RICERCA ITALIANA     

Stratigraphic-paleogeographic and geochemical-petrographic characterization of the events around the Triassic-Jurassic boundary: an integrated approach

Università degli Studi di Milano

Abstract

The Late Triassic was a period of intense biological changes, involving both marine and non-marine biota, culminating at the Triassic/Jurassic (T/J) boundary in one of the five largest extinction events of the Phanerozoic. The biotic crisis was synchronous with a profound reorganisation of mantle and lithospheric plates dynamics related to the incipient phases of Pangea break-up. The opening of the Central Atlantic Ocean and of the Alpine Tethys in the Jurassic were preceded, at the T/J boundary, by the emplacement of the Central Atlantic Magmatic Province (CAMP), one of the largest magmatic provinces of the Phanerozoic.
Aim of this project is to contribute to explain timing and causes of the T/J extinction event. A multidisciplinary approach on selected stratigraphic sections will be adopted, combining lithostratigraphy, biostratigraphy, magnetostratigraphy, chemostratigraphy, geochemistry, geochronology, petrography, and paleogeography. The research fields of this project are outlined below:
a) identification of major physical and biological events occurring across the T/J boundary in sedimentary successions deposited in different paleogeographic settings, evaluating their local as opposed to global significance;
b) age determination, duration assessment, and correlation of the stratigraphic events recognized in the selected sections; radiometric (Ar/Ar on magmatic rocks), biostratigraphic, and magnetostratigraphic dating are planned;
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Principal Investigator

Flavio JADOUL Università degli Studi di MILANO

Research Objectives

FOREWORD
The recent years experienced a general improvement of the biostratigraphic, geochemical, litostratigraphic, and magnetostratigraphic knowledge of key stratigraphic successions deposited in the Central Atlantic and Tethyan domains around the Triassic/Jurassic (T/J) boundary, which is one of the five major biologic crises of the Phanerozic. Nevertheless, a general model able to relate all different events, both biotic and abiotic, which occurred across the boundary, has not yet been proposed. Our multidisciplinary project aims at filling this gap of knowledge. In particular, our project will attempt to determine absolute and/or relative age of all major biotic and abiotic events that occurred across the T/J boundary in different paleoenvironmental settings.

STUDY TOPICS
The following aspects will be studied:
a) Identification and correlation of the physical and biological events in sedimentary successions deposited in different paleogeographic settings, evaluating their local or global significance. Selected taxa (mainly palynomophs and nanoplankton) will be studied in order to unravel their evolution throughout the T/J boundary assess their recovery after the crisis;
b) dating of the stratigraphic events: radiometric (Ar/Ar on magmatic rocks), biostratigraphic (mainly palynological), and magnetostratigraphic dating are planned in order to unravel age, duration, and correlation of the different events recognized in the >>>

Timescale

24 months

National and international background

INTRODUCTION
The mass extinction that occurred about 200 Ma at the Triassic/Jurassic (T/J) boundary (Palfy et al., 2000; Hallam, 2002; Tanner et al., 2004) is one of the five main extinction events of the Phanerozoic (Raup & Sepkoski, 1982). Bivalves, gastropods, corals and brachiopods, which had flourished during the Carnian-Norian, suffered progressive specific reduction during the Rhaetian and became, after a first Late Norian crisis, largely extinct by the end of the Triassic. In the pelagic domain, several families of organisms underwent complete extinction. On the contrary, calcispheres and calcareous nannofossils first appeared (or secreted for the first time a calcareous shell) during the Late Triassic and became a relevant source of carbonate productivity by the Jurassic. The Triassic/Jurassic boundary is marked by a series of biostratigraphic events involving Dynoflagellates and a few shallow water fauna (references in Galli et al., 2005; Barattolo e Romano 2005)
Among vascular plants, microflora analysis showed that the T/J boundary transition was apparently gradual in the Tethyan and Boreal domains (Buratti, 2003), in apparent contradiction with evidences for an abrupt turnover at the boundary in the Newark basins of North America (e.g., Fowell et al. 1994).

PALEOGEOGRAPHY AND GEODYNAMICS
The Norian-Hettangian time interval marks the fragmentation of Pangea, the supercontinent formed by the Variscan coalescence of Gondwana >>>