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The AAPG/Datapages Combined Publications Database
CSPG Bulletin
Abstract
International Permian-Triassic Conference, August 23-26, 1971, Calgary, Alberta
The Permian-Triassic Boundary in the Mediterranean Area [Abstract]
The area of the western Mediterranean and bordering continental Europe appears to have stabilized during Late Paleozoic time, with only minor basins on a continental mass and near-marine margins accumulating red bed deposits, interspersed with variable amounts of evaporites. Local outpourings of volcanic rocks suggest possible advance warnings of tectonic activities to follow, or perhaps only relaxation of compressional forces
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after the last phases of Hercynian activity. Locally, more marine waters deposited the Bellerophon Limestone of the Italy-Yugoslavia area, but the age relationships of this limestone to the other Upper Permian deposits is not clear. The lowermost Triassic rocks may succeed the uppermost Permian in the continental basins and evaporite sequences. No evidence of marine lowermost Triassic has been documented for the western part of the Mediterranean area, but by Late Scythian to Early Anisian time marine deposits extended as far west as the southern Alpine areas and later Triassic marine rocks are not uncommon in that area.
Southeast of the continental mass, marine deposits of Early Permian age accumulated in a shallow seaway. Marine limestones with faunas including brachiopods and fusulinids of Early Permian age are known from Yugoslavia, Greece and Turkey. These are bedded deposits that have been preserved to the present in a disturbed (folded and faulted) condition, but in recognizable sequences. Whatever events took place after their deposition were not enough to metamorphose or destroy those deposits. Most of the marine rocks of later Permian age in the Mediterranean occur only as isolated cobbles, blocks and larger masses in deposits of Triassic or younger age. The rocks are of approximately the same age as the deposits in Tunisia. They are found in Sicily, Yugoslavia, Greece, Cyprus and Turkey. It is not known whether these rocks were originally deposited near their present positions or whether they have been transported tectonically over short or longer distance. The rocks have faunas in common that are of approximately Guadalupian age and they bear typically Tethyan fusulinid faunas rich in verbeekinids and neoschwagerinids.
The almost complete lack of Upper Permian marine beds in depositional sequence between the Afghanistan-Iran area on the east and Tunisia on the west suggests that diastrophic forces, possibly directly related to the closing of the Tethys seaway, have redistributed the rocks of Late Permian and possibly Early Triassic age throughout most of the Mediterranean area. Whether there was continuous deposition of marine Permian across this area is problematical, but it seems reasonable to assume an original break in the depositional pattern, with normal deposition at both ends.
The fusulinid faunas in the Mediterranean area reached their peak of abundance and diversity during the early part of the Guadalupian and then died out gradually in the later part of the Guadalupian. Only a trace of fusulinids lived on into the later Permian, with three or possibly four genera surviving into the Dzhulfian and those represented only in limited areas by few specimens.
The restriction of the continental seaways with the increase in saline deposits did not provide suitable environments for the continued success of the fusulinids. The marine areas marginal to the continental seas might have continued to provide suitable environments but the records of many such areas have since been destroyed by subsequent tectonic events. The few fusulinids that survived to Late Permian times were apparently more adaptable to the restricted environment available.
The Mediterranean area yields little information on the Permian-Triassic boundary because of the paucity of rocks assignable to Late Permian or Early Triassic age in the area. Where the rocks appear to be continuous, the evaporite facies makes age assignment difficult, and where the rocks are marine, the tectonic activity has destroyed the stratigraphic relationships.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
U.S. Geological Survey, Room E 114, U.S. National Museum, Washington, D.C. 20560, U.S.A.
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