Palaeogeography, Palaeoclimatology, Palaeoecology 277 (2009) 173-183 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo A molecular evaluation of bulk organic carbon-isotope chemostratigraphy for terrestrial correlations: An example from two Paleocene-Eocene tropical sequences H. Carvajal-Ortiz a *, G. Mora a , C. Jaramillo b a Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 5001!, USA b STRI— Smithsonian Tropical Research Institute. P.O. Box 0843-03092 Balboa-Ancon, Panama ARTICLE INFO Article history: Received 4 August 2008 Received in revised form 6 March 2009 Accepted 19 March 2009 Keywords: Late Cretaceous-Early Eocene Carbon-isotope chemostratigraphy Geochemical biomarker ratios Terrestrial-derived organic matter Diagenesis ABSTRACT The dynamics associated with the carbon cycle and the linkage between the oceans, the atmosphere, and land plants provide an opportunity to correlate marine and terrestrial sedimentary sequences using stable isotopes of carbon (6" 13 C), but few studies have tested this approach. For instance, it has been proposed that changes in plant community (e.g., gymnosperm-dominated vs. angiosperm-dominated) could have significantly altered/amplified the carbon-isotope ratios of bulk sedimentary organic matter derived from land plants (8 13 C TO M). compared to that of the marine carbonates (8 13 C carbonate ). Here, 6" 13 C TO M values in a terrestrial sequence of the Colombian tropics are compared to the composite Paleocene-Eocene 6" 13 C carbonate curve from Zachos et al. (2001) to evaluate the use of 8 13 C TO M values as a reliable chronostratigraphic tool. Sediments of the studied terrestrial sequences were deposited in a transitional setting dominated by mudstones, coals, and small lenses of sandstones (Late Cretaceous-Middle Paleocene sediments) and in a mixture of deltaic and fluvial conditions (Late Paleocene-Early Eocene sediments). The biostratigraphic control was based on palynological zones for the region. The 6 13 C TO M values for the studied terrestrial sequence show three carbon-isotope excursions, which correlate closely with those present in the marine record. The 6" 13 C TO M values decreased from — 24.2%o to — 26.5%o in sediments accumulated during Early to Middle Paleocene, increased from — 26.5%<> to — 23.8%<> during the Late Paleocene, and decreased from — 23.8%o to — 26.5%o near the Paleocene-Eocene boundary (52-50 Ma). Selected biomarkers indicate that most of the organic matter derived from both gymnosperms and angiosperms. Moreover, the analyses of selected biomarker ratios (CPI, Pr/Ph, P aq , and fWPP + a(3. hopanes) show some diagenetic transformation in the preserved organic matter. However, no correlation between diagenesis and 6" 13 C TO M values was detected, thus suggesting that 8 13 C TO M could be correlated with 8 13 C carbonate values. The close correspondence that was found between 8 13 C TO M and 6 13 C carbonate values (A 13 C TO M-carbonate— 27%«) provides support to the hypothesis that a tight land-plant-oceans linkage exists through geologic timescales via atmospheric carbon dioxide. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Significant chemical, physical, and biological changes in both marine and terrestrial environments have affected the carbon cycle during the Phanerozoic (e.g., Arens and Jahren, 2000; Beetling et al., 2001; Freeman and Colarusso, 2001; Hesselbo et al., 2002; Thomas et al., 2002; Hesselbo et al., 2003; Jahren et al., 2005; Jaramillo et al., 2006; Kaiser et al., 2006; Smith et al., 2007) by affecting the magnitude of carbon fluxes between different carbon reservoirs over geologic time scales and by altering the partitioning of carbon isotopes. If these perturbations of the carbon cycle are global in scale, they could offer an opportunity to correlate marine and * Corresponding author. Present address: Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA Fax: +1 812 855 7961. E-mail addresses: carvajah@indiana.edu (H. Carvajal-Ortiz), gmora@iastate.edu (G. Mora), JaramilloC@si.edu (C. Jaramillo). 0031-0182/$ - see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2009.03.015 terrestrial sedimentary sequences, which at the moment is limited to a few proxies. Some studies have in fact proposed the use of stable isotopes of carbon as a chronostratigraphic tool for marine and terrestrial sequences (e.g., Scholle and Arthur, 1980; Hasegawa, 1997; Arens and Jahren, 2000; Strauss and peters-Kottig, 2003; Hesselbo et al., 2007). These studies rely on two key assumptions: (1) both 6 13 Q:arbonate values and 6 13 C values of organic matter derived from higher plants reflect parallel changes in the carbon isotopic composi- tion of the marine and terrestrial realms, and (2) measured 6 13 C values are identical to those of the pristine materials. The first assumption is based on the notion that isotopic equilibrium is reached within the different reservoirs over geologic timescales (i.e., differences in isotopic values remain constant after equilibration) (e.g., Grocke, 2002; Strauss and peters-Kottig, 2003). Despite the importance of the secular changes over long-term time scales (>10 6 yrs), significant partitioning of carbon isotopes occurs over short-term timescales, which ultimately drives the isotopic