Regional RedOx evolution during the Ediacaran Shuram carbon isotope excursion, Nafun Group, north Oman and southern salt basins Oman

Regional RedOx evolution during the Ediacaran Shuram carbon isotope excursion, Nafun Group, north Oman and southern salt basins Oman Christian J. Bjerrum1, Simon R. Stenger1**, Anne-Sofie C. Ahm1***, 1Department of Geoscience and Natural Resource Management, Nordic Center for Earth Evolution, University of Copenhagen, Copenhagen K, Denmark *[email protected] (corresponding author) **Now at the Norwegian Geotechnical Institute, Trondheim, Norway ***Now at School of Earth and Ocean Sciences, University of Victoria, BC, Canada Geochemical dataset related to the regional RedOx evolution during the Ediacaran Shuram carbon isotope excursion. Geochemical analyses include iron-speciation, redox sensitive element and stable carbon and oxygen isotopes. The sub-regional redox changes likely are reflected in the ratio of highly-reactive Fe (FeHR) to total Fe (FeT) and pyrite Fe to FeHR, in combination with redox-sensitive element enrichments (Alcott et al., 2020; Bennett and Canfield, 2020; Poulton and Canfield, 2005). Dataset samples are from outcrops in Jabal Akhdar area of northern Oman, and borehole cuttings in southern salt basins Oman (TM-6). Outcrops analyzed record an unusual complete representation of the onset of the Shuram excursion exposed along a tributary to Wadi Hajir just east of the Al Hijir village (23°12'12.0 N and 057°30'56.5 E). Samples from the South Oman Salt Basin are borehole cuttings from the TM-6 well, Petroleum Development Oman (PDO). The Shuram Formation in both sections represent the deepest water facies within sub-regional basins that where paleo-geographically separated by more than 800 km (cf. Le Guerroue et al., 2006). From the base to the top the Khufai, Shuram and Buah Formations are part of the The Nafun Group. Limestones and dolostones as part of a prograding shallow marine ramp succession represent the Khufai Formation. The lower Shuram Formation consists of Alternating beds of laminated muddy marls to calcareous mudstones with occasional combined-flow cross-laminated climbing ripples, representing a distal offshore to offshore transitional paleodepositional setting (Le Guerroue et al., 2006). The beds of the lower Shuram Formation grade up into maroon−blue-green verdigris mudstones interbedded with occasional marls and muddy silt beds with combined-flow ripples that represent the middle Shuram Formation. The upper Shuram Formation is composed of interstratified carbonate marls and mudstones where carbonate content increases up section toward the basal Buah Formation. During field work in 2015 the section was measured and sampled along the tributary to Wadi Hajir. For convenience the sub-sections are named Wadi Hajir 4, 5 and 6 (WH4-6). WH4 represents the upper part of the Khufai Formation, WH5 the lower Shuram Formation, while WH6 represent the lower part of the middle Shuram Formation. WH4 section is exposed on the southern side of the tributary canyon with a small gap of 0-1 m to the base of WH5. WH5 and WH6 represent a nearly continuous and fully exposed section on the northern side of the canyon. Geochemical dataset include bulk rock: Iron Speciation (Fecarb, Feox, Femag, FePy, Fetot) Elements (Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Zr, Mo, Th) Stable isotopes d13C, d18O C(tot), C(org), S(tot). Global RedOx context of the dataset is presented in Ostrander et al. (2023) Reference Alcott, L.J., Krause, A.J., Hammarlund, E.U., Bjerrum, C.J., Scholz, F., Xiong, Y.J., Hobson, A.J., Neve, L., Mills, B.J.W., Marz, C., Schnetger, B., Bekker, A. and Poulton, S.W. (2020) Development of Iron Speciation Reference Materials for Palaeoredox Analysis. Geostandards and Geoanalytical Research 44, 581-591. Bennett, W.W. and Canfield, D.E. (2020) Redox-sensitive trace metals as paleoredox proxies: A review and analysis of data from modern sediments. Earth-Sci. Rev. 204, 103175. Le Guerroue, E., Allen, P.A. and Cozzi, A. (2006) Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram. Formation (Nafun Group, Oman). Precambrian Res. 146, 68-92. Ostrander, C.M., Bjerrum, C.J., Ahm, A.-S.C., Stenger, S.R., Bergmann, K.D., El-Ghali, M.A.K., Harthi, A.R., Aisri, Z. and Nielsen, S.G. (2023) Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion. Geobiology. Poulton, S.W. and Canfield, D.E. (2005) Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates. Chem. Geol. 214, 209-221.