15 - Permo-Triassic orogenic, paleoclimatic, and eustatic events and their implications for biotic alteration

Summary

Introduction

It has long been recognized that a major change in fauna and flora was associated with a major regression in the latest Permian and earliest Triassic (see Dickins, 1983). The nature of this regression (or eustatic change) and its relationship to orogenic and tectonic developments in the Upper Paleozoic and Lower Mesozoic are discussed in this paper, which also includes comparisons with the Cretaceous–Tertiary boundary sequence. The climate of the Permo-Triassic boundary interval is also considered and its nature and influence amplified.

Volcanic rocks are widespread in Permo-Triassic boundary sequences but, as indicated elsewhere in this volume, their importance has only recently been recognized. The volcanism indicated by these rocks was related to tectonic and magmatic developments, which, together with the eustatic change and climate, must have had a profound effect on the fauna and flora of the time. These factors and apparently associated changes in the composition of seawater, the atmosphere, and the nature of the land, seem more than adequate to explain changes in the flora and fauna. The latter, in turn, are important potential guides to understanding development of the earth below the crust.

Tectonic and magmatic development

The Permo-Triassic boundary interval includes evidence of a remarkable regression, which represents a large-scale eustatic fall in sea level. Newell (1962, 1967a, 1967b, 1973) advanced strong reasons for recognizing this worldwide regression, which he thought contributed importantly to the change in life that marks the difference between the Paleozoic and Mesozoic. In the decade in which Newell's papers appeared, however, coeval worldwide transgressions and regressions were not accepted in geology, as they are today.