We present Sr-isotope data (87Sr/86Sr ratios) from dolomites of the Triassic Travenanzes Formation (Fm.), Northern Italy. The goal of this study was to determine if ionic solutions conducive to dolomite formation are derived from a continental or a marine source. Results clearly show a marine source.Sr-isotope data are shown in Table 1. Extensive leaching experiments were performed using sequential extractions (labelled "seq") to test for extraction efficiency of each solvent. Solvent and extraction procedure are listed in Table 1 for each extraction step. Control extractions where also performed with different pure minerals (celestine, barite and dolomite) and a mixture thereof. For a few selected samples the concentrations of ions in the leachates were quantified by ICP-OES (Table 2).To rule out any contamination by Sr leached from clay minerals, leaching experiments were performed on clay samples from the Travenanzes Fm. that showed minimal inorganic carbon content. Total organic and inorganic carbon contents in these samples, measured with a Leco carbon analyser, are shown in Table 3.Furthermore, Table 1 shows results from several different ancient and modern dolomites for comparison, including lacustrine dolomite from the Carnian Lehrberg Beds and the Norian Arnstadt Fm. (Germany), from the coastal ephemeral lakes of the Coorong Lagoon (South Australia), and from Deep Springs Lake (California).We also present carbon and oxygen isotope values of different types of dolomite from the Travenanzes Fm. taken from thin section cuttings by micro-drilling. Carbon isotope compositions of the dolomites are similar to inorganic carbon of Carnian seawater with minor influence from organic matter degradation. Oxygen isotopes do not indicate any meteoric influence and no late diagenetic or hydrothermal overprint at elevated temperatures.Location: Rifugio Dibona, Cortina d'Ampezzo, 32043 Belluno, Italy, Bottom of section: 46.534712 / 12.072683, Top of section: 46.535368 / 12.072901.

Supplement to: Rieder, Maximilian; Wegner, Wencke; Horschinegg, Monika; Klackl, Stefanie; Preto, Nereo; Breda, Anna; Gier, Susanne; Klötzli, Urs; Bernasconi, Stefano M; Arp, Gernot; Meister, Patrick (2019): Precipitation of dolomite from seawater on a Carnian coastal plain (Dolomites, northern Italy): evidence from carbonate petrography and Sr isotopes. Solid Earth, 10(4), 1243-1267