Introduction

In 1979 I made a preliminary attempt to correlate three important sections of Permian and Triassic rock graphically (Sweet, 1979). In the sections considered in that study, data on the ranges of conodonts in strata thought to be Lower Triassic were adequate to suggest that further work might result in a high-resolution biostratigraphic scheme of worldwide significance. Consequently, considerable time was invested in assembling data on the ranges of conodonts in widely distributed sections of Lower Triassic strata and, in 1988 (Sweet, 1988b) a high-resolution biostratigraphic framework was established for the Lower Triassic. That scheme resulted from graphic correlation of sections in Kashmir, Pakistan, Japan, western United States, northern Italy, and far-eastern USSR. Correlation based on the measured ranges in those sections of 29 conodont species resulted in a framework that is divisible at the 95% confidence level into 21 chronozones (or Standard Time Units), each equivalent to a unit 5 m thick in the standard reference section at Guryul Ravine, Kashmir, and each representing approximately the same interval of time.

In 1979 data on the scaled ranges of stratigraphically significant invertebrate fossils were sparse for Permian rocks in the three sections I considered. Consequently, I used crude information on the ranges of scaphopods, bellerophontids, productacean brachiopods, and a few species of cephalopods and conodonts. Since 1979, however, there has been a flood of information on the measured ranges of conodonts and other invertebrates in rocks of the Permo-Triassic boundary interval, which it is now possible to use to expand the high-resolution framework begun in my 1988 report.

Introduction

It has long been clear that waning stages of the Permian Period and initial phases of the Triassic make up an interval of time during which there were profound changes in the Earth's internal and surficial features, in its atmosphere and climate, and, conspicuously, in its biota. Unfortunately, however, rocks that record this fascinating segment of Earth history are greatly restricted in distribution by comparison with those from which we reconstruct events in earlier Paleozoic or later Mesozoic history. Furthermore, subsequent orogenic cycles have dismembered, effaced, and in other ways complicated the record. In combination, these factors make development of a stratigraphic scale for the Permo-Triassic boundary interval difficult, and this, in turn, serves to insure that the history of the latest Permian and earliest Triassic has been reconstructed thus far in only very general outline.

Project of 203 of the International Geological Correlation Programme (IGCP) was organized in 1984 with the aim of integrating modern studies of rocks and fossils in the Permo-Triassic boundary interval into an internally coherent and well-controlled body of information from which it might ultimately be possible to infer something meaningful about the history of late Paleozoic and early Mesozoic times. The attention of project participants naturally focused on Permian and Triassic strata in the eastern part of the Tethyan realm, in South China and India, for marine rock sequences of this age are most continuously developed there. However, close cooperation with students of the Permian and Triassic in Italy, Hungary, Yugoslavia, Israel, the Soviet Union, Australia, and New Zealand has enabled development of a data base that now includes information for essentially the entire length and breadth of the former Tethys seaway.

The 16 reports that make up this volume constitute the final report of Project 203 of the International Geological Correlation Programme, which dealt with Permo-Triassic events of the East Tethys and their intercontinental correlation. During the five-year life of Project 203, participants met twice in Beijing, and once each in Columbus, Ohio (USA) and Brescia (Italy), to exchange views, consider new data, and examine pertinent sections in the field. These conferences have provided new insight into the stratigraphy, classification, and relations of strata within the Permo-Triassic boundary interval, and a wider appreciation of the problems involved in the correlation and interpretation of these rocks, which document an unusually significant period in Earth history.

It will be clear to the reader that the 40 contributors to this volume are in substantial agreement in their interpretation of many features of the Permo-Triassic boundary interval, but disagree, at least by implication, in their evaluation of others. Although as editors we have strived to achieve readability and uniformity in basic terminology, we have also attempted to avoid interference with strongly held individual views, even though they run contrary to those of other contributors. In brief, it would be inappropriate to suggest that in five short years participants in Project 203 solved all problems with respect to the Permo-Triassic boundary interval – for many of these are likely to persist as long as vigorous study continues. We do suggest, however, that data and ideas gathered and expressed during the five-year life of Project 203 and summarized in this volume are important contributions toward understanding and interpreting the rock and fossil record of the late Permian and early Triassic.