Elucidating Terrestrial Organic Carbon Burial Mechanisms - Insights from the Western Irish Namurian Basin, County Clare, Ireland

The long-term (> 1 Myr) carbon and oxygen cycles are intimately coupled to the export of organic carbon (OC) from the marine and terrestrial biospheres to sedimentary reservoirs. The export of OC can be decoupled from primary production through oxidation reactions, which degrade OC as it transits through surface environments. In modern fluvial systems, for example, the export of terrestrial OC to oceans greatly exceeds measurements of terrestrial OC preserved in marine sediments. This implies that oxidative remineralization in marine settings strongly modulates terrestrial OC burial, with implications for the long-term C cycle. However, the biogeochemical processes that allow some terrestrial OC to escape oxidation remain enigmatic, making it difficult to discern whether changes in Earth's surface environment facilitated variations of terrestrial OC.

In this study, we explore preservation mechanisms of terrestrial OC through Carboniferous stratigraphy (326-313 Myr) of the Western Irish Namurian Basin (WINB) in County Clare, Ireland. The WINB is an intracontinental basin consisting of alternating fluvial and marine stratigraphy. High OC concentrations in non-marine WINB strata suggest efficient terrestrial OC burial, but the underlying mechanisms responsible for terrestrial OC preservation remain unknown. The presence of marine deposits and exposures of contemporaneous source (terrestrial) to sink (marine) strata allow for a determination of the locus of terrestrial OC and the role of fluid composition (e.g., salinity and oxidant concentrations) in setting terrestrial OC preservation. To explore these ideas, we utilize carbon and nitrogen concentrations and isotopic ratios as well as Time-of-Flight Secondary ionization mass spectrometry to distinguish between marine and terrestrial OC sources. The extent to which OC preservation is driven by mineralogical associations, versus variations in seawater oxidant supply, is also explored.