Abstract

The known Jurassic foraminiferal faunas of the world are classified into five broad types of assemblage rather than into conventional faunal realms, which tend to be geographically exclusive except at the border zones. Each of these broad types retains its general characteristics throughout the Jurassic, although changes occur at species and genus level. Three of the kinds of assemblage are typical of shelf regions, including the western interior region of North America, the northern two-thirds of Europe, and scattered points south of the Tethyan Zone. These three kinds of assemblage often alternate with one another through time. Respectively, they are characterized by simple arenaceous foraminifera including reophacids, simple lituolids, and textulariids; nodosariids, and certain calcareous forms including epistominids, buliminids, or ophthalmidiids. The other two kinds of assemblage are typical of the Tethys seaway and its margins. In these assemblages, either planktonic foraminifera or arenaceous forms including pavonitids, discocyclinids, or others with complex internal structures are characteristic. The planktonic foraminifera invade the shelf region from time to time. In border zones, such as Mexico, Switzerland, and Austria, elements of both shelf and Tethyan assemblages occur. The five broad types of assemblages are considered to be related partly to temperature controls and partly to the broad geotectonic-sedimentary environment. Each group of assemblages contains a number of ecological communities that we cannot define as subunits of the broader pattern until we have more data.

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