The Ain Settara section (Kalaat-Senan area, Tunisia) shows a well-exposed and expanded Cretaceous/Tertiary (K/T) boundary that can be divided into several units of contrasted lithologies. The bolide impact level is identified thanks to the occurrence of a peak of iridium and Ni-rich spinel abundance. The impact level is a jarosite nodule-rich horizon upon which the emphasis is placed: the jarosite nodules, initially present as pyrite nodules, may be interpreted as reflecting reducing depositional conditions at the K/T boundary. Trace metal geochemistry indicates that depositional conditions were not reducing and that the nodules must not have formed during earliest diagenesis. Consequently, water column-scaled anoxia cannot be put forward to account for the mass extinctions observed at the K/T boundary at Ain Settara.

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