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Event succession in marine and continental beds around the Permian-Triassic boundary (PTB)


, : Event succession in marine and continental beds around the Permian-Triassic boundary (PTB). Abstracts with Programs - Geological Society of America 36(4): 67

High-resolution biostratigraphic and event stratigraphic subdivision and correlation is possible around the PTB from open sea PTB successions in central and NW Iran and Transcaucasia. Two conodont faunas unknown from Meishan, the C. iranica Zone and the C. praemeishanensis fauna are present between the Clarkina yini fauna of the uppermost C. changxingensis-C. deflecta Zone and the C. meishanensis-Hindeodus praeparvus Zone of the Boundary Clay. The following events close to the PTB can be found: (1) The normal palaeomagnetic interval which straddles the PTB begins around the base of the C. iranica Zone and ranges up to the I. isarcica Zone. (2) A very sharp facies change occurs at the base of the Boundary Clay, which is connected to a strong high energy event recognizable not only in shallow water sediments but also in sediments deposited down to about 100m water depth well below the base of the storm waves. (3) A distinct maximum of microsphaerules can be observed in the lower, but not lowermost part of the Boundary Clay. (4) A dramatic climatic change can be observed at the base of the Boundary Clay which is characterized by replacement of the warm water conodont fauna by a cold water fauna dominated either by Hindeodus or Merrillina, and by replacement of the diverse Permian warm water ammonoid fauna by a poor Hypophiceras faunas. This cooling event started earlier in the southernmost outcrops (in Abadeh area, central Iran, which was situated during the PTB interval close to the Tropic of Capricorn), than in the northern outcrops (Zal, Jolfa, northwestern Iran) which were situated during the Permian about 1000 km to the north of the Abadeh area. (5) A distinct minimum in the carbon isotope curve occurs around the PTB. (6) In the somewhat shallower sections Abadeh and Shahreza a pronounced stromatolite horizon occurs which starts above the Boundary Clay and continued until the H. parvus Zone. Events 1-6 are also well recognizable in the continental fresh water lake deposits of the central Germanic Basin, in which the Milankovitch cycles are well developed. By these Milankovitch cycles the time span between the events and the duration of the biozones can be calculated.

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