Thallium isotope fingerprints (ε²⁰⁵Tl) of redox dynamics in the Early Cretaceous Yamama Formation

Thallium isotope fingerprints (ε²⁰⁵Tl) of redox dynamics in the Early Cretaceous Yamama Formation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thallium isotope fingerprints (ε²⁰⁵Tl) of redox dynamics in the Early Cretaceous Yamama Formation Rana Abbas Ali This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8040255/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Thallium isotope compositions (ε²⁰⁵Tl, ‱) from the Early Cretaceous Yamama Formation provide a calibrated paleoredox proxy that links Mn-oxide burial efficiency to bottom-water oxygenation. We analyzed four cores from the Ratawi field, southern Iraq (RT-3, RT-4, RT-6, RT-14), pairing bulk carbonates with staged leaches to track the transition from primary carbonate precipitation to diagenetic modification in meteoric, marine-phreatic, and burial settings. Pelagic clays from the Gulf of Oman yield ε²⁰⁵Tl of − 5.8 ± 0.3‱ (SL167) and − 6.1 ± 0.4‱ (SL163/MC681), matching modern seawater (− 6.0 ± 0.3‱) within uncertainty and providing external analytical controls. Within Yamama, deeper dolomite-rich intervals retain seawater-like ε²⁰⁵Tl within the reconstructed Early Cretaceous range ( ≈ − 6.0 ± 0.3‱; 2SD), whereas upper intervals exhibit meteoric overprint with ε²⁰⁵Tl shifted toward less-negative values ( ~ − 2‱), consistent with limited freshwater mixing. After petrographic and geochemical screening (Mn/Sr, Fe/Sr; targeted weak/reductive leaches to minimize Mn-oxide influence), screened carbonates preserve ε²⁰⁵Tl indistinguishable from coeval seawater. Expressed as Δε²⁰⁵Tl (sample − modern seawater), the Yamama trajectory across ~ 120–112 Ma shows coherent variability that parallels published Tethyan–Atlantic ε²⁰⁵Tl trends within age uncertainty, indicating basin-scale modulation of Mn-oxide burial and near-bottom oxygenation rather than local diagenetic control. Collectively, these results validate screened carbonate platforms, particularly dolomite-rich horizons, as robust ε²⁰⁵Tl archives and extend the thallium-isotope paleoredox framework beyond shale and Fe–Mn repositories. The Yamama Formation thus provides a reference for reconstructing Early Cretaceous redox evolution and demonstrates the utility of ε²⁰⁵Tl (‱) for integrating carbonate-dominated and siliciclastic records in basin-scale reconstructions. Geochemistry Yamama Formation ε²⁰⁵Tl (‱) dolomite diagenetic screening Mn-oxide burial Early Cretaceous paleoredox Full Text Additional Declarations The authors declare no competing interests. Supplementary Files SupplementaryMaterial.xlsx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8040255","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":541121838,"identity":"5de39e68-a222-4d3a-8a07-93314f22d3e2","order_by":0,"name":"Rana Abbas 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Baghdad","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Yamama Formation, ε²⁰⁵Tl (‱), dolomite, diagenetic screening, Mn-oxide burial, Early Cretaceous, paleoredox","lastPublishedDoi":"10.21203/rs.3.rs-8040255/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8040255/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThallium isotope compositions (ε\u0026sup2;⁰⁵Tl, ‱) from the Early Cretaceous Yamama Formation provide a calibrated paleoredox proxy that links Mn-oxide burial efficiency to bottom-water oxygenation. We analyzed four cores from the Ratawi field, southern Iraq (RT-3, RT-4, RT-6, RT-14), pairing bulk carbonates with staged leaches to track the transition from primary carbonate precipitation to diagenetic modification in meteoric, marine-phreatic, and burial settings. Pelagic clays from the Gulf of Oman yield ε\u0026sup2;⁰⁵Tl of \u0026minus;\u0026thinsp;5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3‱ (SL167) and \u0026minus;\u0026thinsp;6.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4‱ (SL163/MC681), matching modern seawater (\u0026minus;\u0026thinsp;6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3‱) within uncertainty and providing external analytical controls. Within Yamama, deeper dolomite-rich intervals retain seawater-like ε\u0026sup2;⁰⁵Tl within the reconstructed Early Cretaceous range (\u0026thinsp;\u0026asymp;\u0026thinsp;\u0026minus;\u0026thinsp;6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3‱; 2SD), whereas upper intervals exhibit meteoric overprint with ε\u0026sup2;⁰⁵Tl shifted toward less-negative values (\u0026thinsp;~\u0026thinsp;\u0026minus;\u0026thinsp;2‱), consistent with limited freshwater mixing. After petrographic and geochemical screening (Mn/Sr, Fe/Sr; targeted weak/reductive leaches to minimize Mn-oxide influence), screened carbonates preserve ε\u0026sup2;⁰⁵Tl indistinguishable from coeval seawater. Expressed as Δε\u0026sup2;⁰⁵Tl (sample\u0026thinsp;\u0026minus;\u0026thinsp;modern seawater), the Yamama trajectory across ~\u0026thinsp;120\u0026ndash;112 Ma shows coherent variability that parallels published Tethyan\u0026ndash;Atlantic ε\u0026sup2;⁰⁵Tl trends within age uncertainty, indicating basin-scale modulation of Mn-oxide burial and near-bottom oxygenation rather than local diagenetic control. Collectively, these results validate screened carbonate platforms, particularly dolomite-rich horizons, as robust ε\u0026sup2;⁰⁵Tl archives and extend the thallium-isotope paleoredox framework beyond shale and Fe\u0026ndash;Mn repositories. The Yamama Formation thus provides a reference for reconstructing Early Cretaceous redox evolution and demonstrates the utility of ε\u0026sup2;⁰⁵Tl (‱) for integrating carbonate-dominated and siliciclastic records in basin-scale reconstructions.\u003c/p\u003e","manuscriptTitle":"Thallium isotope fingerprints (ε²⁰⁵Tl) of redox dynamics in the Early Cretaceous Yamama Formation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-07 07:41:27","doi":"10.21203/rs.3.rs-8040255/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b29e51cb-7752-4122-bc42-be5c2a798f3b","owner":[],"postedDate":"November 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":57499513,"name":"Geochemistry"}],"tags":[],"updatedAt":"2025-11-07T07:41:27+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-07 07:41:27","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8040255","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8040255","identity":"rs-8040255","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}