July 22 , 2016

Highlights

First quantitative palaeoclimatic assessment of the continental Triassic-Jurassic boundary succession in southern Africa.

Integrated mineralogical, sedimentological and geochemical proxies (e.g., major, trace, rare earth elements).

Calculated indices of chemical alteration and compositional variability.

Deposition occurred under increasingly dry environmental conditions that inhibited chemical weathering.

Results support predictions of long-term global warming after continental flood basalt emplacements.

Abstract

The Triassic-Jurassic boundary marks a global faunal turnover event that is generally considered as the third largest of five major biological crises in the Phanerozoic geological record of Earth. Determining the controlling factors of this event and their relative contributions to the biotic turnover associated with it is on-going globally. The Upper Triassic and Lower Jurassic rock record of southern Africa presents a unique opportunity for better constraining how and why the biosphere was affected at this time not only because the succession is richly fossiliferous, but also because it contains important palaeoenvironmental clues. Using mainly sedimentary geochemical proxies (i.e., major, trace and rare earth elements), our study is the first quantitative assessment of the palaeoclimatic conditions during the deposition of the Elliot Formation, a continental red bed succession that straddles the Triassic-Jurassic boundary in southern Africa. Employing clay mineralogy as well as the indices of chemical alteration and compositional variability, our results confirm earlier qualitative sedimentological studies and indicate that the deposition of the Upper Triassic and Lower Jurassic Elliot Formation occurred under increasingly dry environmental conditions that inhibited chemical weathering in this southern part of Pangea. Moreover, the study questions the universal validity of those studies that suggest a sudden increase in humidity for the Lower Jurassic record and supports predictions of long-term global warming after continental flood basalt emplacement.

Lara Sciscio & Emese M. Bordy (2016)

Palaeoclimatic conditions in the Late Triassic-Early Jurassic of southern Africa: A geochemical assessment of the Elliot Formation.

Journal of African Earth Sciences 119: 102–119

doi:10.1016/j.jafrearsci.2016.03.014