High latitude meteoric δ18O compositions: Paleosol siderite in the Middle Cretaceous Nanushuk Formation, North Slope, Alaska

Abstract

Research Article| March 01, 2004 High latitude meteoric δ18O compositions: Paleosol siderite in the Middle Cretaceous Nanushuk Formation, North Slope, Alaska David F. Ufnar; David F. Ufnar 1Department of Geology, University of Southern Mississippi, Box 5044, Hattiesburg, Mississippi 39406, USA Search for other works by this author on: GSW Google Scholar Greg A. Ludvigson; Greg A. Ludvigson 2Iowa Geological Survey Bureau, Iowa City, Iowa 52242, USA and Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar Luis A. González; Luis A. González 3Department of Geology, University of Kansas, Lawrence, Kansas 66045-7613, USA Search for other works by this author on: GSW Google Scholar Robert L. Brenner; Robert L. Brenner 4Department of Geoscience, University of Iowa, Iowa City, Iowa 52242-1379, USA Search for other works by this author on: GSW Google Scholar Brian J. Witzke Brian J. Witzke 5Iowa Geological Survey Bureau, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (3-4): 463–473. https://doi.org/10.1130/B25289.1 Article history received: 08 Nov 2002 rev-recd: 24 Jul 2003 accepted: 14 Aug 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation David F. Ufnar, Greg A. Ludvigson, Luis A. González, Robert L. Brenner, Brian J. Witzke; High latitude meteoric δ18O compositions: Paleosol siderite in the Middle Cretaceous Nanushuk Formation, North Slope, Alaska. GSA Bulletin 2004;; 116 (3-4): 463–473. doi: https://doi.org/10.1130/B25289.1 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 Siderite-bearing pedogenic horizons of the Nanushuk Formation of the North Slope, Alaska, provide a critical high paleolatitude oxygen isotopic proxy record of paleoprecipitation, supplying important empirical data needed for paleoclimatic reconstructions and models of "greenhouse- world" precipitation rates. Siderite δ18O values were determined from four paleosol horizons in the National Petroleum Reserve Alaska (NPR-A) Grandstand # 1 Core, and the values range between −17.6‰ and −14.3‰ Peedee belemnite (PDB) with standard deviations generally less than 0.6‰ within individual horizons. The δ13C values are much more variable, ranging from −4.6‰ to +10.8‰ PDB. A covariant δ18O versus δ13C trend in one horizon probably resulted from mixing between modified marine and meteoric phreatic fluids during siderite precipitation.Groundwater values calculated from siderite oxygen isotopic values and paleobotanical temperature estimates range from −23.0‰ to −19.5‰ standard mean ocean water (SMOW). Minor element analyses show that the siderites are impure, having enrichments in Ca, Mg, Mn, and Sr. Minor element substitutions and Mg/Fe and Mg/(Ca + Mg) ratios also suggest the influence of marine fluids upon siderite precipitation.The pedogenic horizons are characterized by gleyed colors, rare root traces, abundant siderite, abundant organic matter, rare clay and silty clay coatings and infillings, some preservation of primary sedimentary stratification, and a lack of ferruginous oxides and mottles. The pedogenic features suggest that these were poorly drained, reducing, hydromorphic soils that developed in coal-bearing delta plain facies and are similar to modern Inceptisols.Model-derived estimates of precipitation rates for the Late Albian of the North Slope, Alaska (485–626 mm/yr), are consistent with precipitation rates necessary to maintain modern peat-forming environments. This information reinforces the mutual consistency between empirical paleotemperature estimates and isotope mass balance models of the hydrologic cycle and can be used in future global circulation modeling (GCM) experiments of "greenhouse- world" climates to constrain high latitude precipitation rates in simulations of ancient worlds with decreased equator-to-pole temperature gradients. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.