preserved Ordovician Dalmatinacean and Acastacean trilobites of the Prague Basin (Czech Republic). In addition, Darriwilian conodont biostratigraphy of the Las Chacritas Formation from the Central Precordillera of San Juan province (Western Argentina) is reported by Heredia, Beresi and Peralta, providing new information on this intriguing unit. At last, a detailed description and analysis is done by Maletz Goldman and Cone, offering an appraisal of the Early to Middle Ordovician faunas of the Trail Creek region of Central Idaho (USA). The set of papers presented in this monographic volume represent a natural continuation of the first issue of Geologica Acta (Vol. 1, Nr. 1, 2003) that focused on the Cambrian Period and provided the status quo of the earliest Phanerozoic system. This volume "Ordovician revisited: reconstructing the puzzle of a unique period in the earth history" is dedicated to Drs. Mario Hünicken (La Rioja) and Alfredo Cuerda (La Plata), whose pioneer work on the Ordovician of Argentina inspired many geologists to focus on the particular geology of the Ordovician from Argentina. Finally, I would like to sincerely thank the editorial board of Geologica Acta for publishing the volume, especially to Lluis Cabrera and Ángeles Santos for their enthusiastic assistance and dedication in the preparation of this volume. We kindly thank the reviewers, who actively participated in the preparation of this monographic volume. Work would have been impossible without the encouragement and guidance from many friends and colleagues, such as Juan Carlos Gutiérrez-Marco, Isabel Rábano, Miguel Ángel San José, Graciela Sarmiento (Madrid), Susana Esteban (Tucumán), Franco Tortello (La Plata) and Silvio Peralta (San Juan).