Résumé
This file gathers the supplementary material and datasets related to the publication "Stable oxygen isotopes of crocodilian tooth enamel allow tracking Plio-Pleistocene evolution of freshwater environments and climate in the Shungura Formation (Turkana Depression, Ethiopia)" published in Biogeosciences.
This study utilizes stable oxygen isotopes (δ18Op) in fossil crocodilian teeth to assess paleohydrology and paleoclimates. Crocodilian teeth, widely available in continental basins since the Mesozoic era, provide a valuable archive for tracking freshwater environmental changes due to their durable enamel phosphate, which preserves their original isotopic composition over geological timescales. The research applies this approach for the first time to the Shungura Formation in the Lower Omo Valley, Ethiopia, a crucial area for understanding environmental shifts in eastern Africa during the Plio-Pleistocene, impacting regional ecosystems, including humans. The δ18Op of coexisting crocodilians reveals (1) stable aquatic environments in the northern Turkana Depression from 2.97 Ma to around 2.57 Ma, followed by a decline in local waterbody diversity after 2.32 Ma, indicative of increasing aridity, and (2) a significant increase in δ18Ow from 2.97 Ma to about 1.14 Ma, likely influenced by changing air stream convergence zones between the West African and Indian Summer Monsoons and/or reduced rainfall over the Ethiopian Highlands.
Age model for the Shungura Formation
The related paper uses a revised age model for the Shungura Formation, interpolated based on the latest published absolute age data. The interpolation was carried out on the R.4.1.3 software, with the function splinefun ("stats" package, R Core Team, 2022) by implementing the data of the maximum cumulative thickness of sediments (Heinzelin and Haesarts, 1983) and the absolute ages known for some units of the Shungura Formation. For the Basal Member and the top of Member L, ages are interpolated by linear fit based on sedimentation rate. this age model is likely to evolve with the addition of new dating data.
Oxygen isotopic composition of crocodilian teeth from the Shungura Formation
Table S2 brings together information on the morphology and isotopic composition of the crocodilian teeth sampled in the Shungura Formation. Abbreviation: ID, tooth inventory number; Age, age of the unit in million years based on the age model of the Shungura Formation given in Table S1. The dental crown height is given for teeth with complete crown only. The details of the method used for the geochemical analyzes are given in the corresponding article, in section 2.4.
Pariwise comparison of the isotopic composition of crocodilian teeth between units of the Shungura Formation
The δ18Op difference between stratigraphical units was investigated with a two-way ANOVA and Pairwise Wilcoxon Rank Sum Tests with Holm correction (non-parametric post-hoc tests), and the results are presented in Table S3.