East Asia occupies the key position in the Triassic correlation of the circum-Pacific region, Tethys, and marginal Gondwana, because it includes important areas from all of those realms. This chapter presents biostratigraphic correlations for the major Triassic groups of organisms (Tables 19.1–19.3). Detailed discussion of how these charts were worked out would be lengthy and will be omitted here.

Early Triassic biogeography of East Asia

The East Asian area of the early Triassic has been subdivided into the following realms and regions: the northern temperate North Laurasian Realm, including the Boreal Sea Region (northeastern Asia, I1) and the North Eurasian Region (I2); the northern warm-temperature Central Laurasian Realm, including the Central Eurasian Region (II2) and its Marginal Seas Region (II1); the tropical–subtropical Laurasian Tethys Realm, including the Cathaysian Tethys Region (III1) and its Southern Margin Region (III2); the southern temperate Gondwanan Realm, including the Indian Subcontinent Region (V); and the Gondwanan Tethys Realm, including the Himalaya–Banda Loop Region (IV) (Figure 19.1)

This region covers the Verkhoyan (Verchojan)–Chukote (Chukchi) and Mongol–Okhotsk areas, where carbonate sediments are extremely rare. The biota was dominated by ammonoids and bivalves (Dagys, Arkhipov, and Bychkov, 1979): early Griesbachian ammonoids Otoceras, Tompophiceras, Hypophiceras, Anotoceras; late Griesbachian Boreal ophiceratids (Ophiceras boreale, Ophiceras indigirense, Ophiceras commune); a Spathian Keyserlingites assemblage, including Olenikites, Svalbar dicer as, Sibirites, and Nordophiceras; there were no Smithian Owenites and Spathian Columbites and Tirolites [Tirolites morpheus (Popov) from Verkhoyan has been renamed Tompoites].

In so many features the Permian and Triassic periods differed from the present that if we could be transported back to that distant past, surely we would think that we were on another planet. The plants and animals would be largely unrecognizable – no mammals, and none of our modern trees or grasses. Although the nature and dispositions of the seas, lands, and mountains during that time are subject to different interpretations and conflicting views, who can doubt that the world's geography would be unrecognizable? The climate would have varied widely, from very cold at the beginning of the Permian (perhaps not unlike the glacial climate of the world a few thousand years ago) to a hot, dry climate during the Triassic, like nothing we see at present, followed by a warm climate continuing into the Jurassic.

Major changes in faunas were associated with the beginning of the Jurassic period, as reviewed by Boucot (1990), Dickins (1993a), and Hallam (1981). Boucot stated that “the modern marine … benthic fauna and communities really begin with the Jurassic.” In the latter part of the Permian and during the Triassic the earth was wracked by vast earthquakes, and great mountain chains were formed. There was magmatic-volcanic activity on an enormous scale. Some of those events are described in this volume, and some of the most interesting problems for future investigation are considered.

Introduction

In this chapter we deal mainly with volcanism in the Permo-Triassic boundary interval in South China, with brief reference to other parts of the Tethyan realm. In much of South China a level commonly regarded as the Permo-Triassic boundary is marked by the so-called ‘boundary clayrock’, which is a layer of montmorillonite or interstratified montmorillonite and illite several centimeters to a few decimeters thick. The boundary clayrock is marine because it yields conodonts, ostracodes, foraminifera, and glauconite, and because its boron content is everywhere much higher than 100 ppm. It is at the level of the boundary clayrock that the strongest phase of Permo-Triassic mass extinction is recorded and it is also at this level that anomalous concentrations of δ13C, iridium, and other elements have been reported.

Permo-Triassic volcanism

Our ideas about volcanism in the Permo-Triassic boundary interval are based on the nature of the boundary clayrock, and on evidence from sphaerules in the boundary clayrock.

Nature of boundary clayrock

More than 30 occurrences of the boundary clayrock and other boundary rocks have been found to be of volcanic origin. The well-known boundary clayrock of the Meishan section, Changxing, Zhejiang Province, was first regarded as sedimentary. However, owing to discoveries in it of high-quartz (beta quartz, Plate 13.1, fig. 8) and other volcanic indicators (He et al., 1987) this layer has been shown to be hydrolyzates of volcanic ash. The equally famous boundary clayrock in the Shangsi section, Guangyuan, Sichuan Province (bed 21 of Yang et al., 1987, or bed 27b of Li et al., 1986) is montmorillonitized tuff (Li et al., 1986).

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.