Miriam E. Katz, PhD , Rensselaer Polytechnic Institute
Carbon isotopes were first shown to be effective for stratigraphic correlation in Neogene and Paleogene sections (e.g., Cramer et al., 2003; Dupuis et al., 2003; Woodruff and Savin, 1991). d13C stratigraphy is now recognized as critical in older records, especially where magnetobiostratigraphy is insufficient to accurate correlate high-resolution datasets (e.g., Cramer and Saltzman, 2005; Grocke, 2006; Muttoni et al., 2004; Weissert et al., 1998). My grant research focuses on identifying d13C events and trends recorded in marine carbonates and organic carbon that can be used for correlation in Triassic sections.
Graduate student David Mosher, supported by this grant, has completed his first year of his M.S. degree. His research focusses on Tethyan Triassic carbonate sections. Two undergraduate students (Brianna King and Pernille Birkeland) assisted with lab work.
For this project, I have established new collaborations with Dennis Kent (Rutgers U.), Giovanni Muttoni (Univ. of Milan), and Atle Mørk (SINTEF Petroleum Research, and Norwegian University of Sciences and Technology). In addition, I have been able to renew an old collaboration with Allen Milligan (Oregon State University), on a new research topic.
In our first year of grant-related research, we presented our initial results at the 2011 AAPG annual meeting in Houston in two posters, one first-authored by graduate student David Mosher, and the other by me. The poster abstracts provide detail on our projects:
1. Mosher, D., Katz, M.E., Muttoni, G., Kent, D.V., Development of High-Resolution d13C Records in Tethyan Limestones from the Anisian to Early Norian.
In this study, we present new high resolution (100 ky) d13C records of bulk sediment carbonates from Tethyan Triassic sections with excellent biomagnetostratigraphy. Our goal is to establish d13C event stratigraphy that can be used for correlation in sections that lack good biomagnetostratigraphy.
We analyzed an Anisian-Ladinian (~240-231 Ma) limestone section from Seceda (northwestern Dolomites, Italy) that spans the entire Buchenstein Beds Formation. These limestones contain radiometrically-dated tuff layers (~238.0-241.2 Ma) (Mundil et al., 1996; Brack et al., 1996). Through U-Pb age dating, a sediment accumulation rate of ~10 m/m.y. was determined, this rate doubled in the Bänderkalke member; where turbidite beds became more prevalent (Maurer el al., 2003). The magnetostratigraphy from this core has been used to define the base of the Ladinian for the Global Stratigraphic Section and Point (GSSP), and to complete the Middle Triassic magnetic polarity time scale; in addition, conodont biostratigraphy has been directly tied to the Seceda core from locations throughout the Dolomites and Alps (Muttoni et al., 2004). This published integrated biomagnetostratigraphic framework makes Seceda the best section to use for our Middle Triassic d13C stratigraphy. In addition, we analyzed a section from Hydra Aghia Marina (Greece) to check Seceda results when the two sections overlap; the Aghia Marina is from Adhami Formation; condont biostratigraphy indicates late Ladinian to early Norian ages.
2. Katz, M.E., Mørk, A., Milligan, A.J., Triassic Carbon Isotope Stratigraphy – Correlations between Panthalassic and Tethyan Sections.
In this study, we build on published high-resolution d13C records of carbonates (d13Ccarb)(Korte et al., 2005; Muttoni et al., 2004a; Payne et al., 2004), which provide important glimpses of carbon cycle dynamics and potential for d13C stratigraphic correlation during the Triassic, which began and ended with large d13C excursions. Large d13Ccarb fluctuations (up to 8‰) in the Tethys accompanied the Early Triassic reorganization of marine ecosystems over 4-8 myr (Payne et al., 2004), followed by more stable values punctuated by occasional smaller events through the rest of the Triassic (Korte et al., 2005; Muttoni et al., 2004a). Although geographically restricted to the Tethys (Europe and China), these Triassic isotopic records demonstrate the potential to establish d13C events that could be used in stratigraphic correlation.
We expand on these published Tethyan d13Ccarb records both geographically and geochemically, with Early to Middle Triassic (Induan-Ladinian) d13Ccarb and d13Corg from the Panthalassic Ocean. We use 11 cores drilled by IKU/SINTEF along a depth transect on Svalis Dome (Barents Sea), recovering 315m of a 650m section of deep shelf to basinal siltstones and shales (Mork and Elvebakk, 1999). The Svalis Dome succession contains an excellent hydrocarbon-rich source rock in the late Olenekian and Anisian with TOC values of 2 to 7%. Ammonoids and palynomorphs provide good age control (Vigran et al., 1998). Our d13Ccarb and d13Corg data both show large fluctuations that are similar to coeval d13Ccarb changes reported from China (Payne et al., 2004), supporting the utility of carbon isotopes for stratigraphic correlation in Triassic sections.
In the second year of research on this project, we are completing isotopic studies on the inorganic bulk sediments. All samples have been crushed and await analysis at Rutgers University. Data analysis and results will be presented at a national meeting, and I anticipate that results will be submitted in 2 manuscripts for journal publication by the end of the year.