Article: Faunal realms and facies in the Jurassic

Differences in the composition and diversity of marine invertebrates in the Tethyan and Boreal Realms of the Jurassic are outlined, and previous interpretations based on control by temperature, physical barriers, and depth of sea are discussed and rejected. Three sedimentary facies associations, termed terrigenous clastic, intermediate, and calcareous, are distinguished in the Jurassic of Europe and a correlation with faunal realms is shown to exist. Taking this into account a hypothesis is proposed relating the establishment and maintenance of the Boreal Realm to an extensive inland sea of slightly reduced salinity in the Northern Hemisphere, which had free connections with the Tethyan and Pacific Oceans. The influence of other environmental factors and some ecological implications are briefly discussed.