Re‐Os isotope systematics in carbonates from Serpent Mound, Ohio: Implications for Re‐Os dating of crustal rocks and the osmium isotopic composition of Ordovician seawater

Abstract

187 Os/ 188 Os signatures for the leached samples are generally lower than those of respective whole rocks. However, five of six leachate samples produce a strong linear correlation on a Re-Os isochron diagram, the slope of which reflects an ''age'' of 443 ± 34 Ma, consistent with biostratigraphic constraints on the depositional ages of the sampled rock units . The calculated initial 187 Os/ 188 Os of 0.53 ± 0.04 is distinctly lower than present-day seawater, and, if representative of Ordovician seawater, may reflect relatively low continental weathering rates due to waning Pan African orogenies as proposed to explain the slow decrease in seawater 87 Sr/ 86 Sr starting in early Ordovician [Qing et al., 1998].

Investigating Complex Isochron Data Using Mixture Models

“…The oldest age produced by the model (453 Ma) is identical to the Upper Ordovician age of the sediments that host the Polaris deposit; however, the low initial of~0.1 for this age is lower the expected osmium isotopic composition of seawater at that time (~0.5-0.3; Turgeon et al, 2007;Widom et al, 2004; Figure 4b).…”

“…The oldest age produced by the model (453 Ma) is identical to the Upper Ordovician age of the sediments that host the Polaris deposit; however, the low initial of ~0.1 for this age is lower the expected osmium isotopic composition of seawater at that time (~0.5-0.3; Turgeon et al, 2007;Widom et al, 2004; Figure 4b). Since organic shales can have orders of magnitude more Re and Os than oils (e.g., Finlay et al, 2012), we tentatively suggest that the old age may result from fine organic sediment powder from the Ordovician sediments being trapped within the bitumen, mixing with the isotopic data from the oils.…”

Geochemistry of basal Cambrian black shales and cherts from the Northern Tarim Basin, Northwest China: Implications for depositional setting and tectonic history

“…Although there is no correlation of 187 Os/ 188 Os with 187 Re/ 188 Os in the other Tarim samples, no correlation should necessarily be expected given the range (albeit small) in depositional ages of these samples, the short residence time of Os in seawater(Widom et al, 2004;Oxburgh, …”

The role of carbon from recycled sediments in the origin of ultrapotassic igneous rocks in the Central Mediterranean

“…The red curve is the mixing curve between the least radiogenic sample (BR 29, see supplementary material) and the crustal rock as representative of a possible crustal contamination pattern. Data are fromGasperini et al (2002),Conticelli et al (2002Conticelli et al ( , 2007Conticelli et al ( , 2010,Martelli et al (2004),Widom et al (2004),Prelević et al (2008Prelević et al ( , 2010Prelević et al ( , 2014, and Tommasini's unpublished data. Mantle Zoo end members are fromStracke et al (2005).…”