Preserved stable isotopic signature of subaerial diagenesis in the 1.2-b.y. Mescal Limestone, central Arizona: Implications for the timing and development of a terrestrial plant cover

Abstract

Research Article| June 01, 1985 Preserved stable isotopic signature of subaerial diagenesis in the 1.2-b.y. Mescal Limestone, central Arizona: Implications for the timing and development of a terrestrial plant cover MARK A. BEEUNAS; MARK A. BEEUNAS 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Search for other works by this author on: GSW Google Scholar L. PAUL KNAUTH L. PAUL KNAUTH 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Search for other works by this author on: GSW Google Scholar Author and Article Information MARK A. BEEUNAS 1Department of Geology, Arizona State University, Tempe, Arizona 85287 L. PAUL KNAUTH 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (6): 737–745. https://doi.org/10.1130/0016-7606(1985)96<737:PSISOS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MARK A. BEEUNAS, L. PAUL KNAUTH; Preserved stable isotopic signature of subaerial diagenesis in the 1.2-b.y. Mescal Limestone, central Arizona: Implications for the timing and development of a terrestrial plant cover. GSA Bulletin 1985;; 96 (6): 737–745. doi: https://doi.org/10.1130/0016-7606(1985)96<737:PSISOS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A Precambrian exposure surface in the 1.2-b.y. Mescal Limestone has been isotopically examined for indications of a carbon isotopic signature that might indicate the presence of a subaerial vegetative cover in the middle Proterozoic.δ18O values of the Mescal carbonates show two distinct data sets: (1) dolomites from an unaltered zone which were unaffected by sub-aerial diagenesis having δ18O values ranging from +19.9 to +25.6‰ Standard Mean Ocean Water (SMOW) with cherts averaging +30‰, and (2) dolomites from a dissolution zone subaerially exposed in the Precambrian with δ18O values ranging from +13.9 to +22.4‰ and cherts averaging +25‰. δ13C of dolomite ranges from +3.7‰ Pee Dee Belemnite (PDB) in the unaltered zone to 0‰ in the dissolution zone. The dissolution zone consists of a karst breccia of recemented dolomite and chert fragments with numerous clastic solution dikes.Isotopic and field data indicate that the δ18O of the unaltered dolomite was fixed during early meteoric-water diagenesis, including dissolution-silicification of evaporites and dolomitization. During a later subaerial exposure event, a large flux of meteoric water flushed through the dissolution zone and produced the same isotopic patterns that Allan and Matthews documented for younger examples as indicative of a vegetatively covered land surface. Alternative explanations for producing the observed δ13C variations in the absence of vegetation do not seem feasible. We therefore suggest that the subaerial environment 1.2 b.y. ago was a biologically active zone. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.