Carbon chemistry of cretaceous marine organic matter

• Main Authors: Dean, Walter E, Arthur, Michael A, Claypool, George E
• Format: Dataset
• Language: English
• Published: PANGAEA 1986
• Subjects: 26-258; 27-259; 27-260; 27-261; 27-263; 33-317A; 41-367; 63-467; 75-530A; BC; Box corer; BX-4; BX-5; BX-6; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; Glomar Challenger; GUB; Gubbio; Indian Ocean//PLAIN; Indian Ocean//PLATEAU; Italy; Leg26; Leg27; Leg33; Leg41; Leg63; Leg75; North Atlantic/BASIN; North Pacific/GAP; South Atlantic/RIDGE; South Pacific/PLATEAU; Indian; Pacific; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.714865; https://doi.org/10.1594/PANGAEA.714865

Geochemical studies of Cretaceous strata rich in organic carbon (OC) from Deep Sea Drilling Project (DSDP) sites and several land sections reveal several consistent relationships among amount of OC, hydrocarbon generating potential of kerogen (measured by pyrolysis as the hydrogen index, HI), and the isotopic composition of the OC. First, there is a positive correlation between HI and OC in strata that contain more than about 1% OC. Second, percent OC and HI often are negatively correlated with carbon isotopic composition (delta13C) of kerogen. The relationship between HI and OC indicates that as the amount of organic matter increases, this organic matter tends to be more lipid rich reflecting the marine source of the organic matter. Cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter. Average delta13C values for organic matter from most Cretaceous sites are between -26 and -28 per mil, and values heavier than about -25 per mil occur at very few sites. Most of the delta13C values of Miocene to Holocene OC-rich strata and modern marine plankton are between -16 to -23 per mil. Values of delta13C of modern terrestrial organic matter are mostly between -23 and -33 per mil. The depletion of terrestial OC in 13C relative to marine planktonic OC is the basis for numerous statements in the literature that isotopically light Cretaceous organic matter is of terrestrial origin, even though other organic geochemical and(or) optical indicators show that the organic matter is mainly of marine origin. A difference of about 5 per mil in delta13C between modern and Cretaceous OC-rich marine strata suggests either that Cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis, or that OC derived from Cretaceous marine plankton was isotopically lighter by about 5 per mil relative to modern plankton OC. Diagenesis does not ...