Positive europium anomaly at the Permo-Triassic boundary, Spiti, India

Abstract

A limonitic layer at the base of the Otoceras-Ophiceras zone in the Lalung section in Spiti valley shows a significant positive europium anomaly with maximum Eu/Eu^∗ = 1.9. This layer defines the contact between the earliest Griesbachian and the Permian Productus shale sequence. The layer shows a small cerium anomaly having the maximum value of (Ce/La)_N = 1.4. The iridium concentration in this layer, at 73 pg/g, is only marginally above the levels found in the adjacent shales although higher than that found in the overlying limestones. Another horizon having 114 pg/g of Ir occurs 70 cm below this limonitic layer in the shale sequence. These observations have important implications, both for the terrestrial (mainly volcanic) and extra-terrestrial impact hypotheses for the Permo-Triassic transition which are discussed.