352 MESOZOIC/Jurassic Jurassic K N Page, University of Plymouth, Plymouth, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction The Jurassic System is the second of the three systems comprising the Mesozoic Era It takes its name from the Jura Mountains of eastern France and Switzerland, where, as long ago as 1795, its distinctive character was recognized, although it was not until 1829 that Alexander Brongniart first used the term ‘Jurassique’ The stratigraphical and palaeontological meaning of the system was first clearly defined, however, by Alcide d’Orbigny’s publication of his classic Palaeontologie Franc¸ aise, terrains Jurassique from 1842 to 1849.This work established a system of remarkably modern-looking stages, most of which are still in use today D’Orbigny’s stages or ‘e´ tages’ were designed to be of worldwide use and were based on the assumption that periodic mass extinctions followed by the rapid re-establishment of new faunas characterized stage boundaries The existence of a particular ‘fauna’ therefore correlated rocks belonging to a specific stage Later research showed that these patterns are little more than an artefact of environmental changes in north-western Europe at the levels taken to represent stage boundaries by d’Orbigny, with faunal changes being more ecological than catastrophic Each of d’Orbigny’s stages included a sequence of fossil ‘zones’, representing the general stratigraphic ranges of specific taxa This term was further refined by Albert Oppel who, from 1856 to 1858 in his Die Juraformation Englands, Frankreichs und des Suă dwestlichen Deutschlands, developed a sequence of such divisions for the entire Jurassic System, crucially using the units in the sense of time divisions Oppel used a very similar sequence of ‘grupen’ or ‘etagen’ to d’Orbigny, and these form the basis of today’s Jurassic System Jurassic Stratigraphy and Chronology Chronostratigraphy: Stages, Standard Zones, Subzones, and Horizons Chronostratigraphy aims to produce rigorous definitions for named subdivisions of geological time, using actual rock units as standards for reference This approach includes the designation of a Global Stratotype Sections and Points (GSSP), through international agreement, for the base of each geological time period (or ‘System’) and each of their component stages The sequence of stages recognized in the Jurassic and their actual or candidate GSSPs are shown in Table Below the level of the stage, subdivisions at the level of chronozones and ultimately zonules can be used In the Jurassic, the frequent abundance of ammonoid cephalopod molluscs in marine sequences and their wide geographical distribution have led to their use for correlating sequences of ‘standard zones’ Such units have, from the days of Oppel, been used in the same sense as the modern concept of chronozones, although they are still frequently confused with biozones, where the use of fossils in correlation has no Table Jurassic stages and their definitions Stage Historical type locality GSSP or candidate GSSPs Tithonian (152 145 Ma) Mont Crussol, Arde`che/Canjuers, Provence, France Kimmeridgian (155 152 Ma) South Eastern France, after the Goddess ‘Tithon’ Kimmeridge Bay, Dorset, England Oxfordian (157 155 Ma) Oxford, Southern Central England Callovian (160 157 Ma) Bathonian (166 160 Ma) Kellaways, Wiltshire, England Bath, South West England Bajocian (174 166 Ma) Aalenian (178 174 Ma) Toarcian (183 178 Ma) Pliensbachian (192 183 Ma) Sinemurian (197 192 Ma) Hettangian (200 197 Ma) Bayeux, Normandy, France Aalen, Wurttemberg, Germany Thouars, Deux Se`vres, France Pliensbach, Wurttemberg, Germany Semur En Auxois, Burgundy, France Hettange, Lorraine, France Staffin Bay, Isle of Skye, Scotland; Mont Crussol, Arde`che, France Savournon/Thoux, Provence, France; Weymouth, Dorset, England Albstadt Pfeffingen, Wurttemberg, southern Germany Cabo Mondego, Portugual; Bas Auran, Provence, France Cabo Mondego, Portugual (GSSP) Fuentalsaz, Iberian Cordillera, Spain (GSSP) Peniche, Portugual Robin Hood’s Bay, North Yorkshire, England East Quantoxhead, Somerset, England (GSSP) St Audries Bay, Somerset, England; Muller Canyon, Nevada, USA; Chilingote, northern Peru; Kunga Island, BC, Canada