Carbon isotopic composition of plant-derived organic matter in tropical sedimentary sequences as a recorder of Late Cretaceous-Early Paleogene changes in the carbon cycle

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 (δC), but few studies have tested this approach. To evaluate the possibility of using carbon isotope ratios of bulk sedimentary organic matter derived from land plants (δCbulk) as a chronostratigraphic tool, we are comparing the composite Paleocene-Eocene marine carbon-isotope (δCcarbonate) record from Zachos et al., (2001) to that of a terrestrial sequence from Colombia. Sediments of the terrestrial rock units were deposited in a transitional setting dominated by mudstones, coals, and small lenses of sandstones (Catatumbo and Barco Formations) and in a mixture of deltaic and fluvial conditions (Cuervos Formation). The stratigraphic control was based on palynological zones for the region. The δCbulk values for the studied terrestrial sequence show three carbon-isotope excursions, which correlate closely with those present in the marine record. The δCbulk values decreased from -24‰ to -26.5‰ in sediments accumulated during early to middle Paleocene. This shift is commonly associated with the slow recovery in marine primary production that occurred in the aftermath of the extinction event of the Cretaceous-Tertiary boundary. The positive shift in sediments accumulated during the late Paleocene shows δCbulk values increasing from -26.5‰ to -23.8‰. This event is commonly associated with the burial of large amounts of organic matter. The third excursion is found near the Paleocene-Eocene boundary, with values changing from -23.8‰ to -26.5‰. This