THE LOWER BOUNDARY OF THE TRIASSIC AND ITS CORRELATION IN MARINE SEDIMENTS: ARTICLE 2. BOREAL SECTIONS OF THE BASAL TRIASSIC AND THEIR CORRELATION WITH THE PERMIAN-TRIASSIC BOUNDARY DEPOSITS OF THE TETHYS

Abstract

The lower boundary of the Triassic should be placed at the base of the Otoceras Beds. In the boreal sections, these beds yield ammonite species of the Otoceras concavum and O. boreale zones. The upper part of the boreale Zone is an equivalent of the O. woodwardi Zone in the Himalayas, where it approximately corresponds to the conodont Hindeodus parvus Zone. The Permian-Triassic boundary, which is traditionally coordinated with the base of the woodwardi Zone, is easily traceable in the Tethyan sections but poorly correlative in the Boreal region. The boundary becomes more convenient and universal when placed at the base of the concavum Zone and its analogues. Everywhere, the woodwardi and concavum zones are separated from the underlying Permian beds by a stratigraphic hiatus. At present none of the sections suggested can be recommended as the Global Boundary Stratotype Section and Point for the lower Triassic boundary.