DOI: 10.5061/dryad.37pvmcvp6
title: Data from: An expanded Smithian-Spathian (Early Triassic) boundary from a reefal build-up record in Oman: Implications for conodont taxonomy, high-resolution biochronology and the carbon isotope record

description: Some 2.7 Ma after the Permian-Triassic boundary mass extinction (PTME), a
 stepwise extinction of the nekton (ammonoids and conodonts) ended at the
 Smithian-Spathian boundary (SSB) during an episode of climate cooling. SSB
 records from continental shelves are usually affected by an unconformity,
 suggesting a forced regression of glacio-eustatic origin. Here, we
 document a new 30 m-thick SSB section from Jebel Aweri (Batain Plain,
 Oman) that provides an exceptionally complete and expanded record
 preserved in an exotic block. Most of this SSB section consists of
 metazoan reefal build-ups that formed in shallow water on an offshore sea
 mount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block
 records the SSB in a deeper water setting represented by Hallstatt-type
 facies. These two sections provide a unique perspective on the early
 Spathian rapid re-diversification of conodonts. They led to a thorough
 revision of conodont taxonomy around the SSB and to the construction of
 the highest resolution biochronological scheme for this time interval in
 the Tethys. A total of five SSB sections from Oman representing both
 offshore sea mounts and lower slope deposits were included in a
 high-resolution, quantitative Unitary Associations analysis. The resulting
 8 conodont biozones are intercalibrated with ammonoid zones and with the
 carbonate carbon isotope record ultimately placing the SSB in the interval
 of separation between UAZ3 and UAZ4. Only the association of Nv.
 pingdingshanensis with Ic. crassatus can be used to unambiguously
 characterize the base of the Spathian.
description: <strong>Sedimentological
 analysis (S1)</strong> The rock samples for the sedimentological
 analysis were recovered during two individual fieldtrips in 2015 and 2017.
 The sedimentological analysis was achieved via a qualitative description
 of the of the lithology by observations in the field and via further
 analysis of the samples wich were sent to the University of Zurich. The
 figures for the microstructures were obtained by cutting the rocks into
 thin sections at the University of
 Lausanne.<br> <strong>Conodont samples for Unitary Association Method
 (S2 and S3)</strong> A total of 60 samples was collected for
 conodonts, 26 from Wadi Musjah and 34 from Jebel Aweri. The spacing
 between the samples varies between 10–40 cm in the Wadi Musjah section and
 0.5–3 m in the Jebel Aweri section. From Wadi Musjah, samples of
 1–3 kg of carbonate rock material were dissolved
 with a 10 % buffered acetic acid solution following the procedure of
 Jeppsson et al. (1999). In Jebel Aweri, the same procedure was applied to
 10–15 kg samples. The residues were treated by
 heavy liquid separation using sodium polytungstate (Jeppsson &
 Anehus 1999), then sieved with a 0.075-mm mesh. The heavy fraction was
 handpicked under a binocular microscope and selected conodont elements
 were coated with carbon and illustrated using Scanning Electron Microscopy
 (SEM) (JEOL JSM-6010). Uncoated elements were illustrated with a Keyence
 VHX 6000 digital microscope. <br>
 Five sections from Oman (Wadi
 Musjah (this study), Jebel Aweri (this study), Jebel Safra (Orchard 1995),
 Radio Tower (Chen et al. 2019) and Wadi Bani Khalid (Chen et al. 2019))
 were included in the analysis. Taxonomic revisions were made to ensure the
 consistency of the data set using all published
 material. <strong>Carbon isotope data
 (S4)</strong><br> We analyzed the micritic matrix of 50 carbonate
 rock samples from Wadi Musjah and 61 samples from Jebel Aweri for bulk
 carbonate carbon isotopes
 (δ<sup>13</sup>C<sub>carb</sub>). The samples were
 carefully cleaned and cut into slabs in order to recover unaltered
 micrite. The most homogenous part was drilled on a sawed surface with a
 diamond-tipped drill to produce a fine powder. All samples were processed
 at the Institute of Mineralogy and Geochemistry of Lausanne University and
 measured with a GasBench II connected to a Finnigan MAT DeltaPlus XL mass
 spectrometer with a He-carrier gas system (Spötl and Vennemann, 2003).
 Reproducibility (n=3 per run) of replicate analysis was better than 0.1 ‰
 for standards and 0.15 ‰ for sediment samples. All reported carbonate
 carbon isotope results are in the standard δ notation (‰ deviation versus
 VPDB). <strong>Conodont biochronozones across the
 Smithian-Spathian boundary (S5)</strong>
 Conodont biochronozones from
 Oman and South China calibrated against U-Pb ages. Intercalibrated with
 ammonoid biochronozones from Oman and China and the δ<sup>13</sup>C<sub>carb</sub> records from Jebel Aweri, Wadi Musjah, Qiakong, Laren, Shanggang and Lilong. Timing of Early Triassic after Bayesian age-depth model by Widmann (2019, thesis), Ammonoid zones after Brayard & Bucher (2008) and Brühwiler et al. (2009, 2010, 2012). South China conodont biochronozones after Leu et al. (subm.).
description: <strong>Unitary
 Association Method (S2 and S3)</strong>
 The Unitary Associations
 method (UAM) is a deterministic approach based on the Graph Theory whose
 goal is to construct a discrete sequence of mutually exclusive maximal
 sets of coexisting species (Guex 1991; Angiolini & Bucher 1999;
 Monnet & Bucher 2002; Brosse et al. 2016). We have used the UAM as
 implemented in the software PAST (Hammer et al. 2001, 2012) using an older
 version (Version 2.17c, 2013) that allows us to detect and analyse Z4-type
 contradictions. This software is free and can be downloaded online. (e.g.
 https://past.en.lo4d.com/windows)