The Tethys Ocean

Originally, Tethys was defined as an equatorial ocean ancestral to the Alpine—Himalayan mountain ranges (Suess, 1893). The concept followed an earlier definition, under the name “Zentrales Mittlemeer,” of a Jurassic seaway that extended from the Caribbean to the Himalayas (Neumayr, 1885) and, thus, included the Jurassic Atlantic Ocean together with the Alpine—Himalayan Belt. Plate tectonic concepts, in contrast with geosynclinal concepts that mingled a past ocean with an orogenic belt, permitted the recognition of parts of the same Jurassic ocean, located in the Atlantic and the Alps, as being either submitted, or not, to later orogeny (Bernoulli, 1972). Since then (Aubouin et al., 1980; Bernoulli and Lemoine, 1980), the name “Tethys” has been applied to the whole oceanic realm, including the Mesozoic Central Atlantic, which separated North America, Europe, and Asia to the north, from South America, Africa, India, Australia, and Antarctica to the south (Fig. 1). Remnants of Tethys now are found within Alpine mountain belts from the Caribbean in the west to the recent collision zone between Australia and Eurasia in the East, and within the still-growing Central Atlantic Ocean between Africa and North America.

The integration of microstructures and crystallographic fabrics of naturally deformed rocks into regional deformation studies helps characterize the mechanisms and tectonic models involved in orogenesis. For this reason, a considerable effort has been made in recent years to develop techniques for assessing the kinematics of deformation events, in particular those associated with ductile deformation at deep levels in the continental crust (Burg et al., 1981; Platt and Behrmann, 1986; Hanmer and Passchier, 1991).

Paleogeography is established using mainly plate kinematics and unfolding mountain belts, but basinal paleodepths are defined using specific facies, among which radiolarites can provide key information. The common equation radiolarites = deep oceanic basin is obviously too simple to be correct; and to infer from the geological message (e.g., radiolarites), the original, environmental, biological signal requires a good knowledge of the successive filters that have changed it and the originators of these signals (e.g., the radiolarians).

For 260 Ma, the Tethys Ocean covered much of the face of the earth, from the Caribbean domain to the west to the Indonesian domain to the east. The Tethys paleoenvironmental atlas (Dercourt et al., 1993) shows 14 stages of evolution, from the most recent Tortonian (10 Ma) to the oldest, Murgabian, time (260 Ma). From the Late Cretaceous to the present, the Tethys has been closing, with sediments in the Caribbean, Alpine-Himalayan, and Indonesian belts. Prior to that, Tethys had spread and cut Pangea as early as the Permian. Remnants of this ocean are found only in the Central Atlantic and the Mediterranean Sea. During each period of time considered here (Tortonian, Late Burdigalian, Late Rupelian, Lutetian, Late Maastrichtian, Late Cenomanian, Early Aptian, Late Tithonian, Early Kimmeridgian, Callovian, Middle Toarcian, Late Norian, Late Anisian, Late Murgabian), Tethys was located in the Northern Hemisphere, forming an E-W oceanic corridor nearly parallel to the equator. The hypothesis that the morphology of Tethys was similar to that of the present Atlantic is accepted in many reconstructions (e.g., Scotese and McKerrow, 1990; Scotese, 1991). Such a picture is an oversimplification, as particularly illustrated in the Cretaceous maps of the atlas. The following Tethyan domains can be defined from west to east: Caribbean, Atlantic Tethys (also named Central Tethys or Central Atlantic), Mediterranean, Eastern Tethys, and Indonesian-Australian. Among them, three particular domains are evident: (1) Indonesian-Australian, (2) Caribbean, and (3) Mediterranean.